全文获取类型
收费全文 | 20188篇 |
免费 | 1525篇 |
国内免费 | 522篇 |
专业分类
电工技术 | 647篇 |
技术理论 | 1篇 |
综合类 | 1734篇 |
化学工业 | 3938篇 |
金属工艺 | 471篇 |
机械仪表 | 751篇 |
建筑科学 | 1817篇 |
矿业工程 | 417篇 |
能源动力 | 378篇 |
轻工业 | 2077篇 |
水利工程 | 267篇 |
石油天然气 | 319篇 |
武器工业 | 73篇 |
无线电 | 905篇 |
一般工业技术 | 3309篇 |
冶金工业 | 917篇 |
原子能技术 | 138篇 |
自动化技术 | 4076篇 |
出版年
2024年 | 76篇 |
2023年 | 271篇 |
2022年 | 350篇 |
2021年 | 573篇 |
2020年 | 573篇 |
2019年 | 585篇 |
2018年 | 544篇 |
2017年 | 650篇 |
2016年 | 725篇 |
2015年 | 732篇 |
2014年 | 1222篇 |
2013年 | 1251篇 |
2012年 | 1434篇 |
2011年 | 1639篇 |
2010年 | 1242篇 |
2009年 | 1246篇 |
2008年 | 1022篇 |
2007年 | 1227篇 |
2006年 | 1024篇 |
2005年 | 834篇 |
2004年 | 729篇 |
2003年 | 634篇 |
2002年 | 541篇 |
2001年 | 412篇 |
2000年 | 338篇 |
1999年 | 318篇 |
1998年 | 275篇 |
1997年 | 229篇 |
1996年 | 168篇 |
1995年 | 184篇 |
1994年 | 120篇 |
1993年 | 112篇 |
1992年 | 85篇 |
1991年 | 65篇 |
1990年 | 67篇 |
1989年 | 76篇 |
1988年 | 77篇 |
1987年 | 46篇 |
1986年 | 43篇 |
1985年 | 58篇 |
1984年 | 73篇 |
1983年 | 89篇 |
1982年 | 90篇 |
1981年 | 29篇 |
1980年 | 30篇 |
1979年 | 21篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1959年 | 5篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
本文介绍溶胶-凝胶法制备均匀PbZr-Ti-B-Si凝胶玻璃,并通过适当热处理在凝胶玻璃中原位生长Pb(Zr;Ti)O3微晶的新工艺·利用IR谱考察了凝胶玻璃中的元素键合结构随温度的变化.结合热分析和XRD;SEM技术,研究了Pb(Zr,Ti)O3微晶在凝胶玻璃中的生长过程及该材料的结构特点.发现Pb2(Zr,Ti)2O6+x立方焦绿石介稳过渡相的纳米微晶首先出现于该体系中,并在更高的温度下先后完全转变成三方和四方Pb(Zr,Ti)O3钙钛矿相.电子显微观察结果表明,该工艺制备的Ph(Zr;Ti)O3玻璃陶瓷具有均匀的细晶结构. 相似文献
92.
Gu Junzhong 《计算机科学技术学报》1993,8(4):3-20
In object-oriented database systems(OOBSs),the traditional transaction models are no longer suitable because of the difference between the object-oriented data model(OODM)and the conventional data models(e.g.relational data model).In this paper,transction models for advanced database applications are reviewed and their shortcomings are analyzed.Exchangeability of operations is proposed instead of commuativity and recoverability for using more semantics in transaction management.As a result,an object-oriented transaction model(in short,OOTM)is presented.It is not modeled for some special application,but directly based on object-oriented paradigms.A transaction is regarded as an interpretation of a metho.Each transaction(even subtransactions)keeps relative ACID(Atomicity,Consistency,Isolation,Durability)properties,therefore the special problems appearing in OOBSs such as“long transactions”,“visibility of inconsistent database state”can be solved. 相似文献
93.
