全文获取类型
收费全文 | 294090篇 |
免费 | 21672篇 |
国内免费 | 74篇 |
专业分类
315836篇 |
出版年
2021年 | 3119篇 |
2020年 | 2286篇 |
2019年 | 2736篇 |
2018年 | 4694篇 |
2017年 | 4293篇 |
2016年 | 5883篇 |
2015年 | 7093篇 |
2014年 | 8286篇 |
2013年 | 10941篇 |
2012年 | 12696篇 |
2011年 | 12392篇 |
2010年 | 8437篇 |
2009年 | 7277篇 |
2008年 | 10536篇 |
2007年 | 10524篇 |
2006年 | 9986篇 |
2005年 | 8991篇 |
2004年 | 9123篇 |
2003年 | 8451篇 |
2002年 | 8239篇 |
2001年 | 10802篇 |
2000年 | 10801篇 |
1999年 | 8195篇 |
1998年 | 3026篇 |
1997年 | 2806篇 |
1996年 | 2601篇 |
1995年 | 2395篇 |
1992年 | 6336篇 |
1991年 | 6433篇 |
1990年 | 6148篇 |
1989年 | 6184篇 |
1988年 | 5621篇 |
1987年 | 5375篇 |
1986年 | 4903篇 |
1985年 | 5090篇 |
1984年 | 4130篇 |
1983年 | 3553篇 |
1982年 | 2486篇 |
1979年 | 3919篇 |
1978年 | 3092篇 |
1977年 | 2812篇 |
1976年 | 2573篇 |
1975年 | 3170篇 |
1974年 | 3563篇 |
1973年 | 3433篇 |
1972年 | 3220篇 |
1971年 | 2926篇 |
1970年 | 2660篇 |
1969年 | 2607篇 |
1968年 | 2484篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
The development of tumorigenic conditions in the carcinogen-exposed rat colon was studied using selected morphological, histochemical, immunohistochemical and biochemical methods of analysis. Rats were treated with two carcinogens: 1,2-dimethylhydrazine and N-methyl-N'-nitro-N-nitrosoguanidine alone or with deoxycholic acid as a tumor promoter. It was found that 3 months after treatment of animals with the carcinogens the following changes were developed in colonic tissue: infiltration of lymphocytes in the mucous membrane, high increase in mitotic index among epithelial cells, negative reactions of colonic cells for neutral mucopolysaccharides and sulfomucins and positive reactions to carboxyl groups, nonsulfated acid mucosubstances and tissue polypeptide antigens. An increase in the activity of ornithine decarboxylase in colonic tissue was developed within the same time period and has been seen only in those tissues which were characterized by the development of precancerous conditions. Individual variations were observed in the manifestation of the studied parameters in rat neoplastic colonic tissues. It is suggested that these differences reflect an individual sensitivity of animals to carcinogens and the magnitude of the dysplastic processes induced in the colon. 相似文献
995.
996.
997.
Changes in composition of both total aerobes and anaerobes of rat intestinal microflora do not appear to affect the metabolism of taurolithocholic acid. 相似文献
998.
999.
1000.
E I Williams 《BMJ (Clinical research ed.)》1984,288(6411):119-121
A study was carried out in two large urban practices to determine the number of patients aged over 75 years who had had no contact with the primary care team during one year and to examine their medical and social characteristics. Although their general health was considered to be good, over half needed treatment or other action and half had no identifiable career. 相似文献