全文获取类型
收费全文 | 5049篇 |
免费 | 366篇 |
国内免费 | 931篇 |
出版年
2023年 | 62篇 |
2022年 | 55篇 |
2021年 | 119篇 |
2020年 | 153篇 |
2019年 | 150篇 |
2018年 | 130篇 |
2017年 | 140篇 |
2016年 | 170篇 |
2015年 | 165篇 |
2014年 | 182篇 |
2013年 | 320篇 |
2012年 | 178篇 |
2011年 | 231篇 |
2010年 | 166篇 |
2009年 | 205篇 |
2008年 | 219篇 |
2007年 | 264篇 |
2006年 | 274篇 |
2005年 | 254篇 |
2004年 | 264篇 |
2003年 | 240篇 |
2002年 | 238篇 |
2001年 | 229篇 |
2000年 | 209篇 |
1999年 | 198篇 |
1998年 | 127篇 |
1997年 | 131篇 |
1996年 | 121篇 |
1995年 | 114篇 |
1994年 | 112篇 |
1993年 | 143篇 |
1992年 | 93篇 |
1991年 | 106篇 |
1990年 | 78篇 |
1989年 | 76篇 |
1988年 | 76篇 |
1987年 | 42篇 |
1986年 | 37篇 |
1985年 | 50篇 |
1984年 | 37篇 |
1983年 | 23篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1974年 | 12篇 |
排序方式: 共有6346条查询结果,搜索用时 15 毫秒
1.
Swanne P. Gordon David Reznick Jeff D. Arendt Allen Roughton Michelle N. Ontiveros Hernandez Paul Bentzen Andrés López-Sepulcre 《Proceedings. Biological sciences / The Royal Society》2015,282(1813)
Evolutionary analyses of population translocations (experimental or accidental) have been important in demonstrating speed of evolution because they subject organisms to abrupt environmental changes that create an episode of selection. However, the strength of selection in such studies is rarely measured, limiting our understanding of the evolutionary process. This contrasts with long-term, mark–recapture studies of unmanipulated populations that measure selection directly, yet rarely reveal evolutionary change. Here, we present a study of experimental evolution of male colour in Trinidadian guppies where we tracked both evolutionary change and individual-based measures of selection. Guppies were translocated from a predator-rich to a low-predation environment within the same stream system. We used a combination of common garden experiments and monthly sampling of individuals to measure the phenotypic and genetic divergence of male coloration between ancestral and derived fish. Results show rapid evolutionary increases in orange coloration in both populations (1 year or three generations), replicating the results of previous studies. Unlike previous studies, we linked this evolution to an individual-based analysis of selection. By quantifying individual reproductive success and survival, we show, for the first time, that males with more orange and black pigment have higher reproductive success, but males with more black pigment also have higher risk of mortality. The net effect of selection is thus an advantage of orange but not black coloration, as reflected in the evolutionary response. This highlights the importance of considering all components of fitness when understanding the evolution of sexually selected traits in the wild. 相似文献
2.
3.
从抗纹枯病小麦品种CI12633中克隆出一个小麦防御素基因TaPDF35,并对其表达特性及功能进行了分析。TaPDF35基因包含一个长为249 bp的开放阅读框(ORF,open reading frame),编码82个氨基酸组成的多肽TaPDF35。预测分析表明,TaPDF35能形成由1个α螺旋和3股反向平行的β-折叠片组成的αβ(CSαβ)基序,αβ(CSαβ)基序由8个半胱氨酸形成的4个二硫键固定。TaPDF35的N端有一段27个氨基酸的信号肽。表达分析结果表明,TaPDF35基因在抗纹枯病小麦品种CI12633和山红麦中的表达量显著高于在感纹枯病小麦品种扬麦158和温麦6号中的表达量;该基因在小麦的叶鞘和茎中均有表达,且受纹枯病原菌诱导而上调表达。利用大麦条形花叶病毒(BSMV,barley stripe mosaic virus)诱导的基因沉默技术(VIGS,virus-induced gene silencing)降低抗纹枯病小麦品种CI12633中TaPDF35基因的转录水平,再接种纹枯病原菌进行纹枯病抗性鉴定。结果显示,与接种BSMV:GFP的CI12633对照植株相比,TaPDF35表达水平降低的CI12633植株对纹枯病的抗性显著降低,表明TaPDF35表达是小麦防御纹枯病反应所需的。 相似文献
4.
Noriko Kohyama Makiko Chono Hiroyuki Nakagawa Yosuke Matsuo Hiroshi Ono Hitoshi Matsunaka 《Bioscience, biotechnology, and biochemistry》2017,81(11):2112-2118
In red wheat, reddish-brown pigments accumulate in testa of mature seeds. Half-cut wheat seeds were immersed in p-dimethylaminocinnamaldehyde (DMACA) reagent that stains flavanol structures blue. Testa of 10–40 days after flowering (DAF) in red wheat (“Norin 61” and “Satonosora”) seeds were stained blue and the reagent color changed to blue with 10–25 DAF seeds. No blue staining was observed in white wheat (“Tamaizumi”) seeds during maturation. “Norin 61” seed coats at 10 DAF contained dihydroquercetin, dihydromyricetin, (+)-catechin, procyanidin B3, and prodelphinidin B3, which were identified by HPLC-diode array detector and LC-MS/MS analyses. These five components began accumulating 7 DAF, reached maxima at 10 or 15 DAF, and then decreased in red wheat seeds, but were not detected in white wheat seeds. These results suggest that flavanol and proanthocyanidins are possible precursors of the reddish-brown pigments of red wheat seeds, and are converted to insoluble compounds as the seeds mature. 相似文献
5.
Hypersensitive response of wheat to the Hessian fly 总被引:3,自引:0,他引:3
Paul B. Grover Jr. 《Entomologia Experimentalis et Applicata》1995,74(3):283-294
Hessian flyMayetiola destructor (Say) larvae are able to obtain food from their host plant without inflicting mechanical damage to the plant surface, apparently
by secreting substances which elicit release of nutrients from plant cells surrounding the feeding site. Cells of fully susceptible
plants retain their normal appearances, while in resistant plants extensive areas of cellular collapse occur. These responses
indicate that hypersensitivity is the basis of wheat's resistance to the Hessian fly. The fly's feeding mechanism more closely
resembles that of a pathogen than of a phytophagous insect; correspondingly, both the genetic relationship and resistance
mechanism of the host plant to the parasite are of the sorts commonly associated with bacterial and fungal pathogens. 相似文献
6.
7.
8.
9.
10.
We have tested the effect of alkaloids (cocaine, morphine) and enkephalins on neutral endopeptidase of peripheral blood mononuclear cells activated by lectins. When treated with concanavalin A and cocaine, peripheral blood mononuclear cells showed an enhanced activity (+110 per cent) of the membrane neutral endopeptidase, which was not related to the expression of the common acute lymphoblastic leukemia antigen at the cell surface, although both molecules have the identical amino acid sequence. Phytohemagglutinin-P, morphine and synthetic enkephalins did not induce the activity of neutral endopeptidase nor the expression of common acute lymphoblastic leukemia antigen. Our findings suggested that the drugs of abuse, cocaine and morphine, affected specific membrane constituents without altering proliferation, subcellular localization of membrane enzymes or the surface immune phenotype of peripheral blood mononuclear cells. 相似文献