全文获取类型
收费全文 | 20793篇 |
免费 | 1263篇 |
国内免费 | 861篇 |
专业分类
电工技术 | 528篇 |
综合类 | 724篇 |
化学工业 | 3205篇 |
金属工艺 | 1345篇 |
机械仪表 | 2576篇 |
建筑科学 | 873篇 |
矿业工程 | 784篇 |
能源动力 | 1148篇 |
轻工业 | 663篇 |
水利工程 | 158篇 |
石油天然气 | 406篇 |
武器工业 | 115篇 |
无线电 | 1268篇 |
一般工业技术 | 1601篇 |
冶金工业 | 1025篇 |
原子能技术 | 156篇 |
自动化技术 | 6342篇 |
出版年
2024年 | 36篇 |
2023年 | 191篇 |
2022年 | 285篇 |
2021年 | 433篇 |
2020年 | 446篇 |
2019年 | 396篇 |
2018年 | 405篇 |
2017年 | 534篇 |
2016年 | 640篇 |
2015年 | 789篇 |
2014年 | 1231篇 |
2013年 | 1444篇 |
2012年 | 1205篇 |
2011年 | 1796篇 |
2010年 | 1058篇 |
2009年 | 1189篇 |
2008年 | 1094篇 |
2007年 | 1321篇 |
2006年 | 1209篇 |
2005年 | 1127篇 |
2004年 | 922篇 |
2003年 | 870篇 |
2002年 | 725篇 |
2001年 | 536篇 |
2000年 | 505篇 |
1999年 | 450篇 |
1998年 | 387篇 |
1997年 | 301篇 |
1996年 | 269篇 |
1995年 | 220篇 |
1994年 | 238篇 |
1993年 | 140篇 |
1992年 | 112篇 |
1991年 | 84篇 |
1990年 | 68篇 |
1989年 | 47篇 |
1988年 | 55篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
本文提出用尿素作为pⅡ调节剂,加快硫酸亚铁单液法调剖剂中亚铁离子在地层温度下的沉淀,增大沉淀率,提高封堵效能。岩芯流动试验结果表明,15%FeSO4.7II 2O/5%尿素调剖剂体系的封堵能力比不含尿素的体系增大近一倍。 相似文献
92.
93.
94.
Muhammad A. Al-ArfajWilliam L. Luyben 《Chemical engineering science》2002,57(5):715-733
This paper considers the design and control of a reactive distillation column in which one reactant is consumed and two products are formed (A?B+C). The volatilities are αB>αA>αC, i.e. the reactant is intermediate boiling between the two products. The metathesis of 2-pentene is considered as the demonstrative example. The column has a single feed of the intermediate boiling reactant. The distillate contains mostly light component and the bottoms mostly heavy.Three designs are considered: the base case (low-conversion/low-pressure), a low-conversion/high-pressure case and a high-conversion/high-pressure case. The base design is obtained from the literature, and the other two steady-state designs are optimized with respect to the total annual cost. All the designs are found to be openloop stable. Five control structures are studied for the base design. Then the best two structures are applied to the remaining two designs. This category of reactive distillation exhibits less challenging problems than other categories since it uses a single feed, which eliminates the need for the control structure to perfectly balance two fresh feeds.Simulation results demonstrate that effective dynamic control is provided by a control structure that uses two temperatures to maintain the purities of both product streams. No internal composition measurement is required. This structure is found to be robust and stable and rejects loads and tracks setpoints very well. 相似文献
95.
基于SDB/SOI材料和硅微机械加工技术,提出了一种含微参比电极和择优差分补偿单元的背面引线PH-ISFET/压力传感器的新结构。并且设计了高稳定的可调芯片自恒温系统,以减少硅材料对温度敏感的效应。这种结构既方便地实现敏感元和信号处理电路的完全隔离,又有效地改善了敏感特性和稳定性。初步实验结果证实了新结构设计是成功的。 相似文献
96.
