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931.
In order to confirm the existence of regions I and II in aqueous solutions of butoxyethanol(BE), the concentration and temperature
dependences of enthalpies of mixing of aqueous BE solutions with some organic solvents were measured. It has been found that
the increments of apparent enthalpies of mixing per mole of water with respect to the mole fraction of BE change irregularly
at a certain concentration. This concentration nearly corresponds to the reported boundary between regions I and II. Although
similar behavior has also been observed in aqueous solutions of iso-butoxyethanol, aqueous solutions oftert-butoxyethanol have shown no anomalous behaviors.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
932.
Direct amination of aryl iodides and bromides with ammonia under 1 atm pressure has been effected using in situ‐generated hemilabile coordinated copper(I) species from copper(I) halides or copper metal in aqueous ethylene glycol, producing primary aromatic amines in good yields. Ammonia pressure and water were found to accelerate the copper‐mediated reaction while strong chelating ligands showed a suppression effect. A rationale for the copper‐mediated amination of aryl halides with ammonia is given based on a double‐face role of chelating effect. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
933.
Analyses of fish and other environmental samples (clams, macrophytes, sediments and waters) from areas upstream and downstream from two alkyllead manufactures beside the St Lawrence and St Clair Rivers, Ontario, show a clear indication of elevated alkyllead levels in samples near the industries. Most species of fish contained alkyllead compounds with tetraethyllead and triethyllead as the predominant forms. Most fish from the contaminated areas contained 50–75% of total lead as alkylleads. Carp, yellow perch and white sucker were generally the most contaminated species while pike, alewife and rock bass were the least contaminated. Average alkyllead levels varied from year to year but declined steadily after 1981. For example, the geometric mean of alkyllead compounds in carp from the St Lawrence River decreased from 4207 μg kg?1 in 1981 to 2000 μg kg?1 in 1982 and to 49 μg kg?1 in 1987, reflecting the reduction of alkylleads in the effluents and the closure of one of the manufactures in 1985. Alkyllead levels were consistently lower in muscle and carcass samples in comparison with whole fish containing fatty intestines. However, muscle levels were generally equal to carcass levels. The concentrations of alkyllead compounds were generally low in clams, macrophytes, sediments and waters except from the immediate vicinity of the manufactures' final effluent discharges. 相似文献
934.
A systematic study of the biomethylation of selenium and the determination of the methylated species indicates preliminarily that selenium is susceptible to natural biomethylation under certain environmental conditions. Detectable levels of methylated selenium species, including dimethyl selenide [(CH3)2Se], dimethyl diselenide [(CH3)2Se2] and dimethylselenone [(CH3)2SeO2] have been detected by gas chromatography – graphite furnace atomic absorption spectrophotometry (GC – GF AA) from a variety of environmental samples. Findings of naturally methylated selenium species from both soil samples and related air samples suggest that there may exist a localized cycle of selenium between ground soil and the ambient air. Factors that influence the sensitivity and accuracy for the determination of alkyl selenide compounds by GC – GF AA have also been investigated. Flashlike injection mode and addition of about 10% of hydrogen gas to the argon carrier gas provide for highly sensitive detection. Reproducible determination can be obtained with a precision of about 6% and the detection limits are 0.3 ng Se m?3. 相似文献
935.
Tsodikov M. V. Slivinskii E. V. Yushchenko V. V. Kitaev L. E. Kriventsov V. V. Kochubei D. I. Teleshev A. T. 《Russian Chemical Bulletin》2000,49(12):2003-2006
The data of temperature-programmed desorption of ammonia from the surface of oxide systems and IR spectroscopy were used to demonstrate that the strength of the surface acid sites in titanium oxides prepared by the alkoxo method and modified by aluminum decreases with respect to that in nonmodified titanium oxide. Modification of titanium oxide with P3+ ions from ethriol phosphite almost completely suppresses the acid properties. Modified oxides are able to chemisorb water. XANES data suggest that modification of titanium oxide with phosphorus ions increases the electron density on the titanium atoms and, correspondingly, the basicity of the materials. 相似文献
936.
Phase inversion refers to the phenomenon whereby a small change in operational flow conditions causes an oil-in-water dispersed flow pattern to suddenly switch to a water-in-oil flow pattern, and viceversa. This paper proposes an interpretation of phase inversion in terms of minimal dissipation rate. To this end, the dissipation rate is computed by a simple homogeneous model together with available correlations for effective viscosity in dispersed flows. It is shown that the data available in the literature can be reasonably interpreted as a manifestation of minimal dissipation rate. Furthermore, if the assumed effective viscosity correlations take into account pipe wettability, the minimal dissipation rate approach is capable to interpret also the so-called ambivalent range (hysteresis effect) and correlate the available data. 相似文献
937.
Markus M. Hoffmann Hanna S. Sobstyl Vincent A. Badali 《Magnetic resonance in chemistry : MRC》2009,47(7):593-600
A number of suppression pulse sequences including Excitation Sculpting and WATERGATE were incorporated into the standard Carr‐Purcell‐Meiboom‐Gill (CPMG) program for T2 measurement and experimentally evaluated. The chosen suppression schemes were of varying complexity encompassing pulse program elements, such as presaturation, gradients, and selective pulses, which are typically utilized for solvent suppression. The quality of the spectral data and the accuracy of T2 measurements of the investigated suppression schemes were evaluated using three aqueous samples with increasing proton content in the water solvent, i.e. by volume 100% D2O, 80/20% D2O/H2O, and 20/80% D2O/H2O. For signals removed from the water signal, the T2 values were generally very consistent between all pulse sequences tested. T2 measurements can be unreliable for signals too close to the water signal such that they are significantly suppressed as well. Their intensity may actually grow initially through cross relaxation that transfers magnetization back to the solute signal. In turn, this relaxation phenomenon can be exploited to improve the spectral quality of conventional solvent suppression schemes. In favorable cases, even signals that are completely masked by the water signal can be recovered by adding a carefully chosen number of spin echoes with optimized evolution time to conventional water suppression pulse programs, such as Excitation Sculpting or WATERGATE. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
938.
939.
940.
M. V. Buntina V. V. Ostapenko 《Computational Mathematics and Mathematical Physics》2008,48(12):2241-2253
For the shallow water equations in the first approximation (Saint-Venant equations), a TVD scheme is developed for shock-capturing computations of open channel flows with discontinuous waves. The scheme is based on a special nondivergence approximation of the total momentum equation that does not involve integrals related to the cross-section pressure force and the channel wall reaction. In standard divergence difference schemes, most of the CPU time is spent on the computation of these integrals. Test computations demonstrate that the discontinuity relations reproduced by the scheme are accurate enough for actual discontinuous wave propagation to be numerically simulated. All the qualitatively distinct solutions for a dam collapsing in a trapezoidal channel with a contraction in the tailwater area are constructed as an example. 相似文献