全文获取类型
收费全文 | 22458篇 |
免费 | 3808篇 |
国内免费 | 2872篇 |
专业分类
化学 | 16220篇 |
晶体学 | 307篇 |
力学 | 1498篇 |
综合类 | 151篇 |
数学 | 2387篇 |
物理学 | 8575篇 |
出版年
2024年 | 88篇 |
2023年 | 517篇 |
2022年 | 932篇 |
2021年 | 932篇 |
2020年 | 1003篇 |
2019年 | 940篇 |
2018年 | 834篇 |
2017年 | 808篇 |
2016年 | 1208篇 |
2015年 | 1131篇 |
2014年 | 1428篇 |
2013年 | 1714篇 |
2012年 | 2075篇 |
2011年 | 2018篇 |
2010年 | 1415篇 |
2009年 | 1331篇 |
2008年 | 1496篇 |
2007年 | 1315篇 |
2006年 | 1188篇 |
2005年 | 999篇 |
2004年 | 739篇 |
2003年 | 560篇 |
2002年 | 602篇 |
2001年 | 497篇 |
2000年 | 425篇 |
1999年 | 410篇 |
1998年 | 329篇 |
1997年 | 274篇 |
1996年 | 305篇 |
1995年 | 288篇 |
1994年 | 217篇 |
1993年 | 161篇 |
1992年 | 162篇 |
1991年 | 165篇 |
1990年 | 136篇 |
1989年 | 106篇 |
1988年 | 89篇 |
1987年 | 72篇 |
1986年 | 52篇 |
1985年 | 47篇 |
1984年 | 33篇 |
1983年 | 28篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1959年 | 2篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Qin Yin Shou-Guo Wang Xiao-Wei Liang De-Wei Gao Jun Zheng Shu-Li You 《Chemical science》2015,6(7):4179-4183
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation. 相似文献
2.
Polypyrrole Shell@3D‐Ni Metal Core Structured Electrodes for High‐Performance Supercapacitors 下载免费PDF全文
Gao‐Feng Chen Yu‐Zhi Su Pan‐Yong Kuang Zhao‐Qing Liu Dao‐Yi Chen Xu Wu Nan Li Prof. Shi‐Zhang Qiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4614-4621
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively). 相似文献
3.
4.
Ji-Dong Lou Chun-Ling Gao Li Li Zhi-Gang Fang 《Monatshefte für Chemie / Chemical Monthly》2006,41(10):1071-1074
A new procedure for the selective oxidation of alcohols to the corresponding aldehydes and ketones with potassium permanganate
supported on aluminum silicate at room temperature under solvent-free conditions and shaking is reported. 相似文献
5.
6.
We analyze the dynamics of an AdS5 braneworld with matter fields when gravity is allowed to deviate from the Einstein form on the brane. We consider exact five-dimensional warped solutions which are associated with conformal bulk fields of weight –4 and describe on the brane the following three dynamics: those of inhomogeneous dust, of generalized dark radiation, and of homogeneous polytropic dark energy. We show that, with modified gravity on the brane, the existence of such dynamical geometries requires the presence of non-conformal matter fields confined to the brane. 相似文献
7.
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
8.
9.
Polypropylene (PP) was modified with elastomer or CaCO3 particles of two different sizes (1 μm and 50 nm) in various volume fractions. The dispersion morphology and mechanical properties of the two systems were investigated as functions of the particle size and volume fraction of the modifier. The brittle‐to‐tough transition occurred when the matrix ligament thickness was less than the critical ligament thickness, which was about 0.1 μm for the PP used here, being independent of the type of modifier. At the same matrix ligament thickness, the improvement of the toughness was obviously higher with the elastomer rather than with CaCO3, but adding CaCO3 increased the modulus of PP. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1656–1662, 2004 相似文献
10.