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   5502篇
  免费   6篇
  5508篇
  2016年   6篇
  2015年   8篇
  2014年   5篇
  2012年   195篇
  2011年   352篇
  2010年   150篇
  2009年   4篇
  2008年   310篇
  2007年   422篇
  2006年   450篇
  2005年   435篇
  2004年   456篇
  2003年   490篇
  2002年   476篇
  2001年   308篇
  2000年   514篇
  1999年   280篇
  1998年   36篇
  1997年   12篇
  1996年   2篇
  1995年   2篇
  1993年   2篇
  1992年   29篇
  1991年   31篇
  1990年   37篇
  1989年   46篇
  1988年   45篇
  1987年   32篇
  1986年   29篇
  1985年   29篇
  1984年   25篇
  1983年   16篇
  1982年   3篇
  1981年   11篇
  1980年   9篇
  1979年   21篇
  1978年   15篇
  1977年   15篇
  1976年   9篇
  1975年   30篇
  1974年   18篇
  1973年   15篇
  1972年   19篇
  1971年   20篇
  1970年   12篇
  1969年   13篇
  1968年   14篇
  1967年   17篇
  1966年   12篇
  1965年   11篇
排序方式: 共有5508条查询结果,搜索用时 11 毫秒
21.
Comparison of the results of the karyologic analysis of two Hela cell sublines (HeLa1 and HeLa2), obtained from different sources, and of Detroit-6 cell line has shown that all the lines contain marker chromosomes characteristic of the HeLa cell line. Detroit-6 cell line marker chromosomes are similar to markers of the HeLa subline (HeLa1). At the same time, part of marker chromosomes in the two sublines of HeLa cell line (HeLa1 and HeLa2) are different. These data show that HeLa1 and Detroit-6 cell lines are more similar than two sublines of the same HeLa cell line.  相似文献   
22.
The importance of spatial organization of DNA for the regulation of genome activity is discussed. The main problem reviewed in this paper includes cooperative interactions of proteins with DNA, formation of DNA loops in the regulatory domains of the genome and conformational mobility of DNA in chromatin.  相似文献   
23.
Multiplex methylation-sensitive PCR and methylation-specific PCR were employed in studying the methylation of CpG islands in the p16/CDKN2A and p14/ARF promoter and the first exon regions in non-small cell lung cancer (54 samples) and acute B-cell lymphoblastic leukemia (61 samples). Differences in methylation were detected between types of neoplasia as well as between CpG islands studied within the same types of tumors. High level of the p16/CDKN2A first exon CpC island methylation was revealed in non-small cell lung cancer (68%) and in acute B-cell lymphoblastic leukemia (55%) and the CpG island of p14/ARF first exon was nonmethylated in these types of tumors. The methylation of CpG-rich fragments of genes p16/CDKN2A and p14/ARF promoters was analysed. As was found out, CpG islands located in 5' areas of one and the same gene can differ in methylation frequencies. The comparison of sensitivity between methylation-specific PCR and methylation-sensitive PCR used in the methylations studies was carried out.  相似文献   
24.
Blood lymphocytes from 26 women were cultivated in RPMI-1640 for 72 hrs with or without dexamethasone, dbcAMP, and TPA. Androstenedione conversion was most often activated by the dbcAMP, then by Dex and TPA. Response to dbcAMP was most obvious in women under 50, whereas response to Dex--in women over 50. Aromatase inhibitor fadrosol displayed a tendency towards prevention of the activation of androstenedione conversion in cultivated lymphocytes. A possibility of aromatase gene induction in cultivated lymphocytes cannot be completely excluded and demands further investigation with the aid of molecular-genetic methods.  相似文献   
25.
26.
