全文获取类型
收费全文 | 14578篇 |
免费 | 2062篇 |
国内免费 | 1360篇 |
专业分类
电工技术 | 635篇 |
技术理论 | 5篇 |
综合类 | 1213篇 |
化学工业 | 1482篇 |
金属工艺 | 1136篇 |
机械仪表 | 675篇 |
建筑科学 | 905篇 |
矿业工程 | 488篇 |
能源动力 | 2111篇 |
轻工业 | 320篇 |
水利工程 | 666篇 |
石油天然气 | 1479篇 |
武器工业 | 69篇 |
无线电 | 1152篇 |
一般工业技术 | 1993篇 |
冶金工业 | 589篇 |
原子能技术 | 72篇 |
自动化技术 | 3010篇 |
出版年
2024年 | 64篇 |
2023年 | 714篇 |
2022年 | 1000篇 |
2021年 | 965篇 |
2020年 | 989篇 |
2019年 | 892篇 |
2018年 | 743篇 |
2017年 | 751篇 |
2016年 | 635篇 |
2015年 | 634篇 |
2014年 | 785篇 |
2013年 | 843篇 |
2012年 | 918篇 |
2011年 | 1069篇 |
2010年 | 818篇 |
2009年 | 766篇 |
2008年 | 701篇 |
2007年 | 776篇 |
2006年 | 740篇 |
2005年 | 625篇 |
2004年 | 499篇 |
2003年 | 451篇 |
2002年 | 359篇 |
2001年 | 245篇 |
2000年 | 211篇 |
1999年 | 170篇 |
1998年 | 113篇 |
1997年 | 95篇 |
1996年 | 86篇 |
1995年 | 58篇 |
1994年 | 74篇 |
1993年 | 29篇 |
1992年 | 28篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 24篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1970年 | 2篇 |
1959年 | 2篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
62.
63.
Like any other domain of human activity, psychology has its fads and fashions. One consequence of fads is an overconcentration of resources on specific problems or approaches, which leaves other important problems or approaches (holes) underappreciated and understudied. This article is primarily about different factors (such as negativity bias, polarization of positions, focus on internal causes of behavior, dedication to a narrow view of what science is) that result in holes and about explorations of some of these holes that have interested the author. Psychologists should look more in the holes left behind by current enthusiasms. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
64.
Reorganisation and evolution of class hierarchies is important for object-oriented system development and has received considerable attention in the literature. The contributions of this paper are: (1) a formal study of a set of extension relations and transformations on class hierarchies; (2) a presentation of a small set of primitive transformations which form a minimal and complete basis for the extension relations; and (3) an analysis of the impact of these transformations at the object level.The study leads to a better understanding of evolution and reuse of object-oriented software and class hierarchies. It also provides a terminology and a means of classification for design reuse. The theory presented in this paper is based on the Demeter data model, which gives a concise mathematical foundation for classes and their inheritance and part-of relationships. Parts of the theory have been implemented in the Demeter System
TM
C++, a CASE tool for object-oriented design and programming. 相似文献
65.
The present paper demonstrates the applicability of population based search optimization method, namely, Differential Evolution
(DE) to a case study of Mahi Bajaj Sagar Project (MBSP), India. Ten different strategies of DE are employed to assess the
ability of DE for solving higher dimensional problems as an alternative methodology for irrigation planning. The parameters
considered in DE are population size, crossover constant and weighting factor. Linear Programming (LP) is utilized as a comparative
approach to assess the ability of DE. Comparison of results of LP and the 10 DE strategies for the given parameters indicated
that both the results are comparable even for high dimensional problems. Extensive sensitivity analysis studies, performed
for 3,600 combinations of above parameters for the 10 DE strategies suggested that DE/rand-to-best/1/bin strategy is the best
strategy giving maximum benefits taking minimum CPU time. It is concluded that DE can be utilized for efficient planning of
any irrigation system with suitable modifications. 相似文献
66.
X-ray microtomography: Application to microstructure analysis of a cementitious material during leaching process 总被引:4,自引:0,他引:4
Leaching of cementitious materials leads to an increase in porosity, which has important consequences on transport and mechanical properties. The present study outlines the characterization of microstructural evolution in a mortar subjected to a chemical attack, by means of a powerful non-intrusive experimental method, namely synchrotron X-ray computed microtomography. This innovative method is used to measure the variation of porosity in a leached mortar. Having described the effects of leaching in mortar (influences on microstructure and on mechanical properties), we present the accelerated leaching process and the microtomographic analysis that have been used to monitor it. We then investigate the capacity of this method to quantify the evolution of porosity during the leaching process. The method is validated by comparison of the results obtained with data available in the literature. 相似文献
67.
煤层气的富集与储层特征密切相关,并受地质条件的制约。在详细研究煤储层特征及煤层气富集机制的基础上,对沁水盆地北端煤层气的开发前景进行了初步评价。煤岩、煤质、煤体结构及孔渗性、吸附性的观察和测试显示,该区煤层厚度大,热演化程度高,局部发育构造煤,裂隙较发育,吸附性能力强,含气量高,含气饱和度偏低,适合煤层气的开发。该区煤层气的富集主要受控于热演化史和埋藏史。在区域变质的背景上,叠加了岩浆热变质作用,生气强度大。另外,煤层的埋深、顶底板封闭性及水文地质条件都会影响煤层含气量的大小,煤层气富集是多因素有效配置的结果。 相似文献
68.
在分析本钢物资计量信息网络系统升级扩展项目需求及技术方案的基础上,重点阐述了系统的设计和实现技术,详细介绍了基于DES算法的操作权限控制、系统数据库与本地数据库业务词典的异步维护等关键技术,解决了ERP下抛数据编码体系与系统数据库数据编码体系不一致的问题。系统设计采用J2EE架构B/S和C/S混合模式,以Oracle 9i为数据库服务器,Tomcat提供应用服务。 相似文献
69.
江汉平原印支期以来的盆山耦合关系及下古生界油气响应 总被引:5,自引:1,他引:4
利用构造地质学和油气系统理论,以盆地构造-沉积分析技术为手段,研究了印支期以来江汉平原与周缘造山带的耦合关系,探讨了江汉平原的构造演化及其对油气成藏的控制作用。印支期以来江汉平原及周缘经历了挤压、拉张、挤压3次大的构造应力场的转换,使古生代海相碳酸盐岩沉积为主的盆地具有改造盆地的特点;一方面强烈的抬升、剥蚀使早期聚集的油气经历改造和再分配、再聚集过程,另一方面燕山期构造活动使逆冲推覆构造成为该区重要勘探领域。综合分析表明,位于台、盆转换带的宜昌-珂理-簰州区带是目前江汉平原及周缘下古生界油气勘探的有利地区。 相似文献
70.
Fumio Negoro 《Knowledge》2003,16(7-8):383-397
The purpose of our study is to build up relationships between requirement and source programs with our originally thought-out rules. When other rules to be derived from these original rules are applied to software development, even a single instruction in a programming language could be determined, and the program would satisfy the requirement. More specifically speaking, these rules will turn into a formula or a prototype of software programs. Hence, when the variables in the requirement are placed in the formula, we can get a required program in an automatic way. 相似文献