全文获取类型
收费全文 | 81494篇 |
免费 | 11514篇 |
国内免费 | 8095篇 |
专业分类
化学 | 42205篇 |
晶体学 | 598篇 |
力学 | 4060篇 |
综合类 | 452篇 |
数学 | 7583篇 |
物理学 | 23610篇 |
无线电 | 22595篇 |
出版年
2024年 | 303篇 |
2023年 | 1926篇 |
2022年 | 2387篇 |
2021年 | 3049篇 |
2020年 | 3011篇 |
2019年 | 2725篇 |
2018年 | 2421篇 |
2017年 | 2362篇 |
2016年 | 3317篇 |
2015年 | 3442篇 |
2014年 | 4213篇 |
2013年 | 5509篇 |
2012年 | 6607篇 |
2011年 | 6501篇 |
2010年 | 4711篇 |
2009年 | 4699篇 |
2008年 | 5042篇 |
2007年 | 4402篇 |
2006年 | 4270篇 |
2005年 | 3703篇 |
2004年 | 2757篇 |
2003年 | 2278篇 |
2002年 | 2033篇 |
2001年 | 1752篇 |
2000年 | 1740篇 |
1999年 | 1984篇 |
1998年 | 1723篇 |
1997年 | 1592篇 |
1996年 | 1598篇 |
1995年 | 1418篇 |
1994年 | 1281篇 |
1993年 | 1083篇 |
1992年 | 967篇 |
1991年 | 774篇 |
1990年 | 671篇 |
1989年 | 502篇 |
1988年 | 413篇 |
1987年 | 365篇 |
1986年 | 259篇 |
1985年 | 278篇 |
1984年 | 218篇 |
1983年 | 178篇 |
1982年 | 152篇 |
1981年 | 90篇 |
1980年 | 73篇 |
1979年 | 43篇 |
1978年 | 30篇 |
1976年 | 32篇 |
1975年 | 36篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
We study a generalization of the notion of the chromatic number of a graph in which the colors assigned to adjacent vertices are required to be, in a certain sense, far apart. © 1993 John Wiley & Sons, Inc. 相似文献
132.
133.
Te-Kao Wu 《Antennas and Propagation, IEEE Transactions on》1987,35(2):205-207
A fast convergent integral equation solution to the scattering problem of a transverse electric/transverse magnetic (TE/TM) plane wave by a one-dimensional periodic array of thin metal strips on a dielectric substrate is described. The formulation of the integral equation is similar to that derived by Montgomery for a two-dimensional periodic array of thin conductors on a dielectric substrate. However, the basis functions which satisfy the appropriate edge conditions are incorporated here for the unknown current expansion on the strips. Following the standard Galerkin's procedure, one may readily determine the induced currents on the strips and thus the reflected and transmitted fields. Sample numerical results are given and good agreement with previously published data is obtained. It is found that the convergence rate of this method is improved by an order of magnitude. Also it is shown that the dielectric substrate has a strong effect on the scattering from the large spacing strip grating. 相似文献
134.
WCDMA与GSM在空中接口上存在较大差异,WCDMA基于码分多址技术,GSM基于时分多址技术。GSM主要处理语音和低速数据,而WCDMA引入了多种速率的数据业务,根据业务的QoS进行资源控制和分配,因此在无线网络规划方法上,WCDMA与GSM存在较大差异。文章从容量规划、覆盖规划、蜂窝布局、规划流程、网络评估等方面对WCDMA与GSM的无线网络规划进行了比较和分析。 相似文献
135.
136.
A fluoroionophore sensor, N-[4-(1-pyrene)butyroyl]-L-tryptophan (PLT), has been reported. It can distinguish lead ion from other 12 metal ions via forming a pyrene dimer and it exhibits a very high sensitivity (0.15 microM) in aqueous solution (Chem. Commun., 2006, 2702). When the indole moiety in PLT was changed to benzene, in forming a new fluoroionophore of N-[4-(1-pyrene)butyroyl]-L-phenylalanine (PLP), it could not form a pyrene dimer in response to Pb(2+) in water. The present study describes the spectroscopic clarification of the intrinsic differences of the binding model between PLP and PLT in binding with Pb(2+). The model shows identical chelating bidentate coordination between COO(-) and Pb(2+) both in PLP-Pb and PLT-Pb; however, there is no indication of the interaction between the phenyl ring and the metal ion or the hydrogen bonding between amide groups in PLP-Pb. These differences in the binding model between PLP-Pb and PLT-Pb illustrate that the indole ring in PLT appears to play a crucial role in the high selectivity and sensitivity of PLT to lead(II) ion. 相似文献
137.
138.
关于多线性振荡奇异积分在加权Hardy-型空间上的一致估计 总被引:1,自引:0,他引:1
本文对一类具有光滑位相函数的多线性振荡奇异积分算子建立了一致的加权(H^1(R^n),L^1(R^n))估计及一致的加权(HKp(R^n),Kp(R^n)估计。 相似文献
139.
Tao Jin Feng-Xian Jiang Xiao-Li Li Fang Wang Xiao-Hua Shen Rui-Qiang Zhang Hai-Shun Wu 《Applied Surface Science》2006,253(5):2708-2712
CoPt/Ag and [C/CoPt]n/Ag thin films have been prepared onto the glass substrates by magnetron sputtering. We investigated the evolution of texture and magnetic properties of CoPt/Ag and [C/CoPt]n/Ag films. The results show that C-doping plays an important role in improving (0 0 1) texture, improving the order parameter S, reducing the intergrain interactions, and making the magnetization reversal mechanism more close to Stoner-Wolfarth rotational mechanism. The growth mechanism of (0 0 1) texture also seems to be related strongly to the films thickness. Our results show that the highly (0 0 1)-oriented films with ordered fct phase have a significant potential for the perpendicular media of extremely high-density recording. 相似文献
140.