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   1827篇
  免费   231篇
  2058篇
  2022年   10篇
  2021年   18篇
  2020年   20篇
  2019年   20篇
  2018年   23篇
  2017年   22篇
  2016年   32篇
  2015年   55篇
  2014年   76篇
  2013年   66篇
  2012年   96篇
  2011年   96篇
  2010年   66篇
  2009年   66篇
  2008年   85篇
  2007年   106篇
  2006年   91篇
  2005年   69篇
  2004年   71篇
  2003年   71篇
  2002年   69篇
  2001年   68篇
  2000年   59篇
  1999年   48篇
  1998年   31篇
  1997年   26篇
  1996年   25篇
  1995年   12篇
  1994年   12篇
  1993年   15篇
  1992年   29篇
  1991年   36篇
  1990年   32篇
  1989年   39篇
  1988年   32篇
  1987年   34篇
  1986年   21篇
  1985年   36篇
  1984年   26篇
  1983年   28篇
  1982年   15篇
  1981年   14篇
  1980年   16篇
  1979年   13篇
  1978年   15篇
  1977年   19篇
  1975年   19篇
  1974年   12篇
  1973年   8篇
  1972年   9篇
排序方式: 共有2058条查询结果,搜索用时 0 毫秒
51.
A case report of a patient with myelosarcomatosis of the skin six months preceding leukemic generalization of acute myelomonocytic leukemia is presented. To the best of our knowledge this is the first case of a myelosarcoma with generalized skin involvement diagnosed before development of an overt myeloproliferative disease.  相似文献   
52.
A total of 226 individuals (101 males and 125 females), from La Sabana, a Venezuelan Negroid isolate, with ages between 8 and 60 years, were studied in order to characterize the population for its craniofacial variables and to study the behavior of these variables in relation to age and sex. The variables studied were grouped in three categories: direct cephalometric variables, which included 6 measurements taken directly on the individuals; indirect cephalometric variables, which included 18 measurements (9 angular and 9 linear), taken on lateral head films; and dental variables, which included 9 measurements taken from dental models. In general the direct variables showed the lowest coefficients of variation (CV), suggesting homogeneity within this sample. They were followed by the dental and the indirect variables, which had the highest CV values. In order to detect age and sex effects on the variables, sex and age group comparisons were performed with Student t tests. A greater proportion of significant differences were found among the direct variables, indicating that age and sex have more influence on this group of variables than upon the other two. Comparisons of our sample from La Sabana, with samples from African Negroid, Caucasoid, and Amerindian population show that La Sabana individuals have a craniofacial pattern basically Negroid, as we expected, although some contribution from Caucasoides and especially Amerindians is also suggested in our data.  相似文献   
53.
Since 1971, several inert particles have been tested and proposed for HBs antigen screening, none of them being really used in routine. An evaluation is realized and presented, pointing out the main characteristics and the practical problems. We report our experience on two types of latex, simultaneously conducted through manual techniques and through Groupamatic 360 equipments. For one of them, TG Antigex, sensitivity and specificity are very satisfying and several batches are presently tested in order to quantify the reproducibility and stability features of the reagent.  相似文献   
54.
The ability to add or delete specific genes in swine will likely provide considerable benefits not just to agriculture but also to medicine, where pigs have potential as models for human disease and as organ donors. Here we have transferred nuclei from a genetically modified fibroblast cell line to porcine oocytes, matured in vitro under defined culture conditions, to create piglets expressing enhanced green fluorescent protein. The nuclear transfer-derived piglets were of normal size, although some mild symptoms of “large offspring syndrome” were evident. These experiments represent a next step towards creating swine with more useful genetic modifications.  相似文献   
55.

Setting

The “Thibela TB” cluster randomised trial of community-wide isoniazid preventive therapy (IPT) to reduce tuberculosis incidence in the South African gold mines.

Objectives

To determine the proportion of participants eligible for IPT and the reasons and risk factors for ineligibility, to inform the scale-up of IPT.

Design

Cross-sectional survey of participants in intervention clusters (mine shafts) consenting to tuberculosis screening and assessment for eligibility to start IPT.

Results

Among 27,126 consenting participants, 94.7% were male, the median age was 41 years, 12.2% reported previous tuberculosis, 0.6% reported ever taking IPT and 2.5% reported currently taking antiretroviral therapy. There were 24,430 (90.1%) assessed as eligible to start IPT, of whom 23,659 started IPT. The most common reasons for ineligibility were having suspected tuberculosis that was subsequently confirmed by a positive smear and/or culture (n=705), excessive alcohol consumption (n=427) and being on tuberculosis treatment at time of initial screen (n=241). Ineligibility was associated with factors including older age, female gender, prior history of tuberculosis and being in “HIV care”. However, at least 78% were eligible for IPT in all of these sub-groups.

