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   1668篇
  免费   118篇
  国内免费   20篇
耳鼻咽喉   12篇
儿科学   40篇
妇产科学   57篇
基础医学   285篇
口腔科学   29篇
临床医学   120篇
内科学   299篇
皮肤病学   50篇
神经病学   231篇
特种医学   37篇
外科学   153篇
综合类   19篇
一般理论   1篇
预防医学   198篇
眼科学   37篇
药学   100篇
中国医学   20篇
肿瘤学   118篇
  2024年   2篇
  2023年   7篇
  2022年   40篇
  2021年   61篇
  2020年   43篇
  2019年   69篇
  2018年   62篇
  2017年   57篇
  2016年   47篇
  2015年   73篇
  2014年   87篇
  2013年   100篇
  2012年   145篇
  2011年   145篇
  2010年   70篇
  2009年   70篇
  2008年   121篇
  2007年   115篇
  2006年   105篇
  2005年   105篇
  2004年   89篇
  2003年   61篇
  2002年   58篇
  2001年   7篇
  2000年   3篇
  1999年   4篇
  1998年   12篇
  1997年   14篇
  1996年   4篇
  1995年   8篇
  1994年   5篇
  1993年   1篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1988年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1973年   2篇
  1968年   1篇
  1905年   1篇
排序方式: 共有1806条查询结果,搜索用时 12 毫秒
1.
Immortalized cell lines offer significant logistical advantages over primary cells when used for in-vitro studies. Immortalized cells may, however, exhibit important differences relative to their primary cell counterparts. In this study, microarrays were used to make a genome-wide comparison between primary human umbilical vein endothelial cells (HUVECs) and EA.hy926, an immortalized HUVEC cell line, in their baseline properties and in their response to inhibition of the mevalonate pathway with an inhibitor of hydroxy methylglutaryl-coenzyme A reductase (statin). HUVECs and EA.hy926 were incubated with control medium, atorvastatin, mevalonate, or a combination of atorvastatin and mevalonate for 24 h. Gene expression profiles were obtained in duplicates using Affymetrix Human Genome U133A 2.0 arrays (Santa Clara, California, USA). Probe-sets were selected according to the following criteria: a twofold or greater increase/decrease in atorvastatin-treated cells compared with untreated cells; a twofold or greater reversal of the effect of atorvastatin by combined treatment with atorvastatin and mevalonate; no significant change in gene expression in cells treated with mevalonate alone compared with untreated cells. Most genes that were expressed by untreated HUVECs, were also expressed by untreated EA.hy926 cells. EA.hy926 cells, however, constitutively expressed a large number of additional genes, many of which were related to cell cycle control and apoptosis. Atorvastatin induced differential expression (> or = twofold) of 103 genes in HUVECs (10 up, 93 down) and 466 genes in EA.hy926 cells (198 up, 268 down). Applying the above selection criteria, thrombomodulin and tissue plasminogen activator were up-regulated in both cell types, whereas, connective tissue growth factor, thrombospondin-1, and cysteine-rich angiogenic inducer 61 were down-regulated. In conclusion, EA.hy926 cells retain most of the characteristics of endothelial cells under baseline conditions as well as after treatment with atorvastatin. It is necessary, however, to carefully select and validate changes in genes that are the focus of studies when using EA.hy926 cells. While this cell line is highly useful in studies on some genes, including genes encoding molecules involved in regulating thrombohemorrhagic homeostasis, they appear to be less suited for studies focused on other genes, particularly those involved in the regulation of cell proliferation and apoptosis.  相似文献   
2.
AIMS: The developing world is particularly at risk of an increasing health burden due to an increased prevalence of Chronic Obstructive Pulmonary Disease (COPD) secondary to increasing tobacco consumption. However, research is scarce. The objectives of this study were to assess the current competence for diagnosing COPD in primary care in a resource-limited setting in Brazil, and to develop a local patient profile for case-finding. METHODS: 34 general practitioners (GPs) in five areas of northern Brazil recruited adult patients with principal complaints of cough and/or shortness of breath who then had spirometry (n = 142). RESULTS: For the dichotomous variable 'COPD' the degree of agreement between GP diagnosis (n = 64, 18.3%) and spirometric outcome (n = 36, 25.4%) was poor, with Kappa = 0.055 (SE 0.087) and DOR = 1.35. False-positive and false-negative diagnosis proportions were 19.8% and 75%, respectively. Independent risk factors were 'smoking history of more than five pack years' and 'presence of both dyspnoea and cough'. It requires the testing of 2.2 smokers with more than five pack years to detect one patient at risk. CONCLUSIONS: COPD is a common yet underdiagnosed disease in Brazilian primary care. Spirometry improves diagnostic competence and case-finding substantially. If applied in a pre-selected high-risk population, we believe spirometry can be a cost-effective diagnostic tool for case-finding in the resource-limited setting. This study provides important baseline information for effective guideline implementation.  相似文献   
3.
