全文获取类型
收费全文 | 12026篇 |
免费 | 1243篇 |
国内免费 | 962篇 |
专业分类
电工技术 | 1300篇 |
综合类 | 925篇 |
化学工业 | 1256篇 |
金属工艺 | 597篇 |
机械仪表 | 1090篇 |
建筑科学 | 846篇 |
矿业工程 | 333篇 |
能源动力 | 354篇 |
轻工业 | 358篇 |
水利工程 | 374篇 |
石油天然气 | 874篇 |
武器工业 | 459篇 |
无线电 | 1162篇 |
一般工业技术 | 2249篇 |
冶金工业 | 479篇 |
原子能技术 | 325篇 |
自动化技术 | 1250篇 |
出版年
2024年 | 47篇 |
2023年 | 185篇 |
2022年 | 325篇 |
2021年 | 358篇 |
2020年 | 435篇 |
2019年 | 404篇 |
2018年 | 396篇 |
2017年 | 472篇 |
2016年 | 533篇 |
2015年 | 595篇 |
2014年 | 731篇 |
2013年 | 895篇 |
2012年 | 793篇 |
2011年 | 951篇 |
2010年 | 715篇 |
2009年 | 759篇 |
2008年 | 680篇 |
2007年 | 711篇 |
2006年 | 702篇 |
2005年 | 560篇 |
2004年 | 478篇 |
2003年 | 402篇 |
2002年 | 329篇 |
2001年 | 274篇 |
2000年 | 269篇 |
1999年 | 189篇 |
1998年 | 166篇 |
1997年 | 148篇 |
1996年 | 124篇 |
1995年 | 113篇 |
1994年 | 113篇 |
1993年 | 66篇 |
1992年 | 55篇 |
1991年 | 51篇 |
1990年 | 46篇 |
1989年 | 35篇 |
1988年 | 27篇 |
1987年 | 22篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1966年 | 4篇 |
1963年 | 4篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
91.
Reiner M. W. Reising Bahram M. Shahrooz Victor J. Hunt Andy R. Neumann Arthur J. Helmicki 《Canadian Metallurgical Quarterly》2004,8(3):265-274
In an effort to assess the constructability and performance of bridges with fiber-reinforced polymer (FRP) composite decks, the short-term and long-term responses of a 207 m, five-span bridge retrofitted with four different FRP panel systems were monitored. The overall aspects of the panel systems, connection details, and construction techniques are presented prior to presentation of the observed and measured responses. Key design parameters (impact factors, girder distribution factors, and level of composite action) for FRP and reinforced concrete decks are evaluated. This paper demonstrates that FRP replacement decks are a viable alternative to reinforced concrete decks and identifies the differences in performances of various FRP deck systems. Two of the FRP panel systems were found to perform considerably better than the other deck systems. Issues that may reduce the service life of FRP deck systems are presented and discussed. 相似文献
92.
水库建成蓄水后,库底土壤中氮、磷的浸出会对库水水质会产生一定影响。本文以南水北调中线工程的调蓄水库———瀑河水库为例,在现场调查基础上,使用蒸馏水和模拟水分别进行模拟实验,分析研究了土壤中氮、磷浸出对库水中总氮、总磷浓度的影响。实验结果表明,总氮、总磷的浓度均发生一定程度的变化,且模拟水中的浓度变化小于蒸馏水中的变化;但从整体趋势看,源于土壤的含量较低,对库水水质未产生明显不良影响。 相似文献
93.
This paper represents a first attempt at a systematic study of sensitivity analysis for scheduling problems. Because schedules contain both combinatorial and temporal structures, scheduling problems present unique issues for sensitivity analysis. Some of the issues that we discuss have not been considered before. Others, while studied before, have not been explored in the context of scheduling. The applicability of these issues is illustrated using well-known scheduling models. We provide fast methods to determine when a previously optimal schedule remains optimal. Other methods restore an optimal schedule after a parameter change. The value of studying the sensitivity of an optimal sequence instead of the sensitivity of an optimal schedule is demonstrated. We show that, for some problems, sensitivity analysis results depend on the positions of jobs with changed parameters. We identify scheduling problems where performing additional or different computations during optimization facilitates sensitivity analysis. To improve the robustness of an optimal schedule, selection among multiple optimal schedules is considered. We discuss which types of sensitivity analysis questions are intractable because the scheduling problem itself is intractable. We also study how heuristic error bounds vary when the data of a scheduling problem is continuously modified. Although we focus on scheduling problems, several of the issues we discuss and our classification scheme can be extended to other optimization problems. 相似文献
94.
