全文获取类型
收费全文 | 29514篇 |
免费 | 2596篇 |
国内免费 | 2317篇 |
专业分类
34427篇 |
出版年
2024年 | 45篇 |
2023年 | 234篇 |
2022年 | 501篇 |
2021年 | 804篇 |
2020年 | 678篇 |
2019年 | 810篇 |
2018年 | 855篇 |
2017年 | 740篇 |
2016年 | 1046篇 |
2015年 | 1625篇 |
2014年 | 1914篇 |
2013年 | 2069篇 |
2012年 | 2661篇 |
2011年 | 2289篇 |
2010年 | 1634篇 |
2009年 | 1479篇 |
2008年 | 1888篇 |
2007年 | 1689篇 |
2006年 | 1611篇 |
2005年 | 1450篇 |
2004年 | 1387篇 |
2003年 | 1243篇 |
2002年 | 1064篇 |
2001年 | 648篇 |
2000年 | 564篇 |
1999年 | 523篇 |
1998年 | 342篇 |
1997年 | 274篇 |
1996年 | 238篇 |
1995年 | 213篇 |
1994年 | 194篇 |
1993年 | 148篇 |
1992年 | 218篇 |
1991年 | 166篇 |
1990年 | 145篇 |
1989年 | 135篇 |
1988年 | 89篇 |
1987年 | 105篇 |
1986年 | 82篇 |
1985年 | 67篇 |
1984年 | 47篇 |
1983年 | 53篇 |
1982年 | 35篇 |
1981年 | 36篇 |
1980年 | 26篇 |
1979年 | 39篇 |
1978年 | 37篇 |
1976年 | 30篇 |
1973年 | 29篇 |
1972年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Secretion of Recombinant Pediocin PA-1 by Bifidobacterium longum, Using the Signal Sequence for Bifidobacterial α-Amylase 下载免费PDF全文
Gi-Seong Moon Yu-Ryang Pyun Myeong Soo Park Geun Eog Ji Wang June Kim 《Applied microbiology》2005,71(9):5630-5632
A recombinant DNA, encoding the chimeric protein of the signal sequence for bifidobacterial α-amylase mature pediocin PA-1, was introduced into Bifidobacterium longum MG1. Biologically active pediocin PA-1 was successfully secreted from the strain and showed bactericidal activity against Listeria monocytogenes and the same molecular mass as native pediocin PA-1. 相似文献
12.
13.
14.
Optimal substrate feeding policy for a fed batch fermentation with substrate and product inhibition kinetics 总被引:1,自引:0,他引:1
Hong J 《Biotechnology and bioengineering》1986,28(9):1421-1431
The optimal substrate feeding policy for the fed batch fermentation which is governed by product and substrate inhibited kinetics is presented. The conjunction point between nonsingular and singular arcs and the feeding policy along the singular arc are derived analytically in terms of the concentrations of substrate and product and the liquid volume. Thus, it is possible to determine the feeding rate by monitoring the state variables (i.e., closed loop control). As a specific example, an optimization study of the fed batch fermentation for ethanol production by Saccharomyces cerevisiae is presented. It is shown that the optimal feeding patterns are heavily dependent upon the initial conditions. The point selectivity provides the guideline for predicting the optimal feeding patterns and explaining the results of rigorous mathematical analysis. 相似文献
15.
epsilon-Crystallin, a novel avian and reptilian eye lens protein 总被引:4,自引:0,他引:4
S O Stapel A Zweers H J Dodemont J H Kan W W de Jong 《European journal of biochemistry》1985,147(1):129-136
Gel filtration of Peking duck eye lens proteins reveals a component eluting just behind delta-crystallin and comprising approximately 10% of the total soluble protein. The native Mr of this additional component is estimated to be 120000; it appears to be composed of three identical chains of Mr 38000 and pI 7.5. Circular dichroic spectroscopy showed a relatively high alpha-helical content. No immunological cross-reactivity is found with alpha-, beta-, gamma- or delta-crystallins, and partial amino acid sequence determinations likewise failed to reveal any similarity with other known crystallins. We conclude that this protein represents another and novel family of eye lens proteins, for which we propose the designation epsilon-crystallin. epsilon-Crystallin is translated from a 1450-base mRNA, which has been partially purified. epsilon-Crystallin is found scattered among avian and reptilian taxa, but not in other vertebrates. Its rate of evolutionary change seems to be as slow as that of alpha- and beta-crystallins. 相似文献
16.
Male, Fischer strain 344 adult rats were given various doses (25-100 mg/kg) of p,p'-DDT by oral gavage, and levels of biogenic amines, their metabolites, and amino acid neurotransmitters, tremor activity, and rectal temperature were measured at several intervals (2, 5, 12, and 24 h) after dosing. Dose-related increases in rectal temperature and in tremor activity were observed at 50-100 mg/kg 12 h after dosing. Tremorigenic doses of DDT increased the 5-hydroxyindoleacetic acid (5-HIAA) level in hypothalamus, brainstem, and striatum, whereas doses of 75 and 100 mg/kg increased the 3-methoxy-4-hydroxyphenylglycol (MHPG) level in hypothalamus and brainstem and the 3,4-dihydroxyphenylacetic acid level in striatum. Six amino acids were assayed in the brainstem, hypothalamus, and striatum; aspartate and glutamate levels were increased only in brainstem at 25-100 mg/kg. No consistent changes in concentrations of taurine, glutamine, glycine, or gamma-aminobutyric acid were observed in any of the regions assayed. Time-related increases in rectal temperature were seen 2-12 h after dosing, and the presence of tremor was observed 5-12 h after dosing; for both the time of peak effect was at 12 h. The DDT-induced hyperthermia and tremor were associated with dose- and time-related increases in levels of 5-HIAA, MHPG, aspartate, and glutamate. It is suggested that an increase in the turnover rate of 5-hydroxytryptamine (5-HT) may be responsible for the DDT-induced hyperthermia, whereas increases in the metabolism of 5-HT and norepinephrine may be involved in the tremor. 相似文献
17.
18.
We treated the glutamine binding protein with diethyl pyrocarbonate (DEPC) and N-bromosuccinimide (NBS) to modify respectively the sole histidine and tryptophan residues and examined the effect of these modifications on the ability of the binding protein to bind glutamine as well as the ability to restore glutamine transport in membrane vesicles of Escherichia coli. Under the conditions used, both DEPC and NBS markedly inhibited the ability to restore glutamine transport in vesicles without any significant effect on glutamine binding. Moreover, saturating quantities of glutamine had no protective effect on the inactivation of the binding protein by DEPC or NBS. Fluorometric measurement and amino acid analysis indicate that the inactivation of the binding protein in restoring vesicle transport by NBS can be attributed to the oxidation of a single tryptophan residue. Similar analysis and the inability of hydroxylamine to reverse the effect of DEPC indicate that the effects of DEPC can probably be attributed to alterations of the sole histidine and/or one or more lysine residues of the binding protein. We conclude that the glutamine binding protein possesses at least two largely nonoverlapping functional domains, one responsible for glutamine binding and the other for the interaction with the other components of the glutamine transport system. 相似文献
19.
The amino-acids sequence of the alphaB2 chain of bovine alpha-crystallin 总被引:16,自引:0,他引:16
F J Van Der Ouderaa W W De Jong A Hilderink H Bloemendal 《European journal of biochemistry》1974,49(1):157-168
20.