全文获取类型
收费全文 | 56690篇 |
免费 | 643篇 |
国内免费 | 904篇 |
专业分类
系统科学 | 850篇 |
丛书文集 | 1136篇 |
教育与普及 | 646篇 |
理论与方法论 | 259篇 |
现状及发展 | 18617篇 |
研究方法 | 1666篇 |
综合类 | 34444篇 |
自然研究 | 619篇 |
出版年
2014年 | 630篇 |
2013年 | 789篇 |
2012年 | 1081篇 |
2011年 | 1744篇 |
2010年 | 835篇 |
2009年 | 815篇 |
2008年 | 1454篇 |
2007年 | 1624篇 |
2006年 | 1418篇 |
2005年 | 1367篇 |
2004年 | 1247篇 |
2003年 | 1099篇 |
2002年 | 1149篇 |
2001年 | 1705篇 |
2000年 | 1658篇 |
1999年 | 1673篇 |
1998年 | 981篇 |
1997年 | 973篇 |
1996年 | 922篇 |
1995年 | 824篇 |
1994年 | 813篇 |
1993年 | 665篇 |
1992年 | 1245篇 |
1991年 | 1019篇 |
1990年 | 1043篇 |
1989年 | 991篇 |
1988年 | 877篇 |
1987年 | 880篇 |
1986年 | 758篇 |
1985年 | 822篇 |
1984年 | 656篇 |
1983年 | 522篇 |
1981年 | 504篇 |
1980年 | 621篇 |
1979年 | 1278篇 |
1978年 | 1044篇 |
1977年 | 1030篇 |
1976年 | 810篇 |
1975年 | 880篇 |
1974年 | 1189篇 |
1973年 | 1068篇 |
1972年 | 1072篇 |
1971年 | 1211篇 |
1970年 | 1559篇 |
1969年 | 1172篇 |
1968年 | 1115篇 |
1967年 | 1144篇 |
1966年 | 984篇 |
1965年 | 686篇 |
1958年 | 653篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
241.
吴小华 《湖南大学学报(自然科学版)》1991,18(5)
心理语言学日新月异的发展推动着“错误分析”理论由外显的,线性平面上的干扰研究发展到内在的,深层的非直接性干扰研究。根据这种发展动态,本文对“回避行为”的假设先决条件与思想动因作了较为深刻的探讨与剖析。 相似文献
242.
本文论述了钴孔灌注桩超声脉中检测法的原理、仪器和方法.分析了当超声脉冲穿过缺陷区时其传播时间、幅值(或衰减)以及接收信号波形所呈现的变化.提出了基于"声时—深度"曲线的缺陷定量判据.即声时差值与斜率乘积判据.该判据能估算缺陷的性质和大小.而且,若将该判据与"幅值—深度"曲线综合运用,则可提高检测和判断结果的精度. 相似文献
243.
Summary N-acyl dehydroalanines react with and scavenge mainly superoxide radical
and hydroxyl radical (HO.). The ortho-methoxyphenylacetyl dehydroalanine derivative, indexed as AD-20, protects mice against damage resulting from total body X-irradiation, as measured by the increase in their survival time. AD-20 increases the LD50 at 30 days from 6.1 to 7.3 Gy in animals exposed to a wide range of X-rays (6 to 10 Gy). The dose reduction factor (D R F) of AD-20 is 1.20. We postulate that such radioprotective effect may result from its free radical scavenging activity. 相似文献
244.
Summary The ability of liposomes composed of different kinds of phospholipid materials to adhere to the surface of the cornea was studied in the rabbit. The liposomes were labelled with tracer amounts of an I125-labelled phosphatidylethanolamine derivative and were instilled in 10 l drops onto the cornea. The retention of radioactivity was monitored. The results show that liposomes containing positively charged phospholipids are better retained than an albumin control. Thus, it may be possible to develop a drug delivery, liposome system which would permit long-term sustained release of ophthalmic drugs onto the cornea. 相似文献
245.
Hypothalamic histamine modulates adaptive behavior of rats at high environmental temperature 总被引:1,自引:0,他引:1
K. Fujimoto T. Sakata K. Ookuma M. Kurokawa A. Yamatodani H. Wada 《Cellular and molecular life sciences : CMLS》1990,46(3):283-285
Summary Histamine content in the rat hypothalamus was lower at 4°C and higher at 31°C compared to that at 21°C. Pretreatment with -fluoromethylhistidine, a suicide inhibitor of histidine decarboxylase, attenuated both the increased level of hypothalamic histamine and rat adaptive behavior at 31°C. Increase of histamine content in the hypothalamus appears to be an important factor contributing to rat adaptive behavior to high environmental temperature. 相似文献
246.
247.
A. Alkofahi J. K. Rupprecht Y. -M. Liu C. -J. Chang D. L. Smith J. L. McLaughlin 《Cellular and molecular life sciences : CMLS》1990,46(5):539-541
Summary Gigantecin (I), a novel tetrahydroxy-di-tetrahydrofuran fatty acid -lactone (acetogenin), was isolated from an ethanolic extract of the stem bark ofGoniothalamus giganteus Hook. f., Thomas (Annonaceae), by means of activity-directed fractionation (brine shrimp lethality test). This new compound is extremely cytotoxic to human tumor cells, inhibits crown gall tumors on potato discs, and is active in an assay designed to detect antimitotic agents (9 ASK). 相似文献
248.
Davies M 《Annals of science》1990,47(6):607-618
249.
A. R. Eynard M. E. Pasqualini R. A. Rovasio 《Cellular and molecular life sciences : CMLS》1990,46(7):680-682
Summary Fibronectins (FN) are adhesive glycoproteins whose role in platelet aggregation is unclear. Addition of 3, 6 and 12 g/ml of human plasma FN in vitro to isolated human platelets, which had been freed from plasma FN by gel filtration and subsequently stimulated with collagen, inhibited the last stage of platelet aggregation. With 3 and 6g/ml of FN a shortening of the lag-time was also observed. These data showed that FN may play a role in platelet-collagen interaction as well as in platelet-platelet interaction. 相似文献
250.
Summary Cyclic voltammetry of molecular oxygen in aprotic media (dimethylformamide) and in the presence of bilirubin and other bile pigments shows that superoxide anion (
) undergoes proton-induced dismutation. Lactam hydrogens of bile pigments are sufficiently acid to induce
disproportionation to O2 and H2O2. Because of its characteristic lipophilic behavior, a biological role for natural bilirubin similar to that of other non-enzymatic lipophilic scavengers of
is suggested. 相似文献