BACKGROUND: The purpose of this study was to describe the health status and work limitations in injured workers with musculoskeletal disorders at 1 month post-injury, stratified by return-to-work status, and to document their return-to-work trajectories 6 months post-injury. METHODS: A sample of 632 workers with a back or upper extremity musculoskeletal disorder, who filed a Workplace Safety and Insurance Board lost-time claim injury, participated in this prospective study. Participants were assessed at baseline (1 month post-injury) and at 6 months follow-up. RESULTS: One month post-injury, poor physical health, high levels of depressive symptoms and high work limitations are prevalent in workers, including in those with a sustained first return to work. Workers with a sustained first return to work report a better health status and fewer work limitations than those who experienced a recurrence of work absence or who never returned to work. Six months post-injury, the rate of recurrence of work absence in the trajectories of injured workers who have made at least one return to work attempt is high (38%), including the rate for workers with an initial sustained first return to work (27%). CONCLUSIONS: There are return-to-work status specific health outcomes in injured workers. A sustained first return to work is not equivalent to a complete recovery from musculoskeletal disorders.  相似文献   
4.
BACKGROUND: Apple allergy is dominated by IgE antibodies against Mal d 1 in areas where birch pollen is endemic. Apples with significantly decreased levels of Mal d 1 would allow most patients in these areas to eat apples without allergic reactions. OBJECTIVE: The aim of this study was to inhibit the expression of Mal d 1 in apple plants by RNA interference. METHODS: In vitro -grown apple plantlets were transformed with a construct coding for an intron-spliced hairpin RNA containing a Mal d 1-specific inverted repeat sequence separated by a Mal d 1-specific intron sequence. The presence of the construct in transformants was checked by PCR. Expression of Mal d 1 in leaves was monitored by prick-to-prick skin testing in 3 patients allergic to apples and by immunoblotting with a Mal d 1-reactive mAb and with IgE antibodies against Mal d 1. RESULTS: After transformation, plantlets were selected on the basis of having a normal phenotype and growth rate. With PCR, in 6 of 9 selected plantlets, the presence of the gene-silencing construct was demonstrated. By skin prick test it was shown that a wild-type plantlet had significantly ( P < .05) higher allergenicity than 5 of the transformants. Reduction of expression of Mal d 1 was confirmed by immunoblotting. In wild-type and unsuccessful transformants, a strong band was detected with Mal d 1-reactive mAb 5H8 at the expected apparent M r of 17 kDa. This band was virtually absent in the transformants that carried the gene-silencing construct. With human IgE antibodies, the same observations were made. CONCLUSIONS: Mal d 1 expression was successfully reduced by RNA interference. This translated into significantly reduced in vivo allergenicity. These observations support the feasibility of the production by gene silencing of apples hypoallergenic for Mal d 1.  相似文献   
5.
6.
The caspase recruitment domain gene CARD15/NOD2, encoding a cellular receptor involved in an NF-kappaB-mediated pathway of innate immunity, was first identified as a major susceptibility gene for Crohn's disease (CD), and more recently, as responsible for Blau syndrome (BS), a rare autosomal-dominant trait characterized by arthritis, uveitis, skin rash and granulomatous inflammation. While CARD15 variants associated with CD are located within or near the C-terminal leucine-rich repeat domain and cause decreased NF-kappaB activation, BS mutations affect the central nucleotide-binding NACHT domain and result in increased NF-kappaB activation. In an Italian family with BS, we detected a novel mutation E383K, whose pathogenicity is strongly supported by cosegregation with the disease in the family and absence in controls, and by the evolutionary conservation and structural role of the affected glutamate close to the Walker B motif of the nucleotide-binding site in the NACHT domain. Interestingly, substitutions at corresponding positions in another NACHT family member cause similar autoinflammatory phenotypes.  相似文献   
7.
The aim of this study was to investigate whether the effect of bacillus Calmette-Guérin (BCG) immunization on ovalbumin-induced allergic inflammation in a rat model depends on the genetic predisposition to react with a T helper cell (Th) 2-type cytokine response. This study was performed in an inbred Th2-predisposed "asthma prone" rat strain (brown Norway [BN]) and in an outbred nonpredisposed strain (Sprague Dawley [SD]), to differentiate between genetic and environmental factors. BCG decreased numbers of lung eosinophils and macrophages in the SD rat. This effect was not seen in the BN rat. In the BN rat, but not in the SD rat, BCG downregulated levels of total serum IgE. No significant differences were found with respect to frequencies of IFNgamma- or interleukin-4-producing cells in the lung in both rat strains. These results indicate that the degree and pathway of immunomodulatory effect of BCG in two genetically different rat strains is dependent on the genetic predisposition to develop a Th2-type response. Therefore, differences in genotype in relation to environment may result in difference in involvement of contributing pathogenic factors and thus different responsiveness to therapeutic strategies.  相似文献   
8.
Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder characterized by oculocutaneous albinism and a platelet storage pool deficiency. Some patients also develop fatal pulmonary fibrosis and some have granulomatous colitis. Six human genes HPS1, ADB3A, HPS3, HPS4, HPS5, and HPS6 have been identified as cause of the six known subtypes of HPS. While there exist nearly 500 Puerto Rican and non-Puerto Rican HPS-1 patients, very few HPS-4 patients have been reported, and most of these have not been described in detail. We now delineate the clinical characteristics of an HPS-4 patient homozygous for a novel HPS-4 mutation, P685delC. The patient, the first individual with HPS reported from Sri Lanka, had severe pulmonary fibrosis, typical of HPS-1 disease, without granulomatous colitis. We conclude that pulmonary fibrosis occurs as part of HPS-4 and that HPS should be considered in all ethnic groups.  相似文献   
9.
10.
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