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   2378篇
  免费   223篇
  国内免费   9篇
耳鼻咽喉   10篇
儿科学   76篇
妇产科学   54篇
基础医学   404篇
口腔科学   61篇
临床医学   258篇
内科学   749篇
皮肤病学   25篇
神经病学   216篇
特种医学   34篇
外科学   201篇
综合类   3篇
一般理论   1篇
预防医学   123篇
眼科学   26篇
药学   136篇
中国医学   3篇
肿瘤学   230篇
  2023年   15篇
  2022年   33篇
  2021年   54篇
  2020年   36篇
  2019年   42篇
  2018年   60篇
  2017年   42篇
  2016年   52篇
  2015年   67篇
  2014年   106篇
  2013年   115篇
  2012年   178篇
  2011年   179篇
  2010年   88篇
  2009年   87篇
  2008年   153篇
  2007年   147篇
  2006年   133篇
  2005年   133篇
  2004年   130篇
  2003年   132篇
  2002年   125篇
  2001年   50篇
  2000年   44篇
  1999年   44篇
  1998年   24篇
  1997年   21篇
  1996年   19篇
  1995年   15篇
  1994年   13篇
  1993年   11篇
  1992年   26篇
  1991年   19篇
  1990年   17篇
  1989年   35篇
  1988年   16篇
  1987年   24篇
  1986年   22篇
  1985年   21篇
  1984年   17篇
  1983年   14篇
  1982年   7篇
  1981年   6篇
  1980年   4篇
  1979年   8篇
  1978年   7篇
  1976年   4篇
  1975年   2篇
  1974年   3篇
  1969年   4篇
排序方式: 共有2610条查询结果,搜索用时 15 毫秒
71.
OBJECTIVE: To assess gender differences in the long-term clinical, virological and immunological outcomes during highly active antiretroviral therapy (HAART). METHODS: This longitudinal observational multicentre study followed 2460 HIV-infected patients who had begun a protease inhibitor-based regimen for a median period of 43 months. Outcome measures were virological suppression (< 500 copies/ml), confirmed virological rebound after suppression, and death or new AIDS-defining illness (ADI). RESULTS: At baseline, 690 female patients (28.0%) had significantly lower age, higher prevalence of heterosexual contact and lower prevalence of intravenous drug use as risk factors for HIV infection compared with males. Furthermore, females had a lower number of AIDS-defining illnesses, higher CD4 cell counts and lower viral loads.No gender differences were reported in terms of proportion of patients achieving viral suppression or exhibiting rebound after achieving viral suppression. Female patients experienced reduced clinical progression during follow-up compared with males (P = 0.008) by Kaplan-Meier analysis; however this difference was not significant in an adjusted analysis. In a multivariate model, the interaction between gender and risk factor for HIV or viral load showed that female drug users and female patients with a baseline HIV RNA viral load of 10(4)-10(5) copies/ml had a favourable clinical outcome compared with males (P = 0.035 and P = 0.015, respectively). CONCLUSION: No differences were found between genders in terms of virological and immunological outcomes during long-term HAART. Nevertheless, a lower risk of clinical progression was reported among female patients with intermediate baseline viral load than in males.  相似文献   
72.
To elucidate the role of thrombocytosis, alone or in combination with standard (age, previous cardiovascular events) and novel (leukocytosis, JAK2(V617F) mutational status) risk factors, in the cardiovascular events of essential thrombocythemia (ET), we analyzed a cohort of 1063 patients. We found that a platelet count at diagnosis greater than 1000 x 10(9)/L was associated with significantly lower rate of thrombosis in multivariable analysis and, if combined with leukocytes less than 11 x 10(9)/L, pointed to a "low-risk" category with a rate of thrombosis of 1.59% of patients/year. On the contrary, the highest risk category (thrombosis rate, 2.95% of patients/year) was constituted of patients with leukocytosis, lower platelet count, and a JAK2(V617F) mutated genotype in most cases (77% vs 26% in the low-risk group), independently from standard risk factors. These data challenge the theory that elevated platelet count increases thrombosis risk in ET and suggest prospective clinical trials to support this hypothesis.  相似文献   
73.

Background

Work engagement is a positive, fulfilling affective and motivational state of work-related wellbeing and a protective factor for workers' mental health. The aim of the present study was to examine the association between psychological distress (conceptualised as the target variable), job satisfaction, and work engagement in contexts of low-intensity warfare and political violence. According to the salutogenic perspective, the relationship between job satisfaction and psychological distress is influenced by the level of work engagement.

Methods

We selected a convenience sample of 380 Palestinian teachers from Gaza (40%, 152 out of 380) and the West Bank (60%, 228 out of 380). The participants were recruited on-site during morning breaks from the classroom teaching activity. The selection criteria were being in a teaching position, and working in a primary or lower secondary school. The participants completed the Arabic versions of the Teacher Job satisfaction Scale (TJSS-9), the General Health Questionnaire (GHQ-12) and the Utrecht Work Engagement Scale (UWE-SF). The statistical strategy was based on structural equation modelling. The study was approved by the Ethical Board of the University of Milano Bicocca. Informed written consent was obtained from all participants.

