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   2994篇
  免费   175篇
  国内免费   3篇
  2022年   13篇
  2021年   33篇
  2020年   18篇
  2019年   19篇
  2018年   38篇
  2017年   26篇
  2016年   38篇
  2015年   95篇
  2014年   104篇
  2013年   166篇
  2012年   148篇
  2011年   180篇
  2010年   95篇
  2009年   89篇
  2008年   135篇
  2007年   152篇
  2006年   150篇
  2005年   131篇
  2004年   153篇
  2003年   145篇
  2002年   150篇
  2001年   106篇
  2000年   89篇
  1999年   73篇
  1998年   34篇
  1997年   34篇
  1996年   36篇
  1995年   26篇
  1994年   21篇
  1993年   22篇
  1992年   66篇
  1991年   52篇
  1990年   41篇
  1989年   45篇
  1988年   42篇
  1987年   45篇
  1986年   39篇
  1985年   51篇
  1984年   32篇
  1983年   25篇
  1982年   22篇
  1981年   24篇
  1980年   12篇
  1979年   26篇
  1976年   12篇
  1975年   14篇
  1974年   14篇
  1972年   13篇
  1971年   11篇
  1967年   9篇
排序方式: 共有3172条查询结果,搜索用时 187 毫秒
111.
We report the case of a 70-year-old man who developed hypothyroidism associated with TSH receptor antibodies and severe ophthalmopathy during lithium therapy. He had received lithium therapy for more than 20 years for manic depression, when ophthalmopathy (class VI of the American Thyroid Association classification) and mild hypothyroidism developed. Orbital magnetic resonance imaging indicated marked enlargement of the superior, medial and inferior rectus muscles in the left eye. He had anti-eye muscle antibodies in his serum, detected by Western blotting and quantified by chromatoscanning, as well as anti-TSH receptor antibodies. He was treated with supplementation of levothyroxine and four cycles of methylprednisolone pulse therapy. After the pulse therapy, both anti-eye muscle antibodies and anti-TSH receptor antibodies decreased and disappeared in parallel with the improvement in eye symptoms and signs. These observations suggest the importance of anti-eye muscle antibodies as clinical markers in the development of thyroid-associated ophthalmopathy.  相似文献   
112.
The combined effects of methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) on the induction of 6-thioguanine (6TG)-resistant mutants and chromosome aberrations were examined in Chinese hamster V79 cells. Cells were simultaneously treated with EMS at a concentration of D20 and MMS at various concentrations for 3, 6 or 9 h. In other experiments cells were simultaneously treated with MMS at a concentration of D20 and EMS at various concentrations for 3, 6 or 9 h. The mathematical analysis of the combined effects of both chemicals for cell killing (cytotoxicity) and 6TG-resistant mutations indicates that synergistic interactions were observed for both cell killing and mutations induced by MMS and EMS. The frequency of chromosome aberrations induced by simultaneous treatment with MMS at a concentration of D20 and EMS at various concentrations for 3 h was additive. However, the frequency of chromosome aberrations induced by EMS at a concentration of D20 and MMS at various concentrations for 3 h was not significantly different from those induced by MMS alone.  相似文献   
113.
Parturition behavior of a multiparous female and her interactions with group members throughout the birth process were recorded for a free-ranging Japanese monkey (Macaca fuscata). The female showed evidence of 18 contractions during the 35 min prior to delivery, with a mean duration and a mean intercontraction interval of 30 sec and 96 sec, respectively. These values were similar to those in individually caged Japanese monkeys. Some adult females remained in proximity to the female who was giving birth during the prepartum phase, and her 2-year-old daughter watched the delivery of the infant. Even during the prepartum phase the female moved in order to keep up with the group which traveled from the feeding site to a sleeping site in the forest.  相似文献   
114.
Platelet aggregation activity due to platelet-activating factor (PAF) was detected at high molecular weight (HMW) and low molecular weight fractions after gel-filtration chromatography of cell lysate of endothelial cells. [3H]PAF added to the cell lysate was similarly distributed after chromatography. The radioactivity associated with HMW fraction was not reduced by digesting the lysate with trypsin, suggesting that PAF was not making complexes with proteins but was included in lipid vesicles in cell lysate. Further evidence showed that an unknown specific factor(s) was needed to form these PAF-containing lipid vesicles. Radioactivity was not found in HMW fraction when [3H]PAF was mixed with cell lysate of vascular smooth muscle cells. When monomeric PAF was added to endothelial cell lysate, the specific activity of aggregation decreased to the level exerted by endogenous PAF-containing lipid vesicles due to incorporation into lipid vesicles. PAF in the form of lipid vesicles was more stable in plasma than monomeric form.  相似文献   
115.
