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   684191篇
  免费   34845篇
  国内免费   612篇
耳鼻咽喉   7987篇
儿科学   23329篇
妇产科学   16457篇
基础医学   100999篇
口腔科学   15975篇
临床医学   56310篇
内科学   123455篇
皮肤病学   12793篇
神经病学   52196篇
特种医学   27204篇
外国民族医学   63篇
外科学   105197篇
综合类   10762篇
一般理论   118篇
预防医学   56620篇
眼科学   14814篇
药学   49715篇
中国医学   1629篇
肿瘤学   44025篇
  2018年   26466篇
  2017年   20661篇
  2016年   23250篇
  2015年   5372篇
  2014年   6807篇
  2013年   10239篇
  2012年   19621篇
  2011年   34833篇
  2010年   26730篇
  2009年   19052篇
  2008年   32769篇
  2007年   35892篇
  2006年   15375篇
  2005年   16387篇
  2004年   17293篇
  2003年   17588篇
  2002年   15639篇
  2001年   24309篇
  2000年   25461篇
  1999年   20701篇
  1998年   5608篇
  1997年   4894篇
  1996年   5113篇
  1995年   4716篇
  1994年   4408篇
  1992年   15755篇
  1991年   16388篇
  1990年   16538篇
  1989年   15867篇
  1988年   14625篇
  1987年   14456篇
  1986年   13618篇
  1985年   13002篇
  1984年   9644篇
  1983年   8267篇
  1982年   4583篇
  1979年   9420篇
  1978年   6863篇
  1977年   5775篇
  1976年   5610篇
  1975年   6401篇
  1974年   7652篇
  1973年   7130篇
  1972年   6960篇
  1971年   6685篇
  1970年   6191篇
  1969年   5908篇
  1968年   5576篇
  1967年   5012篇
  1966年   4452篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
71.
This paper presents an analysis of samples from 75 patients for the presence of rubella virus, viral RNA, and specific antibodies. For all samples, RNA detection was higher than virus isolation. It was found that it was not possible to isolate rubella virus in every sixth clinical sample containing the viral RNA. Primary structures of the site (from the 8072nd to 8291st nucleotide) of the rubella virus genome from 14 samples were determined. This paper shows that all the samples of rubella virus belong to the first genotype, subgroups 1h, and very likely to subgroups 1a and 1F. For the first time, the circulation of rubella virus of the genotype has been shown both prior to the start of mass vaccination in Western Siberia and after.  相似文献   
72.
73.
Dehydrogenase activity is frequently used to assess the general condition of microorganisms in soil and activated sludge. Many studies have investigated the inhibition of dehydrogenase activity by various compounds, including heavy metal ions. However, the time after which the measurements are carried out is often chosen arbitrarily. Thus, it can be difficult to estimate how the toxic effects of compounds vary during the reaction and when the maximum of the effect would be reached. Hence, the aim of this study was to create simple and useful mathematical model describing changes in dehydrogenase activity during exposure to substances that inactivate enzymes. Our model is based on the Lagergrens pseudo-first-order equation, the rate of chemical reactions, enzyme activity, and inactivation and was created to describe short-term changes in dehydrogenase activity. The main assumption of our model is that toxic substances cause irreversible inactivation of enzyme units. The model is able to predict the maximum direct toxic effect (MDTE) and the time to reach this maximum (TMDTE). In order to validate our model, we present two examples: inactivation of dehydrogenase in microorganisms in soil and activated sludge. The model was applied successfully for cadmium and copper ions. Our results indicate that the predicted MDTE and TMDTE are more appropriate than EC50 and IC50 for toxicity assessments, except for long exposure times.  相似文献   
74.
FGFR–TACC, found in different tumor types, is characterized by the fusion of a member of fibroblast grown factor receptor (FGFR) tyrosine kinase (TK) family to a member of the transforming acidic coiled-coil (TACC) proteins. Because chromosome numerical alterations, hallmarks of FGFR–TACC fusions are present in many hematological disorders and there are no data on the prevalence, we studied a series of patients with acute myeloid leukemia and myelodysplastic syndrome who presented numerical alterations using cytogenetic traditional analysis. None of the analyzed samples showed FGFR3–TACC3 gene fusion, so screening for this mutation at diagnosis is not recommended.  相似文献   
75.
76.
Objective:To study the effect of oral administration of dimethyl dimethoxy biphenyl dicarboxylate(DDB) on adjusting angiogeneic/inflammatory mediators and ameliorating the pathology of bones in rats with collagen-induced arthritis(CIA).Methods:Wistar rat model of CIA was set up using bovine collagen type Ⅱ.Fifty rats were divided into five groups randomly:normal,CIA model,DDB treatment,methotrexate(MTX) treatment,and combined DDB+MTX treatment.Ankle joints of rats were imaged with digital X-ray machine to show the destruction of joints.Fore and hind paw and knee joints were removed above the ankle joint then processed for haematoxylin and eosin staining.Plasma levels of vascular endothelial growth factor(VEGF),platelet derived growth factor,interleukin-8(IL-8),IL-4,tumor necrosis factor α(TNF-α),and cyclooxygenase-2(COX-2) were quantified by enzyme-linked immunosorbent assay.Nitric oxide levels were detected by Griess reagent.Results:Compared with the CIA model group,a remarkable reduction in various angiogenic(VEGF and IL-8) and inflammatory mediators(TNF-α,IL-4 and COX-2) after treatment with DDB either alone or combined with MTX(P0.05 or P0.01).Histopathological and X-ray findings were confirmatory to the observed DDB anti-arthritic effect.The DDB-treated group showed amelioration in signs of arthritis which appeared essentially similar to normal.Conclusion:Our data shed light on the therapeutic efficacy of DDB in experimental rheumatoid arthritis(RA) compared with a choice drug(MTX) and it may be offered as a second-line drug in the treatment of RA.  相似文献   
77.
Contraceptive use is an important strategy for the prevention of unwanted pregnancy and avoidance of induced abortion. Of all the contraception methods, emergency contraceptive (EC) offers the last chance to achieve this. However, few studies have documented the use of EC among young people in Ghana. This study explored knowledge and usage of EC as well as the factors associated with it among University of Cape Coast students. Data were obtained on the knowledge and usage of ECs among University of Cape Coast students in 2013. Logistic regression analysis was used to investigate the association between students’ socio-demographic characteristics and EC knowledge and use. More male students (72 %) than females (59 %) were sexually active. Fifty-seven percent of the respondents had ever heard of EC and 36 % had ever used EC. Although males were more likely to be sexually active, females were more likely to have knowledge of EC use compared to males. The study underscores the need to increase awareness regarding EC among University students in order to offer them the opportunity that EC provides if other forms of contraceptives are missed.  相似文献   
78.
79.
80.
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