全文获取类型
收费全文 | 378727篇 |
免费 | 4800篇 |
国内免费 | 1122篇 |
专业分类
电工技术 | 6590篇 |
综合类 | 280篇 |
化学工业 | 56659篇 |
金属工艺 | 17048篇 |
机械仪表 | 12106篇 |
建筑科学 | 8362篇 |
矿业工程 | 3157篇 |
能源动力 | 9262篇 |
轻工业 | 28145篇 |
水利工程 | 4807篇 |
石油天然气 | 10592篇 |
武器工业 | 28篇 |
无线电 | 41697篇 |
一般工业技术 | 78804篇 |
冶金工业 | 68089篇 |
原子能技术 | 10354篇 |
自动化技术 | 28669篇 |
出版年
2021年 | 3396篇 |
2019年 | 3309篇 |
2018年 | 5755篇 |
2017年 | 5870篇 |
2016年 | 6250篇 |
2015年 | 3747篇 |
2014年 | 6289篇 |
2013年 | 16601篇 |
2012年 | 9932篇 |
2011年 | 13197篇 |
2010年 | 10630篇 |
2009年 | 11980篇 |
2008年 | 12181篇 |
2007年 | 12177篇 |
2006年 | 10408篇 |
2005年 | 9664篇 |
2004年 | 8977篇 |
2003年 | 8829篇 |
2002年 | 8374篇 |
2001年 | 8517篇 |
2000年 | 8186篇 |
1999年 | 8362篇 |
1998年 | 20579篇 |
1997年 | 14520篇 |
1996年 | 11339篇 |
1995年 | 8371篇 |
1994年 | 7483篇 |
1993年 | 7493篇 |
1992年 | 5815篇 |
1991年 | 5679篇 |
1990年 | 5371篇 |
1989年 | 5392篇 |
1988年 | 5260篇 |
1987年 | 4575篇 |
1986年 | 4544篇 |
1985年 | 5200篇 |
1984年 | 4853篇 |
1983年 | 4552篇 |
1982年 | 4091篇 |
1981年 | 4166篇 |
1980年 | 4079篇 |
1979年 | 4155篇 |
1978年 | 4142篇 |
1977年 | 4529篇 |
1976年 | 5691篇 |
1975年 | 3698篇 |
1974年 | 3527篇 |
1973年 | 3635篇 |
1972年 | 3113篇 |
1971年 | 2876篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
S. Zh. Davrenbekov E. S. Mustafin B. K. Kasenov S. T. Edil'baeva Sh. B. Kasenova E. K. Zhumadilov Zh. I. Sagintaeva 《Inorganic Materials》2004,40(9):976-978
NdMCr2O5 (M = Na, K, Cs) and NdMgCr2O5.5 are prepared by solid-state reactions between appropriate oxides and carbonates and are shown to have a tetragonal structure. The heat capacity of these chromites, measured from 298.15 to 673 K, exhibits sharp changes attributable to second-order phase transitions. The C
p
0(T) data are represented by quadratic best fit equations. The electrical resistivity of the chromites is measured between 303 and 493 K. The results attest to semiconducting behavior of the materials in certain temperature ranges. 相似文献
872.
A. D. Bulanov A. N. Moiseev O. Yu. Troshin V. V. Balabanov D. V. Isaev 《Inorganic Materials》2004,40(6):555-557
High-purity isotopically enriched (99.98% 28Si, 99.57% 29Si, and 99.83% 30Si) silane samples are prepared for the first time. The total hydrocarbon content of the samples is no higher than 0.1–0.3 ppm. The concentration of electroactive impurities in the silicon prepared from the purified monoisotopic silane is below 1015 cm–3. 相似文献
873.
I. A. Grishin V. A. Gur'ev E. B. Intyushin Yu. E. Elliev A. P. Savikin 《Inorganic Materials》2004,40(4):431-433
TeO2–WO3 glasses coactivated with Er3+ and Yb3+ are prepared. The effect of Yb content on the efficiency of Er photoluminescence (PL) in the visible and IR spectral regions is studied. The highest PL efficiency is achieved at an Er : Yb atomic ratio of 1 : 1. The PL lifetime for the Er3+
4
I
13/2 level is determined to be 7–9 ms. 相似文献
874.
