全文获取类型
收费全文 | 724篇 |
免费 | 12篇 |
专业分类
化学 | 396篇 |
晶体学 | 8篇 |
力学 | 13篇 |
数学 | 96篇 |
物理学 | 223篇 |
出版年
2021年 | 5篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 10篇 |
2013年 | 21篇 |
2012年 | 29篇 |
2011年 | 27篇 |
2010年 | 15篇 |
2009年 | 19篇 |
2008年 | 32篇 |
2007年 | 29篇 |
2006年 | 21篇 |
2005年 | 35篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 21篇 |
1999年 | 16篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 19篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1970年 | 7篇 |
1969年 | 5篇 |
1967年 | 8篇 |
1943年 | 4篇 |
1889年 | 4篇 |
1888年 | 4篇 |
排序方式: 共有736条查询结果,搜索用时 15 毫秒
111.
Ľ. Vrtoch M. Pipíška M. Horník J. Augustín J. Lesný 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):853-862
In order to gain biosorbent that would have the ability to bind cesium ions from water solution effectively, potassium nickel
hexacyanoferrate(II) (KNiFC) was incorporated into the mushroom biomass of Agaricus bisporus. Cesium sorption by KNIFC-modified A. bisporus biosorbent was observed in batch system, using radiotracer technique using 137Cs radioisotope. Kinetic study showed that the cesium sorption was quite rapid and sorption equilibrium was attained within
1 h. Sorption kinetics of cesium was well described by pseudo-second order kinetics. Sorption equilibrium was the best described
by Freundlich isotherm and the distribution coefficient was at interval 7,662–159 cm3 g−1. Cesium sorption depended on initial pH of solution. Cesium sorption was very low at pH0 1.0–3.0. At initial pH 11.0, maximum sorption of cesium was found. Negative effect of monovalent (K+, Na+, NH4
+) and divalent (Ca2+, Mg2+) cations on cesium sorption was observed. Desorption experiments showed that 0.1 M potassium chloride is the most suitable
desorption agent but the complete desorption of cesium ions from KNiFC-modifed biosorbent was not achieved. 相似文献
112.
M. Brando N. Büttgen V. Fritsch J. Hemberger H. Kaps H.-A. Krug von Nidda M. Nicklas K. Pucher W. Trinkl A. Loidl E.W. Scheidt M. Klemm S. Horn 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):289-298
We present susceptibility, microwave resistivity, NMR and heat-capacity results for Li1-xZnx(V1-yTiy)2O4 with 0 ?
x
? 0.3 and 0 ?
y
? 0.3. For all doping levels the susceptibility curves can be fitted with a Curie-Weiss law. The paramagnetic Curie-Weiss temperatures
remain negative with an average value close to that of the pure compound Θ≈ - 36 K. Spin-glass anomalies are observed in the susceptibility, heat-capacity and NMR measurements for both type of dopants.
From the temperature dependence of the spin-lattice relaxation rate we found critical-dynamic behavior in the Zn doped compounds
at the freezing temperatures. For the Ti-doped samples two successive freezing transitions into disordered low-temperature
states can be detected. The temperature dependence of the heat capacity for Zn-doped compounds does not resemble that of canonical
spin glasses and only a small fraction of the total vanadium entropy is frozen at the spin-glass transitions. For pure LiV2O4 the spin-glass transition is completely suppressed. The temperature dependence of the heat capacity for LiV2O4 can be described using a nuclear Schottky contribution and the non-Fermi liquid model, appropriate for a system close to
a spin-glass quantum critical point. Finally an (
x
/
y
,
T
)-phase diagram for the low-doping regime is presented.
Received 16 March 2001 and Received in final form 30 October 2001 相似文献
113.
A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed. 相似文献
114.
Reduction of imine-anthracenone compounds selectively produces secondary alcohols leaving the external imine group unreacted. Addition of the Zn(II) ion induces a metal-mediated imine-enamine tautomerization reaction that is selective for Zn(II), a new fluorescence detection method not previously observed for this important cation. 相似文献
115.
Jana Hudecová Jan Horníček Dr. Miloš Buděšínský Dr. Jaroslav Šebestík Martin Šafařík Ge Zhang Dr. Timothy A. Keiderling Dr. Petr Bouř 《Chemphyschem》2012,13(11):2748-2760
The tryptophan (Trp) aromatic residue in chiral matrices often exhibits a large optical activity and thus provides valuable structural information. However, it can also obscure spectral contributions from other peptide parts. To better understand the induced chirality, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and Raman optical activity (ROA) spectra of Trp‐containing cyclic dipeptides c‐(Trp‐X) (where X=Gly, Ala, Trp, Leu, nLeu, and Pro) are analyzed on the basis of experimental spectra and density functional theory (DFT) computations. The results provide valuable insight into the molecular conformational and spectroscopic behavior of Trp. Whereas the ECD is dominated by Trp π–π* transitions, VCD is dominated by the amide modes, well separated from minor Trp contributions. The ROA signal is the most complex. However, an ROA marker band at 1554 cm?1 indicates the local χ2 angle value in this residue, in accordance with previous theoretical predictions. The spectra and computations also indicate that the peptide ring is nonplanar, with a shallow potential so that the nonplanarity is primarily induced by the side chains. Dispersion‐corrected DFT calculations provide better results than plain DFT, but comparison with experiment suggests that they overestimate the stability of the folded conformers. Molecular dynamics simulations and NMR results also confirm a limited accuracy of the dispersion‐DFT model in nonaqueous solvents. Combination of chiral spectroscopies with theoretical analysis thus significantly enhances the information that can be obtained from the induced chirality of the Trp aromatic residue. 相似文献
116.
