全文获取类型
收费全文 | 8509篇 |
免费 | 280篇 |
国内免费 | 346篇 |
专业分类
化学 | 4061篇 |
晶体学 | 119篇 |
力学 | 166篇 |
综合类 | 31篇 |
数学 | 2477篇 |
物理学 | 1399篇 |
综合类 | 882篇 |
出版年
2023年 | 29篇 |
2022年 | 87篇 |
2021年 | 54篇 |
2020年 | 119篇 |
2019年 | 156篇 |
2018年 | 137篇 |
2017年 | 150篇 |
2016年 | 154篇 |
2015年 | 134篇 |
2014年 | 197篇 |
2013年 | 282篇 |
2012年 | 215篇 |
2011年 | 393篇 |
2010年 | 313篇 |
2009年 | 507篇 |
2008年 | 396篇 |
2007年 | 473篇 |
2006年 | 401篇 |
2005年 | 422篇 |
2004年 | 555篇 |
2003年 | 481篇 |
2002年 | 432篇 |
2001年 | 338篇 |
2000年 | 316篇 |
1999年 | 206篇 |
1998年 | 182篇 |
1997年 | 184篇 |
1996年 | 207篇 |
1995年 | 177篇 |
1994年 | 211篇 |
1993年 | 169篇 |
1992年 | 151篇 |
1991年 | 89篇 |
1990年 | 68篇 |
1989年 | 68篇 |
1988年 | 60篇 |
1987年 | 75篇 |
1986年 | 59篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 13篇 |
1982年 | 38篇 |
1981年 | 41篇 |
1980年 | 48篇 |
1979年 | 67篇 |
1978年 | 52篇 |
1977年 | 52篇 |
1976年 | 37篇 |
1974年 | 13篇 |
1973年 | 17篇 |
排序方式: 共有9135条查询结果,搜索用时 15 毫秒
111.
112.
Victor Myagkov Oleg Bayukov Yurii Mikhlin Victor Zhigalov Liudmila Bykova Galina Bondarenko 《哲学杂志》2013,93(23):2595-2622
The effect of 0, 0.5, and 1?μm-thick Ag interlayers on the chemical interaction between Pd and Fe in epitaxial Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1)/MgO(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1)/MgO(0?0?1) trilayers has been studied using X-ray diffraction, 57Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and magnetic structural measurements. No mixing of Pd and Fe occurs via the chemically inert Ag layer at annealing temperatures up to 400?°C. As the annealing temperature is increased above 400?°C, a solid-state synthesis of an ordered L10-FePd phase begins in the Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1) film trilayers regardless of the thickness of the buffer Ag layer. In all samples, annealing above 500?°C leads to the formation of a disordered FexPd1?x(0?0?1) phase; however, in samples lacking the Ag layer, the synthesis of FexPd1?x is preceded by the formation of an ordered L12-FePd3 phase. An analysis of the X-ray photoelectron spectroscopy results shows that Pd is the dominant moving species in the reaction between Pd and Fe. According to the preliminary results, the 2.2?μm-thick Ag film does not prevent the synthesis of the L10-FePd phase and only slightly increases the phase’s initiation temperature. Data showing the ultra-fast transport of Pd atoms via thick inert Ag layers are interpreted as direct evidence of the long-range character of the chemical interaction between Pd and Fe. Thus, in the reaction state, Pd and Fe interact chemically even though the distance between them is about 104 times greater than an ordinary chemical bond length. 相似文献
113.
在核磁共振(NMR)波谱中,过长的数据采集时间会使很多化学以及分子生物学领域的高分辨率多维谱应用难以实现. 传统的解决办法是使用随机非均匀采样代替奈奎斯特采样,但这样会使谱图质量受损. 压缩传感的出现为此提供了更好的解决办法,合适的压缩传感重建算法可以通过很少的随机非均匀采样将谱图高质量的重建出来. 该文先介绍了一种可用于谱图重建的压缩传感重建算法,名为“平滑l0范数最小化法”,然后针对该算法对采样噪声鲁棒性较差的缺点进行了改进. 通过将改进后的算法与原算法在一维实数域信号以及NMR波谱信号重建实验中进行对比后表明,改进后的算法对噪声的鲁棒性明显提高,并能获得更好的重建性能. 相似文献
114.
