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   542篇
  免费   27篇
  2021年   6篇
  2020年   4篇
  2019年   4篇
  2018年   6篇
  2017年   4篇
  2016年   11篇
  2015年   25篇
  2014年   27篇
  2013年   32篇
  2012年   36篇
  2011年   29篇
  2010年   18篇
  2009年   14篇
  2008年   31篇
  2007年   43篇
  2006年   31篇
  2005年   24篇
  2004年   30篇
  2003年   22篇
  2002年   19篇
  2001年   11篇
  2000年   5篇
  1999年   7篇
  1998年   7篇
  1997年   9篇
  1996年   9篇
  1995年   13篇
  1994年   10篇
  1993年   13篇
  1992年   4篇
  1991年   5篇
  1990年   5篇
  1989年   3篇
  1988年   7篇
  1987年   5篇
  1986年   4篇
  1984年   3篇
  1983年   6篇
  1982年   4篇
  1981年   4篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1974年   2篇
  1973年   3篇
  1972年   1篇
  1971年   1篇
  1967年   1篇
排序方式: 共有569条查询结果,搜索用时 17 毫秒
471.
472.
 Effective treatment of a rat transplanted ascites tumor by i. p. injection of a streptococcal biological response modifier, OK-432, was abrogated by selective in vivo depletion of neutrophils by a monoclonal antibody, RP-3. The mechanisms by which neutrophils participate in the therapeutic action of OK-432 were studied with Winn’s assay using peritoneal exudate cells periodically obtained from rats i. p. injected with this biological response modifier. Intraperitoneal resident macrophages were first activated with OK-432, and within 3 h, tumor-inhibitory activity had moved to the early exuded neutrophils. However, 6 h after injection, exuded macrophages were the only cells involved in tumor inhibition. Considered together with other findings, it is likely that, in this system, neutrophils may transmit information from resident macrophages to exuded inflammatory macrophages in a series of responses induced by i. p. injection of OK-432. Received: 29 April 1996 / Accepted: 27 July 1996  相似文献   
473.
CS-670, a novel nonsteroidal anti-inflammatory drug, is a racemic prodrug. Plasma concentrations and urinary excretion of CS-670 and its metabolites were determined in experimental subjects after oral administration at a single 120 mg dose. CS-670 and four metabolites, the saturated ketone (M-A), unsaturated-alcohol (M-B), cis-alcohol (M-C), and trans-alcohol (M-D), were quantitated by GC-MS. The major metabolites in human plasma were M-B, M-C, and M-D and their terminal half-lives (t½) were 0.9, 2.6, and 1.2 h, respectively. The total recovery in the urine was 26% of the dose, but unchanged CS-670 accounted for less than 2% over a 48 h period. In addition, the absolute configurations of the metabolites were examined by HPLC after derivatization with chiral reagents. It was found that the configuration of the propionic acid moiety of the metabolites, M-B, M-C, and M-D, in human plasma, was rapidly inverted from (-)-(R) to the (+)-(S) configuration in stereoselective biotransformation. Furthermore, the configurations of the 1′- and 2′-carbons of M-C and M-D, were found to be (1′R,2′S) and (1′R,2′S), respectively. These results show that CS-670 is readily biotransformed by chiral inversion of the 2-arylpropionic acid moiety and stereoselective reduction of the α, β-unsaturated ketone moiety in humans. © 1996 Wiley-Liss, Inc.  相似文献   
474.
Acetylcholine and arachidonic acid induced catecholamine secretion from isolated bovine adrenal medullary cells. Protease inhibitors and calmodulin inhibitors inhibited catecholamine secretion induced by acetylcholine but did not inhibit the secretion induced by arachidonic acid. BW 755-C, a lipoxygenase inhibitor, inhibited catecholamine release induced by acetylcholine. These results suggest that a protease and calmodulin are involved in the successive reaction after stimulus-receptor coupling and arachidonic acid or its metabolites might be important in catecholamine secretion from bovine adrenal medullary cells.  相似文献   
475.
The amino acid sequences of human carcinoembryonic antigen deduced from the cDNA sequences have been analysed. This antigen contains seven extracellular domains (previously recognized three highly repetitive domains are further divided into A and B subdomains each) which are strikingly homologous to each other and to immunoglobulin variable regions, poly-Ig receptor and Thy 1.1. The N-terminal domain lacks immunoglobulin-like fold but the other six domains have, suggesting that the CEA belongs to immunoglobulin superfamily.  相似文献   
476.
