全文获取类型
收费全文 | 18614篇 |
免费 | 3097篇 |
国内免费 | 2428篇 |
专业分类
化学 | 13614篇 |
晶体学 | 157篇 |
力学 | 1175篇 |
综合类 | 180篇 |
数学 | 2045篇 |
物理学 | 6968篇 |
出版年
2024年 | 76篇 |
2023年 | 430篇 |
2022年 | 698篇 |
2021年 | 741篇 |
2020年 | 823篇 |
2019年 | 754篇 |
2018年 | 635篇 |
2017年 | 572篇 |
2016年 | 900篇 |
2015年 | 810篇 |
2014年 | 1006篇 |
2013年 | 1397篇 |
2012年 | 1667篇 |
2011年 | 1703篇 |
2010年 | 1125篇 |
2009年 | 1115篇 |
2008年 | 1283篇 |
2007年 | 1101篇 |
2006年 | 948篇 |
2005年 | 842篇 |
2004年 | 643篇 |
2003年 | 567篇 |
2002年 | 500篇 |
2001年 | 414篇 |
2000年 | 373篇 |
1999年 | 410篇 |
1998年 | 347篇 |
1997年 | 318篇 |
1996年 | 336篇 |
1995年 | 295篇 |
1994年 | 244篇 |
1993年 | 201篇 |
1992年 | 177篇 |
1991年 | 138篇 |
1990年 | 133篇 |
1989年 | 92篇 |
1988年 | 75篇 |
1987年 | 74篇 |
1986年 | 42篇 |
1985年 | 50篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
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
3.
4.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
6.
The process of single liquid drop impact on thin liquid surface is numerically simulated with moving particle semi‐implicit method. The mathematical model involves gravity, viscosity and surface tension. The model is validated by the simulation of the experimental cases. It is found that the dynamic processes after impact are sensitive to the liquid pool depth and the initial drop velocity. In the cases that the initial drop velocity is low, the drop will be merged with the liquid pool and no big splash is seen. If the initial drop velocity is high enough, the dynamic process depends on the liquid depth. If the liquid film is very thin, a bowl‐shaped thin crown is formed immediately after the impact. The total crown subsequently expands outward and breaks into many tiny droplets. When the thickness of the liquid film increases, the direction of the liquid crown becomes normal to the surface and the crown propagates outward. It is also found that the radius of the crown is described by a square function of time: rC = [c(t ? t0)]0.5. When the liquid film is thick enough, a crown and a deep cavity inside it are formed shortly after the impact. The bottom of the cavity is initially oblate and then the base grows downward to form a sharp corner and subsequently the corner moves downward. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
7.
We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO3, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO3 crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent. 相似文献
8.
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
9.
报道了KDP晶体中的三倍频产生的实验研究,计算了比较了直接三倍频过程和级联过程对KDP晶体三阶有效非线性系数的贡献,并探讨了KDP作为非线性晶体材料三阶非线性系数测量基准的可行性。 相似文献
10.