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181.
Sebastian Schlund Eline M. Basílio Janke Klaus Weisz Bernd Engels 《Journal of computational chemistry》2010,31(4):665-670
This study investigates how the various components (method, basis set, and treatment of solvent effects) of a theoretical approach influence the relative energies between keto and enol forms of acetylacetone, which is an important model system to study the solvent effects on chemical equilibria from experiment and theory. The computations show that the most popular density functional theory (DFT) approaches, such as B3LYP overestimate the stability of the enol form with respect to the keto form by ~10 kJ mol?1, whereas the very promising SCS‐MP2 approach is underestimating it. MP2 calculations indicate that in particular the basis set size is crucial. The Dunning Huzinaga double ζ basis (D95z(d,p)) used in previous studies overestimates the stability of the keto form considerably as does the popular split‐valence plus polarization (SVP) basis. Bulk properties of the solvent included by continuum approaches strongly stabilize the keto form, but they are not sufficient to reproduce the reversal in stabilities measured by low‐temperature nuclear magnetic resonance experiments in freonic solvents. Enthalpic and entropic effects further stabilize the keto form, however, the reversal is only obtained if also molecular effects are taken into account. Such molecular effects seem to influence only the energy difference between the keto and the enol forms. Trends arising due to variation in the dielectric constant of the solvent result from bulk properties of the solvent, i.e., are already nicely described by continuum approaches. As such this study delivers a deep insight into the abilities of various approaches to describe solvent effects on chemical equilibria. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
182.
Steven J. Shirbin Steven C. Zammit Sebastian M. Marcuccio Spencer J. Williams 《Tetrahedron letters》2010,51(22):2971-1759
Aryl imidazylates are effective electrophilic partners in copper-free palladium-catalyzed Hiyama and Sonogashira cross-coupling reactions. The Sonogashira cross-coupling of estron-3-yl imidazylate afforded the corresponding phenylacetylene derivative in excellent yield. 相似文献
183.
184.
Hoeb M Auernhammer M Schoell SJ Brandt MS Garrido JA Stutzmann M Sharp ID 《Langmuir : the ACS journal of surfaces and colloids》2010,26(24):18862-18867
We present an approach for the thermally activated formation of alkene-derived self-assembled monolayers on oxygen-terminated single and polycrystalline diamond surfaces. Chemical modification of the oxygen and hydrogen plasma-treated samples was achieved by heating in 1-octadecene. The resulting layers were characterized using X-ray photoelectron spectroscopy, thermal desorption spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and water contact angle measurements. This investigation reveals that alkenes selectively attach to the oxygen-terminated sites via covalent C-O-C bonds. The hydrophilic oxygen-terminated diamond is rendered strongly hydrophobic following this reaction. The nature of the process limits the organic layer growth to a single monolayer, and FTIR measurements reveal that such monolayers are dense and well ordered. In contrast, hydrogen-terminated diamond sites remain unaffected by this process. This method is thus complementary to the UV-initiated reaction of alkenes with diamond, which exhibits the opposite reactivity contrast. Thermal alkylation increases the range of available diamond functionalization strategies and provides a means of straightforwardly forming single organic layers in order to engineer the surface properties of diamond. 相似文献
185.
C. Peter Sebastian 《Journal of solid state chemistry》2010,183(4):878-882
The compound CeAu0.28Ge1.72 crystallizes in the ThSi2 structure type in the tetragonal space group I41/amd with lattice parameters a=b=4.2415(6) Å c=14.640(3) Å. CeAu0.28Ge1.72 is a polar intermetallic compound having a three-dimensional Ge/Au polyanion sub-network filled with Ce atoms. The magnetic susceptibility data show Curie-Weiss law behavior above 50 K. The compound orders ferromagnetically at ∼8 K with estimated magnetic moment of 2.48 μB/Ce. The ferromagnetic ordering is confirmed by the heat capacity data which show a rise at ∼8 K. The electronic specific heat coefficient (γ) value obtained from the paramagnetic temperature range 15-25 K is∼124(5) mJ/ mol K2. The entropy change due to the ferromagnetic transition is ∼4.2 J/mol K which is appreciably reduced compared to the value of R ln(2) expected for a crystal-field-split doublet ground state and/or Kondo exchange interactions. 相似文献
186.
Ariane Wohlfarth Wolfgang Weinmann Sebastian Dresen 《Analytical and bioanalytical chemistry》2010,396(7):2403-2414
Since the late 1990s and early 2000s, derivatives of well-known designer drugs as well as new psychoactive compounds have
been sold on the illicit drug market and have led to intoxications and fatalities. The LC-MS/MS screening method presented
covers 31 new designer drugs as well as cathinone, methcathinone, phencyclidine, and ketamine which were included to complete
the screening spectrum. All but the last two are modified molecular structures of amphetamine, tryptamine, or piperazine.
Among the amphetamine derivatives are cathinone, methcathinone, 3,4-DMA, 2,5-DMA, DOB, DOET, DOM, ethylamphetamine, MDDMA,
4-MTA, PMA, PMMA, 3,4,5-TMA, TMA-6 and members of the 2C group: 2C-B, 2C-D, 2C-H, 2C-I, 2C-P, 2C-T-2, 2C-T-4, and 2C-T-7.
AMT, DPT, DiPT, MiPT, DMT, and 5MeO-DMT are contained in the tryptamine group, BZP, MDBP, TFMPP, mCPP, and MeOPP in the piperazine
group. Using an Applied Biosystems LC-MS/MS API 365 TurboIonSpray it is possible to identify all 35 substances. After addition
of internal standards and mixed-mode solid-phase extraction the analytes are separated using a Synergi Polar RP column and
gradient elution with 1 mM ammonium formate and methanol/0.1% formic acid as mobile phases A and B. Data acquisition is performed
in MRM mode with positive electro spray ionization. The assay is selective for all tested substances. Limits of detection
were determined by analyzing S/N-ratios and are between 1.0 and 5.0 ng/mL. Matrix effects lie between 65% and 118%, extraction efficiencies range from 72%
to 90%. 相似文献
187.
Humberto Palza Sebastian Gutirrez Katherine Delgado Oriana Salazar Victor Fuenzalida Jonathan I. Avila Guillermo Figueroa Raúl Quijada 《Macromolecular rapid communications》2010,31(6):563-567
A set of poly(propylene) composites containing different amounts of copper nanoparticles (CNP) were prepared by the melt mixed method and their antimicrobial behavior was quantitatively studied. The time needed to reduce the bacteria to 50% dropped to half with only 1 v/v % of CNP, compared to the polymer without CNP. After 4 h, this composite killed more than 99.9% of the bacteria. The biocide kinetics can be controlled by the nanofiller content; composites with CNP concentrations higher than 10 v/v % eliminated 99% of the bacteria in less than 2 h. X‐ray photoelectron spectroscopy did not detect CNP at the surface, therefore the biocide behavior was attributed to copper in the bulk of the composite.
188.
Jannis W. Ochsmann Sebastian Lenz Sebastian G. J. Emmerling Ralf S. Kappes Sebastian K. Nett Maria C. Lechmann Stephan V. Roth Jochen S. Gutmann 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):1569-1573
Thin films of PS-b-PEO block copolymers were utilized as structured reservoirs for localized nanoscale precipitation reactions. By consecutively immersing the film into solutions of thioacetamide and cadmium chloride, we were able to obtain a monolayer of cadmium sulfide nanostructures on top of the block copolymer film. AFM and grazing incidence small angle X-ray scattering revealed spherical nanostructures (d = 15 nm) corresponding to the dimensions given by the block copolymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1569–1573, 2010 相似文献
189.