全文获取类型
收费全文 | 1353篇 |
免费 | 47篇 |
国内免费 | 74篇 |
专业分类
电工技术 | 35篇 |
综合类 | 63篇 |
化学工业 | 68篇 |
金属工艺 | 226篇 |
机械仪表 | 82篇 |
建筑科学 | 54篇 |
能源动力 | 15篇 |
轻工业 | 465篇 |
水利工程 | 21篇 |
武器工业 | 1篇 |
无线电 | 56篇 |
一般工业技术 | 172篇 |
冶金工业 | 25篇 |
原子能技术 | 26篇 |
自动化技术 | 165篇 |
出版年
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 12篇 |
2014年 | 54篇 |
2013年 | 238篇 |
2012年 | 79篇 |
2011年 | 114篇 |
2010年 | 71篇 |
2009年 | 90篇 |
2008年 | 42篇 |
2007年 | 39篇 |
2006年 | 56篇 |
2005年 | 25篇 |
2004年 | 44篇 |
2003年 | 25篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 9篇 |
1998年 | 21篇 |
1997年 | 69篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1974年 | 9篇 |
1957年 | 7篇 |
排序方式: 共有1474条查询结果,搜索用时 15 毫秒
91.
A shape and size optimization algorithm is developed to incorporate the shape and size variables in a recently developed machine tool simulation and design methodology known as Integrated Machining Process Design Simulator (IMPDS). This shape optimization algorithm, using coordinates of master nodes, parameters of geometric equations, coordinate linking and symmetry option approaches presents a general and flexible way of controlling and optimizing the structural shape of machine tool elements. An application of the proposed shape and size optimization algorithm indicates that the shape and size parameters have significant effects on the structural characteristics and the dynamic behavior of machine tool elements. 相似文献
92.
93.
This paper describes the design and implementation of a 3 KHz band HF data broadcast communication system, using a quantized frequency modulation, adaptive lattice equalizer together with forward error correcting code (FEC) to obtain a high link reliability and low error rate. A frequency diversity approach is also used in the selection of the timely best carrier frequency, and a microcomputer is implemented into the system for automatic best carrier acquisition, data transmission and clock synchronization, with minimum operator's attention. Extensive field experiments were conducted and experimental results indicate that the system can achieve, for daytime operation, a link reliability of 87–98%, with a probability of error between 10?4 to 10?5, depending upon data rate (50, 75bps) and FECs used. For night time operation, the link reliability reduces to from 65–93% with a probability of error down in the order of 10?3. 相似文献
94.
Circular-polarization discrimination appears in many antennas' applications. A compensation approach based on multilayer film structure is proposed to improve the axial ratio of the magnitude of the two perpendicular modes of the lump ports. The goal is to widen the beamwidth of radiation that has an axial ratio less than 3 dB and thus reducing the complexity at the receiver. A transfer matrix method was developed to represent the multilayer film and characterize its performance. Simulation using high frequency structure simulator shows that a crossed dipole, as an example, can achieve a beamwidth of more than at the frequency of 12.45 GHz after compensation. Finally, conclusions and future work about this compensation method are presented. 相似文献
95.
96.
97.
98.
Roughness coefficient and its uncertainty in gravel-bed river 总被引:1,自引:0,他引:1
Manning's roughness coefficient was estimated for a gravel-bed river reach using field measurements of water level and discharge,and the applicability of various methods used for estimation of the roughness coefficient was evaluated.Results show that the roughness coefficient tends to decrease with increasing discharge and water depth,and over a certain range it appears to remain constant.Comparison of roughness coefficients calculated by field measurement data with those estimated by other methods shows that,although the field-measured values provide approximate roughness coefficients for relatively large discharge,there seems to be rather high uncertainty due to the difference in resultant values.For this reason,uncertainty related to the roughness coefficient was analyzed in terms of change in computed variables.On average,a 20%increase of the roughness coefficient causes a 7% increase in the water depth and an 8% decrease in velocity,but there may be about a 15% increase in the water depth and an equivalent decrease in velocity for certain cross-sections in the study reach.Finally,the validity of estimated roughness coefficient based on field measurements was examined.A 10% error in discharge measurement may lead to more than 10% uncertainty in roughness coefficient estimation,but corresponding uncertainty in computed water depth and velocity is reduced to approximately 5%.Conversely,the necessity for roughness coefficient estimation by field measurement is confirmed. 相似文献
99.
One of the most important scheduling and control problems that must be solved concerning the efficient operation of FMS is the part ordering problem, i.e. finding the optimal sequence of parts to be released into the manufacturing system. Methods currently available for handling this problem are based on heuristic dispatching rules. In this paper an approach for solving the problem using the simulation-optimization technique is proposed. Currently available heuristic approaches can only try to get the optimum at a local level because of the complexities of the system and the dependencies of its components, whereas the proposed approach tries to get the global optimum. 相似文献
100.
This paper considers a problem of configuring both backbone and logical networks in a reconfigurable circuit-switched network where links are subject to failures. The objective is to design feasible backbone and logical networks at least cost where the cost includes backbone link capacity expansion cost, lost-call traffic penalty, and hop cost (nodal processing cost). The problem is formulated as a zero-one non-linear mixed integer programming problem, for which a solution procedure is developed by use of a Lagrangean relaxation technique and heuristic methods exploited for improving the lower and upper bounds of any intermediate solution. The solution procedure is tested for its effectiveness with various numerical examples. 相似文献