Conclusions

The vast majority of participants in this community-wide intervention were eligible for IPT.  相似文献   
56.

Background

Previous studies have suggested that melatonin may produce antinociception through peripheral and central mechanisms. Based on the preliminary encouraging results of studies of the effects of melatonin on pain modulation, the important question has been raised of whether there is a dose relationship in humans of melatonin on pain modulation.

Objective

The objective was to evaluate the analgesic dose response of the effects of melatonin on pressure and heat pain threshold and tolerance and the sedative effects.

Methods

Sixty-one healthy subjects aged 19 to 47 y were randomized into one of four groups: placebo, 0.05 mg/kg sublingual melatonin, 0.15 mg/kg sublingual melatonin or 0.25 mg/kg sublingual melatonin. We determine the pressure pain threshold (PPT) and the pressure pain tolerance (PPTo). Quantitative sensory testing (QST) was used to measure the heat pain threshold (HPT) and the heat pain tolerance (HPTo). Sedation was assessed with a visual analogue scale and bispectral analysis.

Results

Serum plasma melatonin levels were directly proportional to the melatonin doses given to each subject. We observed a significant effect associated with dose group. Post hoc analysis indicated significant differences between the placebo vs. the intermediate (0.15 mg/kg) and the highest (0.25 mg/kg) melatonin doses for all pain threshold and sedation level tests. A linear regression model indicated a significant association between the serum melatonin concentrations and changes in pain threshold and pain tolerance (R2 = 0.492 for HPT, R2 = 0.538 for PPT, R2 = 0.558 for HPTo and R2 = 0.584 for PPTo).

Conclusions

The present data indicate that sublingual melatonin exerts well-defined dose-dependent antinociceptive activity. There is a correlation between the plasma melatonin drug concentration and acute changes in the pain threshold. These results provide additional support for the investigation of melatonin as an analgesic agent. Brazilian Clinical Trials Registry (ReBec): (U1111-1123-5109). IRB: Research Ethics Committee at the Hospital de Clínicas de Porto Alegre.  相似文献   
57.
58.
Ubiquitin-like containing PHD and Ring finger 1 (UHRF1) contributes to silencing of tumor suppressor genes by recruiting DNA methyltransferase 1 (DNMT1) to their hemi-methylated promoters. Conversely, demethylation of these promoters has been ascribed to the natural anti-cancer drug, epigallocatechin-3-gallate (EGCG). The aim of the present study was to investigate whether the UHRF1/DNMT1 pair is an important target of EGCG action. Here, we show that EGCG down-regulates UHRF1 and DNMT1 expression in Jurkat cells, with subsequent up-regulation of p73 and p16INK4A genes. The down-regulation of UHRF1 is dependent upon the generation of reactive oxygen species by EGCG. Up-regulation of p16INK4A is strongly correlated with decreased promoter binding by UHRF1. UHRF1 over-expression counteracted EGCG-induced G1-arrested cells, apoptosis, and up-regulation of p16INK4A and p73. Mutants of the Set and Ring Associated (SRA) domain of UHRF1 were unable to down-regulate p16INK4A and p73, either in the presence or absence of EGCG. Our results show that down-regulation of UHRF1 is upstream to many cellular events, including G1 cell arrest, up-regulation of tumor suppressor genes and apoptosis.  相似文献   
59.
IntroductionDespite the advocacy that diet may be a significant contributor to cancer prevention, there is a lack of direct evidence from epidemiological and experimental studies to substantiate such claims. Experimental studies suggest that n-3 polyunsaturated fatty acids (n-3 PUFA) from marine oils may reduce breast cancer risk, however, findings are equivocal. Thus, in this study, novel transgenic mouse models were employed to provide, for the first time, direct evidence for an anti-cancer role of n-3 PUFA in mammary tumorigenesis.Methodsfat-1 Mice, which are capable of endogenous n-3 PUFA synthesis, were bred with mouse mammary tumor virus (MMTV)-neu(ndl)-YD5 mice, an aggressive breast cancer model. The resultant offspring, including novel hybrid progeny, were assessed for tumor onset, size and multiplicity as well as n-3 PUFA composition in mammary gland and tumor tissue. A complementary group of MMTV-neu(ndl)-YD5 mice were fed n-3 PUFA in the diet.ResultsMice expressing MMTV-neu(ndl)-YD5 and fat-1 displayed significant (P<.05) reductions in tumor volume (~30%) and multiplicity (~33%), as well as reduced n-6 PUFA and enriched n-3 PUFA in tumor phospholipids relative to MMTV-neu(ndl)-YD5 control mice. The effect observed in hybrid progeny was similarly observed in n-3 PUFA diet fed mice.ConclusionUsing complementary genetic and conventional dietary approaches we provide, for the first time, unequivocal experimental evidence that n-3 PUFA is causally linked to tumor prevention.  相似文献   
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