全文获取类型
收费全文 | 627篇 |
免费 | 0篇 |
国内免费 | 17篇 |
专业分类
化学 | 358篇 |
物理学 | 286篇 |
出版年
2012年 | 35篇 |
2011年 | 50篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 56篇 |
2007年 | 57篇 |
2006年 | 55篇 |
2005年 | 54篇 |
2004年 | 38篇 |
2003年 | 31篇 |
2002年 | 24篇 |
2001年 | 15篇 |
2000年 | 35篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 9篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1969年 | 1篇 |
1966年 | 2篇 |
1948年 | 3篇 |
排序方式: 共有644条查询结果,搜索用时 8 毫秒
51.
Using a combination of statistical mechanics and finite-element interpolation, we develop a coarse-grained (CG) alternative to molecular dynamics (MD) for crystalline solids at constant temperature. The new approach is significantly more efficient than MD and generalizes earlier work on the quasicontinuum method. The method is validated by recovering equilibrium properties of single crystal Ni as a function of temperature. CG dynamical simulations of nano-indentation reveal a strong dependence on temperature of the critical stress to nucleate dislocations under the indenter. 相似文献
52.
Chen JH Sambol EB Kennealey PT O'Connor RB DeCarolis PL Cory DG Singer S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,171(1):143-150
In cell and tissue samples, water is normally three orders of magnitude more abundant than other metabolites. Thus, water suppression is required in the acquisition of NMR spectra to overcome the dynamic range problem and to recover metabolites that overlap with the broad baseline of the strong water resonance. However, the heterogeneous cellular environment often complicates water suppression and the strong coupling of water to membrane lipids interferes with the NMR detection of membrane associated lipid components. The widely used water suppression techniques including presaturation and double pulsed field gradient selective echo result in more than a 70% reduction in membrane associated lipid components in proton spectra of cells and tissues compared to proton spectra acquired in the absence of water suppression. A water suppression technique based on the combination of selective excitation pulses and pulsed field gradients is proposed to use in the acquisition of high resolution MAS NMR spectra of tissue specimens and cell samples. This pulse sequence methodology enables efficient water suppression for intact cells and tissue samples and eliminates signal loss from cellular metabolites. 相似文献
53.
Carter EB Culver SL Fox PA Goode RD Ntai I Tickell MD Traylor RK Hoffman NW Davis JH 《Chemical communications (Cambridge, England)》2004,(6):630-631
The anions of the sweeteners saccharin and acesulfame form ionic liquids when paired with a variety of organic cations. 相似文献
54.
Karlsson EB 《Physical review letters》2003,90(9):095301
Several recent experiments have shown that protons, and to some extent also deuterons, show anomalous cross sections when the neutrons have energies in the range 10-100 eV (this results in a Compton scattering process where an essential part of the energy is transferred to one of the scattering particles). Here, an experiment on partially deuterated water, carried out by Chatzidimitriou-Dreismann et al., is analyzed in terms of a theory, which assumes that during the short duration (<10(-15) s) of this scattering process, protons are exchange correlated and cannot be considered as independent scattering objects. The quantum decoherence time for protons in liquid water is estimated from a simple model for the interaction of the water protons with hydrogen bonds. 相似文献
55.
Gnida M Margulès L Cosléou J Bocquet R Demaison J Mkadmi EB Bürger H Harder H Mäder H 《Journal of Molecular Spectroscopy》2000,200(1):40-54
The present paper deals with the analysis of the microwave, millimeter-wave, and infrared spectra of (28)SiHF(3) in its ground, v(6) = 1 and v(4) = 1 excited states. The former was observed up to 1055 GHz leading to the determination of one octic centrifugal distortion constant, L(J) = -0.0749(55) μHz. Furthermore the interaction term ||h(3,GS) || = 1.1032(70) mHz has been fitted from splittings of six K = 3 lines. The excited states have been regarded as isolated ones. This enabled fits according the Q-, D-, and QD-reduction schemes proposed by E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev, (J. Mol. Spectrosc. 126, 159-170 (1987)) and further developed by J. K. G. Watson, C. Gerke, H. Harder, and K. Sarka, (J. Mol. Spectrosc. 187, 131-141 (1997)) and Harder (J. Mol. Spectrosc. 194, 145 (1999)). A multiple fit analysis was performed confirming the assumption that the excited states are not affected by intervibrational resonances. Finally the millimeter spectrum of (29)SiHF(3) and (30)SiHF(3) in their ground state was also measured up to 460 GHz and accurate rotational and centrifugal distortion parameters were derived. Copyright 2000 Academic Press. 相似文献
56.
The Gross-Pitaevskii approximation is a long-wavelength theory widely used to describe a variety of properties of dilute Bose condensates, in particular trapped alkali gases. We point out that for short-ranged repulsive interactions this theory fails in dimensions d=2, and we propose the appropriate low-dimensional modifications, which have a universal form. For d = 1 we analyze density profiles in confining potentials, superfluid properties, solitons, and self-similar solutions. 相似文献
57.
Parabolic plasma sheath potentials and their implications for the charge on levitated dust particles
Analysis of several numerical plasma sheath models, as well as data from several previously reported experiments, is shown to indicate that the sheath potential function may often be very closely approximated with a parabola. We also demonstrate that once this potential function is suitably determined the charge on isolated dust particles levitated in the plasma sheath may be calculated directly from their equilibrium heights. 相似文献
58.
We introduce a technique for ultrasensitive absorption spectroscopy using the GHz-rate pulse train from a phase-locked free-electron laser (FEL), in which the fractional power absorbed from one or more laser lines reappears as a signal on the dark background between the pulses emerging from the sample. Preliminary absorption experiments in 15 Torr cm of methane at 3.25 &mgr;m, using phase-locked pulses from the Mark III FEL, clearly reveal an interpulse beat signal due to absorption by adjacent molecular rotational lines which is generated only in the presence of interpulse phase coherence. 相似文献
59.
Joosten R Powell J Guo FQ Haustein PE Larimer R McMahan MA Norman EB O'Neil JP Rowe MW VanBrocklin HF Wutte D Xu XJ Cerny J 《Physical review letters》2000,84(22):5066-5069
A light-element radioactive ion-beam capability has been developed at the LBNL 88-Inch Cyclotron. The system is based on the coupled-cyclotrons method and utilizes short-lived species, e.g., 11C, 14O, 13N produced by (p,n) and (p,alpha) reactions at the LBNL Biomedical Isotope Facility Cyclotron. In a first experiment, 197Au(11C,xn)208-xAt excitation functions have been measured for energies ranging from the Coulomb barrier up to 110 MeV using a beam of 11C with intensities up to (1-2)x10(8) ions/sec on target. The results of this experiment are compared to measurements of 197Au(12C, xn)209-xAt excitation functions. 相似文献
60.
Verma SK Nguyen QH MacDougall JM Fleischer EB Moore HW 《The Journal of organic chemistry》2000,65(11):3379-3386
6-exo-Methylbicyclo[3.2.0]hepten-7-ones and their 2-alkylidene analogues are readily prepared from dialkyl squarates. These compounds undergo facial oxy-Cope ring expansions upon treatment with vinyllithium; the former leads to bicyclo[4.2. 1]non-1(4)-en-6-ones and the latter to the first examples of bicyclo[5.2.1]dec-1(10)-en-5-ones, compounds having exceptionally strained bridgehead double bonds. The transformations are controlled by the 6-exo-methyl group in the starting material along with the substituent at position-1 (bridgehead) which force attack of the lithium reagent from the concave face of the starting material, thus allowing the cyclopentenyl or alkylidene groups to participate in the sigmatropic event. 相似文献