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   445篇
  免费   28篇
  国内免费   1篇
  2023年   5篇
  2022年   9篇
  2021年   16篇
  2020年   16篇
  2019年   43篇
  2018年   22篇
  2017年   15篇
  2016年   25篇
  2015年   31篇
  2014年   20篇
  2013年   53篇
  2012年   42篇
  2011年   27篇
  2010年   23篇
  2009年   14篇
  2008年   16篇
  2007年   12篇
  2006年   17篇
  2005年   15篇
  2004年   10篇
  2003年   8篇
  2002年   5篇
  2001年   3篇
  1999年   1篇
  1998年   1篇
  1996年   1篇
  1995年   1篇
  1993年   1篇
  1990年   2篇
  1988年   1篇
  1987年   2篇
  1986年   1篇
  1985年   2篇
  1984年   3篇
  1983年   5篇
  1981年   1篇
  1979年   1篇
  1973年   2篇
  1972年   2篇
排序方式: 共有474条查询结果,搜索用时 15 毫秒
1.
The chemical synthesis and physical data of several new esters of testosterone (17 beta-hydroxyandrost-4-en-3-one), which contain either a halogeno or an alkoxy substituent in the acid chain, are reported.  相似文献   
2.
The membrane-bound enzyme of microsomes that catalyzes NADPH-dependent reduction of the 14-double bond of conjugated delta 8,14- and delta 7,14-sterols has been studied both as collected in microsomes from broken cell preparations of rat liver and after solubilization. Optimal incubation conditions for assay of the membrane-bound enzyme have been determined, and properties of the microsomal enzyme have been established with respect to cofactor requirements, kinetics, pH, addition of inhibitors, addition of glycerol phosphatides, and sterol substrate specificity. The 14-reductase is readily solubilized with a mixture of octylglucoside and taurodeoxycholic acid. The solubilized enzyme has been enriched by precipitation with polyethylene glycol and chromatography on DEAE-Sephacel and hydroxylapatite columns. The resulting partially purified enzyme has been obtained free of other microsomal enzymes of cholesterol biosynthesis: 4-methyl sterol oxidase, delta 5,7-sterol 7-reductase, delta 8,24-sterol 24-reductase, 3-ketosteroid reductase, and steroid 8----7-ene isomerase, plus microsomal cytochrome P-450, cytochrome P-450 reductase, cytochrome b5 reductase, and cytochrome b5. The partially purified enzyme is stimulated by addition of phospholipids. All of the properties exhibited by partially purified 14-reductase are consistent with the suggestion that the solubilized and enriched enzyme catalyzes the microsomal reduction of the 14-double bond of the sterol-conjugated dienes. However, presence of the enzyme does not prove that the sterol-conjugated dienes are obligatory precursors of cholesterol.  相似文献   
3.
The synthesis of esters of norethisterone (17α-ethynyl-17β-hydroxy-estr-4-en-3-one) with acids containing a benzene ring is described, two methods of esterification being compared in terms of yield and convenience. The activities of these esters as long-acting contraceptive agents have been evaluated.  相似文献   
4.
Summary A polyphasic taxonomic study was undertaken to establish the genetic and phenotypic relationships among six actinomycetes that produce the immunosuppressant macrolides FK506, FK520/FK523 and rapamycin. Chemotaxonomic studies reveal that all have Type I cell walls. Gas chromatography (GC) of fatty acid methyl esters revealed patterns consistent for strains ofStreptomyces with 160 and 150anteiso predominating. Principal component analysis of GC data revealed distinct profiles for each culture. Reciprocal DNA homology studies atT m -25 showed the rapamycin-producing strain and one FK506-producing strain to have 38–50% homology with the type strain ofStreptomyces hygroscopicus (ATCC 27438). The remaining strains exhibited 6–17% homology. To further explore the relationships among these strains all were probed for the presence of anO-methyltransferase gene specific to this biosynthetic pathway. Among the strains of interest, onlyStreptomyces hygroscopicus subsp.yakushimaensis, the patent strain for FK520/FK523, failed to hybridize with the probes.  相似文献   
5.
ABSTRACT