Androić D Armstrong DS Arvieux J Bailey SL Beck DH Beise EJ Benesch J Benmokhtar F Bimbot L Birchall J Bosted P Breuer H Capuano CL Chao YC Coppens A Davis CA Ellis C Flores G Franklin G Furget C Gaskell D Gericke MT Grames J Guillard G Hansknecht J Horn T Jones MK King PM Korsch W Kox S Lee L Liu J Lung A Mammei J Martin JW McKeown RD Micherdzinska A Mihovilovic M Mkrtchyan H Muether M Page SA Papavassiliou V Pate SF Phillips SK Pillot P Pitt ML Poelker M Quinn B Ramsay WD Real JS Roche J 《Physical review letters》2012,108(12):122002
The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2 ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03 ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering. 相似文献
117.
Fomin N Arrington J Asaturyan R Benmokhtar F Boeglin W Bosted P Bruell A Bukhari MH Christy ME Chudakov E Clasie B Connell SH Dalton MM Daniel A Day DB Dutta D Ent R El Fassi L Fenker H Filippone BW Garrow K Gaskell D Hill C Holt RJ Horn T Jones MK Jourdan J Kalantarians N Keppel CE Kiselev D Kotulla M Lindgren R Lung AF Malace S Markowitz P McKee P Meekins DG Mkrtchyan H Navasardyan T Niculescu G Opper AK Perdrisat C Potterveld DH Punjabi V Qian X Reimer PE Roche J Rodriguez VM Rondon O 《Physical review letters》2012,108(9):092502
We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate. 相似文献
118.
Motivated by the observation that the sparse tree‐like subgraphs in a small world graph have large diameter, we analyze random spanning trees in a given host graph. We show that the diameter of a random spanning tree of a given host graph G is between and with high probability., where c and c′ depend on the spectral gap of G and the ratio of the moments of the degree sequence. For the special case of regular graphs, this result improves the previous lower bound by Aldous by a factor of logn. Copyright © 2011 John Wiley Periodicals, Inc. J Graph Theory 69: 223–240, 2012 相似文献
119.
Williams KS Hooper JP Horn JM Lightstone JM Wang H Ko YJ Bowen KH 《The Journal of chemical physics》2012,136(13):134315
Negative-ion photoelectron spectroscopy and ab initio simulations are used to study the variation in magnetic structure in Mn(x)O(y) (x = 3, 4[semicolon] y = 1, 2) clusters. The ferrimagnetic and antiferromagnetic ground-state structures of Mn(x)O(y) are 0.16-1.20 eV lower in energy than their ferromagnetic isomers. The presence of oxygen thus stabilizes low-spin isomers relative to the preferred high-spin ordering of bare Mn(3) and Mn(4). Each cluster has a preferred overall magnetic moment, and no evidence is seen of competing states with different spin multiplicities. However, non-degenerate isomags, which possess the same spin multiplicity but different arrangements of local moments, do contribute additional features and peak broadening in the photoelectron spectra. Proper accounting for all possible isomags is shown to be critical for accurate computational prediction of the spectra. 相似文献
120.
We present two algorithms to compute m-fold hypergeometric solutions of linear recurrence equations for the classical shift case and for the q-case, respectively. The first is an m-fold generalization and q-generalization of the algorithm by van Hoeij (Appl Algebra Eng Commun Comput 17:83–115, 2005; J. Pure Appl Algebra 139:109–131, 1998) for recurrence equations. The second is a combination of an improved version of the algorithms by Petkovšek (Discrete Math
180:3–22, 1998; J Symb Comput 14(2–3):243–264, 1992) for recurrence and q-recurrence equations and the m-fold algorithm from Petkovšek and Salvy (ISSAC 1993 Proceedings, pp 27–33, 1993) for recurrence equations. We will refer to the classical algorithms as van Hoeij or Petkovšek respectively. To formulate our ideas, we first need to introduce an adapted version of an m-fold Newton polygon and its characteristic polynomials for the classical case and q-case, and to prove the important properties in this case. Using the data from the Newton polygon, we are able to present
efficient m-fold versions of the van Hoeij and Petkovšek algorithms for the classical shift case and for the q-case, respectively. Furthermore, we show how one can use the Newton polygon and our characteristic polynomials to conclude
for which
m ? \mathbbN{m\in \mathbb{N}} there might be an m-fold hypergeometric solution at all. Again by using the information obtained from the Newton polygon, the presentation of
the q-Petkovšek algorithm can be simplified and streamlined. Finally, we give timings for the ‘classical’ q-Petkovšek, our q-van Hoeij and our modified q-Petkovšek algorithm on some classes of problems and we present a Maple implementation of the m-fold algorithms for the q-case. 相似文献