全文获取类型
收费全文 | 3735篇 |
免费 | 52篇 |
国内免费 | 52篇 |
专业分类
系统科学 | 87篇 |
丛书文集 | 241篇 |
教育与普及 | 156篇 |
理论与方法论 | 11篇 |
现状及发展 | 339篇 |
研究方法 | 605篇 |
综合类 | 2390篇 |
自然研究 | 10篇 |
出版年
2021年 | 9篇 |
2019年 | 7篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 29篇 |
2013年 | 30篇 |
2012年 | 264篇 |
2011年 | 331篇 |
2010年 | 98篇 |
2009年 | 29篇 |
2008年 | 277篇 |
2007年 | 288篇 |
2006年 | 264篇 |
2005年 | 274篇 |
2004年 | 257篇 |
2003年 | 232篇 |
2002年 | 181篇 |
2001年 | 141篇 |
2000年 | 222篇 |
1999年 | 98篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1971年 | 9篇 |
1970年 | 7篇 |
1966年 | 7篇 |
1959年 | 62篇 |
1958年 | 97篇 |
1957年 | 66篇 |
1956年 | 59篇 |
1955年 | 70篇 |
1954年 | 63篇 |
1948年 | 16篇 |
排序方式: 共有3839条查询结果,搜索用时 46 毫秒
71.
72.
Sicardy B Ortiz JL Assafin M Jehin E Maury A Lellouch E Hutton RG Braga-Ribas F Colas F Hestroffer D Lecacheux J Roques F Santos-Sanz P Widemann T Morales N Duffard R Thirouin A Castro-Tirado AJ Jelínek M Kubánek P Sota A Sánchez-Ramírez R Andrei AH Camargo JI da Silva Neto DN Gomes AR Martins RV Gillon M Manfroid J Tozzi GP Harlingten C Saravia S Behrend R Mottola S Melendo EG Peris V Fabregat J Madiedo JM Cuesta L Eibe MT Ullán A Organero F Pastor S de Los Reyes JA Pedraz S Castro A 《Nature》2011,478(7370):493-496
The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1?AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163?±?6?kilometres, density 2.52?±?0.05 grams per cm(3) and a high visible geometric albedo, Pv = 0.96(+0.09)(-0.04). No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ~1?nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun. 相似文献
73.
Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation 总被引:1,自引:0,他引:1
Kirkby J Curtius J Almeida J Dunne E Duplissy J Ehrhart S Franchin A Gagné S Ickes L Kürten A Kupc A Metzger A Riccobono F Rondo L Schobesberger S Tsagkogeorgas G Wimmer D Amorim A Bianchi F Breitenlechner M David A Dommen J Downard A Ehn M Flagan RC Haider S Hansel A Hauser D Jud W Junninen H Kreissl F Kvashin A Laaksonen A Lehtipalo K Lima J Lovejoy ER Makhmutov V Mathot S Mikkilä J Minginette P Mogo S Nieminen T Onnela A Pereira P Petäjä T Schnitzhofer R Seinfeld JH Sipilä M Stozhkov Y 《Nature》2011,476(7361):429-433
Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100-1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H(2)SO(4)-H(2)O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation. 相似文献
74.
Berger W Steiner E Grusch M Elbling L Micksche M 《Cellular and molecular life sciences : CMLS》2009,66(1):43-61
The unique and evolutionary highly conserved major vault protein (MVP) is the main component of ubiquitous, large cellular
ribonucleoparticles termed vaults. The 100 kDa MVP represents more than 70% of the vault mass which contains two additional
proteins, the vault poly (ADP-ribose) polymerase (vPARP) and the telomerase-associated protein 1 (TEP1), as well as several
short untranslated RNAs (vRNA). Vaults are almost ubiquitously expressed and, besides chemotherapy resistance, have been implicated
in the regulation of several cellular processes including transport mechanisms, signal transmissions and immune responses.
