全文获取类型
收费全文 | 9351篇 |
免费 | 85篇 |
国内免费 | 69篇 |
专业分类
系统科学 | 121篇 |
丛书文集 | 94篇 |
教育与普及 | 20篇 |
理论与方法论 | 42篇 |
现状及发展 | 3566篇 |
研究方法 | 660篇 |
综合类 | 4791篇 |
自然研究 | 211篇 |
出版年
2016年 | 61篇 |
2014年 | 62篇 |
2013年 | 83篇 |
2012年 | 215篇 |
2011年 | 473篇 |
2010年 | 96篇 |
2009年 | 73篇 |
2008年 | 277篇 |
2007年 | 333篇 |
2006年 | 264篇 |
2005年 | 253篇 |
2004年 | 356篇 |
2003年 | 257篇 |
2002年 | 288篇 |
2001年 | 312篇 |
2000年 | 307篇 |
1999年 | 231篇 |
1992年 | 128篇 |
1991年 | 130篇 |
1990年 | 120篇 |
1989年 | 108篇 |
1988年 | 109篇 |
1987年 | 121篇 |
1986年 | 116篇 |
1985年 | 162篇 |
1984年 | 127篇 |
1983年 | 103篇 |
1982年 | 88篇 |
1981年 | 116篇 |
1980年 | 111篇 |
1979年 | 253篇 |
1978年 | 203篇 |
1977年 | 185篇 |
1976年 | 139篇 |
1975年 | 163篇 |
1974年 | 214篇 |
1973年 | 177篇 |
1972年 | 194篇 |
1971年 | 219篇 |
1970年 | 276篇 |
1969年 | 211篇 |
1968年 | 189篇 |
1967年 | 211篇 |
1966年 | 181篇 |
1965年 | 145篇 |
1959年 | 53篇 |
1958年 | 105篇 |
1957年 | 76篇 |
1956年 | 74篇 |
1954年 | 74篇 |
排序方式: 共有9505条查询结果,搜索用时 15 毫秒
201.
Wolfs JL Comfurius P Bekers O Zwaal RF Balasubramanian K Schroit AJ Lindhout T Bevers EM 《Cellular and molecular life sciences : CMLS》2009,66(2):314-323
The exposure of phosphatidylserine (PS) at the cell surface plays a critical role in blood coagulation and serves as a macrophage
recognition moiety for the engulfment of apoptotic cells. Previous observations have shown that a high extracellular [K+] and selective K+ channel blockers inhibit PS exposure in platelets and erythrocytes. Here we show that the rate of PS exposure in erythrocytes
decreases by ~50% when the intracellular [K+] increases from 0 to physiological concentrations. Using resealed erythrocyte membranes, we further show that lipid scrambling
is inducible by raising the intracellular [Ca2+] and that K+ ions have a direct inhibitory effect on this process. Lipid scrambling in resealed ghosts occurs in the absence of cell shrinkage
and microvesicle formation, processes that are generally attributed to Ca2+-induced lipid scrambling in intact erythrocytes. Thus, opening of Ca2+-sensitive K+ channels causes loss of intracellular K+ that results in reduced intrinsic inhibitory effect of these ions on scramblase activity.
Received 11 September 2008; received after revision 17 October 2008; accepted 27 October 2008 相似文献
202.
Dynamic protein methylation in chromatin biology 总被引:1,自引:1,他引:0
203.
204.
205.
Sara Ruane Stephen J. Richards John D. McVay Burhan Tjaturadi Keliopas Krey Christopher C. Austin 《Journal of Natural History》2018,52(13-16):917-944
ABSTRACTThe island of New Guinea has been identified as biologically megadiverse but many taxa are still poorly known. This is especially the case for many of the island’s snakes, which by their very nature can be difficult to collect and study. Here we examine the phylogenetic and phylogeographic structure of a poorly studied snake genus, Stegonotus, focusing on the species of New Guinea; until now, Stegonotus has never been examined using modern phylogenetic methods. Using molecular data from 49 individuals representing eight of the ten described species, and including all New Guinea taxa, we estimate a multilocus phylogeny and examine population structure to help identify undescribed taxa. We use morphological data from the corresponding museum vouchered specimens (where available) and also examine additional specimens for taxa not included in the molecular data set to determine morphological differences among putative taxa. We find molecular evidence for four new species of Stegonotus, both morphologically obvious and cryptic, and describe them herein. The recognition of these four species indicates that Stegonotus diversity has been previously underestimated and also suggests that there are likely additional undescribed taxa within the genus. These four taxa increase the number of described species by 40% and further confirm New Guinea as the centre of diversity for the genus.www.zoobank.org/urn:lsid:zoobank.org:pub:9E21390E-3FD4-40EB-9442-31BC92A76B4F 相似文献
206.
