全文获取类型
收费全文 | 4108篇 |
免费 | 438篇 |
出版年
2021年 | 47篇 |
2020年 | 39篇 |
2019年 | 51篇 |
2018年 | 49篇 |
2017年 | 55篇 |
2016年 | 84篇 |
2015年 | 135篇 |
2014年 | 153篇 |
2013年 | 178篇 |
2012年 | 209篇 |
2011年 | 227篇 |
2010年 | 155篇 |
2009年 | 121篇 |
2008年 | 177篇 |
2007年 | 224篇 |
2006年 | 176篇 |
2005年 | 122篇 |
2004年 | 156篇 |
2003年 | 142篇 |
2002年 | 137篇 |
2001年 | 123篇 |
2000年 | 137篇 |
1999年 | 106篇 |
1998年 | 55篇 |
1997年 | 28篇 |
1996年 | 47篇 |
1995年 | 54篇 |
1994年 | 29篇 |
1993年 | 43篇 |
1992年 | 71篇 |
1991年 | 69篇 |
1990年 | 72篇 |
1989年 | 68篇 |
1988年 | 63篇 |
1987年 | 64篇 |
1986年 | 48篇 |
1985年 | 45篇 |
1984年 | 43篇 |
1983年 | 51篇 |
1982年 | 33篇 |
1981年 | 36篇 |
1979年 | 47篇 |
1978年 | 32篇 |
1977年 | 36篇 |
1976年 | 37篇 |
1975年 | 44篇 |
1974年 | 29篇 |
1973年 | 37篇 |
1971年 | 36篇 |
1970年 | 35篇 |
排序方式: 共有4546条查询结果,搜索用时 15 毫秒
91.
Holger Maier Christine Schütt Ralph Steinkamp Anja Hurt Elida Schneltzer Philipp Gormanns Christoph Lengger Mark Griffiths David Melvin Neha Agrawal Rafael Alcantara Arthur Evans David Gannon Simon Holroyd Christian Kipp Navis Pretheeba Raj David Richardson Sophie LeBlanc Laurent Vasseur Hiroshi Masuya Kimio Kobayashi Tomohiro Suzuki Nobuhiko Tanaka Shigeharu Wakana Alison Walling David Clary Juan Gallegos Helmut Fuchs Martin Hrabě de Angelis Valerie Gailus-Durner 《Mammalian genome》2015,26(9-10):467-481
92.
Oxidative stress conditions increase the frequency of de novo formation of the yeast [PSI+] prion 下载免费PDF全文
Victoria A. Doronina Gemma L. Staniforth Shaun H. Speldewinde Mick F. Tuite Chris M. Grant 《Molecular microbiology》2015,96(1):163-174
Prions are self‐perpetuating amyloid protein aggregates which underlie various neurodegenerative diseases in mammals and heritable traits in yeast. The molecular basis of how yeast and mammalian prions form spontaneously into infectious amyloid‐like structures is poorly understood. We have explored the hypothesis that oxidative stress is a general trigger for prion formation using the yeast [PSI+] prion, which is the altered conformation of the Sup35 translation termination factor. We show that the frequency of [PSI+] prion formation is elevated under conditions of oxidative stress and in mutants lacking key antioxidants. We detect increased oxidation of Sup35 methionine residues in antioxidant mutants and show that overexpression of methionine sulphoxide reductase abrogates both the oxidation of Sup35 and its conversion to the [PSI+] prion. [PSI+] prion formation is particularly elevated in a mutant lacking the Sod1 Cu,Zn‐superoxide dismutase. We have used fluorescence microscopy to show that the de novo appearance of [PSI+] is both rapid and increased in frequency in this mutant. Finally, electron microscopy analysis of native Sup35 reveals that similar fibrillar structures are formed in both the wild‐type and antioxidant mutants. Together, our data indicate that oxidative stress is a general trigger of [PSI+] formation, which can be alleviated by antioxidant defenses. 相似文献
93.
Direct infusion ESI‐IT‐MSn alkaloid profile and isolation of tetrahydroharman and other alkaloids from Bocageopsis pleiosperma maas (Annonaceae) 下载免费PDF全文
94.
95.
Population history,gene flow,and bottlenecks in island populations of a secondary seed disperser,the southern grey shrike (Lanius meridionalis koenigi) 下载免费PDF全文
David P. Padilla Lewis G. Spurgin Eleanor A. Fairfield Juan Carlos Illera David S. Richardson 《Ecology and evolution》2015,5(1):36-45
Studying the population history and demography of organisms with important ecological roles can aid understanding of evolutionary processes at the community level and inform conservation. We screened genetic variation (mtDNA and microsatellite) across the populations of the southern grey shrike (Lanius meridionalis koenigi) in the Canary Islands, where it is an endemic subspecies and an important secondary seed disperser. We show that the Canarian subspecies is polyphyletic with L. meridionalis elegans from North Africa and that shrikes have colonized the Canary Islands from North Africa multiple times. Substantial differences in genetic diversity exist across islands, which are most likely the product of a combination of historical colonization events and recent bottlenecks. The Eastern Canary Islands had the highest overall levels of genetic diversity and have probably been most recently and/or frequently colonized from Africa. Recent or ongoing bottlenecks were detected in three of the islands and are consistent with anecdotal evidence of population declines due to human disturbance. These findings are troubling given the shrike's key ecological role in the Canary Islands, and further research is needed to understand the community‐level consequences of declines in shrike populations. Finally, we found moderate genetic differentiation among populations, which largely reflected the shrike's bottleneck history; however, a significant pattern of isolation‐by‐distance indicated that some gene flow occurs between islands. This study is a useful first step toward understanding how secondary seed dispersal operates over broad spatial scales. 相似文献
96.
97.
98.
99.
100.
Glaucosphaera vacuolata was recently rediscovered, and isolated by Dr. Richard Starr of Indiana University Physiological and ultrastructural studies have been conducted on this cyanome and are reported for the first time. Glaucosphaera has been found to have low rates of photosynthesis, respiration, and Hill activity. Unusual features noted include the presence of R-phycocyanin as the major accessory pigment, phycobilisomes, and eyeshot-like structures in the cyanelles. 相似文献