全文获取类型
收费全文 | 3001篇 |
免费 | 292篇 |
国内免费 | 1篇 |
专业分类
3294篇 |
出版年
2023年 | 17篇 |
2022年 | 26篇 |
2021年 | 59篇 |
2020年 | 48篇 |
2019年 | 73篇 |
2018年 | 83篇 |
2017年 | 73篇 |
2016年 | 113篇 |
2015年 | 139篇 |
2014年 | 169篇 |
2013年 | 213篇 |
2012年 | 184篇 |
2011年 | 192篇 |
2010年 | 137篇 |
2009年 | 135篇 |
2008年 | 158篇 |
2007年 | 132篇 |
2006年 | 112篇 |
2005年 | 104篇 |
2004年 | 108篇 |
2003年 | 114篇 |
2002年 | 98篇 |
2001年 | 72篇 |
2000年 | 78篇 |
1999年 | 58篇 |
1998年 | 37篇 |
1997年 | 23篇 |
1996年 | 26篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 21篇 |
1992年 | 42篇 |
1991年 | 27篇 |
1990年 | 30篇 |
1989年 | 40篇 |
1988年 | 38篇 |
1987年 | 19篇 |
1986年 | 32篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1974年 | 17篇 |
1973年 | 12篇 |
排序方式: 共有3294条查询结果,搜索用时 15 毫秒
11.
12.
The serine carboxylesterase from horse serum was characterized by amino acid composition, peptide mapping, molecular and subunit weights, and sequencing of the amino acids around the essential serine residue at the active site. A protocol was developed for using reversed-phase high-performance liquid chromatography as the final step to obtain homogeneous preparations of horse serum carboxylesterase. Amounts sufficient for determining the amino acid composition and for peptide maps were obtained from a partially purified starting material which contained approximately 55% carboxylesterase. The amino acid composition, like the subunit weight (70,800 +/- 1400), was similar to the corresponding values reported for other serine carboxylesterases. However, the amino acid sequence of the tryptic digest fragment containing the essential nucleophilic seryl residue differed significantly from the corresponding sequences of other mammalian serine carboxylesterases. 相似文献
13.
Isolation and Characterization of an Fe(III)-Chelating Compound Produced by Pseudomonas syringae 总被引:2,自引:2,他引:0 下载免费PDF全文
Luis Torres Jos E. Prez-Ortín Vicente Tordera Jos P. Beltrn 《Applied microbiology》1986,52(1):157-160
The phytopathogenic bacterium Pseudomonas syringae produces a fluorescent pigment when it is grown in iron-deficient media. This pigment forms a very stable Fe(III) complex that was purified in this form by using a novel procedure based on ultrafiltration and column chromatography. The Fe(III) complex has a molecular weight of 1,100 and contains 1 mol of Fe(III). The pigment is composed of an amino acid moiety with three threonines, three serines, one lysine, δ-N-hydroxyornithine, and a quinoline-type fluorescent chromophore. These features and its stability constant (in the range of 1032) suggest that the fluorescent pigment of P. syringae is related to the siderophores produced by another Pseudomonas species. 相似文献
14.
Lipopolysaccharide and polyribonucleotide activation of macrophages: implications for a natural triggering signal in tumor cell killing 总被引:3,自引:0,他引:3
There is evidence that activation of macrophages for tumor cell killing can involve either two signals (interferon/lipopolysaccharide, for example) or one signal (lipopolysaccharide or double-stranded RNA, for example). We investigated the apparent one-signal activation of bone marrow-derived macrophages for P815 mastocytoma killing by treatment with lipopolysaccharide (LPS) or by the synthetic double-stranded polyribonucleotide polyinosinic acid-polycytidylic acid (poly I:C). We found that "direct" activation of macrophages by either LPS or poly I:C was still a two-signal process. Based on antibody neutralizations, the first signal was probably mediated by LPS or poly I:C induced alpha/beta interferon in the macrophage cultures, and the second signal was that of a direct effect of the LPS or poly I:C on the cell. The fact that poly I:C can provide the triggering signal for macrophage activation suggests a possible role for double-stranded RNA structures in macrophage triggering. Such double-stranded RNA requirements could be met by single-stranded RNAs that possess significant double-strandedness in their structures. 相似文献
15.
Characterization of Neurospora crassa cyclic AMP phosphodiesterase activated by calmodulin. 总被引:2,自引:1,他引:1
Activation of cyclic AMP phosphodiesterase I by brain or Neurospora calmodulin was studied. The stimulation required micromolar concentrations of Ca2+, and it was observed at cyclic AMP concentrations between 0.1 and 500 microM. Activation was blocked by EDTA and some neuroleptic drugs such as chlorpromazine and fluphenazine. These drugs inhibit the elongation of N. crassa wild-type aerial hyphae. These results reinforce the evidence towards the recognition of Ca2+-calmodulin as one of the systems controlling cyclic nucleotide concentrations in Neurospora. 相似文献
16.
Dion tomasellii sp. nov. occurs with an interrupted distribution from Guerrero to central Sonora. It is characterized by falcate to subfalcate leaflets. The populations from Sonora and northern Sinaloa are segregated asD. tomasellii var.sonorense on the basis of their narrower and glaucous leaflets. 相似文献
17.
The activity of antidromically identified abducens nucleus motoneurons and inter-nuclear neurons has been recorded during saccadic eye movements in the alert cat. The activity of these neurons has been demonstrated to be the sum of a velocity component proportional to eye velocity plus a position component proportional to instantaneous eye position during the movement. Results are discussed in relation to proposed models about the generation of saccadic eye movements. 相似文献
18.
19.
Summary An isochromosome of 15(q12) was found in a mentally retarded patient with behaviour disorders which included hyperactivity, short attention span, aggression, and autistic behaviour. There were only minor physical anomalies; he did not have the Prader-Willi syndrome. 相似文献
20.
Stability of plasmids R1-19 and R100 in hyper-recombinant Escherichia coli strains and in Salmonella typhimurium strains. 总被引:2,自引:1,他引:1
Plasmids R1-19 and R100 dissociate in hyper-recominant Escherichia coli strains in a way that is similar to but slower than dissociation in Salmonella typhimurium. The results presented suggest that the molecular mechanism for plasmid dissociation in hyper-recombinant E. coli strains is different than that in S. typhimurium strains. 相似文献