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   5602篇
  免费   401篇
  国内免费   18篇
耳鼻咽喉   86篇
儿科学   92篇
妇产科学   75篇
基础医学   967篇
口腔科学   77篇
临床医学   568篇
内科学   1194篇
皮肤病学   147篇
神经病学   514篇
特种医学   324篇
外科学   621篇
综合类   31篇
一般理论   2篇
预防医学   330篇
眼科学   113篇
药学   409篇
中国医学   9篇
肿瘤学   462篇
  2023年   26篇
  2022年   82篇
  2021年   145篇
  2020年   64篇
  2019年   113篇
  2018年   132篇
  2017年   117篇
  2016年   147篇
  2015年   191篇
  2014年   202篇
  2013年   260篇
  2012年   366篇
  2011年   435篇
  2010年   239篇
  2009年   290篇
  2008年   419篇
  2007年   385篇
  2006年   423篇
  2005年   381篇
  2004年   408篇
  2003年   352篇
  2002年   292篇
  2001年   62篇
  2000年   39篇
  1999年   40篇
  1998年   65篇
  1997年   58篇
  1996年   33篇
  1995年   29篇
  1994年   25篇
  1993年   18篇
  1992年   14篇
  1991年   13篇
  1990年   7篇
  1989年   7篇
  1988年   7篇
  1986年   10篇
  1985年   8篇
  1982年   13篇
  1981年   7篇
  1980年   5篇
  1979年   5篇
  1978年   10篇
  1977年   4篇
  1975年   4篇
  1974年   9篇
  1973年   7篇
  1972年   4篇
  1971年   4篇
  1970年   3篇
排序方式: 共有6021条查询结果,搜索用时 15 毫秒
71.
BACKGROUND: Alternatively activated macrophages expressing the CD163 and CD206 surface receptors are the dominant immune-cell type found in the placenta. The placental number and distribution of macrophages is altered in pre-eclampsia, and the generalised inflammatory reaction associated with pre-eclampsia might lead to shedding of soluble CD163 into the circulation. METHODS: Serum samples from 18 women with pre-eclampsia and 90 normal pregnancies were obtained from a longitudinal study of 955 pregnant women at Randers County Hospital, Denmark. sCD163 and Neopterin were measured by ELISA on samples collected in weeks 18, 28, 32, and 38 of pregnancy. RESULTS: sCD163 levels in pregnancy (2-3 mg/l) were similar to previously measured levels in non-pregnant women, and did not increase from week 18 to 38. There was a tendency towards higher sCD163 in week 38 in pre-eclamptic women compared to healthy women. Neopterin increased throughout pregnancy in both healthy (from median 5.4 to 6.7 nmol/l, p<0.0001) and pre-eclamptic women (from 5.0 to 8.0 nmol/l, p<0.0001), but there were no differences between groups at any time-point. sCD163 correlated to neopterin in both the control (r=0.25, p<0.0001) and in the pre-eclampsia group (r=0.32, p=0.011). C-reactive protein was higher in pre-eclampsia than in healthy pregnancies by week 38 (159 versus 91 nmol/l, p=0.0189). CONCLUSIONS: The macrophage serum-markers sCD163 and neopterin are not pre-symptomatic nor prognostic markers for pre-eclampsia.  相似文献   
72.
73.
