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51.
During the last years, weighted timed automata have received much interest in the real-time community. Weighted timed automata form an extension of timed automata and allow us to assign weights (costs) to both locations and edges. This model, introduced by Alur et al. (2001) and Behrmann et al. (2001), permits the treatment of continuous consumption of resources and has led to much research on scheduling problems, optimal reachability and model checking. Also, several authors have derived Kleene-type characterizations of (unweighted) timed automata and their accepted timed languages. The goal of this paper is to provide a characterization of the behaviours of weighted timed automata by rational power series. We define weighted timed automata with weights taken in an arbitrary semiring, resulting in a model that subsumes several weighted timed automata concepts of the literature. For our main result, we combine the methods of Schützenberger, a recent approach for a Kleene-type theorem for unweighted timed automata by Bouyer and Petit as well as new techniques. Our main result also implies Kleene-type theorems for several subclasses of weighted timed automata investigated before, e.g., for timed automata and timed automata with stopwatch observers. 相似文献
52.
Formal power series over non-commuting variables have been investigated as representations of the behavior of automata with
multiplicities. Here we introduce and investigate the concepts of aperiodic and of star-free formal power series over semirings
and partially commuting variables. We prove that if the semiring K is idempotent and commutative, or if K is idempotent and the variables are non-commuting, then the product of any two aperiodic series is again aperiodic. We also
show that if K is idempotent and the matrix monoids over K have a Burnside property (satisfied, e.g. by the tropical semiring), then the aperiodic and the star-free series coincide.
This generalizes a classical result of Schützenberger (Inf. Control 4:245–270, 1961) for aperiodic regular languages and subsumes a result of Guaiana et al. (Theor. Comput. Sci. 97:301–311, 1992) on aperiodic trace languages.
This work partly supported by the DAAD-PROCOPE project Temporal and Quantitative Analysis of Distributed Systems. 相似文献
53.
OBJECTIVE: An evaluation study was conducted to answer the question of which system properties of night vision enhancement systems (NVESs) provide a benefit for drivers without increasing their workload. BACKGROUND: Different infrared sensor, image processing, and display technologies can be integrated into an NVES to support nighttime driving. Because each of these components has its specific strengths and weaknesses, careful testing is required to determine their best combination. METHOD: Six prototypical systems were assessed in two steps. First, a heuristic evaluation with experts from ergonomics, perception, and traffic psychology was conducted. It produced a broad overview of possible effects of system properties on driving. Based on these results, an experimental field study with 15 experienced drivers was performed. Criteria used to evaluate the development potential of the six prototypes were the usability dimensions of effectiveness, efficiency, and user satisfaction (International Organization for Standardization, 1998). RESULTS: Results showed that the intelligibility of information, the easiness with which obstacles could be located in the environment, and the position of the display presenting the output of the system were of crucial importance for the usability of the NVES and its acceptance. Conclusion: All relevant requirements are met best by NVESs that are positioned at an unobtrusive location and are equipped with functions for the automatic identification of objects and for event-based warnings. APPLICATION: These design recommendations and the presented approach to evaluate the systems can be directly incorporated into the development process of future NVESs. 相似文献
54.
Making Workflow Change Acceptable 总被引:1,自引:0,他引:1
Virtual professional communities are supported by network information systems composed from standard Internet tools. To satisfy
the interests of all community members, a user-driven approach to requirements engineering is proposed that produces not only
meaningful but also acceptable specifications. This approach is especially suited for workflow systems that support partially structured, evolving work
processes. To ensure the acceptability, social norms must guide the specification process. The RENISYS specification method
is introduced, which facilitates this process using composition norms as formal representations of social norms. Conceptual
graph theory is used to represent four categories of knowledge definitions: type definitions, state definitions, action norms
and composition norms. It is shown how the composition norms guide the legitimate user-driven specification process by analysing
a case on the development of an electronic law journal. 相似文献
55.
This paper outlines a generic evaluation methodology for multimedia and real time applications. It concentrates on the application layer and the service aspect. Principles of software evaluation for quality assessment and measurement for networked services and distributed applications are used to present a specific method for measuring important characteristics. The method and the measurement procedure allow comparison of the actual characteristics of service quality with the required characteristics and thresholds. The proof of concepts will be made by the implementation of quality measurement agents following the approach outlined in this paper. Our approach of performing service level management (SLM) with agent technology is distributed, slim, minimizable to the maximum, independent in its methodology and offers comparable, objective results. 相似文献
56.
