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   3108篇
  免费   225篇
  国内免费   12篇
耳鼻咽喉   14篇
儿科学   116篇
妇产科学   133篇
基础医学   556篇
口腔科学   6篇
临床医学   177篇
内科学   591篇
皮肤病学   97篇
神经病学   146篇
特种医学   97篇
外科学   329篇
综合类   142篇
一般理论   2篇
预防医学   260篇
眼科学   121篇
药学   335篇
中国医学   39篇
肿瘤学   184篇
  2022年   41篇
  2021年   56篇
  2020年   25篇
  2019年   46篇
  2018年   56篇
  2017年   31篇
  2016年   51篇
  2015年   69篇
  2014年   93篇
  2013年   133篇
  2012年   238篇
  2011年   262篇
  2010年   122篇
  2009年   97篇
  2008年   172篇
  2007年   157篇
  2006年   172篇
  2005年   163篇
  2004年   143篇
  2003年   137篇
  2002年   111篇
  2001年   97篇
  2000年   95篇
  1999年   73篇
  1998年   48篇
  1997年   26篇
  1996年   20篇
  1995年   23篇
  1994年   28篇
  1993年   23篇
  1992年   56篇
  1991年   47篇
  1990年   37篇
  1989年   38篇
  1988年   29篇
  1987年   30篇
  1986年   35篇
  1985年   30篇
  1984年   22篇
  1983年   17篇
  1982年   11篇
  1979年   12篇
  1978年   15篇
  1977年   13篇
  1976年   11篇
  1975年   11篇
  1974年   11篇
  1973年   15篇
  1972年   11篇
  1968年   12篇
排序方式: 共有3345条查询结果,搜索用时 15 毫秒
91.
ObjectivesThe misdiagnosis of acute ischemic stroke in young adults is a significant problem since patients may have many decades of potential disability. Also, proven therapies for acute stroke may not be administered if there is an initial misdiagnosis. We assessed the hypothesis that early use of MRI, arrival by ambulance, and presentation to a Primary Stroke Center (PSC) would be associated with a reduced rate of misdiagnosis.MethodsA prospective database of young adults (ages 16–49 years) with ischemic stroke (final diagnosis provided by vascular neurologists) was reviewed. We collected information on several variables, including age, race, arrival by ambulance, whether brain MRI was performed within 48 h, and initial presentation to a PSC. Variables were tested against emergency department (ED) misdiagnosis using univariate and multivariate methods.Results77 patients with a mean age of 37.9 years were reviewed. 48.3% of patients arrived by ambulance, 53.2% had a brain MRI within 48 h, and 23.4% initially presented to a PSC. The overall rate of ED misdiagnosis was 14.5%. In multivariate testing, performance of MRI within 48 h (p = 0.023) was associated with a lower rate of misdiagnosis and age < 35 years was linked with greater likelihood of misdiagnosis (p = 0.047).ConclusionsEarly performance of MRI leads to greater accuracy of stroke diagnosis in young adults presenting to the ED. Patients less than age 35 years have a greater risk of misdiagnosis. ED physicians and neurologists should consider early use of MRI in young adults with stroke-like deficits and diagnostic uncertainty.  相似文献   
92.
BACKGROUND: In order to develop, implement and evaluate policy for reducing maternal mortality, it is essential to study the risk factors associated with maternal deaths. AIMS: The study aims to determine the epidemiological risk factors and its related causes associated with maternal deaths in Delhi slums. MATERIALS AND METHODS: A community-based case-control study was designed, wherein snowball-sampling method was used to identify the maternal deaths (cases) in the community and circular systematic random sampling procedure was used to select the controls from the same area where a maternal death was found. STATISTICAL ANALYSIS: Data on 70 cases and 384 controls that had live births as the outcome of the pregnancy were analyzed. Logistic regression was applied to identify the risk factors. RESULTS: In the study population, most of the deliveries were conducted at home by untrained 'dais.' Cases were mostly illiterate, young, having high parity and no antenatal care taken during pregnancy (P CONCLUSIONS: The study findings suggest that women should be educated about the importance of antenatal registration and regular checkups. Untrained 'dais' should be trained to recognize the obstetric complications at an early stage and refer high-risk cases for adequate management. These preventive measures could help in reducing maternal mortality at the community level.  相似文献   
93.
Rapid and precise phenotyping analysis of large numbers of wild-type and mutant mouse embryos is essential for characterizing the genetic and epigenetic factors regulating embryogenesis. We present a novel methodology that permits precise high-throughput screening of the phenotype of embryos with both targeted and randomly generated mutations. To demonstrate the potential of this methodology we show embryo phenotyping results produced in a large-scale ENU-mutagenesis study. In essence this represents an analysis pipeline, which starts with simultaneous micro-magentic resonance imaging (microMRI) screening (voxel size: 25.4 x 25.4 x 24.4 microm) of 32 embryos in one run. Embryos with an indistinct phenotype are then cut into parts and suspect organs and structures are analysed with HREM (high-resolution episcopic microscopy). HREM is an imaging technique that employs 'positive' eosin staining and episcopic imaging for generating three-dimensional (3D) high-resolution (voxel size: 1.07 x 1.07 x 2 microm) digital data of near histological contrast and quality. The results show that our method guarantees the rapid availability of comprehensive phenotype information for high numbers of embryos in, if necessary, histological quality and detail. The combination of high-throughput microMRI with HREM provides an alternative screening pipeline with advantages over existing 3D phenotype screening methods as well as traditional histology. Thus, the microMRI-HREM phenotype analysis pipeline recommends itself as a routine tool for analysing the phenotype of transgenic and mutant embryos.  相似文献   
94.
Nodular granulomatous perifolliculitis is a well-recognized infection of the dermal and subcutaneous tissue caused by dermatophytes, which normally do not invade beyond the epidermis. We report here one such case that occurred in an immunosuppressed individual. The patient was a 35-year-old farmer who presented with small pruritic eruption that had initially appeared on the lower leg and then had gradually spread to hair-bearing areas of the body, finally producing nodular and pustular inflammatory lesions with exacerbations and remissions. Fungal examination by direct potassium hydroxide mount and culture revealed Trichophyton rubrum. Granulomatous changes were seen on histopathological examination. The patient completely responded to systemic antifungal therapy.  相似文献   
95.
A class of covariate-adjusted response-adaptive randomization procedures is developed for binary treatment outcomes in a phase III clinical trial set up involving multiple treatments. The target allocation is developed by combining the ethical aspects with statistical precision under the existence of treatment covariate interaction. Relevant measures of the performance for the proposed allocation designs are studied and compared.  相似文献   
96.
97.
98.

