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   26771篇
  免费   582篇
  国内免费   52篇
耳鼻咽喉   801篇
儿科学   646篇
妇产科学   2173篇
基础医学   3764篇
口腔科学   1017篇
临床医学   1001篇
内科学   4748篇
皮肤病学   833篇
神经病学   2407篇
特种医学   389篇
外科学   2545篇
综合类   99篇
一般理论   2篇
预防医学   1934篇
眼科学   1125篇
药学   3164篇
中国医学   43篇
肿瘤学   714篇
  2022年   444篇
  2021年   711篇
  2020年   256篇
  2019年   363篇
  2018年   528篇
  2017年   371篇
  2016年   371篇
  2015年   458篇
  2014年   631篇
  2013年   839篇
  2012年   1139篇
  2011年   1319篇
  2010年   632篇
  2009年   375篇
  2008年   789篇
  2007年   1021篇
  2006年   1082篇
  2005年   1026篇
  2004年   1103篇
  2003年   1057篇
  2002年   865篇
  2001年   692篇
  2000年   685篇
  1999年   574篇
  1998年   170篇
  1992年   375篇
  1991年   322篇
  1990年   349篇
  1989年   403篇
  1988年   457篇
  1987年   444篇
  1986年   448篇
  1985年   423篇
  1984年   344篇
  1983年   254篇
  1979年   521篇
  1978年   315篇
  1977年   255篇
  1976年   244篇
  1975年   335篇
  1974年   504篇
  1973年   509篇
  1972年   424篇
  1971年   399篇
  1970年   387篇
  1969年   407篇
  1968年   352篇
  1967年   267篇
  1966年   293篇
  1965年   176篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A prospective, randomized trial evaluates the effects of two postoperative treatment regimens on survival in 198 adult patients with supratentorial gliomas. All patients were irradiated with 6 000 rads after possibly radical removal of tumors. CCNU administration in the dosis of 100 mg/sq m of body surface every 6–8 weeks following surgery proved to have no significant effect on the survival of patients. The median survival time in patients receiving radiation therapy alone was 61±7 weeks, while in those receiving additional chemotherapy was 56±4 weeks. Tumor histological malignancy and patients age were found to be the only important prognostic factors, irrespective of the treatment modality. Address for offprints: T Trojanowski, Department of Neurosurgery, Medical School, Jaczewskiego 8, 20-950 Lublin, Poland  相似文献   
112.
113.
114.
115.
We report on a case of Prader-Willi syndrome (PWS) with a true reciprocal unbalanced translocation, 45,XX,-15,der(11)t(11;15)pat. The proposita was diagnosed clinically as having severe PWS. Molecular studies revealed loss of the paternal methylation pattern at locus D15S63 and a deletion encompassing the loci from at least D15S10 to D15S97 of paternal chromosome 15. FISH studies confirmed the deletion of 15q11-q13 region and the presence of two telomeres on all chromosomes. The proposita's father, the father's sister and their mother are all carriers of the same balanced translocation t(11;15)(q25;q13). By genomic imprinting we would expect that if the father's sister were to give birth to a child with the same unbalanced translocation as the proband, it would be affected by Angelman syndrome.
To date, a similar familial unbalanced translocation due to loss of the small chromosome 15 derivative has not been described.  相似文献   
116.
The relationship between malignancy and histamine metabolism in the liver and the small intestine has been examined in sarcoma-bearing Wistar rats two weeks after subcutaneous implantation of a transplantable methylcholanthrene sarcoma Sa1828 and on the 3, 7 and 14th days after tumour extirpation. Two weeks after tumour implantation, the histamine level was increased by 100% and 50% in the liver and the small intestine, respectively. On the 3rd day after extirpation of the tumour the level of histamine had returned to the control values and remained unchanged during the next 10 days. Neither of the histamine catabolizing enzymes, diamine oxidase with a putrescine as a substrate or histamine methyltransferase were influenced by the existing tumour or by its extirpation except on the 14th day where a high increase in diamine oxidase activity was found. Some changes in the distribution of histamine metabolites suggest an involvement of an oxidative pathway of histamine catabolism as well as the aldehyde catabolizing enzymes in tumour development.  相似文献   
117.

Objectives

The aim of the study was to characterize the differences in the frequencies of NS3 and NS5A resistance-associated variants (RAVs) among Polish therapy-naive genotype 1 (G1) hepatitis C virus (HCV)-monoinfected and human immunodeficiency virus (HIV)/HCV-coinfected patients including clustering patterns and association of RAV frequency with liver fibrosis.

Methods

NS3/NS5A RAVs were identified by population sequencing in 387 directly acting antiviral treatment-naive G1-infected individuals (54 with genotype 1a (G1a) and 333 with genotype 1b (G1b)). Liver fibrosis was assessed based on histopathology or ultrasound elastography. Phylogenetic clusters were identified using maximum likelihood models. For statistics, chi-squared or two-sided Fisher's exact tests and multivariate logistic regression models were used, as appropriate.

Results

NS3 RAVs were found in 33.33% (18/54) for G1a and 2.62% (8/297) for G1b whereas NS5A variants were present in 5.55% (3/54) G1a and 9.31% (31/333) G1b sequences. Variations in NS5A 31 and 93 codon positions were found only in G1b (4.2% (14/333) for L31I/F/M and 5.39% (17/333) for Y93H). NS5A RAVs were more frequent among patients with advanced liver fibrosis (17.17% (17/99) for F3–F4 versus 6.94% (17/245) for F0–F2; p 0.004) or liver cirrhosis (20.34% (12/59) for F4 versus 7.72% (22/285) for F0–F3; p 0.003). Liver cirrhosis (F4) was associated with higher odds ratio of the NS5A RAVs among HCV-infected patients (odds ratio 2.34, 95% CI 1.004–5.291; p 0.049). NS5A RAVs were less frequent among sequences forming clusters and pairs (5.16% (8/155) versus 11.21% (26/232); p 0.039).

Conclusions

Presence of NS5A RAVs correlated with progression of liver fibrosis and represents de novo selection of variants rather than transmission of drug resistance. Hence, the presence of NS5A RAVs may be a predictor for a long-lasting HCV infection.  相似文献   
118.
119.
120.
Carbon dioxide and propylene oxide (PO) were copolymerized using diethylzinc in addition with benzenedi- and triols, aliphatic diols and triols, and aminophenols as catalyst systems. A large amount of CO2/PO alternating copolymer, {poly(propylene carbonate), poly(oxycarbonyloxypropylene), of high molecular weight was obtained using the homogeneous (C2H5)2Zn/pyrogallol (2:1 by mole) system ( 1 ). The (C2H5)2Zn/o-aminophenol system ( 2 ) (also homogeneous) appeared to be much less active in the copolymerization of CO2 with PO than the former one. From the other studied systems, that appeared to be heterogeneous, (C2H5)2Zn/resorcinol (1:1 by mole) was the most active one, but less active than the system 1 . Further, the copolymerization of CO2 and PO was studied in the presence of the (C2H5)2Zn/resorcinol (1:1 by mole) system at various temperatures and in reaction media of different basicity. On the basis of the obtained results of the copolymerization of CO2 with PO and of measurements of the quantity of ethane evolved in the reactions between the catalytic systems' components, structures of several catalysts, particularly homogeneous ones, are suggested and some aspects of the copolymerization mechanism are discussed.  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