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   56378篇
  免费   4677篇
  国内免费   1589篇
耳鼻咽喉   634篇
儿科学   712篇
妇产科学   1168篇
基础医学   8707篇
口腔科学   1492篇
临床医学   4651篇
内科学   11189篇
皮肤病学   1044篇
神经病学   4126篇
特种医学   1880篇
外国民族医学   6篇
外科学   7931篇
综合类   4004篇
现状与发展   1篇
一般理论   5篇
预防医学   3319篇
眼科学   1441篇
药学   4929篇
中国医学   758篇
肿瘤学   4647篇
  2023年   214篇
  2022年   340篇
  2021年   605篇
  2020年   380篇
  2019年   691篇
  2018年   1183篇
  2017年   936篇
  2016年   926篇
  2015年   1025篇
  2014年   1413篇
  2013年   1727篇
  2012年   2412篇
  2011年   2315篇
  2010年   1398篇
  2009年   1356篇
  2008年   2028篇
  2007年   2162篇
  2006年   2046篇
  2005年   1709篇
  2004年   1546篇
  2003年   1541篇
  2002年   1507篇
  2001年   4814篇
  2000年   4738篇
  1999年   4050篇
  1998年   1434篇
  1997年   1027篇
  1996年   648篇
  1995年   527篇
  1994年   485篇
  1993年   442篇
  1992年   2007篇
  1991年   1728篇
  1990年   1592篇
  1989年   1542篇
  1988年   1353篇
  1987年   1250篇
  1986年   1113篇
  1985年   930篇
  1984年   614篇
  1983年   492篇
  1982年   261篇
  1981年   197篇
  1980年   158篇
  1979年   306篇
  1978年   95篇
  1977年   81篇
  1974年   86篇
  1973年   108篇
  1972年   86篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
There is little agreement about the methodology of clinical trials of antipsychotic drugs in patients with negative symptoms. A literature review revealed wide variation in experimental design, rating scales and study duration. This reflects differing views as to the definition and response to treatment of negative symptoms. Some degree of standardization would improve comparability of studies and aid the development of new compounds. Patients included in such studies should have displayed negative symptoms for at least 6 months. Depressive symptoms, positive schizophrenic symptoms and extrapyramidal signs may all influence or be confused with negative symptoms and may respond to treatment; they should be at a low level at baseline and should be measured during the study period. Studies should last at least 8 weeks. Several scales are available for measuring negative symptoms and are reviewed; a global impression score should be used additionally.  相似文献   
102.
The Authors are reviewing their experience of Obstructive Uropathies diagnosed and treated surgically in neonates, the last 8 years in their Institution. 67 cases were reviewed, in which 37 presented with ureteropelvic junction obstruction (UPJ). 13 with posterior urethral valves, 11 with primary megaureter and 6 with ureterocele. Prenatal ultrasonography allowed the diagnosis to be made in two third of the patients. UPJ is the most common obstructive uropathy observed. Posterior urethral valves the most severe because of high pulmonary and renal (dysplasia) complication rate. Surgery, when indicated, has no more complications to be expected than in general population, if oriented prophylactic measures are taken in the early peri- and postoperative period.  相似文献   
103.
Liver fibrosis was induced in rats by repeated peritoneal injections of carbon tetrachloride (CCl4) over a period of 2-11 weeks. Serum procollagen III peptide (SPIIINP), prolidase (SP) and alanine aminotransferase (SALT) levels were monitored during the period of induction. The extent of fibrosis was semi-quantitatively estimated after collagen staining, and the anti-fibrotic effects of 16,16-dimethyl prostaglandin E2 (DMPGE2), colchicine, and zinc sulphate were studied. SPIIINP and SP were increased the first 2 weeks after CCl4 administration and peaked at 6 weeks. Alterations in SPIIINP and SP correlated well to the semi-quantitative histological score of liver sections during the first 6 weeks, and SP was positively related to SPIIINP throughout the whole induction period. DMPGE2 decreased SPIIINP, SP and SALT significantly in addition to a markedly decreased formation of liver collagens. Colchicine had a similar but less dramatic effect, whereas zinc sulphate only reduced SPIIINP without influencing liver damage. In conclusion SPIIINP seems to be a valuable indicator of liver fibrogenesis, and SP may play a limited role in indicating accelerated collagen metabolism in the liver. DMPGE2 obviously inhibited the production of collagens induced by CCl4. Colchicine also had an apparent effect on liver fibrosis, whereas zinc sulphate merely seemed to postpone it.  相似文献   
104.