Small-angle neutron scattering measurements on a double-crystal spectrometer with perfect monochromator and analyzer crystals were used to follow microstructural changes in the aluminum alloy VD-17, refractory alloy ZhS-6, and dispersion-hardened zirconia-based ceramics with yttria additions. The measurements were carried out by the Warren method, involving determination of the small-angle neutron attenuation coefficient. The experimentally determined total macroscopic small-angle scattering cross section is correlated with different parameters characterizing external influences on the material: the number of loading cycles, heat-treatment temperature, and fracture stress. The potential of the proposed approach for optimizing processing technologies is discussed. 相似文献
875.
S. V. Yakubovskaya L. V. Kul'bitskaya N. L. Budeiko A. A. Korbit 《Inorganic Materials》2004,40(3):221-226
The effect of the composition of sensitizing–activating solutions on the activation efficiency and the chemical coppering of diamond powders is studied. The results demonstrate that stabilizing additives improve the stability of the solutions, influence the average coppering rate, and play a key role in determining the morphology and quality of the resultant coatings. The most effective stabilizing additive is synthamid-10, which ensures the deposition of high-quality copper coatings. 相似文献
876.
The hydrodynamic impact problem is investigated within the framework of potential-flow theory. The vertical load acting on the rigid body is derived based on either momentum or energy conservation, and using the concept of added mass together with a homogeneous Dirichlet condition for the potential on the free surface as usually done to model an impact problem. It is demonstrated that the use of this simplified dynamic free-surface condition, instead of the fully nonlinear one, has a direct influence on the computation of the loads. In particular, the equivalence of momentum and energy analysis is in general not recovered. The situation is then highlighted by performing an asymptotic analysis of the two-dimensional blunt-body asymmetric impact problem. The asymptotic solution is given explicitly and validated through comparisons with experimental results. The energy distribution is then studied. It is shown that the contradiction between momentum and energy analysis can be removed, provided that the flux of energy through the jets is taken into account in the energy balance. If the simplified free-surface condition is indeed valid in the far-field, nonlinear terms must be retained near the body, in the spray-root domains. To leading order, the energy distribution during the gravity-free inertia stage does not depend on the blunt-body shape. The general analysis based on momentum or energy conservation suggests that this result also applies for arbitrary body shape as soon as a homogeneous Dirichlet condition can be applied as a dynamical free-surface boundary condition. In this case, and for a constant vertical impact velocity, half the work performed by the body would seem to be transferred to the fluid as kinetic energy within the spray. 相似文献
877.
Modelling of Diffuse Interfaces with Temperature Gradients 总被引:1,自引:0,他引:1
The work is devoted to capillary phenomena in miscible liquids under the assumption that they have a constant and the same density. The model consists of the heat equation, diffusion equation, and the Navier-Stokes equations with the Korteweg stress. We study several configurations corresponding to the microgravity experiments planned for the International Space Station. The basic conclusion of the numerical simulations is that transient capillary phenomena in miscible liquids exist and can produce convective flows sufficiently strong to be observed experimentally. In particular, there exists a miscible analogue to the Marangoni convection where the temperature gradient is applied along the transition zone between two fluids. Convection also appears if, instead of the temperature gradient, the case where the width of the transition zone varies in space is considered. Finally, similar to the immiscible case, miscible drops move in a temperature gradient. 相似文献
878.
The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb2O3:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature. 相似文献
879.
N. A. Ashurbekov K. O. Iminov V. S. Kobzeva O. V. Kobzev 《Technical Physics Letters》2007,33(6):517-520
The spatial structure of visible emission from plasma of a transverse nanosecond pulsed electric discharge in a gas-filled diode with a hollow (slit) cathode has been experimentally studied. A relation is established between the regime of electron energy relaxation and the plasma-beam discharge structure formation. High values of the electron emission coefficient are observed in the experiment, which cannot be explained using the notion of electron emission from a cathode bombarded by fast heavy particles. 相似文献
880.
V. N. Perevezentsev M. Yu. Shcherban’ M. Yu. Murashkin R. Z. Valiev 《Technical Physics Letters》2007,33(8):648-650
The structure and mechanical properties of nanocrystalline aluminum alloy 1570 obtained by means of severe plastic deformation have been studied. Being tested in a temperature range from 300 to 400°C, the alloy exhibits high-strain-rate superplasticity. At 400°C, the superplasticity is manifested in a very broad range of strain rates, extending from 5 × 10?3 to 1 s?1. 相似文献