全文获取类型
收费全文 | 14162篇 |
免费 | 2518篇 |
国内免费 | 1975篇 |
专业分类
化学 | 10221篇 |
晶体学 | 141篇 |
力学 | 1011篇 |
综合类 | 135篇 |
数学 | 1829篇 |
物理学 | 5318篇 |
出版年
2024年 | 46篇 |
2023年 | 261篇 |
2022年 | 444篇 |
2021年 | 440篇 |
2020年 | 529篇 |
2019年 | 499篇 |
2018年 | 433篇 |
2017年 | 466篇 |
2016年 | 669篇 |
2015年 | 685篇 |
2014年 | 781篇 |
2013年 | 1054篇 |
2012年 | 1210篇 |
2011年 | 1266篇 |
2010年 | 941篇 |
2009年 | 939篇 |
2008年 | 1010篇 |
2007年 | 858篇 |
2006年 | 858篇 |
2005年 | 699篇 |
2004年 | 596篇 |
2003年 | 558篇 |
2002年 | 498篇 |
2001年 | 392篇 |
2000年 | 351篇 |
1999年 | 302篇 |
1998年 | 254篇 |
1997年 | 232篇 |
1996年 | 253篇 |
1995年 | 175篇 |
1994年 | 165篇 |
1993年 | 153篇 |
1992年 | 124篇 |
1991年 | 102篇 |
1990年 | 99篇 |
1989年 | 70篇 |
1988年 | 52篇 |
1987年 | 47篇 |
1986年 | 44篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 18篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
41.
FengSHI HongYangLI XiaoJunPENG RongZHANG XiaoQiangCHEN JiangLiFAN LiChengSUN 《中国化学快报》2004,15(12):1407-1410
As photosensitizer for solar cell, a new ruthenium (Ⅱ) complex with four ester groups had been synthesized, in which a phenol substituted by {[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)amino]methyl} is covalently linked to ruthenium (Ⅱ) tris-bipyridine. The structures of the new compounds were confirmed by NMR and ESI-MS spectra. The electrochemical and photochemical properties were also studied. 相似文献
42.
New heuristics for over-constrained flight to gate assignments 总被引:1,自引:0,他引:1
We consider the over-constrained Airport Gate Assignment Problem where the number of flights exceed the number of gates available, and where the objectives are to minimize the number of ungated flights and the total walking distances. The problem is formulated as a binary quadratic programming problem. We design a greedy algorithm and use a Tabu Search meta-heuristic to solve the problem. The greedy algorithm minimizes ungated flights while we devise a new neighbourhood search technique, the Interval Exchange Move, which allows us flexibility in seeking good solutions, especially when flight schedules are dense in time. Experiments conducted give good results. 相似文献
43.
44.
Two Convergence Problems for Monotone Sequences 总被引:1,自引:0,他引:1
Eight measures of rate of convergence of monotone sequences of real numbers have been proposed and discussed in a paper by Beyer, Ebanks, and Qualls (Acta Appl. Math. 20 (1990), 267–284). These rates arose in discussions of dynamical systems. In the comparisons of these rates, two problems remained. A complete answer is given to one of the problems and a partial answer is given to the other problem. 相似文献
45.
46.
47.
Ross Anderson Cunsheng Ding Tor Helleseth Torleiv Klove 《Designs, Codes and Cryptography》1998,15(2):111-124
Previous researchers have designed shared control schemes with a view to minimising the likelihood that participants will conspire to perform an unauthorised act. But, human nature being what it is, systems inevitably fail; so shared control schemes should also be designed so that the police can identify conspirators after the fact. This requirement leads us to search for schemes with sparse access structures. We show how this can be done using ideas from coding theory. In particular, secret sharing schemes based on geometric codes whose dual [n,k,d] codes have d and n as their only nonzero weights are suitable. We determine their access structures and analyse their properties. We have found almost all of them, and established some relations among codes, designs and secret-sharing schemes. 相似文献
48.
In this paper, a construction of optimal constant composition codes is developed, and used to derive some series of new optimal
constant composition codes meeting the upper bound given by [13]. 相似文献
49.
Hong-Nian Li Xiao-Xiong WangWang-Feng Ding 《Journal of Electron Spectroscopy and Related Phenomena》2006
Using X-ray photoemission measurements, we have determined the attenuation length of C 1s photoelectrons in C60 film to be 21.5 Å with the incident photon energy of Mg Kα radiation. The inelastic mean free path calculated with the TPP-2M algorithm coincides fairly well with the experimentally determined attenuation length, indicating the validity of the algorithm to fullerene and fullerides. The inelastic mean free paths for some fullerides, i.e. K3C60, K6C60, Ba4C60, Sm2.75C60 and Sm6C60 are calculated to help the quantitative analyses of the photoemission spectra for these compounds. 相似文献
50.
采用快速提拉法生长出了透明、完整的γ-LiAlO2晶体,但是晶体的高熔点和易挥发性限制了γ-LiAlO2晶体质量.采用气相传输平衡法(vapor transport equilibration technique,VTE)工艺对晶体改性,半高宽(FWHM)值从116.9arcsec降至44.2arcsec,继续升高VTE处理温度至1300℃,FWHM值反而升高至55.2arcsec.快速提拉法生长出来晶体,[100]方向和[001]方向的热膨胀系数分别为17.2398×10-6/K,10.7664×10-6/K.经过三步VTE处理后[100]和[001]方向热膨胀系数降至16.6539×10-6/K和10.1784×10-6/K. 相似文献