全文获取类型
收费全文 | 10259篇 |
免费 | 25篇 |
国内免费 | 37篇 |
专业分类
系统科学 | 30篇 |
丛书文集 | 48篇 |
教育与普及 | 30篇 |
理论与方法论 | 24篇 |
现状及发展 | 3998篇 |
研究方法 | 530篇 |
综合类 | 5493篇 |
自然研究 | 168篇 |
出版年
2012年 | 153篇 |
2011年 | 326篇 |
2010年 | 60篇 |
2009年 | 54篇 |
2008年 | 169篇 |
2007年 | 213篇 |
2006年 | 192篇 |
2005年 | 216篇 |
2004年 | 211篇 |
2003年 | 192篇 |
2002年 | 208篇 |
2001年 | 430篇 |
2000年 | 437篇 |
1999年 | 295篇 |
1996年 | 52篇 |
1994年 | 269篇 |
1992年 | 253篇 |
1991年 | 203篇 |
1990年 | 233篇 |
1989年 | 196篇 |
1988年 | 190篇 |
1987年 | 192篇 |
1986年 | 203篇 |
1985年 | 268篇 |
1984年 | 202篇 |
1983年 | 163篇 |
1982年 | 137篇 |
1981年 | 141篇 |
1980年 | 144篇 |
1979年 | 327篇 |
1978年 | 264篇 |
1977年 | 218篇 |
1976年 | 193篇 |
1975年 | 197篇 |
1974年 | 207篇 |
1973年 | 177篇 |
1972年 | 207篇 |
1971年 | 246篇 |
1970年 | 305篇 |
1969年 | 229篇 |
1968年 | 227篇 |
1967年 | 194篇 |
1966年 | 224篇 |
1965年 | 149篇 |
1959年 | 75篇 |
1958年 | 123篇 |
1957年 | 81篇 |
1956年 | 58篇 |
1954年 | 62篇 |
1948年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
831.
832.
833.
834.
835.
Limb buds of 11-day-old mouse embryos were cultured for 6 days with insulin, dibutyryl cAMP and X 537 A. The cartilage anlage was reduced by insulin and enlarged by dibutyryl cAMP and X 537 A. The effects are due to changes in the amount of intercellular substance. 相似文献
836.
Lipoperoxidation and drug-metabolizing enzymes were measured in livers and placentas of different mammal species during the perinatal perios. In placentas and fetal livers of rat, rabbit and guinea-pig, cofactor-supported lipoperoxidation was negligible, as were the activities of drug-oxidizing enzymes. Human fetal liver contained an intact drug-oxidizing electron transport chain, and lipoperoxidation activity was accordingly abserved. It is suggested that lesions mediated by lipoperoxidation may be possible in human fetus, but they are less probable in animal fetuses. 相似文献
837.
838.
Summary To obtain sporogonic stages of malaria free from microbial contaminants for in vitro studies,Anopheles stephensi were reared under sterile conditions using a mosquito cell line as larval food. The adult females, kept in sterile humidified containers and allowed to engorge on parasitemic hamsters, supported the sporogonic development of the rodent malarial parasitePlasmodium berghei. In 10 experiments, the proportion of infected mosquitoes varied from 0 to 92%, and the geometric mean number of oocysts per female mosquito from 2.5 to 58,6, with a range of 1 to 548. The average number of salivary gland sporozoites per infected mosquito was determined by direct sporozoite counts in the pooled homogenate of the thoraces of all female mosquitoes. In five experiments, it varied from 2.7×103 to 9.0×103. The sterile sporozoites, harvested on day 19 or 20 after the infective blood meal, were as infective for rodents as nonsterile ones.Supported in part by Public Health Service research grant AI 18345 from the National Institute of Allergy and Infectious Diseases, by a grant from the Agency of International Development DSPE-5542-G-SS-3042-00, and by a Charles and Johanna Busch award. 相似文献
839.
840.
The in situ activity of 3 beta-hydroxysteroid dehydrogenase was detected in clustered cells which showed steroid-producing morphology, within the capsule of the paraaortic lymph node. In light and electron microscopic studies, the positive reaction products were detected on intracapsular cell clusters. This result indicates that these unique cells may have a steroid secreting function within the lymph nodes. 相似文献