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871.
872.
Aaron Bertram Georgios Daskalopoulos Richard Wentworth 《Journal of the American Mathematical Society》1996,9(2):529-571
Two compactifications of the space of holomorphic maps of fixed degree from a compact Riemann surface to a Grassmannian are studied. It is shown that the Uhlenbeck compactification has the structure of a projective variety and is dominated by the algebraic compactification coming from the Grothendieck Quot Scheme. The latter may be embedded into the moduli space of solutions to a generalized version of the vortex equations studied by Bradlow. This gives an effective way of computing certain intersection numbers (known as ``Gromov invariants') on the space of holomorphic maps into Grassmannians. We carry out these computations in the case where the Riemann surface has genus one.
873.
Summary. The one-dimensional discrete Poisson equation on a uniform grid with points produces a linear system of equations with a symmetric, positive-definite coefficient matrix. Hence, the conjugate
gradient method can be used, and standard analysis gives an upper bound of ) on the number of iterations required for convergence. This paper introduces a systematically defined set of solutions dependent
on a parameter , and for several values of , presents exact analytic expressions for the number of steps ) needed to achieve accuracy . The asymptotic behavior of these expressions has the form )} as and )} as . In particular, two choices of corresponding to nonsmooth solutions give , i.e., iteration counts independent of ; this is in contrast to the standard bounds. The standard asymptotic convergence behavior, , is seen for a relatively smooth solution. Numerical examples illustrate and supplement the analysis.
Received August 30, 1995 / Revised version received January 23, 1996 相似文献
874.
Mary E. Neubert Sandra S. Keast Julie M. Kim Kyle J. Miller Rachel M. Murray Aaron G. Norton Raj A. Shenoy Margaret E. Walsh Rolfe G. Petschek 《Liquid crystals》2004,31(2):175-184
A limited selection of ring modified diphenyldiacetylenes of the type where A=, Y=CnH2n+1, CF3, F, COMe, NH2, and NMe2, and A=, trans and cis with Y=F and trans with Y=C3H7, were synthesized. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These properties were generally poorer than those found in the parent benzene compounds. This was also true of some pyrimidine analogues reported earlier. Birefringence values also decreased as expected. 相似文献
875.
Yosef Cohen 《Natural Resource Modeling》1986,1(1):105-110
A discrete optimal control approach is used to show that the intensity of harvest of mallard populations in North America, at steady state, is sensitive to the strength of compensation between natural mortality and harvest mortality. Optimal harvest is less sensitive to changes in the natural mortality rate than to the interaction between natural and harvest mortalities. The management implications are: (1) if compensatory mortality operates, then more animals may be harvested without endangering the population, and (2) managers should pay particular attention to this mechanism in studying population dynamics. 相似文献
876.
Dori Gal Eli Sone R Cohen G Hodes J Libman A Shanzer H-W Schock David Cahen 《Journal of Chemical Sciences》1997,109(6):487-496
The electronic properties of semiconductor surfaces can be controlled by binding tailor-made ligands to them. Here we demonstrate
that deposition of a conducting phase on the treated surface enables control of the performance of the resulting device. We
describe the characteristics of the free surface of single crystals and of polycrystalline thin films of semiconductors that
serve as absorbers in thin film polycrystalline, heterojunction solar cells, and report first data for actual cell structures
obtained by chemical bath deposition of CdS as the window semiconductor. The trend of the characteristics observed by systematically
varying the ligands suggests changes in work function rather than in band bending at the free surface, and implies that changes
in band line-up, which appear to cause changes in band bending, rather than direct, ligand-induced band bending changes, dominate. 相似文献
877.
Shmuel Cohen Georgia Wollmann Lina Ben-Dor Yizhak Marcus 《Journal of Crystal Growth》2004,270(3-4):589-592
Single crystals of the congruently melting equimolar mixture of magnesium nitrate hexahydrate and nickel nitrate hexahydrate have been grown. The compound crystallizes in a structure foreign to both components, namely in the monoclinic cobalt nitrate hexahydrate structure. The cations are located at random on the cation sub-lattice of the latter crystalline structure. 相似文献
878.
879.
Claire Cohen 《The Journal of the Operational Research Society》1994,45(3):255-260
‘Magic’ is an area of creativity that is essential to the life and maintenance of an organization. This paper seeks to define ‘magic’, viewing it in the context of a voluntary organization – a Well Woman Centre in Calderdale. From the evidence of a case study, it is argued that ‘magic’ is particularly at risk when new procedures, or an expansion of procedures, are introduced. ‘Magic’ must be recognized and strategies formulated to preserve it; this is perceived to be commensurate with the aims of community OR. 相似文献
880.
Microwave-enhanced reaction rates for nanoparticle synthesis 总被引:3,自引:0,他引:3
Gerbec JA Magana D Washington A Strouse GF 《Journal of the American Chemical Society》2005,127(45):15791-15800
Microwave reactor methodologies are unique in their ability to be scaled-up without suffering thermal gradient effects, providing a potentially industrially important improvement in nanocrystal synthetic methodology over convective methods. Synthesis of high-quality, near monodispersity nanoscale InGaP, InP, and CdSe have been prepared via direct microwave heating of the molecular precursors rather than convective heating of the solvent. Microwave dielectric heating not only enhances the rate of formation, it also enhances the material quality and size distributions. The reaction rates are influenced by the microwave field and by additives. The final quality of the microwave-generated materials depends on the reactant choice, the applied power, the reaction time, and temperature. CdSe nanocrystals prepared in the presence of a strong microwave absorber exhibit sharp excitonic features and a QY of 68% for microwave-grown materials. InGaP and InP are rapidly formed at 280 degrees C in minutes, yielding clean reactions and monodisperse size distributions that require no size-selective precipitation and result in the highest out of batch quantum efficiency reported to date of 15% prior to chemical etching. The use of microwave (MW) methodology is readily scalable to larger reaction volumes, allows faster reaction times, removes the need for high-temperature injection, and suggests a specific microwave effect may be present in these reactions. 相似文献