Response surface methodology is often used by researchers in different fields to determine the optimum values for controlled variables to maximize or minimize the response variables. Either maximization or minimization might be necessary depending on the response property. For example, if the response variable represents the yield of a process, maximization could be necessary; on the other hand, if the response variable is the biological oxygen demand (BOD) of an effluent the aim would definitely be minimization
Response surface methodology can be used two ways. It can be applied to the full-scale production or it can be scaled to a laboratory or the pilot plant. When applied to the full-scale production, the method is known as evolutionary operation (EVOP). EVOP is the continuous optimization of a process. The optimum conditions in a production plant can change depending on many factors such as raw material, ambient temperature, and equipment wear. Therefore, controlled variables should be optimized continuously to keep the response variable as close as possible to the maximum or minimum value. Hence, controlled variables are systematically changed around a center point to depict any shift of the response variable from the extreme. A thorough discussion of EVOP is given by Box, Evolutionary Operation: A Method for Increasing Industrial Productivity, Appl. Statist., 6, 81-101 (1957). 相似文献
Response surface methodology can be used two ways. It can be applied to the full-scale production or it can be scaled to a laboratory or the pilot plant. When applied to the full-scale production, the method is known as evolutionary operation (EVOP). EVOP is the continuous optimization of a process. The optimum conditions in a production plant can change depending on many factors such as raw material, ambient temperature, and equipment wear. Therefore, controlled variables should be optimized continuously to keep the response variable as close as possible to the maximum or minimum value. Hence, controlled variables are systematically changed around a center point to depict any shift of the response variable from the extreme. A thorough discussion of EVOP is given by Box, Evolutionary Operation: A Method for Increasing Industrial Productivity, Appl. Statist., 6, 81-101 (1957). 相似文献
97.
Evaluation of a two-temperature control structure for a two-reactant/two-product type of reactive distillation column 总被引:1,自引:0,他引:1
Devrim B. Kaymak 《Chemical engineering science》2006,61(13):4432-4450
Several different control structures have been proposed for reactive distillation columns. The appropriate control structure depends on the flowsheet and on the type of reactions occurring in the column. If two reactants are involved and if it is desirable to operate the process without any excess of reactant, it is necessary to manage the fresh feed streams so that the stoichiometry is exactly balanced. A composition analyzer that measures an internal composition in the column is often required. However, if two products are produced, it is possible to avoid the use of an analyzer by using two temperatures in the column to adjust the two feed streams. This type of structure was proposed by Roat et al. [Roat, S., Downs. J., Vogel, E., Doss, J., 1986. Integration of rigorous dynamic modeling and control system synthesis for distillation columns. In: Chemical Process Control—CPC III. Elsevier, Amsterdam.] for the ideal reaction A+B↔C+D in one of the earliest papers dealing with reactive distillation control.The purpose of this paper is to explore the effectiveness of this two-temperature control structure for various column designs (number of reactive stages) to quantify the impact of design on controllability. We also discuss the issues of the selection of the trays whose temperatures are to be controlled and the tuning of the two interacting temperature controllers. Disturbances in production rate and fresh feed compositions are made to examine the rangeability of this control structure. Both an ideal reaction system and the methyl acetate system are studied. One of the main conclusions is that the locations of the temperature control trays should be made such that the two temperature controllers both have direct action (an increase in temperature increases feed), which requires negative openloop process gains for both loops. 相似文献
98.
Hard disk drives continue to increase in areal data density. This requires air bearing sliders with lower and lower flying heights (FH). Also the uniformity of the FH and the flatness of the roll profile with radius become more critical as the FH gets lower. By using modern optimization techniques, it is possible to optimize slider air bearing surface (ABS) designs according to multiple design goals. In this paper, we discuss two modifications to the DIRECT algorithm: one to handle tolerance and one to deal with hidden constraints. Some numerical experiments were carried out using these modifications and the modified DIRECT algorithm was applied to slider ABS optimization. The results show that these two modifications can improve the efficiency of the DIRECT algorithm and they also provide more flexibility in slider ABS optimization. 相似文献
99.
CAPP系统中工艺卡片生成过程的研究 总被引:10,自引:1,他引:9
以AutoCAD2 0 0 0为开发平台、VC + + 6 0为开发环境、ObjectARX2 0 0 0为开发工具、SQLServer为后台数据库 ,通过编写writeText、fillGykztb、fillGykjtb等自定义函数 ,生成工艺卡片 ,并实现工序内容在工艺卡片中的分页显示等功能。 相似文献
100.