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   1807篇
  免费   121篇
  国内免费   17篇
耳鼻咽喉   11篇
儿科学   45篇
妇产科学   51篇
基础医学   368篇
口腔科学   35篇
临床医学   107篇
内科学   344篇
皮肤病学   43篇
神经病学   108篇
特种医学   51篇
外科学   347篇
综合类   23篇
预防医学   142篇
眼科学   27篇
药学   95篇
中国医学   5篇
肿瘤学   143篇
  2023年   8篇
  2022年   12篇
  2021年   23篇
  2020年   22篇
  2019年   44篇
  2018年   44篇
  2017年   27篇
  2016年   35篇
  2015年   41篇
  2014年   57篇
  2013年   66篇
  2012年   114篇
  2011年   107篇
  2010年   77篇
  2009年   59篇
  2008年   83篇
  2007年   81篇
  2006年   75篇
  2005年   91篇
  2004年   85篇
  2003年   79篇
  2002年   74篇
  2001年   71篇
  2000年   41篇
  1999年   45篇
  1998年   15篇
  1997年   12篇
  1996年   9篇
  1995年   8篇
  1994年   9篇
  1992年   25篇
  1991年   33篇
  1990年   28篇
  1989年   28篇
  1988年   31篇
  1987年   33篇
  1986年   25篇
  1985年   16篇
  1984年   23篇
  1983年   19篇
  1979年   16篇
  1978年   22篇
  1977年   10篇
  1976年   8篇
  1975年   8篇
  1974年   12篇
  1972年   10篇
  1971年   12篇
  1969年   8篇
  1968年   13篇
排序方式: 共有1945条查询结果,搜索用时 15 毫秒
51.
We studied vasomotor activity of rat cerebral vessels. Peculiarities of endothelium-dependent reactions of cerebral arteries in induced arterial hypertension were revealed. Quantitative and qualitative relationships between the parameters of the vasomotor apparatus of cerebral arteries and parameters of circulatory homeostasis were determined. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 144, No. 7, pp. 36–38, July, 2007  相似文献   
52.

Background

Lumbar disc disease (LDD) is one of the leading causes of disability in the working‐age population. A functional single‐nucleotide polymorphism (SNP), +1184T→C, in exon 8 of the cartilage intermediate layer protein gene (CILP) was recently identified as a risk factor for LDD in the Japanese population (odds ratio (OR) 1.61, 95% CI 1.31 to 1.98), with implications for impaired transforming growth factorβ1 signalling.

Aim

To validate this finding in two different ethnic cohorts with LDD.

Methods

This SNP and flanking SNPs were analysed in 243 Finnish patients with symptoms of LDD and 259 controls, and in 348 Chinese subjects with MRI‐defined LDD and 343 controls.

