全文获取类型
收费全文 | 25075篇 |
免费 | 2724篇 |
国内免费 | 2273篇 |
专业分类
电工技术 | 1856篇 |
技术理论 | 2篇 |
综合类 | 2994篇 |
化学工业 | 4019篇 |
金属工艺 | 2722篇 |
机械仪表 | 1192篇 |
建筑科学 | 1792篇 |
矿业工程 | 1103篇 |
能源动力 | 735篇 |
轻工业 | 647篇 |
水利工程 | 608篇 |
石油天然气 | 903篇 |
武器工业 | 223篇 |
无线电 | 2030篇 |
一般工业技术 | 2882篇 |
冶金工业 | 1618篇 |
原子能技术 | 248篇 |
自动化技术 | 4498篇 |
出版年
2024年 | 93篇 |
2023年 | 370篇 |
2022年 | 626篇 |
2021年 | 803篇 |
2020年 | 832篇 |
2019年 | 701篇 |
2018年 | 649篇 |
2017年 | 737篇 |
2016年 | 836篇 |
2015年 | 955篇 |
2014年 | 1551篇 |
2013年 | 1587篇 |
2012年 | 1781篇 |
2011年 | 1955篇 |
2010年 | 1488篇 |
2009年 | 1478篇 |
2008年 | 1327篇 |
2007年 | 1704篇 |
2006年 | 1529篇 |
2005年 | 1271篇 |
2004年 | 1047篇 |
2003年 | 922篇 |
2002年 | 827篇 |
2001年 | 703篇 |
2000年 | 634篇 |
1999年 | 528篇 |
1998年 | 456篇 |
1997年 | 441篇 |
1996年 | 350篇 |
1995年 | 336篇 |
1994年 | 318篇 |
1993年 | 205篇 |
1992年 | 224篇 |
1991年 | 181篇 |
1990年 | 157篇 |
1989年 | 161篇 |
1988年 | 100篇 |
1987年 | 59篇 |
1986年 | 23篇 |
1985年 | 32篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1959年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
J. Dingel 《Formal Aspects of Computing》2002,14(2):123-197
Parallel computers have not yet had the expected impact on mainstream computing. Parallelism adds a level of complexity to
the programming task that makes it very error-prone. Moreover, a large variety of very different parallel architectures exists.
Porting an implementation from one machine to another may require substantial changes. This paper addresses some of these
problems by developing a formal basis for the design of parallel programs in the form of a refinement calculus. The calculus
allows the stepwise formal derivation of an abstract, low-level implementation from a trusted, high-level specification. The
calculus thus helps structuring and documenting the development process. Portability is increased, because the introduction
of a machine-dependent feature can be located in the refinement tree. Development efforts above this point in the tree are
independent of that feature and are thus reusable. Moreover, the discovery of new, possibly more efficient solutions is facilitated.
Last but not least, programs are correct by construction, which obviates the need for difficult debugging. Our programming/specification
notation supports fair parallelism, shared-variable and message-passing concurrency, local variables and channels. The calculus
rests on a compositional trace semantics that treats shared-variable and message-passing concurrency uniformly. The refinement
relation combines a context-sensitive notion of trace inclusion and assumption-commitment reasoning to achieve compositionality.
The calculus straddles both concurrency paradigms, that is, a shared-variable program can be refined into a distributed, message-passing
program and vice versa.
Received July 2001 / Accepted in revised form May 2002 相似文献
72.
本文应用配极变换的几何性质来确定锥面截交线的中心及其主要轴线,这对于准确地绘制或使用数控绘图机来绘制二次曲线.是很有意义的. 相似文献
73.
