全文获取类型
收费全文 | 157986篇 |
免费 | 2889篇 |
国内免费 | 1065篇 |
专业分类
化学 | 85985篇 |
晶体学 | 1734篇 |
力学 | 7060篇 |
综合类 | 51篇 |
数学 | 16175篇 |
物理学 | 50935篇 |
出版年
2021年 | 1208篇 |
2020年 | 1450篇 |
2019年 | 1419篇 |
2018年 | 1704篇 |
2017年 | 1666篇 |
2016年 | 2796篇 |
2015年 | 1897篇 |
2014年 | 2802篇 |
2013年 | 6793篇 |
2012年 | 5559篇 |
2011年 | 6947篇 |
2010年 | 4721篇 |
2009年 | 4691篇 |
2008年 | 6128篇 |
2007年 | 6175篇 |
2006年 | 5793篇 |
2005年 | 5272篇 |
2004年 | 4661篇 |
2003年 | 4013篇 |
2002年 | 4070篇 |
2001年 | 4448篇 |
2000年 | 3446篇 |
1999年 | 2717篇 |
1998年 | 2366篇 |
1997年 | 2291篇 |
1996年 | 1961篇 |
1995年 | 1959篇 |
1994年 | 1939篇 |
1993年 | 1769篇 |
1992年 | 2008篇 |
1991年 | 2135篇 |
1990年 | 1922篇 |
1989年 | 1908篇 |
1988年 | 1853篇 |
1987年 | 1749篇 |
1986年 | 1668篇 |
1985年 | 2180篇 |
1984年 | 2309篇 |
1983年 | 1872篇 |
1982年 | 2055篇 |
1981年 | 1943篇 |
1980年 | 1858篇 |
1979年 | 2010篇 |
1978年 | 2177篇 |
1977年 | 2050篇 |
1976年 | 2090篇 |
1975年 | 2004篇 |
1974年 | 2059篇 |
1973年 | 2044篇 |
1972年 | 1341篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
61.
Robin F. Weitkamp Beate Neumann Hans‐Georg Stammler Berthold Hoge 《Angewandte Chemie (International ed. in English)》2020,59(14):5494-5499
We report on the first examples of isolated silanol–silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol–silanolate anions are postulated intermediates in the hydroxide‐mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization. 相似文献
62.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
63.
64.
65.
66.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
67.
金属光阴极因其超短脉冲发射和运行寿命长的特性从而具有重要应用价值,但是较高的功函数和较强的电子散射使其需要采用高能量紫外光子激发且光电发射量子效率极低.本文利用Mie散射共振效应增强银纳米颗粒中的局域光学态密度,提升光吸收率和电子的输运效率,并利用激活层降低银的功函数,从而增强光阴极在可见光区的量子效率.采用时域有限差分方法分析银纳米球阵列的光学共振特性,采用磁控溅射和退火工艺在银/氧化锡铟复合衬底上制备银纳米球,紧接着在其表面沉积制备铯激活层,最后在高真空腔体中测试光电发射量子效率.实验结果表明平均粒径150 nm的银纳米球光阴极在425 nm波长的量子效率超过0.35%,为相同激活条件下银薄膜光阴极的12倍,峰值波长与理论计算的Mie共振波长相符合. 相似文献
68.
Archiv der Mathematik - A generalized Baumslag–Solitar group is a finitely generated group that acts on a tree with infinite cyclic edge and vertex stabilizers. A group G is residually a... 相似文献
69.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
70.
Ortiz Adolfo Yang Jianhua Coccolo Mattia Seoane Jesús M. Sanjuán Miguel A. F. 《Nonlinear dynamics》2020,102(4):2323-2337
Nonlinear Dynamics - The main purpose of this paper is to study both the underdamped and the overdamped dynamics of the nonlinear Helmholtz oscillator with a fractional-order damping. For that... 相似文献