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   2512篇
  免费   166篇
  2678篇
  2022年   13篇
  2021年   32篇
  2020年   14篇
  2019年   24篇
  2018年   39篇
  2017年   29篇
  2016年   52篇
  2015年   66篇
  2014年   69篇
  2013年   115篇
  2012年   130篇
  2011年   133篇
  2010年   86篇
  2009年   74篇
  2008年   147篇
  2007年   128篇
  2006年   134篇
  2005年   154篇
  2004年   115篇
  2003年   113篇
  2002年   128篇
  2001年   90篇
  2000年   75篇
  1999年   74篇
  1998年   33篇
  1997年   35篇
  1996年   28篇
  1995年   30篇
  1994年   25篇
  1993年   19篇
  1992年   49篇
  1991年   45篇
  1990年   43篇
  1989年   52篇
  1988年   42篇
  1987年   20篇
  1986年   31篇
  1985年   18篇
  1984年   18篇
  1983年   11篇
  1982年   11篇
  1981年   10篇
  1980年   8篇
  1979年   11篇
  1978年   16篇
  1976年   7篇
  1975年   17篇
  1974年   8篇
  1973年   7篇
  1971年   9篇
排序方式: 共有2678条查询结果,搜索用时 15 毫秒
151.
In this study, we evaluated the anti-obesity effects of selective beta3 adrenergic receptor agonist (ARa) and/or a diet in oophorectomized (OVX) treatment in obese rats. Ten-week-old female Sprague-Dawley rats were divided into 4 groups: (1) OVX; (2) OVX treated with beta3 ARa, BRL 35 135; (3) sham-operated controls (sham group); (4) sham-treated with beta3 ARa (sham+ARa group). These four groups were divided into two groups, one on ad libitum diet, and the other on a diet of limited chow. The effects of beta3 ARa on body weight, intraabdominal fat weight, adipocyte volume, serum lipid content, and serum leptin were measured after 4 weeks had been completed. On both the ad libitum and the limited diet, ARa significantly reduced the ratio of intraabdominal fat and body weight (IAF ratio) regardless whether in the OVX or sham group, although ARa had no influence on weight gain. On the ad libitum diet, the serum leptin was significantly increased after OVX, and significantly reduced after ARa administration. ARa significantly reduced the volume of intraabdominal adipocytes. We conclude that ARa reduces intraabdominal fat without reducing body weight in oophorectomized rats. The serum parameter affected differently to rats on the ad libitum diet and on the limited diet.  相似文献   
152.
In this study, we created porcine‐induced pluripotent stem (iPS) cells with the expression of six reprogramming factors (Oct3/4, Klf4, Sox2, c‐Myc, Lin28, and Nanog). The resulting cells showed growth dependent on LIF (leukemia inhibitory factor) and expression of multiple stem cell markers. Furthermore, the iPS cells caused teratoma formation with three layers of differentiation and had both active X chromosomes (XaXa). Our iPS cells satisfied the both of important characteristics of stem cells: teratoma formation and activation of both X chromosomes. Injection of these iPS cells into morula stage embryos showed that these cells participate in the early stage of porcine embryogenesis. Furthermore, the RNA‐Seq analysis detected that expression levels of endogenous pluripotent related genes, NANOG, SOX2, ZFP42, OCT3/4, ESRRB, and ERAS were much higher in iPS with six factors than that with four reprogramming factors. We can conclude that the expression of six reprogramming factors enables the creation of porcine iPS cells, which is partially close to naive iPS state. J. Cell. Biochem. 118: 537–553, 2017. © 2016 Wiley Periodicals, Inc.  相似文献   
153.
We examined the carry-over effects of ozone (O3) and/or water stress on leaf phenological characteristics and bud frost hardiness of Fagus crenata seedlings. Three-year-old seedlings were exposed to charcoal-filtered air or 60 nl l–1 O3, 7 h a day, from May to October 1999 in naturally-lit growth chambers. Half of the seedlings in each gas treatment received 250 ml of water at 3-day intervals (well-watered treatment), while the rest received 175 ml of water at the same intervals (water-stressed treatment). All the seedlings were moved from the growth chambers to an experimental field on October 1999, and grown until April 2000 under field conditions. The exposure to O3 during the growing season induced early leaf fall and reduction in leaf non-structural carbohydrates concentrations in the early autumn, as well as resulting in late bud break and reduction in the number of leaves per bud in the following spring. However, O3 did not affect bud frost hardiness in the following winter. On the contrary, water stress did not affect leaf phenological characteristics, leaf and bud non-structural carbohydrates concentrations and bud frost hardiness. There were no significant synergistic or antagonistic effects of O3 and water stress on leaf phenological characteristics, concentrations of leaf and bud non-structural carbohydrates and bud frost hardiness of the seedlings. These results show that the carry-over effects of O3 can be found on the phenological characteristics and leaf non-structural carbohydrates concentrations, although there are almost no carry-over effects of water stress on phenological characteristics and winter hardiness of the seedlings.  相似文献   
154.
