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   1462篇
  免费   100篇
  国内免费   16篇
耳鼻咽喉   6篇
儿科学   61篇
妇产科学   10篇
基础医学   148篇
口腔科学   55篇
临床医学   132篇
内科学   291篇
皮肤病学   132篇
神经病学   81篇
特种医学   114篇
外科学   146篇
综合类   29篇
预防医学   88篇
眼科学   54篇
药学   70篇
中国医学   1篇
肿瘤学   160篇
  2023年   13篇
  2022年   15篇
  2021年   49篇
  2020年   27篇
  2019年   39篇
  2018年   48篇
  2017年   38篇
  2016年   34篇
  2015年   23篇
  2014年   43篇
  2013年   58篇
  2012年   71篇
  2011年   82篇
  2010年   49篇
  2009年   34篇
  2008年   57篇
  2007年   79篇
  2006年   69篇
  2005年   79篇
  2004年   59篇
  2003年   66篇
  2002年   54篇
  2001年   49篇
  2000年   43篇
  1999年   39篇
  1998年   32篇
  1997年   24篇
  1996年   30篇
  1995年   28篇
  1994年   22篇
  1993年   12篇
  1992年   23篇
  1991年   18篇
  1990年   15篇
  1989年   23篇
  1988年   23篇
  1987年   19篇
  1986年   14篇
  1985年   16篇
  1983年   10篇
  1982年   6篇
  1981年   3篇
  1980年   6篇
  1979年   9篇
  1978年   3篇
  1976年   5篇
  1975年   3篇
  1974年   3篇
  1972年   3篇
  1971年   3篇
排序方式: 共有1578条查询结果,搜索用时 203 毫秒
121.
Aging of drug molecules is generally studied following regulatory procedures, i.e. under forced conditions and for relatively limited storage time; therefore naturally aged samples are rare and provide scientific reference data beyond regulatory considerations. Tienoxolol was studied after 25 years of storage in the dark under ambient conditions. About 86% of the samples still consisted of tienoxolol and the main impurity (13%) was caused by the hydrolysis of the ester moiety. Protection from humidity is therefore important. Other sensitive groups containing nitrogen and sulfur appear to be quite stable with less than 0.8% conversion over 25 years. In addition, the crystal structure has been solved. Tienoxolol orange needles were found to crystallize in the orthorhombic non-centrosymmetric space group Iba2, indicating that the crystal is a racemic compound. The unit cell parameters at room temperature are a=10.069(5)?, b=45.831(10)?, and c=9.822(5)? and the unit cell volume is 4533(3)?(3) with Z=8.  相似文献   
122.

Purpose

The aim of this study is to determine if there has been a true, absolute, or apparent relative increase in congenital diaphragmatic hernia (CDH) survival for the last 2 decades.

Method

All neonatal Bochdalek CDH patients admitted to an Ontario pediatric surgical hospital during the period when significant improvements in CDH survival was reported (from January 1, 1992, to December 31, 1999) were analyzed. Patient characteristics were assessed for CDH population homogeneity and differences between institutional and vital statistics-based population survival outcomes. SAS 9.1 (SAS Institute, Cary, NC) was used for analysis.

Result

Of 198 cohorts, demographic parameters including birth weight, gestational age, Apgar scores, sex, and associated congenital anomalies did not change significantly. Preoperative survival was 149 (75.2%) of 198, whereas postoperative survival was 133 (89.3%) of 149, and overall institutional survival was 133 (67.2%) of 198. Comparison of institution and population-based mortality (n = 65 vs 96) during the period yielded 32% of CDH deaths unaccounted for by institutions. Yearly analysis of hidden mortality consistently showed a significantly lower mortality in institution-based reporting than population.

Conclusion

A hidden mortality exists for institutionally reported CDH survival rates. Careful interpretation of research findings and more comprehensive population-based tools are needed for reliable counseling and evaluation of current and future treatments.  相似文献   
123.

