全文获取类型
收费全文 | 29717篇 |
免费 | 4183篇 |
国内免费 | 3019篇 |
专业分类
化学 | 16082篇 |
晶体学 | 276篇 |
力学 | 1353篇 |
综合类 | 187篇 |
数学 | 2296篇 |
物理学 | 8476篇 |
无线电 | 8249篇 |
出版年
2024年 | 114篇 |
2023年 | 688篇 |
2022年 | 841篇 |
2021年 | 1122篇 |
2020年 | 1065篇 |
2019年 | 1013篇 |
2018年 | 874篇 |
2017年 | 916篇 |
2016年 | 1234篇 |
2015年 | 1298篇 |
2014年 | 1496篇 |
2013年 | 1992篇 |
2012年 | 2285篇 |
2011年 | 2382篇 |
2010年 | 1621篇 |
2009年 | 1669篇 |
2008年 | 1864篇 |
2007年 | 1755篇 |
2006年 | 1574篇 |
2005年 | 1311篇 |
2004年 | 1014篇 |
2003年 | 912篇 |
2002年 | 856篇 |
2001年 | 676篇 |
2000年 | 644篇 |
1999年 | 686篇 |
1998年 | 613篇 |
1997年 | 563篇 |
1996年 | 607篇 |
1995年 | 512篇 |
1994年 | 546篇 |
1993年 | 378篇 |
1992年 | 325篇 |
1991年 | 310篇 |
1990年 | 214篇 |
1989年 | 164篇 |
1988年 | 142篇 |
1987年 | 107篇 |
1986年 | 106篇 |
1985年 | 99篇 |
1984年 | 69篇 |
1983年 | 62篇 |
1982年 | 47篇 |
1981年 | 31篇 |
1980年 | 34篇 |
1979年 | 22篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1974年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
n-Propylamine and n-butylamine showed an inhibitory effect on cellulase A and cellulase B, while ethanediamine displayed a positive effect on both of these cellulases. Relative filter paper activity and relative CMCase activity of cellulase A and cellulase B measured at 50 °C were increased by 16.0 and 25.2 %, and 18.9 and 13.9 %, respectively, by the appearance of ethanediamine at a certain concentration. Also the addition of ethanediamine maintained the thermal stability of cellulase A and B at 65 °C to some extent and showed a stronger stabilizing effect on cellulase A than cellulase B. Third, the addition of ethanediamine within a certain concentration range enhanced the bio-polishing effect of cotton fabric enzymatic treatment at 50 °C to some extent, obtaining a close bio-polishing effect of cotton fabrics treated at 50 °C; the addition of ethanediamine saved some of the dose of cellulase A and B. Last but not least, the appearance of ethanediamine broadened the operating temperature of cellulase A to 65 °C, and it had a less positive effect on cellulase B at 65 °C. 相似文献
992.
Neville Boden Richard J. Bushby Kevin Donovan Quanying Liu Zhibao Lu Theo Kreouzis 《Liquid crystals》2013,40(12):1739-1748
A synthesis has been developed for 2,3,7,8,12,13-hexakis[2-(2-methoxyethoxy)ethoxy]-tricycloquinazoline (TCQ6EO2M) in which the ethylenoxy side chains are introduced before elaboration of the heterocylic core. This discogen gives a hexagonal columnar phase (Colh) between 77 and 233°C. n-Doping using potassium metal is facilitated firstly by the electron poor/π-deficient nature of the core and secondly by the polyethylenoxy side chains which complex the potassium K+ counter-ions. The conductivity of the Colh phase of TCQ6EO2M doped with 10 mol % potassium (σ ∥ = 1.1 x 10-3 S m-1) is substantially higher than that previously reported for 2,3,7,8,12,13-hexa(hexylthio)tricycloquinazoline doped with 6 mol % potassium (σ ∥ = 2.9 x 10-5 S m-1). Photoconductivity studies of TCQ6EO2M using a time of flight sample configuration show transient photocurrents for both holes and electrons. From these an upper limit on the mobility for the electrons is estimated as ~10-4 cm2 V-1 s-1 at 150°C which is of the same magnitude as that for hole mobilities in other columnar discotic liquid crystals. 相似文献
993.
Sheng‐wen Lu Ai‐hua Zhang Hui Sun Guang‐li Yan Ying Han Xiu‐hong Wu Xi‐jun Wang 《Biomedical chromatography : BMC》2013,27(12):1657-1663
994.
Guangzhou Lu Limin Yang Liqiang Wu 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):403-408
Abstract A simple, inexpensive, and efficient one-pot synthesis of 2-arylthiazoline derivatives under solvent-free conditions using a catalytic amount of 1-butyl-3-methylimidazolium tribromide with excellent product yields is reported. This methodology provides easy, quantitative access to various 2-arylthiazoline derivatives, using environmentally benign 1-butyl-3-methylimidazolium tribromide as a catalyst. 相似文献
995.
Hong-Hua Fang Shi-Yang Lu Xue-Peng Zhan Jing Feng Qi-Dai Chen Hai-Yu Wang Xing-Yuan Liu Hong-Bo Sun 《Organic Electronics》2013,14(3):762-767
Herein, a low threshold, wavelength-tunable, compact, two-photon pumped upconversion laser is presented. The surface emitting lasers are composed of melt-processed 1,4-bis[2-[4-[N,N-di(p-totyl)amino]phenyl]vinyl]benzene (DADSB) as active media and two designed distributed bragg reflectors. The melting fabrication process is very simple, and the lasing threshold is as low as 150 μJ cm?2 pulse?1, when pumped by a Ti:sapphire amplifier operating at 800 nm with a 150 fs pulse width. To the best of our knowledge, it is one of the lowest values for two-photon lasers. Lasing from multimode to single-mode oscillation is demonstrated. Tunable single mode oscillation was obtained at wavelength from 514 nm to 523 nm with a spectral width of less than 0.2 nm. 相似文献
996.
Yi Song Jiang-Li Ni Zhang-Yin Wang Yan Lu Lian-Fang Han 《International Journal of Theoretical Physics》2017,56(10):3175-3187
We present a new scheme for deterministically realizing the mutual interchange of quantum information between two distant parties via selected quantum states as the shared entangled resource. We first show the symmetric bidirectional remote state preparation (BRSP), where two single-qubit quantum states will be simultaneously exchanged in a deterministic manner provided that each of the users performs single-qubit von Neumann measurements with proper measurement bases as well as appropriate unitary operations, depending essentially on the outcomes of the prior measurements. Then we consider to extend the symmetric protocol to an asymmetric case, in which BRSP of a general single-qubit state and an arbitrary two-qubit state is investigated successfully. The necessary quantum operations and the employed quantum resources are feasible according to the present technology, resulting in that this protocol may be realizable in the realm of current physical experiment. 相似文献
997.
Nonlinear Dynamics - In this paper, we employ a novel method for solving the problem of the global exponential stability of quaternion-valued recurrent neural networks (QVNNs) with time-varying... 相似文献
998.
999.
1000.
Abstract: Titanium tetrachloride was reduced by zinc powder in THF to produce low-valent titanium which reacted with 4,4-dicyano-1,3-diaryl-1-buanone to give the derivatives of 1-amino-2-cyanocyclopentene. 相似文献