Results and conclusion

The results showed no evidence of association in the Finnish (OR = 1.35, 95% CI 0.97 to 1.87; p = 0.14) or the Chinese (OR = 1.05, 95% CI 0.77 to 1.43; p = 0.71) samples, suggesting that cartilage intermediate layer protein gene is not a major risk factor for symptoms of LDD in Caucasians or in the general population that included individuals with or without symptoms.Lumbar disc disease (LDD) is one of the leading causes of disability in the working‐age population. Radiological changes indicative of LDD are common, but only a proportion develops complications such as disc herniation and sciatica. Although the aetiology of LDD is not well understood, there is strong evidence for the involvement of both genetic and environmental factors.1,2A recent study reported an association between LDD and a functional single‐nucleotide polymorphism (SNP) (rs2073711), +1184T→C, in exon 8 of the cartilage intermediate layer protein gene (CILP) in a Japanese group (odds ratio (OR) 1.61, 95% CI 1.31 to –1.98).3 The allelic change resulted in amino acid substitution Ile395Thr. CILP is expressed widely in intervertebral discs and its expression increases as disc degeneration progresses.3 CILP interacts directly with transforming growth factor (TGF)β1, inhibiting the TGFβ1‐mediated induction of extracellular matrix proteins such as aggrecan and collagen II.3 Functional studies showed that the C allele (coding for Thr395) increased binding and inhibition of TGFβ1, suggesting that regulation of TGFβ1 signalling by CILP plays a crucial role in the aetiology and pathogenesis of LDD.3Argument for a causal role would be strengthened if the same association could be replicated in a distinct population, and in clinical cases of LDD defined by MRI changes indicative of LDD in general. Therefore, we investigated the association between CILP polymorphisms and LDD in a Finnish sample with symptoms of LDD, and in a Chinese sample with only MRI‐defined LDD. These samples were informative in previous studies demonstrating association of LDD with the vitamin D receptor gene4 and the Gln326Trp (Trp2) allele of COL9A25 in Chinese and the Arg103Trp (Trp3) allele of COL9A3 in Finns.6 Thus, the Chinese sample is comparable with the Finnish dataset, and a correlation can then be drawn with the Japanese dataset.  相似文献   
53.
Background: Taxation and other policy measures have been implemented across the United States to curb the accessibility of substance use, especially among youth. While the inverse relationship between price and youth consumption is well known, available research on youth earned income and substance use is sparser, particularly among emerging adults. Objectives: We examined the association between emerging adult past-year personal income and 30-day substance use. Methods: We analyzed data from Wave 5 (n = 2,202) of the NEXT Generation Health Study, an annual survey study administered to a nationally representative sample of emerging adults in the U.S. Wave 5 (mean age = 20.28 years, SE = 0.02 years) was administered during the 2013–2014 academic year. After grouping participants into five levels of self-reported, pre-tax personal income, we used binomial logistic regression to examine the association between personal income and cigarette smoking, marijuana use, alcohol use, and heavy episodic drinking (HED). Results: In unadjusted models, those at certain levels of higher past-year income were more likely to smoke cigarettes, consume alcohol, or engage in HED at least once in the past 30 days. Several associations remained significant after controlling for covariates. Most associations were no longer significant after including perceived peer norms as additional covariates. Personal income was not associated with 30-day marijuana use in unadjusted or adjusted models. Conclusions/Importance: Higher earned income may provide emerging adults greater economic access to cigarettes and alcohol, but the association might be partly attenuated by social factors, particularly perceived peer norms.  相似文献   
54.
Although increasingly complex models have been proposed in mediation literature, there is no model nor software that incorporates the multiple possible generalizations of the simple mediation model jointly. We propose a flexible moderated mediation model allowing for (1) a hierarchical structure of clustered data, (2) more and possibly correlated mediators, and (3) an ordinal outcome. The motivating data set is obtained from a European study in nursing research. Patients' willingness to recommend their treating hospital was recorded in an ordinal way. The research question is whether such recommendation directly depends on system‐level features in the organization of nursing care, or whether these associations are mediated by 2 measurements of nursing care left undone and possibly moderated by nurse education. We have developed a Bayesian approach and accompanying program that takes all the above generalizations into account.  相似文献   
55.
56.
57.
Recombinant forms of HIV-1 contribute significantly to the ongoing epidemic. In the present study, we characterized the near full-length genome of one candidate HIV-1 CRF25_cpx strain originating in Cameroon, 06CM-BA-040. Viral RNA was extracted from plasma, and the genome was obtained using RT-PCR amplification to generate 10 overlapping fragments. Bootscanning, recombination breakpoint analysis, and phylogenetic trees confirmed that 06CM-BA-040 had a genomic structure consistent with two available CRF25_cpx reference sequences. The CRF25_cpx mosaic composition consisted of nine segments derived from subtypes A and G as well as unclassified (U) regions. Subtype G and CRF25_cpx clusters diverged from each other with long branch lengths but were distinct from other known subtypes with high bootstrap support (94%). The epidemiological significance of CRF25_cpx strains is unknown; however, the availability of additional genomic sequences will improve our understanding of the overall genetic diversity within this recombinant form of HIV-1.  相似文献   
58.
Epidermal growth factor (EGF) is a potent growth factor for many tissues including the gastrointestinal tract. EGF is present in the gut lumen and is absorbed through the mucosa in the developing animals. In addition, EGF has been found to alter the immune system. In this study, we investigated thein vitro effect of EGF on normal colonic lamina propria lymphocyte DNA synthesis and ornithine decarboxylase activity. Human colonic lamina propria lymphocytes were isolated by collagenase-EDTA digestion. The effect of EGF on Con A-stimulated lymphocyte thymidine incorporation was tested. We observed that EGF suppressed DNA synthesis and ornithine decarboxylase (ODC) activity in lamina propria lymphocytes. EGF did not alter the time course of thymidine incorporation into LPL stimulated by the combination of phorbol 12,13-dibutyrate (PDB) and ionomycin. Our data suggest that (1) EGF suppresses DNA synthesis in human colonic lamina propria lymphocytes as well as ODC activity and (2) this inhibition may be mediated through protein kinase C or calcium flux. We postulate that EGF may have a role in modulating the human gut immune system.This work was supported in part by grant CA43280 from the National Institutes of Health.  相似文献   
59.
60.
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