Background  

Early and intensive treatment is important to inducing remission and preventing joint damage in patients with rheumatoid arthritis. While intensive combination therapy (Disease Modifying Anti-rheumatic Drugs and/or biologicals) is the most effective, rheumatologists in daily clinical practice prefer to start with monotherapy methotrexate and bridging corticosteroids. Intensive treatment should be started as soon as the first symptoms manifest, but at this early stage, ACR criteria may not be fulfilled, and there is a danger of over-treatment. We will therefore determine which induction therapy is most effective in the very early stage of persistent arthritis. To overcome over-treatment and under-treatment, the intensity of induction therapy will be based on a prediction model that predicts patients' propensity for persistent arthritis.  相似文献   
124.
The attributions made by Chinese immigrant (n = 28) and Euro-Canadian (n = 27) mothers of 5- to 9-year-old boys regarding the causes of child prosocial and problem behaviors exhibited by children with and without attention-deficit/hyperactivity disorder (ADHD) were investigated. Mothers’ attributions were elicited using audio-taped scenarios of child behavior. In one-half of the scenarios, the child was described as having ADHD. All mothers attributed less responsibility to the child or to the parent for problem behaviors when the child was described as having ADHD than when the child was described as not having a behavior disorder. Mothers also attributed prosocial child behaviors and the behavior of children without ADHD more to parental factors. In comparison to Euro-Canadian mothers, Chinese immigrant mothers saw children as less responsible for prosocial behavior. Mothers also completed a measure of beliefs about ADHD. Although there were some subtle cultural differences in these beliefs, mothers from both cultural groups endorsed generally accurate beliefs about ADHD. Implications for understanding the cultural uniqueness and similarities of maternal attitudes regarding child behavior and ADHD are discussed.  相似文献   
125.
Functional MRI was used to identify the brain areas underlying automatic beliefs about gender and race, and suppression of those attitudes. Participants (n = 20; 7 females) were scanned at 3 tesla while performing the Implicit Association Test (IAT), an indirect measure of race and gender bias. We hypothesized that ventromedial prefrontal cortex areas (PFC) would mediate gender and racial stereotypic attitudes, and suppression of these beliefs would recruit dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC). Performance data on the IAT revealed gender and racial biases. Racial bias was correlated with an explicit measure of racism. Results showed activation of anteromedial PFC and rostral ACC while participants implicitly made associations consistent with gender and racial biases. In contrast, associations incongruent with stereotypes recruited DLPFC. Implicit gender bias was correlated with amygdala activation during stereotypic conditions. Results suggest there are dissociable roles for anteromedial and dorsolateral PFC circuits in the activation and inhibition of stereotypic attitudes.  相似文献   
126.
Residence time measurements obtained by serial whole-body conjugate-view imaging are commonly used in patient-specific dosimetry for radioimmunotherapy applications. In order to determine the effect of collimator selection on residence time measurements for (131)I, the accuracies of (131)I half-life measurements obtained with multiple gamma-camera and collimator combinations were investigated. METHODS: Serial anterior and posterior whole-body images were acquired over a period of 15 d with 4 different gamma-cameras and medium- or high-energy collimators. Background-corrected geometric mean counts from the images were fitted to a monoexponential curve to determine the half-life of (131)I obtained with the different gamma-camera and collimator combinations. RESULTS: An average half-life of 8.15 d (SD, 0.07 d) was obtained with all gamma-camera and collimator combinations. A half-life of 8.12 d (SD, 0.11 d) was obtained with the high-energy collimators, and a half-life of 8.18 d (SD, 0.04 d) was obtained with the medium-energy collimators. These values are all very close to the (131)I physical half-life of 8.02 d and were not found to be statistically significantly different (P = 0.44). Similar results were obtained for the half-life obtained with single-head gamma-camera configurations (mean half-life, 8.15 d; SD, 0.12 d). The therapeutic (131)I-tositumomab dose resulting from the differences in the measured half-life ranged from 2.58 to 2.6 GBq (69.8-70.4 mCi). CONCLUSION: There is no significant difference in (131)I half-life and residence time measurements obtained with medium- or high-energy collimators in dual-head or single-head imaging configurations.  相似文献   
127.

