全文获取类型
收费全文 | 17770篇 |
免费 | 36篇 |
国内免费 | 86篇 |
专业分类
系统科学 | 134篇 |
丛书文集 | 289篇 |
教育与普及 | 45篇 |
理论与方法论 | 67篇 |
现状及发展 | 7518篇 |
研究方法 | 959篇 |
综合类 | 8607篇 |
自然研究 | 273篇 |
出版年
2013年 | 126篇 |
2012年 | 345篇 |
2011年 | 618篇 |
2010年 | 124篇 |
2009年 | 114篇 |
2008年 | 350篇 |
2007年 | 399篇 |
2006年 | 406篇 |
2005年 | 406篇 |
2004年 | 406篇 |
2003年 | 347篇 |
2002年 | 337篇 |
2001年 | 619篇 |
2000年 | 581篇 |
1999年 | 393篇 |
1992年 | 329篇 |
1991年 | 268篇 |
1990年 | 284篇 |
1989年 | 257篇 |
1988年 | 237篇 |
1987年 | 281篇 |
1986年 | 294篇 |
1985年 | 319篇 |
1984年 | 281篇 |
1983年 | 223篇 |
1982年 | 182篇 |
1981年 | 195篇 |
1980年 | 249篇 |
1979年 | 569篇 |
1978年 | 433篇 |
1977年 | 425篇 |
1976年 | 315篇 |
1975年 | 352篇 |
1974年 | 517篇 |
1973年 | 440篇 |
1972年 | 435篇 |
1971年 | 523篇 |
1970年 | 690篇 |
1969年 | 487篇 |
1968年 | 400篇 |
1967年 | 488篇 |
1966年 | 405篇 |
1965年 | 285篇 |
1959年 | 162篇 |
1958年 | 268篇 |
1957年 | 207篇 |
1956年 | 180篇 |
1955年 | 144篇 |
1954年 | 150篇 |
1948年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Vissers LE van Ravenswaaij CM Admiraal R Hurst JA de Vries BB Janssen IM van der Vliet WA Huys EH de Jong PJ Hamel BC Schoenmakers EF Brunner HG Veltman JA van Kessel AG 《Nature genetics》2004,36(9):955-957
CHARGE syndrome is a common cause of congenital anomalies affecting several tissues in a nonrandom fashion. We report a 2.3-Mb de novo overlapping microdeletion on chromosome 8q12 identified by array comparative genomic hybridization in two individuals with CHARGE syndrome. Sequence analysis of genes located in this region detected mutations in the gene CHD7 in 10 of 17 individuals with CHARGE syndrome without microdeletions, accounting for the disease in most affected individuals. 相似文献
992.
Ding H Wu X Boström H Kim I Wong N Tsoi B O'Rourke M Koh GY Soriano P Betsholtz C Hart TC Marazita ML Field LL Tam PP Nagy A 《Nature genetics》2004,36(10):1111-1116
PDGF-C is a member of the platelet-derived growth factor (PDGF) family, which signals through PDGF receptor (PDGFR) alphaalpha and alphabeta dimers. Here we show that Pdgfc(-/-) mice die in the perinatal period owing to feeding and respiratory difficulties associated with a complete cleft of the secondary palate. This phenotype was less severe than that of Pdgfra(-/-) embryos. Pdgfc(-/-) Pdgfa(-/-) embryos developed a cleft face, subepidermal blistering, deficiency of renal cortex mesenchyme, spina bifida and skeletal and vascular defects. Complete loss of function of both ligands, therefore, phenocopied the loss of PDGFR-alpha function, suggesting that both PDGF-A and PDGF-C signal through PDGFR-alpha to regulate the development of craniofacial structures, the neural tube and mesodermal organs. Our results also show that PDGF-C signaling is a new pathway in palatogenesis, different from, and independent of, those previously implicated. 相似文献
993.
The genetic association database 总被引:1,自引:0,他引:1
994.
Krantz ID McCallum J DeScipio C Kaur M Gillis LA Yaeger D Jukofsky L Wasserman N Bottani A Morris CA Nowaczyk MJ Toriello H Bamshad MJ Carey JC Rappaport E Kawauchi S Lander AD Calof AL Li HH Devoto M Jackson LG 《Nature genetics》2004,36(6):631-635
Cornelia de Lange syndrome (CdLS; OMIM 122470) is a dominantly inherited multisystem developmental disorder characterized by growth and cognitive retardation; abnormalities of the upper limbs; gastroesophageal dysfunction; cardiac, ophthalmologic and genitourinary anomalies; hirsutism; and characteristic facial features. Genital anomalies, pyloric stenosis, congenital diaphragmatic hernias, cardiac septal defects, hearing loss and autistic and self-injurious tendencies also frequently occur. Prevalence is estimated to be as high as 1 in 10,000 (ref. 4). We carried out genome-wide linkage exclusion analysis in 12 families with CdLS and identified four candidate regions, of which chromosome 5p13.1 gave the highest multipoint lod score of 2.7. This information, together with the previous identification of a child with CdLS with a de novo t(5;13)(p13.1;q12.1) translocation, allowed delineation of a 1.1-Mb critical region on chromosome 5 for the gene mutated in CdLS. We identified mutations in one gene in this region, which we named NIPBL, in four sporadic and two familial cases of CdLS. We characterized the genomic structure of NIPBL and found that it is widely expressed in fetal and adult tissues. The fly homolog of NIPBL, Nipped-B, facilitates enhancer-promoter communication and regulates Notch signaling and other developmental pathways in Drosophila melanogaster. 相似文献
995.
