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   1898篇
  免费   114篇
  国内免费   1篇
  2022年   4篇
  2021年   16篇
  2020年   12篇
  2019年   12篇
  2018年   13篇
  2017年   20篇
  2016年   40篇
  2015年   52篇
  2014年   61篇
  2013年   126篇
  2012年   112篇
  2011年   103篇
  2010年   72篇
  2009年   82篇
  2008年   92篇
  2007年   118篇
  2006年   118篇
  2005年   160篇
  2004年   147篇
  2003年   142篇
  2002年   141篇
  2001年   21篇
  2000年   17篇
  1999年   23篇
  1998年   36篇
  1997年   20篇
  1996年   16篇
  1995年   21篇
  1994年   26篇
  1993年   18篇
  1992年   17篇
  1991年   11篇
  1990年   8篇
  1989年   16篇
  1988年   10篇
  1987年   10篇
  1986年   6篇
  1985年   7篇
  1984年   7篇
  1983年   14篇
  1982年   15篇
  1981年   14篇
  1980年   7篇
  1979年   5篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1975年   5篇
  1971年   2篇
  1959年   2篇
排序方式: 共有2013条查询结果,搜索用时 140 毫秒
1.
In order to evaluate the importance of estrogen production in tumor and surrounding tissues, we measured mRNA expression levels of 5 enzymes participating to estrogen synthesis in situ and 4 breast cancer-related proteins in 27 pairs of tumor and non-malignant tissues. Steroid sulfatase (STS) mRNA was more frequently detected in tumor tissues rather than in their non-malignant counterparts. Estrogen sulfotransferase (EST) was constantly expressed with high level not only in tumor tissues but also in their surrounding non-malignant counterparts. In contrast, mRNA expression levels of aromatase, and 17β-hydroxysteroid dehydrogenase type I and II were relatively low and detected only in small proportion of the patients. We also measured the mRNA expression levels of the same nine genes in tumor tissues of 197 breast cancer patients, and analyzed relationship between the mRNA expression level and the clinicopathological parameters. The mRNA expression levels of STS, aromatase and erbB2 in tumor tissues increased as breast cancer progressed. The tumoral mRNA expression levels of STS, estrogen receptor β, and erbB2 in patients with recurrence were higher than those in patients without recurrence. Upregulation of STS expression plays an important role in tumor progression of human breast cancer and is considered to be responsible for estrogen production in tumor and surrounding tissues.  相似文献   
2.
A respiration-deficient (RD) mutant was isolated from the petite-negative, salt-tolerant yeast Zygosaccharomyces rouxii. One strain among sixteen glycerol-non-utilizing mutants exhibited vigorous liberation of CO2 but no uptake of O2. Furthermore, this strain lacked cytochrome aa3 and had a reduced level of cytochrome b. The few mitochondria found in cells of this strain contained few or no cristae. Salt tolerance and intracellular accumulation of glycerol by the RD strain were almost equal to that of the wild-type strain in media containing NaCl up to 2.5 M. In media with more than 3 M NaCl, the growth of the RD mutant was retarded and the intracellular accumulation of glycerol was depressed in spite of ample production.  相似文献   
3.
Bacterial cometabolic degradation of chlorinated paraffins   总被引:1,自引:0,他引:1  
Summary Cometabolic dechlorination of chlorinated paraffins was demonstrated in the presence of n-hexadecane by bacterial strains (HK-3, HK-6, HK-8, and HK-10) isolated from soil samples.Eleven per cent of chlorine of chlorinated paraffin-150 (CP-150) was released by strain HK-3. The mixed culture of strain HK-3, catalyzing the dechlorination of terminal chlorine of chloroalkane, and strain H15-4, capable of releasing the chlorine from 2-chlorinated fatty acids, dechlorinated CP-150 up to 13%. The mixed culture of the four strains (HK-3, HK-6, HK-8, and HK-10) performed the dechlorination of CP-150 by cometabolism in a jar fermentor pH at 7.0. The amount of chloride released from the chlorinated paraffins tested was in the range of 15–57%.The activated sludge acclimatized to n-hexadecane for 60 days showed a little dechlorination activity to CP-150.  相似文献   
4.
5.
