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901.
S. N. M. Ruijsenaars 《Communications in Mathematical Physics》1989,124(4):553-593
The kernels of operators associated with special chiral gauge transformations (kinks) in the 2N-dimensional Dirac theory are explicitly determined. The result is used to obtain index formulas for Fredholm operators corresponding to continuous chiral gauge transformations. Moreover, the Fock space quadratic forms corresponding to the kinks are proved to converge to the Dirac field as the kink size goes to zero. It is also shown that forN 1, 2(mod 4) the Majorana field can be reached in a similar fashion.Work supported by the Netherlands Organisation for the Advancement of Research (NWO) 相似文献
902.
S. Bamidele Sanni H. Behm Paul T. Beurskens E. Kayode Adesogan James I. Durodola 《Journal of chemical crystallography》1988,18(5):575-582
A new cytotoxic macrocyclic diterpenoid named Japodagrol, C20H28O4, has been isolated from the ornamental plantJatropha podagrica, family Euphorbiaceae, grown in Nigeria. The structure of the title compound, C20H28O4, was solved by X-ray analysis.M
r
=332.44, monoclinic space groupC2,a=23.285(4),b=6.5105(12),c=12.505(3) Å,=98.504(17),V=1874.8 Å3,Z=4,D
c
=1.178 Mg/m3. CuK radiation (graphite crystal monochromator, =1.54184 A), (CuK)=6.13 cm–1,F(000)=720,T=290 K. Final conventionalR factor=0.035,R
w
=0.038 for 3349 observed reflections. The structure was solved with the programDirdif. The 5-membered ring is closed to a half-chair form. The compound contains inter- and intramolecular hydrogen bonds. 相似文献
903.
Every simple graphG=(V, E) can be represented by a family of equal nonoverlapping spheres {S
v
:v V} in a Euclidean spaceR
n
in such a way thatuv E if and only ifS
u
andS
v
touch each other. The smallest dimensionn needed to representG in such a way is called the contact dimension ofG and it is denoted by cd(G). We prove that (1) cd(T)<(7.3) log |T| for every treeT, and (2)
相似文献
904.
905.
During ageing the Al-2·0 at. %Zn-1·0 at. % Mg alloy at elevated temperatures the width of the precipitation free zone (PFZ) at both sides of the grain boundaries (GB) is identical with that free of quenched-in dislocation loops (DL). After sufficiently long ageing a band of precipitates is growing inside the former PFZ and the DLs in the midgrain regions act as sites for the heterogeneous nucleation of the-phase. Two precipitation processes significantly affect the mechanical properties. TEM correlates grain boundary precipitate density and morphology with grain boundary misorientation. 相似文献
906.
Persistent currents in polycrystalline YBa2Cu3O7 rings have been investigated by measuring the spatial distribution of the magnetic flux trapped in field-cooled samples. The results unambiguously show that macroscopic persistent ring currents exist. The critical current density depends very sensitively on the sample quality, reachingj
c
250 A/cm2 at 77 K for our best samples. 相似文献
907.
A. Vanelstraete C. Laermans L. Lejarraga M. von Schickfus S. Hunklinger 《Zeitschrift für Physik B Condensed Matter》1988,70(1):19-23
The internal friction of two neutron-irradiated quartz samples was measured at audio-frequency as a function of temperature. This is an extension of acoustic measurements to much lower frequencies and thus to much longer time scales. A temperature independent behaviour has been observed and is discussed in the framework of the tunnelling model. One of the major assumptions of this model regarding the tunnelling states with long relaxation time could be verified for neutron-irradiated quartz. 相似文献
908.
P. Ruján 《Zeitschrift für Physik B Condensed Matter》1988,73(3):391-416
Optimization theory deals with algorithms finding the lowest cost (energy) configuration in a minimal number of steps. When the cost function has many local minima, the deterministic algorithms become easily trapped in suboptimal solutions. The simulated annealing method tries to overcome this difficulty by introducting thermal noise in the problem. Here we explore the possibility of implementing search procedures analogous to the quantum tunneling effect. The suggested dynamics is a guided diffusion process of an interactingpopulation of configurations. Different dynamical aspects of the search process are formulated first in a simple one-dimensional tight-binding model with a hierarchical potential. The new algorithm is then applied to the Traveling Salesman Problem. It is demonstrated that the use of interacting, evolving populations of tours representing our wave packet leads to systematic improvements and possibly, to the optimal tour. In addition, the structure of the cost function landscape for a given instance becomes locally accessible. The performance of the algorithm and its implications for parallel computing and genetic programming are briefly discussed. 相似文献
909.
The retarding-potential and LEED methods are used for obtaining information about the structure and uniformity of alkali (K and CS) and alkali-coadsorbate (CO and O) layers on Ru(0001) and Ru
surfaces at 300 K. It was established that for alkali layers on the anisotropic Ru
surface and for mixed coadsorbate layer the shape of the retarding potential curves, used for the work function measurements, becomes anomalous which indicates coexistence of patches of different work function on the surface. LEED data on these patchy surfaces showed the formation of a variety of ordered structures depending on the coadsorbate coverages. On the basis of the existing theory a simple mathematical simulation was performed in an attempt to interpret the observed changes in the retarding potential curves. The possible changes of this curves, induced by the formation of patches with varying contribution to the total retarding potential signal and the advantage of the retarding field method for determination the uniformity of surface overlayers are discussed. 相似文献
910.
The reaction between thiocarbamate herbicides and 2,6-dichlorobenzoquinone-N-chloroimine or 2,6-dibromobenzoquinone-N-chloroimine is suitable for the detection of these herbicides on thin-layer plates with high sensitivity. The reactions were followed by infrared, nuclear magnetic resonance and mass spectrometry. We have established the formation of 2,6-dichlorobenzoquinone-S-alkyl sulphenylimines. In the case of the bromo-derivative, halogen exchange and substitution on the quinone ring took place simultaneously leading to the formation of mixed halogenated 2,6-dihalo- and, in addition, 2,3,6-trihalobenzoquinone-S-alkyl sulphenylimines. The final product of the detection reaction, i.e. 2,6-dichlorobenzoquinone-S-alkyl sulphenylimine was reacted with 2,6-dibromobenzoquinone-N-chloroimine where 2,6-dichloro-3-bromobenzoquinone-S-alkyl sulphenylimine formed as a consequence of the looser bromine-carbon linkage on the 2 and 6 positions of the quinone ring. 相似文献
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