全文获取类型
收费全文 | 366807篇 |
免费 | 19591篇 |
国内免费 | 11282篇 |
专业分类
电工技术 | 18305篇 |
技术理论 | 4篇 |
综合类 | 14357篇 |
化学工业 | 50174篇 |
金属工艺 | 17877篇 |
机械仪表 | 16934篇 |
建筑科学 | 18304篇 |
矿业工程 | 6407篇 |
能源动力 | 9758篇 |
轻工业 | 27334篇 |
水利工程 | 5930篇 |
石油天然气 | 11183篇 |
武器工业 | 2016篇 |
无线电 | 47827篇 |
一般工业技术 | 54193篇 |
冶金工业 | 52053篇 |
原子能技术 | 5484篇 |
自动化技术 | 39540篇 |
出版年
2023年 | 3055篇 |
2022年 | 6291篇 |
2021年 | 8878篇 |
2020年 | 6664篇 |
2019年 | 5703篇 |
2018年 | 7051篇 |
2017年 | 7997篇 |
2016年 | 7239篇 |
2015年 | 9111篇 |
2014年 | 12215篇 |
2013年 | 19295篇 |
2012年 | 17711篇 |
2011年 | 19877篇 |
2010年 | 17724篇 |
2009年 | 17797篇 |
2008年 | 18015篇 |
2007年 | 17427篇 |
2006年 | 15794篇 |
2005年 | 13249篇 |
2004年 | 10783篇 |
2003年 | 9769篇 |
2002年 | 9399篇 |
2001年 | 9270篇 |
2000年 | 8074篇 |
1999年 | 7941篇 |
1998年 | 17201篇 |
1997年 | 11608篇 |
1996年 | 9133篇 |
1995年 | 6810篇 |
1994年 | 5855篇 |
1993年 | 5541篇 |
1992年 | 3806篇 |
1991年 | 3560篇 |
1990年 | 3457篇 |
1989年 | 3249篇 |
1988年 | 2929篇 |
1987年 | 2330篇 |
1986年 | 2390篇 |
1985年 | 2643篇 |
1984年 | 2348篇 |
1983年 | 2085篇 |
1982年 | 1930篇 |
1981年 | 2082篇 |
1980年 | 1828篇 |
1979年 | 1684篇 |
1978年 | 1665篇 |
1977年 | 2028篇 |
1976年 | 2712篇 |
1975年 | 1430篇 |
1974年 | 1374篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
101.
Emmerich M.T.M. Giannakoglou K.C. Naujoks B. 《Evolutionary Computation, IEEE Transactions on》2006,10(4):421-439
This paper presents and analyzes in detail an efficient search method based on evolutionary algorithms (EA) assisted by local Gaussian random field metamodels (GRFM). It is created for the use in optimization problems with one (or many) computationally expensive evaluation function(s). The role of GRFM is to predict objective function values for new candidate solutions by exploiting information recorded during previous evaluations. Moreover, GRFM are able to provide estimates of the confidence of their predictions. Predictions and their confidence intervals predicted by GRFM are used by the metamodel assisted EA. It selects the promising members in each generation and carries out exact, costly evaluations only for them. The extensive use of the uncertainty information of predictions for screening the candidate solutions makes it possible to significantly reduce the computational cost of singleand multiobjective EA. This is adequately demonstrated in this paper by means of mathematical test cases and a multipoint airfoil design in aerodynamics. 相似文献
102.
'Software defined radio' (SDR) is a technology that will appear in future generations of mobile phones, i.e. following the third-generation mobile phone technology that is currently being defined and developed. Early versions of 'pragmatic' SDR will allow the terminal to be reconfigured at any level of its protocol stack. Ultimately, the 'pure' SDR technology will allow a mobile phone or terminal to have its air interface software configured or reconfigured by other software (or software parameters) that have been downloaded to the terminal, e.g. over the air, or from a remote server via the Internet and one's personal computer (PC). A number of security issues arise with downloaded code that implements the air interface functions, and these may not be obvious simply from looking at the way PC software is updated on-line today. This paper starts with an outline of the code that allows a mobile phone to operate over a particular air interface. This sets the baseline for a discussion of the security issues surrounding the change of this code from one that is fixed and downloaded once only, to code that is reconfigurable during the life of a product. 相似文献
103.
In this paper, a localized MEI method (L-MEI) is developed and combined with the domain decomposition method (DDM) for the simulation of scattering by a concave cylinder. In the L-MEI, the whole domain is decomposed into many subdomains. Different from the conventional MEI method, the MEI coefficients of the L-MEI method in each subdomain are only dependent on the localized metrons that are defined in the subdomain. The localization of metrons has the following advantages: (1) speeding up the calculation of MEI coefficients and saving memory, (2) making the MEI method available for concave structures, and (3) obtaining a band sparse matrix directly without any modification 相似文献
104.
105.
106.
T Kita 《Canadian Metallurgical Quarterly》1989,40(16):10816-10830
107.
108.
109.
In this paper, the space-vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and to analyze power sources and loads with different connections (delta and wye). This method can also be applied to analyze steady-state (or transient phenomena) and unbalanced sources, including harmonics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits. 相似文献
110.
R. Sankarasubramanian C. S. Jog T. A. Abinandanan 《Metallurgical and Materials Transactions A》2002,33(4):1083-1090
We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems
under a plane-strain condition with the principal misfit strain components ε*
xx
and ε*
yy
. For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε*
yy
/ε*
xx
. We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For
systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems
with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant
line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness;
moreover, the transition is also forbidden when the particle stiffness is greater than a critical value. 相似文献