全文获取类型
收费全文 | 1316篇 |
免费 | 59篇 |
国内免费 | 8篇 |
专业分类
化学 | 785篇 |
晶体学 | 2篇 |
力学 | 20篇 |
数学 | 320篇 |
物理学 | 256篇 |
出版年
2023年 | 10篇 |
2022年 | 15篇 |
2021年 | 13篇 |
2020年 | 25篇 |
2019年 | 30篇 |
2018年 | 13篇 |
2017年 | 18篇 |
2016年 | 45篇 |
2015年 | 38篇 |
2014年 | 42篇 |
2013年 | 73篇 |
2012年 | 62篇 |
2011年 | 89篇 |
2010年 | 52篇 |
2009年 | 56篇 |
2008年 | 67篇 |
2007年 | 42篇 |
2006年 | 50篇 |
2005年 | 51篇 |
2004年 | 49篇 |
2003年 | 33篇 |
2002年 | 29篇 |
2001年 | 20篇 |
2000年 | 31篇 |
1999年 | 23篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 21篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1989年 | 7篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 21篇 |
1976年 | 11篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1971年 | 8篇 |
1970年 | 8篇 |
1969年 | 8篇 |
排序方式: 共有1383条查询结果,搜索用时 15 毫秒
71.
We present several results concerning the asymptotic behavior of (random) infinite products of generic sequences of positive linear operators on an ordered Banach space. In addition to a weak ergodic theorem we also obtain convergence to an operator of the formf(·) wheref is a continuous linear functional and is a common fixed point. 相似文献
72.
R.C. Greenwood C.W. Reich H.A. Baader H.R. Koch D. Breitig O.W.B. Schult B. Fogelberg A. B?cklin W. Mampe T. Von Egdy K. Schreckenbach 《Nuclear Physics A》1978,304(2):327-428
The level structure of 158Gd has been studied using the prompt γ-rays and conversion electrons emitted following neutron capture in 157Gd. The γ-ray energy and intensity measurements were made using both Ge(Li) detectors and a curved-crystal spectrometer. Conversion-electron energy and intensity measurements were made using two separate magnetic spectrometers: one to measure the primary electron spectrum and the other to measure the lower energy secondary electron spectrum. Some γ-γ coincidence measurements were also made among the secondary γ-rays. From these data, a neutron separation energy of 7937.1 ± 0.5 keV has been determined for 158Gd. A level scheme containing 59 excited states with energies < 2.25 MeV, for which de-excitation modes have been identified, is proposed for 158Gd. Many of these states have been grouped into rotational bands. A total of thirteen excited rotational bands with band-head energies below 2.0 MeV are contained in the level scheme. Features of the proposed level scheme include: the Kπ = 0?, 1? and 2? octupole-vibrational bands with band-head energies of 1263, 977 and 1793 keV, respectively; the γ-vibrational band at 1187 keV; three excited Kπ = 0+ bands with band-head energies of 1196, 1452 and 1743 keV; several two-quasiparticle bands with band-head energies in keV (and Kπ assignments) of 1380 (4+), 1636 (4?), 1847 (1+), 1856 (1?), 1920 (4+) and 1930 (1+). An analysis of (d, p) reaction data is presented which permits definite two-quasiparticle configuration assignments to be made to most of these latter bands. Evidence is presented which suggests strong mixing of some two-neutron and two-proton bands. A phenomenological four-band mixing analysis is made of the energy and E2 transition-probability data for the ground-state band and the three lowest-lying excited collective positive-parity bands. Good agreement with experiment is obtained. A Coriolis-mixing analysis of the octupole bands has been carried out and good agreement with the data on level energies and E1 transition probabilities to the ground-state band has been achieved. Values of Z, the ratio of the E1 transition matrix element with ΔK = 1 to that with ΔK = 0, involving the octupole bands and the first four 0+ bands are derived. For three of these 0+ bands, absolute values of these matrix elements are deduced. An interesting alternation in the sign of Z is observed for these four 0+ bands. 相似文献
73.
Details are given of a selective negative-ion mass-spectrometric method appropriate for the ultratrace determination of metals and organic compounds by means of their complexes. Direct introduction of the sample into the ion-source, attachment of low-energy electrons, and selected-ion monitoring are described, and comparative data are given relating to surface effects at the tips of insertion-probes on detection limits. Detection limits for chromium and cobalt, determined as their tris(2,2,6,6-tetramethylheptane-3,5-dione) chelates, were respectively 1.0 and 0.16 pg, and that for nickel [as its bis(N,N-diethyldithiocarbamate) complex] was 1.0 pg. Detection limits of 2.0 and 1.0 ng are attainable for malathion and ethion by measurement of the nickel(II) complexes of their O,O'-dialkyldithiophosphate hydrolysis products. 相似文献
74.
The β-spectrum of the second non-unique forbidden 9/2+?5/2+ transition in the decay of99Tc has been investigated with a 4π – Si (Li)-semiconductor-spectrometer. The shape factor has been determined: S(W)=k (1?3.97 W+1.15/W+3.05 W2). It was also possible to fit the data with the normal ξ-Approximation to the theoretical shape factorS(W)=k(q12+0.54 p2). The second forbidden 2+? 0+ β?-transition in the decay of36Cl was reinvestigated to test the spectrometer as well as the fitting-technique. 相似文献
75.
76.
Morfill GE Rubin-Zuzic M Rothermel H Ivlev AV Klumov BA Thomas HM Konopka U Steinberg V 《Physical review letters》2004,92(17):175004
Fluid flow around an obstacle was observed at the kinetic (individual particle) level using "complex (dusty) plasmas" in their liquid state. These "liquid plasmas" have bulk properties similar to water (e.g., viscosity), and a comparison in terms of similarity parameters suggests that they can provide a unique tool to model classical fluids. This allows us to study "nanofluidics" at the most elementary-the particle-level, including the transition from fluid behavior to purely kinetic transport. In this (first) experimental investigation we describe the kinetic flow topology, discuss our observations in terms of fluid theories, and follow this up with numerical simulations. 相似文献
77.
78.
79.
80.
Malcolm H. Mac Gregor 《Foundations of Physics Letters》2004,17(4):381-391
Quantum Hall plateaus are entered via quantized cyclotron (QC) cloud-chamber orbits that have Landau-level (LL) energies and uniquely-defined angular momenta. The conservation of angular momentum in the quantum Hall system requires both canonical and magnetic angular momentum components, which add together to form the invariant kinematic angular momentum. The only LL radial eigenfunctions that satisfy the conservation-law requirements of the QC to LL transition are the u
n,l eigenstates u
n,2n+1, where n = 0, 1, 2, .... These same eigenstates uniquely have the correct scaled sizes to tile the observed families of = 1/(2n + 1) Hall plateaus. Quantum Hall plateau formation is a direct consequence of this tiling. 相似文献