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991.
Jacek G. So?nicki 《Tetrahedron letters》2005,46(25):4295-4298
A new, highly efficient allylation reagent—lithium allyldibutylmagnesate (allylBu2MgLi)—was obtained by mixing allyl-magnesium chloride (1 equiv) and n-BuLi (2 equiv). N-Lithiated and N-methyl substituted 1H-pyridine-2-thiones and -ones were successfully and regioselectively allylated by treatment with allylBu2MgLi yielding 6-allyl-3,6-dihydro-1H-pyridine-2-(thio)ones and 4-allyl-3,4-di-hydro-1H-pyridine-2-(thio)ones. The latter were formed by a 3,3-sigmatropic Cope rearrangement of the former. 相似文献
992.
Agnieszka Sawicka Iwona Anusiewicz Piotr Skurski Jack Simons 《International journal of quantum chemistry》2003,92(4):367-375
The possibility of electron binding to five molecules (i.e., F3N → BH3, H2FN → BH3, HF2N → BH3, H3N → BH2F, H3N → BHF2) was studied at the coupled cluster level of theory with single, double, and noniterative triple excitations and compared to earlier results for H3N → BH3 and H3N → BF3. All these neutral complexes involve dative bonds that are responsible for significant polarization of these species that generates large dipole moments. As a consequence, all of the neutral systems studied, except F3N → BH3, support electronically stable dipole‐bound anionic states whose calculated vertical electron detachment energies are 648 cm?1 ([H2FN → BH3]?), 234 cm?1 ([HF2N → BH3]?), 1207 cm?1 ([H3N → BH2F]?), and 1484 cm?1 ([H3N → BHF2]?). In addition, we present numerical results for a model designed to mimic charge–transfer (CT) and show that the electron binding energy correlates with the magnitude of the charge flow in the CT complex. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
993.
Numerous mutations and polymorphisms in human genes remain to be identified using reliable methods. Of the available mutation scanning methods those dependent on structural change-induced mobility shifts are highly effective. Their efficiency is, however, DNA length-sensitive and the reasons for that are poorly understood. In this study, we explain why scanning genes for mutations is less effective in longer DNA fragments, and reveal the factors which are behind this effect. We have performed a systematic analysis of the same sequence variants of exon 11 of the BRCA1 gene in DNA fragments of three different lengths using the combined single-strand conformation polymorphism (SSCP) and heteroduplex analysis (DA) by capillary electrophoresis (CE). There are two major structural factors responsible for the reduced mutation detection rate in long amplicons. The first is increased contribution from other secondary structure modules and domains in longer fragments, which mask the structural change induced by the mutation. The second is higher frequency of single-nucleotide polymorphisms (SNPs) including common polymorphisms in longer fragments. This makes it necessary to distinguish the structural effect of the mutation from that of each polymorphic variant, which is often difficult to achieve. Taking these factors into account, an efficient scanning of genes for sequence variants by conformation-sensitive methods may be performed. 相似文献
994.
A capillary electrophoretic (CE) method has been developed for the determination of ivermectin (CAS 70288-86-7), a new generation drug with antiparasitic activity, in pig and horse plasma. The method was statistically validated for its linearity, accuracy, precision and selectivity. The linear range was from 1 to 30 ng mL(-1) with correlation coefficients greater than 0.999. The limit of detection was 0.3 ng mL(-1), while the quantitative limit was 1 ng mL(-1), using a 0.5 mL sample size. The validated procedure was used to determination of pharmacokinetic parameters of ivermectin after ingestion of 0.1 mg for pigs and 0.2 mg dose per kg body weight for horses, respectively. Studies were performed on a group of eight pigs and six horses. There were no significant differences between pigs and horses in any of the estimated pharmacokinetic parameters. 相似文献
995.
Chmielewski PJ 《Organic letters》2005,7(9):1789-1792
[reaction: see text] A simple method of modification of N-confused porphyrin is provided by reactions of 5,10,15,20-tetraaryl-2-aza-21-carbaporphyrin with alpha,alpha'-dibromoxylene. The N-bromoxylene-substituted monomer formed in a first step of alkylation can be converted to the products with the extended structure on the N-confused pyrrole for which formation of organometallic silver(III) complexes has been shown. 相似文献
996.
