全文获取类型
收费全文 | 79267篇 |
免费 | 6591篇 |
国内免费 | 3428篇 |
专业分类
电工技术 | 2926篇 |
技术理论 | 5篇 |
综合类 | 6010篇 |
化学工业 | 17717篇 |
金属工艺 | 7239篇 |
机械仪表 | 5209篇 |
建筑科学 | 4857篇 |
矿业工程 | 2932篇 |
能源动力 | 1864篇 |
轻工业 | 7541篇 |
水利工程 | 1358篇 |
石油天然气 | 3736篇 |
武器工业 | 681篇 |
无线电 | 4422篇 |
一般工业技术 | 7034篇 |
冶金工业 | 6354篇 |
原子能技术 | 459篇 |
自动化技术 | 8942篇 |
出版年
2024年 | 341篇 |
2023年 | 937篇 |
2022年 | 1769篇 |
2021年 | 2191篇 |
2020年 | 2498篇 |
2019年 | 1899篇 |
2018年 | 1649篇 |
2017年 | 2076篇 |
2016年 | 2524篇 |
2015年 | 2708篇 |
2014年 | 4741篇 |
2013年 | 4974篇 |
2012年 | 5782篇 |
2011年 | 6027篇 |
2010年 | 4393篇 |
2009年 | 4504篇 |
2008年 | 3880篇 |
2007年 | 5068篇 |
2006年 | 4864篇 |
2005年 | 4262篇 |
2004年 | 3617篇 |
2003年 | 3270篇 |
2002年 | 2743篇 |
2001年 | 2406篇 |
2000年 | 1997篇 |
1999年 | 1672篇 |
1998年 | 1279篇 |
1997年 | 990篇 |
1996年 | 941篇 |
1995年 | 708篇 |
1994年 | 605篇 |
1993年 | 413篇 |
1992年 | 359篇 |
1991年 | 279篇 |
1990年 | 185篇 |
1989年 | 161篇 |
1988年 | 116篇 |
1987年 | 84篇 |
1986年 | 59篇 |
1985年 | 40篇 |
1984年 | 43篇 |
1983年 | 33篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1977年 | 14篇 |
1961年 | 8篇 |
1959年 | 8篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献
4.
基于扩展分形和CFAR特征融合的SAR图像目标识别 总被引:3,自引:0,他引:3
研究了多信息融合技术在SAR图像目标识别中的应用。将扩展分形特征(Extended Fractal)与双参数恒虚警特征(Double Parameter CFAR)形成的多信息进行融合处理。运用Dempster-Shafer证据理论,在决策层对SAR图像中的像素进行识别分类。实验结果表明通过融合对像素分类的准确性明显好于单特征的检测结果,减少了虚警概率,提高了系统的识别能力。 相似文献
5.
对己二腈工业反应器提出了两釜串联带回流的模型,通过模拟计算得出模型的级间返混系数 f=6的结论。该模型能较好地预测工业反应器中物料组分浓度变化和气、液两相的流动特性;指出了现工业反应器的鼓泡中和段体积偏小是造成己二酸浓度偏高的关键;提出了可以通过增加串连一个鼓泡预反应段的改造方案,能有效地降低己二酸的浓度,从7%降至4%左右,从而能较好地减缓腐蚀和结焦。 相似文献
6.
实体造型中的几何约束 总被引:5,自引:0,他引:5
实体造型是一个基于约束的过程,完成从功能约束到几何约束、再到代数约束的转化而得到实体模型。本文讨论了几何约束的层次性及其表示,并且对几何约束同设计意图的关系进行了研究,提出了基于CSG/GCG/B-rep的模型表示。 相似文献
7.
Takeshi Nakajo 《Quality and Reliability Engineering International》1993,9(2):111-119
Work system improvements are implemented in various manufacturing processes to prevent problems caused by human errors. However, they are almost always applied to problems which have already occurred. This paper examines a method of identifying latent human errors existing within the work systems beforehand. A procedure for applying failure mode and effect analysis to this identification problem was defined based on over 1000 empirical errors: a work system decomposition criterion and fundamental error modes for listing latent human errors, and then applied to three practical manufacturing processes in order to evaluate its effectiveness. 相似文献
8.
The evaluation of microcomputer programs: an area of debate 总被引:1,自引:0,他引:1
V. M. Johnston 《Journal of Computer Assisted Learning》1987,3(1):40-50
9.
Reports an error in "Interactive use of lexical information in speech perception" by Cynthia M. Connine and Charles Clifton (Journal of Experimental Psychology: Human Perception and Performance, 1987[May], Vol 13[2], 291-299). In the aforementioned article, Figures 1 and 2 were inadvertently transposed. The figure on p. 294 is actually Figure 2, and the figure on p. 296 is actually Figure 1. The captions are correct as they stand. (The following abstract of the original article appeared in record 1987-23984-001.) Two experiments are reported that demonstrate contextual effects on identification of speech voicing continua. Experiment 1 demonstrated the infuence of lexical knowledge on identification of ambiguous tokens from word–nonword and nonword–word continua. Reaction times for word and nonword responses showed a word advantage only for ambiguous stimulus tokens (at the category boundary); no word advantage was found for clear stimuli (at the continua endpoints). Experiment 2 demonstrated an effect of a postperceptual variable, monetary payoff, on nonword–nonword continua. Identification responses were influenced by monetary payoff, but reaction times for bias-consistent and bias-inconsistent responses did not differ at the category boundary. An advantage for bias-consistent responses was evident at the continua endpoints. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
J.A. Giroto A.C.S.C. Teixeira C.A.O. Nascimento R. Guardani 《Chemical Engineering and Processing: Process Intensification》2008,47(12):2361-2369
This paper presents the results of experiments carried out in a laboratory-scale photochemical reactor on the photodegradation of different polymers in aqueous solutions by the photo-Fenton process. Solutions of three polymers, polyethyleneglicol (PEG), polyacrylamide (PAM), and polyvinylpyrrolidone (PVP), were tested under different conditions. The reaction progress was evaluated by sampling and analyzing the total organic carbon concentration in solution (TOC) along the reaction time. The behavior of the different polymers is discussed, based on the evolution of the TOC–time curves. Under specific reaction conditions, the formation and coalescence of solid particles was visually observed. Solids formation occurred simultaneously to a sharp decrease in the TOC of the liquid phase. This may be favorable for the treatment of industrial wastewater containing polymers, since the photodegradation process can be coupled with solid separation systems, which may reduce the treatment cost. 相似文献