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   46478篇
  免费   4865篇
  国内免费   112篇
耳鼻咽喉   440篇
儿科学   1232篇
妇产科学   1096篇
基础医学   6947篇
口腔科学   1092篇
临床医学   5713篇
内科学   8543篇
皮肤病学   560篇
神经病学   4461篇
特种医学   1858篇
外国民族医学   57篇
外科学   5977篇
综合类   1008篇
一般理论   43篇
预防医学   5174篇
眼科学   1132篇
药学   3483篇
中国医学   25篇
肿瘤学   2614篇
  2021年   671篇
  2020年   412篇
  2019年   644篇
  2018年   722篇
  2017年   555篇
  2016年   615篇
  2015年   651篇
  2014年   973篇
  2013年   1539篇
  2012年   2047篇
  2011年   2075篇
  2010年   1257篇
  2009年   1094篇
  2008年   1977篇
  2007年   1973篇
  2006年   2015篇
  2005年   1921篇
  2004年   1953篇
  2003年   1725篇
  2002年   1701篇
  2001年   1493篇
  2000年   1615篇
  1999年   1383篇
  1998年   617篇
  1997年   532篇
  1996年   485篇
  1995年   483篇
  1994年   454篇
  1993年   419篇
  1992年   1077篇
  1991年   1118篇
  1990年   1026篇
  1989年   1016篇
  1988年   1020篇
  1987年   884篇
  1986年   880篇
  1985年   846篇
  1984年   707篇
  1983年   586篇
  1982年   390篇
  1981年   369篇
  1980年   357篇
  1979年   661篇
  1978年   519篇
  1977年   442篇
  1976年   422篇
  1975年   383篇
  1974年   439篇
  1973年   435篇
  1972年   377篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Aim : The study was designed to determine the effect of computerized nutrition information on consumer food choice in two workplace restaurants, one in which customers had to pay for their lunch and the other providing a free lunch. Methods : Customers entering the restaurants were asked to make selections from the menu on a computer screen. The energy, saturated fatty acids, non-milk extrinsic sugars and non-starch polysaccharide content of the meal selected was displayed graphically in proportion to the dietary reference values. They were given the opportunity to change their selected meal and the composition of all meals was recorded. Results : The nutritional composition of the first meal provoked 16% of customers to make a second selection. The proportion of energy in the first selection had been 31% higher for saturated fatty acids and 23% higher for non-milk extrinsic sugars than the first selection made by people who were satisfied with their first choice. In their second attempt they succeeded in reducing both nutrients to levels similar to those present in the meals selected by people who had been satisfied with their first selection. Customers>> selections for non-starch polysaccharide and energy did not differ between the groups. The main changes made by customers to achieve improved second choices were to omit dishes (44%), add dishes (19%), make changes within a menu category (46%), and make changes from one menu category to another (26%). Conclusion : It was concluded that provision of graphical nutrition information on a computer screen could be used by a subset of the users of both restaurants to enable them to improve their menu selections to a similar composition to that selected by the other people who used the computer system.  相似文献   
12.
Netlines     
  相似文献   
13.
14.
The effects of two promoters of hepatocarcinogenesis--phenobarbital and butylated hydroxytoluene (BHT)--on five hepatic biochemical parameters were examined in adult female rats. Phenobarbital given orally in two doses each of 110 mg/kg 21 and 4 hr before the rats were killed caused large increases in hepatic ornithine decarboxylase (ODC) activity and cytochrome P-450 content. Extending the number of phenobarbital treatments to five increased the hepatic enzyme induction and also caused a minor decrease in hepatic glutathione and a small increase in serum alanine aminotransferase activity. Two oral doses of 700 mg BHT/kg (20% of the LD50) caused hepatic DNA damage and induction of both ODC activity and cytochrome P-450 content. When the dose of BHT was reduced from 700 to 140 mg/kg no significant effects on the biochemical parameters were found. Both promoters of hepatocarcinogenesis were identified by their induction of ODC, a marker for promotional potential, but only BHT showed a potential for carcinogenic initiation. The biochemical parameters examined, particularly the alkaline elution technique for DNA damage, ornithine decarboxylase activity and serum alanine aminotransferase, may constitute a useful assay system for examining a compound's potential for carcinogenic initiation, carcinogenic promotion and cellular toxicity.  相似文献   
15.
16.
We have used a novel method to identify genes expressed in the hypothalamus which may be potentially involved in controlling food intake and energy metabolism. We assumed that food deprivation, a powerful stimulus of food intake, would stimulate the activity of neural pathways involved in feeding behavior which should be reflected in an increase in the synthesis of any relevant neuropeptide and its messenger RNA. A study of 5 neuropeptides in 5 strains of mice has identified neuropeptide Y (NPY) as a gene whose expression in the hypothalamus is controlled by nutritional status, suggesting that hypothalamic NPY neurons are a link in the neural network regulating feeding behavior and energy metabolism. In addition, we have studied the effect of the diabetes mutation on neuropeptide gene expression during fasting and refeeding. Our findings suggest that abnormal NPY and enkephalin gene expression in the hypothalamus may be two important determinants of the expression of the diabetes mutation.  相似文献   
17.
Power density producing damage at a probability of 0.5 (ie, damage threshold, DT-50) was determined for PMMA (with/without UV absorber) and Silicone intraocular lenses. Scattered light from a collinear diagnostic He:Ne beam was one of four damage monitors deployed to enhance the sensitivity of the system. In order of increasing laser resistance the following results were obtained: injection molded PMMA (1.9/GW/cm2) Silicone (2.63 GW/cm2) Lathe-cut PMMA (4.47 GW/cm2), Lathe-cut PMMA with UV absorber (8.32 GW/cm2), Cast-molded PMMA (12.30 GW/cm2). An analysis of variance revealed interclass differences significant at the .01 level. Cast-molded PMMA was the most laser-resistant IOL material.  相似文献   
18.
19.
20.
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