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961.
O-Alkylation of the dinitro calix[4]arene 2, easily available by selective ipso-nitration of the di-cyanomethyl ether 1, with allylbromide (DMF/Cs2CO3) gave tetraethers 3 and 4 with anti- and syn-orientations of the two allyl ether residues. The two possible stereoisomers of in the partial cone and 1,2-alternate conformation exist as an equilibrium mixture which could be quantitatively analysed by 1H NMR spectroscopy. The temperature dependence of this equilibrium leads to deltaH0 = -7.6 to -9.7 kJ mol(-1) in different solvents (tetrachloroethane, benzene, dimethylsulfoxide). Since 3(1,2-alt) could be obtained in pure form, its isomerisation to the equilibrium mixture with 3(paco) could be followed also kinetically. An activation energy of E(a) = 110.5 kJ mol(-1) was found for this reaction in DMSO-d6. The results were confirmed by similar studies with tetraethers 5 and 6 obtained by O-allylation of 1, although exact thermodynamic and kinetic studies were not possible in this case, since the NMR signals of the respective isomers were strongly overlapping. Single crystal X-ray structures were obtained for 2, 3(1,2-alt), 4(paco) and 5(1,2-alt). 相似文献
962.
Stochastic modelling of tropical cyclone tracks 总被引:5,自引:0,他引:5
Jonas Rumpf Helga Weindl Peter Höppe Ernst Rauch Volker Schmidt 《Mathematical Methods of Operations Research》2007,66(3):475-490
A stochastic model for the tracks of tropical cyclones that allows for the computerised generation of a large number of synthetic
cyclone tracks is introduced. This will provide a larger dataset than previously available for the assessment of risks in
areas affected by tropical cyclones. To improve homogeneity, the historical tracks are first split into six classes. The points
of cyclone genesis are modelled as a spatial Poisson point process, the intensity of which is estimated using a generalised
version of a kernel estimator. For these points, initial values of direction, translation speed, and wind speed are drawn
from histograms of the historical values of these variables observed in the neighbourhood of the respective points, thereby
generating a first 6-h segment of a track. The subsequent segments are then generated by drawing changes in theses variables
from histograms of the historical data available near the cyclone’s current location. A termination probability for the track
is determined after each segment as a function of wind speed and location. In the present paper, the model is applied to historical
cyclone data from the western North Pacific, but it is general enough to be transferred to other ocean basins with only minor
adjustments. A version for the North Atlantic is currently under preparation. 相似文献
963.
Phytosiderophores of the mugineic acid family, and the respective iron species, have been separated by anion-exchange chromatography with NaOH gradient elution. Two different detection methods were used in parallel, pulsed amperometry (PAD) for phytosiderophores and atomic absorption spectrometry (AAS) for iron. This combination enables identification of separated iron species. Up to five different iron species were separated and detected within 30 min - two different phytosiderophore species, two amino acid species, and one species which has not yet been identified but which is most probably a decomposition product of phytosiderophores. The detection limit was in the low micro mol L(-1) concentration range, which is sufficiently low for determination in real plant samples, even after dilution. The method has been applied to root washings of iron-deficient wheat and barley plants and to a xylem exudate of non-deficient maize. 相似文献
964.
Dietrich B Holtin K Bayer M Friebolin V Kühnle M Albert K 《Analytical and bioanalytical chemistry》2008,391(7):2627-2633
Reversed-phase materials with branched and unbranched alkyl groups were prepared by modifying porous, spherical silica gel
in a two-step reaction—immobilization of a trifunctional alkoxysilane (3-glycidoxypropyltrimethoxysilane) on the silica surface
followed by reaction with a branched and an unbranched octanoic acid. The chromatographic sorbents were characterized by solid-state
29Si and 13C NMR spectroscopy. The chromatographic behaviour of the stationary phases was evaluated by use of a test mixture according
to the Standard Reference Material 870 set from the US National Institute of Standards and Technology, in order to study the
effect of branched and unbranched alkyl chains. 相似文献
965.
966.
Mark J. Rhoades-Brown Volker E. Oberacker Martin Seiwert Walter Greiner 《Zeitschrift für Physik A Hadrons and Nuclei》1983,310(4):287-294
Within the double-folding model the separation, shape, and orientation dependence of the interaction potential is studied for two heavy ions. An effective nucleon-nucleon interaction (M3Y) derived fromG-matrix elements and based upon the Reid soft-core potential is used. Deformed Fermi-type matter densities with static quadrupole and hexadecapole deformations were utilized. The model is applied to the238U+238U system and shows dramatic dependence on the deformations and orientations. 相似文献
967.
968.
969.
Volker Branding 《Potential Analysis》2016,45(4):737-754
We derive gradient and energy estimates for critical points of the full supersymmetric sigma model and discuss several applications. 相似文献
970.
The Future of (Radio)-Labeled Compounds in Research and Development within the Life Science Industry
Dr. Volker Derdau Dr. Charles S. Elmore Dr. Thomas Hartung Dr. Bruce McKillican Dr. Tom Mejuch Claudia Rosenbaum Prof. Dr. Christine Wiebe 《Angewandte Chemie (International ed. in English)》2023,62(52):e202306019
In this review the applications of isotopically labeled compounds are discussed and put into the context of their future impact in the life sciences. Especially discussing their use in the pharma and crop science industries to follow their fate in the environment, in vivo or in complex matrices to understand the potential harm of new chemical structures and to increase the safety of human society. 相似文献