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排序方式: 共有640条查询结果,搜索用时 18 毫秒
1.
Stanislav I. StoliarovPhillip R. Westmoreland Marc R. Nyden Glenn P. Forney 《Polymer》2003,44(3):883-894
The theory and implementation of reactive molecular dynamics (RMD) are presented. The capabilities of RMD and its potential use as a tool for investigating the mechanisms of thermal transformations in materials are demonstrated by presenting results from simulations of the thermal degradation of poly(methyl methacrylate) (PMMA). While it is known that depolymerization must be the major decomposition channel for PMMA, there are unanswered questions about the nature of the initiation reaction and the relative reactivities of the tertiary and primary radicals formed in the degradation process. The results of our RMD simulations, performed directly in the condensed phase, are consistent with available experimental information. They also provide new insights into the mechanism of the thermally induced conversion of this polymer into its constituent monomers. 相似文献
2.
The polymorphism of Ca3SiO5 has been studied microscopically by following changes in optic properties and modes of twinning of the crystal as a function of temperature. Besides the six modifications already established, a hitherto-unidentified monoclinic phase M3, which can be characterized only by microscopy at present, has been found to exist just below the rhombohedral phase (R). The transitions that give clear thermal effects on the DTA curve show no corresponding change under the microscope. 相似文献
3.
A computationally efficient algorithm for electromagnetic (EM)‐simulation‐driven design optimization of microwave structures is proposed. Our technique exploits variable‐fidelity EM simulations and the multilevel design approach where an approximate optimum of the lower accuracy but faster EM model of the structure under design is used as a starting point for optimizing a more accurate model. Several enhancements of the basic multifidelity method are introduced, including an efficient algorithm of optimizing EM models that is based on local response surface approximations, as well as automated adjustment of model fidelity. Convergence of the procedure to the optimum design is ensured by defaulting to the higher fidelity model whenever the prediction given by the lower fidelity fails to improve the design. Distribution of the computational effort between the models of different fidelity allows for making larger steps in the design space at a low cost, as well as substantial reduction of the number of high‐fidelity model evaluations, because the high‐fidelity model is only referred to in the last design stage. The article provides comprehensive numerical verification of our technique. Substantial computational savings are demonstrated in comparison to the benchmark methods: over 40% on average as compared to a basic version of the multifidelity optimization approach and over 95% as compared to direct optimization of the high‐fidelity model. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:281–288, 2014. 相似文献
4.
Summary The synthesis is reported of copolymers of styrene with methacrylic acid and of methyl methacrylate with methacrylic acid by radical copolymerization, of copolymers of methyl methacrylate with methacrylic acid by partial alkaline hydrolysis of poly(methyl methacrylate), and of block copolymers of styrene with methacrylic acid. Modified titration curves of all these copolymers were recorded in water and water-ethanol solutions. In a solution containing 50 mass.% ethanol, only small differences could be observed between the potentiometric behaviour of the individual copolymers and polymethacrylic acid. Also, there were no essential differences in any of the solvents used between the potentiometric behaviour of block copolymers of styrene with methacrylic acid, on the one hand, and polymethacrylic acid, on the other. On the contrary, maxima and minima were always observed on the modified titration curves of statistical copolymers with a higher content of the hydrophobic comonomer in solutions with a high water content. Thus, using the modified titration curves, it is possible to decide whether a given copolymer is of the block or statistical type. 相似文献
5.
André Stork Clemens-August Thole Stanislav Klimenko Igor Nikitin Lialia Nikitina Yuri Astakhov 《The Visual computer》2008,24(11):947-953
One of the important tasks in Mechanical Engineering is to increase the safety of the vehicle and decrease its production
costs. This task is typically solved by means of Multiobjective Optimization, which formulates the problem as a mapping from
the space of design variables to the space of target criteria and tries to find an optimal region in these multidimensional
spaces. Due to high computational costs of numerical simulations, the sampling of this mapping is usually very sparse and
scattered. Combining design of experiments methods, metamodeling, new interpolation schemes and innovative graphics methods,
we enable the user to interact with simulation parameters, optimization criteria, and come to a new interpolated crash result
within seconds. We denote this approach as Simulated Reality, a new concept for the interplay between simulation, optimization
and interactive visualization. In this paper we show the application of Simulated Reality for solution of real life car design
optimization problems.
相似文献
Lialia NikitinaEmail: |
6.
7.