In this paper,a new method is presented for 3D motion estimation by image region correspondences using stereo cameras.Under the weak perspectivity assumption.we first employ the moment tensor theory (Cyganski and Orr^[11]) to compute the monocular affine transformations relating images taken by the same camera at different time instants and the binocular affine transformations relating images taken by different cameras at the same time instant.We then show that 3D motion can be recovered from these 2D transformations.A space-time fusion strategy is proposed to aim at robust results.No knowledge of point correspondences if requred in the above processes and the computations involved are linear.To find corresponding image regions,new affine invariants,which show stronger invariance,are derived in term of tensor contraction theory.Experiments on real motion images are conducted to verify the proposed method. 相似文献
74.
75.
Sandra A. Yost Peter H. Bauer Kasyapa Balemarthy 《Multidimensional Systems and Signal Processing》1996,7(2):211-220
This paper addresses the BIBO (bounded-input bounded-output) stability of a class of discrete 2-D quarter-plane filters in the presence of nonessential singularities of the second kind (NSSK's) on the unit bidisk. Conditions under which the double bilinear transformation (DBT) preserves stability are derived. The results presented here also extend the class of systems whose stability can be predicted. Use of the inverse DBT to produce a continuous equivalent of the discrete 2-D transfer function allows easy application of a continuous-domain equivalent of a criterion developed by Dautov. The necessary and sufficient condition for stability derived in this work provides a simple check for the class of systems under consideration. From this class of systems, it is also possible to construct stable pairs of mutually inverse transfer functions. 相似文献
76.
Investigations have been carried out on an erosion-corrosion apparatus to investigate the behaviour of corrosion-resistant highalloy iron-base materials containing hard phases. These materials had been optimized for increased wear resistance under complex stress conditions. As expected, in dry erosion tests, very low mass losses were established; there was little difference between the materials. Also, in corrosive environments (NaCl, H2SO4), the materials showed good stability; however, the duplex structures were superior to the martensitic ones. The combination of erosion and corrosion produced large differences and, in some cases, markedly reduced resistance to damage. These results confirmed observations that it is impossible to deduce the environmentally influenced mechanical behaviour of an alloy from its behaviour in separate corrosion and erosion experiments. The basic mechanisms underlying these processes have been investigated only tentatively. 相似文献
77.
78.
Gorgievski-Duijvesteijn Marjan J.; Bakker Arnold B.; Schaufeli Wilmar B.; van der Heijden Peter G. M. 《Canadian Metallurgical Quarterly》2005,10(3):210
This study of 513 Dutch farmers tested a dynamic equilibrium model of resources (an extension of the conservation of resources theory; S. E. Hobfoll, 1989, 1998, 2001). With structural equation modeling, the advantages of a 3-wave longitudinal design were comprehensively used, such as addressing bidirectional causal effects and within-individual vs. between-individual change. This allowed for a careful analysis of the management function of resources in the stress process. Results showed that well-being had stronger within-person stability than finances. Increased levels of financial problems temporarily increased psychological distress but not self-reported illness. Conversely, farmers with higher stable baselines of psychological distress also had higher baselines of self-reported illness and experienced more negative changes in their financial situation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
80.
Nourh ne Boudhrioua Bertrand Broyart Catherine Bonazzi Jean-Dominique Daudin 《Drying Technology》2005,23(12):2313-2335
A method is presented for computing the values of apparent diffusivity in solids with respect to the concentration of the diffusing substance (water or sodium chloride). This method does not require any assumption upon the mathematical relationship between diffusivity and concentration. It can be applied to experimental measurements of local concentration versus position within the solid (profiles) with relatively few measurements (circa 10) and a mathematical smoothing of the experimental data by using an artificial neural network model. The method was first validated on simulated data obtained by using a constant diffusivity value and on experimental profiles when the relation between diffusivity and concentration was given. It was then applied to original experimental moisture profiles obtained by putting gelatin gels with different initial moisture contents into contact for up to 14 days. The method was also successfully applied to five sets of experimental moisture and sodium chloride profiles taken from the literature and obtained from different food products. Apparent diffusivities calculated by our method were found in agreement with those obtained by authors using different numerical methods to compute the diffusivity values. 相似文献