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51.
Mustafa Barri George K. El Khoury Helge I. Andersson Bjrnar Pettersen 《国际流体数值方法杂志》2010,64(7):777-792
Direct numerical simulation (DNS) has been performed to study the channel flow over a backward‐facing step at a Reynolds number Reb=5600 based on the step height h and the inflow bulk velocity Ub. A dynamic method has been used in order to generate realistic turbulent inflow conditions. The results upstream of the step compared well with the fully developed channel flow. Downstream of the step our results show excellent agreement with experimental data. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
52.
We develop an analog of classical oscillation theory for Sturm–Liouville operators which, rather than measuring the spectrum
of one single operator, measures the difference between the spectra of two different operators.
This is done by replacing zeros of solutions of one operator by weighted zeros of Wronskians of solutions of two different
operators. In particular, we show that a Sturm-type comparison theorem still holds in this situation and demonstrate how this
can be used to investigate the number of eigenvalues in essential spectral gaps. Furthermore, the connection with Krein’s
spectral shift function is established.
Research supported by the Austrian Science Fund (FWF) under Grant No. Y330. 相似文献
53.
54.
Helge Glöckner 《Semigroup Forum》2000,60(2):326-333
55.
Sarifuddin Santabrata Chakravarty Prashanta Kumar Mandal Helge I. Andersson 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2009,56(Z2):299-323
The present investigation deals with a mathematical model representing the mass transfer to blood streaming through the arteries
under stenotic condition. The mass transport refers to the movement of atherogenic molecules, that is, blood-borne components,
such as oxygen and low-density lipoproteins from flowing blood into the arterial walls or vice versa. The blood flowing through
the artery is treated to be Newtonian and the arterial wall is considered to be rigid having differently shaped stenoses in
its lumen arising from various types of abnormal growth or plaque formation. The nonlinear unsteady pulsatile flow phenomenon
unaffected by concentration-field of the macromolecules is governed by the Navier–Stokes equations together with the equation
of continuity while that of mass transfer is controlled by the convection-diffusion equation. The governing equations of motion
accompanied by appropriate choice of the boundary conditions are solved numerically by MAC(Marker and Cell) method and checked
numerical stability with desired degree of accuracy. The quantitative analysis carried out finally includes the respective
profiles of the flow-field and concentration along with their distributions over the entire arterial segment as well. The
key factors like the wall shear stress and Sherwood number are also examined for further qualitative insight into the flow
and mass transport phenomena through arterial stenosis. The present results show quite consistency with several existing results
in the literature which substantiate sufficiently to validate the applicability of the model under consideration. 相似文献
56.
57.
58.
Xiaoqing Zeng Helmut Beckers Helge Willner Raphael J. F. Berger Stuart A. Hayes Norbert W. Mitzel 《ChemInform》2011,42(19):no-no
The title compound is characterized by IR (gas phase, Ar matrix), Raman (liquid, amorphous, and crystalline solid), and 19F, 31P, 14N and 15N NMR spectroscopy, as well as by quantum chemical DFT calculations. 相似文献
59.
Bulut S Klose P Huang MM Weingärtner H Dyson PJ Laurenczy G Friedrich C Menz J Kümmerer K Krossing I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(44):13139-13154
A large series of ionic liquids (ILs) based on the weakly coordinating alkoxyaluminate [Al(hfip)(4)](-) (hfip: hexafluoroisopropoxy) with classical as well as functionalized cations were prepared, and their principal physical properties determined. Melting points are between 0 ([C(4)MMIM][Al(hfip)(4)]) and 69 °C ([C(3)MPip][Al(hfip)(4)]); three qualify as room-temperature ILs (RTILs). Crystal structures for six ILs were determined; their structural parameters and anion-cation contacts are compared here with known ILs, with a special focus on their influence on physical properties. Moreover, the biodegradability of the compounds was investigated by using the closed-bottle and the manometric respirometry test. Temperature-dependent viscosities and conductivities were measured between 0 and 80 °C, and described by either the Vogel-Fulcher-Tammann (VFT) or the Arrhenius equations. Moreover, conductivities and viscosities were investigated in the context of the molecular volume, V(m). Physical property-V(m) correlations were carried out for various temperatures, and the temperature dependence of the molecular volume was analyzed by using crystal structure data and DFT calculations. The IL ionicity was investigated by Walden plots; according to this analysis, [Al(hfip)(4)](-) ILs may be classified as "very good to good ILs"; while [C(2)MIM][Al(hfip)(4)] is a better IL than [C(2)MIM][NTf(2)]. The dielectric constants of ten [Al(hfip)(4)](-) ILs were determined, and are unexpectedly high (ε(r)=11.5 to 16.8). This could be rationalized by considering additional calculated dipole moments of the structures frozen in the solid state by DFT. The determination of hydrogen gas solubility in [Al(hfip)(4)](-) RTILs by high-pressure NMR spectroscopy revealed very high hydrogen solubilities at 25 °C and 1 atm. These results indicate the significant potential of this class of ILs in manifold applications. 相似文献
60.
Helmut Beckers Dr. Xiaoqing Zeng Dr. Helge Willner Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1506-1520
Pure sym‐N2O4 isolated in solid Ne was obtained by passing cold neon gas over solid N2O4 at ?115 °C and quenching the resulting gaseous mixture at 6.3 K. Filtered UV irradiation (260–400 nm) converts sym‐N2O4 into trans‐ONONO2, a weakly interacting (NO2)2 radical pair, and traces of the cis‐N2O2?O2 complex. Besides the weakly bound ON?O2 complex, cis‐N2O2?O2 was also obtained by co‐deposition of NO and O2 in solid Ne at 6.3 K, and both complexes were characterised by their matrix IR spectra. Concomitantly formed cis‐N2O2 dissociated on exposure to filtered IR irradiation (400–8000 cm?1), and the cis‐N2O2?O2 complex rearranged to sym‐N2O4 and trans‐ONONO2. Experiments using 18O2 in place of 16O2 revealed a non‐concerted conversion of cis‐N2O2?O2 into these species, and gave access to four selectively di‐18O‐substituted trans‐ONONO2 isotopomers. No isotopic scrambling occurred. The IR spectra of sym‐N2O4 and of trans‐ONONO2 in solid Ne were recorded. IR fundamentals of trans‐ONONO2 were assigned based on experimental 16/18O isotopic shifts and guided by DFT calculations. Previously reported contradictory measurements on cis‐ and trans‐ONONO2 are discussed. Dinitroso peroxide, ONOONO, a proposed intermediate in the IR photoinduced rearrangement of cis‐N2O2?O2 to the various N2O4 species, was not detected. Its absence in the photolysis products indicates a low barrier (≤10 kJ mol?1) for its exothermic O? O bond homolysis into a (NO2)2 radical pair. 相似文献