全文获取类型
收费全文 | 590篇 |
免费 | 31篇 |
国内免费 | 7篇 |
专业分类
化学 | 400篇 |
晶体学 | 36篇 |
力学 | 14篇 |
数学 | 62篇 |
物理学 | 116篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 15篇 |
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 38篇 |
2013年 | 47篇 |
2012年 | 52篇 |
2011年 | 56篇 |
2010年 | 20篇 |
2009年 | 28篇 |
2008年 | 22篇 |
2007年 | 25篇 |
2006年 | 28篇 |
2005年 | 19篇 |
2004年 | 26篇 |
2003年 | 23篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有628条查询结果,搜索用时 15 毫秒
171.
The NiBr(2)(dppe)-Zn system effectively catalyzes the [2+2+2] cocyclotrimerization of arynes with allenes, leading to 10-methylene-9,10-dihydrophenanthrenes in moderate to good yields. The cocyclotrimerization is highly selective with only the internal double bond of the allenes being involved in the reaction. 相似文献
172.
Rajnikant Dinesh Mousmi M.B. Deshmukh S.S. Patil Anshu Sawhney 《Journal of chemical crystallography》2004,34(10):693-696
The three-dimensional molecular and crystal structure of 2-(2'-propanonylthio)3-(o-methyl phenyl)quinazol-4(3H)-one has been determined by X-ray crystallographic methods. This compound crystallizes in the orthorhombic space group Pbca with unit cell parameters: a=9.649(5), b=30.102(10), c=11.403(9)Å. It has been solved by direct methods and refined to a residual index of 0.054. The magnitude of torsion along C16— C11— N3— C4 bond is 93.5(4)°. The dihedral angle between the plane comprising all the ring atoms of quinazoline moiety and the atoms of the methyl substituted phenyl ring is 94.12(1)°. The crystal structure is stabilized by one intramolecular C— HsO interaction and three intermolecular C— HsN contacts. 相似文献
173.
An element in a ring R is said to be clean (respectively unit-regular) if it is the sum (respectively product) of an idempotent element and an invertible element. If all elements in R are unit-regular, it is known that all elements in R are clean. In this note, we show that a single unit-regular element in a ring need not be clean. More generally, a criterion is given for a matrix to be clean in a matrix ring M2(K) over any commutative ring K. For K=Z, this criterion shows, for instance, that the unit-regular matrix is not clean. Also, this turns out to be the “smallest” such example. 相似文献
174.
[reaction: see text] Treatment of 7-oxa- and 7-azabenzonorbornadienes with terminal acetylenes in the presence of Ni(dppe)Cl2, ZnCl2, and Zn powder in toluene at 90 degrees C afforded the corresponding cis-2-alkynyl-1,2-dihydronaphthalene derivatives in moderate to excellent yields with remarkably high stereoselectivity. 相似文献
175.
Rayabarapu DK Sambaiah T Cheng CH 《Angewandte Chemie (International ed. in English)》2001,40(7):1286-1288
176.
Dipankar Bandyopadhyay P. Dinesh Sankar Reddy Ashutosh Sharma Sang Woo Joo Shizhi Qian 《Theoretical and Computational Fluid Dynamics》2012,26(1-4):23-28
The electro-magneto-hydrodynamic (EMHD) flow and instabilities engendered by the Lorenz force arising from interaction between externally applied perpendicular electric and magnetic fields are investigated in layers of two immiscible liquids in a channel. A new finite wave-number EMHD instability mode is uncovered by the Orr–Sommerfeld analysis, in addition to the interfacial and shear modes which also arise in the pressure-driven flows. Thus, EMHD can be controlled for micro-channel transport, heat and mass transfer, mixing, micro-emulsion generation, etc. 相似文献
177.
