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   4544篇
  免费   333篇
  国内免费   10篇
耳鼻咽喉   56篇
儿科学   107篇
妇产科学   87篇
基础医学   770篇
口腔科学   66篇
临床医学   572篇
内科学   889篇
皮肤病学   81篇
神经病学   535篇
特种医学   136篇
外科学   435篇
综合类   39篇
一般理论   2篇
预防医学   391篇
眼科学   31篇
药学   263篇
中国医学   25篇
肿瘤学   402篇
  2024年   4篇
  2023年   62篇
  2022年   94篇
  2021年   156篇
  2020年   99篇
  2019年   153篇
  2018年   157篇
  2017年   118篇
  2016年   152篇
  2015年   164篇
  2014年   189篇
  2013年   259篇
  2012年   404篇
  2011年   408篇
  2010年   220篇
  2009年   202篇
  2008年   288篇
  2007年   299篇
  2006年   301篇
  2005年   262篇
  2004年   222篇
  2003年   211篇
  2002年   204篇
  2001年   21篇
  2000年   19篇
  1999年   23篇
  1998年   32篇
  1997年   20篇
  1996年   13篇
  1995年   10篇
  1994年   18篇
  1993年   15篇
  1992年   10篇
  1991年   8篇
  1990年   8篇
  1989年   6篇
  1988年   3篇
  1987年   3篇
  1986年   7篇
  1985年   4篇
  1984年   7篇
  1983年   9篇
  1982年   7篇
  1979年   1篇
  1976年   4篇
  1975年   1篇
  1974年   6篇
  1973年   1篇
  1970年   1篇
  1894年   1篇
排序方式: 共有4887条查询结果,搜索用时 31 毫秒
81.
Recent studies have shown that ultrasound (US)-mediated transdermal drug delivery offers a promising potential for noninvasive drug administration. The purpose of this study was to improve low-frequency (20 kHz) US methods for enhancing the transport of insulin in vitro across human skin. The feasibility of using US produced by small, lightweight novel transducers was explored for enhancing the transport of insulin across skin. Previous investigators have used US devices such as large, heavy sonicators or commercially obtained transducers for this type of research. The experiments carried out in this study used two low-profile novel US transducer arrays, the stack and standard array, for improved transport of insulin. The stack array generated a spatial peak temporal peak intensity (I(SPTP)) of 15.4 +/- 0.6 mW/cm(2) and the standard array had an I(SPTP) of 173.7 +/- 1.2 mW/cm(2). Spectrophotometeric absorption techniques were used for determining insulin transport in vitro across human skin. Compared with passive transmission (4.1 +/- 0.5 U) over an exposure period of 1 h, the standard array facilitated over a sevenfold increase in the noninvasive transdermal transport of Humulin R insulin (45.9 +/- 12.9 U). Using Humalog insulin with the standard array, there was a fourfold increase in the US-facilitated transmission over that in the control. These promising results indicate that low-frequency US can be used in a practical device for enhanced transport across the stratum corneum.  相似文献   
82.
83.
84.
85.
86.

Background

Left ventricular (LV) trabeculation is highly variable among individuals and is increased in some diseases (e.g., congenital heart disease or cardiomyopathies), but its significance in population-representative individuals is unknown.

Objectives

The goal of this study was to determine if excessive LV trabeculation in population-representative individuals is associated with preceding changes in cardiac volumes and function.

Methods

For technical reasons, the extent of trabeculation, which is expressed as the ratio of noncompacted to compacted (NC/C) myocardium, was measured on cardiac magnetic resonance (CMR) long-axis cine images in 2,742 participants in the MESA (Multi-Ethnic Study of Atherosclerosis) (mean age 68.7 years; 52.3% women; 56.4% with hypertension; 16.8% with diabetes) at examination 5. These were considered in quintiles of trabeculation extent; the NC/C ratio of quintile 5 was 2.46 to 5.41. We determined the relationship between the maximal NC/C ratio and the preceding change (9.5 years between examinations 1 and 5) in end-systolic volume indexed (ESVi) to body surface area. Secondary analyses assessed the associations between the maximal NC/C ratio and preceding changes in end-diastolic volume indexed (EDVi) to body surface area and the ejection fraction (EF).

Results

Over 9.5 years, the ESVi decreased by 1.3 ml/m2, the EDVi decreased by 5.1 ml/m2, and the EF decreased by 0.6% (p < 0.0001). Even in subjects with excessive trabeculation, there were no clinically relevant differences in LV volumes and systolic function changes among the quintiles of trabeculation extent.

