全文获取类型
收费全文 | 158594篇 |
免费 | 25783篇 |
国内免费 | 16867篇 |
专业分类
化学 | 108457篇 |
晶体学 | 1746篇 |
力学 | 10441篇 |
综合类 | 986篇 |
数学 | 20666篇 |
物理学 | 58948篇 |
出版年
2024年 | 328篇 |
2023年 | 2895篇 |
2022年 | 3661篇 |
2021年 | 5170篇 |
2020年 | 6160篇 |
2019年 | 5891篇 |
2018年 | 5130篇 |
2017年 | 4940篇 |
2016年 | 7308篇 |
2015年 | 7120篇 |
2014年 | 8658篇 |
2013年 | 11398篇 |
2012年 | 14124篇 |
2011年 | 14726篇 |
2010年 | 10043篇 |
2009年 | 9494篇 |
2008年 | 10313篇 |
2007年 | 9343篇 |
2006年 | 8593篇 |
2005年 | 7315篇 |
2004年 | 5597篇 |
2003年 | 4560篇 |
2002年 | 4405篇 |
2001年 | 3558篇 |
2000年 | 3154篇 |
1999年 | 3454篇 |
1998年 | 2891篇 |
1997年 | 2787篇 |
1996年 | 2831篇 |
1995年 | 2400篇 |
1994年 | 2076篇 |
1993年 | 1688篇 |
1992年 | 1564篇 |
1991年 | 1398篇 |
1990年 | 1144篇 |
1989年 | 896篇 |
1988年 | 686篇 |
1987年 | 605篇 |
1986年 | 592篇 |
1985年 | 491篇 |
1984年 | 339篇 |
1983年 | 286篇 |
1982年 | 197篇 |
1981年 | 161篇 |
1980年 | 133篇 |
1979年 | 75篇 |
1977年 | 84篇 |
1976年 | 78篇 |
1975年 | 70篇 |
1973年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
891.
Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into
nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm.
The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires
have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer
(VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated
domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices. 相似文献
892.
通过分析耦合参数作用、系统所呈现大尺度周期相态的复杂性以及与系统在无噪声条件下状态的比较,得出耦合振子系统的动力学行为比同类单振子系统的复杂,周期相态更稳定、抗噪能力更强.用构造的一类含特定恢复力项双中强度耦合Duffing振子系统检测色噪声背景中的谐波、方波信号,信噪比分别达到-111.0和-108.45dB.
关键词:
特定双耦合 Duffing振子系统
色噪声
周期信号
信噪比 相似文献
893.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
894.
Kang Hai TAN Xiao Ping YANG 《数学学报(英文版)》2006,22(3):701-710
In this paper we give a geometric interpretation of the notion of the horizontal mean curvature which is introduced by Danielli Garofalo-Nhieu and Pauls who recently introduced sub- Riemannian minimal surfaces in Carnot groups. This will be done by introducing a natural nonholonomic connection which is the restriction (projection) of the natural Riemannian connection on the horizontal bundle. For this nonholonomic connection and (intrinsic) regular hypersurfaces we introduce the notions of the horizontal second fundamental form and the horizontal shape operator. It turns out that the horizontal mean curvature is the trace of the horizontal shape operator. 相似文献
895.
896.
The FRS-ESR facility at GSI provides one of the most efficient methods for direct mass measurements. In the present experiment,
exotic nuclei were produced via fragmentation of 152Sm projectiles in a thick beryllium target at 500-600 MeV/u, separated in-flight with the fragment separator FRS, and injected
into the storage-cooler ring ESR. Time-resolved Schottky Mass Spectrometry was applied for mass measurements of stored and
electron-cooled bare and few-electron ions. 373 different nuclides were identified by means of the spectra of their revolution
frequencies. Masses for 18 nuclides (84Zr, 92Ru, 94Rh, 107,108,110Sb, 111,112,114I, 118Ba, 122,123La, 124Ce, 127Pr, 129Nd, 132Pm, 134Sm, 137Eu) have been determined for the first time. Masses for 111,112I and 113Xe have been obtained via known α-decay energies. The experiment and first results will be presented. 相似文献
897.
Jing Ping YANG Shi Hong CHENG Xiao Qian WANG 《数学学报(英文版)》2007,23(3):467-478
This paper investigates bivariate recursive equations on excess-of-loss reinsurance. For an insurance portfolio, under the assumptions that the individual claim severity distribution has bounded continuous density and the number of claims belongs to R1 (a, b) family, bivariate recursive equations for the joint distribution of the cedent's aggregate claims and the reinsurer's aggregate claims are obtained. 相似文献
898.
899.
In this paper, we study a micro‐macro model for polymeric fluid. The system involves coupling between the macroscopic momentum equation and a microscopic evolution equation describing the combined effects of the microscopic potential and thermofluctuation. We employ an energetic variation procedure to explore the relation between the macroscopic transport of the particles and the induced elastic stress due to the microscopic structure. For the initial data not far from the equilibrium, we prove the global existence and uniqueness of classical solutions to the system. © 2006 Wiley Periodicals, Inc. 相似文献
900.
本文利用85年5—6月间对乌鲁木齐市主要商业区及部分中、小商业区的实地调查资料,对乌市商业中心等级系统进行了定性和定量的分级分类,将全市商业中心划分为五个等级,八组商业中心,对已形成的商业中心分布现状进行了初步探讨,并对今后商业网点的合理布局提出了建议。 相似文献