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   11193篇
  免费   682篇
  国内免费   85篇
耳鼻咽喉   88篇
儿科学   156篇
妇产科学   161篇
基础医学   1355篇
口腔科学   206篇
临床医学   1112篇
内科学   3100篇
皮肤病学   150篇
神经病学   922篇
特种医学   376篇
外科学   1834篇
综合类   62篇
一般理论   1篇
预防医学   773篇
眼科学   87篇
药学   692篇
中国医学   20篇
肿瘤学   865篇
  2024年   6篇
  2023年   79篇
  2022年   128篇
  2021年   385篇
  2020年   199篇
  2019年   373篇
  2018年   464篇
  2017年   295篇
  2016年   295篇
  2015年   364篇
  2014年   500篇
  2013年   616篇
  2012年   974篇
  2011年   993篇
  2010年   559篇
  2009年   455篇
  2008年   724篇
  2007年   765篇
  2006年   628篇
  2005年   676篇
  2004年   623篇
  2003年   557篇
  2002年   549篇
  2001年   95篇
  2000年   67篇
  1999年   84篇
  1998年   96篇
  1997年   57篇
  1996年   55篇
  1995年   46篇
  1994年   32篇
  1993年   35篇
  1992年   31篇
  1991年   27篇
  1990年   12篇
  1989年   14篇
  1988年   11篇
  1987年   6篇
  1986年   16篇
  1985年   9篇
  1984年   5篇
  1983年   8篇
  1982年   3篇
  1981年   5篇
  1979年   5篇
  1975年   4篇
  1974年   5篇
  1973年   3篇
  1971年   5篇
  1970年   3篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
101.
We describe herein the structural optimization of new piperamide analogues, designed from two natural prototypes, piperine 1 and piperdardine 2, obtained from Piper tuberculatum Jacq. (Piperaceae). Molecular modeling studies using semiempirical AM1 method were made in order to establish rational modifications to optimize them by molecular simplification. The targeted compounds (10) and (11) were respectively obtained using benzaldehyde (12) and para-anisaldehyde (13) as starting materials. 1H NMR spectra showed that the target compounds were diastereoselectively obtained as the (E)-isomer, the same geometry of the natural prototypes. These new synthetic amides presented significant hypotensive effects in cardiovascular essays using in vivo methodologies. Compound 11 (N-[5-(4′-methoxyphenyl)-2(E)-pentenoyl]thiomorpholine) showed a potency 10,000 times greater than its prototype 5, evidencing an optimization of the molecular architecture for this class of hypotensive drug candidates.  相似文献   
102.
In the approach to lipid-related risk factors for cardiovascular diseases, serum high density lipoprotein-cholesterol (HDL-C) levels bear a particular significance as this lipoprotein is considered to be an antiatherogenic factor mainly, but not only, because of its influence and impact on reverse cholesterol transport. Hence the need and requirement to consider serum HDL-C levels for both primary and secondary prevention of cardiovascular disease. A particularly important aspect is the association of the 'low HDL syndrome' with the metabolic syndrome. These factors force us to consider serum HDL-C level as a therapeutic target by itself, or even in association with low density lipoprotein-cholesterol (LDL-C) levels when the latter are increased. This review stresses the aspects connecting serum HDL-C levels and cardiovascular risk, and looks at the populations that should be considered amenable to therapeutic management because of low serum HDL-C levels. We review therapeutic strategies, both pharmacological and nonpharmacological. The aim of this review is to present therapeutic management recommendations for correcting the proportion of cardiovascular risk that is attributable to changes in HDL-C. Serum HDL-C levels of >40 mg/dL must be a therapeutic target in primary and secondary prevention. This goal is particularly important in patients with low serum HDL-C levels and ischemic heart disease (IHD) or its equivalents, even if the therapeutic target for serum LDL-C levels (<100 mg/dL) has been achieved. The first choice for this clinical condition is fibric acid derivates. The same therapeutic option should be considered in patients without IHD with low serum HDL-C levels and high cardiovascular risk (>20%), hypertriglyceridemia, type 2 diabetes mellitus, or metabolic syndrome.  相似文献   
103.
104.
ObjectivesTo use an “evidence-mapping” approach to assess the usefulness of Cochrane reviews in identifying research gaps in the maternal health.Study Design and SettingThe article describes the general mapping, prioritizing, reconciling, and updating approach: (1) identifying gaps in the maternal health research using published systematic reviews and formulating research questions, (2) prioritizing questions using Delphi method, (3) reconciling identified research priorities with the existing literature (i.e., searching of ongoing trials in trials registries), (4) updating the process. A comprehensive search of Cochrane systematic reviews published or updated from January 2006 to March 2011 was performed. We evaluated the “Implications for Research” section to identify gaps in the research.ResultsOur search strategy identified 695 references; 178 systematic reviews identifying at least one research gap were used. We formulated 319 research questions, which were classified into 11 different categories based on the direct and indirect causes of maternal mortality: postpartum hemorrhage, abortion, hypertensive disorders, infection/sepsis, caesarean section, diabetes, pregnancy prevention, preterm labor, other direct causes, indirect causes, and health policies and systems. Most research questions concerned the effectiveness of clinical interventions, including drugs (42.6%), nonpharmacologic interventions (16.3%), and health system (14.7%).ConclusionIt is possible to identify gaps in the maternal health research by using this approach.  相似文献   
105.
106.
107.
During 2003–2012, 8 clusters of meningococcal disease were identified in Rio de Janeiro State, Brazil, all caused by serogroup C Neisseria meningitidis. The isolates were assigned to 3 clonal complexes (cc): cc11, cc32, and cc103. These hyperinvasive disease lineages were associated with endemic disease, outbreaks, and high case-fatality rates.  相似文献   
108.
Estimates of occult hepatitis B virus (HBV) infection prevalence varies among different studies depending on the prevalence of HBV infection in the study population and on the sensitivity of the assay used to detect HBV DNA. We investigated the prevalence of occult HBV infection in cirrhotic patients undergoing liver transplantation in a Brazilian referral center. Frozen liver samples from 68 adults were analyzed using a nested polymerase chain reaction assay for HBV DNA. The specificity of the amplified HBV sequences was confirmed by direct sequencing of the amplicons. The patient population comprised 49 (72.1%) males and 19 (27.9%) females with a median age of 53 years (range=18-67 years). Occult HBV infection was diagnosed in three (4.4%) patients. The etiologies of the underlying chronic liver disease in these cases were alcohol abuse, HBV infection, and cryptogenic cirrhosis. Two of the patients with cryptic HBV infection also presented hepatocellular carcinoma. Markers of previous HBV infection were available in two patients with occult HBV infection and were negative in both. In conclusion, using a sensitive nested polymerase chain reaction assay to detect HBV DNA in frozen liver tissue, we found a low prevalence of occult HBV infection in cirrhotic patients undergoing liver transplant, probably due to the low prevalence of HBV infection in our population.  相似文献   
109.
110.
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