全文获取类型
收费全文 | 43964篇 |
免费 | 4718篇 |
国内免费 | 13篇 |
专业分类
48695篇 |
出版年
2022年 | 329篇 |
2021年 | 583篇 |
2020年 | 402篇 |
2019年 | 484篇 |
2018年 | 617篇 |
2017年 | 560篇 |
2016年 | 998篇 |
2015年 | 1769篇 |
2014年 | 1734篇 |
2013年 | 2274篇 |
2012年 | 2627篇 |
2011年 | 2344篇 |
2010年 | 1585篇 |
2009年 | 1476篇 |
2008年 | 2019篇 |
2007年 | 1972篇 |
2006年 | 1808篇 |
2005年 | 1753篇 |
2004年 | 1678篇 |
2003年 | 1451篇 |
2002年 | 1453篇 |
2001年 | 1264篇 |
2000年 | 1259篇 |
1999年 | 1149篇 |
1998年 | 666篇 |
1997年 | 603篇 |
1996年 | 597篇 |
1995年 | 579篇 |
1994年 | 521篇 |
1993年 | 551篇 |
1992年 | 1030篇 |
1991年 | 774篇 |
1990年 | 803篇 |
1989年 | 777篇 |
1988年 | 676篇 |
1987年 | 621篇 |
1986年 | 627篇 |
1985年 | 729篇 |
1984年 | 561篇 |
1983年 | 442篇 |
1982年 | 367篇 |
1981年 | 344篇 |
1980年 | 266篇 |
1979年 | 390篇 |
1978年 | 357篇 |
1977年 | 260篇 |
1976年 | 244篇 |
1975年 | 205篇 |
1974年 | 303篇 |
1973年 | 259篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Theo J. Visser Ellen Van Overmeeren-Kaptein 《Biochimica et Biophysica Acta (BBA)/General Subjects》1980,631(2):246-252
A radioimmunoassay for 3′-iodothyronine has been developed. All iodothyronine analogues (except 3,3′-diiodothyronine) showed very little (0.02% at most) cross-reactivity, and the assay was sensitive to 1 pg 3′-iodothyronine/ tube. We have studied the 5′-deiodination of 3′,5′-diiodothyronine by rat liver microsomal fraction in the presence of dithiothreitol. Production of 3′-iodothyronine at 37°C was found to be linear with time of incubation up to 30 min and with concentration of microsomal protein up to 100 μg/ml. The reaction rate reached a limit on increasing 3′,5′-diiodothyronine concentration to 10 μM. The effect of pH on 3′-iodothyronine production was found to depend on 3′,5′-diiodothyronine concentration. Increasing 3′,5′-diiodothyronine concentration from 0.1 to 10 μM resulted in a shift of the pH optimum from 6–6.5 to 7.5. Similar effects on the 5′-deiodination of 3,3′,5′-triiodothyronine were observed, supporting the hypothesis that these reactions are catalysed by a single enzyme (iodothyronine 5′-deiodinase). 相似文献
23.
The Wageningen Delivery of Functionality symposium covered all aspects involved with food structural design to arrive at high-quality
foods which meet demanding customer expectations and regulatory requirements. The symposium integrated aspects from the structural
organization of foods at molecular and supramolecular scales to dedicated techniques required to describe and visualize such
structures, the gastro-intestinal events and how to model these in a laboratory setting, and finally the impact those food
structures and ingredients have on the consumer’s physiology and on the human perception. As an interdisciplinary platform,
bringing together more than 160 researchers from academia and industry, the symposium meanwhile fulfills an important role
in the food science community. 相似文献
24.
Nitracrine is used clinically as an antitumour agent, and analogues are actively being developed in some laboratories. The mutagenic activity of 9-[(3-dimethylaminopropyl)amino]-acridine and its 1-nitro (nitracrine), 2-, 3- and 4-nitro derivatives was evaluated at the 6-thioguanine and ouabain resistance loci in cultured Chinese hamster fibroblasts (V79-171b cell line). The des-nitro, 2- and 3-nitro caused no statistically significant mutagenic activity at either locus. Each of these 3 compounds weakly increased (approximately 2-fold) the incidence of micronuclei in the same cell line when tested at cytotoxic doses. Both the 1- and 4-nitro compounds increased the incidence of 6-thioguanine resistant cells from around 1 in 10(-6) to approximately 1 in 10(-4). The former compound significantly increased the frequency of ouabain-resistant cells. Both of these compounds were potent inducers of micronuclei in V79-171b cells, indicating high clastogenic activity. It would appear prudent to regard both of these compounds as potential human carcinogens. 相似文献
25.
F. D. Miller K. F. Jorgenson R. J. Winkfein J. H. van de Sande D. A. Zarling J. Stockton 《Journal of biomolecular structure & dynamics》2013,31(3):611-620
Abstract Bacteriophage PM2 DNA, a ccc genome of high apparent superhelical density, contains left-handed (Z) regions as detected by competitive radioimmunoassay, agarose gel electrophoresis of DNA: antibody complexes and immunoelectron microscopy. The latter technique, in conjunction with partial blockage of restriction endonuclease sites by bound antibody, was used to map the left-handed regions along the DNA molecule. A cluster of four to five antibody molecules (approximately 25% of bound antibody) was located within map units 0.05–0.18 of the single Hpa II restriction site. Sequence analysis of part of this region showed the presence of several areas of high alternating purine-pyrimidine content. A strong correlation is observed between alternating pyrimidine-purine tracts of significant length and antibody binding sites. 相似文献
26.
27.
J. A. Roubos C. D. de Gooijer G. van Straten A. J. B. van Boxtel 《Bioprocess and biosystems engineering》1997,17(2):99-102
Two methods for the calculation of optimal trajectories for the input variables of a fed-batch culture of hybridoma cells are compared. It pointed out that a gradient method based on Pontryagins' minimum principle based yields a significant better performance with respect to computational effort and the calculated minimum than a dynamic programming approach which has been presented in a previous paper [1] as the most suitable method. 相似文献
28.
M Lebl E E Sugg G van Binst P Vander Elst D Tourwé J Slaninová V J Hruby 《International journal of peptide and protein research》1987,30(3):318-322
Analogs of deamino-oxytocin and deamino-oxypressin containing a CH2-NH group instead of an amide bond between positions 8 and 9 were synthesized. All tested compounds exhibit significantly lowered biological activities. 相似文献
29.
30.