全文获取类型
收费全文 | 441篇 |
免费 | 0篇 |
专业分类
系统科学 | 3篇 |
理论与方法论 | 3篇 |
现状及发展 | 108篇 |
研究方法 | 20篇 |
综合类 | 287篇 |
自然研究 | 20篇 |
出版年
2016年 | 2篇 |
2013年 | 6篇 |
2012年 | 15篇 |
2011年 | 34篇 |
2010年 | 5篇 |
2008年 | 15篇 |
2007年 | 11篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 8篇 |
2002年 | 15篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 3篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1972年 | 10篇 |
1971年 | 8篇 |
1970年 | 10篇 |
1969年 | 7篇 |
1968年 | 9篇 |
1967年 | 4篇 |
1966年 | 7篇 |
1965年 | 9篇 |
1960年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有441条查询结果,搜索用时 15 毫秒
71.
T. L. Akasaka Lynne Olds-Arroyo J. J. Miller III 《Cellular and molecular life sciences : CMLS》1979,35(5):673-674
Summary Human lymphocytes stimulated in vitro by PHA or PWM incorporate3H-CdR into DNA, but less well than3H-TdR. More3H-CdR is incorporated in populations enriched for T cells. No3H-CdR is used by cells stimulated by lipopolysaccharides under circumstances in which3H-TdR is incorporated. We conclude that human T cells and B cells differ in their ability to use3H-CdR. 相似文献
72.
R F Miller 《Nature》1988,336(6199):517-518
73.
Cloning and sequence analysis of the cDNA for the rat atrial natriuretic factor precursor 总被引:4,自引:0,他引:4
M Yamanaka B Greenberg L Johnson J Seilhamer M Brewer T Friedemann J Miller S Atlas J Laragh J Lewicki 《Nature》1984,309(5970):719-722
Atrial extracts contain factors which induce potent natriuresis changes in renal haemodynamics, and relax pre-contracted vascular smooth muscle. Low-molecular-weight peptides which mimic these actions have now been purified by several groups, including ours (see accompanying paper), and higher-molecular-weight proteins with similar but less potent biological activities have also been identified and are presumed to be precursors. If released into the circulation, these peptides, collectively called atrial natriuretic factor (ANF), may play a significant part in blood-pressure homeostasis, regulation of extracellular fluid volume and as antagonists to the hypertensive effects of the renin-angiotensin system and other hormonal and neurotransmitter systems. We describe here the isolation and characterization of rat atrial cDNA clones which encode ANF. Nucleotide sequence analysis shows that auriculin corresponds to the 25 amino acids located close to the C-terminus of a 152-amino acid ANF precursor. Analysis of the in vitro translation products of precursor ANF mRNA suggests that multiple forms of the precursor may exist. 相似文献
74.
Several a-pyrones have been synthesized and investigated for their in vitro inhibitory activity using a-chymotrypsin (a-CT), porcine pancreatic elastase (PPE) and human leukocyte elastase (HLE). 4-Hydroxy-6-undecyl-2H-pyran-2-one 4, 4-Hydroxy-6-[(1-butyl)heptyl]-2H-pyran-2-one 5 and 4-Methoxy-6-[(1-butyl) heptyl]-2H-pyran-2-one 6 were found to be specific inhibitors of HLE. These compounds constitute a promising new class of HLE inhibitors. 相似文献
75.
Sharing of an idiotypic marker by monoclonal antibodies specific for distinct regions of hen lysozyme 总被引:14,自引:0,他引:14
Idiotypes have been defined serologically as variable-region markers present on unique subsets of antibody molecules. Most studies involving myeloma proteins and antibody responses in inbred mice have indicated that idiotypy is closely related to antigenic specificity. However, indirect evidence suggests that idiotypy can sometimes be dissociated from specificity. In the response to the small monomeric protein, hen egg-white lysozyme (HEL), previous results demonstrated that 70--95% of the anti-HEL antibody found in sera of primed and boosted mice is specific for a particular region of HEL and bears a predominant idiotype (IdX-HEL). In this report, hybridoma anti-HEL antibodies tested with well-characterized peptide fragments of HEL show that the IdX-HEL marker can be found on antibodies of completely distinct antigen specificities. Thus, a mode of recognition other than antigenic recognition probably plays a major role in the immune response to HEL. 相似文献
76.
77.
78.
To navigate our complex world, our brains have evolved a sophisticated ability to quickly learn arbitrary rules such as 'stop at red'. Studies in monkeys using a laboratory test of this capacity--conditional association learning--have revealed that frontal lobe structures (including the prefrontal cortex) as well as subcortical nuclei of the basal ganglia are involved in such learning. Neural correlates of associative learning have been observed in both brain regions, but whether or not these regions have unique functions is unclear, as they have typically been studied separately using different tasks. Here we show that during associative learning in monkeys, neural activity in these areas changes at different rates: the striatum (an input structure of the basal ganglia) showed rapid, almost bistable, changes compared with a slower trend in the prefrontal cortex that was more in accordance with slow improvements in behavioural performance. Also, pre-saccadic activity began progressively earlier in the striatum but not in the prefrontal cortex as learning took place. These results support the hypothesis that rewarded associations are first identified by the basal ganglia, the output of which 'trains' slower learning mechanisms in the frontal cortex. 相似文献
79.
Site of action of general anaesthetics 总被引:1,自引:0,他引:1
80.
The thymus and the precursors of antigen reactive cells 总被引:22,自引:0,他引:22