Twelve zinc(II) complexes with thiosemicarbazone and semicarbazone ligands were prepared and characterized by elemental analysis, thermogravimetric and differential thermal analysis (TG/DTA), FT-IR and 1H and 13C NMR spectroscopy. Seven three-dimensional structures of zinc(II) complexes were determined by single-crystal X-ray analysis. Their antimicrobial activities were evaluated by MIC against four bacteria (B. subtilis, S. aureus, E. coli and P. aeruginosa), two yeasts (C. albicans and S. cerevisiae) and two molds (A. niger and P. citrinum). The 5- and 6-coordinate zinc(II) complexes with a tridentate thiosemicarbazone ligand (Hatsc), ([Zn(atsc)(OAc)](n) 1, [Zn(Hatsc)(2)](NO(3))(2).0.3H(2)O 2, [ZnCl(2)(Hatsc)] 3 and [Zn(SO(4))(Hatsc)(H(2)O)].H(2)O 4 [Hatsc=2-acetylpyridine(thiosemicarbazone)]), showed antimicrobial activities against test organisms, which were different from those of free ligands or the starting zinc(II) compounds. Especially, complex 2 showed effective activities against P. aeruginosa, C. albicans and moderate activities against S. cerevisiae and two molds. These facts are in contrast to the results that the 5- or 6-coordinate zinc(II) complexes with a tridentate 2-acetylpyridine-4N-morpholinethiosemicarbazone, ([Zn(mtsc)(2)].0.2EtOH 5, the previously reported catena-poly [Zn(mtsc)-mu-(OAc-O,O')](n) and [Zn(NO(3))(2)(Hmtsc)] [Hmtsc=2-acetylpyridine (4N-morpholyl thiosemicarbazone)]), showed no activities against the test microorganisms. The 5- and 6-coordinate zinc(II) complexes with a tridentate 2-acetylpyridinesemicarbazone, ([Zn(OAc)(2)(Hasc)] 6 and [Zn(Hasc)(2)](NO(3))(2) 7 [Hasc=2-acetylpyridine(semicarbazone)]), showed no antimicrobial activities against bacteria, yeasts and molds. Complex [ZnCl(2)(Hasc)] 8, which was isostructural to complex 3, showed modest activity against Gram-positive bacterium, B. subtilis. The 1:1 complexes of zinc(II) with pentadentate thiosemicarbazone ligands, ([Zn(dmtsc)](n) 9 and [Zn(datsc)](n) 10 [H(2)dmtsc=2,6-diacetylpyridine bis(4N-morpholyl thiosemicarbazone) and H(2)datsc=2,6-diacetylpyridine bis(thiosemicarbazone)]), did not inhibit the growth of the test organisms. On the contrary, 7-coordinate zinc(II) complexes with one pentadentate semicarbazone ligand and two water molecules, ([Zn(H(2)dasc)(H(2)O)(2)](OAc)(2).5.3H(2)O 11 and [Zn(H(2)dasc)(H(2)O)(2)](NO(3))(2).H(2)O 12 [H(2)dasc=2,6-diacetylpyridine bis(semicarbazone)]), showed modest to moderate activities against bacteria. Based on the X-ray structures, the structure-activity correlation for the antimicrobial activities was elucidated. The zinc(II) complexes with 4N-substituted ligands showed no antimicrobial activities. In contrast to the previously reported nickel(II) complexes, properties of the ligands such as the ability to form hydrogen bonding with a counter anion or hydrated water molecules or the less bulkiness of the 4N moiety would be a more important factor for antimicrobial activities than the coordination number of the metal ion for the zinc(II) complexes.  相似文献   
155.
