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   4816篇
  免费   0篇
  4816篇
  2012年   188篇
  2011年   349篇
  2010年   144篇
  2009年   1篇
  2008年   303篇
  2007年   419篇
  2006年   447篇
  2005年   431篇
  2004年   451篇
  2003年   485篇
  2002年   474篇
  2001年   298篇
  2000年   513篇
  1999年   261篇
  1998年   34篇
  1997年   12篇
  1992年   1篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1983年   1篇
  1967年   1篇
排序方式: 共有4816条查询结果,搜索用时 15 毫秒
1.
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   
2.
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   
3.
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   
4.
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   
5.
6.
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   
7.
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   
8.
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   
9.
Higher harmonics of alternating current in bilayer lipid membranes caused by sinusoidal voltage applied to the membrane were measured. The bilayer lipid membranes were prepared from diphytanoylphosphatidylcholine in n-decane and n-tetradecane, and measurements were conducted with the aid of an analog-to-digital converter of 16th category. Sinusoidal voltage was formed using a digital-to-analog converter of the 16th category. The dynamic region of measurements was up 90 dB. The results of measurements were used to determine the alpha and beta coefficients of the expansion of membrane capacity C in terms of membrane voltage U C = C0 (1 + alphaU2 + betaU4). We showed in the framework of the electrostriction model that the relation between the alpha and beta coefficients characterizes the inhomogeneity of bilayer lipid membrane with respect to its thickness and Young modulus of elasticity.  相似文献   
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