全文获取类型
收费全文 | 48536篇 |
免费 | 5202篇 |
国内免费 | 109篇 |
专业分类
耳鼻咽喉 | 441篇 |
儿科学 | 1304篇 |
妇产科学 | 1130篇 |
基础医学 | 6978篇 |
口腔科学 | 1125篇 |
临床医学 | 5772篇 |
内科学 | 8732篇 |
皮肤病学 | 557篇 |
神经病学 | 4480篇 |
特种医学 | 1903篇 |
外国民族医学 | 57篇 |
外科学 | 6027篇 |
综合类 | 997篇 |
一般理论 | 43篇 |
预防医学 | 7010篇 |
眼科学 | 1136篇 |
药学 | 3453篇 |
中国医学 | 24篇 |
肿瘤学 | 2678篇 |
出版年
2021年 | 681篇 |
2020年 | 495篇 |
2019年 | 668篇 |
2018年 | 807篇 |
2017年 | 650篇 |
2016年 | 702篇 |
2015年 | 728篇 |
2014年 | 1046篇 |
2013年 | 1672篇 |
2012年 | 2052篇 |
2011年 | 2096篇 |
2010年 | 1336篇 |
2009年 | 1195篇 |
2008年 | 2022篇 |
2007年 | 2020篇 |
2006年 | 2066篇 |
2005年 | 1959篇 |
2004年 | 1987篇 |
2003年 | 1737篇 |
2002年 | 1773篇 |
2001年 | 1572篇 |
2000年 | 1661篇 |
1999年 | 1496篇 |
1998年 | 738篇 |
1997年 | 700篇 |
1996年 | 670篇 |
1995年 | 599篇 |
1994年 | 486篇 |
1993年 | 517篇 |
1992年 | 1088篇 |
1991年 | 1122篇 |
1990年 | 1036篇 |
1989年 | 1032篇 |
1988年 | 1036篇 |
1987年 | 898篇 |
1986年 | 894篇 |
1985年 | 860篇 |
1984年 | 710篇 |
1983年 | 596篇 |
1982年 | 396篇 |
1981年 | 372篇 |
1980年 | 356篇 |
1979年 | 670篇 |
1978年 | 523篇 |
1977年 | 446篇 |
1976年 | 429篇 |
1975年 | 388篇 |
1974年 | 443篇 |
1973年 | 436篇 |
1972年 | 379篇 |
排序方式: 共有10000条查询结果,搜索用时 11 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.
13.
F Brown 《British medical journal》1987,295(6594):347-348
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.
S C Chua A W Brown J Kim K L Hennessey R L Leibel J Hirsch 《Brain research. Molecular brain research》1991,11(3-4):291-299
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.