全文获取类型
收费全文 | 78717篇 |
免费 | 10375篇 |
国内免费 | 6123篇 |
专业分类
电工技术 | 12801篇 |
技术理论 | 4篇 |
综合类 | 7582篇 |
化学工业 | 6768篇 |
金属工艺 | 2357篇 |
机械仪表 | 6696篇 |
建筑科学 | 4293篇 |
矿业工程 | 2652篇 |
能源动力 | 4194篇 |
轻工业 | 4033篇 |
水利工程 | 3229篇 |
石油天然气 | 3503篇 |
武器工业 | 968篇 |
无线电 | 6166篇 |
一般工业技术 | 5922篇 |
冶金工业 | 2914篇 |
原子能技术 | 470篇 |
自动化技术 | 20663篇 |
出版年
2024年 | 663篇 |
2023年 | 1715篇 |
2022年 | 2992篇 |
2021年 | 3250篇 |
2020年 | 3580篇 |
2019年 | 2961篇 |
2018年 | 2652篇 |
2017年 | 3230篇 |
2016年 | 3655篇 |
2015年 | 3994篇 |
2014年 | 6004篇 |
2013年 | 5544篇 |
2012年 | 6698篇 |
2011年 | 6635篇 |
2010年 | 4721篇 |
2009年 | 4906篇 |
2008年 | 4316篇 |
2007年 | 4933篇 |
2006年 | 4224篇 |
2005年 | 3446篇 |
2004年 | 2781篇 |
2003年 | 2269篇 |
2002年 | 1951篇 |
2001年 | 1586篇 |
2000年 | 1340篇 |
1999年 | 934篇 |
1998年 | 815篇 |
1997年 | 664篇 |
1996年 | 561篇 |
1995年 | 487篇 |
1994年 | 382篇 |
1993年 | 263篇 |
1992年 | 227篇 |
1991年 | 194篇 |
1990年 | 161篇 |
1989年 | 134篇 |
1988年 | 88篇 |
1987年 | 41篇 |
1986年 | 33篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1975年 | 6篇 |
1959年 | 7篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
简单回顾了国内外在火电机组运行优化领域的研究历程,列举了目前国内外市场上针对火电机组的各种主流运行优化产品的功能特点和应用情况,分析了国外引进产品和国内自主研发产品在中国当前市场环境下各自的优势和劣势。介绍了当前运行优化系统在国内电站机组的应用现状,阐述了国内外运行优化系统在实际应用中存在的问题,并提出了相应的改进意见。对机组运行优化系统的未来发展进行了展望,指出机组运行优化系统将利用先进技术设备和信息平台,与电站管理紧密结合,在日益规范的市场中不断发展完善,为提高电站经济性发挥更大的作用。 相似文献
12.
Combined shape and sizing optimization of truss structures 总被引:1,自引:0,他引:1
In this paper, an evolutionary optimization method is presented for weight minimum problem of a 3-dimensional truss structure
in terms of nodal coordinates and element cross-sectional areas. The structure is subject to stress, local buckling and displacement
constraints. Two types of design variables with different natures are optimized separately: (1) a fully stressed design (FSD)
and scaling techniques are applied to sizing variables and (2) the evolutionary node shift method is applied to shape variables.
Alternating procedure is utilized to couple the two types of variables and to combine the results. The optimum solution is
achieved gradually from the initial configuration design. Two typical truss structures are examined to illustrate the validity
of the method.
Received: 22 October 2001 / Accepted: 04 June 2002
This research work is supported by the National Natural Science Foundation of China under the guarantees no. 10072050 and
10172072, respectively. 相似文献
13.
Damiana Chinese Antonella Meneghetti Gioacchino Nardin Patrizia Simeoni 《国际能源研究杂志》2007,31(9):829-848
A mixed integer linear programming model combined with a more traditional design by scenarios is proposed to optimize facilities size and operation mode of a municipal energy system involving significant civil centres and a hospital. Moving from the need of a new heat and power station for the local hospital due to the construction of new pavilions, the opportunity of involving other centres in the neighbourhood in a distributed cogeneration system is analysed, increasing system complexity step by step. Smaller cogeneration units tailored to hospital needs are rewarding ventures with relatively low risks but, in a country whose traditional power generation systems heavily rely on fossil fuels and where energy policy and market conditions can make it profitable to sell surplus power, district heating systems foster the installation of larger cogenerators and lead thereby to higher profits and to better performance as for primary energy savings and greenhouse gases emission reduction. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
14.
15.
Evan E. Anderson 《Information Systems》1988,13(4):327-333
Many organizations, best illustrated by libraries, have access to hundreds of databases possessing varying degrees of complimentary and overlapping records. While users may receive positive marginal benefits from data duplications, all databases and their services cannot be supported because of resource limitations. This paper attempts to conceptualize the problem of database collection in an environment of multiple databases, with differential content and performance characteristics, diverse users, and limited resources. It defines the database collection problem as a constrained zero-one integer programming problem and solves for the optimal combination or union of databases. Several extensions are shown, where special conditions are imposed on the relationships between databases and/or their availability. 相似文献
16.
论述了重构轮式工程机械轮边减速器优化设计数学模型的必要性,给出了精确化的目标函数,全面化和准确化的设计变量、基于并行设计的约束条件;介绍了对优化解适用性评价的方法和手段。巧妙地解决了优化解中离散变量的圆整问题,提供了基于MATLAB的求解反渐开线函数的M文件。 相似文献
17.
18.
19.
In this study, crisp and fuzzy multiple-goal optimization approaches are respectively introduced to design an optimal biocompatible solvent to a two-stage extractive fermentation with cell recycling for ethanol production. When designing a biocompatible solvent for the extractive fermentation process, many issues, such as extractive efficiency, conversion, amount of solvent utilized and so on, have to be considered. An interactive multiple-goal design procedure is introduced to determine a trade-off result in order to satisfy such contradicted goals. Both approaches could be iterated to solve the interactive multiple-goal design problem in order to yield a trade-off result. However, the crisp optimization design is a tedious task that requires the designer to provide various pairs of the upper bounds for the design problem to obtain the corresponding solution. The fuzzy optimization approach is able to be trade-off several goals simultaneously and to yield the overall satisfactory grade for the product/process design problem. 相似文献
20.
分析实现永州电力通信交换网集中操作和维护的必要性,介绍了实现程控交换机远程操作和维护的两种方式,总结在实践过程中所得到的经验和教训。 相似文献