全文获取类型
收费全文 | 3782篇 |
免费 | 335篇 |
国内免费 | 1篇 |
出版年
2023年 | 30篇 |
2022年 | 21篇 |
2021年 | 55篇 |
2020年 | 78篇 |
2019年 | 52篇 |
2018年 | 132篇 |
2017年 | 113篇 |
2016年 | 128篇 |
2015年 | 113篇 |
2014年 | 103篇 |
2013年 | 276篇 |
2012年 | 322篇 |
2011年 | 362篇 |
2010年 | 173篇 |
2009年 | 135篇 |
2008年 | 316篇 |
2007年 | 283篇 |
2006年 | 263篇 |
2005年 | 190篇 |
2004年 | 191篇 |
2003年 | 185篇 |
2002年 | 137篇 |
2001年 | 54篇 |
2000年 | 53篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1973年 | 12篇 |
1972年 | 7篇 |
排序方式: 共有4118条查询结果,搜索用时 78 毫秒
1.
2.
Hydrobiologia - In this study we examine the influence of environmental variability on the α and β diversity of testate amoeba assemblages from plankton samples. The samples were... 相似文献
3.
Yosiaki Itô 《Population Ecology》1952,1(1):36-48
National Institute of Agricultural Sciences 相似文献
4.
An exocellular D- glucansucrase that synthesizes a water-soluble, alpha-D-(1----6)-linked D-glucan having a high proportion of alpha-D-(1----3) branches was purified from the culture broth of Streptococcus mutans 6715. The rate of incorporation of D-[14C]glucose from [14C]sucrose into D-glucan of high molecular weight by this enzyme was increased (stimulated) by the presence of exogenous Leuconostoc mesenteroides B- 512F dextran, and it was found that this dextran could act as an acceptor. A highly branched dextran, containing 45-50% of alpha-D-(1----3) branch linkages, did not stimulate the enzyme nearly so much as B- 512F dextran, which has a low degree (5%) of alpha-D-(1----3) branches. We interpret this as evidence that the stimulating effects of dextran are not due to priming. If they were, the more highly branched dextran should have produced the greatest stimulation per unit weight, because a much greater number of nonreducing-end, priming sites would be available. We show that the D- glucansucrase was capable of transferring D-glucosyl groups from sucrose to B- 512F dextran to form alpha-D-(1----3) branches, thereby rendering the dextran more resistant to hydrolysis by endodextranase . The presence of 1.6M ammonium sulfate caused the enzyme to synthesize a D-glucan having a much higher percentage of alpha-D-(1----3) linkages. 相似文献
5.
6.
7.
Wnts as kidney tubule inducing factors. 总被引:4,自引:0,他引:4
S J Vainio P V It?ranta J P Per?saari M S Uusitalo 《The International journal of developmental biology》1999,43(5):419-423
Since the discovery that inductive tissue interactions regulate nephrogenesis, one of the aims has been to identify the molecules that mediate this induction. The small size of embryonic tissue has limited the possibilities to identify the inducers biochemically, even though such efforts were directed to study, e.g. neural induction (for a comprehensive review, Saxén and Toivonen, Primary embryonic induction, Academic Press, London, 1962). The rapid progress in molecular biology made it possible to identify genes from minute amounts of tissue and provided techniques to generate recombinant proteins to assay their action in classic experimental systems. This led to the identification of some signals that are involved in primary and secondary inductive interactions during embryogenesis. Here, we will review evidence suggesting that secreted signaling molecules from the Wnt gene family mediate kidney tubule induction. 相似文献
8.
9.
A two-step process to synthesize racemic lorcaserin was developed from 2-(4-chlorophenyl)ethanol via formation of bromide or tosylate derivatives. These derivatives were reacted with allylamine in neat conditions to provide pure N-(4-chlorophenethyl)allylammonium chloride. This compound was cyclized in neat conditions using aluminum or zinc chloride to give racemic lorcaserin. After resolution of enantiomers, the wrong enantiomer was racemized and recycled to give new R-lorcaserin. 相似文献
10.
Corynebacterium equi IFO 3730 was found to oxidize a wide variety of sec-alcohols, including alkanols, substituted alkanols, alkenols and cyclic alcohols, in moderate to high yields. Among them, the sec-alcohols which have longer carbon chains were oxidized more smoothly than those with smaller numbers of carbon. Although both enantiomers of unsymmetrically disubstituted carbinols were oxidized, the S form of 2-dodecanol was converted to the corresponding ketone a little faster than the other enantiomer. 相似文献