全文获取类型
收费全文 | 62502篇 |
免费 | 8270篇 |
国内免费 | 6308篇 |
专业分类
电工技术 | 6009篇 |
技术理论 | 9篇 |
综合类 | 6811篇 |
化学工业 | 1451篇 |
金属工艺 | 740篇 |
机械仪表 | 3951篇 |
建筑科学 | 2342篇 |
矿业工程 | 1594篇 |
能源动力 | 826篇 |
轻工业 | 751篇 |
水利工程 | 1398篇 |
石油天然气 | 2935篇 |
武器工业 | 835篇 |
无线电 | 9652篇 |
一般工业技术 | 3377篇 |
冶金工业 | 1106篇 |
原子能技术 | 744篇 |
自动化技术 | 32549篇 |
出版年
2024年 | 351篇 |
2023年 | 936篇 |
2022年 | 1860篇 |
2021年 | 2279篇 |
2020年 | 2440篇 |
2019年 | 1960篇 |
2018年 | 1766篇 |
2017年 | 2173篇 |
2016年 | 2410篇 |
2015年 | 2738篇 |
2014年 | 4293篇 |
2013年 | 3907篇 |
2012年 | 4623篇 |
2011年 | 4987篇 |
2010年 | 3875篇 |
2009年 | 3862篇 |
2008年 | 4304篇 |
2007年 | 4798篇 |
2006年 | 4052篇 |
2005年 | 3647篇 |
2004年 | 3130篇 |
2003年 | 2637篇 |
2002年 | 2008篇 |
2001年 | 1535篇 |
2000年 | 1311篇 |
1999年 | 938篇 |
1998年 | 724篇 |
1997年 | 616篇 |
1996年 | 507篇 |
1995年 | 460篇 |
1994年 | 357篇 |
1993年 | 263篇 |
1992年 | 183篇 |
1991年 | 190篇 |
1990年 | 140篇 |
1989年 | 111篇 |
1988年 | 87篇 |
1987年 | 74篇 |
1986年 | 59篇 |
1985年 | 88篇 |
1984年 | 62篇 |
1983年 | 75篇 |
1982年 | 60篇 |
1981年 | 38篇 |
1980年 | 20篇 |
1979年 | 34篇 |
1978年 | 12篇 |
1977年 | 20篇 |
1976年 | 13篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
本文以云杉八齿小蠹Ips typographus Linnaeus为例,经标本选取,观察虫体整体形态,绘制整体结构草图,电子显微镜观察局部、得到局部数字图像,分别建立虫体每一部分的高精度细节。把模型每部分拼装在一起组成整体模型,构建出了云杉八齿小蠹三维虚拟昆虫数字化模型。 相似文献
3.
5.
An engineered variant of the yeast Pichia pastoris was used to produce the potential malaria vaccine D1M1. This paper describes the implementation of an expanded bed adsorption chromatography step into a sequential cultivation process of the yeast in order to link protein expression, cell release, and product capture of the secreted protein in a fully automated plant. The process is operated with a semi-continuous strategy for an integrated production. Process improvements have been achieved using design of experiments. Resulting purities of product achieved up to 87% with recoveries of 51% in a single downstream operation. Furthermore, a multivariate analysis of historical batch data was used to develop a golden batch model for process monitoring. 相似文献
6.
7.
大坝运行监测易受自然环境和监测条件影响,存在时间和空间上的变异性,监测数据具有不确定性。以云理论的随机性和不确定性分析方法为基础,并与空间数据辐射思想相结合,建立了云滴概率密度分布估计模型,然后导出云概率密度分布函数,依据样本监测数据推求母体空间数据的分布特征,并设计了基于逆向云算法云变换的计算程序。分析陆浑水库1979~1999年测压管监测数据和位移变形数据的云概率密度分布特征和云数字特征,得出了20 a来大坝的数据分布特征和运行状态。监测数据分析结果表明,云概率密度分布估计不仅能有效合理地分析大坝的运行状态,而且能够依据云数字特征来判断监测状态和监测环境的异常变化。
相似文献
8.
9.
根据某面板堆石坝施工期、蓄水初期以及几年来的沉降观测资料,对坝体填筑材料计算参数进行反馈分析,得出了能够反映坝体实际变形的弹塑性应力变形计算参数,有利于今后建立大坝变形预报模型,更准确地把握大坝实时运行状态。 相似文献
10.
Depending on whether bidirectional links or unidirectional links are used for communications, the network topology under a
given range assignment is either an undirected graph referred to as the bidirectional topology, or a directed graph referred
to as the unidirectional topology. The Min-Power Bidirectional (resp., Unidirectional) k-Node Connectivity problem seeks a range assignment of minimum total power subject to the constraint that the produced bidirectional
(resp. unidirectional) topology is k-vertex connected. Similarly, the Min-Power Bidirectional (resp., Unidirectional) k-Edge Connectivity problem seeks a range assignment of minimum total power subject to the constraint the produced bidirectional
(resp., unidirectional) topology is k-edge connected.
The Min-Power Bidirectional Biconnectivity problem and the Min-Power Bidirectional Edge-Biconnectivity problem have been studied
by Lloyd et al. [23]. They show that range assignment based the approximation algorithm of Khuller and Raghavachari [18],
which we refer to as Algorithm KR, has an approximation ratio of at most 2(2 – 2/n)(2 + 1/n) for Min-Power Bidirectional Biconnectivity, and range assignment based on the approximation algorithm of Khuller and Vishkin [19],
which we refer to as Algorithm KV, has an approximation ratio of at most 8(1 – 1/n) for Min-Power Bidirectional Edge-Biconnectivity.
In this paper, we first establish the NP-hardness of Min-Power Bidirectional (Edge-) Biconnectivity. Then we show that Algorithm KR has an approximation ratio of at most 4 for both Min-Power Bidirectional Biconnectivity and Min-Power Unidirectional Biconnectivity,
and Algorithm KV has an approximation ratio of at most 2k for both Min-Power Bidirectional k-Edge Connectivity and Min-Power Unidirectional k-Edge Connectivity. We also propose a new simple constant-approximation algorithm for both Min-Power Bidirectional Biconnectivity
and Min-Power Unidirectional Biconnectivity. This new algorithm applies only to Euclidean instances, but is best suited for
distributed implementation.
A preliminary version of this work appeared in the proceedings of the 2nd International Conference on AD-HOC Network and Wireless
(Adhoc-Now 2003).
Research performed in part while visiting the Max-Plank-Institut fur Informatik.
Gruia Calinescu is an Assistant Professor of Computer Science at the Illinois Institute of Technology since 2000. He held postdoc or visiting
researcher positions at DIMACS, University of Waterloo, and Max-Plank Institut fur Informatik. Gruia has a Diploma from University
of Bucharest and a Ph.D. from Georgia Insitute of Technology. His research interests are in the area of algorithms.
Peng-Jun Wan has joined the Computer Science Department at Illinois Institute of Technology in 1997 and has been an Associate Professor
since 2004. He received his Ph.D. in Computer Science from University of Minnesota in 1997, M.S. in Operations Research and
Control Theory from Chinese Academy of Science in 1993, and B.S. in Applied Mathematics from Tsinghua University in 1990.
His research interests include optical networks and wireless networks. 相似文献