全文获取类型
收费全文 | 84808篇 |
免费 | 6754篇 |
国内免费 | 5353篇 |
专业分类
化学 | 24060篇 |
晶体学 | 1808篇 |
力学 | 3791篇 |
综合类 | 469篇 |
数学 | 23471篇 |
物理学 | 43316篇 |
出版年
2023年 | 203篇 |
2021年 | 399篇 |
2020年 | 728篇 |
2019年 | 1058篇 |
2018年 | 1015篇 |
2017年 | 740篇 |
2016年 | 593篇 |
2015年 | 494篇 |
2014年 | 1261篇 |
2013年 | 2040篇 |
2012年 | 1381篇 |
2011年 | 1980篇 |
2010年 | 2511篇 |
2009年 | 7146篇 |
2008年 | 8162篇 |
2007年 | 6657篇 |
2006年 | 6062篇 |
2005年 | 4179篇 |
2004年 | 3953篇 |
2003年 | 4165篇 |
2002年 | 5403篇 |
2001年 | 3928篇 |
2000年 | 3700篇 |
1999年 | 3517篇 |
1998年 | 2896篇 |
1997年 | 2047篇 |
1996年 | 1825篇 |
1995年 | 2282篇 |
1994年 | 2213篇 |
1993年 | 1650篇 |
1992年 | 1147篇 |
1991年 | 876篇 |
1990年 | 728篇 |
1989年 | 623篇 |
1988年 | 582篇 |
1987年 | 426篇 |
1986年 | 214篇 |
1985年 | 971篇 |
1984年 | 642篇 |
1983年 | 502篇 |
1982年 | 669篇 |
1981年 | 813篇 |
1980年 | 736篇 |
1979年 | 579篇 |
1978年 | 603篇 |
1977年 | 552篇 |
1976年 | 549篇 |
1975年 | 321篇 |
1974年 | 357篇 |
1973年 | 464篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
15.
16.
In this work, the variation of the magnetic moments of the Ni/Pt multilayers are studied using the linearized augmented plane waves (LAPW) method in the framework of the density functional theory (DFT) implemented in the version of WIEN2K program. The systems have been modeled by seven layers slab separated in z direction by a vacuum region of four substrate layers. We present the results of the dependence of the magnetic properties with respect to the thickness variation of the different multilayers. The modeling of these systems finds an important empirical support. Experiment and theory show the same trends for the magnetic moments: hybridization effects between Ni and Pt are mostly localized at the interface. 相似文献
17.
Single-crystalline gallium nitride nanobelts have been synthesized through the reaction of gallium vapor with flowing ammonia using nickel as a catalyst. The as-synthesized products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction (SAED). XRD and SAED results revealed that the products are pure, single-crystalline GaN with hexagonal structure. The widths and thickness of the nanobelts ranged from 80 to 200 nm, and 10 to 30 nm, respectively. The lengths were up to several tens of micrometers. The nanobelts had smooth surface with no amorphous sheath, and a sharp-tip end. The growth mechanism of nanobelts was discussed. 相似文献
18.
In this paper, we study the existence of the uniformly minimum risk equivariant (UMRE) estimators of parameters in a class
of normal linear models, which include the normal variance components model, the growth curve model, the extended growth curve
model, and the seemingly unrelated regression equations model, and so on. The necessary and sufficient conditions are given
for the existence of UMRE estimators of the estimable linear functions of regression coefficients, the covariance matrixV and (trV)α, where α > 0 is known, in the models under an affine group of transformations for quadratic losses and matrix losses, respectively.
Under the (extended) growth curve model and the seemingly unrelated regression equations model, the conclusions given in literature
for estimating regression coefficients can be derived by applying the general results in this paper, and the sufficient conditions
for non-existence of UMRE estimators ofV and tr(V) are expanded to be necessary and sufficient conditions. In addition, the necessary and sufficient conditions that there
exist UMRE estimators of parameters in the variance components model are obtained for the first time. 相似文献
19.
非线性互补问题的一种全局收敛的显式光滑Newton方法 总被引:2,自引:0,他引:2
本针对Po函数非线性互补问题,给出了一种显式光滑Newton方法,该方法将光滑参数μ进行显式迭代而不依赖于Newton方向的搜索过程,并在适当的假设条件下,证明了算法的全局收敛性。 相似文献
20.