全文获取类型
收费全文 | 6221篇 |
免费 | 140篇 |
国内免费 | 44篇 |
专业分类
化学 | 4613篇 |
晶体学 | 66篇 |
力学 | 143篇 |
数学 | 659篇 |
物理学 | 924篇 |
出版年
2023年 | 26篇 |
2022年 | 48篇 |
2021年 | 50篇 |
2020年 | 76篇 |
2019年 | 94篇 |
2018年 | 65篇 |
2017年 | 45篇 |
2016年 | 128篇 |
2015年 | 107篇 |
2014年 | 119篇 |
2013年 | 274篇 |
2012年 | 371篇 |
2011年 | 460篇 |
2010年 | 220篇 |
2009年 | 190篇 |
2008年 | 392篇 |
2007年 | 445篇 |
2006年 | 439篇 |
2005年 | 432篇 |
2004年 | 397篇 |
2003年 | 314篇 |
2002年 | 278篇 |
2001年 | 88篇 |
2000年 | 68篇 |
1999年 | 73篇 |
1998年 | 80篇 |
1997年 | 55篇 |
1996年 | 83篇 |
1995年 | 63篇 |
1994年 | 60篇 |
1993年 | 43篇 |
1992年 | 43篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 39篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1986年 | 30篇 |
1985年 | 53篇 |
1984年 | 53篇 |
1983年 | 50篇 |
1982年 | 46篇 |
1981年 | 48篇 |
1980年 | 44篇 |
1979年 | 45篇 |
1978年 | 49篇 |
1977年 | 40篇 |
1976年 | 37篇 |
1975年 | 24篇 |
1974年 | 24篇 |
排序方式: 共有6405条查询结果,搜索用时 0 毫秒
981.
Jiang Wang Brian P. Cary Peyton D. Beyer Samuel H. Gellman Daniel J. Weix 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(35):12209-12213
Synthesis of the C?C bonds of ketones relies upon one high‐availability reagent (carboxylic acids) and one low‐availability reagent (organometallic reagents or alkyl iodides). We demonstrate here a ketone synthesis that couples two different carboxylic acid esters, N‐hydroxyphthalimide esters and S‐2‐pyridyl thioesters, to form aryl alkyl and dialkyl ketones in high yields. The keys to this approach are the use of a nickel catalyst with an electron‐poor bipyridine or terpyridine ligand, a THF/DMA mixed solvent system, and ZnCl2 to enhance the reactivity of the NHP ester. The resulting reaction can be used to form ketones that have previously been difficult to access, such as hindered tertiary/tertiary ketones with strained rings and ketones with α‐heteroatoms. The conditions can be employed in the coupling of complex fragments, including a 20‐mer peptide fragment analog of Exendin(9–39) on solid support. 相似文献
982.
Conrad A. P. Goodwin Jing Su Thomas E. Albrecht‐Schmitt Anastasia V. Blake Enrique R. Batista Scott R. Daly Stefanie Dehnen William J. Evans Andrew J. Gaunt Stosh A. Kozimor Niels Lichtenberger Brian L. Scott Ping Yang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(34):12050-12050
983.
984.
Melissa D'Ascenzio Kathryn M. Pugh Rebecca Konietzny Georgina Berridge Cynthia Tallant Shaima Hashem Octovia Monteiro Jason R. Thomas Markus Schirle Stefan Knapp Brian Marsden Oleg Fedorov Chas Bountra Benedikt M. Kessler Paul E. Brennan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(4):1019-1024
985.
Plasma Chemistry and Plasma Processing - The destruction of nitrous oxide in oxygen using plasma and post-plasma catalytic treatments was investigated experimentally in atmospheric-pressure... 相似文献
986.
987.
Anderson BE Hughes WJ Hambric SA 《The Journal of the Acoustical Society of America》2008,123(5):2613-2619
The ability to direct sound energy through the flexural vibrations of a submerged plate at various angles of incidence using a near-field transducer array is investigated. An alumina bar is placed in front of a one-dimensional, eight-element transducer array, between the array and the water. Operating in a receive mode, data were taken as a function of angle of incidence and compared to data taken without the presence of the alumina bar. The array was also operated in transmit mode and results were compared to corresponding receive mode data, showing that reciprocity holds. Results show that in fact sound energy can be steered through a plate, and that the measurement method used provides a convenient method of measuring the angular dependence of transmission through a plate, including measurements at frequencies above the plate's critical frequency. Experimental results of sound transmission versus angle of incidence of finite sized plates agree qualitatively with theoretical results from an analysis of the transmission through an unbounded flexible partition. 相似文献
988.
Groshaus JG Dujovne I Gallais Y Hirjibehedin CF Pinczuk A Tan YW Stormer H Dennis BS Pfeiffer LN West KW 《Physical review letters》2008,100(4):046804
Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020+/-0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3. 相似文献
989.
Through 2D granular Couette flow experiments, we probe failure and deformation of disordered solids under shear. Shear produces a mean azimuthal flow, smooth affine deformations, and irreversible so-called nonaffine particle displacements. We find that these processes are all of comparable magnitude and depend on the local shear rate. We compute the parameter of Falk and Langer characterizing nonaffine motion, Dmin2, and find that it is reasonably well described in terms of collections of single particles making locally nearly isotropic random steps, delta ri. Distributions for single particle nonaffine displacements, delta ri, satisfy P1(delta ri) proportional, variantexp[-|delta ri/Delta r|alpha] (alpha < or approximately 2). 相似文献
990.
We introduce a method for optical characterization of hollow-core optical waveguides. Radiation pressure exerted by the waveguide modes on dielectric microspheres is used to analyze salient properties such as propagation loss and waveguide mode profiles. These quantities were measured for quasi-single-mode and multimode propagation in on-chip liquid-filled hollow-core antiresonant reflecting optical waveguides. Excellent agreement with analytical and numerical models is found, demonstrating that optically induced particle transport provides a simple, inexpensive, and nondestructive alternative to other characterization methods. 相似文献