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   749498篇
  免费   84823篇
  国内免费   452篇
  2018年   6945篇
  2017年   6623篇
  2016年   9138篇
  2015年   11774篇
  2014年   14147篇
  2013年   20389篇
  2012年   22676篇
  2011年   23164篇
  2010年   15583篇
  2009年   14530篇
  2008年   20462篇
  2007年   21127篇
  2006年   19985篇
  2005年   19265篇
  2004年   18991篇
  2003年   18290篇
  2002年   17683篇
  2001年   39279篇
  2000年   39442篇
  1999年   30579篇
  1998年   9587篇
  1997年   10249篇
  1996年   9504篇
  1995年   8771篇
  1994年   8526篇
  1993年   8595篇
  1992年   24325篇
  1991年   23500篇
  1990年   22655篇
  1989年   22042篇
  1988年   20455篇
  1987年   19042篇
  1986年   17588篇
  1985年   17333篇
  1984年   14090篇
  1983年   11950篇
  1982年   8784篇
  1981年   7882篇
  1980年   7538篇
  1979年   13086篇
  1978年   10075篇
  1977年   9293篇
  1976年   8317篇
  1975年   9286篇
  1974年   10040篇
  1973年   9748篇
  1972年   8785篇
  1971年   8048篇
  1970年   7009篇
  1969年   6693篇
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
901.
We have taxonomically and phylogenetically characterized a new aerobic bacterial strain (JF-1) that contains photosynthetic pigment-protein complexes and which was recently isolated from black smoker plume waters of the Juan de Fuca Ridge. Strain JF-1 is a gram-negative, yellow-pigmented, motile bacterium that is salt-, pH-, and thermotolerant. These properties are consistent with an oligotrophic adaptation to varied environmental conditions thought to exist around deep-sea hydrothermal vents. The analysis of 16S rDNA sequences revealed that strain JF-1 forms a separate phylogenetic branch between the genus Erythromonas and the Erythromicrobium-Porphyrobacter-Erythrobacter cluster within the alpha subclass of the Proteobacteria. The taxonomic name Citromicrobium bathyomarinum (gen. nov., sp. nov.) is proposed for strain JF-1.  相似文献   
902.
The objective of the study was to evaluate the use of targeted multiplex Nanopore MinION amplicon re-sequencing of key Candida spp. from blood culture bottles to identify azole and echinocandin resistance associated SNPs. Targeted PCR amplification of azole (ERG11 and ERG3) and echinocandin (FKS) resistance-associated loci was performed on positive blood culture media. Sequencing was performed using MinION nanopore device with R9.4.1 Flow Cells. Twenty-eight spiked blood cultures (ATCC strains and clinical isolates) and 12 prospectively collected positive blood cultures with candidaemia were included. Isolate species included Candida albicans, Candida glabrata, Candida krusei, Candida parapsilosis, Candida tropicalis and Candida auris. SNPs that were identified on ERG and FKS genes using Snippy tool and CLC Genomic Workbench were correlated with phenotypic testing by broth microdilution (YeastOne™ Sensititre). Illumina whole-genome-sequencing and Sanger-sequencing were also performed as confirmatory testing of the mutations identified from nanopore sequencing data. There was a perfect agreement of the resistance-associated mutations detected by MinION-nanopore-sequencing compared to phenotypic testing for acquired resistance (16 with azole resistance; 3 with echinocandin resistance), and perfect concordance of the nanopore sequence mutations to Illumina and Sanger data. Mutations with no known association with phenotypic drug resistance and novel mutations were also detected.  相似文献   
903.
Degeneracy of antibody specificity   总被引:2,自引:0,他引:2  
Evidence was obtained, by direct binding assays (radioimmunoassays) and by inhibition of binding assays, that after immunization some of the antibody molecules produced are degenerate in that they bind not only the immunizing antigen, but also unrelated ligands. It can be concluded that the exquisite specificity of the immune response is not necessarily a property of any given antibody molecule but is, at least to some extent, due to the summation of specificities held in common by the population of antibody molecules produced during the response.  相似文献   
904.
