全文获取类型
收费全文 | 1855篇 |
免费 | 127篇 |
国内免费 | 2篇 |
专业分类
1984篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 27篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 31篇 |
2016年 | 39篇 |
2015年 | 61篇 |
2014年 | 70篇 |
2013年 | 109篇 |
2012年 | 105篇 |
2011年 | 110篇 |
2010年 | 74篇 |
2009年 | 82篇 |
2008年 | 99篇 |
2007年 | 92篇 |
2006年 | 104篇 |
2005年 | 74篇 |
2004年 | 83篇 |
2003年 | 84篇 |
2002年 | 75篇 |
2001年 | 40篇 |
2000年 | 44篇 |
1999年 | 38篇 |
1998年 | 27篇 |
1997年 | 18篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 22篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 15篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1975年 | 10篇 |
1974年 | 12篇 |
1966年 | 9篇 |
排序方式: 共有1984条查询结果,搜索用时 15 毫秒
11.
12.
A Marino E Salgado M Trueba J M Macarulla 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,85(4):795-803
The synthesis of phosphatidylcholine from phosphatidylethanolamine is carried out by chick liver microsomes (Gallus domesticus). Different concentrations of PE, NPE and NNPE were used as exogenous substrates. Saturation of the S-adenosylmethionine has been found for the three different reactions with or without exogenous substrate. Kinetic parameters have been determined for this enzyme system in chick liver microsomes. The three methyl reactions had a similar pH profile with an optimum at pH = 8. Divalent ions such as Ca2+ or Mg2+ did not stimulate the enzyme activity. The results suggest that the synthesis of phosphatidylcholine from phosphatidylethanolamine by chick liver microsomes exhibits a kinetic pattern with different aspects than that described for other animal or human preparations. 相似文献
13.
Annarosa Selli Franca Crociani Diego Matteuzzi Giorgio Crisetig 《Current microbiology》1986,13(1):33-38
Feedback inhibition of crude and purified extracts of homoserine dehydrogenase and threonine deaminase activities in the genusBifidobacterium was studied. Homoserine dehydrogenase was partially or completely inhibited byl-threonine, and a marked inhibitory effect byl-isoleucine on threonine deaminase was observed. In the speciesBifidobacterium cuniculi high levels ofl-valine reversed the inhibitory effect ofl-isoleucine. The -aminobutyric acid-resistant mutant Ru 326/106 of the speciesB. ruminale, overproducer ofl-isoleucine, had a derepressed homoserine dehydrogenase and a lesser feedback inhibition byl-threonine. Homoserine dehydrogenase appeared to be in bifids specifically NAD dependent. The regulatory mechanisms of aspartate family amino acid biosynthesis in bifidobacteria was discussed. 相似文献
14.
15.
16.
17.
1. The amino acid composition of highly purified aspartate aminotransferase from ox heart was determined. 2. Alanine is the only N-terminal residue. 3. Leucine was identified as the only C-terminal residue. 4. No disulphide bridges are present in the enzyme molecule. 5. The thiol groups are not equally accessible, the accessibility being comparatively easier in the apoenzyme molecule. 相似文献
18.
Norepinephrine stimulates the growth in size of non-dividing, neonatal cardiac muscle cells, and it can stimulate the growth in numbers of dividing hepatocytes and endothelial cells in culture. The objective of this study was to test the hypothesis that in dividing fetal cardiocytes, norepinephrine would stimulate growth in cell number rather than in cell size. Fourteen-day fetal heart cells were placed in serum-free or serum-supplemented cultures in the presence or absence of norepinephrine (NE), NE plus propranolol, or isoproterenol for 4 days. Almost 90% of the cardiocytes in serum-supplemented medium were in the cell cycle as determined by proliferating cell nuclear antigen (PCNA) antibody staining during this period. In addition, between days 2 and 4 of culture, 35% and 40% of these cardiocytes were labeled with 3H-thymidine. After 4 days the cardiocytes increased in cell number in the serum-supplemented NE cultures as compared to serum-free cultures. In contrast, there was no significant change in cardiocyte volume between any of the groups examined. It was concluded that in dividing muscle cell populations the effect of norepinephrine was to enhance cell proliferation rather than to stimulate cell growth in size. 相似文献
19.
Chymotrypsin-like enzymes are involved in sperm penetration through the vitelline coat of Ciona intestinalis egg 总被引:2,自引:0,他引:2
M R Pinto M Hoshi R Marino A Amoroso R De Santis 《Molecular reproduction and development》1990,26(4):319-323
In Ciona intestinalis, sperm penetration through the egg vitelline coat is an essential event of fertilization. We investigated whether trypsin- and chymotrypsin-like enzymes are involved in this event. Inhibitors and peptide substrates for chymotrypsin-like enzymes blocked the overall process of fertilization in a concentration-dependent manner. The inhibitory activity was specifically exerted on the step of sperm penetration. Chymotrypsin-like protease activity was identified in spermatozoa with the fluorogenic synthetic substrate Suc-Ala-Ala-Phe-AMC, which was the most effective substrate in blocking sperm penetration. These data indicate that a chymotrypsin-like protease activity is a sperm lysin of Ciona intestinalis. 相似文献
20.
Marcello Franco Eduardo Bagagli Marino Cunha Luiz Gastão Chamma Denise Fecchio 《Mycopathologia》1996,135(1):13-19
We investigated the occurrence of antigenic and biochemical variability among Paracoccidioides brasiliensis antigen batches prepared according to the same protocol. Initially (experiment #1), we analyzed two antigen lots of two human isolates (Bt1 & Bt2), cultured in two media (PYG: bactopeptone, yeast extract, glucose; MMM: McVeigh & Morton medium) in SDS-PAGE and in two immunological tests (imunodiffusion-ID and footpad swelling test-FPT). Afterwards (experiment #2), we compared the antigenic profile of three antigen batches from three human isolates (Bt1, Bt2 & Bt3) by two-dimensional immunoelectrophoresis (2 D-IEP) against a reference system for P. brasiliensis antigens. In experiment #1, there were important intra- and inter-strain antigenic differences between batches of the fungal isolates cultured on both media. The block titration of the antigen batches for the immunological tests revealed correlation between protein concentration and biological activity in ID and no correlation in FPT. In experiment #2, the reference system for P. brasiliensis showed 26 antigen peaks. There were important differences between batches prepared from the same isolate and between batches from different isolates. Our data suggested the occurrence of instability in the synthesis of antigenic components by a same P. brasiliensis isolate, under controlled incubation conditions. 相似文献