全文获取类型
收费全文 | 29896篇 |
免费 | 4312篇 |
国内免费 | 3755篇 |
专业分类
化学 | 22405篇 |
晶体学 | 417篇 |
力学 | 1731篇 |
综合类 | 322篇 |
数学 | 3172篇 |
物理学 | 9916篇 |
出版年
2024年 | 81篇 |
2023年 | 486篇 |
2022年 | 956篇 |
2021年 | 1021篇 |
2020年 | 1088篇 |
2019年 | 1107篇 |
2018年 | 917篇 |
2017年 | 881篇 |
2016年 | 1382篇 |
2015年 | 1308篇 |
2014年 | 1609篇 |
2013年 | 2185篇 |
2012年 | 2539篇 |
2011年 | 2655篇 |
2010年 | 1849篇 |
2009年 | 1701篇 |
2008年 | 1973篇 |
2007年 | 1675篇 |
2006年 | 1602篇 |
2005年 | 1458篇 |
2004年 | 1168篇 |
2003年 | 1025篇 |
2002年 | 1106篇 |
2001年 | 799篇 |
2000年 | 693篇 |
1999年 | 641篇 |
1998年 | 504篇 |
1997年 | 470篇 |
1996年 | 430篇 |
1995年 | 425篇 |
1994年 | 348篇 |
1993年 | 297篇 |
1992年 | 284篇 |
1991年 | 229篇 |
1990年 | 206篇 |
1989年 | 148篇 |
1988年 | 129篇 |
1987年 | 99篇 |
1986年 | 98篇 |
1985年 | 109篇 |
1984年 | 57篇 |
1983年 | 51篇 |
1982年 | 36篇 |
1981年 | 37篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1971年 | 5篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
玻璃陶瓷材料中Tm3+离子红外到蓝色上转换发光 总被引:4,自引:0,他引:4
系统研究了PbF2+GeO2+WO3ⅩⅣTmF3玻璃陶瓷材料中,在近红外光(1.06μm)激发下,Tm3+离子的发光特性.实验中观测到Tm3+离子的两组峰值位置分别在20920cm-1和22173cm-1的蓝色上转换发光,并证实这两组上转换发光分别与吸收三个和四个光子有关,同时建立了上转换发光的模型.为了选择最佳掺杂浓度,详细地测量了Tm3+离子峰值为20920cm-1的蓝色上转换发光强度与TmF3浓度的关系. 相似文献
2.
Guofen Yu Yuanci Gao Shenggang Liu Wenxiang Wang Jin Wu 《International Journal of Infrared and Millimeter Waves》2002,23(8):1261-1269
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources. 相似文献
3.
Syntheses, structures, and properties of novel molybdenum and tungsten complexes of fullerenes 总被引:1,自引:0,他引:1
The synthesis and characterization of several fullerene-based organometallic complexes containing Mo and W is reported. 相似文献
4.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
5.
使用Monte Carlo模拟的方法得出了随机粗糙表面,在Kirchhoff近似的基础上,利用数值分析的方法分析了一维随机粗糙表面的散射特征,得出了一维随机粗糙表面散射分布曲线,我们还考虑了遮蔽效应的影响,并且讨论了Kirchhoff近似的有效性。 相似文献
6.
7.
5-Perfluorophenyl 4,5-dihydro-1H-pyrazoles were synthesized from 1,3-dipolar cycloaddition reaction of perfluorobenyl 2,4,6-triisopropylbenzenesulfonylhydrazone and α,β-unsaturated carbonyl compounds or acrylonitrile in THF or water. It was worthy to note that better results were obtained when water was employed as the solvent, which was considered as an effective, economic and environmentally friendly method to synthesize these pyrazole derivatives. 相似文献
8.
9.
A novel and simple two-frequency Brillouin fiber laser is presented. It is based on a fiber Fabry-Perot cavity with fiber Bragg gratings as reflectors. The model of stimulated Brillouin scattering in fiber grating-based Fabry-Perot resonator is investigated. The laser allows conversion efficiency of close to 100% and suppresses the higher-order Stokes waves. The theoretical prediction is presented and the experimental demonstration is realized. 相似文献
10.
Zhaoqiang Lu Lin Cheng Jun Li Kai Zhang Song Yi Jingui Qin 《Journal of polymer science. Part A, Polymer chemistry》2004,42(4):925-932
The synthesis and structural characterization of a series of novel, fluorinated poly(phthalazinone ether)s containing perfluorophenylene moieties are described. The monomers, 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a – 2d ), were conveniently and efficiently synthesized from phenols and phthalic anhydride in two steps via 2‐(4′‐hydroxybenzoyl)benzoic acids, which were first obtained by the Friedel–Crafts reaction in good yields and with high stereoselectivity and were then converted into 2a – 2d by fusion with hydrazine. All the polymers were prepared by nucleophilic aromatic substitution (SNAr) polycondensation between the compounds perfluorobiphenyl and 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a ‐ 2d ). The resulting fluorinated polymers were readily soluble in common organic solvents (e.g., CHCl3, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, N‐methylpyrrolidone, etc.) at room temperature. Their weight‐average molecular weights and the polydispersities ranged from (7.96–18.25) × 103 to 1.31–2.71, respectively. Their glass‐transition temperatures varied from 213 to 263 °C. They were all stable up to 390 °C both in air and in argon. The 5% weight‐loss temperatures of these polymers in air and argon ranged from 393–487 to 437–509 °C, respectively. Wide‐angle X‐ray diffraction studies indicated they were all amorphous and could be attributed to the presence of kink nonplanar moiety, phenyl phthalazinone along the polymer backbone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 925–932, 2004 相似文献