Microstructure,Phase Composition,and Thermal Stability of Two Zirconium Alloys Subjected to High‐Pressure Torsion at Different Temperatures 下载免费PDF全文
Stanislav. O. Rogachev Sergey A. Nikulin Andrey B. Rozhnov Mikhail V. Gorshenkov 《Advanced Engineering Materials》2018,20(9)
8.
Matej Perše Author Vitae Matej Kristan Author Vitae Author Vitae Gašper Muši? Author Vitae Author Vitae Stanislav Kova?i? Author Vitae 《Pattern recognition》2010,43(4):1491-1501
This paper presents the use of place/transition petri nets (PNs) for the recognition and evaluation of complex multi-agent activities. The PNs were built automatically from the activity templates that are routinely used by experts to encode domain-specific knowledge. The PNs were built in such a way that they encoded the complex temporal relations between the individual activity actions. We extended the original PN formalism to handle the propagation of evidence using net tokens. The evaluation of the spatial and temporal properties of the actions was carried out using trajectory-based action detectors and probabilistic models of the action durations. The presented approach was evaluated using several examples of real basketball activities. The obtained experimental results suggest that this approach can be used to determine the type of activity that a team has performed as well as the stage at which the activity ended. 相似文献
9.
Self-assembly is a process in which small building blocks interact autonomously to form larger structures. A recently studied
model of self-assembly is the Accretive Graph Assembly Model whereby an edge-weighted graph is assembled one vertex at a time
starting from a designated seed vertex. The weight of an edge specifies the magnitude of attraction (positive weight) or repulsion
(negative weight) between adjacent vertices. It is feasible to add a vertex to the assembly if the total attraction minus repulsion of the already built neighbors exceeds a certain threshold,
called the assembly temperature. This model naturally generalizes the extensively studied Tile Assembly Model. A natural question
in graph self-assembly is to determine whether or not there exists a sequence of feasible vertex additions to realize the
entire graph. However, even when it is feasible to realize the assembly, not much can be inferred about its likelihood of
realization in practice due to the uncontrolled nature of the self-assembly process. Motivated by this, we introduce the robust self-assembly problem where the goal is to determine if every possible sequence of feasible vertex additions leads to the
completion of the assembly. We show that the robust self-assembly problem is co-NP-complete even on planar graphs with two
distinct edge weights. We then examine the tractability of the robust self-assembly problem on a natural subclass of planar
graphs, namely grid graphs. We identify structural conditions that determine whether or not a grid graph can be robustly self-assembled,
and give poly-time algorithms to determine this for several interesting cases of the problem. Finally, we also show that the
problem of counting the number of feasible orderings that lead to the completion of an assembly is #P-complete. 相似文献
10.
We study dynamic routing in store-and-forward packet networks where each network link has bounded buffer capacity for receiving
incoming packets and is capable of transmitting a fixed number of packets per unit of time. At any moment in time, packets
are injected at various network nodes with each packet specifying its destination node. The goal is to maximize the throughput, defined as the number of packets delivered to their destinations.
In this paper, we make some progress on throughput maximization in various network topologies. Let n and m denote the number of nodes and links in the network, respectively. For line networks, we show that Nearest-to-Go (NTG), a
natural distributed greedy algorithm, is
-competitive, essentially matching a known
lower bound on the performance of any greedy algorithm. We also show that if we allow the online routing algorithm to make centralized decisions, there is a randomized
polylog(n)-competitive algorithm for line networks as well as for rooted tree networks, where each packet is destined for the root
of the tree. For grid graphs, we show that NTG has a competitive ratio of
while no greedy algorithm can achieve a ratio better than
. Finally, for arbitrary network topologies, we show that NTG is
-competitive, improving upon an earlier bound of O(mn).
An extended abstract appeared in the Proceedings of the 8th Workshop on Approximation Algorithms for Combinatorial Optimization Problems, APPROX 2005, Berkeley, CA, USA, pp. 1–13, Lecture Notes in Computer Science, vol. 1741, Springer, Berlin.
S. Angelov is supported in part by NSF Career Award CCR-0093117, NSF Award ITR 0205456 and NIGMS Award 1-P20-GM-6912-1.
S. Khanna is supported in part by an NSF Career Award CCR-0093117, NSF Award CCF-0429836, and a US-Israel Binational Science
Foundation Grant.
K. Kunal is supported in part by an NSF Career Award CCR-0093117 and NSF Award CCF-0429836. 相似文献