全文获取类型
收费全文 | 666502篇 |
免费 | 5781篇 |
国内免费 | 1516篇 |
专业分类
化学 | 327969篇 |
晶体学 | 9596篇 |
力学 | 35633篇 |
综合类 | 19篇 |
数学 | 95682篇 |
物理学 | 204900篇 |
出版年
2021年 | 6200篇 |
2020年 | 6719篇 |
2019年 | 7688篇 |
2018年 | 10508篇 |
2017年 | 10738篇 |
2016年 | 14663篇 |
2015年 | 7724篇 |
2014年 | 13314篇 |
2013年 | 29118篇 |
2012年 | 22868篇 |
2011年 | 27062篇 |
2010年 | 20719篇 |
2009年 | 20637篇 |
2008年 | 25726篇 |
2007年 | 25543篇 |
2006年 | 23318篇 |
2005年 | 20744篇 |
2004年 | 19378篇 |
2003年 | 17583篇 |
2002年 | 17541篇 |
2001年 | 18235篇 |
2000年 | 14210篇 |
1999年 | 10997篇 |
1998年 | 9760篇 |
1997年 | 9531篇 |
1996年 | 8895篇 |
1995年 | 7930篇 |
1994年 | 8020篇 |
1993年 | 7806篇 |
1992年 | 8107篇 |
1991年 | 8656篇 |
1990年 | 8371篇 |
1989年 | 8266篇 |
1988年 | 7972篇 |
1987年 | 7820篇 |
1986年 | 7402篇 |
1985年 | 9310篇 |
1984年 | 9833篇 |
1983年 | 8293篇 |
1982年 | 8645篇 |
1981年 | 8088篇 |
1980年 | 7624篇 |
1979年 | 8382篇 |
1978年 | 8585篇 |
1977年 | 8627篇 |
1976年 | 8626篇 |
1975年 | 8231篇 |
1974年 | 8046篇 |
1973年 | 8272篇 |
1972年 | 6348篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
A tomographic reconstruction method based on Monte Carlo random searching guided by the information contained in the projections
of radiographed objects is presented. In order to solve the optimization problem, a multiscale algorithm is proposed to reduce
computation. The reconstruction is performed in a coarse-to-fine multigrid scale that initializes each resolution level with
the reconstruction of the previous coarser level, which substantially improves the performance. The method was applied to
a real case reconstructing the internal structure of a small metallic object with internal components, showing excellent results. 相似文献
994.
Ya. I. Kurys’ N. S. Netyaga V. G. Koshechko V. D. Pokhodenko 《Theoretical and Experimental Chemistry》2007,43(5):334-342
A guest-host nanocomposite based on electroconducting polyaniline doped with 12-phosphotungstic acid and V2O5 as well as its bifunctional analog containing not more than 5 mass% nanosized platinum were obtained. A study was carried
out on the structure of these nanocomposites, their redox characteristics, and electrocatalytic activity in the reduction
of oxygen. These nanocomposites were found to display catalytic properties in the electrochemical reduction of oxygen, while
the presence of even a slight amount of nanosized platinum in the bifunctional composite leads to a significant increase in
its electrocatalytic activity.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 307–314, September–October, 2007. 相似文献
995.
The influence of the well width fluctuations on the dependence of the binding energy of excitonic complexes in quantum wells is studied by using the path-integral Monte-Carlo technique. The results are compared with available experimental data and a good agreement is found.Postdoctoral researcher of FWO-Vlaanderen 相似文献
996.
V. I. Sakharov 《Fluid Dynamics》2007,42(6):1007-1016
The results of numerical simulation are presented for thermally and chemically nonequilibrium air plasma flows in a plasmatron discharge channel and underexpanded dissociated and partially ionized air jets flowing past a cylindrical model with a blunt leading edge and cooled copper surface under the experimental conditions realized in a VGU-4 100 kW induction plasmatron (Institute for Problems in Mechanics of the Russian Academy of Sciences) (see, for example, [1, 2]). The nonequilibrium excitation of the vibrational degrees of freedom of the molecules in the modal approximation and the difference between the electron and translational heavy-particle temperatures are taken into account in the calculations. The calculated data on the heat transfer and pressure at the stagnation point are compared with the results obtained within the framework of the thermally equilibrium model. Comparison with the experimental data obtained in the Institute for Problem in Mechanics of the Russian Academy of Sciences (Laboratory for interaction between plasma and radiation and materials) and kindly provided for comparison purposes gives satisfactory agreement. 相似文献
997.
Electron spin resonance (ESR) study was done on calcite encrustation on Fili neotectonic fault surface, Greece. Normally such
calcite encrustations on fault surfaces are not observed. Significantly, the ESR study has detected the presence of nitrate
NO32− radical in this calcite encrustation, havingg
⊥=2.0063±0.0001 and hyperfine coupling constantA
⊥=3.44 mT, the second such detection of nitrate NO32− radical following a sample from Scott Glacier, Antarctica. From isochronal thermal annealing measurement the NO32− radical was found to be quite stable, only fully annealed at 475°C. This study also shows that the ESR, as a tool, can be
suitably applied to date the age of formation of the calcite encrustation with SO3− as an ESR dating signal by additive γ-ray irradiation. A preliminary estimation indicates the age of formation of calcite
precipitation at Fili fault, Greece to be about 5600 years. 相似文献
998.
E. Rodriguez E. Jimenez G.J. Jacob A.A.R. Neves C.L. Cesar L.C. Barbosa 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):361
Multilayer PbTe quantum dots (QDs) and SiO2 were grown by pulsed laser deposition (PLD) and Plasma enhanced chemical vapor deposition (PECVD) techniques. The crystalline structure, QD size and size dispersion were observed by high-resolution transmission electron microscopy (HRTEM) measurements. This technique allows one to grow PbTe QDs as small as 1.8 nm diameter and 0.6 nm size dispersion. The whole structure can be used in a Fabry–Perot cavity for an optical device operating at the mid-infrared region. 相似文献
999.
A switching of the S-type in the 20–200 μm thick polycrystalline n-CdTe:In layers with resistance of 103–106 Ω·cm is studied. The electric instability in the layers is found to be due to the electron-thermal breakdown mechanism. The
dependence of the switching threshold parameters on the intensity of exposure can be used for fabrication of infrared-radiation
controlled electric switches on the basis of n-CdTe:In layers.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 28–30, June, 2005. 相似文献
1000.
S. V. Semikolenov K. A. Dubkov E. V. Starokon' D. E. Babushkin G. I. Panov 《Russian Chemical Bulletin》2005,54(4):948-956
The kinetics and mechanism of noncatalytic liquid-phase oxidation of but-1-ene and but-2-ene with nitrous oxide in a benzene
solution in the temperature range from 180 to 240°C were studied. Oxidation proceeds via the 1,3-dipolar cycloaddition mechanism to form carbonyl compounds. Both of these reactions occur with close rates and activation
energies and have the first orders with respect to the alkene and N2O. A considerable fraction (39%) of but-1-ene involved in oxidation undergoes cleavage at the double bond yielding propanal
and an equivalent amount of methylene, the latter producing ethylcyclopropane and cycloheptatriene. The oxidation of but-2-ene
proceeds with a minimum bond cleavage and affords methyl ethyl ketone with 84% selectivity. Regularities of the oxidation
of terminal and internal alkenes C2—C8 with nitrous oxide were analyzed using the previously published data.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 925–933, April, 2005. 相似文献