全文获取类型
收费全文 | 4091篇 |
免费 | 250篇 |
国内免费 | 5篇 |
出版年
2022年 | 24篇 |
2021年 | 23篇 |
2019年 | 22篇 |
2018年 | 34篇 |
2017年 | 39篇 |
2016年 | 42篇 |
2015年 | 67篇 |
2014年 | 95篇 |
2013年 | 271篇 |
2012年 | 160篇 |
2011年 | 216篇 |
2010年 | 121篇 |
2009年 | 141篇 |
2008年 | 236篇 |
2007年 | 242篇 |
2006年 | 212篇 |
2005年 | 230篇 |
2004年 | 239篇 |
2003年 | 241篇 |
2002年 | 232篇 |
2001年 | 86篇 |
2000年 | 78篇 |
1999年 | 85篇 |
1998年 | 76篇 |
1997年 | 55篇 |
1996年 | 58篇 |
1995年 | 49篇 |
1994年 | 47篇 |
1993年 | 56篇 |
1992年 | 69篇 |
1991年 | 61篇 |
1990年 | 65篇 |
1989年 | 47篇 |
1988年 | 53篇 |
1987年 | 40篇 |
1986年 | 51篇 |
1985年 | 35篇 |
1984年 | 29篇 |
1983年 | 32篇 |
1982年 | 25篇 |
1981年 | 32篇 |
1980年 | 35篇 |
1979年 | 31篇 |
1978年 | 19篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1975年 | 28篇 |
1974年 | 29篇 |
1973年 | 27篇 |
1970年 | 20篇 |
排序方式: 共有4346条查询结果,搜索用时 31 毫秒
41.
Effect of polyamines on synthesis and degradation of guanosine 5'-diphosphate 3'-diphosphate 总被引:2,自引:0,他引:2
K Igarashi K Mitsui M Kubota M Shirakuma R Ohnishi S Hirose 《Biochimica et biophysica acta》1983,755(3):326-331
The effect of polyamines on the in vitro and in vivo synthesis and degradation on guanosine 5'-diphosphate 3'-diphosphate (ppGpp) has been studied in Escherichia coli. The presence of 2 mM spermidine lowered the optimal Mg2+ concentration for ppGpp formation from 17 mM to 11 mM. The formation of ppGpp in the presence of 2 mM spermidine and 11 mM Mg2+ was about 15% greater than that in the presence of 17 mM Mg2+. At a concentration of less than 11 mM Mg2+, spermidine was found to stimulate ppGpp formation greatly. Putrescine did not cause any effect. When a polyamine-requiring mutant of E. coli (EWH319) was starved for an amino acid by the addition of valine, spermidine stimulated ppGpp formation. The degradation of ppGpp was not influenced significantly by polyamines. 相似文献
42.
Identification of Cytokinins in Root Exudate of the Rice Plant 总被引:4,自引:0,他引:4
Murofushi Noboru; Inoue Ayumu; Watanabe Naoharu; Ota Yasuo; Takahashi Nobutaka 《Plant & cell physiology》1983,24(1):87-92
Cytokinins, cis-zeatin and cis- and (trans-ribosylzeatin, wereidentified in the root exudate of the rice plant (Oryza sativa,indica cultivar IR-24) after several chromatographic separationsand combined gas-liquid chromatography-selected ion monitoring(GC-SIM) analysis. The presence of trans-zeatin ribotide wassuggested by enzyme hydrolysis, subsequent chromatographic separationand GC-SIM. The comparatively high content of the ribotide inthe root exudate suggests the form of cytokinins to be transportedfrom roots to other parts in the rice plant. (Received July 22, 1982; Accepted November 25, 1982) 相似文献
43.
44.
