全文获取类型
收费全文 | 36452篇 |
免费 | 5668篇 |
国内免费 | 4239篇 |
专业分类
化学 | 26912篇 |
晶体学 | 558篇 |
力学 | 1941篇 |
综合类 | 260篇 |
数学 | 4201篇 |
物理学 | 12487篇 |
出版年
2024年 | 59篇 |
2023年 | 635篇 |
2022年 | 903篇 |
2021年 | 1164篇 |
2020年 | 1397篇 |
2019年 | 1426篇 |
2018年 | 1137篇 |
2017年 | 1105篇 |
2016年 | 1674篇 |
2015年 | 1688篇 |
2014年 | 2027篇 |
2013年 | 2645篇 |
2012年 | 3397篇 |
2011年 | 3500篇 |
2010年 | 2414篇 |
2009年 | 2296篇 |
2008年 | 2612篇 |
2007年 | 2299篇 |
2006年 | 2121篇 |
2005年 | 1784篇 |
2004年 | 1360篇 |
2003年 | 1054篇 |
2002年 | 1101篇 |
2001年 | 782篇 |
2000年 | 680篇 |
1999年 | 709篇 |
1998年 | 576篇 |
1997年 | 532篇 |
1996年 | 548篇 |
1995年 | 427篇 |
1994年 | 365篇 |
1993年 | 294篇 |
1992年 | 279篇 |
1991年 | 260篇 |
1990年 | 201篇 |
1989年 | 182篇 |
1988年 | 111篇 |
1987年 | 134篇 |
1986年 | 103篇 |
1985年 | 104篇 |
1984年 | 59篇 |
1983年 | 52篇 |
1982年 | 40篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 14篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
101.
102.
The Existence of Solutions to Sturm-Liouville Boundary Value Problems with Laplacian-like Operator 总被引:2,自引:0,他引:2
Wei-ping Sun Wei-gao GeDepartment of Applied Mathematics Beijing Institute of Technology Beijing China 《应用数学学报(英文版)》2002,18(2):341-348
Abstract The existence of infinitely many solutions to Sturm-Liouville boundary value problem with aLaplacian-like operator is studied by applying generalized polar coordinates. 相似文献
103.
To incorporate an acceptor type polythiophene segment onto a supramolecular block copolymer for potential light harvesting applications, effective synthetic routes for the end‐functionalized and acceptor‐substituted polythiophenes are critical. The Ullmann coupling reaction can be utilized to obtain electron‐deficient polythiophenes and to attach terminal thiophene units that carry functional groups. In this article, the reactions involving a 2,5‐dibromothiophene monomer containing an electron‐withdrawing fluorinated ester and 5‐bromo‐2‐thiophenecarboxaldehyde (the end‐capper) were studied in detail. It was found that the Ullmann coupling reaction of the dibromide is very fast (completed in a few minutes) and the terminal bromine group does not survive long under the reaction condition. These findings lead to the development of an effective procedure for aldehyde end‐capping of electron‐deficient polythiophenes. Polymers with molecular weights around 4000 Da are routinely obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 41–47, 2007 相似文献
104.
Outline imaging by THz time domain spectroscopy is proposed. Spectroscopic splitting at interface is reported, The principle of outline imaging is put forward. Experimental results demonstrate the feasibility of outline imaging by spectroscopic splitting, It is shown that clear out:line image of sample interface could be achieved easily by this technique. The spatial resolution is about 0.6mm. The THz-beam focus, the scanning step and the THz pulse width are the critical foctors affecting the imaging resolution. The signal-to-noise ratio of this technique could be improved greatly compared to the conventional transsion imaging. 相似文献
105.
106.
Sang Kyu Lee Min Ju Cho Jung‐Il Jin Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2007,45(3):531-542
New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene‐based chromophore. The 2‐(3‐cyano‐4‐(2‐{4‐[hexyl‐(6‐hydroxy‐hexyl)‐amino]‐phenyl}‐vinyl)‐5‐oxo‐1‐{4‐[4‐(3‐oxo‐3‐phenyl‐propenyl)‐ phenoxy]‐butyl}‐1,5‐dihydro‐pyrrol‐2‐ylidene)‐malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (λ = 330–360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531–542, 2007 相似文献
107.
Xinhuan Feng Lei Sun Yange Liu Lingyun Xiong Shuzhong Yuan Guiyun Kai Xiaoyi Dong 《Optical and Quantum Electronics》2004,36(10):919-926
A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated. 相似文献
108.
109.
CHEN Yue WANG Xuan-jun CONG Xian-ling ZHANG Pei-yin WU Xiu-li WEI Hong-fei WANG Li WAN Min WANG Li-ying YU Yong-li 《高等学校化学研究》2006,22(6):712-716
IntroductionClassical swine fever(CSF), included in the listA of the Office International des Epizooties(OIE), is ahighly contagious disease of domestic pigs and is con-sidered as the mostharmful disease occurring in pigs allover the world[1]. Outbreaks o… 相似文献
110.