OBJECTIVE: To study if spontaneous contractions augmented by proteinase-activated receptor-2 (PAR-2)-activating peptide serine-leucine-isoleucine-glycine-arginine-leucine (SLIGRL) involve coactivation of membrane chemoceptors and are associated with expression of PAR-2 mRNA in non-pregnant and pregnant rat myometrium. MATERIALS AND METHODS: Non-pregnant, mid-pregnant, and late pregnant rat uterine horn and small intestine segments were snap-frozen in liquid nitrogen to determine PAR-2 mRNA levels by real time polymerase chain reaction (PCR). Uterine rings were used for isometric tension recording. Effect of SLIGRL (0.1 mM) on spontaneous contractions before and after exposure to ibuprofen (cyclooxygenase inhibitor, 1.0 microM), SQ-29548 (thromboxane A(2) receptor inhibitor, 1.0 microM), ketotifen (histamine 1 receptor inhibitor, 10 microM), WEB-2170BS (platelet-activating factor (PAF) receptor inhibitor, 10 microM), atropine (muscarinic receptor inhibitor, 0.1 microM), or ketanserin (serotonin receptor inhibitor, 10 microM) were compared. Paired t-test and one-way ANOVA followed by Dunnett's or Newman-Keuls post hoc tests were used for statistical analysis when appropriate. SIGNIFICANCE: P<0.05. RESULTS: The agents did not significantly affect time-associated decay in spontaneous contractile activity in any group of the tissues. Activation of spontaneous contractions induced by SLIGRL in non-pregnant rat myometrium did not involve coactivation of membrane chemoceptors, while in mid-pregnant rat myometrium coactivation of prostanoid, histamine, and serotonin receptors and in late pregnant rat myometrium coactivation of thromboxane receptors was noted. Expression of PAR-2 mRNA was similar in non-pregnant, mid-pregnant, and late pregnant rat myometrium. CONCLUSIONS: Expression of PAR-2 in rat myometrium is not dependent on gestational age. Stimulation of PAR-2 is associated with production/release of cyclooxygenase pathway product(s) activating thromboxane/prostaglandin H2 receptors, partial involvement of histamine H1 receptors and serotonin receptors in midpregnancy and thromboxane A2/prostaglandin H2 receptors in late pregnancy.  相似文献   
74.
75.
Presenting continuous outcomes in Summary of Findings tables presents particular challenges to interpretation. When each study uses the same outcome measure, and the units of that measure are intuitively interpretable (e.g., duration of hospitalization, duration of symptoms), presenting differences in means is usually desirable. When the natural units of the outcome measure are not easily interpretable, choosing a threshold to create a binary outcome and presenting relative and absolute effects become a more attractive alternative.When studies use different measures of the same construct, calculating summary measures requires converting to the same units of measurement for each study. The longest standing and most widely used approach is to divide the difference in means in each study by its standard deviation and present pooled results in standard deviation units (standardized mean difference). Disadvantages of this approach include vulnerability to varying degrees of heterogeneity in the underlying populations and difficulties in interpretation. Alternatives include presenting results in the units of the most popular or interpretable measure, converting to dichotomous measures and presenting relative and absolute effects, presenting the ratio of the means of intervention and control groups, and presenting the results in minimally important difference units. We outline the merits and limitations of each alternative and provide guidance for meta-analysts and guideline developers.  相似文献   
76.
77.