The partition model of retention is developed for reversed phase liquid chromatography with multicomponent mobile phases. Simple equations for the retention and selectivity in ternary mobile phases are derived. For the systems in which the ratio of volume fractions of organic modifiers remains fixed, new linear dependences for retention factor and selectivity are proposed. These equations are successfully used to describe experimental data found in the literature. An influence of the nature of organic solvents and proportion in which they are mixed on retention and selectivity is discussed. 相似文献
997.
Piotr Petelenz 《Chemical physics letters》1995,240(5-6):605-609
Based on a simple dimer model of vibronic coupling it is demonstrated that, contrary to the conventional notion, the Davydov splitting of the fundamental vibronic transition in non-totally symmetric vibrations, induced by the Herzberg—Teller mechanism, does not need to be very small. 相似文献
998.
[reaction: see text]. We herein report the development of one-pot procedures for the conversion of allyl aryl ethers to 2-methylbenzofurans (via sequential Claisen rearrangement and oxidative cyclization) and for the conversion of aryl homoallyl ethers to chromenes (via direct oxidative cyclization). It is likely that both reactions proceed via a common Pd-catalyzed pathway involving olefin activation, nucleophilic attack, and beta-hydride elimination. 相似文献
999.
A point-charge force field for molecular mechanics simulations of proteins based on condensed-phase quantum mechanical calculations 总被引:2,自引:0,他引:2
Duan Y Wu C Chowdhury S Lee MC Xiong G Zhang W Yang R Cieplak P Luo R Lee T Caldwell J Wang J Kollman P 《Journal of computational chemistry》2003,24(16):1999-2012
Molecular mechanics models have been applied extensively to study the dynamics of proteins and nucleic acids. Here we report the development of a third-generation point-charge all-atom force field for proteins. Following the earlier approach of Cornell et al., the charge set was obtained by fitting to the electrostatic potentials of dipeptides calculated using B3LYP/cc-pVTZ//HF/6-31G** quantum mechanical methods. The main-chain torsion parameters were obtained by fitting to the energy profiles of Ace-Ala-Nme and Ace-Gly-Nme di-peptides calculated using MP2/cc-pVTZ//HF/6-31G** quantum mechanical methods. All other parameters were taken from the existing AMBER data base. The major departure from previous force fields is that all quantum mechanical calculations were done in the condensed phase with continuum solvent models and an effective dielectric constant of epsilon = 4. We anticipate that this force field parameter set will address certain critical short comings of previous force fields in condensed-phase simulations of proteins. Initial tests on peptides demonstrated a high-degree of similarity between the calculated and the statistically measured Ramanchandran maps for both Ace-Gly-Nme and Ace-Ala-Nme di-peptides. Some highlights of our results include (1) well-preserved balance between the extended and helical region distributions, and (2) favorable type-II poly-proline helical region in agreement with recent experiments. Backward compatibility between the new and Cornell et al. charge sets, as judged by overall agreement between dipole moments, allows a smooth transition to the new force field in the area of ligand-binding calculations. Test simulations on a large set of proteins are also discussed. 相似文献
1000.
Zbigniew Gregorowicz Ryszard Baranowski Jerzy Ciba und Piotr Górka 《Fresenius' Journal of Analytical Chemistry》1966,217(1):18-22
Zusammenfassung Auf Grund der quantitativen Fällung von Sebacinsäure mit Blei(II)ionen wurden die direkte gravimetrische Bestimmung sowie Methoden zur indirekten Bestimmung der Sebacinsäure entwickelt. Je nach dem Gehalt der Probe werden je eine polarographische in Ammoniumacetatlösung und eine spektralphotometrische Methode nach Dithizonextraktion empfohlen.
Summary The quantitative precipitation of sebacic acid with lead(II) ions has been employed for a gravimetric method of determination and also for an indirect polarographic (in ammonium acetate solution) and spectrophotometric one (using dithizone extraction). Concentration ranges are 20–200 mg, 2–15 mg, and 0,5 to 2 mg, respectively.相似文献