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81.
82.
Two ways to predict pVT behavior of hard-dumbbell mixtures in the fluid region are proposed. These are adaptations of the hard convex body equation devised by Boublik and an extension of the first Barker-Henderson perturbation theory. Calculated compressibility factors show good agreement with the ideal mixing assumption and yield a useful equation of state. 相似文献
83.
The first solid-phase methodology for the preparation of pyrrolo[3,2-d]pyrimidines is presented. Merrifield resin bearing a cysteamine "traceless" linker was treated with 4-oxo-N-(PhF)proline benzyl ester (10; PhF = 9-(9-phenylfluorenyl)) to provide resin-bound aminopyrrole 20, which was treated with ethyl, phenyl, 4-phenoxyphenyl, and 2,4-dimethoxyphenyl isocyanates to furnish resin-bound ureidopyrroles 21a-d. Resin-bound pyrrolo[3,2-d]pyrimidines 22a-d were then obtained by acylation of 21 using trichloroacetyl chloride in dioxane followed by treatment with Cs2CO3 in DMF. Cleavage of pyrrolo[3,2-d]pyrimidines 22a-d from the resin was achieved in two steps, by oxidation of the sulfur to the sulfone followed by beta-elimination in the presence of t-BuONa. Four pyrrolo[3,2-d]pyrimidines, 24a-d, with different alkyl and aryl substituents at the N3 pyrimidine nitrogen, were thus obtained in overall yields of 42-50% and purities of 90-100%. 相似文献
84.
Krystyna Bogdanowicz-Szwed Regina Gil 《Monatshefte für Chemie / Chemical Monthly》2004,35(12):1415-1425
A convenient method is described for the synthesis of functionalized spiro[cycloalkanono-2,3-thiophenes] by treatment of cyclic 3-oxoacid thioanilides with -nitrostyrenes. Reaction of the obtained products with acetic anhydride yielded the corresponding oxime acetates. 相似文献
85.
Nuclear Overhauser Effect (NOE) methods in NMR are an important tool for 3D structural analysis of small molecules. Quantitative NOE methods conventionally rely on reference distances, known distances that have to be spectrally separated and are not always available. Here we present a new method for evaluation and 3D structure selection that does not require a reference distance, instead utilizing structures optimized by molecular mechanics, enabling NOE evaluation even on molecules without suitable reference groups.A quantitative Nuclear Overhauser Effect (NOE) analysis approach that avoids the use of and internal reference distance to perform molecular configuration selection. 相似文献
86.
Mauricio Alcolea Palafox Nerea Iza Manuel Gil Jos Luís Núez 《International journal of quantum chemistry》2002,89(1):25-47
A quantum chemical study of several complex monocyclic 4‐benzoyl‐4‐phenyl‐β‐lactam derivatives was carried out using cyclobutane, azetidine, 2‐azetidinone, 1‐methyl‐2‐azetidinone, and 3‐methyl‐2‐azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the β‐lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform–infrared (FT‐IR) spectra of the β‐lactam monocyclic derivatives were recorded in CCl4, C6H6, and CHCl3 solutions. The normal vibrations of the β‐lactam ring in the model compounds were characterized and used in the analysis of the β‐ring of more complex derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
87.
Ashraf Ghanem Author Vitae 《Tetrahedron》2007,63(8):1721-1754
Over the last few years, there has been a dramatic increase in the number of publications in the field of lipase-catalyzed reactions performed in common organic solvents, ionic liquids or even non-conventional solvents. A fairly large percentage of these publications have emerged from organic chemists who have recognized the potential of biocatalysis as a viable and popular technique in organic synthesis. Considerable research has shown that reactions catalyzed by enzymes are more selective and efficiently performed than many of their analogues in the organic chemistry laboratory. This review article focuses on some of the recent developments in the rapidly growing field of lipase-catalyzed asymmetric access to enantiomerically pure/enriched compounds. The literature search is dated back to the last five years and covers some comprehensive examples. 相似文献
88.
Strong pulse sequences can be used to control the position and width of the molecular wave packet. In this paper we propose a new scheme to maximally compress the wave packet in a quasistatic way by freezing it at a peculiar adiabatic potential shaped by two laser pulses. The dynamic principles of the scheme and the characteristic effect of the different control parameters are presented and analyzed. We use two different molecular models, electronic potentials modeled by harmonic oscillators, with the same force constants, and the Na(2) dimer, to show the typical yield that can be obtained in compressing the initial (minimum width) molecular wave function. 相似文献
89.
Ignacio Delso 《Tetrahedron letters》2007,48(23):4101-4104
1H-15N HMBC has been evaluated as an efficient and high-speed method to determine 15N chemical shifts for nitrones, which can be used to identify aromatic nitrones and to extract structural information by comparison with reference data. Substituent effects have been measured on C and N aryl groups separately, showing up the influence of electronic effects on C-aryl groups rather than N-aryl groups on the 15N chemical shifts. Steric effects are remarkable in the case of C-aryl-N-alkyl nitrones. Depending on N or C substitution, chemical shift changes in such an additive way that it is possible to predict chemical shifts for unknown nitrones. 相似文献
90.
Basis sets ranging in size from (16, 10, 7) to (20, 14, 11) have been derived for the atoms Y–Cd. Separate sets represent the energy optimized wave functions for each of the s2dn, s1dn+1, and s0dn+2 configurations. The energies from the largest sets are within 3 mhartrees of the values obtained in numerical Hartree–Fock calculations. Reasonable Hartree–Fock s2dn– s1dn+1 and s2dn– s0dn+2 excitation energies may be obtained either using the largest basis sets, or using d-orbitals optimized for the s0dn+2 configurations. The basis sets are slightly unbalanced in favor of the s-functions and in disfavor of the d-functions, but various alternative basis sets may be derived by combining parts of the five parent sets. The convergence of radial expectation values is discussed. 相似文献