全文获取类型
收费全文 | 119525篇 |
免费 | 9510篇 |
国内免费 | 5638篇 |
专业分类
电工技术 | 7227篇 |
技术理论 | 10篇 |
综合类 | 9042篇 |
化学工业 | 19750篇 |
金属工艺 | 7145篇 |
机械仪表 | 8014篇 |
建筑科学 | 8236篇 |
矿业工程 | 3860篇 |
能源动力 | 3384篇 |
轻工业 | 9059篇 |
水利工程 | 2187篇 |
石油天然气 | 7492篇 |
武器工业 | 979篇 |
无线电 | 12349篇 |
一般工业技术 | 13728篇 |
冶金工业 | 6050篇 |
原子能技术 | 1332篇 |
自动化技术 | 14829篇 |
出版年
2024年 | 449篇 |
2023年 | 1706篇 |
2022年 | 3160篇 |
2021年 | 4302篇 |
2020年 | 3250篇 |
2019年 | 2883篇 |
2018年 | 3339篇 |
2017年 | 3649篇 |
2016年 | 3186篇 |
2015年 | 4434篇 |
2014年 | 5653篇 |
2013年 | 7002篇 |
2012年 | 7751篇 |
2011年 | 8464篇 |
2010年 | 7665篇 |
2009年 | 7389篇 |
2008年 | 7515篇 |
2007年 | 7333篇 |
2006年 | 7164篇 |
2005年 | 6206篇 |
2004年 | 4389篇 |
2003年 | 3628篇 |
2002年 | 3292篇 |
2001年 | 2880篇 |
2000年 | 2816篇 |
1999年 | 2767篇 |
1998年 | 2251篇 |
1997年 | 1848篇 |
1996年 | 1762篇 |
1995年 | 1485篇 |
1994年 | 1246篇 |
1993年 | 889篇 |
1992年 | 688篇 |
1991年 | 513篇 |
1990年 | 388篇 |
1989年 | 327篇 |
1988年 | 271篇 |
1987年 | 174篇 |
1986年 | 140篇 |
1985年 | 100篇 |
1984年 | 71篇 |
1983年 | 46篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 30篇 |
1979年 | 15篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
42.
Xiaojun Xie Yonghong Cheng Hong Wang Qian Wang Xiaolin Chen Caixin Sun 《Ceramics International》2008,34(4):689-693
In the ideal A2B2O6O′ pyrochlore structure, the x-value of O atom position is a variable parameter. In Bi1.5ZnNb1.5−xTaxO7 (BZNT) cubic pyrochlores, the x-values alter with the different compositions of Nb/Ta. In this work, a series of initial models for BZNT were established by analyzing X-ray diffraction data. Then three structure modifying methods, including Rietveld refinement, Rietveld refinement with energy and geometry optimization based on quantum mechanics, were employed to obtain the precise models using Materials Studio. Moreover, the reflectivities of BZNT were computed by quantum mechanical simulation based on the refined models. Comparing the simulation results from different modifying models with the experimental results, it is found that Rietveld refinement with energy optimization is the most accurate method for BZNT pyrochlores. According to the simulation results, the different reflectivities correspond well with various x-values of O atom positions in BZNT pyrochlores. 相似文献
43.
44.
The acquisition of new skills over a life span is a remarkable human ability. This ability, however, is constrained by age of acquisition (AoA); that is, the age at which learning occurs significantly affects the outcome. This is most clearly reflected in domains such as language, music, and athletics. This article provides a perspective on the neural and computational mechanisms underlying AoA in language acquisition. The authors show how AoA modulates both monolingual lexical processing and bilingual language acquisition. They consider the conditions under which syntactic processing and semantic processing may be differentially sensitive to AoA effects in second-language acquisition. The authors conclude that AoA effects are pervasive and that the neural and computational mechanisms underlying learning and sensorimotor integration provide a general account of these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
45.
Qingzhao Yao Yuming Zhou Yanqing Sun Xiaoyun Ye 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(4):477-484
TiO2 hybrid molecular imprinted polymer (MIP) for ethofumesate using methacrylic acid (MAA) as the functional monomer and silane
coupling agent 3-(trimethoxysilyl) propylmethacrylate (KH570) as organic–inorganic connective bridge was synthesized via photo-excitation
method. Hydrogen bond was proved to act between MAA and ethofumesate for pre- and post-polymerization binding properties as
testified by UV spectrometric method. KH570 modified TiO2 nanoparticles were prepared via sonochemical reaction, which can accelerate hydrolysis, increase collision chance for the
reactive system and improve the dispersion of the nanoparticles. Scanning electron microscope (SEM), transmission electron
microscope (TEM), binding and the adsorption kinetics experiments as well as thermogravimetric analysis (TGA) were employed
for characterization. The results indicated that the hybrid MIP revealed a larger surface area and more ordered imprinting
cavities with improved thermal stability compared to organic-only MIP. Furthermore, faster adsorption kinetics and enhancive
adsorption capacity were achieved, which made it promising in chemical sensor applications. 相似文献
46.
L. A. Kosyachenko I. M. Rarenko E. F. Sklyarchuk I. I. German Sun Weiguo 《Semiconductors》2006,40(5):554-557
Photodiodes designed to be sensitive in the region 0.5–1.7 μm and obtained by vacuum magnetron sputtering of the ITO (SnO2 + In2O3) layer on the surface of the Hg3In2Te6 single crystal are studied. The electrical characteristics, measured at 265–333 K, indicate that the mechanism of charge
transport in the diodes under study is thermionic. The current-voltage characteristic and its temperature variations are described
quantitatively based on the energy diagram and the found parameters of the heterojunction.
Original Russian Text ? L.A. Kosyachenko, I.M. Rarenko, E.F. Sklyarchuk, I.I. German, Sun Weiguo, 2006, published in Fizika
i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 5, pp. 568–571. 相似文献
47.
Hydrate formation rate plays an important role in making hydrates for the storage and transport of natural gas. Micellar surfactant solutions were found to increase gas hydrate formation rate and storage capacity. With the presence of surfactant, hydrate could form quickly in a quiescent system and the energy costs of hydrate formation reduced. Surfactants (an anionic surfactant, a non‐ionic surfactant and their mixtures) and liquid hydrocarbons (cyclopentane and methylcyclohexane) were used to improve hydrate formation. The experiments of hydrate formation were carried out in the pressure range 3.69–6.82 MPa and the temperature range 274.05–277.55 K. The experimental pressures were kept constant during hydrate formation in each experimental run. The effect of anionic surfactant (sodium dodecyl sulphate (SDS)) on natural gas storage in hydrates is more pronounced compared to a non‐ionic surfactant (dodecyl polysaccharide glycoside (DPG)). The induction time of hydrate formation was reduced with the presence of cyclopentane (CP). Cyclopentane and methylcyclohexane (MCH) could increase hydrate formation rate, but reduced hydrate storage capacity The higher methylcyclohexane concentration, the lower the hydrate storage capacity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
48.
The effect of pressure on combustion and heat transfer is analyzed. The research is based on the basic combustion and heat
transfer theorem. A correction for the heat calculation method for pressurized furnace is made on the basis of the normal
pressure case. The correction takes the effect of pressurizing into account. The results show that the correction is reasonable
and the method is applicable to combustion and heat transfer of the marine supercharged boiler. 相似文献
49.
50.
Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays 总被引:5,自引:0,他引:5
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results. 相似文献