全文获取类型
收费全文 | 682090篇 |
免费 | 9021篇 |
国内免费 | 1604篇 |
专业分类
电工技术 | 12230篇 |
综合类 | 677篇 |
化学工业 | 100997篇 |
金属工艺 | 30840篇 |
机械仪表 | 22284篇 |
建筑科学 | 15703篇 |
矿业工程 | 4127篇 |
能源动力 | 16631篇 |
轻工业 | 53220篇 |
水利工程 | 7918篇 |
石油天然气 | 15570篇 |
武器工业 | 43篇 |
无线电 | 73351篇 |
一般工业技术 | 138821篇 |
冶金工业 | 125704篇 |
原子能技术 | 15400篇 |
自动化技术 | 59199篇 |
出版年
2021年 | 5828篇 |
2020年 | 4265篇 |
2019年 | 5516篇 |
2018年 | 14643篇 |
2017年 | 14843篇 |
2016年 | 13029篇 |
2015年 | 6933篇 |
2014年 | 11154篇 |
2013年 | 28320篇 |
2012年 | 18864篇 |
2011年 | 28649篇 |
2010年 | 23667篇 |
2009年 | 25111篇 |
2008年 | 25417篇 |
2007年 | 26446篇 |
2006年 | 18221篇 |
2005年 | 18757篇 |
2004年 | 17285篇 |
2003年 | 16836篇 |
2002年 | 15442篇 |
2001年 | 15209篇 |
2000年 | 14257篇 |
1999年 | 14717篇 |
1998年 | 37434篇 |
1997年 | 26278篇 |
1996年 | 20029篇 |
1995年 | 15025篇 |
1994年 | 13104篇 |
1993年 | 12877篇 |
1992年 | 9428篇 |
1991年 | 8979篇 |
1990年 | 8910篇 |
1989年 | 8595篇 |
1988年 | 8077篇 |
1987年 | 7267篇 |
1986年 | 7175篇 |
1985年 | 7823篇 |
1984年 | 7387篇 |
1983年 | 6636篇 |
1982年 | 6276篇 |
1981年 | 6458篇 |
1980年 | 6149篇 |
1979年 | 6158篇 |
1978年 | 6109篇 |
1977年 | 7011篇 |
1976年 | 9189篇 |
1975年 | 5399篇 |
1974年 | 5167篇 |
1973年 | 5302篇 |
1972年 | 4491篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen 相似文献
974.
Dimitris Papadias M.Sc. Ph.D. candidate Timos Sellis Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):479-516
Various relation-based systems, concerned with the qualitative representation and processing of spatial knowledge, have been developed in numerous application domains. In this article, we identify the common concepts underlying qualitative spatial knowledge representation, we compare the representational properties of the different systems, and we outline the computational tasks involved in relation-based spatial information processing. We also describesymbolic spatial indexes, relation-based structures that combine several ideas in spatial knowledge representation. A symbolic spatial index is an array that preserves only a set of spatial relations among distinct objects in an image, called the modeling space; the index array discards information, such as shape and size of objects, and irrelevant spatial relations. The construction of a symbolic spatial index from an input image can be thought of as a transformation that keeps only a set of representative points needed to define the relations of the modeling space. By keeping the relative arrangements of the representative points in symbolic spatial indexes and discarding all other points, we maintain enough information to answer queries regarding the spatial relations of the modeling space without the need to access the initial image or an object database. Symbolic spatial indexes can be used to solve problems involving route planning, composition of spatial relations, and update operations. 相似文献
975.
Robotica is a computer aided design package for robotic manipulators developed in the Coordinated Science Laboratory at the University of Illinois at Urbana-Champaign. It encapsulates over 30 functions into a Mathematica package allowing efficient symbolic and numeric calculation of kinematic and dynamic equations for multi-degree-of-freedom manipulators. An X-Windows front end that utilizes the interprocess communication features of Mathematica 2.1 has also been created for ease of use. This paper describes the most important features of the package and how they are used 相似文献
976.
A. V. Mishuev S. I. Levina A. A. Komarov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1993,27(8):484-487
Conclusion On the basis of data of model tests it can be stated that substantial deformation of the Usoi landslide will not be observed as a result of a surge overtopping it with the proposed parameters.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 8, pp. 38–40, August, 1993. 相似文献
977.
978.
979.
In 50 patients auditory threshold and brain stem evoked potential studies were carried out before and after myelography. Due to the analysis of amplitudes and latencies of auditory brain stem measurements, significant functional disorders of the hearing organ and the auditory pathway could be demonstrated. In most of the patients these functional disorders were found to be subclinical, whereas 12 patients showed alterations extending from a subjectively slight hearing loss to an audiometrically objectified acute hearing loss depending on its intensity in each case. The reasons of these functional disorders could not be clarified. An open cochlear aqueduct through which perilymph enters the subarachnoidal space leading to a secondary endolymphatic hydrops can be considered as the cause in cases where manifest symptoms develop. The changes in brain stem audiometry can be additionally explained by changes in osmolality of the inner ear fluids which may lead to the development of an endolymphatic hydrops. 相似文献
980.