全文获取类型
收费全文 | 15892篇 |
免费 | 1784篇 |
国内免费 | 2077篇 |
专业分类
化学 | 11071篇 |
晶体学 | 253篇 |
力学 | 744篇 |
综合类 | 216篇 |
数学 | 1894篇 |
物理学 | 5575篇 |
出版年
2023年 | 176篇 |
2022年 | 288篇 |
2021年 | 387篇 |
2020年 | 402篇 |
2019年 | 435篇 |
2018年 | 358篇 |
2017年 | 419篇 |
2016年 | 507篇 |
2015年 | 574篇 |
2014年 | 683篇 |
2013年 | 971篇 |
2012年 | 1130篇 |
2011年 | 1302篇 |
2010年 | 955篇 |
2009年 | 1018篇 |
2008年 | 1151篇 |
2007年 | 1051篇 |
2006年 | 986篇 |
2005年 | 863篇 |
2004年 | 775篇 |
2003年 | 627篇 |
2002年 | 595篇 |
2001年 | 505篇 |
2000年 | 438篇 |
1999年 | 334篇 |
1998年 | 248篇 |
1997年 | 196篇 |
1996年 | 212篇 |
1995年 | 188篇 |
1994年 | 179篇 |
1993年 | 162篇 |
1992年 | 158篇 |
1991年 | 117篇 |
1990年 | 137篇 |
1989年 | 104篇 |
1988年 | 123篇 |
1987年 | 85篇 |
1986年 | 88篇 |
1985年 | 105篇 |
1984年 | 84篇 |
1983年 | 76篇 |
1982年 | 59篇 |
1981年 | 50篇 |
1980年 | 54篇 |
1979年 | 44篇 |
1978年 | 35篇 |
1977年 | 39篇 |
1976年 | 37篇 |
1974年 | 51篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
51.
52.
J.S. Tsay H.W. Chang Y.L. Chiou K.T. Huang W.Y. Chan Y.D. Yao 《Journal of magnetism and magnetic materials》2006
Influences of oxygen exposure on the magnetic properties of Co/Ge(1 1 1) ultrathin films have been investigated by surface magneto-optic Kerr effect technique. As the oxygen exposure increases on Co/Ge(1 1 1) films, their magnetic properties could be modified. As an example for 15 ML Co/Ge(1 1 1) films, the coercivity increases from 730 to 920 Oe and the remanence Kerr intensity is reduced for 500 Langmuir (L) of oxygen exposure. Corresponding compositions analyzed by Auger electron spectroscopy measurement shows that the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. Oxygen distributes on the topmost layers of the film. The adsorbed oxygen influences the electronic density of states of Co and results in the changes of the magnetic properties. Besides, the appearance of O/Co/Ge interface could modify the stress anisotropy, and as a result the coercivity of ultrathin Co/Ge(1 1 1) film is enhanced. 相似文献
53.
54.
The new phenylpropanoid diglycoside ligusinenoside A ( 1 ), and the two new 8,4′‐oxyneolignan(‘8‐O‐4′‐neolignan’) diglycosides ligusinenosides B ( 2 ) and C ( 3 ), together with nine known compounds, were isolated from the rhizomes of Ligusticum sinensis Oliv. The structures of 1 – 3 were elucidated on the basis of spectroscopic analyses. 相似文献
55.
Zhihui Zhao Hui Dai Xiangmei Wu Haitao Chang Xiaoming Gao Mengjun Liu Pengfei Tu 《Chemistry of Natural Compounds》2007,43(4):374-376
A pectic polysaccharide was isolated from the fruits of Ziziphus jujuba Mill. cv. jinsixiaozao Hort. and its structure was characterized by acid hydrolysis, methylation, and NMR spectroscopies.
The purified fraction Ju-B-7 had a molecular mass of over 2000 kDa. Chemical and spectroscopic analyses indicated that Ju-B-7
is composed mainly of α-1,4-linked D-galactopyranosyluronic acid and 1,2-linked L-rhamnose with a molar ratio of 8.1:1. It can significantly stimulate
spleen cell proliferation in vitro (P<0.01, 10 μmg/mL).
Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 311–312, July–August, 2007. 相似文献
56.
57.
Ju Yeon Woo Eun Hee Kim Tae Hoon Yoon Jae Chang Kim Byung Kyu Kim 《Liquid crystals》2007,34(9):1115-1120
Chiral dopants were added to the formulation of holographic polymer-dispersed liquid crystals and the effects studied in terms of grating formation dynamics, morphology, diffraction efficiency, contrast ratio and electro-optical properties of the films. A gradual increase of real-time diffraction efficiency, decrease of droplet size and increase of diffraction efficiency of the composite film were obtained with the addition and increasing content of chiral dopant, due to the increased viscosity of the liquid crystal (LC) doped with the chiral dopant leading to decreased droplet coalescence. The contrast ratio decreased with increasing content of chiral dopant due to the difficult orientation of LC molecules caused by the formation of a helical structure. Addition of a small amount of the chiral dopant increased the driving voltage slightly, whereas the decay time is decreased significantly as a result of the high twisting of the helical structure. 相似文献
58.
59.
LI Cun YANG Bai-Feng CAI Hao HUANG Nian-Ning 《理论物理通讯》2006,46(2):244-248
One of the basic problems about the inverse scattering transform for solving a completely integrable nonlinear evolutions equation is to demonstrate that the Jost solutions obtained from the inverse scattering equations of Cauchy integral satisfy the Lax equations. Such a basic problem still exists in the procedure of deriving the dark soliton solutions of the NLS equation in normal dispersion with non-vanishing boundary conditions through the inverse scattering transform. In this paper, a pair of Jost solutions with same analytic properties are composed to be a 2 × 2 matrix and then another pair are introduced to be its right inverse confirmed by the Liouville theorem. As they are both 2 × 2 matrices, the right inverse should be the left inverse too, based upon which it is not difficult to show that these Jost solutions satisfy both the first and second Lax equations. As a result of compatibility condition, the dark soliton solutions definitely satisfy the NLS equation in normal dispersion with non-vanishing boundary conditions. 相似文献
60.
可提前还款的定期贷款是隐含着期权的利率衍生物,本文建立CIR利率模型下可提前还款的定期贷款的数学模型,通过离散偏微分方程,建立了模型的计算方法,讨论了随机利率对提前还贷的影响. 相似文献