全文获取类型
收费全文 | 14258篇 |
免费 | 2626篇 |
国内免费 | 1694篇 |
专业分类
化学 | 11109篇 |
晶体学 | 263篇 |
力学 | 760篇 |
综合类 | 207篇 |
数学 | 1344篇 |
物理学 | 4895篇 |
出版年
2024年 | 44篇 |
2023年 | 308篇 |
2022年 | 483篇 |
2021年 | 585篇 |
2020年 | 778篇 |
2019年 | 711篇 |
2018年 | 599篇 |
2017年 | 557篇 |
2016年 | 827篇 |
2015年 | 890篇 |
2014年 | 991篇 |
2013年 | 1219篇 |
2012年 | 1334篇 |
2011年 | 1366篇 |
2010年 | 992篇 |
2009年 | 864篇 |
2008年 | 897篇 |
2007年 | 779篇 |
2006年 | 659篇 |
2005年 | 590篇 |
2004年 | 457篇 |
2003年 | 403篇 |
2002年 | 392篇 |
2001年 | 277篇 |
2000年 | 202篇 |
1999年 | 184篇 |
1998年 | 122篇 |
1997年 | 95篇 |
1996年 | 95篇 |
1995年 | 78篇 |
1994年 | 75篇 |
1993年 | 62篇 |
1992年 | 65篇 |
1991年 | 48篇 |
1990年 | 55篇 |
1989年 | 37篇 |
1988年 | 40篇 |
1987年 | 34篇 |
1986年 | 25篇 |
1985年 | 35篇 |
1984年 | 29篇 |
1983年 | 31篇 |
1982年 | 24篇 |
1981年 | 30篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 22篇 |
1974年 | 24篇 |
1972年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
71.
72.
基于免疫算法的组合预测方法 总被引:3,自引:0,他引:3
利用免疫算法搜索全局最优解能力,提出了一种其于免疫算法的组合预测权系数确定的新方法,并给出了具体算法.仿真实验结果表明了免疫算法在组合预测方面具有很好的可行性和有效性. 相似文献
73.
Synthesis and herbicidal activity of O,O-dialkyl phenoxyacetoxyalkylphosphonates containing fluorine
Ting Chen 《Journal of fluorine chemistry》2006,127(2):291-295
A series of substituted phenoxyacetoxyalkylphosphonates bearing fluorine were designed and synthesized. All the new compounds were identified by elemental analysis, IR, 1H NMR and MS and were tested for herbicidal activity in greenhouse at a rate of 1.5 kg/ha. The results of preliminary bioassay showed that fluorine moiety introduced to the core structure could help to improve the herbicidal activity, and compounds with a 3-trifluoromethyl in benzene ring exhibited higher inhibitory activity. 相似文献
74.
Many natural products contain carbohydrate moieties that contribute to their biological activity. Manipulation of the carbohydrate domain of natural products through multiple glycosylations to identify new derivatives with novel biological activities has been a difficult and impractical process. We report a practical one‐pot enzymatic approach with regeneration of cosubstrates to synthesize analogues of vancomycin that contain an N‐alkyl glucosamine, which exhibited marked improvement in antibiotic activity against a vancomycin‐resistant strain of Enterococcus. 相似文献
75.
76.
本探讨了高等代数与解析几何进行一体化教学的必要性,研究了高等代数与解析几何进行一体化教学以后教学内容的协调性与教学手段的合理性,强调了数学实验在高等代数与解析几何一体化教学中的重要性。 相似文献
77.
Chi Kin Chau Kwang Mong Sim 《Operations Research Letters》2003,31(5):327-334
By showing that there is an upper bound for the price of anarchyρ(Γ) for a non-atomic congestion game Γ with only separable cost maps and fixed demands, Roughgarden and Tardos show that the cost of forgoing centralized control is mild. This letter shows that there is an upper bound for ρ(Γ) in Γ for fixed demands with symmetric cost maps. It also shows that there is a weaker bound for ρ(Γ) in Γ with elastic demands. 相似文献
78.
InAs/GaSb/AlSb resonant tunneling spin device concepts 总被引:1,自引:0,他引:1
David Z. -Y. Ting Xavier Cartoix 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):350
We discuss device concepts for creating spin-polarized current sources without external magnetic fields, using non-magnetic 6.1 Å semiconductor resonant tunneling structures. Spin filters, spin pumps, and spin transistors that exploit structural and bulk inversion asymmetries will be examined. 相似文献
79.
We report on Raman scattering of VO2 films prepared by radio frequency magnetron sputtering under different conditions. Our investigations revealed that the dominated Raman peaks shift towards high frequency for both V-rich and O-rich VO2 films, compared with the stoichiometry VO2 films. The experimental evidence is presented and the cause for nonstoichiometry dependence of Raman spectra of VO2 films is discussed. 相似文献
80.
Hong-jun Liu Wei Zhao Guo-fu Chen Yi-shan Wang Lian-jun Yu Chi Ruan Xue-feng Li 《Optics & Laser Technology》2004,36(4):3482-314
Experimental investigations of a type-I noncollinear phase-matched optical parametric amplification based on lithium triborate, which was pumped by a 5-ns second-harmonic pulses from a Q-switched Nd:YAG, seeded by a cw Ti:sapphire laser at 800 nm, was presented. The experiments generated 2-ns signal output pulses at 800 nm, the maximum signal output pulse energy reached 19 μJ, the corresponding parametric gain was 44 dB. Furthermore, the experiments demonstrate that the 65 nm-FWHM parametric fluorescence gain spectrum could also be observed. A quantitative account of the ultrabroadband parametric fluorescence gain spectrum was given with our theory. The experimental measurements are in agreement with theoretical calculations. 相似文献