全文获取类型
收费全文 | 27176篇 |
免费 | 1223篇 |
国内免费 | 5023篇 |
专业分类
化学 | 30642篇 |
晶体学 | 315篇 |
力学 | 56篇 |
综合类 | 244篇 |
数学 | 123篇 |
物理学 | 2042篇 |
出版年
2024年 | 30篇 |
2023年 | 305篇 |
2022年 | 807篇 |
2021年 | 796篇 |
2020年 | 815篇 |
2019年 | 823篇 |
2018年 | 723篇 |
2017年 | 916篇 |
2016年 | 1058篇 |
2015年 | 950篇 |
2014年 | 1161篇 |
2013年 | 2669篇 |
2012年 | 2007篇 |
2011年 | 1521篇 |
2010年 | 1322篇 |
2009年 | 1556篇 |
2008年 | 1645篇 |
2007年 | 1798篇 |
2006年 | 1705篇 |
2005年 | 1572篇 |
2004年 | 1447篇 |
2003年 | 1136篇 |
2002年 | 946篇 |
2001年 | 687篇 |
2000年 | 669篇 |
1999年 | 555篇 |
1998年 | 450篇 |
1997年 | 477篇 |
1996年 | 429篇 |
1995年 | 394篇 |
1994年 | 343篇 |
1993年 | 295篇 |
1992年 | 285篇 |
1991年 | 215篇 |
1990年 | 163篇 |
1989年 | 174篇 |
1988年 | 125篇 |
1987年 | 86篇 |
1986年 | 59篇 |
1985年 | 48篇 |
1984年 | 58篇 |
1983年 | 29篇 |
1982年 | 43篇 |
1981年 | 29篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 22篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
Lokenath Debnath 《Journal of Mathematical Analysis and Applications》2007,333(1):164-190
This paper deals with recent developments of linear and nonlinear Rossby waves in an ocean. Included are also linear Poincaré, Rossby, and Kelvin waves in an ocean. The dispersion diagrams for Poincaré, Kelvin and Rossby waves are presented. Special attention is given to the nonlinear Rossby waves on a β-plane ocean. Based on the perturbation analysis, it is shown that the nonlinear evolution equation for the wave amplitude satisfies a modified nonlinear Schrödinger equation. The solution of this equation represents solitary waves in a dispersive medium. In other words, the envelope of the amplitude of the waves has a soliton structure and these envelope solitons propagate with the group velocity of the Rossby waves. Finally, a nonlinear analytical model is presented for long Rossby waves in a meridional channel with weak shear. A new nonlinear wave equation for the amplitude of large Rossby waves is derived in a region where fluid flows over the recirculation core. It is shown that the governing amplitude equations for the inner and outer zones are both KdV type, where weak nonlinearity is balanced by weak dispersion. In the inner zone, the nonlinear amplitude equation has a new term proportional to the 3/2 power of the difference between the wave amplitude and the critical amplitude, and this term occurs to account for a nonlinearity due to the flow over the vortex core. The solution of the amplitude equations with the linear shear flow represents the solitary waves. The present study deals with the lowest mode (n=1) analysis. An extension of the higher modes (n?2) of this work will be made in a subsequent paper. 相似文献
82.
The reactions of 5-methyl-3-hydroxyisoxazole with 2, 2-dimethyl, 3-substituted cyclopropanecarboxylic chlorides give O-acyl-5-methyl-3-hydroxyisoxazole and N-acyl-5-methylisoxazolin-3-one derivatives. The ratio of O-acyl to N-acyl product depends upon the acylation reagents. O-acyl derivatives can be converted to the N-acyl compounds by isomerization under acidic conditions or heating. 相似文献
83.
The lantadenes fraction from Lantana camara was isolated and transformed to the medicinally important intermediate 22β-hydroxyoleanonic
acid. The compound was studied for hepatotoxicity using lantadene A as standard and found to be nontoxic.
Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 357–358, July–August, 2006. 相似文献
84.
Maryam Mirza-Aghayan Rabah Boukherroub Mahshid Rahimifard 《Journal of organometallic chemistry》2007,692(23):5113-5116
The palladium(II) chloride/triethylsilane system has been successfully applied for the selective hydrogenation of the carbon-carbon double bond of α,β-unsaturated ketones to yield the corresponding saturated carbonyl compounds. The reaction takes place under mild conditions and affords high yields. 相似文献
85.
We review the unusual structural, transport and magnetic properties of highly conducting polyaniline, doped with boron trifluoride.
Our studies establish the unique conducting state of this system, which is in distinct contrast with the conventional proton-doped
polyaniline samples. 相似文献
86.
氨酪酸(am inobutyric acid),化学名称为γ-氨基丁酸。本品在体内与血氨结合生成尿毒排出体外,有降低血氨及促进大脑新陈代谢的作用,能够增强葡萄糖磷酸酯化酶的活性,利于脑细胞功能的恢复。主要用于脑卒中后遗症、脑动脉硬化症、头部外伤后以及一氧化碳中毒所致昏迷的辅助治疗 相似文献
87.
88.
Katsumi Kubota 《Tetrahedron》2006,62(49):11397-11401
The first highly enantioselective silicon Lewis acid catalyst for an asymmetric organic transformation has been developed. The catalyst derives its activity from the strain induced in the silicon center by virtue of being constrained in a five-membered ring. A simple tridentate ligand has been developed and the derived chlorosilane complex catalyzes the Diels-Alder cycloaddition of methacrolein and cyclopentadiene with 94% ee. 相似文献
89.
Marina DellaGreca 《Tetrahedron》2006,62(12):2877-2882
Examination of the hydroalcoholic extract of the leaves of Aptenia cordifolia has afforded three cinnamic acid amides and two lignanamides. Structures were established on the basis of spectroscopic data, including 2D-NMR analyses. 相似文献
90.
脑细胞激活素药物的化学成分分析 总被引:1,自引:0,他引:1
采用日本岛津LC-60A型高压液相色谱仪和美国P-E3030型原子吸收分光光度计,对该药进行了氨基酸、维生素和化学元素的含量测定。结果表明,该药含有18种氨基酸,不少于3种维生素和20几种化学元素,为进一步改进该药物的合理配制方法和临床应用提供了参考数据。 相似文献