全文获取类型
收费全文 | 23359篇 |
免费 | 102篇 |
国内免费 | 118篇 |
专业分类
系统科学 | 163篇 |
丛书文集 | 368篇 |
教育与普及 | 56篇 |
理论与方法论 | 80篇 |
现状及发展 | 10228篇 |
研究方法 | 1113篇 |
综合类 | 11237篇 |
自然研究 | 334篇 |
出版年
2013年 | 151篇 |
2012年 | 368篇 |
2011年 | 723篇 |
2010年 | 145篇 |
2009年 | 145篇 |
2008年 | 432篇 |
2007年 | 485篇 |
2006年 | 466篇 |
2005年 | 476篇 |
2004年 | 558篇 |
2003年 | 413篇 |
2002年 | 414篇 |
2001年 | 786篇 |
2000年 | 765篇 |
1999年 | 528篇 |
1992年 | 403篇 |
1991年 | 355篇 |
1990年 | 362篇 |
1989年 | 334篇 |
1988年 | 315篇 |
1987年 | 369篇 |
1986年 | 373篇 |
1985年 | 452篇 |
1984年 | 376篇 |
1983年 | 300篇 |
1982年 | 253篇 |
1981年 | 294篇 |
1980年 | 336篇 |
1979年 | 758篇 |
1978年 | 597篇 |
1977年 | 585篇 |
1976年 | 426篇 |
1975年 | 487篇 |
1974年 | 681篇 |
1973年 | 584篇 |
1972年 | 600篇 |
1971年 | 702篇 |
1970年 | 910篇 |
1969年 | 662篇 |
1968年 | 564篇 |
1967年 | 661篇 |
1966年 | 556篇 |
1965年 | 405篇 |
1959年 | 208篇 |
1958年 | 355篇 |
1957年 | 272篇 |
1956年 | 241篇 |
1955年 | 190篇 |
1954年 | 215篇 |
1948年 | 172篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Kang J.Y. Xu F.C. 《中国科学基金(英文版)》2004,(2):57-58,64
1 Introduction
Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].
…… 相似文献
22.
23.
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
24.
The timing of sleep and sleep EEG parameters in 10 healthy male subjects were investigated in four seasons under controlled conditions. The phase of nocturnal sleep was delayed about one and a half hours in winter as compared to that in summer. The duration of stage 4 sleep decreased and REM sleep increased significantly in winter compared with summer. The seasonality in the timing of sleep can be explained by photoperiodic time cues, but the changes in sleep EEG parameters are difficult to explain in terms of photoperiod. 相似文献
25.
DNA fingerprinting transforms the art of cell authentication. 总被引:4,自引:0,他引:4
The increasing diversity of new cell cultures is seriously stretching the capabilities of traditional methods of identification. DNA fingerprinting is set to play an important role in increasing confidence in the authenticity of cultures in research and industry. 相似文献
26.
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
27.
Thyroid cancer after Chernobyl. 总被引:17,自引:0,他引:17
28.
Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. 总被引:149,自引:0,他引:149
M M Shull I Ormsby A B Kier S Pawlowski R J Diebold M Yin R Allen C Sidman G Proetzel D Calvin 《Nature》1992,359(6397):693-699
Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions. 相似文献
29.
The failing heart. 总被引:19,自引:0,他引:19
Cardiomyopathies are disorders affecting heart muscle that usually result in inadequate pumping of the heart. They are the most common cause of heart failure and each year kill more than 10,000 people in the United States. In recent years, there have been breakthroughs in understanding the molecular mechanisms involved in this group of conditions, with knowledge of the genetic basis for cardiomyopathies perhaps seeing the largest advance, enabling clinicians to devise improved diagnostic strategies and preparing the stage for new therapies. 相似文献
30.
N. Ait-Langomazino R. Sellier G. Jouquet M. Trescinski 《Cellular and molecular life sciences : CMLS》1991,47(6):533-539
Summary A blown bitumen Mexphalte R 90/40 with a high content of saturated hydrocarbons was degraded by several microorganisms to the same extent. In batch cultures ofSaccharomycopsis lipolytica, maximal biodegradation was estimated to be about 9% w/w, 3.2·10–3 g/cm2 and 3.1·10–3 cm of degraded bitumen. The Mexphalte R 90/40 degradation rate was closely coupled to biofilm formation. The microbial activity concerned predominantly the oxidation of saturated hydrocarbons. A direct distillation bitumen 80/100 with a low content of saturated hydrocarbons and a high content of aromatic hydrocarbons and resins was more resistant to biodegradation. 相似文献