全文获取类型
收费全文 | 14892篇 |
免费 | 792篇 |
国内免费 | 695篇 |
专业分类
化学 | 5237篇 |
晶体学 | 192篇 |
力学 | 617篇 |
综合类 | 89篇 |
数学 | 5502篇 |
物理学 | 3484篇 |
无线电 | 1258篇 |
出版年
2023年 | 70篇 |
2022年 | 127篇 |
2021年 | 121篇 |
2020年 | 217篇 |
2019年 | 252篇 |
2018年 | 222篇 |
2017年 | 287篇 |
2016年 | 279篇 |
2015年 | 258篇 |
2014年 | 367篇 |
2013年 | 713篇 |
2012年 | 449篇 |
2011年 | 674篇 |
2010年 | 581篇 |
2009年 | 1175篇 |
2008年 | 1092篇 |
2007年 | 1058篇 |
2006年 | 948篇 |
2005年 | 757篇 |
2004年 | 800篇 |
2003年 | 736篇 |
2002年 | 665篇 |
2001年 | 560篇 |
2000年 | 479篇 |
1999年 | 391篇 |
1998年 | 365篇 |
1997年 | 306篇 |
1996年 | 298篇 |
1995年 | 234篇 |
1994年 | 288篇 |
1993年 | 204篇 |
1992年 | 180篇 |
1991年 | 121篇 |
1990年 | 98篇 |
1989年 | 89篇 |
1988年 | 80篇 |
1987年 | 91篇 |
1986年 | 77篇 |
1985年 | 68篇 |
1984年 | 72篇 |
1983年 | 29篇 |
1982年 | 64篇 |
1981年 | 58篇 |
1980年 | 59篇 |
1979年 | 80篇 |
1978年 | 62篇 |
1977年 | 63篇 |
1976年 | 47篇 |
1974年 | 18篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 239 毫秒
61.
X. Yang 《Applied Surface Science》2006,252(10):3647-3657
The room-temperature adsorption and thermally induced processes of propionic acid and pyruvic acid on Ni(1 0 0) have been investigated by electron energy loss spectroscopy (EELS). Computational vibrational analysis of the optimized bidentate structures for acid-Ni model complexes (involving the organic acid and a Ni atom) has been performed by using the two-layer ONIOM method with the Density Functional Theory and used to interpret the vibrational EELS data. Dehydrogenation of the hydroxyl group is found to result in bonding of the carboxylate group in the propionate and pyruvate adspecies to either a single Ni surface atom in a bidentate configuration or two neighbouring Ni atoms in a bridge configuration. Given the similarities in the total energies and related vibrational frequencies obtained by the calculations in the case of pyruvate adspecies, it is difficult to differentiate the alternate adsorption structure, in which the keto O and hydroxyl O atoms are bonded to a Ni atom in a five-member chelate ring configuration. Furthermore, temperature-dependent EELS studies show that both the propionate and pyruvate adspecies could decompose upon annealing to above 400 K and further dissociate to CO adspecies above 550 K and to C and/or O above 600 K. 相似文献
62.
We study the existence and the continuity properties of the boundary values on the real axis of the resolvent of a self-adjoint operator H in the framework of the conjugate operator method initiated by Mourre. We allow the conjugate operator A to be the generator of a C0-semigroup (finer estimates require A to be maximal symmetric) and we consider situations where the first commutator [H,iA] is not comparable to H. The applications include the spectral theory of zero mass quantum field models. 相似文献
63.
T. Domínguez Benavides 《Journal of Mathematical Analysis and Applications》2004,291(1):100-108
Let X be a Banach space whose characteristic of noncompact convexity is less than 1 and satisfies the nonstrict Opial condition. Let C be a bounded closed convex subset of X, KC(X) the family of all compact convex subsets of X and T a nonexpansive mapping from C into KC(X) with bounded range. We prove that T has a fixed point. The nonstrict Opial condition can be removed if, in addition, T is an 1-χ-contractive mapping. 相似文献
64.
Using Lagrange's multiplier rule, we find upper and lower bounds of the energy of a bipartite graph G, in terms of the number of vertices, edges and the spectral moment of fourth order. Moreover, the upper bound is attained in a graph G if and only if G is the graph of a symmetric balanced incomplete block design (BIBD). Also, we determine the graphs for which the lower bound is sharp. 相似文献
65.
继续作者最近的研究,用所谓的Hankel向量方法建立S[a,b]函数类中带边界插值数据的Nevanlinna-Pick插值问题与[a,b]上的某种带约束条件的Hausdorff矩量问题之间解集之间明确的一一对应关系.通过N[a,b]函数类与S[a,b]函数类之间的联系,从而由BNP(N[a,b])问题的可解性准则和解的参数化描述获得BNP(S[a,b)问题的可解性准则和解的参数化表示. 相似文献
66.
基于Gibbs模型的提高图像分辨率方法 总被引:5,自引:3,他引:2
在提高图像分辨率过程中,选择合适的成像模型是获得高分辨率图像的一个关键因素。提出一种基于最大后验概率、采用Gibbs成像模型,并利用多帧序列图像重构高分辨率图像的方法,充分利用序列图像之间的累加信息,从而快速地获得较其他方法更优的高分辨率图像。 相似文献
67.
68.
69.
Linear mixed 0–1 integer programming problems may be reformulated as equivalent continuous bilevel linear programming (BLP)
problems. We exploit these equivalences to transpose the concept of mixed 0–1 Gomory cuts to BLP. The first phase of our new
algorithm generates Gomory-like cuts. The second phase consists of a branch-and-bound procedure to ensure finite termination
with a global optimal solution. Different features of the algorithm, in particular, the cut selection and branching criteria
are studied in details. We propose also a set of algorithmic tests and procedures to improve the method. Finally, we illustrate
the performance through numerical experiments. Our algorithm outperforms pure branch-and-bound when tested on a series of
randomly generated problems.
Work of the authors was partially supported by FCAR, MITACS and NSERC grants. 相似文献
70.
D. Guidotti J. G. Wilman A. J. Ricci 《Applied Physics A: Materials Science & Processing》1992,54(6):570-573
An instrument is described that can be used to monitor, with unprecedented sensitivity, changes in the optical reflectivity due to crystailine damage incurred during ion implantation. It is shown that at the shot-noise limit, changes in the optical reflectivity of silicon as small as 5·10–7 can be measured in a 10 Hz bandwidth with a signal-to-noise ratio of 100, corresponding to an extrapolated uniform implantation dose of 5·108 cm–2 for 11B+ at 50 keV in silicon. 相似文献