Grass culms are known to differ in breaking strength, but there is little physicochemical data to explain the response. The fourth internode of four brittle and two nonbrittle barley (Hordeum vulgare L.) strains were used for physical and chemical studies of culm strength. Inner and outer culm diameters of brittle strains (3.6 ± 0.2 and 5.0 ± 0.1 millimeters) were not significantly different from those of nonbrittle strains (3.9 ± 0.2 and 5.2 ± 0.2 millimeters). Maximum bending stress, at which the culm was broken, was 192 ± 34 g/mm2 for brittle and 490 ± 38 g/mm2 for nonbrittle strains. Wall thickness and cell dimensions of epidermal, sclerenchyma, and parenchyma cells were measured in culm cross sections. The area of cell wall per unit cell area for each tissue was significantly correlated with the maximum bending stress (r = 0.93 for epidermis, 0.90 for sclerenchyma, and 0.84 for parenchyma). Cell walls of brittle culms had 6 to 64% as much cellulose content as those of nonbrittle culms. Maximum bending stress correlated significantly with cellulose content of the cell walls (r = 0.93), but not with the contents of noncellulosic compounds. The lower cellulose content of the brittle culm was significantly correlated with brittleness.  相似文献   
6.
Summary The immunohistochemical localization of large proteoglycan and small proteoglycan was observed, using antibodies 2B1 and 6B6 (Sobueet al., 1988, 1989a), in fetal and adult pancreas and biliary system as well as in tumour tissues, obtained from 11 autopsies and 74 biopsies. The distribution of chondroitin 4- and 6-sulphate side chains, type I and IV collagen and elastin were also studied. In adult pancreas and all the biliary tracts examined, periductal fibrous tissues consisted mainly of dermatan sulphate small proteoglycan with networks of fibrous elements, which were composed of large proteoglycan, elastin, type I collagen and type IV collagen. In the interstitial components of cystadenoma of pancreas and biliary duct carcinoma, similar small proteoglycan-rich components were relatively abundant, although large proteoglycan was present in much larger amounts than that in non-neoplastic adult tissues. In some cholangiomas, the extra-and intracellular hyaline globules formed by the carcinoma cells were found to contain chondroitin sulphate large proteoglycan, laminin and fibronectin.The distribution of proteoglycans was observed to be different in the arterial walls of the interlobular tissues of the adult and the fetal pancreas. The biological significance of large and small proteoglycans in the interstitial connective tissues was discussed.  相似文献   
7.
The cellular distribution of S100 subunits in human brain and peripheral nerves was studied by means of an immunohistochemical technique using antibodies specific to the alpha subunit or the beta subunit of S100 protein. The results indicate that the distribution of the alpha subunit and the beta subunit is different among cell types in the nervous tissue, and that neurons in the brain and peripheral nerves contain only the alpha subunit, or S100a0 protein. The subunit distribution also appears to be different at an intracellular level, where the immunoreaction products for the alpha subunit show granular arrangement whereas those for the beta subunit are found diffusely in the cytoplasm.  相似文献   
8.
9.
ICR female mice were exposed to either 22 (L11, D11) or 26 hour day (L13, D13) light/dark cycles for at least 2 weeks before mating and/or during pregnancy. The mating rates of these animals decreased considerably. When pregnant females were examined at gestation days 12.0 or 17.5, resorption rates were increased, the embryos weighed less, and development was retarded in the experimental groups with preconceptional exposure to non-24-hour days. We speculate that in mice maternal and paternal pre- and periconceptional environment of daily light/dark cycles is important for normal reproductive efficacy and normal embryonic development during pregnancy.  相似文献   
10.
Trihydroxy and tetrahydroxy bile acid metabolites substituted at the C-1 or C-6 position were studied using the urine, serum and liver tissue from sixteen patients with cholestatic liver diseases. Following extraction, isolation and hydrolysis, bile acids were converted into the dimethylethylsilyl derivatives and assayed by capillary gas chromatography—mass spectrometry. Five 1β-hydroxylated bile acids, viz. 1β,3α,12α-trihydroxy-, 1β,3α,7β-trihydroxy-1, 1β,3α,7α,12α-tetrahydroxy-5β-cholanoic acids and an epimer of the first compound, and two 6α-hydroxylated bile acids, viz. 3α,6α,7α-trihydroxy-, 3α,6α,7α,12α-tetrahydroxy-5β-cholanoic acids, were completely or partially identified. Large amounts of 1β-hydroxylated and 6α-hydroxylated bile acids were found in the urine, whereas only trace amounts were detected in the serum and liver tissue. These findings indicate that altered metabolism, such as 1β- or 6α-hydroxylation of bile acids, is enhanced in cholestasis, and that the resulting hydroxylated metabolites are eliminated in the urine.  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