On invexity-type nonlinear programming problems 总被引:3,自引:0,他引:3
Z. K. Xu 《Journal of Optimization Theory and Applications》1994,80(1):135-148
In this paper, we propose a new class of nonlinear programing, called SFJ-invex programming. The optimality characterization shows that a problem is SFJ-invex if and only if a Fritz John point together with its multiplier, is a Fritz John saddle point of the problem. Under any constraint qualification assumption, a problem is SFJ-invex if and only if a Kuhn-Tucker point together with its multiplier is a Kuhn-Tucker saddle point of the problem. Furthermore, a generalization of the SFJ-invex, class is developed; the applications to (h, )-convex programming, particularly geometric programming, and to generalized fractional programming provide a relaxation in constraint qualification for differentiable problems to get saddle-point type optimality criteria.The author wishes to thank the referee for helpful comments. 相似文献
115.
In this paper we consider a class of systems described by singular integrodifferential equations. This type of systems appear, for example, in the modeling of certain aeroelastic control problems. We study these systems in frequency domain framework and show the existence of finite-dimensional stabilizing controllers. An algorithmic procedure is outlined for the construction of such controllers. In order to illustrate the numerical aspects of this algorithm, we present an example involving the classical Theodorsen model of an airfoil, which fits in the class of systems considered here.This work was supported in part by the National Science Foundation under Grants DMS-8907019 and MSS-9203418. 相似文献
116.
Yoshinobu Kamishima 《Annals of Global Analysis and Geometry》1994,12(1):261-289
A strictly pseudoconvex pseudo-Hermitian manifoldM admits a canonical Lorentz metric as well as a canonical Riemannian metric. Using these metrics, we can define a curvaturelike function onM. AsM supports a contact form, there exists a characteristic vector field dual to the contact structure. If induces a local one-parameter group ofCR transformations, then a strictly pseudoconvex pseudo-Hermitian manifoldM is said to be a standard pseudo-Hermitian manifold. We study topological and geometric properties of standard pseudo-Hermitian manifolds of positive curvature or of nonpositive curvature . By the definition, standard pseudo-Hermitian manifolds are calledK-contact manifolds by Sasaki. In particular, standard pseudo-Hermitian manifolds of constant curvature turn out to be Sasakian space forms. It is well known that a conformally flat manifold contains a class of Riemannian manifolds of constant curvature. A sphericalCR manifold is aCR manifold whose Chern-Moser curvature form vanishes (equivalently, Weyl pseudo-conformal curvature tensor vanishes). In contrast, it is emphasized that a sphericalCR manifold contains a class of standard pseudo-Hermitian manifolds of constant curvature (i.e., Sasakian space forms). We shall classify those compact Sasakian space forms. When 0, standard pseudo-Hermitian closed aspherical manifolds are shown to be Seifert fiber spaces. We consider a deformation of standard pseudo-Hermitian structure preserving a sphericalCR structure.Dedicated to Professor Sasao Seiya for his sixtieth birthday 相似文献
117.
关于低阶K群的若干问题 总被引:1,自引:0,他引:1
本文主要介绍了低阶K群K_0,K_1,K_2及与它们相关的Bass-Quillen猜测、Birch-Tate猜测研究的最新进展.K_0与K_1方面主要通过对Bass~Quillen猜测研究说明K_0,K_1的作用,同时也给出了一些多项式环上投射模自同构群的计算公式.在K_2群方面,我们主要介绍了域上K_2群,代数整数环上K_2群以及著名的Birch-Tate猜想.并且也给出了K_2群一些计算方面的结果. 相似文献
118.
Singular Points Near an X_0-breaking Double Singular Fold Point in Z_2-symmetric Nonlinear Equations
SingularPointsNearanX_0-breakingDoubleSingularFoldPointinZ_2-symmetricNonlinearEquationsSuYi(苏毅)andWuwei(吴微)(DepartmentofMathe... 相似文献
119.
120.