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   42652篇
  免费   3104篇
  国内免费   147篇
耳鼻咽喉   464篇
儿科学   1380篇
妇产科学   1181篇
基础医学   5908篇
口腔科学   510篇
临床医学   6256篇
内科学   8096篇
皮肤病学   713篇
神经病学   4370篇
特种医学   808篇
外国民族医学   1篇
外科学   3459篇
综合类   771篇
一般理论   45篇
预防医学   4915篇
眼科学   879篇
药学   2978篇
中国医学   80篇
肿瘤学   3089篇
  2023年   210篇
  2022年   168篇
  2021年   867篇
  2020年   479篇
  2019年   804篇
  2018年   934篇
  2017年   723篇
  2016年   806篇
  2015年   976篇
  2014年   1312篇
  2013年   1995篇
  2012年   3014篇
  2011年   3174篇
  2010年   1606篇
  2009年   1562篇
  2008年   2852篇
  2007年   3070篇
  2006年   3148篇
  2005年   3109篇
  2004年   3015篇
  2003年   2836篇
  2002年   2618篇
  2001年   380篇
  2000年   275篇
  1999年   377篇
  1998年   483篇
  1997年   420篇
  1996年   382篇
  1995年   364篇
  1994年   268篇
  1993年   282篇
  1992年   194篇
  1991年   205篇
  1990年   181篇
  1989年   177篇
  1988年   190篇
  1987年   152篇
  1986年   130篇
  1985年   150篇
  1984年   181篇
  1983年   186篇
  1982年   238篇
  1981年   171篇
  1980年   178篇
  1979年   110篇
  1978年   106篇
  1977年   110篇
  1976年   87篇
  1975年   72篇
  1974年   76篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
61.
Cationic block copolymers spontaneously assemble via electrostatic interactions with DNA molecules in aqueous solution giving rise to micellar structures that protect the DNA from enzymatic degradation both in vitro and in vivo. In addition, we have previously shown that they are safe, not immunogenic and greatly increased antigen-specific CTL responses following six intramuscular inoculations of a very low dose (1 μg) of the vaccine DNA as compared to naked DNA. Nevertheless, they failed to elicit detectable humoral responses against the antigen. To gain further insight in the potential application of this technology, here we show that a shorter immunization protocol based on two DNA intramuscular inoculations of 1 μg of DNA delivered by these copolymers and a protein boost elicits in mice broad (both humoral and cellular) and long-lasting responses and increases the antigen-specific Th1-type T cell responses and CTLs as compared to priming with naked DNA. These results indicate that cationic block copolymers represent a promising adjuvant and delivery technology for DNA vaccination strategies aimed at combating intracellular pathogens.  相似文献   
62.
The use of epidemiologic research designs and analytical methods is common in dietetics research. Food and nutrition professionals who seek to perform evidence-based practice or participate in research design, analysis, and communication need skills in the essentials of epidemiology. This is one of a series of monographs on research methodology that addresses these needs and supports the goals of the Board of Editors of the Journal of the American Dietetic Association to further enhance competency and skills. This monograph focuses on statistical approaches for univariate analyses used with the primary observational study designs associated with epidemiology. Tables illustrating the presentation and interpretation of these results are included.  相似文献   
63.

Background  

Total hip arthroplasty is a successful surgery, that fails at a rate of approximately 10% at ten years from surgery. Causes for failure are mainly aseptic loosening of one or both components partially due to wear of articular surfaces and partially to design. The present analysis aimed to identify risk factors and quantify their effects on aseptic failure.  相似文献   
64.
65.
66.
African Americans experience household food insecurity, ie, the limited availability of nutritionally adequate and safe food, or ability to acquire acceptable foods in socially acceptable ways, at three times the rate of non-Hispanic whites. Thirty percent of all African-American children live in food-insecure households. The purpose of this study was to identify characteristics associated with household food insecurity among a high-risk postpartum population. Two-hundred six low-income, African-American mother−infant dyads were recruited through the Special Supplemental Nutrition Program for Women, Infants, and Children clinics. The six-item US Department of Agriculture food security scale was used to classify households as food secure, marginally food secure, or food insecure. Multinomial logistic regression was used to estimate the association between selected maternal/household characteristics and household food-security status. Fifty-three percent of households were food secure, 34% were marginally food secure, and 13% were food insecure. Maternal education less than college (relative risk ratio [RRR]=0.46; 95% confidence interval [CI]: 0.22 to 0.98) was inversely associated with marginal food security. Depressive symptoms (RRR=1.09; 95% CI: 1.02 to 1.16) and having the baby's father in the household (RRR=3.46; 95% CI: 1.22 to 9.82) were associated with household food insecurity, while having a grandmother in the household (RRR=0.15; 95% CI: 0.03 to 0.80) was inversely associated with experiencing household food insecurity. Findings from this study suggest that young, low-income, African-American families with only one child are particularly susceptible to experiencing household food insecurity. Intergenerational support and transfer of knowledge can be a key protective attribute among low-income African-American households.  相似文献   
67.
68.
Evidence that genetic disposition for adult lactose intolerance significantly affects calcium intake, bone density, and fractures in postmenopausal women is presented. PCR-based genotyping of lactase gene polymorphisms may complement diagnostic procedures to identify persons at risk for both lactose malabsorption and osteoporosis. INTRODUCTION: Lactase deficiency is a common autosomal recessive condition resulting in decreased intestinal lactose degradation. A -13910 T/C dimorphism (LCT) near the lactase phlorizin hydrolase gene, reported to be strongly associated with adult lactase nonpersistence, may have an impact on calcium supply, bone density, and osteoporotic fractures in the elderly. MATERIALS AND METHODS: We determined LCT genotypes TT, TC, and CC in 258 postmenopausal women using a polymerase chain reaction-based assay. Genotypes were related to milk intolerance, nutritional calcium intake, intestinal calcium absorption, bone mineral density (BMD), and nonvertebral fractures. RESULTS: Twenty-four percent of all women were found to have CC genotypes and genetic lactase deficiency. Age-adjusted BMD at the hip in CC genotypes and at the spine in CC and TC genotypes was reduced by -7% to -11% depending on the site measured (p = 0.04). LCT(T/C-13910) polymorphisms alone accounted for 2-4% of BMD in a multiple regression model. Bone fracture incidence was significantly associated with CC genotypes (p = 0.001). Milk calcium intake was significantly lower (-55%, p = 0.004) and aversion to milk consumption was significantly higher (+166%, p = 0.01) in women with the CC genotype, but there were no differences in overall dietary calcium intake or in intestinal calcium absorption test values. CONCLUSION: The LCT(T/C-13910) polymorphism is associated with subjective milk intolerance, reduced milk calcium intake, and reduced BMD at the hip and the lumbar spine and may predispose to bone fractures. Genetic testing for lactase deficiency may complement indirect methods in the detection of individuals at risk for both lactose malabsorption and osteoporosis.  相似文献   
69.
70.
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