Manfred Thaller 《Computers and the Humanities》1991,25(2-3):149-162
Since 1978 research in the development of software dedicated to the specific problems of historical research has been undertaken at the Max-Planck-Institute für Geschichte in Göttingen. From a background of practical experiences during these years, a concept of what an appropriate workstation for an historian would be has been derived. It stresses the necessity of three components: (a) software, derived from a detailed analysis of what differentiates information contained in historical sources from such present in current material, (b) databases which are as easily available as printed books and (c) knowledge bases which allow software and data bases to draw upon the information contained in historical reference works. A loose network of European research projects, dedicated to the realization of such a setup, is described.Manfred Thaller has a Ph.D. (1975) in Modern and Medieval History and held a post-doctoral fellowship in sociology at the Institute for Advanced Studies (Vienna). Since 1978 he has been at the Max-Planck-Institute for History, where he is a research fellow for Historical Information Science. 相似文献
57.
Thomas?ZolperEmail author Zhi?Li Manfred?Jungk Andreas?Stammer Herbert?Stoegbauer Tobin?Marks Yip-Wah?Chung Qian?Wang 《Tribology Letters》2013,49(2):301-311
The molecular structures, rheological properties, and friction coefficients of several new siloxane-based polymers were studied to explore their traction characteristics. The molecular structures including branch content were established by nuclear magnetic resonance spectroscopy, while the molecular mass distributions were determined by gel permeation chromatography. Density, viscosity, elastohydrodynamic film formation, and friction were investigated over a temperature range of 303–398 K. Film thickness and friction measurements were studied under the conditions that are representative of boundary, mixed, and full-film lubrication regimes, aiming at maximizing traction performance and temperature stability by simultaneous optimization of the size and content of ring-shaped branch structures. This study provides quantitative insight into the effect of siloxane molecular structure on the tribological performance for traction drive applications such as continuously variable transmissions. 相似文献
58.
We consider the following type of online variance minimization problem: In every trial t our algorithms get a covariance matrix C
t
and try to select a parameter vector w
t−1 such that the total variance over a sequence of trials ?t=1T (wt-1)T Ctwt-1\sum_{t=1}^{T} (\boldsymbol {w}^{t-1})^{\top} \boldsymbol {C}^{t}\boldsymbol {w}^{t-1} is not much larger than the total variance of the best parameter vector u chosen in hindsight. Two parameter spaces in ℝ
n
are considered—the probability simplex and the unit sphere. The first space is associated with the problem of minimizing
risk in stock portfolios and the second space leads to an online calculation of the eigenvector with minimum eigenvalue of
the total covariance matrix ?t=1T Ct\sum_{t=1}^{T} \boldsymbol {C}^{t}. For the first parameter space we apply the Exponentiated Gradient algorithm which is motivated with a relative entropy regularization.
In the second case, the algorithm has to maintain uncertainty information over all unit directions u. For this purpose, directions are represented as dyads uu
⊤ and the uncertainty over all directions as a mixture of dyads which is a density matrix. The motivating divergence for density
matrices is the quantum version of the relative entropy and the resulting algorithm is a special case of the Matrix Exponentiated
Gradient algorithm. In each of the two cases we prove bounds on the additional total variance incurred by the online algorithm
over the best offline parameter. 相似文献
59.
The new composite material Textile Reinforced Concrete (TRC) is a promising development which may open up entirely new fields for the application of the construction material concrete. The possible more filigree structures with high quality surfaces make TRC an attractive choice for the architect and give the engineer more freedom in design. However, the use of TRC requires design rules which are currently being developed at RWTH Aachen University, Germany. In this article, recent experimental results as well as modeling techniques are described. 相似文献
60.
Friction stir welding undergoes a steep evolution in industrial applications since the invention in the early 1990s. Especially for aluminium alloys in sheet thicknesses over 2 mm a lot of applications are established, whereas a lack in knowledge about friction stir welding of thin sheets with sheet thickness less than 2 mm exists. This article deals with friction stir welding of thin sheet aluminium steel tailored hybrids and their formability. These investigations tend to close the gap of availability of friction stir welded blanks in the range of 1 mm sheet thickness and to offer new applications of this joining technology. For production of aluminium steel tailored hybrids AA5182 with a thickness of 1.2 mm and DC04 in 1.0 mm are used, the joining partners are friction stir welded in a lap joint. Different tool geometries and process parameters are performed to achieve the highest strength and elongation at fracture of the tailored hybrids. The influence of the stirring on the arrangement and distribution of both materials in the welding zone and its microstructure is analysed using light optical and scanning electron microscopy. In addition to tensile tests planar microhardness measurements help to detect the local changes of the mechanical properties in the characteristic zones of the weld seam. Tailored hybrids, which were friction stir welded with the best welding parameters in accordance to the mechanical properties of the weld seams, were used for deep drawing tests of friction stir welded thin sheet aluminium steel tailored hybrids. The maximum drawing ratio of these tailored hybrids coincides with the one of the parent material of AA5182. 相似文献