全文获取类型
收费全文 | 6863篇 |
免费 | 733篇 |
国内免费 | 1篇 |
出版年
2022年 | 43篇 |
2021年 | 98篇 |
2020年 | 71篇 |
2019年 | 85篇 |
2018年 | 63篇 |
2017年 | 79篇 |
2016年 | 116篇 |
2015年 | 277篇 |
2014年 | 278篇 |
2013年 | 345篇 |
2012年 | 467篇 |
2011年 | 475篇 |
2010年 | 301篇 |
2009年 | 246篇 |
2008年 | 341篇 |
2007年 | 371篇 |
2006年 | 353篇 |
2005年 | 369篇 |
2004年 | 329篇 |
2003年 | 298篇 |
2002年 | 297篇 |
2001年 | 98篇 |
2000年 | 92篇 |
1999年 | 91篇 |
1998年 | 108篇 |
1997年 | 67篇 |
1996年 | 53篇 |
1995年 | 59篇 |
1994年 | 59篇 |
1993年 | 63篇 |
1992年 | 70篇 |
1991年 | 74篇 |
1990年 | 84篇 |
1989年 | 56篇 |
1988年 | 55篇 |
1987年 | 84篇 |
1986年 | 58篇 |
1985年 | 67篇 |
1984年 | 77篇 |
1983年 | 74篇 |
1982年 | 55篇 |
1981年 | 50篇 |
1980年 | 70篇 |
1979年 | 60篇 |
1978年 | 62篇 |
1977年 | 48篇 |
1976年 | 54篇 |
1974年 | 50篇 |
1973年 | 50篇 |
1971年 | 44篇 |
排序方式: 共有7597条查询结果,搜索用时 15 毫秒
1.
A Rauch R A Pfeiffer G Leipold H Singer M Tigges M Hofbeck 《American journal of human genetics》1999,64(2):659-666
2.
Kevin Karbstein Kathleen Prinz Frank Hellwig Christine Rmermann 《Ecology and evolution》2020,10(11):5015-5033
Intraspecific trait variation (ITV), based on available genetic diversity, is one of the major means plant populations can respond to environmental variability. The study of functional trait variation and diversity has become popular in ecological research, for example, as a proxy for plant performance influencing fitness. Up to now, it is unclear which aspects of intraspecific functional trait variation (iFDCV) can be attributed to the environment or genetics under natural conditions. Here, we examined 260 individuals from 13 locations of the rare (semi‐)dry calcareous grassland species Trifolium montanum L. in terms of iFDCV, within‐habitat heterogeneity, and genetic diversity. The iFDCV was assessed by measuring functional traits (releasing height, biomass, leaf area, specific leaf area, leaf dry matter content, Fv/Fm, performance index, stomatal pore surface, and stomatal pore area index). Abiotic within‐habitat heterogeneity was derived from altitude, slope exposure, slope, leaf area index, soil depth, and further soil factors. Based on microsatellites, we calculated expected heterozygosity (He) because it best‐explained, among other indices, iFDCV. We performed multiple linear regression models quantifying relationships among iFDCV, abiotic within‐habitat heterogeneity and genetic diversity, and also between separate functional traits and abiotic within‐habitat heterogeneity or genetic diversity. We found that abiotic within‐habitat heterogeneity influenced iFDCV twice as strong compared to genetic diversity. Both aspects together explained 77% of variation in iFDCV ( = .77, F2, 10 = 21.66, p < .001). The majority of functional traits (releasing height, biomass, specific leaf area, leaf dry matter content, Fv/Fm, and performance index) were related to abiotic habitat conditions indicating responses to environmental heterogeneity. In contrast, only morphology‐related functional traits (releasing height, biomass, and leaf area) were related to genetics. Our results suggest that both within‐habitat heterogeneity and genetic diversity affect iFDCV and are thus crucial to consider when aiming to understand or predict changes of plant species performance under changing environmental conditions. 相似文献
3.
Shira Weingarten-Gabbay Susan Klaeger Siranush Sarkizova Leah R. Pearlman Da-Yuan Chen Kathleen M.E. Gallagher Matthew R. Bauer Hannah B. Taylor W. Augustine Dunn Christina Tarr John Sidney Suzanna Rachimi Hasahn L. Conway Katelin Katsis Yuntong Wang Del Leistritz-Edwards Melissa R. Durkin Christopher H. Tomkins-Tinch Pardis C. Sabeti 《Cell》2021,184(15):3962-3980.e17
- Download : Download high-res image (225KB)
- Download : Download full-size image
4.
5.
6.
The specificity of the syngeneic mixed leukocyte response, a primary anti-I region T cell proliferative response, is determined intrathymically 总被引:6,自引:0,他引:6
L H Glimcher R H Schwartz D L Longo A Singer 《Journal of immunology (Baltimore, Md. : 1950)》1982,129(3):987-991
In previous studies, the syngeneic MLR of peripheral T cells was shown to be predominantly an I region-restricted function. In this report we show that adult thymocytes are also capable of responding to syngeneic irradiated stimulator cells in a syngeneic MLR, provided that TCGF is added to the culture system. Using this assay, it was possible for the first time to examine the pattern of I region restriction within the thymus itself. Analysis of the thymocyte syngeneic MLR in thymuses from radiation-induced bone marrow chimeras demonstrated that the MHC preference seen in the peripheral T cell population also existed in cells resident within the thymus. Experiments utilizing congenitally athymic mice transplanted with allogeneic thymic grafts demonstrated that both peripheral T cells and thymocytes from such animals displayed a strong preferential proliferation toward stimulator cells bearing thymic-type MHC determinants. The results in the nude model thus demonstrate that the thymus by itself is sufficient to impart such restriction specificity on a developing T cell repertoire. These results are consistent with the notion that the thymus exerts selective pressure on maturing T cell populations that results in a skewing of the T cell repertoire toward the recognition of thymic-type I region products, and that this MHC preference exists before expansion of T cells in the periphery. 相似文献
7.
8.
9.
10.
Eliot C. Bush Anne E. Clark Chris M. DeBoever Lillian E. Haynes Sidra Hussain Singer Ma Matthew M. McDermott Adam M. Novak John S. Wentworth 《PloS one》2012,7(11)
A significant proportion of enzymes display cooperativity in binding ligand molecules, and such effects have an important impact on metabolic regulation. This is easiest to understand in the case of positive cooperativity. Sharp responses to changes in metabolite concentrations can allow organisms to better respond to environmental changes and maintain metabolic homeostasis. However, despite the fact that negative cooperativity is almost as common as positive, it has been harder to imagine what advantages it provides. Here we use computational models to explore the utility of negative cooperativity in one particular context: that of an inhibitor binding to an enzyme. We identify several factors which may contribute, and show that acting together they can make negative cooperativity advantageous. 相似文献