全文获取类型
收费全文 | 16715篇 |
免费 | 2174篇 |
国内免费 | 1138篇 |
专业分类
电工技术 | 1311篇 |
综合类 | 2067篇 |
化学工业 | 2303篇 |
金属工艺 | 470篇 |
机械仪表 | 942篇 |
建筑科学 | 1155篇 |
矿业工程 | 462篇 |
能源动力 | 622篇 |
轻工业 | 1131篇 |
水利工程 | 300篇 |
石油天然气 | 602篇 |
武器工业 | 132篇 |
无线电 | 1631篇 |
一般工业技术 | 2460篇 |
冶金工业 | 739篇 |
原子能技术 | 162篇 |
自动化技术 | 3538篇 |
出版年
2024年 | 82篇 |
2023年 | 292篇 |
2022年 | 395篇 |
2021年 | 541篇 |
2020年 | 688篇 |
2019年 | 640篇 |
2018年 | 620篇 |
2017年 | 702篇 |
2016年 | 736篇 |
2015年 | 727篇 |
2014年 | 974篇 |
2013年 | 1176篇 |
2012年 | 1142篇 |
2011年 | 1166篇 |
2010年 | 858篇 |
2009年 | 881篇 |
2008年 | 862篇 |
2007年 | 1002篇 |
2006年 | 914篇 |
2005年 | 768篇 |
2004年 | 669篇 |
2003年 | 652篇 |
2002年 | 542篇 |
2001年 | 470篇 |
2000年 | 460篇 |
1999年 | 335篇 |
1998年 | 280篇 |
1997年 | 291篇 |
1996年 | 205篇 |
1995年 | 165篇 |
1994年 | 143篇 |
1993年 | 109篇 |
1992年 | 109篇 |
1991年 | 75篇 |
1990年 | 74篇 |
1989年 | 50篇 |
1988年 | 41篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1966年 | 6篇 |
1964年 | 14篇 |
1963年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
本文叙述了马钢引进美国FLUID DATA公司的热值仪与计算机控制系统,有效地解决了煤气混合加压生产中热值的检测与控制问题。 相似文献
32.
T. Hasegawa M. Nantoh M. Ogino H. Sugawara M. Kawasaki H. Koinuma K. Kitazawa 《Journal of Superconductivity》1995,8(4):467-470
STM tunneling spectroscopy has been performed on the bulk single crystals of BiSrCaCuO (BSCCO) and the epitaxial thin films of YBaCuO (YBCO) at cryogenic temperatures. The STM images and tunneling spectra observed on the (001) surfaces can be classified into three cases; 1) Atomic image is visible. However, the tunneling spectrum shows semiconducting or smeared superconducting gap structures, depending on the tip-sample distance. 2) Clear atomic image can not be obtained. But, the tunneling spectrum shows flat bottom region with quite low zero bias conductance. 3) Tunneling spectra demonstrate gapless behavior, independent of the tip-sample separation. These observations support the quasi-2D electronic picture in whichs-wave like 2D superconducting layers are coupled with each other through the Josephson effect. 相似文献
33.
Ken Mattsson 《Journal of scientific computing》2003,18(1):133-153
Four different methods of imposing boundary conditions for the linear advection-diffusion equation and a linear hyperbolic system are considered. The methods are analyzed using the energy method and the Laplace transform technique. Numerical calculations are done, considering in particular the case when the initial data and boundary data are inconsistent. 相似文献
34.
A new efficient numerical method and the dynamic analysis of composite laminates with piezoelectric layers 总被引:1,自引:0,他引:1
Firstly, a numerical method for the inversion of Laplace transform is developed and its accuracy is shown through examples. Then, a state-vector equation for the dynamic problems of piezoelectric plates is deduced directly from a modified mixed variational principle for piezoelectric bodies and its exact solution for the dynamic problems of simply supported rectangle piezoelectric plate is simply given. For multilayered hybrid plates, we derive the solution in terms of the propagator matrices. The techniques accounts for the compatibility of generalized displacements and generalized stresses on the interface both the elastic layers and piezoelectric layers, and the transverse shear deformation and the rotary inertia of laminate are also considered in the global algebraic equation of structure. Meanwhile, there is no restriction on the thickness and the number of layers. As an application of the numerical inversion of Laplace transform presented in this paper, typical numerical examples of the harmonic vibration and transient response are proposed and discussed. Since the highly accurate numerical results, they can serve as benchmarks to test various thick plate theories and various numerical methods, such as the finite and boundary element methods for transient response problems. 相似文献
35.
Debasmita Das Purabi Rani Samaddar Pratik Kumar Sen Kaushik Das 《Journal of Applied Electrochemistry》2008,38(6):743-749
Galvanostatic steady state current potential measurements were carried out for oxidation of a series of aliphatic alcohols
having varying number of hydroxyl groups. The anodically deposited layer of MnO2 on platinum was used as the electrode material. The deposit was characterised by scanning electron microscopy (SEM), energy
dispersive X-ray analysis (EDAX) and electrode potential measurements. The catalytic role of MnO2 in the electro-oxidation of alcohols was indicated by the chronopotentiograms and the cyclic voltammograms. An analysis of
the electrochemical data indicated a catalytic EC mechanism in which Mn (V) is generated electrochemically and consumed chemically
in succession. Based on this and the hydrogen bonding interaction between alcoholic hydroxyl groups and MnO2 layer, a mechanism was proposed which accounts for the variation in the observed electrochemical reaction orders. Tafel behaviour
was found to be followed only approximately. Current efficiency of the electrochemical oxidation of polyols was studied. Replacement
of platinum by carbon as current collector was found to leave the electrocatalytic activity of the MnO2 deposit practically unaltered. 相似文献
36.
后仙峪硼矿区地表大多为混合花岗岩覆盖。从前人们认为该岩石为岩浆岩,其下不可能存在硼矿床。通过近年对该岩石的研究分析,以及野外工作我门认为该岩石为正常地层,并经钻探验证在该岩层下发现了隐伏硼矿体。 相似文献
37.
38.
39.
In this paper, the effectiveness of the approximate motion equations of a flexible structure, obtained by the RitzKantorovich method, is analysed by using Lyapunov functions. The analysis, which is restricted to the case of a single flexible beam for the sake of simplicity, is carried out under the assumption that a partial dissipation is present, affecting only the first degrees of freedom of the system. By means of suitable Lyapunov functions, an overbounding estimate of the quadratic approximation error is determined as a decreasing function of the approximation order. The analysis is completed by considering the two ‘extreme’ cases: the theoretical absence of dissipation and the presence of structural dissipation, affecting all the infinite degrees of freedom. 相似文献
40.
Oils in Jinghu sag are abundant with high content of polar compounds and have a low ratio of saturate to aromatic hydrocarbons and a high ratio of resin to asphaltene. The gross composition of oils in the Jinghu sag suggests typical immature to low mature characteristics. Some compounds with low thermal stability were identified. Light hydrocarbons, a carbon preference index, an odd even index, n-alkane and hopane maturity parameters show mature features and little differences in the maturity level among oils. Sterane isomerization parameters indicate an immature to low mature status of oil. Transfer of the sedimentary center during sedimentation has led to different thermal histories among subsags and thus generated oils with different maturities. On the basis of source analyses, four migration and accumulation patterns with different maturity can be classified. Combined with available information on mergers of source, reservoir and long distance oil lateral migration, mixing conditions were present in the Jinghu sag. Experimental results indicate that maturity variations are caused by mixtures of hydrocarbons with different maturity. 相似文献