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   525篇
  免费   21篇
  国内免费   6篇
耳鼻咽喉   6篇
儿科学   42篇
妇产科学   5篇
基础医学   126篇
口腔科学   16篇
临床医学   62篇
内科学   65篇
皮肤病学   14篇
神经病学   9篇
特种医学   23篇
外科学   34篇
综合类   30篇
预防医学   72篇
眼科学   6篇
药学   20篇
中国医学   7篇
肿瘤学   15篇
  2022年   4篇
  2021年   12篇
  2020年   8篇
  2019年   9篇
  2017年   7篇
  2015年   12篇
  2014年   12篇
  2013年   14篇
  2012年   22篇
  2011年   18篇
  2010年   19篇
  2009年   17篇
  2008年   21篇
  2007年   25篇
  2006年   21篇
  2005年   19篇
  2004年   18篇
  2003年   18篇
  2002年   10篇
  2001年   12篇
  2000年   17篇
  1999年   9篇
  1998年   9篇
  1997年   13篇
  1996年   15篇
  1995年   10篇
  1994年   5篇
  1993年   7篇
  1992年   6篇
  1991年   11篇
  1990年   4篇
  1989年   9篇
  1988年   5篇
  1986年   6篇
  1985年   11篇
  1984年   10篇
  1983年   5篇
  1982年   6篇
  1980年   4篇
  1979年   7篇
  1978年   6篇
  1977年   11篇
  1976年   8篇
  1975年   10篇
  1974年   4篇
  1973年   4篇
  1970年   3篇
  1969年   7篇
  1968年   3篇
  1965年   4篇
排序方式: 共有552条查询结果,搜索用时 31 毫秒
91.
BACKGROUND: The potential of dietary habits to confound the association between alcohol consumption and health needs further study. OBJECTIVE: We examined whether eating habits differed according to alcohol consumption in a large cohort of French women. DESIGN: This was a cross-sectional study of the French cohort of the European Prospective Investigation into Cancer and Nutrition (E3N-EPIC). The cohort was established in 1990 and includes 100000 women born between 1925 and 1950. Dietary data were obtained between 1993 and 1995 by using self-administered food-frequency questionnaires. About 73000 questionnaires were analyzed, and women were placed into 7 categories of alcohol consumption. RESULTS: After adjustment for energy derived from alcohol, increasing alcohol consumption was associated with a higher total energy intake, a higher percentage of energy intake as protein and lipids, and higher intakes of cholesterol, fatty acids, retinol, iron, and vitamin E. Conversely, energy provided by carbohydrates decreased with increasing alcohol consumption, as did beta-carotene intake. Increasing alcohol consumption was associated with higher consumption of animal products, cheese, potatoes, oil, bread, and breakfast cereals and with lower consumption of vegetables and dairy products. CONCLUSION: In this population of middle-aged, highly educated French women, marked differences in dietary patterns and nutrient intakes were found according to alcohol consumption. Part of the detrimental effect of alcohol on health may be due to the less healthy dietary habits of drinkers. This points to a confounding role of eating habits and nutrient intakes in the relation between alcohol and health.  相似文献   
92.
OBJECTIVE: This paper describes a pilot project to develop and implement a low-cost system for ongoing surveillance of childhood asthma in Milwaukee County, Wisconsin. METHODS: The authors organized a planning workshop to solicit information and ideas for an asthma surveillance system, bringing together national experts with Milwaukee professionals and community representatives involved in the prevention and treatment of asthma. Based on recommendations from the workshop, a pilot surveillance project was implemented in Milwaukee County using records of emergency room visits and hospital admissions for asthma abstracted from the computerized billing records of the Children's Hospital of Wisconsin (CHW), retrospectively for 1993 and prospectively for 1994. Retrospective data were also sought from the other hospital emergency departments in Milwaukee County to evaluate the representativeness of the CHW data. Surveillance data were used to evaluate utilization of care by patient subgroups and to describe temporal patterns in emergency room visits. RESULTS: Of the emergency department visits for asthma in Milwaukee County in 1993, CHW accounted for 94% among infants less than 1 year of age, 89% among children ages 1 through 5 years, and only 59% among children between the ages of 6 and 18 years. In 1994, the 7% of asthmatic children with repeat hospital admissions accounted for 38% of all hospital admissions for asthma and the 20% with repeat emergency department visits accounted for 50% of all emergency visits. Emergency visits for asthma showed clear seasonality, with a peak in the fall and a smaller peak in the spring. CONCLUSIONS: Computerized medical billing data provide an opportunity for asthma surveillance at a relatively low cost. The data obtained are useful for tracking trends in exacerbations of asthma and the use of medical services for asthma care and should prove valuable in targeting interventions.  相似文献   
93.

