全文获取类型
收费全文 | 217683篇 |
免费 | 19854篇 |
国内免费 | 15678篇 |
专业分类
化学 | 94401篇 |
晶体学 | 1850篇 |
力学 | 12062篇 |
综合类 | 668篇 |
数学 | 43451篇 |
物理学 | 53516篇 |
无线电 | 47267篇 |
出版年
2024年 | 550篇 |
2023年 | 3151篇 |
2022年 | 4189篇 |
2021年 | 5332篇 |
2020年 | 5208篇 |
2019年 | 4704篇 |
2018年 | 15241篇 |
2017年 | 14694篇 |
2016年 | 12232篇 |
2015年 | 7069篇 |
2014年 | 7980篇 |
2013年 | 10053篇 |
2012年 | 15312篇 |
2011年 | 22519篇 |
2010年 | 14979篇 |
2009年 | 14779篇 |
2008年 | 15523篇 |
2007年 | 17028篇 |
2006年 | 7737篇 |
2005年 | 8085篇 |
2004年 | 6470篇 |
2003年 | 6096篇 |
2002年 | 4647篇 |
2001年 | 3332篇 |
2000年 | 3094篇 |
1999年 | 3082篇 |
1998年 | 2689篇 |
1997年 | 2310篇 |
1996年 | 2338篇 |
1995年 | 2015篇 |
1994年 | 1690篇 |
1993年 | 1432篇 |
1992年 | 1227篇 |
1991年 | 1056篇 |
1990年 | 876篇 |
1989年 | 647篇 |
1988年 | 519篇 |
1987年 | 434篇 |
1986年 | 440篇 |
1985年 | 339篇 |
1984年 | 263篇 |
1983年 | 227篇 |
1982年 | 182篇 |
1981年 | 122篇 |
1980年 | 111篇 |
1979年 | 71篇 |
1978年 | 62篇 |
1973年 | 43篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A hybrid cluster complex, formed by chelating a chromogenic ligand to a [2Fe-2S] cluster, sensitively exhibited differential colorimetric responses towards Hg2+, Cd2+, Cr3+, Pb2, Sn2+, Cu2+, Zn2+, Fe3+ and Co2+ in water at physiological pH. Speciation of some of these metal elements, such as Cr(III) and Sn(IV), was also studied by UV/Vis absorption. 相似文献
92.
Raymond Mackay Jie Zhang Qi Wu Yuzhuo Li 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):343-348
The longitudinal relaxation times (T1) of water in concentrated silica and alumina slurries were measured as a function of solids content. It was shown that the results could be fit very well with a two-phase fast-exchange model between free and surface-bound water. As expected, values of T1 for bound water were in the order of 20–2000 times lower than that for free water, indicating a higher effective viscosity of the surface-bound water. The strength of the interaction depended on the particular surface, and all of the aluminas examined interacted more strongly with water than the two silicas studied, which themselves differed considerably. The chemical mechanical polishing (CMP) removal rate of tantalum by silica slurries was shown to be directly correlated with the interaction parameters, derived from the NMR relation times rather than with total surface hydroxyl group concentration. 相似文献
93.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
94.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
95.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
96.
Harish C. Bahl Stanley Zionts 《The Journal of the Operational Research Society》1987,38(12):1141-1148
Scheduling the production of several items requires the determination of production quantities in different periods in the presence of resource constraints. Several approximate and heuristic algorithms have been proposed to solve this problem. However, no method for finding an optimal solution has as yet been developed. It is shown that the problem may be solved advantageously using Benders' decomposition. The subproblem in Benders' decomposition is shown to be a transportation problem, and some strategies for solving the master problem are indicated. The paper concludes with a sample problem demonstrating the application of the method. 相似文献
97.
Jensen and Toft 8 conjectured that every 2‐edge‐connected graph without a K5‐minor has a nowhere zero 4‐flow. Walton and Welsh 19 proved that if a coloopless regular matroid M does not have a minor in {M(K3,3), M*(K5)}, then M admits a nowhere zero 4‐flow. In this note, we prove that if a coloopless regular matroid M does not have a minor in {M(K5), M*(K5)}, then M admits a nowhere zero 4‐flow. Our result implies the Jensen and Toft conjecture. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
98.
99.
100.