首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2073篇
  免费   96篇
  2023年   2篇
  2022年   5篇
  2021年   22篇
  2020年   13篇
  2019年   21篇
  2018年   25篇
  2017年   23篇
  2016年   47篇
  2015年   71篇
  2014年   82篇
  2013年   109篇
  2012年   156篇
  2011年   147篇
  2010年   88篇
  2009年   82篇
  2008年   132篇
  2007年   168篇
  2006年   129篇
  2005年   151篇
  2004年   135篇
  2003年   129篇
  2002年   130篇
  2001年   16篇
  2000年   21篇
  1999年   25篇
  1998年   22篇
  1997年   21篇
  1996年   12篇
  1995年   17篇
  1994年   20篇
  1993年   16篇
  1992年   21篇
  1991年   15篇
  1990年   13篇
  1989年   12篇
  1988年   5篇
  1987年   12篇
  1986年   5篇
  1985年   4篇
  1984年   4篇
  1983年   5篇
  1982年   5篇
  1981年   7篇
  1980年   3篇
  1979年   2篇
  1978年   3篇
  1976年   2篇
  1974年   2篇
  1971年   2篇
  1966年   2篇
排序方式: 共有2169条查询结果,搜索用时 296 毫秒
1.
The first 12 NH2-terminal amino acids of the Pseudomonas putida putidaredoxin reductase were shown to be Met-Asn-Ala-Asn-Asp-Asn-Val-Val-Ile-Val-Gly-Thr. Comparison of these data with the DNA sequence of the BamHI-HindIII 197-base fragment derived from the PstI 2.2-kb fragment obtained from the P. putida plasmid showed that the putidaredoxin reductase gene was downstream from the cytochrome P-450 gene and the intergenic region had the 24-nucleotide sequence TAAACACATGGGAGTGCGTGCTAA. The Shine-Dalgarno sequence GGAG was detected in this region. The initiating triplet for the reductase gene was GTG, which normally codes for valine, but in the initiating codon position codes for methionine. From the amino acid sequence and X-ray data comparisons with other flavoproteins, what appears to be the AMP binding region of the FAD can be recognized in the NH2-terminal portion of the reductase involving residues 5–35.This article was presented during the proceedings of the International Conference on Macromolecular Structure and Function, held at the National Defence Medical College, Tokorozawa, Japan, December 1985.  相似文献   
2.
The role of cell-mediated immunity in recovery from rinderpest virus infection in rabbits was investigated by application of immunosuppressive procedures, i.e., treatment with anti-thymocyte serum and combined treatment with thymectomy and anti-thymocyte serum, both of which were confirmed to depress significantly cell-mediated immunity in rabbits. The immunosuppressed animals recovered in almost the normal fashion in terms of clinical signs, of virus clearance from the blood and lymphoid tissues and of repair of the lesions. It was suggested that the thymus-dependent cell-mediated immunity may not be essential in recovery from rinderpest virus infection. Possibility of participation of other recovery mechanisms was discussed.  相似文献   
3.
Biosynthesis of locust apolipophorin-III (apo-III) was studied in vitro. Gel electrophoresis and immunoblotting analyses of the locust hemolymph demonstrated that apo-III first appears in the hemolymph on the day 3 of the adult stage after the final molt and its hemolymph concentration increases thereafter. When incubated in vitro in a medium containing radioactive amino acid, the fat body cells synthesized the radiolabeled apo-III and released it into the medium. The developmental change in the apo-III synthesizing activity in the fat body reflected that of the apo-III concentration in the hemolymph. RNA isolated from the adult fat body directed the synthesis of apo-III as a major translation product in a cell-free system. These results indicate that the fat body is the tissue responsible for the synthesis of the locust apo-III, and biosynthesis of apo-III is developmentally regulated at the level of mRNA in accordance with the flight activity of the locust.  相似文献   
4.
Summary Among 200 strains of marine bluegreen algae isolated from the coastal areas of Japan, the marine blue-green alga Synechococcus sp. NKBG 040607 excreted glutamate at the highest rate, 82.6% of total amino acids production being glutamate. Synechococcus sp. NKBG 40607 was immobilized in calcium alginate gel. Glutamate production by immobilized cells was double that of native cells. Maximal glutamate production (25 g/cm3 gel per day) of the immobilized cells was observed under a light intensity of 144 Einstein/m2 per second at a cell concentration of 7.5 mg dry cells/cm3 gel. Immobilized cells of Synechococcus sp. can use nitrate as a nitrogen source. Immobilized marine Synechococcus sp. produced 0265 mg/cm3 gel of glutamate for 7 days in the presence of chloramphenicol.  相似文献   
5.
Libraries of cosmid and plasmid clones covering the entire region of mtDNA from the liverwortMarchantia polymorpha were constructed. These clones were used for the determination of the complete nucleotide sequence of the liverwort mtDNA totally 186,608 bp (GenBank no. M68929) and including genes for 3 species of ribosomal RNAs, 29 genes for 27 species of transfer RNAs, and 30 genes for functionally known proteins (16 ribosomal proteins, 3 subunits of cytochromec oxidase, apocytochromeb protein, 3 subunits of H+-ATPase, and 7 subunits of NADH ubiquinone oxidoreductase). The genome also contains 32 unidentified open reading frames. Thus the complete nucleotide sequences from both chloroplast and mitochondrial genomes have been determined in the same organism. Plasmid clones are available upon the request. Gene names are represented according to Lonsdale and Leaver (1988) with modifications recommended by Lonsdale (personal communication).  相似文献   
6.
