全文获取类型
收费全文 | 2569篇 |
免费 | 86篇 |
国内免费 | 64篇 |
专业分类
电工技术 | 6篇 |
综合类 | 70篇 |
化学工业 | 18篇 |
金属工艺 | 6篇 |
机械仪表 | 9篇 |
建筑科学 | 32篇 |
矿业工程 | 1篇 |
能源动力 | 1篇 |
轻工业 | 6篇 |
水利工程 | 3篇 |
无线电 | 65篇 |
一般工业技术 | 58篇 |
冶金工业 | 25篇 |
自动化技术 | 2419篇 |
出版年
2022年 | 10篇 |
2021年 | 15篇 |
2020年 | 13篇 |
2019年 | 15篇 |
2018年 | 21篇 |
2017年 | 52篇 |
2016年 | 57篇 |
2015年 | 54篇 |
2014年 | 112篇 |
2013年 | 90篇 |
2012年 | 102篇 |
2011年 | 125篇 |
2010年 | 104篇 |
2009年 | 126篇 |
2008年 | 154篇 |
2007年 | 152篇 |
2006年 | 173篇 |
2005年 | 124篇 |
2004年 | 101篇 |
2003年 | 117篇 |
2002年 | 83篇 |
2001年 | 64篇 |
2000年 | 77篇 |
1999年 | 53篇 |
1998年 | 61篇 |
1997年 | 54篇 |
1996年 | 44篇 |
1995年 | 53篇 |
1994年 | 56篇 |
1993年 | 32篇 |
1992年 | 36篇 |
1991年 | 36篇 |
1990年 | 15篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 26篇 |
1984年 | 19篇 |
1983年 | 30篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 13篇 |
1979年 | 32篇 |
1978年 | 24篇 |
1977年 | 15篇 |
1976年 | 22篇 |
1975年 | 14篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有2719条查询结果,搜索用时 31 毫秒
1.
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
2.
We consider a language of operations which pass parameters by means of a stack. An algebra over the set of type signatures is introduced, which allows the type signature of a program to be obtained from the type signatures of its constituent operations.Although the theories apply in principle to any stack based language, they have been evolved with particular regard to the proposed ANSI Standard Forth language, which is currently implemented in a type free manner. We hope this work will stimulate an interest in Forth amongst those applying algebraic techniques in software engineering, and we hope to lay the theoretical foundations for implementing practical type checkers to support Forth. 相似文献
3.
Motivated by a study of similar problems stated for factors of words, we study forbidden subwords of a language or a word. A procedure for obtaining the set of all words avoiding a given set of subwords is presented. On the other hand, an algorithm for computing the set of minimal forbidden subwords for a word is given. The case of a two-letter alphabet appears to be particularly interesting and it is considered separately. 相似文献
4.
Cezar Câmpeanu 《Information Processing Letters》2004,92(6):267-274
We define the pattern expressions as an extension of both regular expressions and patterns. We prove several properties of the new family of languages, similar to those of extended regex languages [Câmpeanu et al., Int. J. Found. Comput. Sci. 14 (6) (2003) 1007-1018]. We also define an automata system that recognizes these languages. Differences between regex and pattern expressions are also discussed. 相似文献
5.
Gennaro Costagliola Vincenzo Deufemia Filomena Ferrucci Carmine Gravino 《Information and Computation》2003,187(2):209-245
Drawn symbolic pictures are an extension of drawn pictures obtained by associating a symbol from an alphabet to each point of the picture. In the paper we will address some new interesting issues derived from the introduction of the symbols and we will identify the conditions, which ensure the preservation of properties holding for drawn pictures in the setting of the proposed extension. 相似文献
6.
The goal of the PMS project is to produce an environment in which the intelligent online assessment of the design for large-scale ADA programming projects is provided. The focus is on the representation of knowledge about the design process for an individual module. Changes in pseudocode complexity are measured in terms of partial metrics. These metrics can take the designers inferences about the pseudocode program structure into account when assessing module complexity. Next, a model of the stepwise refinement process is given which demonstrates how pseudocode elaboration decisions can be modelled in partial metric terms. Finally, the decisions associated with each refinement step for 17 example refinements taken from the computer science literature are described using partial metrics. 相似文献
7.
This paper presents the main current theoretical issues in Information Retrieval. The principles of conceptual modelling, as they have emerged in the database area, are presented and their application to document modelling in order to enhance document retrieval is discussed. Finally, the main features of the MULTOS project are presented and critically reviewed confronting them with the requirements which have been identified during the general discussion on document conceptual modelling for information retrieval. 相似文献
8.
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
9.
The MSMIE protocol [SBC89] allows processors in a distributed system to communicate via shared memory. It was designed to meet the reliability and efficiency needs of applications such as nuclear safety systems. We present a formal model of the MSMIE protocol expressed in the notation CCS. Desirable properties of the protocol are expressed in the modal mu-calculus, an expressive modal logic. We show that the protocol lacks an important liveness property. In actual operation, additional operating constraints are checked to avoid potential problems. We present a modified protocol and show that it possesses the liveness property even without checking operating constraints. We also show how parts of the analysis were automated with the Concurrency Workbench. 相似文献
10.
Due to the unique requirements of a series of projects to specify communications architectures using graphical representations (Cara and MFD), we have developed the communications-oriented rule-based language Carla (Cara Rule Language), which provides an executable specification of the architecture being developed. Carla is designed to provide the ability to specify and simulate high-level, possibly incomplete, specifications of communications architectures, and to allow the developer to refine the specification through the addition of behavior-describing rules. Carla is also well-suited to creating black-box specifications of any system whose behavior depends on input/output history. We describe the features of the language, discuss various design issues, and provide examples of various communications protocols specified in Carla. 相似文献