The potentialities of diffuse optical spectroscopy for the noninvasive estimation of the oxygen state of experimental tumors have been demonstrated. The distribution of total, oxygenated and deoxygenated hemoglobin, as well as the level oxygen saturation of blood have been shown using two tumor models differing in the histological structure and functional characteristics. The results obtained by the optical method have been verified by immunohistochemical examination of tissue specimens with the exogenous hypoxia marker pimonidazole.  相似文献   
27.
The human CKAP2 gene, which is involved in diffuse large B-cell lymphomas, was localized via screening the GeneBridge 4 somatic cell radiation hybrid panel by means of the polymerase chain reaction (PCR). The CKAP2 gene was mapped between the WI-15460 and WI-3673 markers at the boundary between regions 13q14.3 and 13q21.1, at the distance of 14.39 cR (with 4.8 cR per cM) from the WI-5867 framework marker (lod score > 2.26). The human CKAP2 gene displayed high homology to mouse and rat expressed orthologs, A CKAP2-like sequence was found in human chromosome 14 and assumed to be a pseudogene resulting from duplication and subsequent mutations of the CKAP2 gene on chromosome 13. A possible role of the CKAP2 gene in oncogenesis associated with deletions and rearrangements of region 13q14.3-21.1 is discussed.  相似文献   
28.
Mixed urogenital infection in men   总被引:1,自引:0,他引:1  
High occurrence of sexually transmitted diseases (STD) caused by a combination of different infective agents was established. In 62.5% of cases such diseases took a course typical for mixed infections. Combinations of infective agents of STD were found to have several typical associations, e.g. Ureaplasma urealyticum and Mycoplasma hominis in combination with opportunistic microflora. The microbiocenosis of the reproductive tract was shown to form under the influence of a complex of endogenous (natural biological) and exogenous (sexual behavioral) factors leading, in each particular case, to the formation of stable associations.  相似文献   
29.
Two new steroid glycosides from the starfish Fromia milleporella collected in the Seychelles were isolated and characterized: milleporoside A, (20R, 24R)-29-O-[3-O-methyl-beta-D-xylopyranosyl-(1-->4)-3-O-methyl-beta-D-xylopyranosyl]-24-ethyl-5alpha-cholestane-3beta,4beta,6alpha,8,15beta,16beta,29-heptaol, and milleporoside B, (20R, 24R)-(22E)-28-O-[3-O-methyl-beta-D-xylopyranosyl-(1-->4)-3-O-methyl-beta-D-xylopyranosyl]-24-methyl-5alpha-cholest-22-ene-3beta,4beta,6alpha,8,15beta,16beta,28-heptaol. The structures of the glycosides were determined from their spectra and a comparison with spectral characteristics of known compounds. These compounds exhibit a moderate cytostatic activity toward the embryos of the sea urchin Strongylocentrotus intermedius.  相似文献   
30.
Microbiological technology for the enhancement of oil recovery based on the activation of the stratal microflora was tested in the high-temperature horizons of the Kongdian bed (60 degrees C) of the Dagang oil field (China). This biotechnology consists in the pumping of a water-air mixture and nitrogen and phosphorus mineral salts into the oil stratum through injection wells in order to stimulate the activity of the stratal microflora which produce oil-releasing metabolites. Monitoring of the physicochemical, microbiological, and production characteristics of the test site has revealed large changes in the ecosystem as a result of the application of biotechnology. The cell numbers of thermophilic hydrocarbon-oxidizing, fermentative, sulfate-reducing, and methanogenic microorganisms increased 10-10 000-fold. The rates of methanogenesis and sulfate reduction increased in the near-bottom zone of the injection wells and of some production wells. The microbial oil transformation was accompanied by the accumulation of bicarbonate ions, volatile fatty acids, and biosurfactants in the formation waters, as well as of CH4 and CO2 both in the gas phase and in the oil. Microbial metabolites promoted the additional recovery of oil. As a result of the application of biotechnology, the water content in the production liquid from the test site decreased, and the oil content increased. This allowed the recovery of more than 14000 tons of additional oil over 3.5 years.  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