T Kurokawa M Seno R Sasada Y Ono H Onda K Igarashi M Kikuchi Y Sugino T Honjo 《Nucleic acids research》1983,11(10):3077-3085
Using the cDNA of human epsilon chain, three expression plasmids that code directly the constant portion of the epsilon chain (C epsilon 1-C epsilon 4, C epsilon 2-C epsilon 4 and C epsilon 3-C epsilon 4 domains) were constructed. These epsilon chain peptides were synthesized in E. coli under the control of the trp promoter-operator. The bacterially produced peptides have the antigenicity of human epsilon chain and gave the molecular weights equal to the values calculated from the amino acid sequence of the constructed plasmids. 相似文献
45.
Molecular cloning and nucleotide sequencing of human immunoglobulin epsilon chain cDNA. 总被引:4,自引:1,他引:3
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M Seno T Kurokawa Y Ono H Onda R Sasada K Igarashi M Kikuchi Y Sugino Y Nishida T Honjo 《Nucleic acids research》1983,11(3):719-726
DNA complementary to mRNA of human immunoglobulin E heavy chain (epsilon chain) isolated and purified from U266 cells has been synthesized and inserted into the PstI site of pBR322 by G-C tailing. This recombinant plasmid was used to transform E. coli chi 1776 to screen 1445 tetracycline resistant colonies. Nine clones (pGETI - 9) containing cDNA coding for the human epsilon chain were recognized by colony hybridization and Southern blotting analysis with a nick-translated human IgE genome fragment. The nucleotide sequence of the longest cDNA contained in pGET2 was determined. The results indicate that the sequence of 1657 nucleotides codes for 494 amino acids covering a part of the variable region and all of the constant region of the human epsilon chain. Most of the amino acid sequence deduced from the nucleotide sequence is in substantial agreement with that reported. Furthermore a termination codon after the -COOH terminal amino acid marks the beginning of a 3' untranslated region of 125 nucleotides with a poly A tail. Taking this into account, the structure of the human epsilon chain mRNA, except a part of the 5' end, is conserved fairly well in the cDNA insert in pGET2. 相似文献
46.
47.
48.
49.
Yasuo Nakajima Totada R. Shantha Geoffrey H. Bourne 《Histochemistry and cell biology》1969,18(4):293-301
Summary An improved detection of activity of l-gulonolactone oxidase, which is responsible for the final oxidative step in the synthetic process of l-ascorbate from glucose in animals, was achieved using phenazine methosulfate and cyanide. Cold acetone fixation eliminated non-specific deposition of formazan on lipid droplets. The specificity of the method was tested and proven by a biological control, histochemical controls, inhibitors and activators. By application of the method, strong reactivity was found in the cytoplasm of centrilobular parenchymal cells of livers of the opossum, rat, ground squirrel and flying squirrel. Staining of dog liver was moderate and centrilobular. Prosimians were strongly positive: The centrilobular localization was found in the tree shrew and galago; slow lorises and some pottos showed strong reactivity in centrilobular cells and some peripheral cells as well. These prosimians seem to be able to synthesize l-ascorbate as many lower mammals are. On the contrary, true simians (i.e. the squirrel monkey, spider monkey, rhesus monkey and chimpanzee) were negative as guinea pigs were, suggesting their probable inability for l-ascorbate synthesis.Visiting scientist from the Department of Anatomy, Tokyo Medical and Dental University, Tokyo, Japan.
T. R. Shanthaveerappa in previous publications, also fellow, Department of Anesthesiology, Emory University. 相似文献
50.
Histochemical studies on urate oxidase in several mammals with special reference to uricolytic ability of primates 总被引:1,自引:0,他引:1
Summary Strong reactivity for urate oxidase was found in the liver parenchymal cells of the prosimians (i.e. the tree shrew, slow loris, potto and galago) as well as those of lower mammals. The liver parenchymal cells of the platyrrhine monkeys (i.e. the marmoset, owl monkey, squirrel monkey, capuchin monkey and spider monkey) were moderately positive. There was no preferential distribution of granular reaction products in zones of liver lobules of these species. The prosimians and platyrrhine monkeys seem to be uricolytic as lower mammals are. On the other hand, the old world monkeys (i.e. Java monkey and rhesus monkey) and the apes (i.e. the orang-utan and chimpanzee) were histochemically negative. 相似文献