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31.
Maria Grzegozek Marian Wo
niak Andrzej Baraski Henk C. Van Der Plas 《Journal of heterocyclic chemistry》1991,28(4):1075-1077
A number of 2-X-3-nitro-1,8-naphthyridines (X= H,D,OH,Cl,NH2, OEt) react with the anion of chloromethyl phenyl sulfone exclusively into 2-X-3-nitro-4-(phenylsulfonylmethyl)-1,8-naphthyridines in high yield. The reaction is found by quantum chemical calculations to be controlled by the interactions of the HOMO of the nucleophile with the LUMO of the substrate, and not by charge. 相似文献
32.
Theoretical and experimental studies of radiative lifetimes of excited electronic states in CO 总被引:1,自引:0,他引:1
The electronic dipole transition moment functions of the A 2Π-X 2Σ+, B 2Σ+-X 2Σ+ and B 2Σ+-A 2Π transitions and the dipole moment function of the X 2Σ+ state of CO+ have been calculated using large contracted CI wavefunctions. The computed transition moment functions together with experimental potential energy curves were used to obtain radiative lifetimes of the excited electronic states B 2Σ+ and A 2Π. Radiative lifetimes of vibrational levels of the X 2Σ+ state were derived from the calculated dipole moment function. The high-frequency deflection technique was used to obtain radiative lifetimes of the ν′ = 0, 1,2 and 3 vibrational levels of the B 2Σ+ state and also radiative lifetimes of individual rotational levels of ν′ =0. The calculated radiative lifetimes are shorter than the measured ones by about 10%. The experimental ν′ dependence is reproduced by theoretical calculation. The calculated radiative lifetimes for the A 2Π state are in excellent agreement with lifetimes measured with an ion trap technique. 相似文献
33.
Marian Čerňanský Přemysl Vaněk Karel Král Radmila Krupková 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):799-806
Summary. In this investigation the crystallization of PbTiO3 upon annealing of pure nanopowders and PbTiO3–SiO2 (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the
start of PbTiO3 crystallization in pure PbTiO3 powders was detected at 400°C. Distinct crystallization of PbTiO3 in PbTiO3–SiO2 nanocomposites starts at 700°C, whereas SiO2 remains amorphous. There are indications that an interface interaction between the PbTiO3 and the SiO2 phase plays an important role in hindering the crystallization of PbTiO3. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line
profiles. The average size of PbTiO3 nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than
that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect
to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution
of the grain size and the morphology of the powder grains, showing that each grain of the powders contains several nanocrystallites
(coherently scattering regions).
Received October 4, 2001. Accepted (revised) December 14, 2001 相似文献
34.
35.
Joseph Páez Chávez Marian Wiercigroch 《Communications in Nonlinear Science & Numerical Simulation》2013,18(9):2571-2580
We investigate complex dynamics occurring in a non-smooth model of a Jeffcott rotor with a bearing clearance. A bifurcation analysis of the rotor system is carried out by means of the software TC-HAT [25], a toolbox of AUTO 97 [6] allowing path-following and detection of bifurcations of periodic trajectories of non-smooth dynamical systems. The study reveals a rich variety of dynamics, which includes grazing-induced fold and period-doubling bifurcations, as well as hysteresis loops produced by a cusp singularity. Furthermore, an analytical expression predicting grazing incidences is derived. 相似文献
36.
Volodymyr O. Knizhnikov Zoia V. Voitenko Vladimir B. Golovko Marian V. Gorichko 《Tetrahedron: Asymmetry》2012,23(14):1080-1083
A novel regio- and diastereospecific ring cleavage of bornane-2,3-dione (camphor quinone) under Bucherer-Bergs reaction conditions has been investigated. The simplicity of this transformation provides a novel and straightforward synthetic pathway to enantiopure derivatives of cyclopentane carboxylic acid as well as functionalized hydantoins in just two steps, starting from inexpensive and easily available camphor. 相似文献
37.
Kristin Voiges Roland Adden Marian Rinken Petra Mischnick 《Cellulose (London, England)》2012,19(3):993-1004
The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution
in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation
and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single
constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in
dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict
but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the
tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility.
Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained.
Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as
solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error. 相似文献
38.
39.
Jan Maier Marian Deutsch Dr. Julia Merz Prof. Dr. Qing Ye Oliver Diamond Maja-Tessa Schilling Dr. Alexandra Friedrich Prof. Dr. Bernd Engels Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):15989-16000
We have investigated the cannibalistic self-trapping reaction of an ortho-benzyne derivative generated from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction. Without adding any specific trapping agent, the highly reactive benzyne is trapped by another bisdiyne molecule in at least three different modes. We have isolated and characterized the resulting products and performed high-level calculations concerning the reaction mechanism. During the cannibalistic self-trapping process, either a C≡C triple bond or an sp–sp3 C−C single bond is cleaved. Up to seven rings and nine C−C bonds are formed starting from two 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne molecules. Our experiments and calculations provide considerable insight into the variety of reaction pathways which the ortho-benzyne derivative, generated from a bisdiyne, can take when reacting with another bisdiyne molecule. 相似文献
40.
Marian Apostol Victor Barsan Constantin Nantea 《Molecular Crystals and Liquid Crystals》2013,570(1):453-456
Jordan's boson representation and cut-off repolarization for the one-dimensional two-fermion model (TFT) is used to get the equivalence of the model with the two-dimensional Coulomb gas and sine-Gordon model. The scaling equations for the coupling constants are thereby obtained up to the third order. 相似文献