首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1829篇
  免费   43篇
  国内免费   5篇
化学   1186篇
晶体学   23篇
力学   47篇
数学   322篇
物理学   299篇
  2023年   11篇
  2022年   33篇
  2021年   42篇
  2020年   40篇
  2019年   31篇
  2018年   22篇
  2017年   11篇
  2016年   63篇
  2015年   42篇
  2014年   46篇
  2013年   88篇
  2012年   104篇
  2011年   111篇
  2010年   79篇
  2009年   63篇
  2008年   110篇
  2007年   96篇
  2006年   94篇
  2005年   103篇
  2004年   84篇
  2003年   58篇
  2002年   63篇
  2001年   21篇
  2000年   30篇
  1999年   23篇
  1998年   22篇
  1997年   12篇
  1996年   27篇
  1995年   12篇
  1994年   19篇
  1993年   15篇
  1992年   22篇
  1991年   11篇
  1990年   16篇
  1989年   20篇
  1988年   17篇
  1987年   26篇
  1986年   15篇
  1985年   23篇
  1984年   19篇
  1983年   16篇
  1982年   19篇
  1981年   12篇
  1980年   10篇
  1979年   9篇
  1978年   11篇
  1977年   13篇
  1976年   5篇
  1975年   3篇
  1974年   5篇
排序方式: 共有1877条查询结果,搜索用时 15 毫秒
101.
A series of regioisomers of the hydroxystearic acid (HSA) was prepared, and the effect of the position of the hydroxyl group along the chain on a panel of human cancer cell lines was investigated. Among the various regioisomers, those carrying the hydroxyl at positions 5, 7, and 9 had growth inhibitor activity against various human tumor cell lines, including CaCo-2, HT29, HeLa, MCF7, PC3, and NLF cells. 10-HSA and 11-HSA showed a very weak effect. 8-HSA did not show inhibitory activity in all cell lines. The biological role of 7-HSA and 9-HSA is widely recognized, while little is known about the effects of 5-HSA. Therefore, the biological effects of 5-HSA in HeLa, HT29, MCF7, and NLF cell lines were investigated using the Livecyte’s ptychography technology, which allows correlating changes in proliferation, motility, and morphology as a function of treatment at the same time. 5-HSA not only reduces cell proliferation but also induces changes in cell displacement, directionality, and speed. It is important to characterize the biological effects of 5-HSA, this molecule being an important component of fatty acyl esters of hydroxy fatty acids (FAHFA), a class of endogenous mammalian lipids with noticeable anti-diabetic and anti-inflammatory effects.  相似文献   
102.
Middle ear prosthesis: significance in magnetic resonance imaging   总被引:1,自引:0,他引:1  
The Armstrong model of the Schuknecht gel foam and wire prosthesis was tested in the magnetic field of a 1.5 Tesla magnet. The wire component of the prosthesis was found to be non-magnetic. Patients with this prosthesis can therefore undergo MRI examination safely. Two previous articles from the non radiologic literature concerning the magnetic properties of metallic middle ear prostheses are reviewed.  相似文献   
103.
104.
The nν1 SiH stretching overtone transitions of trideuterosilane, HSiD3, have been recorded by Fourier transform spectroscopy (n=3 and 4) and by intracavity laser absorption spectroscopy (n=5 and 6). The unusually weak 3ν1 band is affected by considerable intensity and energy perturbations. The 4ν1 band is also strongly perturbed but the interaction with the dark states is more limited and part of the rotational structure of the v1=4 upper state could be satisfactorily modeled. Less pronounced perturbations affect the v1=5 level, newly detected by ICLAS. Its rotational structure is locally perturbed by anharmonic coupling with an unidentified vibrational dark state. The global modeling of the interacting dyad allowed the determination of the perturber parameters and the assignment of extra lines due to an intensity transfer from the v1=5 bright state to the dark state. In agreement with a previous ICLAS study, the 6ν1 band near 12 113 cm−1 was found free of perturbation. About six hundred line positions could be reproduced with an rms of 4.6×10−3 cm−1, leading to a significantly improved set of rovibrational parameters. The striking evolution of the rotational structure, which exhibits fewer and fewer perturbations when the SiH excitation increases, is discussed.  相似文献   
105.
106.
It is shown that radiation pressure can be profitably used to entangle macroscopic oscillators like movable mirrors, using present technology. We prove a new sufficient criterion for entanglement and show that the achievable entanglement is robust against thermal noise. Its signature can be revealed using common optomechanical readout apparatus.  相似文献   
107.
Synthesis and single-crystal X-ray structures are recorded for three adducts of SbF3 with different azacrown ethers. [SbF3·H2O·L1], 1, (L1 = 12,13-benz-1,10-di(azamethyl)-4,7-dioxacyclotetradecane-1,14-dione), triclinic, , a = 11.234(2), b = 11.691(2), c = 8.869(2) Å, = 94.66(3), = 113.12(3), = 67.82(3)°, Z = 2. [SbF3Cl·H2O·(HL2)], 2, (L2 = monoaza-18-crown-6), orthorhombic, P212121, a = 8.763(2), b = 13.003(3), a = 16.836(3) Å, Z = 4. [(SbF3)2Cl2·(H2L3)], 3, (L3 = 1,10-diaza-18-crown-6), triclinic, , a = 8.284(2), b = 9.016(2), c = 9.134(2) Å, = 82.92(3), = 65.24(3), = 63.38(3)°, Z = 1. All three structures include SbF3 neutral molecules in the pyramidal mode and the antimony second coordination sphere is completed up to six in different fashions. In 1 the dimeric (SbF3)2 adducts are made up due to the involvement of the symmetry-related fluorine atom in coordination. The distorted octahedron is then completed by water molecule and carbonyl oxygen of L1. The neutral molecules are joined by coordination and hydrogen bonds in the infinite ribbons. 2 and 3 are both comprised of neutral and charged species also bounded via coordination and hydrogen bonds. L2 and L3 in the complexes adopt the form of single and double-charged cations, respectively. The inorganic backbone unites the neutral SbF3 molecules and chloride anions in the alternative mode. The sixth coordination site in the antimony polyhedron is completed by the water molecule in 2 and the ethereal oxygen atom in 3. Alignment of the inorganic entities within the structures of 2 and 3 is strikingly similar. Hydrogen bonding patterns are discussed.  相似文献   
108.
New rhodium-catalyzed amination reactions of arylacetylenes and cyclohexen-1-ylacetylene in the presence of strong bases with the use of carbon dioxide as an auxiliary are described. Secondary amines attack the terminal carbon atom of the triple bond followed by protonation of the adjacent carbon atom. Alternatively, the reaction can proceed further with the addition of the second alkyne molecule. The conditions for the selective synthesis of enamines (up to 87% yield) or α-substituted propynylamines (up to 86% yield) are reported. Dipartimento di Chimica Organica e Industriale dell'Università, Viale delle Scienze, I-43100 Parma, Italia. Dipartimento di Chimica, Università della Calabria, Arcavacata di Rende, I-80036 Cosenza, Italia. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 966–970, May, 1998.  相似文献   
109.
110.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号