A three‐dimensional nuclear magnetic resonance (NMR) pulse sequence named as hNCOcanH has been described to aid rapid sequential assignment of backbone resonances in 15N/13C‐labeled proteins. The experiment has been derived by a simple modification of the previously described HN(C)N pulse sequence [Panchal et al., J. Biomol. NMR 20 (2001) 135–147]; t2 evolution is used to frequency label 13C′ rather than 15N (similar trick has also been used in the design of hNCAnH pulse sequence from hNcaNH [Frueh et al., JACS, 131 (2009) 12880–12881]). The modification results in a spectrum equivalent to HNCO, but in addition to inter‐residue correlation peaks (i.e. Hi, Ci?1), the spectrum also contains additional intra‐residue correlation peaks (i.e. Hi?1, Ci?1) in the direct proton dimension which has maximum resolution. This is the main strength of the experiment and thus, even a small difference in amide 1H chemical shifts (5–6 Hz) can be used for establishing a sequential connectivity. This experiment in combination with the HNN experiment described previously [Panchal et al., J. Biomol. NMR 20 (2001) 135–147] leads to a more robust assignment protocol for backbone resonances (1HN, 15N) than could be derived from the combination of HNN and HN(C)N experiments [Bhavesh et al., Biochemistry, 40 (2001) 14727–14735]. Further, this new protocol enables assignment of 13C′ resonances as well. We believe that the experiment and the protocol presented here will be of immense value for structural—and functional—proteomics research by NMR. Performance of this experiment has been demonstrated using 13C/15N labeled ubiquitin. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
178.
Dayong Chen Jinhwan Yoon Dinesh Chandra Alfred J. Crosby Ryan C. Hayward 《Journal of Polymer Science.Polymer Physics》2014,52(22):1441-1461
Thin polymer films may undergo a wide variety of elastic instabilities that include global buckling modes, wrinkling and creasing of surfaces, and snapping transitions. Traditionally, these deformations have usually been avoided as they often represent a means of mechanical failure. However, a new trend has emerged in recent years in which buckling mechanics can be harnessed to endow materials with beneficial functions. For many such applications, it is desirable that such deformations happen reversibly and in response to well‐defined signals or changes in their environment. While significant progress has been made on understanding and exploiting each type of deformation in its own right, here we focus on recent advances in the control and application of stimuli‐responsive mechanical instabilities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1441–1461 相似文献
179.
This contribution deals with the numerical modelling of polycrystalline ferroelectric materials considering a sequential laminate-based approach established for tetragonal single-crystal ferroelectrics. The particular model [1] is considered and extended to predict the material behaviour of poly-crystal tetragonal ferroelectric ceramics. The derived laminate-based model is implemented in a finite element environment to simulate the time-dependent domain evolution and switching response of a bulk polycrystalline ferroelectric ceramic. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
180.
Sonu Sen Meenu Asthana Varshney Dinesh Varshney 《Applied physics. B, Lasers and optics》2014,116(4):811-819
In the present work, we investigate the distributed regimes of an intense laser beam in a self-consistent plasma channel. As the intensity of the laser beam increases, the relativistic mass effect as well as the ponderomotive expulsion of electrons modifies the dielectric function of the medium due to which the medium exhibits nonlinearity. Based on Wentzel–Kramers–Brillouin and paraxial ray theory, the steady-state solution of an intense, Gaussian electromagnetic beam is studied. A differential equation of the beamwidth parameter with the distance of propagation is derived, including the effects of relativistic self-focusing (SF) and ponderomotive self-channeling. The nature of propagation and radial dynamics of the beam in plasma depend on the power, width of the beam, and Ω p, the ratio of plasma to wave frequency. For a given value of Ω p (<1), the distribution regimes have been obtained in beampower–beamwidth plane, characterizing the regimes of propagation as steady divergence, oscillatory divergence, and SF. The related focusing parameters are optimized introducing plasma density ramp function, and spot size of the laser beam is analyzed for inhomogeneous plasma. This results in overcoming the diffraction and guiding the laser beam over long distance. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction studies. 相似文献