Solution techniques for Markov decision problems rely on exact knowledge of the transition rates, which may be difficult or impossible to obtain. In this paper, we consider Markov decision problems with uncertain transition rates represented as compact sets. We first consider the problem of sensitivity analysis where the aim is to quantify the range of uncertainty of the average per‐unit‐time reward given the range of uncertainty of the transition rates. We then develop solution techniques for the problem of obtaining the max‐min optimal policy, which maximizes the worst‐case average per‐unit‐time reward. In each of these problems, we distinguish between systems that can have their transition rates chosen independently and those where the transition rates depend on each other. Our solution techniques are applicable to Markov decision processes with fixed but unknown transition rates and to those with time‐varying transition rates. 相似文献
95.
贫化铀的环境污染影响及其对人体健康的危害 总被引:5,自引:0,他引:5
贫化铀是铀富集过程中产生的副产品。由于其独特的物理特性,被广泛开发利用到民用和军事用途。“海湾战争综合症”和“巴尔干综合症”引起了人们对贫铀使用后,对环境污染的影响和对人体健康效应研究的重视。贫铀的危害来自化学毒性和放射性毒性两个方面。由于贫铀的放射性比活度低,而且主要发射α粒子,所以来自贫铀的辐射伤害主要是吸入贫铀气溶胶后对肺和其他器官较长时间的内照射。 相似文献
96.
《Journal of Nuclear Science and Technology》2013,50(11):1164-1173
Sensitivity analysis of model output is relevant to a number of practices, including verification of models and computer code quality assurance. It deals with the identification of influential model parameters, especially in complex models implemented in computer programs with many uncertain input variables. In a recent article a new method for sensitivity analysis, named HIM* based on a rank transformation of the uncertainty importance measure suggested by Hora and Iman was proved very powerful for performing automated sensitivity analysis of model output, even in presence of model non-monotonicity. The same was not true of other widely used non-parametric techniques such as standardized rank regression coefficients. A drawback of the HIM* method was the large dimension of the stochastic sample needed for its estimation, which made HIM* impracticable for systems with large number of uncertain parameters. In the present note a more effective sampling algorithm, based on Sobol's quasirandom generator is coupled with HIM*, thereby greatly reducing the sample size needed for an effective identification of influential variables. The performances of the new technique are investigated for two different benchmarks. 相似文献
97.
98.
在不同偏置条件下,对基于互补双极工艺生产的电流反馈运算放大器(CFA)进行了高低剂量率下的电离辐射效应研究。研究发现,在不同偏置条件下,器件损伤差异明显。在零偏条件下,器件在低剂量率下损伤显著增强,表现为低剂量率损伤增强效应(ELDRS);在小工作电压下辐照时,器件损伤较小,且不同剂量率之间损伤差异不明显;而在大工作电压下辐照时,器件在高剂量率下的损伤明显大于低剂量率下的损伤,在随后的室温退火中,又恢复到与低剂量率损伤相当的程度,表现为时间相关效应。结果表明,双极器件是否具有ELDRS效应与实验偏置条件有重要关系。 相似文献
99.
100.
为研究PMOSFET的低剂量率辐射损伤增强效应,本文对4007电路中PMOSFET在不同剂量率、不同偏置条件下的辐射响应特性及高剂量率辐照后不同温度下的退火效应进行了讨论。实验结果表明:相比高剂量率,低剂量率辐照时PMOSFET阈值电压漂移更明显,此种PMOSFET具有低剂量率辐射损伤增强效应;高剂量率辐照后进行室温退火时,由于界面陷阱电荷的影响,PMOSFET阈值电压继续负向漂移,退火温度越高,阈值电压回漂越明显;辐照时,零偏置条件下器件阈值电压的漂移较负偏置时的大,认为是最劣偏置。 相似文献