全文获取类型
收费全文 | 1252篇 |
免费 | 39篇 |
国内免费 | 2篇 |
专业分类
化学 | 771篇 |
晶体学 | 8篇 |
力学 | 37篇 |
数学 | 173篇 |
物理学 | 304篇 |
出版年
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 36篇 |
2020年 | 32篇 |
2019年 | 31篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 59篇 |
2015年 | 32篇 |
2014年 | 56篇 |
2013年 | 86篇 |
2012年 | 78篇 |
2011年 | 95篇 |
2010年 | 72篇 |
2009年 | 97篇 |
2008年 | 83篇 |
2007年 | 76篇 |
2006年 | 49篇 |
2005年 | 35篇 |
2004年 | 35篇 |
2003年 | 27篇 |
2002年 | 20篇 |
2001年 | 29篇 |
2000年 | 29篇 |
1999年 | 14篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 25篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1937年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有1293条查询结果,搜索用时 375 毫秒
91.
We study the dynamics of multipartite entanglement under the influence of decoherence. A suitable generalization of concurrence reveals distinct scaling of the entanglement decay rate of Greenberger-Horne-Zeilinger and W states, for various environments. 相似文献
92.
We show that heating of harmonically trapped ions by periodic delta kicks is dramatically enhanced at isolated values of the Lamb-Dicke parameter. At these values, quasienergy eigenstates localized on island structures undergo avoided crossings with extended web states. 相似文献
93.
Low-pump-power,short-fiber copropagating dual-pumped (800 and 1050 nm) thulium-doped fiber amplifier
Gomes AS Carvalho MT Sundheimer ML Bastos-Filho CJ Martins-Filho JF Von der Weid JP Margulis W 《Optics letters》2003,28(5):334-336
Using optical frequency-domain reflectometry to reveal the gain distribution and allow us to optimize a thulium-doped fiber amplifier, we have demonstrated 18-dB gain by employing only 5 m of a 2000-parts-in-10(6)-Tm-doped fiber pumped with 145 mW of power at dual wavelengths of 800 and 1050 nm. The role of the 800-nm pump, which by itself does not permit population inversion, was clearly observed experimentally. 相似文献
94.
Aitala EM Amato S Anjos JC Appel JA Ashery D Banerjee S Bediaga I Blaylock G Bracker SB Burchat PR Burnstein RA Carter T Carvalho HS Copty NK Cremaldi LM Darling C Denisenko K Devmal S Fernandez A Fox GF Gagnon P Gobel C Gounder K Halling AM Herrera G Hurvits G James C Kasper PA Kwan S Langs DC Leslie J Lundberg B Magnin J Massafferri A MayTal-Beck S Meadows B de Mello Neto JR Mihalcea D Milburn RH de Miranda JM Napier A Nguyen A d'Oliveira AB O'Shaughnessy K Peng KC Perera LP Purohit MV 《Physical review letters》2001,86(5):770-774
From a sample of 1172 +/- 61 D(+)-->pi(-)pi(+)pi(+) decays, we find gamma(D(+)-->pi(-)pi(+)pi(+))/gamma(D(+)-->K-pi(+)pi(+)) = 0.0311 +/- 0.0018(+0.0016)(-0.0026). Using a coherent amplitude analysis to fit the Dalitz plot of these decays, we find strong evidence that a scalar resonance of mass 478(+24)(-23) +/- 17 MeV/c(2) and width 324(+42)(-40) +/- 21 MeV/c(2) accounts for approximately half of all decays. 相似文献
95.
José M. Arrieta Alexandre N. Carvalho 《Transactions of the American Mathematical Society》2000,352(1):285-310
We prove a local existence and uniqueness theorem for abstract parabolic problems of the type when the nonlinearity satisfies certain critical conditions. We apply this abstract result to the Navier-Stokes and heat equations.
96.
97.
