全文获取类型
收费全文 | 10548篇 |
免费 | 2199篇 |
国内免费 | 782篇 |
专业分类
化学 | 4104篇 |
晶体学 | 128篇 |
力学 | 1336篇 |
综合类 | 105篇 |
数学 | 1074篇 |
物理学 | 6782篇 |
出版年
2024年 | 13篇 |
2023年 | 74篇 |
2022年 | 165篇 |
2021年 | 156篇 |
2020年 | 237篇 |
2019年 | 205篇 |
2018年 | 214篇 |
2017年 | 287篇 |
2016年 | 330篇 |
2015年 | 312篇 |
2014年 | 555篇 |
2013年 | 672篇 |
2012年 | 730篇 |
2011年 | 783篇 |
2010年 | 618篇 |
2009年 | 744篇 |
2008年 | 719篇 |
2007年 | 829篇 |
2006年 | 739篇 |
2005年 | 636篇 |
2004年 | 661篇 |
2003年 | 520篇 |
2002年 | 485篇 |
2001年 | 404篇 |
2000年 | 387篇 |
1999年 | 297篇 |
1998年 | 283篇 |
1997年 | 248篇 |
1996年 | 192篇 |
1995年 | 182篇 |
1994年 | 112篇 |
1993年 | 130篇 |
1992年 | 113篇 |
1991年 | 84篇 |
1990年 | 84篇 |
1989年 | 69篇 |
1988年 | 48篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 24篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 873 毫秒
41.
In this article we prove the existence of the solution to the mixed problem for Euler–Bernoulli beam equation with memory term. The existence is proved by means of the Faedo–Galerkin method and the exponential decay is obtained by making use of the multiplier technique combined with integral inequalities due to Komornik. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
42.
本文通过研究匹配问题的实例空间,匈牙利算法和解空间三者之间的关系,指出S实例空间的数目与问题复杂度之间的关系既不是充分也不是必要的,而如何对问题的解空间进行合理的分解才能是问题的关键。 相似文献
43.
A hybrid heuristic method for combinatorial optimization problems is proposed that combines different classical techniques such as tree search procedures, bounding schemes and local search. The proposed method enhances the classic beam search approach by applying to each partial solution corresponding to a node selected by the beam, a further test that checks whether the current partial solution is dominated by another partial solution at the same level of the search tree. If this is the case, the latter solution becomes the new current partial solution. This step allows to partially recover from previous wrong decisions of the beam search procedure and can be seen as a local search step on the partial solution. We present here the application to two well known combinatorial optimization problems: the two-machine total completion time flow shop scheduling problem and the uncapacitated p-median location problem. In both cases the method strongly improves the performances with respect to the basic beam search approach and is competitive with the state of the art heuristics. 相似文献
44.
I. Peshko G. Galich M. Lopiychuk A. Khizhnyak V. Nakvasuk 《Optics & Laser Technology》1997,29(4):211-215
A laser system containing four CW Nd:YAG double-rod lasers, transforming optics and a fibre with input-output optics has been designed and investigated. It is shown that reduction of the beam parameter product of the non-Gaussian beams in the image space of the lens has made it possible to collect the emission of four lasers to the same fibre. Independent laser operation has provided the output power control in the range of 10–900 W with a stable light spot size on the input end of the fibre. 相似文献
45.
46.
I. Ogawa Y. Miyake T. Idehara S. Sabchevski 《International Journal of Infrared and Millimeter Waves》2002,23(1):1-19
A novel focusing mirror based on the shifting of the beam phase according to the Gaussian beam optics enabled us to realize a focusing elements with different focal lengths in different directions and to convert the gyrotron output into a Gaussian-like beam. In this paper, we compare the quality of beams produced by the new system (which includes novel mirrors) and a conventional system consisting of a quasi-optical antenna, an ellipsoidal mirror and two parabolic cylinder mirrors. 相似文献
47.
The response to Hg(II) of a thin all-solid-state Te-doped silver chalcogenide membrane, described by the general formula Ag2 + δSe1 − xTex, which has been electrochemically prepared following a previously proposed approach, has been investigated. The kinetics of formation of the membrane's secondary dynamic response to Hg(II) has been successfully combined with the precise timing and transient signal, typical for flow-injection (FI) measurements, in developing a sensitive and reliable mercury FI detector. Under optimized stream conditions it exhibits a linear Nernstian response, with a double slope of the calibration graph of 59 mV dec−1, over the mercury(II) concentration range 10−6 − 10−3 M, the typical sample throughput amounting to about 70 samples per hour. The observed chemical amplification of the signal is due to the specificity of the processes dominating the initial step in formation of the steady-state signal of the membrane to mercury. The analytical performance of the Hg(II) FI detector, as regards sensitivity, reproducibility, selectivity and long-term stability has been thoroughly investigated. The exact procedure for membrane electrodeposition is given and the potential of the proposed approach as a cost-effective way for preparing chalcogenides of unique structure and properties has been outlined in the above context. 相似文献
48.
A flow-injection system for the determination of 3-hydroxybutyrate in serum is described. 3-Hydroxybutyrate dehydrogenase is immobilized on poly(vinyl alcohol) beads and incorporated in a flow-injection system. 1-Methoxy-5-methylphenazinium methylsulphate reacts with enzymatically generated NADH to give H2O2, which is detected chemiluminometrically with the reaction of luminol and hexacynoferrate(III). Serum is diluted and filtered through an ultrafiltration membrane. The system responds linearly to injected samples (80 μl) in the concentration range 0.5–300 μM; the detection limit is 0.1 μM. The within-day relative standard deviation (n = 90) for 58 μM 3-hydroxybutyrate in serum is 0.8%. The maximum throughout is 20 samples per hour. The immobilized enzyme is stable for at least 1 month. 相似文献
49.
50.