Despite a growing amount of data from diverse species and systems, the definition of precise vault functions is still highly
complex and challenging. Here we review the current knowledge on MVP and vaults with focus on regulatory functions in intracellular
signal transduction and immune defence.
Received 27 June 2008; received after revision 25 July 2008; accepted 30 July 2008 相似文献
75.
Pappas G Panagopoulou P Christou L Akritidis N 《Cellular and molecular life sciences : CMLS》2006,63(19-20):2229-2236
Brucella has traditionally been considered a biological weapon. It was the subject of extensive offensive research in the past, and still belongs to category B pathogens on most lists. Its propensity for airborne transmission and induction of chronic debilitating disease requiring combined antibiotic regimens for treatment, its abundance around the world and its vague clinical characteristics defying rapid clinical diagnosis are some of the characteristics that apply to the pathogen's weapons potential. Yet minimal mortality, availability of treatment options, protracted inoculation period and the emergence of new, more virulent potential weapons means that its inclusion among agents of bioterrorism is nowadays mainly of historical significance. Nevertheless, in the interest of literacy and of avoiding panic, physicians and the public both should be aware of the most common zoonosis worldwide. 相似文献
76.
Gandhi TK Zhong J Mathivanan S Karthick L Chandrika KN Mohan SS Sharma S Pinkert S Nagaraju S Periaswamy B Mishra G Nandakumar K Shen B Deshpande N Nayak R Sarker M Boeke JD Parmigiani G Schultz J Bader JS Pandey A 《Nature genetics》2006,38(3):285-293
We present the first analysis of the human proteome with regard to interactions between proteins. We also compare the human interactome with the available interaction datasets from yeast (Saccharomyces cerevisiae), worm (Caenorhabditis elegans) and fly (Drosophila melanogaster). Of >70,000 binary interactions, only 42 were common to human, worm and fly, and only 16 were common to all four datasets. An additional 36 interactions were common to fly and worm but were not observed in humans, although a coimmunoprecipitation assay showed that 9 of the interactions do occur in humans. A re-examination of the connectivity of essential genes in yeast and humans indicated that the available data do not support the presumption that the number of interaction partners can accurately predict whether a gene is essential. Finally, we found that proteins encoded by genes mutated in inherited genetic disorders are likely to interact with proteins known to cause similar disorders, suggesting the existence of disease subnetworks. The human interaction map constructed from our analysis should facilitate an integrative systems biology approach to elucidating the cellular networks that contribute to health and disease states. 相似文献
77.
Horvath A Boikos S Giatzakis C Robinson-White A Groussin L Griffin KJ Stein E Levine E Delimpasi G Hsiao HP Keil M Heyerdahl S Matyakhina L Libè R Fratticci A Kirschner LS Cramer K Gaillard RC Bertagna X Carney JA Bertherat J Bossis I Stratakis CA 《Nature genetics》2006,38(7):794-800
Phosphodiesterases (PDEs) regulate cyclic nucleotide levels. Increased cyclic AMP (cAMP) signaling has been associated with PRKAR1A or GNAS mutations and leads to adrenocortical tumors and Cushing syndrome. We investigated the genetic source of Cushing syndrome in individuals with adrenocortical hyperplasia that was not caused by known defects. We performed genome-wide SNP genotyping, including the adrenocortical tumor DNA. The region with the highest probability to harbor a susceptibility gene by loss of heterozygosity (LOH) and other analyses was 2q31-2q35. We identified mutations disrupting the expression of the PDE11A isoform-4 gene (PDE11A) in three kindreds. Tumor tissues showed 2q31-2q35 LOH, decreased protein expression and high cyclic nucleotide levels and cAMP-responsive element binding protein (CREB) phosphorylation. PDE11A codes for a dual-specificity PDE that is expressed in adrenal cortex and is partially inhibited by tadalafil and other PDE inhibitors; its germline inactivation is associated with adrenocortical hyperplasia, suggesting another means by which dysregulation of cAMP signaling causes endocrine tumors. 相似文献
78.