Conclusions

Greater extent of, and even excessive, LV trabeculation measured in end-diastole in asymptomatic population-representative individuals appeared benign and was not associated with deterioration in LV volumes or function during an almost 10-year period.  相似文献   
87.
Diabetes induces vasoregression, neurodegeneration and glial activation in the retina. Formation of advanced glycation endoproducts (AGEs) is increased in diabetes and contributes to the pathogenesis of diabetic retinopathy. CD74 is increased in activated microglia in a rat model developing both neurodegeneration and vasoregression. In this study, we aimed at investigating whether glucose and major AGE precursor methylglyoxal induce increased CD74 expression in the retina. Expression of CD74 in retinal microglia was analyzed in streptozotocin-diabetic rats by wholemount immunofluorescence. Nondiabetic mice were intravitreally injected with methylglyoxal. Expression of CD74 was studied by retinal wholemount immunofluorescence and quantitative real-time PCR, 48 h after the injection. CD74-positive cells were increased in diabetic 4-month retinas. These cells represented a subpopulation of CD11b-labeled activated microglia and were mainly located in the superficial vascular layer (13.7-fold increase compared to nondiabetic group). Methylglyoxal induced an 9.4-fold increase of CD74-positive cells in the superficial vascular layer and elevated gene expression of CD74 in the mouse retina 2.8-fold. In summary, we identified CD74 as a microglial activation marker in the diabetic retina. Exogenous methylglyoxal mimics the response in normoglycemic retina. This suggests that methylglyoxal is important in mediating microglial activation in the diabetic retina.  相似文献   
88.
May  Nadine  Niehaus-Gebele  Christa  Reichenberger  Frank  Behr  Jürgen  Gesierich  Wolfgang 《Lung》2020,198(1):221-228
Background

Evidence for bronchoscopic lung volume reduction (BLVR) is based on phase 2 studies and small randomized controlled trials with in- and exclusion criteria defining a therapeutic window and contraindications. Little is known about the applicability in routine clinical practice.

Aim

Which percentage of patients with severe emphysema referred to a specialized treatment center for BLVR is ultimately suitable for interventional bronchoscopic treatment? What is the relevance of the different contraindications?

Methods

Retrospective evaluation of emphysema patients referred to Asklepios Fachkliniken Munich-Gauting for BLVR between January 2014 and June 2015.

Results

138 patients were referred for evaluation of BLVR. 38 patients (27.5%) underwent BLVR procedures (valves n = 18; coils n = 18; thermal vapor ablation n = 2). 100 patients (72.5%) were deemed not eligible for BLVR based on the following contraindications: 34% emphysema morphology and emphysema-related findings (severe homogeneous emphysema, extensive pleuropulmonary adhesions, postinflammatory scaring with natural volume reduction, giant bullae), 16% active smoking; 9% pulmonary function not within indication range; 8% unexpected CT findings (nodules, cancer, interstitial disease); 8% chronic ventilatory failure; 8% patient refused BLVR; 5% relevant comorbidity; 5% frequent exacerbations, 3% preserved quality of life, 4% other.

Conclusion

BLVR is a therapeutic option for highly selected patients. In our cohort, one in four could be treated. These data highlight the limitations of BLVR under real-life conditions.

  相似文献   
89.
This case of secondary infertility with an associated intraabdominal levonorgestrel intrauterine system (LNG-IUS) demonstrates the importance of adequate imaging in women with a missing intrauterine contraceptive device and the possible fertility implications of an extrauterine LNG-IUS.  相似文献   
90.

OBJECTIVE

To evaluate the larvicidal activity of Azadirachta indica, Melaleuca alternifolia, carapa guianensis essential oils and fermented extract of Carica papaya against Aedes aegypti (Linnaeus, 1762) (Diptera: Culicidae).

METHODS

The larvicide test was performed in triplicate with 300 larvae for each experimental group using the third larval stage, which were exposed for 24h. The groups were: positive control with industrial larvicide (BTI) in concentrations of 0.37 ppm (PC1) and 0.06 ppm (PC2); treated with compounds of essential oils and fermented extract, 50.0% concentration (G1); treated with compounds of essential oils and fermented extract, 25.0% concentration (G2); treated with compounds of essential oils and fermented extract, 12.5% concentration (G3); and negative control group using water (NC1) and using dimethyl (NC2). The larvae were monitored every 60 min using direct visualization.

RESULTS

No mortality occurred in experimental groups NC1 and NC2 in the 24h exposure period, whereas there was 100% mortality in the PC1 and PC2 groups compared to NC1 and NC2. Mortality rates of 65.0%, 50.0% and 78.0% were observed in the groups G1, G2 and G3 respectively, compared with NC1 and NC2.

CONCLUSIONS

The association between three essential oils from Azadirachta indica, Melaleuca alternifolia, Carapa guianensis and fermented extract of Carica papaya was efficient at all concentrations. Therefore, it can be used in Aedes aegypti Liverpool third larvae stage control programs.  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