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排序方式: 共有691条查询结果,搜索用时 652 毫秒
31.
Charlie A. Ernesto Rida T. Farouki 《The International Journal of Advanced Manufacturing Technology》2012,58(1-4):327-338
To exactly execute a sharp corner in the toolpath, the feedrate of a CNC machine must instantaneously drop to zero at that point. This constraint is problematic in the context of high-speed machining, since it incurs very high deceleration/acceleration rates near sharp corners, which increase the total machining time, and may incur significant path deviations (contour errors) at these points. A strategy for negotiating sharp corners in high-speed machining is proposed herein, based upon a priori toolpath/feedrate modifications in their vicinity. Each corner is smoothed by replacing a subset of the path that contains it with a conic “splice” segment, deviating from the exact corner by no more than a prescribed tolerance ?, along which the square of the feedrate is specified as a Bernstein-form polynomial. The problem of determining the fastest traversal of the conic segments under known axis acceleration bounds can then be formulated as a constrained optimization problem, and by exploiting some well-known properties of Bernstein-form polynomials this can be approximated by a simple linear programming task. Some computed examples are presented to illustrate the implementation and performance of the high-speed cornering strategy. 相似文献
32.
This paper proposes an analytical model for line (1D) and point contacts (2D), based upon the Ertel’s hypothesis to predict the evolution of film thickness in steady-state and transient conditions in elastohydrodynamic lubrication. This theoretical approach, applied to a velocity ramp at constant deceleration, is perfectly supported by experimental results in terms of film thickness distribution during the deceleration process and in terms of central film thickness at the vanishing of the entrainment velocity. This work emphasizes the role of the transport effects of the lubricant at the instantaneous entrainment velocity on the time and length scales at which the film thickness disturbances induced by the deceleration process occur until the complete halting of the surfaces. 相似文献
33.
Cristian Martín Mikel Larrea Ernesto Jiménez 《Journal of Computer and System Sciences》2009,75(3):178-189
Unreliable failure detectors are mechanisms providing information about process failures, that allow to solve several problems in asynchronous systems, e.g., Consensus. A particular failure detector, Omega, provides an eventual leader election functionality. This paper addresses the implementation of Omega in the crash-recovery failure model. We first propose an algorithm assuming that processes are reachable from the correct process that crashes and recovers a minimum number of times. Then, we propose two algorithms which assume only that processes are reachable from some correct process. Besides this, one of the algorithms requires the membership to be known a priori, while the other two do not. 相似文献
34.
Atmospheric DMSO degradation in the gas phase: Cl-DMSO reaction. Temperature dependence and products
Martínez E Aranda A de MY Rodríguez D López MR Albaladejo J 《Environmental science & technology》2002,36(6):1226-1230
The reactions of Cl atoms and ClO radicals with CH3-SOCH3 (DMSO) have been studied using the discharge flow method with direct detection of DMSO, CO, and products by mass spectrometry. The absolute rate constant at room temperature measured for reaction 1, (CH3)2SO + Cl --> products, was k(1) = (1.7 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1). For reaction 2, (CH3)2SO + ClO --> products, only an upper limit could be established, k(2) < or = 6 x 10(-14) cm3 molecule(-1) s(-1) Reaction 1 has been found to proceed through adduct formation and further decomposition involving the cleavage of the C-S bound. The pressure effect on the Cl-DMSO reaction from 0.5 to 3 Torr was negligible, and the temperature dependence in the range 273-335 K was also very slight. The results obtained are related to previous studies of sulfur compounds, and the atmospheric implications are also discussed in relation to the homogeneous sinks of DMSO. Tropospheric lifetimes of DMSO based on average Cl and ClO concentrations and the measured rate constants have been calculated showing that the contribution of reaction 1 must be of minor relevance in the marine boundary layer. Reaction 2 is so slow that it does not play any role within the atmospheric sulfur chemistry. 相似文献
35.
36.
This paper brings into focus the topological and geographical evaluation of metro networks through the definition of a methodological
approach based on a set of indicators, a lot of which are defined in the sector literature. Once the methodology was stated,
the results of an application on the metro networks of 13 big metropolitan areas were illustrated. Statistical comparative
analyses are proposed to classify networks. 相似文献
37.
38.
Rodrigo Scherer Paula Rossini Augusti Vivian Caetano Bochi Camila Steffens Leadir Lucy Martins Fries Ana Paula Daniel Ernesto Hashime Kubota João Radünz Neto Tatiana Emanuelli 《Food chemistry》2006,99(1):136-142
The effect of two slaughter methods (immersion in ice-water slurry and electrical stunning followed by ice slurry asphyxiation) on chemical and microbiological parameters of grass carp (Ctenopharyngodon idella) stored in ice for 20 days was evaluated. No differences in total volatile basic nitrogen (TVB-N), pH, carbohydrate or protein content of mucus were observed between the slaughter methods. Ice-slaughtered fish had lower bacteria counts at the beginning of storage, but higher counts than fish slaughtered by electricity at the end of storage (p < 0.05). However, no significant differences in the shelf life were observed between the slaughter methods evaluated (limit of acceptability – counts > 3 × 106 CFU g−1 – attained after 13–16 days). Results indicated that the chemical parameters evaluated have a limited applicability to assess the shelf life of grass carp stored in ice, since pH limit (6.8) was exceeded after 4 days, while TVB-N limit (30 mg%) was not attained after 20 days of storage. 相似文献
39.
Accidents caused by domino effect are among the more severe that took place in the chemical and process industry. However, a well established and widely accepted methodology for the quantitative assessment of domino accidents contribution to industrial risk is still missing. Hence, available data on damage to process equipment caused by blast waves were revised in the framework of quantitative risk analysis, aiming at the quantitative assessment of domino effects caused by overpressure. Specific probit models were derived for several categories of process equipment and were compared to other literature approaches for the prediction of probability of damage of equipment loaded by overpressure. The results evidence the importance of using equipment-specific models for the probability of damage and equipment-specific damage threshold values, rather than general equipment correlation, which may lead to errors up to 500%. 相似文献
40.
The local spatial autocorrelation and the kernel method for identifying black zones. A comparative approach 总被引:3,自引:0,他引:3
This article aims to determine the location and the length of road sections characterized by a concentration of accidents (black zones). Two methods are compared: one based on a local decomposition of a global autocorrelation index, the other on kernel estimation. After explanation, both methods are applied and compared in terms of operational results, respective advantages and shortcomings, as well as underlying conceptual elements. The operationality of both methods is illustrated by an application to one Belgian road. 相似文献