Sung LY Gao S Shen H Yu H Song Y Smith SL Chang CC Inoue K Kuo L Lian J Li A Tian XC Tuck DP Weissman SM Yang X Cheng T 《Nature genetics》2006,38(11):1323-1328
Since the creation of Dolly via somatic cell nuclear transfer (SCNT), more than a dozen species of mammals have been cloned using this technology. One hypothesis for the limited success of cloning via SCNT (1%-5%) is that the clones are likely to be derived from adult stem cells. Support for this hypothesis comes from the findings that the reproductive cloning efficiency for embryonic stem cells is five to ten times higher than that for somatic cells as donors and that cloned pups cannot be produced directly from cloned embryos derived from differentiated B and T cells or neuronal cells. The question remains as to whether SCNT-derived animal clones can be derived from truly differentiated somatic cells. We tested this hypothesis with mouse hematopoietic cells at different differentiation stages: hematopoietic stem cells, progenitor cells and granulocytes. We found that cloning efficiency increases over the differentiation hierarchy, and terminally differentiated postmitotic granulocytes yield cloned pups with the greatest cloning efficiency. 相似文献
79.
Richardson RJ Dixon J Malhotra S Hardman MJ Knowles L Boot-Handford RP Shore P Whitmarsh A Dixon MJ 《Nature genetics》2006,38(11):1329-1334
The epidermis is a highly organized structure, the integrity of which is central to the protection of an organism. Development and subsequent maintenance of this tissue depends critically on the intricate balance between proliferation and differentiation of a resident stem cell population; however, the signals controlling the proliferation-differentiation switch in vivo remain elusive. Here, we show that mice carrying a homozygous missense mutation in interferon regulatory factor 6 (Irf6), the homolog of the gene mutated in the human congenital disorders Van der Woude syndrome and popliteal pterygium syndrome, have a hyperproliferative epidermis that fails to undergo terminal differentiation, resulting in soft tissue fusions. We further demonstrate that mice that are compound heterozygotes for mutations in Irf6 and the gene encoding the cell cycle regulator protein stratifin (Sfn; also known as 14-3-3sigma) show similar defects of keratinizing epithelia. Our results indicate that Irf6 is a key determinant of the keratinocyte proliferation-differentiation switch and that Irf6 and Sfn interact genetically in this process. 相似文献
80.
Amundadottir LT Sulem P Gudmundsson J Helgason A Baker A Agnarsson BA Sigurdsson A Benediktsdottir KR Cazier JB Sainz J Jakobsdottir M Kostic J Magnusdottir DN Ghosh S Agnarsson K Birgisdottir B Le Roux L Olafsdottir A Blondal T Andresdottir M Gretarsdottir OS Bergthorsson JT Gudbjartsson D Gylfason A Thorleifsson G Manolescu A Kristjansson K Geirsson G Isaksson H Douglas J Johansson JE Bälter K Wiklund F Montie JE Yu X Suarez BK Ober C Cooney KA Gronberg H Catalona WJ Einarsson GV 《Nature genetics》2006,38(6):652-658
With the increasing incidence of prostate cancer, identifying common genetic variants that confer risk of the disease is important. Here we report such a variant on chromosome 8q24, a region initially identified through a study of Icelandic families. Allele -8 of the microsatellite DG8S737 was associated with prostate cancer in three case-control series of European ancestry from Iceland, Sweden and the US. The estimated odds ratio (OR) of the allele is 1.62 (P = 2.7 x 10(-11)). About 19% of affected men and 13% of the general population carry at least one copy, yielding a population attributable risk (PAR) of approximately 8%. The association was also replicated in an African American case-control group with a similar OR, in which 41% of affected individuals and 30% of the population are carriers. This leads to a greater estimated PAR (16%) that may contribute to higher incidence of prostate cancer in African American men than in men of European ancestry. 相似文献