The pea phytochrome I (PI) cDNA clone, pPP1001, was expressedin E. coli. The plasmid pPP1001 contains pea PI cDNA which coversthe entire coding region with the Shine-Dalgarno consensus sequencejoined upstream of the cDNA in an expression vector pNUT6. ThepPP1001 transformants formed typical inclusion bodies when culturedat 32?C. However, when cultured at 37?C or in the presence ofisopropyl-ß-D-thiogalactopyranoside (IPTG) at 32?C,the bacteria lysed before inclusion body formation. Immuno-stainingwith anti-PI monoclonal antibody, mAP5, of transformants fixedby cold methanol showed that stainable materials were distributedin whole cytoplasmic region. When the inclusion bodies wereobserved clearly, the regions corresponding to the inclusionbodies became difficult to stain. Western blot analysis, however,showed that a ca. 100 kDa PI polypeptide was detected in thefraction from inclusion bodies and a ca. 90 kDa PI polypeptidefrom the soluble fraction. The amino acid sequence analysisof purified 100 kDa PI sample indicated that its amino terminusis blocked. However, minor signals in one experiment yieldeda sequence corresponding to the expected amino terminus of peaPI except for the initiation methionine. One of the anti-peaPI monoclonal antibodies, mAP9, that recognizes the near N-terminusof pea phytochrome was reactive to the 100 kDa polypeptide. (Received June 22, 1990; Accepted November 18, 1990)  相似文献   
7.
To obtain antiparallel and parallel dimers of alpha-human atrial natriuretic peptide (alpha-hANP), two fully protected peptides I and II having the same amino acid sequence as alpha-hANP with different protective groups at the cysteinyl residues were synthesized, the former having Acm and Npys and the latter MeBzl and Acm. Equivalent amounts of peptides I and II were mixed and subjected to HF deprotection. Next, the first disulfide bond was linked between the remaining Npys group in I and the liberated SH group in II to form a monodisulfide dimer. The second disulfide bond was formed within the newly formed dimer between the remaining Acm groups by treatment with iodine, giving an antiparallel dimer. The parallel dimer of alpha-hANP was synthesized similarly starting from the protected peptide II. These dimers could be clearly segregated on HPLC. The retention time on HPLC of the antiparallel dimer was identical with that of natural beta-hANP. Both dimers showed biological activities as high as one third to one sixth of alpha-hANP in smooth muscle spasmolytic activity, and almost the same level of natriuretic activity as alpha-hANP at a high dose (10 nmol/kg) but about one fifth the activity at a low dose (1 nmol/kg). In these assay systems, the antiparallel dimer showed a slower onset and a tendency of longer duration than alpha-hANP.  相似文献   
8.
Nitrate and Other Anions in the Rice Phloem Sap   总被引:1,自引:0,他引:1  
The anionic composition was determined for pure rice phloemsap which had been collected from brown planthopper styletsby cutting them with a YAG laser beam. The most abundant inorganicanion was Cl at 52.1 mM. PO43– and SO42–were found at 8.1 mM and 1.8 mM, respectively. NO3 waspresent at 1.9 mM when the rice had been grown with nutrientsolution containing 0.35 m of NO3 The phloem sap alsocontained malic, succinic and citric acid at 7.3, 3.0 and 3.2mM respectively. Small amounts of other organic acids were alsofound. (Received October 4, 1984; Accepted December 14, 1984)  相似文献   
9.
Summary The antitumor activities and capacity for tumor necrosis factor (TNF) production of traditional Chinese herbal preparations (Zhu-ling-tang, Xiao-chai-hu-tang), crude drugs (Polyporus, Hoelen, Bupleuri radix, Angelica radix, Cnidii rhizoma, Cinnamomum cortex), and Krestin (PSK) were investigated. These drugs were given to DDY mice in the drinking water before and after transplantation of Ehrlich tumors, and the development of the intradermally transplanted Ehrlich tumors and survival rate were observed. A good survival rate and sometimes a complete cure were found in the groups administered Bupleuri radix, Xiao-chai-hu-tang, Angelica radix, or Cinnamomum cortex, while the group given Hoelen showed poor results. To examine the capacity for TNF production these drugs were given to DDY mice PO as initial stimulating agents, to stimulate the reticuloendothelial system (RES) prior to lipopolysaccharide injection. The TNF activity was tested from the cytotoxicity against L cells. Significant differences in capacity for TNF production were observed among the drugs. Relatively high levels of TNF activity were noted in the groups given Angelica radix, Bupleuri radix, Cnidii rhizoma, or Cinnamomum cortex, very low activities in the groups given Xiao-chai-hu-tang, Zhu-ling-tang, or Krestin, and no TNF activities in the groups given Polyporus or Hoelen. The TNF capacity for production broadly paralleled the survival rate of the mice transplanted to Ehrlich tumors. Our findings suggest that one mechanism underlying the antitumor activities of these drugs is based on stimulation of the RES and is closely related of TNF production.This work was supported in part by a grant-in-aid from the Ministry of Education, Japan  相似文献   
10.
The first 12 NH2-terminal amino acids of the Pseudomonas putida putidaredoxin reductase were shown to be Met-Asn-Ala-Asn-Asp-Asn-Val-Val-Ile-Val-Gly-Thr. Comparison of these data with the DNA sequence of the BamHI-HindIII 197-base fragment derived from the PstI 2.2-kb fragment obtained from the P. putida plasmid showed that the putidaredoxin reductase gene was downstream from the cytochrome P-450 gene and the intergenic region had the 24-nucleotide sequence TAAACACATGGGAGTGCGTGCTAA. The Shine-Dalgarno sequence GGAG was detected in this region. The initiating triplet for the reductase gene was GTG, which normally codes for valine, but in the initiating codon position codes for methionine. From the amino acid sequence and X-ray data comparisons with other flavoproteins, what appears to be the AMP binding region of the FAD can be recognized in the NH2-terminal portion of the reductase involving residues 5–35.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号