全文获取类型
收费全文 | 44038篇 |
免费 | 4155篇 |
国内免费 | 32篇 |
出版年
2021年 | 551篇 |
2020年 | 346篇 |
2019年 | 424篇 |
2018年 | 561篇 |
2017年 | 521篇 |
2016年 | 936篇 |
2015年 | 1603篇 |
2014年 | 1744篇 |
2013年 | 2214篇 |
2012年 | 2777篇 |
2011年 | 2854篇 |
2010年 | 1867篇 |
2009年 | 1801篇 |
2008年 | 2615篇 |
2007年 | 2635篇 |
2006年 | 2557篇 |
2005年 | 2537篇 |
2004年 | 2462篇 |
2003年 | 2425篇 |
2002年 | 2372篇 |
2001年 | 502篇 |
2000年 | 385篇 |
1999年 | 547篇 |
1998年 | 626篇 |
1997年 | 435篇 |
1996年 | 387篇 |
1995年 | 419篇 |
1994年 | 403篇 |
1993年 | 409篇 |
1992年 | 347篇 |
1991年 | 314篇 |
1990年 | 333篇 |
1989年 | 246篇 |
1988年 | 300篇 |
1987年 | 273篇 |
1986年 | 271篇 |
1985年 | 332篇 |
1984年 | 375篇 |
1983年 | 337篇 |
1982年 | 435篇 |
1981年 | 433篇 |
1980年 | 417篇 |
1979年 | 266篇 |
1978年 | 298篇 |
1977年 | 263篇 |
1976年 | 273篇 |
1975年 | 212篇 |
1974年 | 279篇 |
1973年 | 250篇 |
1972年 | 159篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
22.
Benjamin S. Chambers Yang Li Richard L. Hodinka Scott E. Hensley 《Journal of virology》2014,88(18):10986-10989
Prior to serological testing, influenza viruses are typically propagated in eggs or cell culture. Recent human H3N2 strains bind to cells with low avidity. Here, we isolated nine primary H3N2 viral isolates from respiratory secretions of children. Upon propagation in vitro, five of these isolates acquired hemagglutinin or neuraminidase mutations that increased virus binding to cell surfaces. These mutations can potentially confound serological assays commonly used to identify antigenically novel influenza viruses. 相似文献
23.
24.
Katherina Walz Devon Cohen Paul M. Neilsen Joseph Foster II. Francesco Brancati Korcan Demir Richard Fisher Michelle Moffat Nienke E. Verbeek Kathrine Bjørgo Adriana Lo Castro Paolo Curatolo Giuseppe Novelli Clemer Abad Cao Lei Lily Zhang Oscar Diaz-Horta Juan I. Young David F. Callen Mustafa Tekin 《Human genetics》2015,134(2):181-190
25.
The neutralization of acidic coal mine lakes by additions of natural organic matter: a mesocosm test
Cylindrical polyethylene enclosures 3 m in length and 1 m in diameter reaching from the surface to the bottom were constructed in an acid (pH=3.1) lake on a coal surface mine in southern Illinois. Wheat straw was added to the enclosures to test the effects of dissimilatory sulfate reduction on water chemistry. Added straw increased sulfide concentrations, raised pH to 6.5, reduced O2 and increased acid neutralizing capacity of the enclosed water columns when compared with a control enclosure and with the open lake. Generation of acid neutralizing capacity exceeded the standing stock of sulfide indicating that sulfide was removed either by precipitation of FeS or outgassing of H2S. The pH and acid neutralizing capacity within the enclosures eventually returned to the level of the surrounding lake because of water exchange around the enclosure walls. Our results show that additions of organic matter to acid surface mine lakes result in the generation of acid neutralizing capacity. 相似文献
26.
27.
28.
In Saccharomyces cerevisiae, the unconventional myosin Myo2p is of fundamental importance in polarized growth. We explore the role of the neck region and its associated light chains in regulating Myo2p function. Surprisingly, we find that precise deletion of the six IQ sites in the neck region results in a myosin, Myo2-Δ6IQp, that can support the growth of a yeast strain at 90% the rate of a wild-type isogenic strain. We exploit this mutant in a characterization of the light chains of Myo2p. First, we demonstrate that the localization of calmodulin to sites of polarized growth largely depends on the IQ sites in the neck of Myo2p. Second, we demonstrate that a previously uncharacterized protein, Mlc1p, is a myosin light chain of Myo2p. MLC1 (YGL106w) is an essential gene that exhibits haploinsufficiency. Reduced levels of MYO2 overcome the haploinsufficiency of MLC1. The mutant MYO2-Δ6IQ is able to suppress haploinsufficiency but not deletion of MLC1. We used a modified gel overlay assay to demonstrate a direct interaction between Mlc1p and the neck of Myo2p. Overexpression of MYO2 is toxic, causing a severe decrease in growth rate. When MYO2 is overexpressed, Myo2p is fourfold less stable than in a wild-type strain. High copies of MLC1 completely overcome the growth defects and increase the stability of Myo2p. Our results suggest that Mlc1p is responsible for stabilizing this myosin by binding to the neck region. 相似文献
29.
Species-area curves and estimates of total species richness in an old-field chronosequence 总被引:1,自引:0,他引:1
Average species-area curves were generated for vascular plants in 20 old-fields that were sampled in 1983, 1989, and 1994. These curves were fit with a saturating function to estimate total species richness for each old-field. Additional estimates of total species richness were generated by fitting the same saturating function to subsets of the species area curves and with a first-order jackknife procedure. Estimates of total species richness were strongly correlated with observed species richness. There was limited evidence suggesting that greater sampling was necessary to identify the same proportion of species in older, more species-rich old-fields. 相似文献
30.