J.A. Aguilar-Saavedra J. Carvalho N. Castro A. Onofre F. Veloso 《The European Physical Journal C - Particles and Fields》2007,50(3):519-533
We investigate several quantities, defined in the decays of top quark pairs, which can be used to explore non-standard Wtb interactions. Two new angular asymmetries are introduced in the leptonic decay of top (anti)quarks. Both are very sensitive
to anomalous Wtb couplings, and their measurement allows for a precise determination of the W helicity fractions. We also examine other angular
and energy asymmetries, the W helicity fractions and their ratios, as well as spin correlation asymmetries, analysing their
dependence on anomalous Wtb couplings and identifing the quantities which are most sensitive to them. It is explicitly shown that spin correlation asymmetries
are less sensitive to new interactions in the decay of the top quark; therefore, when combined with the measurement of other
observables, they can be used to determine the tt̄ spin correlation even in the presence of anomalous Wtb couplings. We finally discuss some asymmetries which can be used to test CP violation in tt̄ production and complex phases
in the effective Wtb vertex. 相似文献
98.
Carvalho Andrade Carolina M. M. Aguiar Wilson Bucker Antranikian Garo 《Applied biochemistry and biotechnology》2001,91(1-9):655-669
Xylanases (EC3.2.1.8) catalyze the hydrolysis of xylan, the major constituent of hemicellulose. The use of these enzymes could
greatly improve the overall economics of processing lignocellulosic materials for the generation of liquid fuels and chemicals.
The hyperthermophilic archaeon Pyrodictium abyssi, which was originally isolated from marine hot abyssal sites, grows optimally at 97°C and is a prospective source of highly
thermostable xylanase. Its endoxylanase was shown to be highly thermostable (over 100 m in at 105°C) and active even at 110°C.
The growth of the deep-sea archaeon P. abyssi was investigated using different culture techniques. Among the carbohydrates used, beech wood xylan, birch wood glucuronoxylan
and the arabinoxylan from oats pelt appeared to be good inducers for endoxylanase and β-xylosidase production. The highest
production of arabinofuranosidase, however, was detected in the cell extracts after growth on xylose and pyruvate, indicating
that the intermediate of the tricarboxylic acid cycle acted as a nonrepressing carbon source for the production of thi enzyme.
Electron microscopic studies did not show a significant difference in the cell surface (e.g., xylanosomes) when P. abyssi cells were grown on different carbohydrates. The main kinetic parameters of the organism have been determined. The cell yield
was shown to be very low owing to incomplete substrate utilization, but a very high maximal specific growth rate was determined
(μmax=0.0195) at 90°C and pH 6.0. We also give information on the problems that arise during the fermentation of this hyperthermophilic
archaeon at elevated temperatures. 相似文献
99.
M. I. Yoshida V. R. Silva P. C. C. Pinto S. S. Sant’Anna M. C. Silva C. F. Carvalho 《Journal of Thermal Analysis and Calorimetry》2012,109(3):1429-1433
In the aluminum industries, there are several steps involved in processing since the extraction of bauxite to obtain the final product (Al). During the development of these, various steps generated wastes. One of them, from the electrostatic filter of the calcination step of the Bayer process is a very fine black powder, rich in alumina (Al2O3) that does not meet industry specifications, and it is discarded in the industry yard. Alumina is a noble material and has high commercial value. This black powder has great prospects for recovery, recycling, and future applications. Therefore, it is important to perform characterization of tailings and to do that we have used XRD, SEM, EDS, FTIR, Raman, and thermal analysis. 相似文献
100.
S. Pessanha M.L. Carvalho M. Manso A. Guilherme A.F. Marques C.A. Perez 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009,64(8):805
The pigment vermilion (HgS) was used to color the fore edge, tail and head of books. Dissemination and quantification of Hg present in the ink used to color books from XVIII and XIX centuries are reported. Mercury is a very toxic element for the human body, therefore it is extremely important to know whether Hg tends to disseminate throughout the paper or stays confined to the borders of the books with less danger for readers. Synchrotron X-ray microprobe was used to evaluate Hg dissemination from the border to the centre of the paper sheet. The diffusion pattern of Hg was compared with the results obtained by a portable X-ray fluorescence spectrometer and mean quantitative calculations were obtained by a stationary X-ray fluorescence system with triaxial geometry. The results showed high concentrations of Hg in the external regions, but no diffusion was observed for the inner parts of the paper. 相似文献