Fusarium oxysporum f. sp. lycopersici and Rhizoctonal solani were grown in a complete 1.0 mM nutrient solution, and in solutions where Ca, Fe, K, Mg, N, P, and S were either excluded (0.0 mM) or included at depleted levels (0.1 mM) while all other constituents were maintained at 1.0 mM levels. Dry weight of both fungi were determined. For both fungi some of the lowest dry weights were recorded for samples grown in the complete solution. Exclusion of K, Mg, and S significantly increased dry weight of Fusarium. Inclusion at the 0.1 mM level of most components significantly increased Fusarium dry weight over values for both the complete and corresponding excluded nutrient solutions. The exception was S where there was no difference between excluded and 0.1 mM solutions. For Rhizoctonia dry weights in Fe excluded solutions were less than the complete solution, while dry weights in S excluded solutions were greater than the complete solution. At the 1.0 mM level Fe, K, and Mg dry weights were significantly increased over the dry weights produced in both the complete and deficient solutions.  相似文献   
905.
Beta-adrenoceptors have been discovered on the surface of cells of leukaemia L1210 and its variant resistant to sarcolysine (D, L-melphalan). One type of functionally active receptors with dissociation constant Kd for L-[3H] dihydroalprenolol about 0.02 nM and 360 receptors per cell have been revealed in leukaemia L1210 cells. In the resistant cells two types of functionally inactive receptors with Kd1 approximately 0.02 nM (420 receptors per cell) and Kd2 approximately 2.5 nM (3000 receptors per cell) have been revealed. This property of beta-adrenoceptors may be one of the causes of tumour cell resistance to sarcolysine.  相似文献   
906.
A rapid, sensitive method has been developed to detect antibody-antigen complexes on “Western blots.” The methods of H. Towbin, T. Staehlin, and J. Gordon were used to separate and blot the antigens onto nitrocellulose. The remaining sites of attachment were blocked and the nitrocellulose was washed with polyoxyethylenesorbitan monolaurate (Tween 20). The blot was then reacted with the antiserum or hybridoma supernate to be tested. After the antigen-antibody reaction was completed, the blot was washed and treated with anti-antibody which has been conjugated to alkaline phosphatase. The alkaline phosphatase was detected by the reduction of the tetrazolium salt to diformazan by the hydrogen ions released in the formation of indigo by the reaction of the phosphatase on the indoxyl phosphate. The advantages of this method over previously described techniques are (1) use of Tween 20 allows the blot to be stained with Coomassie blue, (2) the substrates of the alkaline phosphatase reaction are stable for long periods of time, (3) the reaction products form an intense blue color which does not fade, (4) the resolution is extremely good with little to no band broadening, (5) the reaction is sensitive to picogram quantities of antigen, and (6) the reaction is quantitative.  相似文献   
907.
908.
909.
A new mutation, mpo, which affects the synthesis of some membrane proteins and sporulation in Bacillus subtilis was identified. The mpo mutation was tightly linked to the overproduction of membrane proteins MP32 and MP18 (molecular weights of 32,000 and 18,000, respectively) and the temperature-sensitive sporulation phenotype. Genetic analysis showed that the mpo mutation maps between the spoIIIB and lys loci.  相似文献   
910.
Several phenotypic and functional defects have been described within the residual T-lymphocyte population of patients with B-cell chronic lymphocytic leukemia (B-CLL), particularly in those in the more advanced stages of the disease. In this study, we review these abnormalities and discuss their possible effects on the course of the illness. Particular emphasis is devoted to the role of interleukin 2 (IL-2) in B-CLL. Evidence is provided that the IL-2 released by B-CLL T-lymphocytes may be utilized by the neoplastic B-cell clone that expresses the IL-2 receptor and that decreased availability of IL-2 may play a contributory role in some of the T-cell defects encountered in B-CLL.  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