全文获取类型
收费全文 | 7477篇 |
免费 | 180篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 83篇 |
综合类 | 2篇 |
化学工业 | 1303篇 |
金属工艺 | 71篇 |
机械仪表 | 108篇 |
建筑科学 | 241篇 |
矿业工程 | 68篇 |
能源动力 | 152篇 |
轻工业 | 619篇 |
水利工程 | 51篇 |
石油天然气 | 14篇 |
无线电 | 802篇 |
一般工业技术 | 1107篇 |
冶金工业 | 2335篇 |
原子能技术 | 83篇 |
自动化技术 | 621篇 |
出版年
2021年 | 51篇 |
2019年 | 68篇 |
2018年 | 80篇 |
2017年 | 89篇 |
2016年 | 85篇 |
2015年 | 76篇 |
2014年 | 119篇 |
2013年 | 267篇 |
2012年 | 151篇 |
2011年 | 241篇 |
2010年 | 172篇 |
2009年 | 177篇 |
2008年 | 227篇 |
2007年 | 220篇 |
2006年 | 196篇 |
2005年 | 187篇 |
2004年 | 154篇 |
2003年 | 132篇 |
2002年 | 139篇 |
2001年 | 124篇 |
2000年 | 151篇 |
1999年 | 164篇 |
1998年 | 725篇 |
1997年 | 434篇 |
1996年 | 302篇 |
1995年 | 212篇 |
1994年 | 200篇 |
1993年 | 173篇 |
1992年 | 117篇 |
1991年 | 103篇 |
1990年 | 123篇 |
1989年 | 127篇 |
1988年 | 97篇 |
1987年 | 113篇 |
1986年 | 84篇 |
1985年 | 117篇 |
1984年 | 106篇 |
1983年 | 96篇 |
1982年 | 85篇 |
1981年 | 72篇 |
1980年 | 81篇 |
1979年 | 71篇 |
1978年 | 81篇 |
1977年 | 107篇 |
1976年 | 169篇 |
1975年 | 66篇 |
1974年 | 72篇 |
1973年 | 46篇 |
1972年 | 53篇 |
1971年 | 58篇 |
排序方式: 共有7660条查询结果,搜索用时 31 毫秒
1.
M. J. O’Sullivan C. G. Walker M. L. O’Sullivan T. D. Thompson A. B. Philpott 《Telecommunication Systems》2006,33(4):353-376
The problem of designing fibre-optic networks for local-access telecommunications generates (at least) three non-trivial subproblems.
In the first of these subproblems one must determine how many fibre-optic cables (fibres) are required at either end of a
street. In the next subproblem a minimum-cost network must be designed to support the fibres. The network must also provide
distinct paths from either end of the street to the central exchange(s). Finally, the fibre-optic cables must be placed in
protective covers. These covers are available in a number of different sizes, allowing some flexibility when covering each
section of the network. In this paper we describe a dynamic programming (DP) formulation for finding a minimum-cost (protective)
covering for the network (the third of the subproblems). This problem is a generalised set covering problem with side constraints
and is further complicated by the introduction of fixed and variable welding costs. The DP formulation selects covers along
each arc (in the network), but cannot exactly model the fixed costs and so does not guarantee optimality. We also describe
an integer programming (IP) formulation for assessing the quality of the DP solutions. The cost of the networks constructed
by the IP model is less than those designed using the DP model, but the saving is not significant for the problems examined
(less than 0.1%). This indicates that the DP model will generally give very good solutions. Furthermore, as the problem dimensions
grow, DP gives significantly better solution times than IP. 相似文献
2.
Alan Bivens Rashim Gupta Ingo McLean Boleslaw Szymanski Jerome White 《International Journal of Network Management》2004,14(2):131-146
Rapid growth of computer network sizes and uses necessitate analysis of network application middleware in terms of its scalability as well as performance. In this paper we analyze a distributed network management middleware based on agents that can be dispatched to locations where they can execute close to the managed nodes. The described middleware operates between the network protocol layer and the application layer and uses standard TCP protocol and SNMP probes to interface the network. By aggregating requests from many users into a single agent, our system allows multiple managers to probe problem areas with minimal management traffic overhead. We discuss and quantify the benefits of the described middleware by implementing real‐time network managers using our system. The main result of this paper is a comparison of scalability and efficiency of our agent‐based management middleware and traditional SNMP‐based data collection. To this end, we measured traffic in both real and simulated networks. In the latter case, we designed, used and described here a method of separating simulated application flow into separate subflows to simplify design of simulations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
3.