Imaging proliferation in lung tumors with PET: 18F-FLT versus 18F-FDG.   总被引:19,自引:0,他引:19  
Recently, the thymidine analog 3'-deoxy-3'-(18)F-fluorothymidine (FLT) was suggested for imaging tumoral proliferation. In this prospective study, we examined whether (18)F-FLT better determines proliferative activity in newly diagnosed lung nodules than does (18)F-FDG. METHODS: Twenty-six patients with pulmonary nodules on chest CT were examined with PET and the tracers (18)F-FDG and (18)F-FLT. Tumoral uptake was determined by calculation of standardized uptake value (SUV). Within 2 wk, patients underwent resective surgery or had core biopsy. Proliferative activity was estimated by counting nuclei stained with the Ki-67-specific monoclonal antibody MIB-1 per total number of nuclei in representative tissue specimens. The correlation between the percentage of proliferating cells and the SUVs for (18)F-FLT and (18)F-FDG was determined using linear regression analysis. RESULTS: Eighteen patients had malignant tumors (13 with non-small cell lung cancer [NSCLC], 1 with small cell lung cancer, and 4 with pulmonary metastases from extrapulmonary tumors); 8 had benign lesions. In all visible lesions, mean (18)F-FDG uptake was 4.1 (median, 4.4; SD, 3.0; range, 1.0-10.6), and mean (18)F-FLT uptake was 1.8 (median, 1.2; SD, 2.0; range, 0.8-6.4). Statistical analysis revealed a significantly higher uptake of (18)F-FDG than of (18)F-FLT (Mann-Whitney U test, P < 0.05). (18)F-FLT SUV correlated better with proliferation index (P < 0.0001; r = 0.92) than did (18)F-FDG SUV (P < 0.001; r = 0.59). With the exception of 1 carcinoma in situ, all malignant tumors showed increased (18)F-FDG PET uptake. (18)F-FLT PET was false-negative in the carcinoma in situ, in another NSCLC with a low proliferation index, and in a patient with lung metastases from colorectal cancer. Increased (18)F-FLT uptake was related exclusively to malignant tumors. By contrast, (18)F-FDG PET was false-positive in 4 of 8 patients with benign lesions. CONCLUSION: (18)F-FLT uptake correlates better with proliferation of lung tumors than does uptake of (18)F-FDG and might be more useful as a selective biomarker for tumor proliferation.  相似文献   
78.
The necessity for resource-efficient manufacturing technologies requires new developments within the field of plastic processing. Lightweight design using wood fibers as sustainable reinforcement for thermoplastics might be one solution. The processing of wood fibers requires special attention to the applied thermal load. Even at low processing temperatures, the influence of the dwell time, temperature and shear force is critical to ensure the structural integrity of fibers. Therefore, this article compares different compounding rates for polypropylene with wood fibers and highlights their effects on the olfactory, visual and mechanical properties of the injection-molded part. The study compares one-step processing, using an injection-molding compounder (IMC), with two-step processing, using a twin-scew-extruder (TSE), a heating/cooling mixer (HCM) and an internal mixer (IM) with subsequent injection molding. Although the highest fiber length was achieved by using the IMC, the best mechanical properties were achieved by the HCM and IM. The measured oxidation induction time and volatile organic compound content indicate that the lowest amount of thermal damage occurred when using the HCM and IM. The advantage of one-time melting was evened out by the dwell time. The reinforcement of thermoplastics by wood fibers depends more strongly on the structural integrity of the fibers compared to their length and homogeneity.  相似文献   
79.
The pandemic spread of an infectious disease poses a plethora of challenges to society, clinicians, health care providers and regulating authorities. In order to mount a rapid response and to provide hope in a potentially catastrophic situation as the current COVID-19 pandemic, emergency plans, regulations and funding strategies have to be developed on regional, national and international levels. The speed needed to establish rapid response programs is challenged by the dynamics of the spread of the disease, the concurrent and competing development of different and potentially more effective treatment options, and not the least by regulatory uncertainty. Convalescent plasma, that is plasma collected from patients who have recovered from COVID-19 infections, has emerged as one of the first potential treatment options in the absence of drugs or vaccines with proven efficacy against SARS-CoV-2. The societal aspects of convalescent plasma and the public awareness gave an additional boost to the rapid employment of convalescent plasma donation platforms immediately after the SARS-CoV-2 outbreak. At the same time, uncertainty remains as to the efficacy of convalescent plasma. With evidence mostly limited to empirical reports, convalescent plasma has been used for decades for the prophylaxis and treatment of various infectious diseases. Clinical trials have addressed different infectious agents, stages of disease, target groups of patients and yielded sometimes inconclusive results. The aim of this short review is to delineate the regulatory background for the emergency use of convalescent plasma in the USA, in the European Union and in Germany, and the transition to the setting of clinical trials. In addition, we describe observations made in the process of collecting COVID-19 convalescent plasma (herein referred to as CCP), and formulate proposals to further improve the framework for rapid responses in future emergency situations.  相似文献   
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