全文获取类型
收费全文 | 20883篇 |
免费 | 1755篇 |
国内免费 | 59篇 |
出版年
2021年 | 253篇 |
2020年 | 152篇 |
2019年 | 206篇 |
2018年 | 248篇 |
2017年 | 211篇 |
2016年 | 349篇 |
2015年 | 648篇 |
2014年 | 685篇 |
2013年 | 1058篇 |
2012年 | 1165篇 |
2011年 | 1187篇 |
2010年 | 732篇 |
2009年 | 692篇 |
2008年 | 1083篇 |
2007年 | 1115篇 |
2006年 | 1031篇 |
2005年 | 1026篇 |
2004年 | 956篇 |
2003年 | 947篇 |
2002年 | 917篇 |
2001年 | 227篇 |
2000年 | 183篇 |
1999年 | 265篇 |
1998年 | 269篇 |
1997年 | 195篇 |
1996年 | 210篇 |
1995年 | 183篇 |
1994年 | 200篇 |
1993年 | 168篇 |
1992年 | 182篇 |
1991年 | 170篇 |
1990年 | 146篇 |
1989年 | 156篇 |
1988年 | 172篇 |
1987年 | 159篇 |
1986年 | 147篇 |
1985年 | 185篇 |
1984年 | 199篇 |
1983年 | 189篇 |
1982年 | 206篇 |
1981年 | 239篇 |
1980年 | 208篇 |
1979年 | 163篇 |
1978年 | 191篇 |
1977年 | 169篇 |
1976年 | 141篇 |
1975年 | 146篇 |
1974年 | 164篇 |
1973年 | 161篇 |
1968年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
The health profile of cloned animals. 总被引:17,自引:0,他引:17
4.
George John Acton 《Phytochemistry》1974,13(8):1303-1310
The light-dependent increment in RNase activity (which is ribosome bound in cell extracts) is distributed as a gradient increasing from base to hook of lupin hypocotyls. No evidence was found of non-specific or of specific activation of pre-formed enzyme molecules following isolation, either before or after (latent activity) destruction of particles. The autodegradation capacity of ribosomes isolated from irradiated cells was almost double that of ribosomes from etiolated tissue. It is proposed that association between the bulk of the light-controlled RNase fraction and lupin ribosomes results from binding of soluble protein. It is not clear whether binding is specific or an artifact of isolation. 相似文献
5.
Tarjan Kaliaperumal S. Kumar Sathyanarayana N. Gummadi Anju Chadha 《Journal of industrial microbiology & biotechnology》2010,37(2):159-165
Asymmetric reduction of ethyl-4-chloro-3-oxobutanoate to (S)-ethyl-4-chloro-3-hydroxybutanoate in aqueous medium by resting cells of Candida parapsilosis ATCC 7330 was optimized. The influence of culture parameters (inoculum size, inoculum age and biocatalyst harvest time) and reaction parameters (co-substrate, resting cell, pH and substrate concentrations) on the asymmetric reduction were studied. It was found that these parameters significantly influenced the rate of the asymmetric reduction. Under the optimum conditions, the final concentration of (S)-ethyl-4-chloro-3-hydroxybutanoate, enantiomeric excess and the isolated yield of (S)-ethyl-4-chloro-3-hydroxybutanoate were 1.38 M (230 g/l), >99 and 95%, respectively. The space time yield was 115 mmol/lh, which is significantly higher than other whole cell biocatalysts reported so far. 相似文献
6.
7.
8.
9.
In the development of the horseshoe crab, Limulus polyphemus, the fertilized egg undergoes a complicated cleavage (Stages 1–3) resulting in blastoderm formation (Stage 4). Stage 1 involves intralecithal cleavage and consists of nine discrete surface modifications (events) which have been briefly described with light microscopy by Brown and Barnum ('83). Since in Stage 1 the cortical reaction (events 1–4) has already been examined with ultrastructural methods, the objectives of the present study were to examine with scanning electron microscopy: (1) the first two of three intermittent granulations (events 5 and 7), and (2) the associated events characterized by smooth surfaces (events 4, 6, and 8). The first granulation occurs 2 1/2 to 3 hours after fertilization (22°C) and lasts approximately 1 1/2 hours. The second granulation appears approximately 5 hours after fertilization and lasts about 3 hours. The dynamic changes that occur during the two granulations involve the transformation of a smooth appearing embryonic surface, liberally coated with microvilli, into a granule-dominated surface on which microvilli are greatly reduced in number. Also of considerable interest are the numerous projections which begin to appear on the surface near the end of the second granulation (event 7) and dominate the surface of the following smooth step stage (event 8). Hypotheses on the significance of these dynamic changes and surface modifications involve relationships to the cell cycle, possible mechanisms for membrane storage, and secretory function. 相似文献
10.