Thomas S. Lowry John C. Bright Murray E. Close Christina A. Robb Paul A. White Stewart G. Cameron 《国际水资源开发杂志》2003,19(4):579-592
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps. 相似文献
4.
Dual command travel times and miniload system throughput with turnover-based storage 总被引:2,自引:0,他引:2
Byung Chun Park Robert D. Foley John A. White Edward H. Frazelle 《IIE Transactions》2003,35(4):343-355
We analyze travel times for automated storage/retrieval systems. In particular, we apply our travel time model to turnover-based storage systems and determine the mean and variance of dual command travel times. We present detailed numerical results for selected rack shape factors and ABC inventory profiles. We then investigate the effect of alternative rack configurations on travel time performance measures. We also show how to determine the throughput of miniload systems with turnover-based storage and exponentially distributed pick times. 相似文献
5.
Life is pleasant--and memory helps to keep it that way! 总被引:1,自引:0,他引:1
Walker W. Richard; Skowronski John J.; Thompson Charles P. 《Canadian Metallurgical Quarterly》2003,7(2):203
People's recollections of the past are often positively biased. This bias has 2 causes. The 1st cause lies in people's perceptions of events. The authors review the results of several studies and present several new comparative analyses of these studies, all of which indicate that people perceive events in their lives to more often be pleasant than unpleasant. A 2nd cause is the fading affect bias: The affect associated with unpleasant events fades faster than the affect associated with pleasant events. The authors review the results of several studies documenting this bias and present evidence indicating that dysphoria (mild depression) disrupts such bias. Taken together, this evidence suggests that autobiographical memory represents an important exception to the theoretical claim that bad is stronger than good. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
This paper focuses on a class of robot manipulators termed "continuum" robots - robots that exhibit behavior similar to tentacles, trunks, and snakes. In previous work, we studied details of the mechanical design, kinematics, path-planning and small-deflection dynamics for continuum robots such as the Clemson "tentacle manipulator". In this paper, we discuss the dynamics of a planar continuum backbone section, incorporating a large-deflection dynamic model. Based on these dynamics, we formulate a vibration-damping setpoint controller, and include experimental results to illustrate the efficacy of the proposed controller. 相似文献
7.
8.
Twenty-six patients with an intracardiac myxoma underwent surgical resection at our institution from 1977 through 1992. Left atrial myxoma was diagnosed in 22 patients, left ventricular in 1, right atrial in 2, and right ventricular in 1. Six patients were asymptomatic; preoperative symptoms included dyspnea, arrhythmias, embolic episodes, and syncope. The diagnosis was established with transthoracic echocardiography in all cases but one. Surgery was performed in all cases with the aid of cardiopulmonary bypass with moderate hypothermia and cold crystalloid cardioplegia. One patient with a left ventricular myxoma died in a comatose state during the immediate postoperative period. Long-term clinical and echocardiographic evaluation was performed in 19 patients; results were excellent (all the patients were in New York Heart Association functional class I or II), and no recurrences were documented. The clinical characteristics, diagnostic methods, and surgical approach are presented and discussed. 相似文献
9.
10.
K-winner networks. 总被引:2,自引:0,他引:2
W J Wolfe D Mathis C Anderson J Rothman M Gottler G Brady R Walker G Duane G Alaghband 《Neural Networks, IEEE Transactions on》1991,2(2):310-315
A special class of mutually inhibitory networks is analyzed, and parameters for reliable K-winner performance are presented. The network dynamics are modeled using interactive activation, and results are compared with the sigmoid model. For equal external inputs, network parameters that select the units with the larger initial activations (the network converges to the nearest stable state) are derived. Conversely, for equal initial activations, networks that select the units with larger external inputs (the network converges to the lowest energy stable state) are derived. When initial activations are mixed with external inputs, anomalous behavior results. These discrepancies are analyzed with several examples. Restrictions on initial states are derived which ensure accurate K-winner performance when unequal external inputs are used. 相似文献