To develop a dominant genetic marker inPleurotus ostreatus, mutant strains resistant to a carboxin-derived fungicide, flutolanil, were isolated. These mutants included strains which showed resistance to 50-fold higher concentration of fluotolanil than the wild-type strain, even after successive cultivations in the absence of the drug. Dominance of the phenotype was confirmed by back-crossing between the resistant and wild-type monokaryons. The flutolanilresistance was also shown to be stably inherited by the basidiospore-derived progenies of the mutant strains.  相似文献   
156.
Roberts syndrome and SC phocomelia (RBS/SC) are genetic autosomal recessive syndromes caused by establishment of cohesion 1 homolog 2 ( ESCO 2) mutation. RBS/SC appear to have a variety of clinical features, even with the same mutation of the ESCO2 gene. Here, we established and genetically characterized a medaka model of RBS/SC by reverse genetics. The RBS/SC model was screened from a mutant medaka library produced by the Targeting Induced Local Lesions in Genomes method. The medaka mutant carrying the homozygous mutation at R80S in the conserved region of ESCO2 exhibited clinical variety (i.e. developmental arrest with craniofacial and chromosomal abnormalities and embryonic lethality) as characterized in RBS/SC. Moreover, widespread apoptosis and downregulation of some gene expression, including notch1a, were detected in the R80S mutant. The R80S mutant is the animal model for RBS/SC and a valuable resource that provides the opportunity to extend knowledge of ESCO2. Downregulation of some gene expression in the R80S mutant is an important clue explaining non-correlation between genotype and phenotype in RBS/SC.  相似文献   
157.
We investigated cholecystokinin (CCK) receptors on isolated gastric chief cells from guinea pig. CCK stimulated pepsinogen secretion from chief cells at the same efficacy as that induced by carbamylcholine. Binding of 125I-labeled CCK-33 (125I-CCK) to chief cells was temperature-dependent, and was saturable and reversible at 37 degrees C. Hofstee plots of the ability of CCK-8 to inhibit binding of 125I-CCK showed a linear regression line, suggesting that CCK receptors possessed one binding site. The dissociation constant of the binding site was calculated to be 3.8 x 10(-10) M. The dose-response curve of CCK for pepsinogen secretion was superimposed on that for the binding to its receptors. These results indicated that gastric chief cells from the guinea pig possess CCK receptors that relate closely to the action of CCK involved in pepsinogen secretion.  相似文献   
158.
159.
We assayed N-methyl-d-aspartate (NMDA) receptors [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid ([3H]CPP) bindings) and evaluated their distribution in the brain by quantitative autoradiography in young adult and aged rats. In the young adult rats, NMDA receptors were present at relatively high concentrations in the cerebral cortex and hippocampus. In the aged rats, NMDA receptors were decreased in the nealy all areas of the brain, especially in the cerebral cortex and hippocampus. Chronic administration of bifemelane hydrochloride, a drug for sequela of cerebrovascular diseased, at a dose of 15 mg/kg/day for 14 days, markedly attenuated these decrease in NMDA receptors. Since NMDA receptors are considered to be involved in memory and learning processes, our results suggest that bifemelane hydrochloride may be applicable to the treatment of disturbed memory and learning.  相似文献   
160.

Uridine 5′-triphosphate (UTP) has an important role as an extracellular signaling molecule that regulates inflammation, angiogenesis, and vascular tone. While chronic hypertension has been shown to promote alterations in arterial vascular tone regulation, carotid artery responses to UTP under hypertensive conditions have remained unclear. The present study investigated carotid artery responses to UTP in spontaneously hypertensive rats (SHR) and control Wistar Kyoto rats (WKY). Accordingly, our results found that although UTP promotes concentration-dependent relaxation in isolated carotid artery segments from both SHR and WKY after pretreatment with phenylephrine, SHR exhibited significantly lower arterial relaxation responses compared with WKY. Moreover, UTP-induced relaxation was substantially reduced by endothelial denudation and by the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine in both SHR and WKY. The difference in UTP-induced relaxation between both groups was abolished by the selective P2Y2 receptor antagonist AR-C118925XX and the cyclooxygenase (COX) inhibitor indomethacin but not by the thromboxane-prostanoid receptor antagonist SQ29548. Furthermore, we detected the release of PGE2, PGF, and PGI2 in the carotid arteries of SHR and WKY, both at baseline and in response to UTP. UTP administration also increased TXA2 levels in WKY but not SHR. Overall, our results suggest that UTP-induced relaxation in carotid arteries is impaired in SHR perhaps due to impaired P2Y2 receptor signaling, reductions in endothelial NO, and increases in the levels of COX-derived vasoconstrictor prostanoids.

  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