全文获取类型
收费全文 | 335篇 |
免费 | 12篇 |
专业分类
化学 | 179篇 |
力学 | 22篇 |
数学 | 32篇 |
物理学 | 114篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 17篇 |
2012年 | 16篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 9篇 |
2006年 | 20篇 |
2005年 | 11篇 |
2004年 | 12篇 |
2003年 | 6篇 |
2002年 | 18篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1992年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1971年 | 3篇 |
1933年 | 5篇 |
1930年 | 2篇 |
1929年 | 2篇 |
1886年 | 2篇 |
1883年 | 2篇 |
排序方式: 共有347条查询结果,搜索用时 0 毫秒
321.
Bornheim A Lipeles E Pappas SP Weinstein AJ Briere RA Chen GP Ferguson T Tatishvili G Vogel H Watkins ME Adam NE Alexander JP Berkelman K Cassel DG Duboscq JE Ecklund KM Ehrlich R Fields L Galik RS Gibbons L Gittelman B Gray R Gray SW Hartill DL Heltsley BK Hertz D Hsu L Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Pivarski J Riley D Rosner JL Ryd A Sadoff AJ Schwarthoff H Shepherd MR Sun WM Thayer JG Urner D Wilksen T Weinberger M 《Physical review letters》2004,93(24):241802
We have searched a sample of 9.6 x 10(6) BB events for the lepton-flavor-violating leptonic B decays, B(0)-->mu(+/-)tau(-/+) and B(0)-->e(+/-)tau(-/+). The tau lepton was detected through the decay modes tau-->lnunu(-) , where l=e, mu. There is no indication of a signal, and we obtain the 90% confidence level upper limits B(B(0)-->mu(+/-)tau(-/+))<3.8 x 10(-5) and B(B(0)-->e(+/-)tau(-/+))<1.3 x 10(-4). 相似文献
322.
Briere RA Chen GP Chen J Ferguson T Tatishvili G Vogel H Watkins ME Rosner JL Adam NE Alexander JP Berkelman K Cassel DG Crede V Duboscq JE Ecklund KM Ehrlich R Fields L Gibbons L Gittelman B Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Meyer TO Onyisi PU Patterson JR Peterson D Phillips EA Pivarski J Riley D Ryd A Sadoff AJ Schwarthoff H Shi X Shepherd MR Stroiney S Sun WM Urner D Wilksen T Weaver KM Weinberger M Athar SB Avery P 《Physical review letters》2005,95(6):062001
Using data accumulated with the CLEO detector corresponding to an integrated luminosity of [symbol: see text] = 5.63 pb(-1) on the peak of the psi(2S) [3.08 x 10(6) psi(2S) decays] and 20.70 pb(-1) at square root of[s] = 3.67 GeV, we report first measurements of the branching fractions for the following 13 decay modes of the psi(2S): eta3pi, &eta'3pi, rhoK+K-, K+K-pi+pi-pi0, 2(K+K-), 2(K+K-)pi0, rhopp, pppi+pi-pi0, etapp, ppK+K-, lambdalambdapi+pi-, lambdapK+, and lambdapK+pi+pi-, and more precise measurements of 8 previously measured modes: 2(pi+pi-), rhopi+pi-, 2(pi+pi-)pi0, omegapi+pi-, K+K-pi+pi-, omegaK+K-, phiK+K-, and pppi+pi-. We also report new branching fraction measurements of phipi+pi- and omegapp and upper limits for etapi+pi-, etaK+K-, and phivpp. Results are compared, where possible, with the corresponding J/psi branching ratios to provide new tests of the 12% rule. 相似文献
323.
We demonstrate the suitability of a simple continuous-wave-pumped transition-metal-ion-doped waveguide as a broadband light source in the wavelength region 600-1000 nm for interferometric applications. Spatially coherent (single mode in the confined direction), spectrally broadband (~130-nm FWHM) luminescence with output powers of several hundreds of microwatts is obtained from a Ti:sapphire planar waveguide with incident pump powers from an Ar-ion laser of up to 1 W. This result represents an increase in power by several orders of magnitude from previously reported simple broadband light sources in this wavelength range. 相似文献
324.
Beach RJ Mitchell SC Meissner HE Meissner OR Krupke WF McMahon JM Bennett WJ Shepherd DP 《Optics letters》2001,26(12):881-883
Greater than 12 W of average output power has been generated from a diode-pumped Yb:YAG cladding-pumped planar waveguide laser. The laser radiation developed is linearly polarized and diffraction limited in the guiding dimension. A slope efficiency of 0.5 W/W with a peak optical-optical conversion efficiency of 0.31 W/W is achieved. In a related structure, greater than 8 W of Q -switched average output power has been generated from a Nd:YAG cladding-pumped planar waveguide laser by incorporation of a Cr(4+): YAG passive Q switch monolithically into the waveguide structure. Pulse widths of 3 ns and pulse-repetition frequencies as high as 80 kHz have been demonstrated. A slope efficiency of 0.28 W/W with a peak optical-optical conversion efficiency of 0.21 W/W is achieved. 相似文献
325.
Summary The principal parameters which determine the operation of a high-resolution, high-sensitivity radioactive flow monitor are described: a) Sample preparation to ensure adequate recovery of radiolabelled sample, metabolites and internal standard. b) The instrument background count rate, when no sample or radiolabel is present in the flow cell, is a function of shielding and a reduction in noise obtained with a coincidence time below one microsecond. c) The minimum detectable amount of label depends upon the machine background, HPLC eluent and scintillator flow, whether or not packed flow cells are used, flow cell geometry, and the scintillator used. d) Three types of flow cell have been designed to cover the majority of HPLC and isotope applications. e) The performance of solid and liquid scintillators. It is shown that an instrument has been designed taking account of these parameters. The resulting design satisfies present high sensitivity counting requirements and maintains the resolution of current HPLC procedures when detection is by simultaneous flow radioassay and by optical methods. 相似文献
326.
Large changes in depolarization ratio of Raman bands in poly(dimethylsiloxane) have been observed as a function of temperature and strain. Analysis in terms of rotational isomeric state populations yields a configurational energy difference of 1000 ± 140 cal/mole. 相似文献
327.
328.
Raman depolarization (ρ) measurements have been made over the temperature range 20 > T > 60°C for solutions of poly(dimethyl siloxane) (mol wt 7.7 × 104 and 2.0 × 104) for several concentrations up to 100%. The band studied was the highly polarized methyl stretch at 2907 cm?1. Computer calculations of the probability pt of a rotational isomer being trans allow the ρ values to be related to ΔG, the free energy of mixing. ΔG is plotted as a function of concentration and minima are observed at 60 ± 3% (mol wt = 7.7 × 104) and 70 ± 3% (mol wt = 2 × 104). 相似文献
329.
330.
Gabriel Chuchani Ignacio Martin Alexandra Rotinov Rosa M. Dominguez David G. Morris Alistair G. Shepherd 《国际化学动力学杂志》1988,20(2):145-151
The rates of elimination of seven cycloalkyl acetates containing between 5 and 15 ring carbons have been determined in a static system over a temperature range 280–370°C and a pressure range 35–234 torr. The unimolecular reactions, carried out in the presence of the inhibitor cyclohexene, are homogeneous in seasoned vessels and follow a first-order rate law. The rate coefficients are exemplified by that found for cyclopentyl acetate: The sequence of relative rates is analogous to that found in most solution reactions of these compounds. The contribution of ring strain to energy barriers of these compounds is described. 相似文献