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141.
A theoretical generalisation of the Fokker/Planck equation for atomic and molecular diffusion is compared with the results of a molecular dynamics simulation of a triatomic molecule ofC
2v symmetry. The molecular dynamics results are non-Markhovian and non-Gaussian in nature, markedly so in the case of the centre of mass linear velocityV. This may be ascertained by simulating the long-time limit of the three dimensional kinetic energy autocorrelation function <V
2(t)V
2(0)>/<V
2(0)V
2(0)>, which falls well below the theoretical Gaussian value of 3/5. By expressing the Mori continued fraction as a multidimensional Markhovian chain of differential equations and expressing this in turn as a non-Gaussian probability-diffusion equation of the Kramers/Moyal type it is possible to account for the simulation results in a qualitative fashion. 相似文献
142.
143.
F. Grüner S. Becker U. Schramm T. Eichner M. Fuchs R. Weingartner D. Habs J. Meyer-ter-Vehn M. Geissler M. Ferrario L. Serafini B. van der Geer H. Backe W. Lauth S. Reiche 《Applied physics. B, Lasers and optics》2007,86(3):431-435
A recent breakthrough in laser-plasma accelerators, based upon ultrashort high-intensity lasers, demonstrated the generation
of quasi-monoenergetic GeV-electrons. With future Petawatt lasers ultra-high beam currents of ∼100 kA in ∼10 fs can be expected,
allowing for drastic reduction in the undulator length of free-electron-lasers (FELs). We present a discussion of the key
aspects of a table-top FEL design, including energy loss and chirps induced by space-charge and wakefields. These effects
become important for an optimized table-top FEL operation. A first proof-of-principle VUV case is considered as well as a
table-top X-ray-FEL which may also open a brilliant light source for new methods in clinical diagnostics.
PACS 41.60.Cr; 52.38.Kd 相似文献
144.
Guizzardi B Mella M Fagnoni M Albini A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(7):1549-1555
The irradiation of N,N-dimethyl-4-chloroaniline in the presence of open-chain dienes in acetonitrile leads to addition of the aminophenyl and chloro groups across one of the double bonds; transannular cyclization takes place with cyclic dienes, leading to an arylnortricyclene from norbornadiene and to 1-arylbicyclo[3.3.0]octanes from 1,5-cyclooctadiene. The reaction proceeds by photoheterolysis of the chloroaniline to yield the 4-aminophenyl cation and addition to a CdoublebondC . The chemistry of the adduct cation depends on structure and medium, involving ion pairs in MeCN and solvated ions in CF(3)CH(2)OH. In the latter solvent, formation of ethers from open-chain alkenes is accompanied by Wagner-Meerwein hydride shift. In acetonitrile, the cation from cyclooctadiene partitions between deprotonation and Ritter addition, while the one from norbornadiene is reduced; both cations undergo nucleophilic addition in trifluoroethanol. The relevance of these cationic reactions under unusually mild conditions is discussed. 相似文献
145.
146.
Scholes GD Curutchet C Mennucci B Cammi R Tomasi J 《The journal of physical chemistry. B》2007,111(25):6978-6982
The way that solvent (or host medium) modifies the rate of electronic energy transfer (EET) has eluded researchers for decades. By applying quantum chemical methods that account for the way solvent (in general any host medium including liquid, solid, or protein, etc.) responds to the interaction between transition densities, we quantify the solvent screening. We find that it attains a striking exponential attenuation at separations less than about 20 A, thus interpolating between the limits of no apparent screening and a significant attenuation of the EET rate. That observation reveals a previously unidentified contribution to the distance dependence of the EET rate. 相似文献
147.
Calucci L Forte C Csorba KF Mennucci B Pizzanelli S 《The journal of physical chemistry. B》2007,111(1):53-61
ClPbis11BB and Pbis11BB, two banana-shaped mesogens differing by a chlorine substituent on the central phenyl ring, show a nematic and a B2 phase, respectively. To obtain information on the structural features responsible for their different mesomorphic behavior, a study of the preferred conformations of these mesogens has been performed by NMR spectroscopy in two nematic media (Phase IV and ZLI1167), which should mimic the environment of the molecules in their own mesophases, avoiding problems of sample alignment by a magnetic field. To this aim, 2H NMR experiments have been performed on selectively deuterated isotopomers of ClPbis11BB and Pbis11BB and of two parent molecules, ClPbisB and PbisB, assumed as models in previous theoretical and experimental conformational studies. We found that only a limited number of conformations is compatible with experimental data, often very different from those inferred from theoretical calculations in vacuo, indicating a strong influence of the liquid crystalline environment on molecular conformation. No significant differences between chlorinated and non-chlorinated molecules were found, this suggesting that chlorine does not change the molecular conformational equilibrium, as previously proposed. 相似文献
148.
149.
Clarissa Coccia Dr. Marta Morana Dr. Arup Mahata Dr. Waldemar Kaiser Dr. Marco Moroni Dr. Benedetta Albini Prof. Pietro Galinetto Dr. Giulia Folpini Prof. Chiara Milanese Prof. Alessio Porta Dr. Edoardo Mosconi Dr. Annamaria Petrozza Prof. Filippo De Angelis Prof. Lorenzo Malavasi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(10):e202318557
Chiral perovskites possess a huge applicative potential in several areas of optoelectronics and spintronics. The development of novel lead-free perovskites with tunable properties is a key topic of current research. Herein, we report a novel lead-free chiral perovskite, namely (R/S−)ClMBA2SnI4 (ClMBA=1-(4-chlorophenyl)ethanamine) and the corresponding racemic system. ClMBA2SnI4 samples exhibit a low band gap (2.12 eV) together with broad emission extending in the red region of the spectrum (∼1.7 eV). Chirality transfer from the organic ligand induces chiroptical activity in the 465–530 nm range. Density functional theory calculations show a Rashba type band splitting for the chiral samples and no band splitting for the racemic isomer. Self-trapped exciton formation is at the origin of the large Stokes shift in the emission. Careful correlation with analogous lead and lead-free 2D chiral perovskites confirms the role of the symmetry-breaking distortions in the inorganic layers associated with the ligands as the source of the observed chiroptical properties providing also preliminary structure-property correlation in 2D chiral perovskites. 相似文献
150.
Vivina Barutello Davide L. Ferrario Susanna Terracini 《Archive for Rational Mechanics and Analysis》2008,190(2):189-226
We consider periodic and quasi-periodic solutions of the three-body problem with homogeneous potential from the point of view
of equivariant calculus of variations. First, we show that symmetry groups of the Lagrangian action functional can be reduced
to groups in a finite explicitly given list, after a suitable change of coordinates. Then, we show that local symmetric minimizers
are always collisionless, without any assumption on the group other than the fact that collisions are not forced by the group
itself. Moreover, we describe some properties of the resulting symmetric collisionless minimizers (Lagrange, Euler, Hill-type
orbits and Chenciner–Montgomery figure-eights). 相似文献