Purpose

To determine the effect of annealing on the two secondary relaxations in amorphous sucrose and in sucrose solid dispersions.

Methods

Sucrose was co-lyophilized with either PVP or sorbitol, annealed for different time periods and analyzed by dielectric spectroscopy.

Results

In an earlier investigation, we had documented the effect of PVP and sorbitol on the primary and the two secondary relaxations in amorphous sucrose solid dispersions (1). Here we investigated the effect of annealing on local motions, both in amorphous sucrose and in the dispersions. The average relaxation time of the local motion (irrespective of origin) in sucrose, decreased upon annealing. However, the heterogeneity in relaxation time distribution as well as the dielectric strength decreased only for β1- (the slower relaxation) but not for β2-relaxations. The effect of annealing on β2-relaxation times was neutralized by sorbitol while PVP negated the effect of annealing on both β1- and β2-relaxations.

Conclusions

An increase in local mobility of sucrose brought about by annealing could be negated with an additive.  相似文献   
99.
Human bocavirus 1 (HBoV1) has gained attention as a gene delivery vector with its ability to infect polarized human airway epithelia and 5.5 kb genome packaging capacity. Gorilla bocavirus 1 (GBoV1) VP3 shares 86% amino acid sequence identity with HBoV1 but has better transduction efficiency in several human cell types. Here, we report the capsid structure of GBoV1 determined to 2.76 Å resolution using cryo-electron microscopy (cryo-EM) and its interaction with mouse monoclonal antibodies (mAbs) and human sera. GBoV1 shares capsid surface morphologies with other parvoviruses, with a channel at the 5-fold symmetry axis, protrusions surrounding the 3-fold axis and a depression at the 2-fold axis. A 2/5-fold wall separates the 2-fold and 5-fold axes. Compared to HBoV1, differences are localized to the 3-fold protrusions. Consistently, native dot immunoblots and cryo-EM showed cross-reactivity and binding, respectively, by a 5-fold targeted HBoV1 mAb, 15C6. Surprisingly, recognition was observed for one out of three 3-fold targeted mAbs, 12C1, indicating some structural similarity at this region. In addition, GBoV1, tested against 40 human sera, showed the similar rates of seropositivity as HBoV1. Immunogenic reactivity against parvoviral vectors is a significant barrier to efficient gene delivery. This study is a step towards optimizing bocaparvovirus vectors with antibody escape properties.  相似文献   
100.
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