Poly(dG-dC).poly(dG-dC) was modified by the reaction with 4-hydroxyaminoquinoline 1-oxide (4HAQO) in the presence of seryl-AMP. The conformations of 4HAQO-modified poly(dG-dC).poly(dG-dC) and of poly(dG-dC).poly(dG-dC) were studied by circular dichroism spectra under various salt concentration conditions. 4HAQO residues to guanine bases are inefficient in inducing the transition of poly(dG-dC).poly(dG-dC) from B-form to Z-form conformation. We have elicited monoclonal antibodies against 4HAQO-poly(dG-dC).poly(dG-dC). They were characterized using enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA) and binding to supercoiled DNA. These antibodies reacted with 4HAQO-poly(dG-dC).poly(dG-dC) specifically but not with 4HAQO-modified DNA or poly(dG).poly(dC). However, they cross-reacted with N-acetoxy-2-acetylaminofluorene-modified poly(dG-dC).poly(dG-dC) in Z-form conformation. These monoclonal antibodies may recognize a unique conformation in poly(dG-dC).poly(dG-dC) after 4HAQO modification.  相似文献   
116.
Possible formation of a P4O10 molecule in magma, the stability of the molecule in hydrous volcanic gas at high temperatures and a possible prebiotic phosphate cycle were discussed in relation to chemical evolution. To demonstrate the utility of phosphorus pentoxide as a phosphorylating agent, aqueous solutions of adenosine (0.02M) and phosphorus pentoxide (0.2M) were incubated at 37°C for 5 months. The pH of the solutions was adjusted every day or every few days to each fixed value (9.0, 10.5, 11.5, 12.5) with 10 N NaOH. The HPLC analysis showed the formation of 2-AMP, 3-AMP, 5-AMP, cyclic (2–3)-AMP and cyclic (3–5)-AMP. The main components of the products were 2- and 3-AMP, though cyclic (2–3)-AMP was the main component in the early period of the incubation at pH 9.0. The yields (conversion rate of adenosine to AMPs) were increased almost linearly with the incubation time for 5 months in the case of pH 9.0. The final yields were about 3% (pH 9.0), 6% (pH 9.0, 1 M NaCl), 5% (pH 9.0, 0.01 M CaCl2, 0.01 M MgCl2), 7% (pH 9.0, 0.5 M NaCl, 0.01 M CaCl2, 0.01 M MgCl2), 9% (pH 9.0, 1 M NaCl, 0.01 M CaCl2, 0.01 M MgCl2), 32% (pH 10.5), 43% (pH 11.5), 35% (pH 12.5).  相似文献   
117.
Hydrophobic and charge-charge interactions of Salmonella typhimirium and Serratia marcescens were determined and related to their content of fimbriae and lipopolysaccharide (LPS). The cell surface structures were characterized with hydrophobic interaction chromatography (HIC), electrostatic interaction chromatography (ESIC) and particle electrophoresis measurements. The degree of interaction at the air-water interface was tested using a monolayered lipid film applied to an aqueous surface. The cell surface hydrophobicity of S. typhimurium in the presence of fimbriae was less in smooth than in rought bacteria. Examination of a series of rough mutants of S. typhimurium indicates that reduction of the O-side chain and core oligosaccharides was correlated with increased cell hydrophobicity. The enrichment factors at the air-water interface were significantly higher for fimbriated than for non-fimbriated S. typhimurium cells. Fimbriated S. marcescens cells were less hydrophobic and adhered to a lesser degree at the air-water surface than non-fimbriated counterparts. Electrophoretic measurements and adsorption to ion exchangers gives different information about the surface charge of bacteria. The latter technique gives the interaction between localized charged surfaces.Abbreviations HIC hydrophobic interaction chromatography - ESIC electrostatic interaction chromatography - LPS lipopolysaccharide - PBS phosphate buffered saline solution  相似文献   
118.
Abstract: Bullfrog spinal ganglia were subjected to two types of examination to determine whether catecholamines were present. A biochemical microassay developed by Kissinger and co-workers and a histofluorescence technique for cellular demonstration of biogenic monoamines developed earlier by Falck and co-workers were used. Bullfrog spinal ganglia and dorsal roots were found to contain catecholamines, primarily adrenaline.  相似文献   
119.
Intravenous administration of short-chain fatty acid (SCFA), such as propionate, butyrate, valerate and caproate, caused a transient increase in transmural potential difference (p.d.) across the small intestine of rat in vivo. There was a sigmoid relationship between the change in the p.d. and the logarithm of the dose of SCFA. The median effective dose of propionate, n-butyrate, n-valerate and n-caproate, which was calculated from the each dose-response curve obtained from the terminal ileum, 1.31, 1.43, 0.83 and 0.81 μmole, respectively. Repeated administrations of the same dose of propionate evoked progressively smaller response. The dose-response curve of propionate was shifted to the left by neostigmine and to the right by atropine, suggesting that the action of SCFA may be mediated by acetylcholine, which was released from a nerve ending.  相似文献   
120.
Anti-platelet aggregating and disaggregating activities of the chemically stable 6,9-methano prostaglandin I2 (6,9-methano PGI2) were investigated. 6,9-Methano PGI2 inhibited ADP-induced platelet aggregation in PRP from humans, rabbits and rats. 6,9-Methano PGI2 also inhibited rabbit platelet aggregation induced by ADP, collagen, thrombin, arachidonic acid and 11,9-epoxy-methano PGH2. Antiaggregating activities of 6,9-methano PGI2 were 0.3 to 2.0 times greater than those of PGE1. 6,9-Methano PGI2 facilitated platelet disaggregation in a dose related manner. Antiaggregating and disaggregating activities of 6,9-methano PGI2 were markedly enhanced by incubation with the phosphodiesterase inhibitor, theophylline.  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