全文获取类型
收费全文 | 20978篇 |
免费 | 1660篇 |
国内免费 | 1226篇 |
专业分类
电工技术 | 1713篇 |
综合类 | 2383篇 |
化学工业 | 1326篇 |
金属工艺 | 546篇 |
机械仪表 | 1420篇 |
建筑科学 | 626篇 |
矿业工程 | 420篇 |
能源动力 | 842篇 |
轻工业 | 324篇 |
水利工程 | 400篇 |
石油天然气 | 306篇 |
武器工业 | 160篇 |
无线电 | 1494篇 |
一般工业技术 | 1843篇 |
冶金工业 | 300篇 |
原子能技术 | 86篇 |
自动化技术 | 9675篇 |
出版年
2024年 | 54篇 |
2023年 | 198篇 |
2022年 | 313篇 |
2021年 | 387篇 |
2020年 | 465篇 |
2019年 | 527篇 |
2018年 | 428篇 |
2017年 | 608篇 |
2016年 | 674篇 |
2015年 | 777篇 |
2014年 | 1096篇 |
2013年 | 1586篇 |
2012年 | 1215篇 |
2011年 | 1413篇 |
2010年 | 1060篇 |
2009年 | 1210篇 |
2008年 | 1297篇 |
2007年 | 1343篇 |
2006年 | 1210篇 |
2005年 | 1029篇 |
2004年 | 881篇 |
2003年 | 812篇 |
2002年 | 713篇 |
2001年 | 603篇 |
2000年 | 533篇 |
1999年 | 465篇 |
1998年 | 371篇 |
1997年 | 389篇 |
1996年 | 332篇 |
1995年 | 283篇 |
1994年 | 279篇 |
1993年 | 204篇 |
1992年 | 198篇 |
1991年 | 156篇 |
1990年 | 116篇 |
1989年 | 106篇 |
1988年 | 95篇 |
1987年 | 55篇 |
1986年 | 57篇 |
1985年 | 37篇 |
1984年 | 59篇 |
1983年 | 31篇 |
1982年 | 38篇 |
1981年 | 25篇 |
1980年 | 26篇 |
1979年 | 30篇 |
1978年 | 11篇 |
1977年 | 25篇 |
1976年 | 14篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
首先介绍了HART通信协议及他的优点,然后介绍了HART通信协议在汽油机测速方面的软件实现。该软件主要采用目前流行的VB编程语言。可设计出界面友好、功能强大的测量和监控软件。 相似文献
32.
In this paper we study the optimization issues of ring networks employing novel parallel multi‐granularity hierarchical optical add‐drop multiplexers (OADMs). In particular, we attempt to minimize the number of control elements for the off‐line case. We present an integer linear programming formulation to obtain the lower bound in optimization, and propose an efficient heuristic algorithm called global bandwidth resource assignment that is suitable for the design of large‐scale OADM networks. 相似文献
33.
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
34.
This review article is devoted to the materials containing niobium, which have been discovered or developed in the past few years and exhibit the potential application in heterogeneous catalysis. Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered. Among the catalytic processes in which Nb-containing materials were tested, liquid and gas phase oxidation is described in details, and the role of niobium in the prevention of the catalyst from SO2 poisoning is mentioned. 相似文献
35.
G. Martinez 《Journal of Low Temperature Physics》2003,133(1-2):61-95
High magnetic fields are one of the most powerful tools available to scientists for the study, modification and control of matter. This includes the knowledge on correlations effects, interaction mechanisms, structural information and understanding of mesoscopic effects. In this context, a review of recent scientific achievements at the Grenoble High Magnetic Laboratory is given to illustrate, on specific examples, the power of the Magnetic Field probe. 相似文献
36.
随着各高校校园网络规模的不断扩大和各种应用的急剧增加,各种新的网络问题也在不断出现。Sniffer是网络管理员进行网络管理的有效工具,可以有效地对网络进行实时监控,及时发现网络中存在的各种问题。本文首先介绍了Sniffer的工作原理,其次给出了实现Sniffer功能的编程流程图,并用C语言给出了编程所需的关键代码。 相似文献
37.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
38.
39.
一种实现最佳用户检测的非线性优化神经网络 总被引:2,自引:0,他引:2
本文提出并讨论了实现码分多址(CDMA)系统上最佳多用户检测(MUD)的一种神经网络方法。该方法通过将最佳多用户检测视为非线性优化组合问题,利用神经网络能有效求解非线性优化问题的优势,导出了一种非线性优化神经网络来实现最佳多用户检测,理论分析和计算机模拟表明,所提出的神经网络具有可实时应用的动态性能和较传统方法优越得多的误码率性能和抗多址干扰的性能。 相似文献
40.
Sme concepts used in knowledge base maintenace,such as sequence,new law,user‘s rejection and reconstructions of a knowledge base,are first introduced,and then a framework for extended logic programming(ELP)is given,where an extended logic program is equivalent to a knowledge base.A transition system called R-calculus for ELP is provided.For a given knowledge base and a user‘s rejection,the R-calculus for ELP will deduce best revisions of the base.The soundness and the completeness of the R-calculus for ELP are proved,and the R-calculus for ELP is implemented in Prolog.In addition,the research is compared with other relevant work. 相似文献