This study was conducted to assess the effect of feeding high-surface ZnO instead of common ZnO on the performance, rumen fermentation, blood minerals, leukocytes and antioxidant capacity of pre- and post-weaning calves. Thirty male suckling Holstein calves were allotted to one of three experimental groups (10 replicates) in a completely randomised design. Calves received: (1) a low Zn diet without Zn supplementation (control diet), (2) a high Zn diet containing 50 mg supplementary Zn/kg dry matter (DM) as common ZnO or (3) a high Zn diet containing 50 mg supplementary Zn/kg DM as high-surface ZnO (nano-ZnO). The control diet contained a native Zn content of 35.5, 34.7 or 33.7 mg/kg DM for the age periods of 7 to 30, 31 to 70 and 71 to 100 d, respectively. Supplementation of the diet with Zn did not change the dry matter intake (DMI) of calves during d 7 to 30 but increased the ADG in this period (p < 0.05). During age periods of 31 to 70 and 71 to 100 d, DMI and ADG of the Zn supplemented calves were higher (p < 0.05) than the control animals. The nutrient digestibility and the concentration of rumen volatile fatty acids were positively affected (p < 0.05) and the rumen ammonia-N concentration decreased (p < 0.05) by dietary Zn supplementation. Furthermore, the incidence of diarrhoea and pneumonia was lower in calves receiving the Zn supplemented diets. Irrespective of ZnO source, the blood total antioxidant capacity, leukocyte and haematocrit levels significantly increased (p < 0.05) with the ZnO supplemented diets. The post-weaning DMI, nutrient digestibility and blood haematocrit levels were higher in calves receiving high-surface ZnO, compared to those supplemented with common ZnO. With inclusion of the Zn sources in pre- and post-weaning diets, the blood Zn concentration increased (p < 0.05), but the blood Cu, Fe, Ca, P and Mg levels remained unchanged. Regardless of source, dietary supplementation of young calves with ZnO improved the performance and decreased rumen ammonia-N and the incidence of diseases. Moreover, high-surface ZnO had advantages over common ZnO in increasing the post-weaning feed intake, digestibility and blood Zn concentration.  相似文献   
6.
Abstract

Several factors may affect erythropoietin (EPO) sugar structures including designing cell culture procedure, pH, concentration of additives, dissolved oxygen, and other physicochemical parameters. In this study, we investigated the influence of changes in effective parameters and compounds on the growth rate of Chinese hamster ovary cell (CHO) cells producing recombinant EPO. Cell culture was performed at different temperature, buffering conditions, and varied concentrations of additives such as pyruvic acid, insulin, GlutaMAX, and sodium butyrate. Results indicated that the optimal temperature and pH were 37?°C and 7.2, respectively. Also, optimal concentrations for pyruvic acid, butyrate, glutamate, and insulin were obtained to be 20?mM, 1?mM, 2?mM, and 40?μg/mL, respectively. Then, cell culture was performed in microcarrier-coated spinner flasks under the optimized condition. The results showed recombinant human EPO (rhEPO) production with adequate purity. Optimization of physicochemical conditions and culture media are important factors to improve the quantity and quality of protein products. This study showed that cell growth and recombinant EPO protein production significantly increased under the optimized conditions. The results of this research can also be used in scale-up to increase the efficiency of EPO production.

Abbreviations: EPO: erythropoietin; CHO cell: Chinese hamster ovary cell; rhEPO: recombinant human EPO; DMEM: modified eagle’s medium; FBS: fetal bovine serum; SDS-PAGE: sodium dodecyl sulfate–polyacrylamide gel electrophoresis; IGF-1: insulin-like growth factor 1  相似文献   
7.
8.
The International Journal of Life Cycle Assessment - As wind power generation increases globally, there will be a substantial number of wind turbines that need to be decommissioned in the coming...  相似文献   
9.
10.
Adipose tissue‐derived mesenchymal stem cells (AD‐MSCs) have been shown to be capable of differentiating into multiple cell type and exert immunomodulatory effects. Since the selection of ideal stem cell is apparently crucial for the outcome of experimental stem cell therapies, therefore, in this study we compared AD‐MSCs conditioned media (CM) from BALB/c, C57BL/6, and DBA mouse strains. No significant difference was found in the morphology, cell surface markers, in vitro differentiation and proliferation potentials of AD‐MSCs isolated from C57BL/6, BALB/c, and DBA mice. The immunological assays showed some variation among the strains in the cytokines, nitric oxide (NO), and indoleamine 2,3‐dioxygenase (IDO) production and immunomodulatory effects on splenocytes functions. Our results indicated a suppression of splenocytes proliferation in the presence of AD‐MSC CM from the three inbred mouse strains. However, BALB/c CM exerted a higher suppression of splenocytes proliferation. AD‐MSCs isolated from C57BL/6 and BALB/c mice produced higher levels of TGF‐β than those from DBA mice. Furthermore, IL‐17 and IDO production was higher in AD‐MSCs isolated from BALB/c mice. Our results indicated an increased production of TGF‐β, IL‐4, IL‐10, NO, and IDO by splenocytes in response to CM from BALB/c AD‐MSCs. In conclusion, our results showed that the immunomodulatory properties of mouse AD‐MSCs is strain‐dependent and this variation should be considered during selection of appropriate stem cell source for in vivo experiments and stem cell therapy strategies. J. Cell. Biochem. 114: 955–965, 2013. © 2012 Wiley Periodicals, Inc.  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