A cDNA containing the entire coding region for a member of carcinoembryonic antigen (CEA) gene family has been cloned from cDNA library of HLC-1 cells by immunochemical screening with the antibody specific to nonspecific crossreacting antigen (NCA). The cDNA encodes a precursor form of a polypeptide consisting of a 34-residue signal sequence, a 108-residue N-terminal (N-) domain, a 178-residue domain (NCA-I domain) and a 24-residue domain rich in hydrophobic amino acids (M-domain). Each domain has a distinct but homologous amino acid sequence to that of the corresponding domain of CEA. Unlike the coding sequences, the 3'-untranslated sequences differ markedly in the NCA and CEA cDNAs facilitating the preparation of probes that will discriminate between nucleotide sequences for CEA and NCA.  相似文献   
477.
Subcellular localization of indole-3-acetic acid (IAA) in leaf cells of peach ( Prunus persica [L.] Batsch 'Hakuho') was investigated using imuno-gold electron microscopy. The distribution pattern of the gold particles, which detected IAA, changed as cells matured. The most prominent feature was the accumulation of the gold label in the chloroplasts and mitochondria of the parenchyma cells of opened leaves. Throughout the development, the cytosol, nuclei, and cell wall were labelled, although the level was low and no significant changes occurred. The density of colloidal gold at each stage of leaf development was well correlated with the analytical data obtained by high-performance liquid chromatography (HPLC).  相似文献   
478.
Changes in insulin-stimulated glucose metabolism were studied in young and aged subjects, subjects with impaired glucose tolerance, and patients with NIDDM by means of the glucose clamp technique. The diabetic group includes obese and non-obese patients treated without insulin and non-obese patients treated with insulin. The glucose disposal rate (GDR) was decreased in aged subjects (5.8 +/- 0.4 mg/kg/min) compared with young controls (7.4 +/- 0.3 mg/kg/min). In patients with IGT, it was further decreased to 3.6 +/- 0.5 mg/kg/min, which was comparable to the rate in NIDDM without insulin treatment (3.3 +/- 0.4 mg/kg/min). There were no differences in the GDR between obese (3.0 +/- 0.3 mg/kg/min) and non-obese (3.4 +/- 0.6 mg/kg/min) diabetic patients. In insulin-treated diabetic patients, GDR ranged widely, but the mean value was partially normalized (5.2 +/- 0.9 mg/kg/min). In the diabetic group, no correlation was observed between fasting blood glucose and GDR. These results suggest that in the course of developing NIDDM, a decrease in insulin-stimulated glucose uptake precedes a rise in fasting blood glucose. Thus, as previously reported for Caucasian NIDDM patients, resistance to insulin-stimulated glucose uptake may be one of the basic defects in Japanese patients with NIDDM. The degree of glycemia, however, is not directly related to the magnitude of the defect in insulin action.  相似文献   
479.
The gene for the light-harvesting chlorophyll a/b binding proteinfrom rice was cloned and se-quenced. The clone contains a 798-bpcoding sequence, which is identical to that of a cDNA for typeI LHCPII (Matsuoka 1990), and its 5'- and 3'-flanking regions.The coding region of this gene is not interrupted by interveningsequences, as reported for type I genes from other plants. Inthe 5'-flanking region, typical TATA and CAAT boxes are located30 and 92 bp upstream from the capping site (positions –30and –92), respectively. A putative phytochrome-responsiveelement (AAGATAAGG) is located at position –65 betweenthe TATA and CAAT boxes. Comparison of sequences in the 5'-flankingregions between this gene and genes for LHCPII from other gramineousplants indicates that the rice sequence has no apparent homologyto that of wheat. However, the rice sequence is highly homologousto the maize sequence, not only around the TATA and CAAT boxesbut also in regions further upstream. To investigate the promoter activity of the 5'-flanking regionof the gene, a chimeric gene was constructed by fusing the 5'-flankingregion to the coding sequence for ß-glucuronidase(GUS), and this chimeric gene was introduced into tobacco. Thehighest activity of GUS was observed in leaf tissue, indicatingthat the 5'-flanking region of the gene can act as a promoterin an organ-specific manner in tobacco. Histochemical analysisin situ was also performed to determine where GUS activity wasexpressed. The highest activity was found in leaf mesophyllcells. High activity was also observed in the vascular systemof stems and petioles, and low activity was found in root tissue. (Received August 20, 1990; Accepted January 21, 1991)  相似文献   
480.
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