996.
The knockout mouse project 总被引:1,自引:0,他引:1
Austin CP Battey JF Bradley A Bucan M Capecchi M Collins FS Dove WF Duyk G Dymecki S Eppig JT Grieder FB Heintz N Hicks G Insel TR Joyner A Koller BH Lloyd KC Magnuson T Moore MW Nagy A Pollock JD Roses AD Sands AT Seed B Skarnes WC Snoddy J Soriano P Stewart DJ Stewart F Stillman B Varmus H Varticovski L Verma IM Vogt TF von Melchner H Witkowski J Woychik RP Wurst W Yancopoulos GD Young SG Zambrowicz B 《Nature genetics》2004,36(9):921-924
Mouse knockout technology provides a powerful means of elucidating gene function in vivo, and a publicly available genome-wide collection of mouse knockouts would be significantly enabling for biomedical discovery. To date, published knockouts exist for only about 10% of mouse genes. Furthermore, many of these are limited in utility because they have not been made or phenotyped in standardized ways, and many are not freely available to researchers. It is time to harness new technologies and efficiencies of production to mount a high-throughput international effort to produce and phenotype knockouts for all mouse genes, and place these resources into the public domain. 相似文献
997.
BMP signaling inhibits intestinal stem cell self-renewal through suppression of Wnt-beta-catenin signaling 总被引:21,自引:0,他引:21
He XC Zhang J Tong WG Tawfik O Ross J Scoville DH Tian Q Zeng X He X Wiedemann LM Mishina Y Li L 《Nature genetics》2004,36(10):1117-1121
In humans, mutations in BMPR1A, SMAD4 and PTEN are responsible for juvenile polyposis syndrome, juvenile intestinal polyposis and Cowden disease, respectively. The development of polyposis is a common feature of these diseases, suggesting that there is an association between BMP and PTEN pathways. The mechanistic link between BMP and PTEN pathways and the related etiology of juvenile polyposis is unresolved. Here we show that conditional inactivation of Bmpr1a in mice disturbs homeostasis of intestinal epithelial regeneration with an expansion of the stem and progenitor cell populations, eventually leading to intestinal polyposis resembling human juvenile polyposis syndrome. We show that BMP signaling suppresses Wnt signaling to ensure a balanced control of stem cell self-renewal. Mechanistically, PTEN, through phosphatidylinosital-3 kinase-Akt, mediates the convergence of the BMP and Wnt pathways on control of beta-catenin. Thus, BMP signaling may control the duplication of intestinal stem cells, thereby preventing crypt fission and the subsequent increase in crypt number. 相似文献
998.
Gabrielli P Barbante C Plane JM Varga A Hong S Cozzi G Gaspari V Planchon FA Cairns W Ferrari C Crutzen P Cescon P Boutron CF 《Nature》2004,432(7020):1011-1014
An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65 million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000 years ago, from a Greenland ice core. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre-sized meteoric smoke particles, formed from the recondensation of ablated meteoroids in the atmosphere at altitudes >70 kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 +/- 5 kilotons per year of meteoric smoke during the Holocene. 相似文献
999.
1000.
Mercury is locked into a 3/2 spin-orbit resonance where it rotates three times on its axis for every two orbits around the sun. The stability of this equilibrium state is well established, but our understanding of how this state initially arose remains unsatisfactory. Unless one uses an unrealistic tidal model with constant torques (which cannot account for the observed damping of the libration of the planet) the computed probability of capture into 3/2 resonance is very low (about 7 per cent). This led to the proposal that core-mantle friction may have increased the capture probability, but such a process requires very specific values of the core viscosity. Here we show that the chaotic evolution of Mercury's orbit can drive its eccentricity beyond 0.325 during the planet's history, which very efficiently leads to its capture into the 3/2 resonance. In our numerical integrations of 1,000 orbits of Mercury over 4 Gyr, capture into the 3/2 spin-orbit resonant state was the most probable final outcome of the planet's evolution, occurring 55.4 per cent of the time. 相似文献