Objectives

We assessed associations between community-level socioeconomic, demographic, and environmental characteristics, and the presence of two potentially waterborne infectious diseases, cryptosporidiosis and giardiasis, as reported to the Massachusetts Department of Public Health.

Methods

We created a series of maps showing the spatial distribution of cryptosporidiosis and giardiasis in Massachusetts (1993-2002) overall and by age, using logistic regression to analyze associations between community-level characteristics and the presence of at least one reported case of each disease. This analysis was repeated for communities with predominantly private water supplies.

Result

After adjusting for population size, higher population density and larger than average household sizes were associated with increased odds of reported cases of cryptosporidiosis. Giardiasis was also associated with high population density, but was not associated with household size. In the elderly, income was positively associated with the presence of giardiasis.

Discussion

These findings suggest that greater population density and larger household sizes may increase the likelihood of protozoan gastrointestinal infection. The results emphasize the necessity to account for distal factors, such as demographic characteristics, that may ultimately play a role in the transmission or reporting of disease.  相似文献   
94.
Different conclusions have been reached with regard to the effect of endothelin (ET-1) on cardiac contractility. We examined systolic and diastolic function in response to constant known concentrations of ET-1 with or without ET-1 induced reductions in coronary flow (CF). Rat hearts (n= 21) were buffer-perfused using constant coronary flow (cCF) or constant perfusion pressure (cPP). Left ventricular function was assessed isovolumically. Addition of ET-1 (10-9 M) in the cCF group caused a gradual increase in PP from 61 ± 2 to 165±6mmHg (mean±SE) (P < 0.01). Within 10 min left ventricular systolic pressure (LVSP) increased from 111 ± 2 to a maximum of 134±4mmHg (P < 0.01) and [L\dP/dt] increased from 1640 ± 81 to a maximum of 2020 ± 92 mmHg s“1 (P < 0.01). After 15 min left ventricular end diastolic pressure (LVEDP), a measure of diastolic stiffness (DS), also increased. With ET-1 (10 8 M), similar haemodynamic alterations appeared more rapidly. In the cPP group, ET-1 (10”9 M) caused a sharp decrease in CF and LVSP fell from 115 ± 8 to 62±12 mmHg at 10 min (P < 0.001). Systolic function remained stable at a reduced level for 1 h. DS did not change. Thus, ET-1 possesses positive inotropic effects and increases diastolic stiffness. Both effects may be masked by vasoconstriction-induced ischaemia.  相似文献   
95.
Oncogenic K-ras is one of the most common genetic alterations in human lung adenocarcinomas. In addition, inactivation of clusters of tumor suppressor genes is required to bring about classical characteristics of cancer including angiogenesis as a prelude to invasion and metastasis. Transforming growth factor-beta (TGF-beta) 1 is a tumor suppressor gene that is implicated in lung cancer progression. Although in vitro studies have shown that TGF-beta1 and Ras pathways cooperate during tumorigenesis, the biology of interaction of TGF-beta1 and Ras has not been studied in in vivo tumorigenesis. We hypothesized that inactivation of TGF-beta1 in addition to oncogeneic activation of K-ras would lead to early initiation and faster progression to lung adenocarcinoma and invasion and metastasis. Heterozygous (HT) TGF-beta1 mice were mated with latent activatable (LA) mutated K-ras mice to generate TGF-beta1(+/+), K-ras LA (wild-type (WT)/LA) and TGF-beta1(+/-), K-ras LA (HT/LA) mice. Both HT/LA and WT/LA mice developed spontaneous lung tumors, but HT/LA mice progressed to adenocarcinomas significantly earlier compared with WT/LA mice. In addition, WT/LA adenocarcinomas had significantly higher angiogenic activity compared with HT/LA adenocarcinomas. Thus, while oncogenic K-ras mutation and insensitivity to the growth regulatory effects of TGF-beta1 is essential for initiation and progression of mouse lung tumors to adenocarcinoma, a full gene dosage of TGF-beta1 is required for tumor-induced angiogenesis and invasive potential. This study identifies a number of genes not previously associated with lung cancer that are involved in tumor induction and progression. In addition, we provide evidence that progression to invasive angiogenic lesions requires TGF-beta1 responsiveness in addition to Ras mutation.  相似文献   
96.
MPL exon 10 mutations were the second class of mutations shown to be associated with the pathogenesis of some Philadelphia chromosome - negative myeloproliferative neoplasms (MPNs). Recently, their identification gained wide recognition in the diagnostic work-up for suspected cases of JAK2 V617F negative MPNs. Various molecular approaches have been applied, yet universally accepted method is still lacking. We aimed at development and validation of a novel bead-based liquid assay using Locked nucleic acids (LNA)-modified oligonucleotide probes for multiplexed detection of the following MPL mutations: W515L/K/A/R. Testing on both artificial plasmid constructs and on clinical samples revealed that the method was comparable in terms of specificity to direct sequencing and had a much higher sensitivity of 1% mutant alleles. This method could be successfully implemented in the diagnostic work-up for MPNs. Furthermore, this system allows further multiplexing for single-tube identification of different mutations associated with MPNs.  相似文献   
97.
The surface-associated glycopeptides gp40, one of the most polymorphic Cryptosporidium antigens, and gp15, one of the most immunodominant Cryptosporidium antigens, are putative vaccine candidates because they mediate infection in vitro and induce immune responses in vivo. We evaluated antibody responses to these antigens before and after the first episode of symptomatic cryptosporidiosis in 51 children from a birth cohort study in an area in South India where Cryptosporidium is endemic and a major cause of parasitic diarrhea. IgG levels to gp15 and to homotypic and heterotypic gp40 antigens were measured in pre- and postdiarrheal sera by enzyme-linked immunosorbent assay (ELISA). There was a significant IgG response to gp15 (P < 0.001) following the first episode of cryptosporidial diarrhea. Using a general additive model, we determined the estimated time of the peak IgG response to gp15 to be 9.3 weeks (confidence interval, 5.2 to 13.4) following the diarrheal episode. In a subset of 30 children infected with Cryptosporidium hominis subtype Ia, there was a significant difference in IgG responses to homotypic C. hominis Ia and to heterotypic Cryptosporidium parvum II gp40 antigens (P = 0.035). However, there was also a significant correlation (P = 0.001) in the responses to both antigens in individual children, suggesting that while responses are in part subtype specific, there is significant cross-reactivity to both antigens. This is the first report of the characterization of immune responses to cryptosporidiosis in Indian children and the first study to investigate human immune responses to the polymorphic gp40 antigen. However, further studies are needed to determine whether immune responses to these antigens are protective against subsequent infections.  相似文献   
98.

