全文获取类型
收费全文 | 45631篇 |
免费 | 5376篇 |
国内免费 | 3066篇 |
专业分类
电工技术 | 6415篇 |
技术理论 | 2篇 |
综合类 | 5091篇 |
化学工业 | 3431篇 |
金属工艺 | 854篇 |
机械仪表 | 2489篇 |
建筑科学 | 2624篇 |
矿业工程 | 950篇 |
能源动力 | 1017篇 |
轻工业 | 2326篇 |
水利工程 | 1211篇 |
石油天然气 | 766篇 |
武器工业 | 466篇 |
无线电 | 5657篇 |
一般工业技术 | 4393篇 |
冶金工业 | 1434篇 |
原子能技术 | 226篇 |
自动化技术 | 14721篇 |
出版年
2024年 | 225篇 |
2023年 | 626篇 |
2022年 | 1058篇 |
2021年 | 1324篇 |
2020年 | 1395篇 |
2019年 | 1385篇 |
2018年 | 1276篇 |
2017年 | 1659篇 |
2016年 | 1871篇 |
2015年 | 2067篇 |
2014年 | 3043篇 |
2013年 | 2928篇 |
2012年 | 3689篇 |
2011年 | 3960篇 |
2010年 | 3081篇 |
2009年 | 3163篇 |
2008年 | 2953篇 |
2007年 | 3371篇 |
2006年 | 2749篇 |
2005年 | 2205篇 |
2004年 | 1721篇 |
2003年 | 1470篇 |
2002年 | 1193篇 |
2001年 | 882篇 |
2000年 | 779篇 |
1999年 | 596篇 |
1998年 | 501篇 |
1997年 | 418篇 |
1996年 | 335篇 |
1995年 | 319篇 |
1994年 | 245篇 |
1993年 | 199篇 |
1992年 | 163篇 |
1991年 | 117篇 |
1990年 | 137篇 |
1989年 | 131篇 |
1988年 | 114篇 |
1987年 | 64篇 |
1986年 | 65篇 |
1985年 | 76篇 |
1984年 | 86篇 |
1983年 | 99篇 |
1982年 | 103篇 |
1981年 | 32篇 |
1980年 | 39篇 |
1979年 | 28篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1976年 | 10篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
寻找非构造油气藏的新思路 总被引:3,自引:0,他引:3
目前,一种新的理论体系和研究方法已经形成,并正在发展和逐步完善。那就是层序地层学和油气成藏系统理论的诞生和发展;以及由计算机的快速发展带动起来的地震测井资料的采集、处理、显示和各种地质问题的计算机模拟技术,使得地质学和石油地质学都在朝着从定性到定量,从推测到更科学的预测方向发展。在今后的5~10年中,中国的石油地质家们不仅要注意方法和技术方面的进步,还应当重视在陆相层序地层学和陆相层序中油气成藏机制等基本理论方面的研究。 相似文献
43.
线性时变系统的区间稳定性与鲁棒稳定性 总被引:7,自引:0,他引:7
本文应用向量比较定理研究线性时变系统的区间稳定性和具非线性时变摄动的线性时变系统的鲁棒稳定性,所得的新结果包含文献的一些主要结果作为特例,本文的研究方法说明向量比较方法是分析区间稳定性和鲁棒稳定性的一种自然而有力的工具。 相似文献
44.
The MSMIE protocol [SBC89] allows processors in a distributed system to communicate via shared memory. It was designed to meet the reliability and efficiency needs of applications such as nuclear safety systems. We present a formal model of the MSMIE protocol expressed in the notation CCS. Desirable properties of the protocol are expressed in the modal mu-calculus, an expressive modal logic. We show that the protocol lacks an important liveness property. In actual operation, additional operating constraints are checked to avoid potential problems. We present a modified protocol and show that it possesses the liveness property even without checking operating constraints. We also show how parts of the analysis were automated with the Concurrency Workbench. 相似文献
45.
46.
Annual commercial poplar wood production in Turkey is about 3.6 million cubic meters, half of which comes from hybrid poplar I-214. The poplar plantation areas of Turkey are 70% of the poplar plantation areas of the Near and Middle Eastern countries, and nearly 5% of the world. In this study, unit times of standard operations were investigated in poplar nurseries and plantations in which new mechanical technology was applied and compared with traditional methods. Analyses of unit times were made on 11 treatments for poplar nurseries and nine treatments for poplar plantations; some new methods are also recommended. Mechanization methods based on new technologies give promising results in poplar nurseries and plantations. 相似文献
47.
The general mixed μ problem has been shown to be NP hard, so that the exact solution of the general problem is computationally intractable, except for small problems. In this paper we consider not the general problem, but a particular special case of this problem, the rank one mixed μ problem. We show that for this case the mixed μ problem is equivalent to its upper bound (which is convex), and it can in fact be computed easily (and exactly). This special case is shown to be equivalent to the so-called ‘affine parameter variation’ problem (for a polynomial with perturbed coefficients) which has been examined in detail in the literature, and for which several celebrated ‘Kharitonov-type’ results have been proven. 相似文献
48.
This article is the second of two papers that review the field of spatially sensitive social scientific research into the links between social status and transport disadvantage. The first paper undertook a comprehensive review of the social scientific and transport planning literature to mark the level of development in the field and identify conceptual and methodological issues and constraints in this field of inquiry. The present article supports the advancement of socially and geographically sensitive transport research by opportunities for the development of more sophisticated spatial analytical methodologies. The approach we present is able to account for factors not previously addressed in either social or transport planning research, in particular the temporal dimensions of transport service accessibility. The article articulates the methodology through an empirical case study of socio-spatial transport disadvantage within the Gold Coast City. The article demonstrates that there are important theoretical and practical lessons to be gained for researchers and policy makers in addressing the social dimensions of transport and infrastructure provision. Further, the article argues that an attentiveness to new ways of combining and representing social and transport data-sets can promote policy relevant empirical social inquiry. The article also contributes in a productive way to the empirical knowledge of Australia's sixth-largest metropolitan area, which is often overlooked by urban scholars. 相似文献
49.
Melt index is considered an important quality variable determining product specifications. Reliable prediction of melt index (MI) is crucial in quality control of practical propylene polymerization processes. In this paper a least squares support vector machines (LS‐SVM) soft‐sensor model of propylene polymerization process is developed to infer the MI of polypropylene from other process variables. Considering the use of a SSE cost function without regularization might lead to less robust estimates; the weighted least squares support vector machines (weighted LS‐SVM) approach of propylene polymerization process is further proposed to obtain a robust estimation of melt index. The performance of standard SVM model is taken as a basis of comparison. A detailed comparison research among the standard SVM, LS‐SVM, and weighted LS‐SVM models is carried out. The research results confirm the effectiveness of the presented methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 285–289, 2006 相似文献
50.