全文获取类型
收费全文 | 14237篇 |
免费 | 1680篇 |
国内免费 | 1497篇 |
专业分类
化学 | 6869篇 |
晶体学 | 146篇 |
力学 | 405篇 |
综合类 | 107篇 |
数学 | 1086篇 |
物理学 | 3400篇 |
综合类 | 5401篇 |
出版年
2024年 | 36篇 |
2023年 | 194篇 |
2022年 | 340篇 |
2021年 | 395篇 |
2020年 | 392篇 |
2019年 | 452篇 |
2018年 | 341篇 |
2017年 | 339篇 |
2016年 | 455篇 |
2015年 | 598篇 |
2014年 | 781篇 |
2013年 | 954篇 |
2012年 | 1119篇 |
2011年 | 1177篇 |
2010年 | 963篇 |
2009年 | 995篇 |
2008年 | 1062篇 |
2007年 | 962篇 |
2006年 | 829篇 |
2005年 | 692篇 |
2004年 | 563篇 |
2003年 | 417篇 |
2002年 | 408篇 |
2001年 | 347篇 |
2000年 | 278篇 |
1999年 | 365篇 |
1998年 | 300篇 |
1997年 | 235篇 |
1996年 | 239篇 |
1995年 | 207篇 |
1994年 | 179篇 |
1993年 | 147篇 |
1992年 | 146篇 |
1991年 | 119篇 |
1990年 | 95篇 |
1989年 | 81篇 |
1988年 | 57篇 |
1987年 | 52篇 |
1986年 | 37篇 |
1985年 | 29篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
41.
Wei Jun Liao Xianfeng Chen Fucheng Chen Yuping Chen Yuxing Xia Yingli Chen 《Optics & Laser Technology》2004,36(8):603-606
In this paper, we first report that a new proton source, glutaric acid, has been used to fabricate optical waveguides in Z-cut lithium niobate crystals. The relationship was experimentally established between proton-exchanged (PE) waveguide parameters and fabrication conditions. It is shown that this new organic acid can be used to obtain deep PE waveguides in fast diffusion speed (0.275 μm2/h at 221°C) and with low loss (0.2 dB/cm). It provides an alternative approach for fabricating PE waveguides in lithium niobate substrate. 相似文献
42.
Under the nonresonant case where the carrier frequency of a Gaussian beam deviates from the resonant frequency of a Fabry–Perot etalon, the transmission of a Gaussian beam after incidenting nonnormally on a Fabry–Perot etalon has been investigated. The results show that under the nonresonant case, variations of the peak intensity, the position of the peak intensity and the spot size of the transmitted beam with the input angle behave differently and even with a reversed tendency compared with those obtained under the resonant case. 相似文献
43.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
44.
Optical characterization of bromo-alkoxyl-substituted copper phthalocyanine derivative thin films 总被引:2,自引:0,他引:2
A series of thin films of copper phthalocyanine derivatives with bromine and alkoxyl substituents [CuPc(OC8H17)4Brm, m=0,1,2,4] were prepared on single-crystal silicon substrates by spin coating. The ellipsometric spectra of the films have been studied on a rotating analyzer–polarizer type of scanning ellipsometer. The optical, dielectric constants and absorption coefficients of the films in 500–800 nm wavelength region were obtained. The results show that the complex refractive index, dielectric constants and absorption coefficient of these thin films are influenced regularly by bromine substituent on conjugated macrocycle. It was found that there are approximately linear relationships between the resonance absorption wavelengths of the films and the average number of bromine atoms substituted on the phthalocyanine ring. 相似文献
45.
46.
47.
KunHuaLIN MaoPingSONG ChenXiaDU QiaoHongZHANG YangJieWU 《中国化学快报》2003,14(7):673-676
The cyclomercurated ferrocenylimines containing heterocyclic ring were prepared by the condensation of cyclomercuration of acylferrocene with the appropriate heterocyclic amine.This procedure provides an efficient method for the synthesis of cyclomerucurated ferrocenylimines containing heterocyclic ring which are difficultly synthesized by the conventional method.The reaction mechanism is proposed. 相似文献
48.
基于SQL的报表生成系统 总被引:1,自引:0,他引:1
本文介绍的报表生成系统的取数方式可用SQL语句,使系统具有通用性,灵活性等特点。在系统实现中采用了多窗口全屏幕方式定义报表格式及取数方式。系统用户界面友好,直观、简单易学。 相似文献
49.
50.
本文根据空间的欧拉示性数是否为零.来确定该空间的自映射是否有不动点的几个方面的应用。 相似文献