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   1228篇
  免费   59篇
  1287篇
  2022年   8篇
  2021年   15篇
  2020年   10篇
  2019年   11篇
  2018年   19篇
  2017年   14篇
  2016年   18篇
  2015年   33篇
  2014年   44篇
  2013年   76篇
  2012年   85篇
  2011年   74篇
  2010年   42篇
  2009年   38篇
  2008年   92篇
  2007年   62篇
  2006年   68篇
  2005年   57篇
  2004年   73篇
  2003年   67篇
  2002年   62篇
  2001年   23篇
  2000年   16篇
  1999年   22篇
  1998年   19篇
  1997年   20篇
  1996年   13篇
  1995年   17篇
  1994年   5篇
  1993年   3篇
  1992年   14篇
  1991年   18篇
  1990年   14篇
  1989年   10篇
  1988年   9篇
  1987年   14篇
  1986年   9篇
  1985年   9篇
  1984年   13篇
  1983年   16篇
  1982年   16篇
  1981年   7篇
  1979年   3篇
  1977年   4篇
  1976年   4篇
  1975年   2篇
  1974年   2篇
  1973年   4篇
  1972年   3篇
  1971年   2篇
排序方式: 共有1287条查询结果,搜索用时 15 毫秒
1.
Axonal transport of peptidylglycine alpha-amidating monooxygenase (PAM) activity was studied in rat sciatic nerves from 12 to 120 h after double ligations. The anterograde axonal transport increased and reached a plateau between 48 and 72 h and then decreased. The flow rate was 100 mm/day, and the molecular mass of the active entity was 70 kDa, which was determined by gel filtration. In contrast, there was no evidence for significant retrograde axonal transport. Anterograde axonal transport of immunoreactive cholecystokinin, a carboxy-terminal-amidated putative neuropeptide, was also found. These results suggest that PAM is transported by a rapid axonal flow and may play a role as a processing enzyme during transport or in the terminals of rat sciatic nerves.  相似文献   
2.
Sequence analyses of the complete brown bear, Ursus arctos, mitochondrial DNA (mtDNA) genome have detected scattered single nucleotide polymorphisms (SNPs) that define distinct mtDNA haplogroups in phylogeographical studies. The degraded DNA in historical samples, such as stuffed or excavated specimens, however, is often not suitable for sequence analyses. To address this problem, we developed an amplified product length polymorphism (APLP) analysis for mtDNA‐haplogrouping U. arctos specimens by detecting haplogroup‐specific SNPs. We verified the validity and utility of this method by analysing up to 170‐year‐old skin samples from U. arctos specimens collected widely across continental Eurasia. We detected some of the same haplogroups as those occurring in eastern Hokkaido (Japan) and eastern Alaska in continental Eurasia (the Altai and the Caucasus). Our results show that U. arctos in eastern Hokkaido and eastern Alaska descended from a common ancestor in continental Eurasia, and suggest that U. arctos occupied several refugia in southern Asia during the Last Glacial Maximum. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 627–635.  相似文献   
3.
Abstract Over 200 strains of marine purple photosynthetic bacteria were isolated. Two strains showed antibiotic activity towards Saccharomyces cerevisiae and were tentatively identified as Chromatium purpuratum . Crude antibiotic, prepared by solvent extraction, showed a broad antimicrobial spectrum. The highest activity was found in the chromatophore fraction. Chromatographic separation of purified light harvesting complex from one strain, NKPB 031704, showed the presence of two separate pigmented compounds which were responsible for antimicrobial activity. Our findings reveal the unexpected ability of photosynthetic bacteria to produce broad spectrum antibiotics. In addition, this is the first example of intracellular localization of antibiotic activity in a marine bacterium.  相似文献   
4.
In lactate dehydrogenase (LDH) A subunit deficiency, is there not only a lack of activity but also a lack of subunit production? We demonstrated three remarkable points to answer this question: There are no proteins that immunologically react with anti-A subunits. There are no heterotetramers that react with anti-B subunits. B subunits seem to be genetically produced at normal level, and all of them form only one isoenzyme, LDH-B4. From these points, we concluded that there is a complete lack of A subunit production or production of incomplete A subunits that can neither react with anti-A subunits nor form heterotetramers.  相似文献   
5.
