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991.
Geometries, relative energies, and stabilities of endo- and exohedral complexes, X@Si20H20 and XSi20H20, (X = H+, H, N, P, C?, and Si?) are calculated at B3LYP/6-31G* level. The energy minimum structure of Si20H21 + shows that the proton cannot be positioned in the Si20H20 centre, but prefers attach to Si20H20 exohedrally with C2v symmetry. Most investigated Ih endohedral complexes X@Si20H20 (X = H, N, P, C?, and Si?) are local minima, except for 2N@Si20H20, which is a high-order saddle point. Inclusions energies of the endohedral complexes are calculated, and it reveals that energy penalties caused by encapsulation are rather small. Exohedral complexes XSi20H20 (X = H, N, P, C?, and Si?) have C2v or Cs local minima, and most of them are more stable than their endohedral isomers with the exception of C2v 4PSi20H20 and 4Si?Si20H20. 相似文献
992.
993.
Hong Kyung Choi Jeong Ho Chang Il Hwan Ko Bong Yong Jeong Jung Bae Kim 《Journal of solid state chemistry》2011,184(4):805-2221
This work describes the development of highly efficient human DNA separation with functionalized mesoporous silica (FMS) materials. To demonstrate the electrostatic interaction effect between the target DNA molecules and FMS, three aminofunctionality types comprised of a mono-, a di-, and a tri-amine functional group were introduced on the inner surfaces of mesoporous silica particles. Systematic characterization of the synthesized materials was achieved by solid-state 29Si and 13C-NMR techniques, BET, FT-IR, and XPS. The DNA separation efficiency was explored via the function of the amino-group number, the amount used, and the added NaCl concentration. The DNA adsorption yields were high in terms of the use of triaminofunctionalized FMS at the 10 ng/L level, and the DNA desorption efficiency showed the optimum level at over 3.0 M NaCl concentration. The use of FMS in a DNA separation process provides numerous advantages over the conventional silica-based process. 相似文献
994.
Hyunpyo Lee Jun Beum Park Ji Young Chang 《Journal of polymer science. Part A, Polymer chemistry》2011,49(13):2859-2865
Core‐shell structured nanoparticles of poly(ethylene glycol) (PEG)/polypeptide/poly(D ,L ‐lactide) (PLA) copolymers were prepared and their properties were investigated. The copolymers had a poly(L ‐serine) or poly(L ‐phenylalanine) block as a linker between a hydrophilic PEG and a hydrophobic PLA unit. They formed core‐shell structured nanoparticles, where the polypeptide block resided at the interface between a hydrophilic PEG shell and a hydrophobic PLA core. In the synthesis, poly(ethylene glycol)‐b‐poly(L ‐serine) (PEG‐PSER) was prepared by ring opening polymerization of N‐carboxyanhydride of O‐(tert‐butyl)‐L ‐serine and subsequent removal of tert‐butyl groups. Poly(ethylene glycol)‐b‐poly(L ‐phenylalanine) (PEG‐PPA) was obtained by ring opening polymerization of N‐carboxyanhydride of L ‐phenylalanine. Methoxy‐poly(ethylene glycol)‐amine with a MW of 5000 was used as an initiator for both polymerizations. The polymerization of D ,L ‐lactide by initiation with PEG‐PSER and PEG‐PPA produced a comb‐like copolymer, poly(ethylene glycol)‐b‐[poly(L ‐serine)‐g‐poly(D ,L ‐lactide)] (PEG‐PSER‐PLA) and a linear copolymer, poly(ethylene glycol)‐b‐poly(L ‐phenylalanine)‐b‐poly(D ,L ‐lactide) (PEG‐PPA‐PLA), respectively. The nanoparticles obtained from PEG‐PPA‐PLA showed a negative zeta potential value of ?16.6 mV, while those of PEG‐PSER‐PLA exhibited a positive value of about 19.3 mV. In pH 7.0 phosphate buffer solution at 36 °C, the nanoparticles of PEG/polypeptide/PLA copolymers showed much better stability than those of a linear PEG‐PLA copolymer having a comparable molecular weight. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
995.
996.
997.
Keith D. Barnes Ping Chen Yingyan Chang Robert M. Lewis Christopher M. Manley Nicholas J. Mayhew 《合成通讯》2013,43(1):67-72
A convergent synthesis of indoprofen via a Buchwald coupling approach is reported. Using this methodology, indoprofen and a set of analogs of indoprofen were readily prepared. 相似文献
998.
999.
Sin-Chung Chang Yuhui Wu Xiao-Yen Wang 《International Journal of Computational Fluid Dynamics》2013,27(5):359-380
A local time-stepping procedure for the space-time conservation element and solution element (CESE) method has been developed. This new procedure allows for variation of time-step size in both space and time, and can also be extended to become multi-dimensional solvers with structured/unstructured spatial grids. Moreover, it differs substantially in concept and methodology from the existing approaches. By taking full advantage of key concepts of the CESE method, in a simple and efficient manner it can enforce flux conservation across an interface separating grid zones of different time-step sizes. In particular, no correction pass is needed. Numerical experiments show that, for a variety of flow problems involving moving shock and flame discontinuities, accurate and robust numerical simulations can be achieved even with a reduction in time-step size on the order of 10 or higher for grids across a single interface. 相似文献
1000.
In this note, we revisit the single-index model with heteroscedastic error, and recommend an estimating equation method in terms of transferring restricted least squares to unrestricted least squares: the estimator of the index parameter is asymptotically more efficient than existing estimators in the literature in the sense that it is of a smaller limiting variance. 相似文献