Background  

Weight-bearing and high intensity physical activities are particularly beneficial for stimulating bone growth in children given that bone responds favorably to mechanical load. While it is important to assess the contribution and impact of weight-bearing physical activity on health outcomes, measurement tools that quantify and provide information on these activities separately from overall physical activity are limited. This study describes the development and evaluation of a pictorial physical activity survey (PAS) that measures children's participation and knowledge of high-intensity, weight-bearing ("bone smart") physical activity.  相似文献   
99.
OBJECTIVE: To investigate childhood to adulthood weight change associated with anxiety and depression. DESIGN: The Children in the Community Study. A prospective longitudinal investigation. SETTING: Albany and Saratoga Counties, New York. PARTICIPANTS: Eight hundred twenty individuals (403 females and 417 males) assessed at 4 time points: in 1983 when they were 9 to 18 years old (n = 776), in 1985 to 1986 when they were 11 to 22 years old (n = 775), in 1991 to 1994 when they were 17 to 28 years old (n = 776), and in 2001 to 2003 when they were 28 to 40 years old (n = 661). MAIN EXPOSURES: Anxiety disorders and depression assessed by structured diagnostic interview. MAIN OUTCOME MEASURES: Centers for Disease Control and Prevention body mass index z score (BMIz), a measure of weight status; and association of anxiety and depression with BMIz level and annual change. RESULTS: In females, anxiety disorders were associated with higher weight status, a BMIz of 0.13 (95% confidence interval, 0.01-0.25) units higher compared with females without anxiety disorders. Female depression was associated with a gain in BMIz of 0.09 units/y (95% confidence interval, 0.03-0.15 units/y), modified by the age when depression was first observed, such that early depression onset was associated with a higher subsequent BMIz than depression onset at older ages. In males, childhood depression was associated with a lower BMIz (-0.46; 95% confidence interval, -0.93 to 0.02 units lower at the age of 9 years), but BMIz trajectories for males with or without depression converged in adulthood; male anxiety disorders were not substantively associated with weight status. CONCLUSIONS: Anxiety disorders and depression were associated with a higher BMIz in females, whereas these disorders in males were not associated with a higher BMIz. These results, if causal and confirmed in other prospective studies, support treating female anxiety and depression as part of comprehensive obesity prevention efforts.  相似文献   
100.
Summary We used a combination of genetic hybridization analysis and electrokaryotyping with radioactively labelled MEL1 gene probe hybridization to isolate and identify seven polymeric genes for the fermentation of melibiose in strain CBS 5378 of Saccharomyces cerevisiae (syn. norbensis). Four of the MEL genes, i.e. MEL3, MEL4, MEL6 and MEL7, were allelic to those found in S. cerevisiae strain CBS 4411 (syn. S. oleaginosus) whereas three genes, i.e. MEL8, MEL9 and MEL10 occupied new loci. Electrokaryotyping showed that all seven MEL genes in CBS 5378 were located on different chromosomes. The new MEL8, MEL9 and MEL10 genes were found on chromosomes XV, X/XIV and XII, respectively.  相似文献   
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