全文获取类型
收费全文 | 95382篇 |
免费 | 8563篇 |
国内免费 | 43篇 |
专业分类
103988篇 |
出版年
2023年 | 357篇 |
2022年 | 804篇 |
2021年 | 1660篇 |
2020年 | 940篇 |
2019年 | 1241篇 |
2018年 | 1527篇 |
2017年 | 1398篇 |
2016年 | 2259篇 |
2015年 | 3883篇 |
2014年 | 4402篇 |
2013年 | 5260篇 |
2012年 | 7071篇 |
2011年 | 6863篇 |
2010年 | 4378篇 |
2009年 | 4135篇 |
2008年 | 5857篇 |
2007年 | 5893篇 |
2006年 | 5499篇 |
2005年 | 5331篇 |
2004年 | 5133篇 |
2003年 | 4932篇 |
2002年 | 4639篇 |
2001年 | 958篇 |
2000年 | 719篇 |
1999年 | 1000篇 |
1998年 | 1303篇 |
1997年 | 886篇 |
1996年 | 814篇 |
1995年 | 768篇 |
1994年 | 655篇 |
1993年 | 736篇 |
1992年 | 662篇 |
1991年 | 560篇 |
1990年 | 563篇 |
1989年 | 545篇 |
1988年 | 506篇 |
1987年 | 472篇 |
1986年 | 436篇 |
1985年 | 609篇 |
1984年 | 680篇 |
1983年 | 619篇 |
1982年 | 719篇 |
1981年 | 659篇 |
1980年 | 659篇 |
1979年 | 387篇 |
1978年 | 465篇 |
1977年 | 396篇 |
1976年 | 398篇 |
1974年 | 351篇 |
1973年 | 346篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
173.
Abstract: Schwannoma-derived growth factor (SDGF) is a potent mitogen and neuronal differentiation factor. Because of its relationship to epidermal growth factor (EGF) and the heregulins, it was asked if SDGF interacts with the EGF receptor or HER2/neu. SDGF binds to and causes the phosphorylation on tyrosine of the EGF receptor but not HER2/neu. 相似文献
174.
Kevin Dougherty Brian A. Smith Autumn F. Moore Shannon Maitland Chris Fanger Rachel Murillo David A. Baltrus 《PloS one》2014,9(7)
Horizontal gene transfer often leads to phenotypic changes within recipient organisms independent of any immediate evolutionary benefits. While secondary phenotypic effects of horizontal transfer (i.e., changes in growth rates) have been demonstrated and studied across a variety of systems using relatively small plasmids and phage, little is known about the magnitude or number of such costs after the transfer of larger regions. Here we describe numerous phenotypic changes that occur after a large-scale horizontal transfer event (∼1 Mb megaplasmid) within Pseudomonas stutzeri including sensitization to various stresses as well as changes in bacterial behavior. These results highlight the power of horizontal transfer to shift pleiotropic relationships and cellular networks within bacterial genomes. They also provide an important context for how secondary effects of transfer can bias evolutionary trajectories and interactions between species. Lastly, these results and system provide a foundation to investigate evolutionary consequences in real time as newly acquired regions are ameliorated and integrated into new genomic contexts. 相似文献
175.
176.
Fire regimes have three inter-related components that can affect population dynamics: frequency, intensity and season. However,
there has been little effort to study the effects of any of these components on arbuscular mycorrhizas (AM). In order to examine
the long-term effects of fire frequency on AM colonization, the roots of Dillwynia retorta were examined at 32 sites supporting Hawkesbury Sandstone vegetation in the Sydney region of southeastern Australia. These
sites were representative of the broad-scale variability in fire frequencies with respect to the length and timing of inter-fire
intervals found in the Sydney region during the previous 30 years. The length of the shortest inter-fire interval was significantly
correlated with total AM colonization, and the length of the longest inter-fire interval was related to the arbuscular colonization.
The length of the most-recent inter-fire interval and the time since the shortest inter-fire interval were not related to
AM colonization in D. retorta. Furthermore, AM colonization was directly related to the local abundance of the host plant, indicating that the effects
of fire frequency on AM colonization are likely to occur indirectly via direct effects on the host plant. Canonical correspondence
analysis demonstrated that the presence and abundance of alternate potential hosts had no influence on mycotrophy in D. retorta. Thus, the impact of fire on D. retorta was probably the main factor influencing its mycorrhizal status in relation to fire history.
Accepted: 16 October 1998 相似文献
177.
Little work has been carried out on the sperm recognition systems present on the egg plasma membrane. Here it is shown that wheat germ agglutinin (WGA) interferes with the sperm-interacting system on the plasma membrane of eggs of the ascidian, Ascidia ceratodes. The WGA activates the dechorionated egg, indicating that a plasma membrane sugar residue can be directly tied to egg activation. Low concentrations of this lectin do not activate the eggs, but reduce fertilizability. This observation suggests that the WGA binding site might be part of a sperm reception–activation complex in the plasma membrane. While WGA also affects sperm binding to the chorion, the mechanisms of sperm interaction at the plasma membrane and chorion show different sensitivities to lectins, sugars and enzymes. 相似文献
178.
Tristan J. Iseli Nigel Turner Xiao-Yi Zeng Gregory J. Cooney Edward W. Kraegen Sheng Yao Yang Ye David E. James Ji-Ming Ye 《PloS one》2013,8(4)
We recently showed that bitter melon-derived triterpenoids (BMTs) activate AMPK and increase GLUT4 translocation to the plasma membrane in vitro, and improve glucose disposal in insulin resistant models in vivo. Here we interrogated the mechanism by which these novel compounds activate AMPK, a leading anti-diabetic drug target. BMTs did not activate AMPK directly in an allosteric manner as AMP or the Abbott compound (A-769662) does, nor did they activate AMPK by inhibiting cellular respiration like many commonly used anti-diabetic medications. BMTs increased AMPK activity in both L6 myotubes and LKB1-deficient HeLa cells by 20–35%. Incubation with the CaMKKβ inhibitor, STO-609, completely attenuated this effect suggesting a key role for CaMKKβ in this activation. Incubation of L6 myotubes with the calcium chelator EGTA-AM did not alter this activation suggesting that the BMT-dependent activation was Ca2+-independent. We therefore propose that CaMKKβ is a key upstream kinase for BMT-induced activation of AMPK. 相似文献
179.
180.