Nádia Caldato Luiz Carlos Forti Ana Paula Protti de Andrade Juliane Floriano Santos Lopes 《Journal of Natural History》2016,50(25-26):1561-1581
Acromyrmex balzani is a grass-cutting ant species frequently found in Cerrado areas. However, little is known about the architecture of the polydomous nests of this ant. Fifteen A. balzani nests located in a cerrado region in Botucatu, São Paulo, Brazil, were studied. The polydomous nests were studied in three ways. First, we investigated the architecture in nests moulded with cement and without moulding. Second, we performed an aggressiveness test among workers in different subnests and nests. Third, we excavated the nest and collected the colony to measure the population, verifying the existence or not of a queen in all nests. A cement mould was made of seven nests to permit better visualization of internal structures such as chambers and tunnels. Eight nests were excavated without moulding and white neutral talc was used to highlight the parts of the nests. After excavation, the depth and dimensions (length, width and height) of the chambers were measured. The results showed that the nests had a single entrance hole whose structure consisted of straw and other plant residues in winter. Mounds of loose soil, if present, were found 6–48 cm from the hole. The number of chambers containing fungus ranged from one to five, with the first being found a few centimetres beneath the ground surface (4 cm) and the last up to a maximum depth of 160 cm. The length of the tunnels ranged from 12 to 28 cm. These tunnels were built in a vertical or inclined position, leading to the chambers. No waste chambers were found, with the waste being deposited externally. Additionally, the polydomous nests contained one to eight subnests. In the aggressiveness test, when concolonial workers were confronted, no aggressiveness was observed. In contrast, when allocolonial workers were confronted, there was a high incidence of aggression among them. Excavation of polydomous nests showed only one queen for each polydomous nest, i.e. subnests with a single queen. Our study contributes to a better understanding of the so far unknown nest architecture of the polydomous grass-cutting ant A. balzani. 相似文献
207.
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
208.
Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis 总被引:21,自引:0,他引:21
Palmer CN Irvine AD Terron-Kwiatkowski A Zhao Y Liao H Lee SP Goudie DR Sandilands A Campbell LE Smith FJ O'Regan GM Watson RM Cecil JE Bale SJ Compton JG DiGiovanna JJ Fleckman P Lewis-Jones S Arseculeratne G Sergeant A Munro CS El Houate B McElreavey K Halkjaer LB Bisgaard H Mukhopadhyay S McLean WH 《Nature genetics》2006,38(4):441-446
Atopic disease, including atopic dermatitis (eczema), allergy and asthma, has increased in frequency in recent decades and now affects approximately 20% of the population in the developed world. Twin and family studies have shown that predisposition to atopic disease is highly heritable. Although most genetic studies have focused on immunological mechanisms, a primary epithelial barrier defect has been anticipated. Filaggrin is a key protein that facilitates terminal differentiation of the epidermis and formation of the skin barrier. Here we show that two independent loss-of-function genetic variants (R510X and 2282del4) in the gene encoding filaggrin (FLG) are very strong predisposing factors for atopic dermatitis. These variants are carried by approximately 9% of people of European origin. These variants also show highly significant association with asthma occurring in the context of atopic dermatitis. This work establishes a key role for impaired skin barrier function in the development of atopic disease. 相似文献
209.
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
210.
Balasubramanian S Sureshkumar S Agrawal M Michael TP Wessinger C Maloof JN Clark R Warthmann N Chory J Weigel D 《Nature genetics》2006,38(6):711-715
Light has an important role in modulating seedling growth and flowering time. We show that allelic variation at the PHYTOCHROME C (PHYC) photoreceptor locus affects both traits in natural populations of A. thaliana. Two functionally distinct PHYC haplotype groups are distributed in a latitudinal cline dependent on FRIGIDA, a locus that together with FLOWERING LOCUS C explains a large portion of the variation in A. thaliana flowering time. In a genome-wide scan for association of 65 loci with latitude, there was an excess of significant P values, indicative of population structure. Nevertheless, PHYC was the most strongly associated locus across 163 strains, suggesting that PHYC alleles are under diversifying selection in A. thaliana. Our work, together with previous findings, suggests that photoreceptor genes are major agents of natural variation in plant flowering and growth response. 相似文献