In order to study the possible regressive changes of left ventricular hypertrophy in treated hypertensive patients and to correlate them either with the drugs they received and/or the blood pressure reduction obtained, a long-term (6 years) echocardiographic follow-up study was performed in 61 patients. B and M mode echocardiographic septum and posterior wall thickness and left ventricular mass index were measured yearly and the type of ventricular hypertrophy, asymmetric septal or concentric (symmetric), were compared before and after the follow-up. Sixteen patients received only diuretics; 14, only propranolol, and associated therapy was used in the remaining 31 patients. Average blood pressure was significantly reduced in the whole group of patients, but, individually, 30 of them achieved normal levels for the diastolic (90 mmHg), remaining it over this value in the other, although all of them experienced an average reduction 10 mmHg with therapy. Those patients with concentric hypertrophy at entry showed a significant septal, posterior wall thickness and total ventricular mass reduction during the follow-up, those with initial asymmetric septal hypertrophy, a significant septal thickness and ventricular mass reduction, and those without hypertrophy on admission, showed an average paradoxical increase in septal thickness. We conclude that left ventricular hypertrophy disappeared or decreased in 48% of the patients and that treatment seems to prevent its progression or development in the 43% of all patients. The regressive or favorable changes were significantly more frequent among patients with normal blood pressure after treatment as well as among patients treated only with propranolol in comparison to those treated only with diuretics.  相似文献   
105.
106.
107.
108.
石杉碱甲对基底核大细胞部损毁所致工作记忆障碍的影响   总被引:7,自引:1,他引:6  
目的:研究石杉碱甲对基底核大细胞部(NBM)损毁诱导的工作记忆障碍的影响。方法:采用八臂迷宫延迟板程序研究空间记忆。胆碱乙酰转移酶(ChAT)活力测定采用[^3H]乙酰辅酶A转变成[^3H]乙酰胆碱的方法。结果:单侧损毁NBM(卡因酸0.02μmol)导致空间记忆障碍。在不同的延迟间隔,大鼠完成程序产生的正确数减少和错误数增多。损毁侧大脑皮层ChAT酶的含量下降了大约40%。石杉碱甲(0.2mg·  相似文献   
109.
110.
It was previously proposed that the activation of rat liver phenylalanine hydroxylase (EC 1.14.16.1) by cAMP-dependent protein kinase-mediated phosphorylation of Ser-16 is due to the introduction of the negatively charged phosphate group. To explore the validity of this proposal, we have applied site-directed mutagenesis to specifically replace Ser-16 with negatively charged amino acids, glutamic and aspartic; with polar uncharged amino acids, asparagine and glutamine; with the positively charged amino acid lysine; and with the nonpolar hydrophobic amino acid alanine. The wild-type and mutant enzymes were purified to homogeneity, and the importance of Ser-16 in the activation of phenylalanine hydroxylase was examined by comparing the state of activation of the phosphorylated form of the wild-type hydroxylase with that of the mutants. The kinetic studies carried out on the wild-type phosphorylated hydroxylase showed that all the activation could be accounted for by an increase in Vmax with no change in Km for either phenylalanine or the pterin cofactor. Replacement of Ser-16 with a negatively charged residue, glutamate of aspartate, resulted in the activation of the hydroxylase by 2- to 4-fold, whereas replacement with glutamine, asparagine, lysine, or alanine resulted in a much more modest increase. Further, lysolecithin was found to stimulate the phosphorylated hydroxylase and the mutant enzymes S16E and S16D by a factor of 6-7. In contrast, the mutants S16Q, S16N, and S16A all showed the same magnitude of activation as the wild-type with lysolecithin. Therefore, this study demonstrates that activation of the enzyme by phosphorylation of Ser-16 by cAMP-dependent protein kinase is due to the introduction of negative charge(s) and strongly suggests the involvement of electrostatic interaction between the regulatory and catalytic domains of the hydroxylase.  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