全文获取类型
收费全文 | 4513篇 |
免费 | 129篇 |
国内免费 | 19篇 |
专业分类
化学 | 2992篇 |
晶体学 | 30篇 |
力学 | 101篇 |
数学 | 765篇 |
物理学 | 773篇 |
出版年
2023年 | 38篇 |
2022年 | 30篇 |
2021年 | 99篇 |
2020年 | 106篇 |
2019年 | 86篇 |
2018年 | 60篇 |
2017年 | 43篇 |
2016年 | 130篇 |
2015年 | 107篇 |
2014年 | 120篇 |
2013年 | 256篇 |
2012年 | 267篇 |
2011年 | 319篇 |
2010年 | 149篇 |
2009年 | 146篇 |
2008年 | 200篇 |
2007年 | 225篇 |
2006年 | 220篇 |
2005年 | 190篇 |
2004年 | 131篇 |
2003年 | 143篇 |
2002年 | 130篇 |
2001年 | 60篇 |
2000年 | 67篇 |
1999年 | 30篇 |
1998年 | 52篇 |
1997年 | 40篇 |
1996年 | 57篇 |
1995年 | 38篇 |
1994年 | 49篇 |
1993年 | 47篇 |
1992年 | 49篇 |
1991年 | 44篇 |
1990年 | 58篇 |
1989年 | 42篇 |
1988年 | 41篇 |
1987年 | 34篇 |
1985年 | 37篇 |
1984年 | 42篇 |
1983年 | 40篇 |
1982年 | 45篇 |
1981年 | 57篇 |
1980年 | 35篇 |
1979年 | 42篇 |
1978年 | 42篇 |
1977年 | 37篇 |
1976年 | 38篇 |
1975年 | 36篇 |
1974年 | 32篇 |
1973年 | 35篇 |
排序方式: 共有4661条查询结果,搜索用时 484 毫秒
21.
Francis J. Narcowich Joseph D. Ward Holger Wendland. 《Mathematics of Computation》2005,74(250):743-763
In this paper we discuss Sobolev bounds on functions that vanish at scattered points in a bounded, Lipschitz domain that satisfies a uniform interior cone condition. The Sobolev spaces involved may have fractional as well as integer order. We then apply these results to obtain estimates for continuous and discrete least squares surface fits via radial basis functions (RBFs). These estimates include situations in which the target function does not belong to the native space of the RBF.
22.
Applications of electronic speckle interferometry (ESI) techniques for spacecraft structural components 总被引:1,自引:0,他引:1
Laser-based electronic speckle interferometry (ESI) techniques, viz., electronic speckle pattern interferometry (ESPI) and electronic speckle shearographic interferometry (ESSI) are used for testing of spacecraft structural components. The combined ESPI and ESSI system developed in house was successfully used for the non-destructive evaluation (NDE) of honeycomb sandwich panels and propellant tanks of Indian Space Research Organization (ISRO). Debonds between face sheet and the honeycomb core were identified using (i) thermal and (ii) dual vacuum stressing methods. On-line NDE of the propellant tanks under internal pressure loading for identification of the minute cracks and thickness reduction areas were successfully implemented by ESI. 相似文献
23.
L. Ward 《Optics & Laser Technology》1993,25(6):393-395
The well-known equations for the optical functions of reflectance, transmittance and phase changes on reflection and transmission for a solid material have been rearranged into the form of simple geometric figures in the u, v (n, k) plane. The curves for Fp show a singularity on the n-axis. 相似文献
24.
Ross W. Mair David G. Cory Sharon Peled Ching-Hua Tseng Samuel Patz Ronald L. Walsworth 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,135(2):478-486
Pulsed-field-gradient NMR techniques are demonstrated for measurements of time-dependent gas diffusion. The standard PGSE technique and variants, applied to a free gas mixture of thermally polarized xenon and O2, are found to provide a reproducible measure of the xenon diffusion coefficient (5.71 × 10−6m2s−1for 1 atm of pure xenon), in excellent agreement with previous, non-NMR measurements. The utility of pulsed-field-gradient NMR techniques is demonstrated by the first measurement of time-dependent (i.e., restricted) gas diffusion inside a porous medium (a random pack of glass beads), with results that agree well with theory. Two modified NMR pulse sequences derived from the PGSE technique (named the Pulsed Gradient Echo, or PGE, and the Pulsed Gradient Multiple Spin Echo, or PGMSE) are also applied to measurements of time dependent diffusion of laser polarized xenon gas, with results in good agreement with previous measurements on thermally polarized gas. The PGMSE technique is found to be superior to the PGE method, and to standard PGSE techniques and variants, for efficiently measuring laser polarized noble gas diffusion over a wide range of diffusion times. 相似文献
25.
The recently proposed Harbola–Sahni local potential in its exchange-only version [Phys. Rev. Lett. 62 , 689 (1989)] is found to give the static dipole and quadrupole polarizabilities for the Neisoelectronic series in excellent agreement with the corresponding Hartree–Fock estimates. © 1992 John Wiley & Sons, Inc. 相似文献
26.
Summary Laser ablation inductively coupled plasma-source mass spectrometry has been used to determine thirty elements (Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, As, Rb, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Dy, Ho, Yb, Hf, Ta, W, Th, U) in seven Chinese reference soils. The Surrey prototype spectrometer was employed with sample ablation by a free-running ruby laser. Concentrations in the soils (GSS-2 to GSS-8) were calculated from elemental responses and sensitivities derived from another soil in the series, namely GSS-1. Comparisons with previous neutron activation analyses are made. Rapid semiquantitative analyses are proved feasible. About eighty percent of the LA-ICP-MS determined concentrations were within a factor of two of the concentrations measured by INAA, and many were considerably closer than this. Precisions were typically in the range 2–10% RSD, but some were considerably poorer for elements present at trace levels. 相似文献
27.
Ward S 《OR manager》1990,6(9):19-20
This is the fourth in a series on management strategies for "turning around an OR." The first three articles appeared in the January, April, and June issues of OR Manager. 相似文献
28.
29.
By means of exponential laws we show a Bianchi Type I model of the universe where we define overall deceleration and Hubble's parameters that have constant values. We employ a convenient relation for defining the radius of the universe. Pressure and density have constant values, too. 相似文献
30.
Gregory H. Robinson Fritz Moise William T. Pennington Samuel A. Sangokoya 《Journal of chemical crystallography》1988,18(4):387-393
The crystalline condensation product [Al(CH3)2]2[C10H22N4][Al(CH3)3]2 is prepared from reaction of the multidentate open-chain amine 1,4-bis(3-aminopropyl)piperazine with trimethylaluminum in methylene chloride. The compound crystallized in the monoclinic space groupC2/c with unit cell parametersa=25.166(12),b=7.268(4),c=17.316(4) Å,=115.3(4)°, andD
c
=1.06 g cm–3 forZ=4. Least-squares refinement based on 1054 observed reflections with intensitiesI 3(I) in the range 2<2<45° led to a finalR factor of 0.053 (R
w
=0.064). The title compound resides on a crystallographic center of symmetry with independent Al-N distances of 1.889(5), 2.058(5), and 2.030(5) Å. 相似文献