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   360656篇
  免费   28042篇
  国内免费   96篇
  388794篇
  2018年   4182篇
  2017年   4033篇
  2016年   5093篇
  2015年   4957篇
  2014年   6608篇
  2013年   9473篇
  2012年   11067篇
  2011年   11918篇
  2010年   8298篇
  2009年   7314篇
  2008年   10596篇
  2007年   11074篇
  2006年   10582篇
  2005年   9875篇
  2004年   10100篇
  2003年   9733篇
  2002年   9709篇
  2001年   15829篇
  2000年   15707篇
  1999年   12021篇
  1998年   3817篇
  1997年   3774篇
  1996年   3427篇
  1995年   3164篇
  1992年   9531篇
  1991年   9726篇
  1990年   9487篇
  1989年   9491篇
  1988年   8753篇
  1987年   8245篇
  1986年   7530篇
  1985年   7852篇
  1984年   6333篇
  1983年   5317篇
  1982年   3614篇
  1981年   3180篇
  1980年   3132篇
  1979年   5962篇
  1978年   4646篇
  1977年   4230篇
  1976年   3993篇
  1975年   4803篇
  1974年   5313篇
  1973年   5269篇
  1972年   4790篇
  1971年   4485篇
  1970年   3896篇
  1969年   3795篇
  1968年   3554篇
  1967年   3201篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Intensive synthesis of collagen-like substance was revealed in the rabbit myocardium during experimental diphtheria intoxication. It was more marked in the right ventricle 24 hours after the injection of diphtheria toxin. Since similar changes (the substance was mainly formed around blood vessels) have been observed in other cases of toxic myocardial alterations (i.e. ethanol intoxication, injection of pharmacological agents, etc.), it can be assumed that it is a standard protective reaction of the altered heart to the penetration of toxic agents from the blood into the myocardial tissue.  相似文献   
52.
Study of serial semi-thin (0.5 micron) metacrylate and paraffinic (8 microns) of rat kidney sections 6, 12, 24 and 48 h after subcutaneous injection of mercury bichloride at a dose of 0.6 mg/100 g bw has revealed that injury to different parts of the canalicular nephron is of heterogeneous character. The proximal part of the nephron demonstrates both complete and partial necrosis of nephrocyte cytoplasm. The distal parts of the nephron and collecting tubules are characterized by partial necrosis of the apical cytoplasm. Within the period between 12 and 24 h after the mercury bichloride injection, intracellular reparative processes are observed, in addition to destruction, in partially damaged but viable nephrocytes, which is confirmed by the enlargement of the nucleolic size. Regeneration of the tubular epithelium due to cellular restoration was unmarked 24 h after the mercury bichloride injection.  相似文献   
53.
The gene encoding the circumsporozoite (CS) protein of the rodent malaria parasite Plasmodium berghei was cloned and characterized. A cDNA library made from P. berghei sporozoite RNA was screened with a monoclonal antibody for expression of CS protein epitopes. The resulting cDNA clone was used to isolate the CS protein gene from a lambda library containing parasite blood-stage DNA. The CS protein gene contains a central region encoding two types of tandemly repeated amino acid units, flanked by nonrepeated regions encoding amino- and carboxy-terminal signal and anchorlike sequences, respectively. One of the central repeated amino acid unit types contains the immunodominant epitopes.  相似文献   
54.
The authors studied the anabolic effect of peptide morphogen of the hydra undecapeptide on normal and regenerating rat liver. Ornithine decarboxylase (EC 4.1.1.17) activity served as a marker. Intraperitoneal injection of the peptide into intact animals stimulated ornithine decarboxylase activity in a dose-dependent manner. In partially hepatectomized rats the peptide stimulated ornithine decarboxylase activity in the dose of 20 micrograms/kg body weight while greater doses inhibited the enzyme activity.  相似文献   
55.
56.
