全文获取类型
收费全文 | 1590篇 |
免费 | 29篇 |
国内免费 | 6篇 |
专业分类
化学 | 977篇 |
晶体学 | 8篇 |
力学 | 60篇 |
数学 | 92篇 |
物理学 | 488篇 |
出版年
2020年 | 19篇 |
2019年 | 14篇 |
2016年 | 21篇 |
2015年 | 15篇 |
2014年 | 31篇 |
2013年 | 64篇 |
2012年 | 43篇 |
2011年 | 68篇 |
2010年 | 49篇 |
2009年 | 36篇 |
2008年 | 60篇 |
2007年 | 42篇 |
2006年 | 53篇 |
2005年 | 28篇 |
2004年 | 40篇 |
2003年 | 24篇 |
2002年 | 46篇 |
2001年 | 41篇 |
2000年 | 38篇 |
1999年 | 37篇 |
1998年 | 25篇 |
1997年 | 26篇 |
1996年 | 41篇 |
1995年 | 41篇 |
1994年 | 33篇 |
1993年 | 35篇 |
1992年 | 35篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 30篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 32篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1975年 | 15篇 |
1974年 | 20篇 |
1973年 | 23篇 |
1970年 | 19篇 |
1969年 | 18篇 |
1968年 | 14篇 |
1967年 | 16篇 |
排序方式: 共有1625条查询结果,搜索用时 312 毫秒
931.
DIeter Klapstein Jonhn P. Maier Martin Ochsner Werner Zanbach 《Journal of Electron Spectroscopy and Related Phenomena》1984,34(2):161-162
Rotationally cooled bromochloroacetylene cations have been studied in the ≈X2Πω and ≈A2Πω (ω = , ) states in the gas phase by two complementary spectroscopic techniques. The ≈A2Π ? ≈X2π band system was excited in emission by electron impact of a seeded supersonic helium free jet and as fluorescence by laser excitation of cations formed by Penning ionisation in a cooled environment. Comparison of the two sets of data locates the spin—orbit component bands and the origins of the systems, and allows the main spectral features to be vibronically assigned. The vibrational frequencies of most of the fundamentals are thus obtained to within ±2 cm?1 for this cation in both the states. 相似文献
932.
933.
From an invariant expansion, we construct the exciton Hamiltonian for the Γ6×Γ8 excitons in theT d -type material ZnTe represented by an 8×8 matrix including the influences of a finite wave vector and an external magnetic field. We diagonalize the Hamiltonian matrix to obtain the exciton states. Then the excitons are coupled to the electromagnetic radiation field thus giving the polariton states. The theoretical dispersion curves are fitted to the results of two-photon Raman scattering and reflection experiments in magnetic fields up to 22 T. From this fit we deduce precise values for the eigenergies, exciton masses,g-factors, and diamagnetic shifts. 相似文献
934.
Rudolf Maier 《Archiv der Mathematik》1976,27(1):576-583
Ohne Zusammenfassung 相似文献
935.
Rudolf Maier 《Archiv der Mathematik》1976,27(1):480-483
Ohne Zusammenfassung 相似文献
936.
Leonova MA Krisch AD Morozov VS Raymond RS Wong VK Gebel R Lehrach A Lorentz B Maier R Prasuhn D Schnase A Stockhorst H Eversheim D Hinterberger F Ulbrich K 《Physical review letters》2004,93(22):224801
We recently used a new ferrite rf dipole to study spin flipping of a 2.1 GeV/c vertically polarized proton beam stored in the COSY Cooler Synchrotron in Jülich, Germany. We swept the rf dipole's frequency through an rf-induced spin resonance to flip the beam's polarization direction. After determining the resonance's frequency, we varied the frequency range, frequency ramp time, and number of flips. At the rf dipole's maximum strength and optimum frequency range and ramp time, we measured a spin-flip efficiency of 99.92+/-0.04%. This result, along with a similar 0.49 GeV/c IUCF result, indicates that, due to the Lorentz invariance of an rf dipole's transverse integralBdl and the weak energy dependence of its spin-resonance strength, an only 35% stronger rf dipole should allow efficient spin flipping in the 100 GeV BNL RHIC Collider or even the 7 TeV CERN Large Hadron Collider. 相似文献
937.
Steffen Maier Robin Heckershoff Nikolai Hippchen Kerstin Brödner Dr. Frank Rominger Dr. Jan Freudenberg Prof. A. Stephen K. Hashmi Prof. Uwe H. F. Bunz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(64):e202201842
Brominated pentannulated dihydrotetraazapentacenes were prepared by gold- or palladium-catalyzed 5-endo-dig cyclization of TIPS-ethynylated dihydrotetraazaacenes (TIPS = triisopropylsilyl). Post-functionalization was demonstrated by Sonogashira alkynylation and Rosenmund-von Braun cyanation. Calculations predict these species to act as n-type semiconductors, which was verified for two derivates through characterization in organic field-effect transistors. 相似文献
938.
In this paper, the integrity assessment of pressurized pipelines containing defects is performed by direct simplified methods
of limit and shakedown analysis. The defects considered are part-through slots of various geometrical configurations. The
engineering situation considered here has practical importance in the pressure vessel and pipe industry. The results are compared
with those obtained by a step-by-step procedure using the professional code ABAQUS and where possible, with those provided
by semi-empirical formulae used in engineering. The simplified methods are found more economical and more reliable than marching
solutions achieved by step-by-step evolutive elastic-plastic analysis. The effects of various part-through slots on the load-carrying
capacities of pipelines are investigated.
The project was supported by the National Science and Technology Commission of China and by the Department of Structural Engineering,
Technical University of Milan, Italy 相似文献
939.
Summary This note contains some remarks on the analysis of bifurcation phenomena, specifically strain localization (onset of a strain rate discontinuity), in small-deformation elastoplasticity. Nonassociative flow rules are allowed for to cover constitutive models frequently adopted for frictional (and softening) materials such as concrete. The conventional derivation of the localization criterion resting on an incrementally linear comparison material is critically reviewed and compared to the criterion resulting from actual nonlinear plastic flow laws.
Sommario Si svolgono alcune considerazioni sui fenomeni di biforcazione in solidi elastoplastici in regime di piccole deformazioni (di linearità geometrica) e precisamente sul manifestarsi di localizzazioni intese come discontinuità nel campo delle deformazioni incrementali. Si considerano leggi nonassociate. Vengono così inclusi nella trattazione modelli costitutivi frequentemente adottati per descrivere il comportamento di materiali ad attrito interno e soggetti a danneggiamento (nel senso di degrado di rigidezze elastiche in seguito a deformazioni anelastiche), oltre che soggetti a manifestazioni di instabilità per incrudimento negativo (softening). Si esamina criticamente il criterio, frequentemente adottato in letteratura, di localizzazione fondato su materiale di confronto incrementalmente lineare e si fornisce, corredato da osservazioni comparative, il criterio che risulta dall'assunzione del modello di materiale incrementale non lineare相似文献
940.
Robert S. Maier. 《Mathematics of Computation》2007,76(258):811-843
A machine-generated list of local solutions of the Heun equation is given. They are analogous to Kummer's solutions of the Gauss hypergeometric equation, since the two equations are canonical Fuchsian differential equations on the Riemann sphere with four and three singular points, respectively. Tabulation is facilitated by the identification of the automorphism group of the equation with singular points as the Coxeter group . Each of the expressions is labeled by an element of . Of the , are equivalent expressions for the local Heun function , and it is shown that the resulting order- group of transformations of is isomorphic to the symmetric group . The isomorphism encodes each transformation as a permutation of an abstract four-element set, not identical to the set of singular points.