Objective

Aicardi‐Goutières syndrome (AGS) is an early‐onset encephalopathy resembling congenital viral infection that is characterized by basal ganglia calcifications, loss of white matter, cerebrospinal fluid (CSF) lymphocytosis, and elevated interferon‐α levels in the CSF. Studies have shown that AGS is an autosomal‐recessive disease linked to mutations in 5 genes, encoding the 3′‐repair DNA exonuclease 1 (TREX1), the 3 subunits of ribonuclease H2 (RNASEH2A–C), and sterile alpha motif domain and HD domain–containing protein 1 (SAMHD1). In this study we further characterized the phenotypic spectrum of this disease.

Methods

Clinical and laboratory data were obtained from 26 patients fulfilling the clinical diagnostic criteria for AGS. Genomic DNA was screened for mutations in all 5 AGS genes by direct sequencing, and sera were analyzed for autoantibodies.

Results

In 20 patients with AGS, 20 mutations, 12 of which were novel, were identified in all 5 AGS genes. Clinical and laboratory investigations revealed a high prevalence of features (some not previously described in patients with AGS) that are commonly seen in patients with systemic lupus erythematosus (SLE), such as thrombocytopenia, leukocytopenia, antinuclear antibodies, erythematous lesions, oral ulcers, and arthritis, which were observed in 12 (60%) of 20 patients with AGS. Moreover, the coexistence of AGS and SLE, was for the first time, demonstrated in 2 patients with molecularly proven AGS.

Conclusion

These findings expand the phenotypic spectrum of lupus erythematosus in AGS and provide further insight into its disease mechanisms by showing that activation of the innate immune system as a result of inherited defects in nucleic acid metabolism could lead to systemic autoimmunity.
  相似文献   
128.
Mah JT  Low ES  Lee E 《Drug discovery today》2011,16(17-18):800-809
SNPs can alter protein function and phenotype, leading to altered pharmacogenomic drug profiles. The exponential number of SNPs makes it impossible to perform wet laboratory experiments to determine the biological significance of each one. However, bioinformatics tools can be used to screen for potentially deleterious SNPs that might affect important drug targets before further investigation by wet laboratory techniques. As there are numerous web-based bioinformatics tools, much time and effort is needed to select the most appropriate tool to use. Here, we review state-of-the-art bioinformatics tools to help researchers analyze and select the most promising SNPs for drug discovery in the shortest time possible.  相似文献   
129.
130.

Background:

Bile duct obstruction is associated with hepatic accumulation of leukocytes and liver injury. The aim of this study was to evaluate the effect of simvastatin on cholestasis-induced liver inflammation and tissue damage.

Experimental approach:

C57BL/6 mice were treated with simvastatin (0.02 and 0.2 mg·kg−1) and vehicle before and after undergoing bile duct ligation (BDL) for 12 h. Leukocyte recruitment and microvascular perfusion in the liver were analysed using intravital fluorescence microscopy. CXC chemokines in the liver were determined by enzyme-linked immunosorbent assay. Liver damage was monitored by measuring serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Hepatic levels of myeloperoxidase (MPO) were also determined.

Key results:

Administration of 0.2 mg·kg−1 simvastatin decreased ALT and AST by 87% and 83%, respectively, in BDL mice. This dose of simvastatin reduced hepatic formation of CXC chemokines by 37–82% and restored sinusoidal perfusion in cholestatic animals. Moreover, BDL-induced leukocyte adhesion in sinusoids and postsinusoidal venules, as well as MPO levels in the liver, was significantly reduced by simvastatin. Notably, administration of 0.2 mg·kg−1 simvastatin 2 h after BDL induction also decreased cholestatic liver injury and inflammation.

Conclusions and implications:

These findings show that simvastatin protects against BDL-induced liver injury. The hepatoprotective effect of simvastatin is mediated, at least in part, by reduced formation of CXC chemokines and leukocyte recruitment. Thus, our novel data suggest that the use of statins may be an effective strategy to protect against the hepatic injury associated with obstructive jaundice.  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