Peptide material has been first isolated from k-casein pepsin hydrolysate. Its subcutaneous injection to hungry animals induced high amplitude (250-350 mV) and high frequency (16-20 Hz) oscillations of electrical potentials usually observed in food satiety and cholecystokinin administration. The peptide reduced respiratory and to a lesser extent heart rate. Its effect is temporary eliminated by naloxone. According to an aminogram, the peptide is a fragment of para-k-casein. A neurotropic peptide effect is connected with satiety regulation and milk consumption in the postnatal period.  相似文献   
57.
Structure of the spectrin-actin binding site of erythrocyte protein 4.1   总被引:9,自引:0,他引:9  
The complete primary structure of the functional site of erythrocyte protein 4.1 involved in spectrin-actin associations has been determined. The sequence of this domain, which contains 67 amino acids and has a molecular mass of 8045 daltons, has been obtained by NH2-terminal sequence analysis of an 8-kDa chymotryptic peptide, three endoproteinase lysine C-cleaved peptides and two peptides obtained by Staphylococcus aureus protease V8 cleavage. All peptides including the 8-kDa domain peptide were purified by reverse-phase high performance liquid chromatography. Antibodies against two different synthetic peptides of the 8-kDa domain are able to inhibit the association between protein 4.1, spectrin, and F-actin, corroborating that the 8-kDa domain is responsible for the formation of a ternary complex. A computer search of the 8-kDa sequence with the National Biomedical Research Foundation database did not detect any significant homologies to known sequences. Protein 4.1 is not related to any known proteins and may represent a new protein superfamily.  相似文献   
58.
59.
DANIEL  V.; GAFF  D. F. 《Annals of botany》1980,45(2):163-171
Significant changes in sulphydryl (‘SH’) and disulphide(‘SS’) levels during air-drying in leaves of ‘resurrection’plants (whose protoplasm survives dehydration) stemmed mainlyfrom protein turnover effects. No significant changes were foundin the SH, SS levels in leaves of the desiccation sensitivespecies Sporobolus pyramidalis following air-drying. The three tolerant species studied differed in the directionof change. Some data were consistent with Levitt's SH, SS hypothesis:increases in protein-SS levels in Sporobolus stapfianus (desiccationtolerant) were consistent with a stabilization of new proteinby SS bonds; lower reactivity of protein-SH in the tolerantspecies Talbotia elegans (which on the other hand has decreasedprotein-SS) is consistent with a second mechanism of decreasingprotein denaturation proposed in Levitt's hypothesis. Evidence of some conversion of SH to SS in the soluble proteinsof Xerophyta viscosa (a tolerant species) would on Levitt'shypothesis indicate an injurious process. Some degree of proteindenaturation might be indicated by partial inactivation of thesoluble enzyme ribulose bisphosphate carboxylase in this species,and loss of some soluble isoenzymes (peroxidase and alkalinephosphatase). An apparent lack of SH conversion to SS in thesensitive species Sporobolus pyramidalis was not consistentwith the SH, SS hypothesis. Resurrection plants, Sporobolus pyramidalis, Sporobolus stapfianus, Talbotia elegans, Xerophyta viscosa, drought resistance, desiccation tolerance, protein turnover, sulphydryl groups  相似文献   
60.
With the use of a patch-clamp technique in the whole-cell configuration, we studied the effects of pinacidil and its fluorine derivatives on A-type potassium current (I A) through the membrane of pyramidal neurons of the rat hippocampus. Hydrogen peroxide (10 mM) exerted no influence on the rate of inactivation ofI A; therefore, this current is probably mediated by Shal Kv4.2 potassium channels. Pinacidil demonstrated the properties of a weakI A blocker: in the 500 μM concentration it blocked about 45% of the current, while 50 μM of pinacidil fluorine derivatives were capable of blocking up to 30% ofI A. The effects of pinacidil and its derivatives showed no dependence on the stimulating potential. A similar pattern of the effects of pinacidil fluorine derivatives, which are an order of magnitude stronger than those of pinacidil itself, allows us to suppose that the imine nitrogen of the tested compounds is significantly more involved in the molecular interaction with the site of an A-type potassium channel than the pyridine nitrogen.  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