Mike Schofield 《Quality and Reliability Engineering International》1992,8(6):549-555
Because of the growing demand for increasingly complex computer-based systems there is now an urgent need to provide tools to assist during the design of such systems. Formal specifications and formal methods provide such assistance but their widespread adoption has been hindered by the so-called ‘math fear’ and the perception that the tools are too difficult, too time consuming and too costly to use in a commercial environment. The aim of this article is to dispel the mystery surrounding the topic and to explain what formal methods are, how and why they are used, the benefits that accrue and why the technology should be accepted on a broader front. The application of formal methods to the design of computer-based systems will be discussed without resorting to jargon or mathematics. The discussion will concentrate more on the software content of systems but the arguments apply equally well to hardware. Some of the available tools will also be introduced. 相似文献
94.
三维结构可靠度对随机变量的敏感性研究 总被引:13,自引:2,他引:11
本文基于三维随机有限元提出了结构点可靠度、失效模式的可靠度及整个结构体系的可靠度分别对随机变量的"分布参数"和"极限状态方程参数"的敏感性计算方法,并以一典型重力坝为例进行了计算,得出了若干有益的结论。 相似文献
95.
Optical measurements of thermal diffusivity of a material 总被引:2,自引:0,他引:2
The measurement of thermal diffusivity of a material (in particular, a thin film) is important for various reasons, e.g., to predict the heat transfer in the solid subjected to a thermal process, to monitor surface composition or morphology, or to detect invisible subsurface defects like delaminations. This measurement can be done in a noncontact manner using various photothermal methods. Such methods typically involve pulsed heating of the surface by small amounts using a laser source; the decay of the surface temperature after this pulsed photothermal heating is then probed to provide the thermal diffusivity. Various probing methods have been developed in the literature, including the probing of reflection, refraction, and diffraction from the pulsed heated area, infrared thermal radiometry, and surface deformation. This paper provides an overview of such techniques and some examples of their applications. 相似文献
96.
Contemporary approaches to the certification of measurement provision software are considered in domestic and overseas publications.
Normative documentation is analyzed and a scheme is proposed for certification that takes account of the features of programs
used for metrological purposes.
__________
Translated from Izmeritel’naya Tekhnika, No. 5, pp. 65–68, May, 2007. 相似文献
97.
Teaching-Material Design Center: An ontology-based system for customizing reusable e-materials 总被引:2,自引:1,他引:1
Use of electronic teaching materials (e-material) to support teaching is a trend. e-Material design is therefore an important issue. Currently, most e-material providers offer a package of solutions for different purposes. However, not all teachers and learners need everything from a single package. A preferable alternative is to find useful material from different packages and combine them for a particular course. Currently, most educators collect the material manually, which is time-consuming and may result in missed material. In this paper, we describe a system – the Teaching-Material Design Center, which follows the standard of Sharable Content Object Reference Model – to separate e-material for use as teaching templates and learning objects and to label the material with use of semantic metadata for searching. This system can find existing teaching templates and learning objects for e-material designers and provide a convenient environment for constructing customized e-material for different requirements. We describe the implementation and evaluation of the proposed system for a course. Our system is efficient in finding teaching templates and learning objects and shortening the e-material development process. 相似文献
98.
99.
碳酸二甲酯的市场需求和生产技术进展 总被引:8,自引:1,他引:7
介绍了碳酸二甲酯的价格、生产情况及国内外市场需求 ,指出碳酸二甲酯在我国具有极大的市场潜力。综述了生产碳酸二甲酯的三类主要方法 ,介绍了光气法、酯交换法和氧化羰基化法的各种具体方法及尚未实现工业化仍在研究中的其他方法。并对各种工业化的生产方法从技术、经济和清洁性的角度进行了分析 ,指出适合我国采用的工业合成方法是气相氧化羰基化法和甲醇与 CO2 直接合成法 相似文献
100.