Findings

The General Health Questionnaire cumulative score revealed a medium to high level of psychological distress (mean 18·68 [SD 4·03]) among teachers, but high job satisfaction (mean 27·18 [SD 5·65]). The structural model showed an excellent fit (χ2 (23)=69·6, p<0·0001, NC=3·021, NFI=0·939, NNFI=0·959, CFI=0·958, RMSEA=0·073). Job satisfaction and psychological distress had a moderate and inverse relationship that was, statistically speaking, fully mediated by the level of work engagement (F=17·05, p<0·001, R2=0·16). The direct effect of job satisfaction on work engagement was positive and medium (according to Cohen, 1988) in strength.

Interpretation

The main finding of the study is that work engagement may mediate the impact of job satisfaction on teachers' psychological distress by lessening the effect of difficult working conditions. It further suggests that in order to mediate the effect of low job satisfaction on psychological distress of teachers, organisational policies and practices should focus on improving employees' work engagement. This means that, in developing job programmes for teachers in contexts characterised by difficult working conditions, the main focus must be to increase the level of subjective resources (eg, inner states, emotional activation, personal motivational processes) and workers' engagement rather than focusing primarily on job satisfaction.

Funding

None.  相似文献   
74.
Image file format is often a confusing aspect for someone wishing to process medical images. This article presents a demystifying overview of the major file formats currently used in medical imaging: Analyze, Neuroimaging Informatics Technology Initiative (Nifti), Minc, and Digital Imaging and Communications in Medicine (Dicom). Concepts common to all file formats, such as pixel depth, photometric interpretation, metadata, and pixel data, are first presented. Then, the characteristics and strengths of the various formats are discussed. The review concludes with some predictive considerations about the future trends in medical image file formats.  相似文献   
75.
76.
Prednisone and prednisolone are two anti‐inflammatory steroidal drugs listed by the World Anti‐Doping Agency (WADA) within the class of glucocorticoids, which are prohibited “in competition” and when administered systemically. Their presence in collected urine samples may be attributed, if no exogenous administration has occurred, to an in situ microbial formation from endogenous steroids. In this work, a gas chromatography coupled to carbon isotope ratio mass spectrometry (GC‐C‐IRMS) method was developed and validated to distinguish an exogenous origin from an endogenous one. Eight prednisone/prednisolone pharmaceutical preparations commercially available in Italy were analysed to establish an exogenous δ13C value reference range (?28.96 ± 0.39‰). No more than 25 mL of urine was processed and no derivatization nor intentional steroids structure modifications were performed before the GC‐C‐IRMS analysis. A first HPLC purification step was set up to isolate the three endogenous reference compounds (ERCs) selected (tetrahydro‐11‐deoxycortisol (THS), pregnanediol (PD), and pregnanetriol (PT)), while a second LC purification was necessary to separate prednisone from prednisolone. In the GC‐C‐IRMS analysis, two different GC run methods were set up to guarantee better sensitivity and selectivity for each compound. Both prednisone and prednisolone showed signals (m/z 44) with amplitudes within the method linearity range to a lower urinary concentration of 20 ng/mL (< WADA reporting level, 30 ng/mL). The method was fully validated according to WADA requirements. As a proof of concept, urine samples collected from two excretion studies in healthy male volunteers, after a prednisone or prednisolone administration, were analysed by the proposed method, demonstrating its applicability for the analysis of real samples.  相似文献   
77.
78.
The orexins A (oxA) and B are peptides discovered in the rat hypothalamus and successively found in some peripheral organs of the mammalian body. They binds two protein G-coupled receptors defined receptor 1 (ox1r) and 2 for orexins, the first of which is highly specific for oxA while the second binds both the peptides with equal affinity. This work aimed to detect the presence of oxA and ox1r in the testis of the South American camelid alpaca (Vicugna pacos) and investigate the role played by them on Leydig cell steroidogenesis. The species alpaca acquired, in the last years, increasing zootechnical interest for the quality of the wool produced and its breeding spread from the country of origin to USA, Australia and Europe. Immunohistochemistry allowed us to detect oxA in Leydig and Sertoli cells, spermatogonia, resting spermatocytes, round and oval spermatids. Ox1r-immunoreactivity was found in Leydig cells and round, oval and elongated spermatids. The expression of the two peptides in tissue extracts was established by using Western blotting technique. Such results demonstrated that in the alpaca testis exists in a cellular complex able to produce and/or internalize oxA. Finally, the effect of oxA on steroidogenesis was investigated by means of in vitro cultured thin testis slices which were added with oxA or/and Müllerian Inhibiting Substance (MIS), a steroidolitic agent basally produced by the Sertoli cell. OxA evoked increase of testosterone production while MIS a decrease. The consecutive addition of oxA and MIS, or vice versa, highlighted an antagonistic interplay between the two substances which has been thought to be the main molecular event at the basis of the oxA-stimulated steroidogenesis mechanism.  相似文献   
79.
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