全文获取类型
收费全文 | 473篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
化学 | 278篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 62篇 |
物理学 | 149篇 |
出版年
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 32篇 |
2012年 | 26篇 |
2011年 | 31篇 |
2010年 | 26篇 |
2009年 | 19篇 |
2008年 | 20篇 |
2007年 | 34篇 |
2006年 | 28篇 |
2005年 | 31篇 |
2004年 | 25篇 |
2003年 | 14篇 |
2002年 | 18篇 |
2001年 | 8篇 |
2000年 | 18篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1934年 | 2篇 |
1933年 | 2篇 |
排序方式: 共有492条查询结果,搜索用时 15 毫秒
161.
Bertoncini J Nazzi T Cabrera L Lorenzi C 《The Journal of the Acoustical Society of America》2011,129(5):2761-2764
Young deaf children using a cochlear implant develop speech abilities on the basis of speech temporal-envelope signals distributed over a limited number of frequency bands. A Headturn Preference Procedure was used to measure looking times in 6-month-old, normal-hearing infants during presentation of repeating or alternating sequences composed of different tokens of /aba/and /apa/ processed to retain envelope information below 64 Hz while degrading temporal fine structure cues. Infants attended longer to the alternating sequences, indicating that they perceive the voicing contrast on the basis of envelope cues alone in the absence of fine spectral and temporal structure information. 相似文献
162.
Ahmed Z Akerib DS Arrenberg S Bailey CN Balakishiyeva D Baudis L Bauer DA Brink PL Bruch T Bunker R Cabrera B Caldwell DO Cooley J do Couto e Silva E Cushman P Daal M DeJongh F Di Stefano P Dragowsky MR Duong L Fallows S Figueroa-Feliciano E Filippini J Fox J Fritts M Golwala SR Hall J Hennings-Yeomans R Hertel SA Holmgren D Hsu L Huber ME Kamaev O Kiveni M Kos M Leman SW Liu S Mahapatra R Mandic V McCarthy KA Mirabolfathi N Moore D Nelson H Ogburn RW Phipps A Pyle M Qiu X Ramberg E Rau W 《Physical review letters》2011,106(13):131302
We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from weakly interacting massive particles (WIMPs) with masses below ~10 GeV/c(2). This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c(2) and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments. 相似文献
163.
The reactions of secondary alicyclic amines with the title substrate (PDTC) are subjected to a kinetic study in 44 wt.% aqueous ethanol, 25.0°C, ionic strength 0.2 M (KCl). Pseudo-first-order rate coefficients (kobs) are found under amine excess. Linear plots of [N]/kobs against 1/[N], where N is the free amine, are obtained for the reactions with piperidine, piperazine, 1-(2-hydroxyethyl)piperazine, and morpholine. The reaction with 1-formylpiperazine exhibits a linear plot of kobs against [N]2. These results are interpreted through a mechanism consisting of two tetrahedral intermediates: a zwitterionic ( T ±) and an anionic ( T ?), where the amine catalyzed proton transfer from T ± to T ? is partially rate determining for the four former reactions and is fully rate determining for the reaction of 1-formylpiperazine. The rate microcoefficients involved in the reaction scheme are either determined experimentally or estimated. Comparison with the corresponding microcoefficients reported for the same reactions in water reveals that the rate coefficient for formation of T ± from reactants (k1) is smaller and that for the reversal of this (k?1) is larger in aqueous ethanol compared to water, in agreement with the expected structure of the corresponding transition state. Bronsted-type plots are obtained for k1, k?1, and K1 (=k1/k?1) with slopes ca. 0.4, ?0.6, and 1.0, respectively. Comparison of the present stepwise reactions with the concerted ones found in the same aminolysis of O-ethyl 2,4,6,-(trinitrophenyl) dithiocarbonate indicates that T ± is so destabilized by the change of PhS by the 2,4,6-trinitrobenzenethio group that T ± no longer exists and becomes a transition state. © 1995 John Wiley & Sons, Inc. 相似文献
164.
We prove that, ifA is a complex Banach algebra with a unit 1 and a conjugate-linear vector space involution* such that 1*=1 and‖a
*a‖=‖a*‖ ‖a‖ for alla inA, and ifdim(A)≥3, thenA is a C*-algebra. The two-dimensional case is also considered and described. 相似文献
165.
In this paper, a new proposal of the quantum potential theory is presented, along with a discussion of the two-slit interference experiment and the Aharonov-Bohm effect, which are explicitly calculated within the scheme adopted. The present formulation holds the notion of particle trajectory and follows the interpretation suggested by de Broglie and Bohm, the quantum potential being a manifestation of the quantum wave. This wave always satisfies the Schrödinger equation and is considered as areal and separate entity from the particle with which is associated. In our approach we try to circumvent some conceptual difficulties that prevent the de Broglie-Bohm's theory from fulfilling a complete objective program. New effects are predicted, specially for the Aharonov-Bohm experiment in the regime of high magnetic fields, and a setup for their detection is proposed. 相似文献
166.
A. Calles E. Yepez J. J. Castro A. Salcido A. Cabrera R. Gomez S. Aburto V. Marquina M. L. Marquina M. Jimenez R. Escudero 《Hyperfine Interactions》1991,66(1-4):429-433
The Jahn-Teller distortion mechanism in the Nd2?x Ce x CuO4 is analyzed. This analysis is based on a quasi-molecular model for the CuO4 cluster havingD 4h symmetry. In order to compare with experimental Mössbauer measurements in the doped Nd1.85Ce0.15Cu0.99Fe0.01O4?δ superconductor, the FeO4 cluster is also analyzed for the case of Fe2+ in the high spin state. The results show not evidence of a Jahn-Teller effect in these superconductors. 相似文献
167.
Pankaj Sharma Armando Cabrera Cecilio Alvarez Noe Rosas Elizabeth Gomez Alfredo Toscano 《Analytical sciences》2003,19(9):1341-1342
Crystal structure of trans-dibromobis(triphenylphosphine)platinum(II) was determined by X-ray-crystallography. The complex crystallizes on an inversion center in distorted square planar coordination around platinum with triphenylphosphine ligands in trans positions to each other and with two molecules of dichloromethane as solvate. 相似文献
168.
J. M. Navarrete J. Campos T. Martínez L. Cabrera 《Journal of Radioanalytical and Nuclear Chemistry》2005,265(1):133-135
Summary After the Chernobyl accident in April 1986, Mexico imported from one European country a shipment of 28,000 tons of milk powder contaminated with the fission product 137Cs. Since then, the local authorities of Public Health have established as a compulsory condition to obtain through gamma-spectroscopy a certificate of no radioactive contamination either to imported or exported foodstuffs. But at the same time, the absence of long-lived, gamma-emitters fission products is certified, it is also possible to find the concentration of the important trace element K in foodstuffs, by the peak of 1461 keV from 40K, invariably present in the gamma-spectra. Taking advantage of the fact that it does not require any previous manipulation of the sample, this paper describes the general procedure in milk powder or any other foodstuff. 相似文献
169.
170.
Alvarez-Manzaneda EJ Chahboun R Cabrera E Alvarez E Haidour A Ramos JM Alvarez-Manzaneda R Hmamouchi M Bouanou H 《The Journal of organic chemistry》2007,72(9):3332-3339
A new synthetic strategy toward puupehenone-related bioactive metabolites from sclareol oxide, based on a Diels-Alder cycloaddition approach, is described. Utilizing this, marine ent-chromazonarol and the potent angiogenesis inhibitor 8-epipuupehedione have been synthesized. 相似文献