全文获取类型
收费全文 | 172923篇 |
免费 | 14730篇 |
国内免费 | 11457篇 |
专业分类
电工技术 | 29420篇 |
技术理论 | 7篇 |
综合类 | 16283篇 |
化学工业 | 9039篇 |
金属工艺 | 6607篇 |
机械仪表 | 15984篇 |
建筑科学 | 14891篇 |
矿业工程 | 7020篇 |
能源动力 | 4698篇 |
轻工业 | 4583篇 |
水利工程 | 5434篇 |
石油天然气 | 5608篇 |
武器工业 | 2643篇 |
无线电 | 12996篇 |
一般工业技术 | 7980篇 |
冶金工业 | 7810篇 |
原子能技术 | 1196篇 |
自动化技术 | 46911篇 |
出版年
2024年 | 721篇 |
2023年 | 1945篇 |
2022年 | 3137篇 |
2021年 | 3911篇 |
2020年 | 4730篇 |
2019年 | 3732篇 |
2018年 | 3316篇 |
2017年 | 4872篇 |
2016年 | 5419篇 |
2015年 | 5998篇 |
2014年 | 11533篇 |
2013年 | 9915篇 |
2012年 | 12559篇 |
2011年 | 13476篇 |
2010年 | 10185篇 |
2009年 | 10484篇 |
2008年 | 10456篇 |
2007年 | 12904篇 |
2006年 | 11561篇 |
2005年 | 10103篇 |
2004年 | 8374篇 |
2003年 | 7399篇 |
2002年 | 5925篇 |
2001年 | 4912篇 |
2000年 | 4238篇 |
1999年 | 3407篇 |
1998年 | 2605篇 |
1997年 | 2307篇 |
1996年 | 1833篇 |
1995年 | 1489篇 |
1994年 | 1271篇 |
1993年 | 911篇 |
1992年 | 730篇 |
1991年 | 550篇 |
1990年 | 417篇 |
1989年 | 368篇 |
1988年 | 261篇 |
1987年 | 156篇 |
1986年 | 112篇 |
1985年 | 109篇 |
1984年 | 154篇 |
1983年 | 118篇 |
1982年 | 113篇 |
1981年 | 79篇 |
1980年 | 53篇 |
1979年 | 64篇 |
1978年 | 48篇 |
1977年 | 48篇 |
1964年 | 13篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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
2.
Temperature control offers benefits in land‐based marine aquaculture: stock growth rates may be enhanced by heating in winter; mortality rates in summer may be reduced by cooling. However, if the plant is not well designed, temperature control may create very large energy demands. This paper describes the application of temperature control in abalone aquaculture in New Zealand, with a focus on energy considerations in plant design. An abalone farm using a semi‐closed water conditioning system is used as a case study for which an energy model, based on a heat pump system, is developed. The model is used to determine the impact of plant design and tank conditions on the economics of the operation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
3.
Xuejun Xie Siying Zhang 《International Journal of Adaptive Control and Signal Processing》2002,16(1):39-59
This paper considers the adaptive pole‐placement control problem for system (1) with unmodelled dynamics ηn dominated by a small constant ε multiplied by a quantity independent of ε but tending to infinity as the past input, output, and noise grow. Using bounded external excitation and randomly varying truncation techniques, we give a design method of adaptive pole‐placement controller. It is shown that the closed‐loop system is globally stable, the estimation error for the parameter contained in the modelled part is of order ε, and the closed‐loop system under the adaptive pole‐placement control law is suboptimal in the sense of $$\mathop{\lim\sup}\limits_{{n\to\infty }}{1\over n}\mathop{\sum}\limits_{i=0}^n{\left({A^{*}(z)y_{n}‐L(z)C(z)w_{n}‐B(z)R(z)y_{n}^{*}}\right)^{2}{\leq}O({\varepsilon}^{2})+\gamma^{2}\mathop{\sum}\limits_{j=1}^q{b_{j}^{2}}}$$\nopagenumbers\end while the SPR condition used usually in other papers is replaced by a stability condition. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
4.
Timothy Thomasma Kurt Hilbrecht 《International Journal of Flexible Manufacturing Systems》1991,3(3-4):231-250
Good methods are needed to specify, test, and debug material-handling control logic. This article surveys a number of representative methods for defining and describing control algorithms for programmable material-handling equipment used in flexible manufacturing systems. The methods are evaluated with regard to their suitability for communication between people and as bases for interfaces to automatic program generators. It is concluded that no single method is entirely satisfactory. Three methods (position diagrams, function block diagrams, and operation networks) have potential to be combined into an effective hybrid approach that minimizes the need for the user to switch between various conceptual models. 相似文献
5.
The objective of this note is to propose a method for stabilization of structurally fixed modes in expansions of LTI dynamic systems in the scope of overlapping decentralized control design based on the expansion/contraction framework, enabling successful design for a broader class of problems than considered so far. The method is based on a judicious choice of complementary matrices in the expanded space. Numerical examples are provided to illustrate simplicity and efficiency of the proposed approach. 相似文献
6.
7.
肖起清 《机械工业高教研究》2008,(2):34-37
大学在办学资源、办学过程、办学质量、办学形象的竞争中出现大量的不良倾向。大学的不良竞争是由于政府主导资源配置、资源和制度供给不足、大学系统重构等因素导致。必须通过控制主体、控制手段的转变和控制对象的发展形成新的控制机制,以保证大学竞争的秩序化和规范化。 相似文献
8.
介绍煤炭码头带式输送机联锁控制系统设计的一种方法,详细阐述了整个系统的工艺流程、启动方式以及控制原理等。这种方法可以实现带式输送机远程中控室控制,也可进行就地带式输送机机侧控制。 相似文献
9.
Ali J. Koshkouei 《International Journal of Adaptive Control and Signal Processing》2008,22(9):859-874
Passivity with sliding mode control for a class of nonlinear systems with and without unknown parameters is considered in this paper. In fact, a method for deriving a nonlinear system with external disturbances to a passive system is considered. Then a passive sliding mode control is designed corresponding to a given storage function. The passivity property guarantees the system stability while sliding mode control techniques assures the robustness of the proposed controller. When the system includes unknown parameters, an appropriate updated law is obtained so that the new transformed system is passive. The passivation property of linear systems with sliding mode is also analysed. The linear and nonlinear theories are applied to a simple pendulum model and the gravity‐flow/pipeline system, respectively. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
10.
影响混凝土强度的因素及控制措施 总被引:3,自引:3,他引:0
分析了水泥强度等级、水灰比和骨料质量等内因,及施工条件、养护温度、湿度、龄期等外因对混凝土强度的影响,并提出了控制混凝土强度的相应措施,以确保混凝土强度符合设计及施工要求,从而保证建筑物结构安全。 相似文献