全文获取类型
收费全文 | 9575篇 |
免费 | 239篇 |
国内免费 | 329篇 |
专业分类
系统科学 | 221篇 |
丛书文集 | 244篇 |
教育与普及 | 183篇 |
理论与方法论 | 20篇 |
现状及发展 | 1989篇 |
研究方法 | 210篇 |
综合类 | 7262篇 |
自然研究 | 14篇 |
出版年
2022年 | 107篇 |
2021年 | 103篇 |
2017年 | 69篇 |
2015年 | 127篇 |
2014年 | 146篇 |
2013年 | 133篇 |
2012年 | 210篇 |
2011年 | 287篇 |
2010年 | 200篇 |
2009年 | 306篇 |
2008年 | 330篇 |
2007年 | 355篇 |
2006年 | 255篇 |
2005年 | 340篇 |
2004年 | 273篇 |
2003年 | 224篇 |
2002年 | 216篇 |
2001年 | 382篇 |
2000年 | 334篇 |
1999年 | 435篇 |
1998年 | 339篇 |
1997年 | 344篇 |
1996年 | 284篇 |
1995年 | 260篇 |
1994年 | 219篇 |
1993年 | 195篇 |
1992年 | 255篇 |
1991年 | 233篇 |
1990年 | 213篇 |
1989年 | 176篇 |
1988年 | 164篇 |
1987年 | 149篇 |
1986年 | 83篇 |
1985年 | 114篇 |
1984年 | 84篇 |
1980年 | 75篇 |
1979年 | 146篇 |
1978年 | 134篇 |
1977年 | 107篇 |
1976年 | 79篇 |
1975年 | 73篇 |
1974年 | 98篇 |
1973年 | 103篇 |
1972年 | 89篇 |
1971年 | 111篇 |
1970年 | 100篇 |
1969年 | 96篇 |
1968年 | 95篇 |
1967年 | 87篇 |
1966年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
溶胶法制备了不同粒度的FeCu纳米颗粒体,X射线衍射(XRD)确定了样品的相组成和颗粒的平均粒度,振动样品磁强计(VSM)测量了样品在不同温度下的磁化曲线,磁滞回线,涨落场和有效激活体积.“趋近饱和定律”方法求出了样品的有效磁各向异性常数.利用均匀反磁化模型计算了样品的矫顽力,计算值与测量值基本相符.结果表明,样品的激活体积随颗粒体积的增大而增大,激活体积与颗粒的平均体积的大小基本属于同一数量级,粒状FeCu纳米颗粒的反磁化基本符合均匀反磁化. 相似文献
92.
93.
Summary 7 monoterpenes, -pinene, -pinene, myrcene, p-cymene, limonene, neral and geranial, were identified together with n-undecane in the scent scales ofP. melete, and also, together with considerable amounts of linalool, in the scent scales ofP. napi. Content ratio of neral to geranial inP. melete ranged from 0.77 to 1.04, and that inP. napi from 1.84 to 2.43. The present chemotaxonomic approach shows the 2 species ofPieris to be distinct.The authors thank Dr T. Yushima (National Institute of Agricultural Science, Japan) for supplying the references 3 and 4. 相似文献
94.
At ambient temperatures (Ta) of both 8 and 22 degrees C, intraventricular administration of TRH (10-80 microgram) produced a dose-dependent hypothermia in rats. The hypothermia was due to both decreased metabolic heat production and cutaneous vasodilatation. In contrast, at 30 degrees C Ta, TRH increased metabolic heat production (due to behavioral excitation) and led to hyperthermia. 相似文献
95.
Summary The C-terminal amino acid sequences of human and of porcine antithrombin III have been determined as Gly-Arg-Val-Ala-Asn-Pro-Cys-Val-Lys and Gly-Arg-Val-Ala-Asn-Pro-Cys, respectively. These sequences are highly homologous with the C-terminal sequence of human -1-proteinase inhibitor. 相似文献
96.
Summary 2-Halogeno-ethanols change the active site structure of -chymotrypsin more rapidly and effectively than ethanol, 1-propanol and urea, probably before producing an extensive conformation change. 相似文献
97.
D. Sabourault Françoise Bauché Y. Giudicelli J. Nordmann R. Nordmann 《Cellular and molecular life sciences : CMLS》1981,37(3):227-229
Summary After 3 weeks of continuous ethanol intoxication by inhalation, the maximal number and affinity of the -and -receptors of rat heart were unchanged. These data indicate that adrenergic receptor disturbances are not involved in the mechanism of chronic ethanol-induced triglyceride deposition in the heart.Acknowledgments. This work was supported by grants from the Institut National de la Santé et de la Recherche Médicale. We wish to thank Mr M. Clément for skilled technical assistance in performing chronic ethanol inhalation treatments. 相似文献
98.
R. L. Tyson C. -j. Chang J. L. McLaughlin Y. Aynehchi J. M. Cassady 《Cellular and molecular life sciences : CMLS》1981,37(5):441-442
Summary A novel sesquiterpene lactone, 9--hydroxyparthenolide (1) was isolated from a chloroform extract ofAnvillea garcini that was collected in Iran. The structure of1 was assigned on the basis of high field NMR decoupling experiments and other spectroscopic evidence. This -methylene lactone has shown significant activity in both the 9KB cell culture and P388 mouse leukemia test systems.The authors acknowledge the support of contract No. N01-CM-97296 from the National Cancer Institute and the use of the Purdue University Biochemical Magnetic Resonance Laboratory (NIH grant No. RR01077). This is paper 16 in the series Potential Antitumor Agents. 相似文献
99.
Y. Kakiuchi G. M. Hughes T. Arai M. Horimoto Y. Kikuchi T. Koyama 《Cellular and molecular life sciences : CMLS》1981,37(4):376-377
Summary A needle type of colloid osmometer has been devised with special attachments which made it useable with 3-l samples. It has been used in oncometry of fresh water teleosts to give the following results: 5.1±1.0 mm Hg for goldfish, 5.2±0.71 mm Hg for carp, and 14.3±0.75 mm Hg for eel.This study was supported in part by Research Grant 387036 from the Ministry of Education of Japan.invited to National Institute of Physiological Sciences, Okazaki, Japan. 相似文献
100.
H Meves Y Pichon 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1977,284(14):1325-1328
Most of the effects of 4-aminopyridine on the potassium conductance of the giant axon of the Squid can be explained in terms of a simple model based on the physicochemical properties of the molecule and what is known about the structure of the potassium "channels". 相似文献