Summary -Galactosidase-2 (-d-galactoside galactohydrolase, EC 3.2.1.23) from Bacillus circulans was purified using hydroxyapatite gel chromatography and immobilized onto Duolite ES-762 (phenolformaldehyde resin) and Merckogel (controlled pore silica gel) for continuous production of galacto-oligosaccharides using lactose as the substrate. The maximum amount of ologosaccharides produced by the immobilized enzyme was 35–40% of the total sugar during hydrolysis of 4.56% lactose. Partially purified -galactosidase from B. circulans was also immobilized onto various supports for the same purpose. The stability of the immobilized -galactosidase-2 or partially purified enzyme during a continuous reaction depended on their supports and specific activity. Of the supports tested, Merckogel was best for operational stability. With this support, the enzyme was quite stable with specific activity up to 15 units/g of wet gel; it was reversibly inactivated with more.  相似文献   
6.
IL-7 induced the proliferation of normal thymocytes and the effect was synergistically potentiated by a small dose of IL-2, which by itself hardly affected thymocyte proliferation. No synergism was observed between IL-7 and any one of the other lymphokines including IL-1, IL-3, and IL-4. The thymocyte culture stimulated with IL-7 and IL-2 consisted of single positive (CD4+CD8- and CD4-CD8+) and double negative (CD4-CD8-) populations, and double positive (CD4+CD8+) cells were completely deleted. Both single positive and double negative thymocytes expressed CD3, but only the former exhibited V beta 8 and V beta 6 in an expected proportion (approximately 30% in BALB/c mice) and the latter none at all. Immunoprecipitation of the cultured thymocytes by anti-TCR gamma antibody, on the other hand, revealed the presence of a TCR gamma chain. Taken together, these results indicated that the thymocyte cultured with IL-7 and IL-2 consisted of mature T cells bearing alpha beta or gamma delta TCR. Experiments using preselected thymocyte subpopulations indicated that double negative cells responded to both IL-7 and IL-2 with positive synergism when combined, while thymocytes enriched for single positive cells preferentially responded to IL-7 with little response to IL-2 and no detectable synergism. Double positive thymocytes showed no proliferation in response to IL-7 and IL-2. In contrast to single positive thymocytes, splenic T cells hardly responded to IL-7, although significant proliferation was induced in the presence of a low dose of IL-2. Thymocytes cultured with IL-7 and IL-2 showed little nonspecific cytotoxic activity, but responded to Con A or alloantigen, whereas those stimulated with a high dose of IL-2 alone exhibited potent cytotoxic activity. These results indicated that IL-7 was involved in the generation of immunocompetent T cells in the thymus in concert with IL-2.  相似文献   
7.
Polymorphism of the ABO blood group gene was investigated in 262 healthy Japanese donors by a polymerase chain reactions-single-strand conformation polymorphism (PCR-SSCP) method, and 13 different alleles were identified. The number of alleles identified in each group was 4 for A1 (provisionally called ABO*A101, *A102, *A103 and *A104 according to the guidelines for human gene nomenclature), 3 for B (ABO*B101, *B102 and *B103), and 6 for O (ABO*O101, *O102, *O103, *O201, *O202 and *O203). Nucleotide sequences of the amplified fragments with different SSCP patterns were determined by direct sequencing. Phylogenetic network analysis revealed that these alleles could be classified into three major lineages, *A/*O1, *B and *O2. In Japanese, *A102 and *13101 were the predominant alleles with frequencies of 83% and 97% in each group, respectively, whereas in group O, two common alleles, *O101 (43%) and *O201 (53%), were observed. These results may be useful for the establishment of ABO genotyping, and these newly described ABO alleles would be advantageous indicators for population studies.  相似文献   
8.
 The cyanobacterium, Aphanocapsa halo-phytia MN-11, was immobilized in calcium alginate gel and coated on light-diffusing optical fibers (LDOF) for sulfated extracellular polysaccharide production. Results indicated that sulfated extracellular polysaccharide production depends on the number of immobilized cells and the light intensity. In addition, the production rate reached 116.0 mg (mg dry cells)-1 day-1 when the cells that were immobilized on LDOF were incubated under a light intensity of 1380 cd sr m-2 at a cell concentration of 1.0×108 cells/cm3 gel. Cells immobilized on LDOF produced about ten times more sulfated extracellular polysaccharide than those immobilized in calcium alginate beads only (11.7 mg(mg dry cells)-1 day-1). Received: 31 March 1995/Revised last revision 12 June 1995/Accepted 26 July 1995  相似文献   
9.
10.
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