全文获取类型
收费全文 | 178673篇 |
免费 | 17755篇 |
国内免费 | 10413篇 |
专业分类
化学 | 92936篇 |
晶体学 | 1924篇 |
力学 | 13041篇 |
综合类 | 534篇 |
数学 | 42768篇 |
物理学 | 55638篇 |
出版年
2024年 | 369篇 |
2023年 | 2134篇 |
2022年 | 3645篇 |
2021年 | 3964篇 |
2020年 | 4249篇 |
2019年 | 4139篇 |
2018年 | 13046篇 |
2017年 | 12646篇 |
2016年 | 10744篇 |
2015年 | 5716篇 |
2014年 | 6291篇 |
2013年 | 8064篇 |
2012年 | 12939篇 |
2011年 | 19593篇 |
2010年 | 11678篇 |
2009年 | 11785篇 |
2008年 | 12761篇 |
2007年 | 14285篇 |
2006年 | 5668篇 |
2005年 | 5840篇 |
2004年 | 4841篇 |
2003年 | 4530篇 |
2002年 | 3371篇 |
2001年 | 2211篇 |
2000年 | 2044篇 |
1999年 | 2219篇 |
1998年 | 2032篇 |
1997年 | 1856篇 |
1996年 | 2080篇 |
1995年 | 1614篇 |
1994年 | 1531篇 |
1993年 | 1257篇 |
1992年 | 1121篇 |
1991年 | 1045篇 |
1990年 | 840篇 |
1989年 | 621篇 |
1988年 | 522篇 |
1987年 | 439篇 |
1986年 | 431篇 |
1985年 | 364篇 |
1984年 | 283篇 |
1983年 | 190篇 |
1982年 | 183篇 |
1981年 | 145篇 |
1980年 | 122篇 |
1979年 | 88篇 |
1978年 | 68篇 |
1976年 | 52篇 |
1974年 | 56篇 |
1973年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Tuning the Basicity of Cyano‐Containing Ionic Liquids to Improve SO2 Capture through Cyano–Sulfur Interactions 下载免费PDF全文
Dr. Guokai Cui Fengtao Zhang Xiuyuan Zhou Prof. Haoran Li Prof. Jianji Wang Prof. Congmin Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(14):5632-5639
A new approach has been developed to improve SO2 sorption by cyano‐containing ionic liquids (ILs) through tuning the basicity of ILs and cyano–sulfur interaction. Several kinds of cyano‐containing ILs with different basicity were designed, prepared, and used for SO2 capture. The interaction between these cyano‐containing ILs and SO2 was investigated by FTIR and NMR methods. Spectroscopic investigations and quantum chemical calculations showed that dramatic effects on SO2 capacity originate from the basicity of the ILs and enhanced cyano–sulfur interaction. Furthermore, the captured SO2 was easy to release by heating or bubbling N2 through the ILs. This efficient and reversible process, achieved by tuning the basicity of ILs, is an excellent alternative to current technologies for SO2 capture. 相似文献
22.
Simultaneous quantitative determination of 20 active components in the traditional Chinese medicine formula Zhi‐Zi‐Da‐Huang decoction by liquid chromatography coupled with mass spectrometry: application to study the chemical composition variations in different combinations 下载免费PDF全文
Zheng Tang Ran Yin Kaishun Bi Heyun Zhu Fei Han Kelin Chen Fenrong Wang 《Biomedical chromatography : BMC》2015,29(9):1406-1414
23.
24.
25.
26.
We propose a system of time-division multiplexing(TDM) and spatial frequency-division multiplexing(SFDM). Extrinsic Fabry–Perot interferometric sensors are applied to detect weak acoustic signals. The broadband source is employed, the light from it is modulated by a pulse signal sequence and is efficiently amplified by semiconductor optical amplifiers. Experimental results show that the equivalent noise pressure spectrum level is-97.2 d B re 1 rad/√Hz below 1250 Hz, and the cross talk between two sensors in one TDM channel is-32.7 d B with a cavity length difference of 60 μm. The number of sensors in this multiplexing system can theoretically reach 160. 相似文献
27.
S. V. Panin I. V. Vlasov V. P. Sergeev B. B. Ovechkin P. O. Marushchak Sunder Ramasubbu P. S. Lyubutin V. V. Titkov 《Physical Mesomechanics》2015,18(3):261-272
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method. 相似文献
28.
29.
He Haidong Yang Haifeng Zhou Longpeng Chen Tianchi 《Journal of Russian Laser Research》2015,36(3):292-299
Ni–Co alloys have a wide range of applications in various fields owning to their excellent physical, chemical, and mechanical properties. In this paper, we prepare Ni–Co alloy coatings on 316L stain steel surfaces by electroplating. We present a novel approach utilizing a nanosecond laser to induce microtextures on Ni–Co alloy coatings. We study experimentally the effects of laser power and scanning rate on the surface morphologies of Ni–Co alloy coatings. The results indicate that the shape and size of induced microtextures can be controlled by the laser power and scanning rate. The size of grains increases with increase in the work current of the laser (WCL) at a certain scanning rate. With the WCL constant, the size of grains decreases with increase in scanning rate while their average height increases. It is a simple and easily-controlled method for the fabrication of microstructures on Ni–Co alloy coatings, which has promising applications in investigations of the properties of microtextured surfaces, such as friction, adhesion, and wetting. 相似文献
30.
DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex 下载免费PDF全文
Cheng‐Gen Zhang Shu‐Yuan Yu Liaoyun Zhang Huayi Li Zhi‐Xiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):576-585
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585 相似文献