全文获取类型
收费全文 | 30816篇 |
免费 | 638篇 |
国内免费 | 98篇 |
专业分类
系统科学 | 1198篇 |
丛书文集 | 335篇 |
教育与普及 | 66篇 |
理论与方法论 | 351篇 |
现状及发展 | 11609篇 |
研究方法 | 1220篇 |
综合类 | 16361篇 |
自然研究 | 412篇 |
出版年
2018年 | 758篇 |
2017年 | 771篇 |
2016年 | 511篇 |
2012年 | 655篇 |
2011年 | 1739篇 |
2010年 | 952篇 |
2009年 | 590篇 |
2008年 | 941篇 |
2007年 | 1251篇 |
2006年 | 508篇 |
2005年 | 575篇 |
2004年 | 647篇 |
2003年 | 611篇 |
2002年 | 534篇 |
2001年 | 885篇 |
2000年 | 856篇 |
1999年 | 601篇 |
1994年 | 314篇 |
1992年 | 520篇 |
1991年 | 424篇 |
1990年 | 457篇 |
1989年 | 413篇 |
1988年 | 380篇 |
1987年 | 437篇 |
1986年 | 449篇 |
1985年 | 538篇 |
1984年 | 453篇 |
1983年 | 358篇 |
1982年 | 301篇 |
1981年 | 316篇 |
1980年 | 374篇 |
1979年 | 848篇 |
1978年 | 661篇 |
1977年 | 607篇 |
1976年 | 470篇 |
1975年 | 515篇 |
1974年 | 684篇 |
1973年 | 587篇 |
1972年 | 614篇 |
1971年 | 735篇 |
1970年 | 941篇 |
1969年 | 672篇 |
1968年 | 600篇 |
1967年 | 655篇 |
1966年 | 579篇 |
1965年 | 409篇 |
1959年 | 229篇 |
1958年 | 379篇 |
1957年 | 285篇 |
1956年 | 232篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Obese postmenopausal female volunteers were given timed daily oral dosages of bromocriptine, and tested for reduction of body fat stores. This dopamine agonist has been shown to reset circadian rhythms that are altered in obese animals and to reduce body fat levels in several animal models. The participants were instructed not to alter their existing exercise and eating behavior during treatment. Skinfold measurements were taken on 33 subjects as indices of body fat. The measurements (e.g., suprailiac) were reduced after six weeks by about 25%, which represents a reduction of 11.7% of the total body fat. These dramatic decreases in body fat, which are equivalent to that produced by severe caloric restriction, were accompanied by more modest reductions of body weight (2.5%), indicating a possible conservation of protein that is usually lost as a consequence of such caloric restriction. The effects of bromocriptine treatment on body fat and hyperglycemia were also examined in non-insulin dependent diabetics being treated with oral hypoglycemics (7 subjects) or insulin (7 subjects). Total body fat was reduced by 10.7% and 5.1% in diabetics on oral hypoglycemics and insulin, respectively, without any significant reductions in body weight. Hyperglycemia was reduced in most of the 15 diabetic subjects treated leading to euglycemia and even cessation of hypoglycemic drugs in 3 of the 7 subjects during 4-8 weeks of bromocriptine treatment. These findings support the hypothesis that obesity and type II diabetes may be treated effectively with bromocriptine when administered at the proper times and dosages. 相似文献
12.
We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium-induced attacks of skeletal muscle paralysis. HYPP co-segregated with the equine adult skeletal muscle sodium channel alpha subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS3 which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition. 相似文献
13.
J. W. Faigle H. Stierlin H. Mory T. Winkler H. -P. Kriemler 《Cellular and molecular life sciences : CMLS》1985,41(4):476-478
Summary Indoxyl derivatives were detected as minor products among the urinary metabolites of two trial drugs, a benzodiazepine (GP 55 129) and a benzophenone (CGP 11 952). Their structures were elucidated by NMR and mass spectroscopy. Presumably, metabolites containing potential aldehyde functions react spontaneously with endogenous indoxyl. Such derivatives have not hitherto been encountered in drug metabolism. 相似文献
14.
就近几年图书馆界关于新世纪馆员意识转换及社会角色转换等方面的研究进行了综述,指出新时期的馆员要实现自我社会角色的转换,首先是要明确转换的必要性,然后采取有效的策略逐步地、系统地推进转换,才能取得较好的效果。 相似文献
15.
C. Ambrogi Lorenzini C. Bucherelli A. Giachetti G. Tassoni 《Cellular and molecular life sciences : CMLS》1991,47(10):1019-1026
Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals.In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation. 相似文献
16.
The genetic engineering of production traits in domestic animals 总被引:1,自引:0,他引:1
17.
M. Ishibashi M. Tsuda Y. Ohizumi T. Sasaki J. Kobayashi 《Cellular and molecular life sciences : CMLS》1991,47(3):299-300
Summary A new bromotyrosine-derived alkaloid with antileukemic activity, purealidin A (5), has been isolated from the Okinawan marine spongePsammaplysilla purea and its chemical structure elucidated on the basis of the spectroscopic data. 相似文献
18.
M E MacDonald A Novelletto C Lin D Tagle G Barnes G Bates S Taylor B Allitto M Altherr R Myers 《Nature genetics》1992,1(2):99-103
Analysis of 78 Huntington's disease (HD) chromosomes with multi-allele markers revealed 26 different haplotypes, suggesting a variety of independent HD mutations. The most frequent haplotype, accounting for about one third of disease chromosomes, suggests that the disease gene is between D4S182 and D4S180. However, the paucity of an expected class of chromosomes that can be related to this major haplotype by assuming single crossovers may reflect the operation of other mechanisms in creating haplotype diversity. Some of these mechanisms sustain alternative scenarios that do not require a multiple mutational origin for HD and/or its positioning between D4S182 and D4S180. 相似文献
19.
Genotoxic effects of dithane M-45 were studied on the bone marrow cells of male albino mice (Lacca strain) in vivo. Different doses (30 mg, 40 mg and 300 mg/kg b.wt) of dithane M-45 were injected intraperitoneally and their effects were investigated after time intervals of 1, 2, 5 and 10 days. The chromosomal aberrations observed in the bone marrow cells of male mice after treatment with dithane M-45 were fragments, rings, dicentric chromosomes, terminal chromatid deletions, chromatid gaps and breaks. In addition to these chromosomal aberrations, physiological effects such as uneven stretching of chromatin material, end-to-end chromosomal associations, exchange configurations, clumping, stickiness and centromeric associations were also observed. 相似文献
20.