全文获取类型
收费全文 | 24316篇 |
免费 | 2502篇 |
国内免费 | 1594篇 |
专业分类
电工技术 | 1524篇 |
综合类 | 3501篇 |
化学工业 | 4712篇 |
金属工艺 | 2217篇 |
机械仪表 | 1006篇 |
建筑科学 | 1379篇 |
矿业工程 | 706篇 |
能源动力 | 791篇 |
轻工业 | 1076篇 |
水利工程 | 424篇 |
石油天然气 | 966篇 |
武器工业 | 148篇 |
无线电 | 1405篇 |
一般工业技术 | 3214篇 |
冶金工业 | 1855篇 |
原子能技术 | 256篇 |
自动化技术 | 3232篇 |
出版年
2024年 | 82篇 |
2023年 | 286篇 |
2022年 | 475篇 |
2021年 | 640篇 |
2020年 | 719篇 |
2019年 | 683篇 |
2018年 | 591篇 |
2017年 | 790篇 |
2016年 | 836篇 |
2015年 | 888篇 |
2014年 | 1318篇 |
2013年 | 1608篇 |
2012年 | 1734篇 |
2011年 | 1793篇 |
2010年 | 1326篇 |
2009年 | 1433篇 |
2008年 | 1357篇 |
2007年 | 1515篇 |
2006年 | 1472篇 |
2005年 | 1305篇 |
2004年 | 1166篇 |
2003年 | 1043篇 |
2002年 | 869篇 |
2001年 | 686篇 |
2000年 | 590篇 |
1999年 | 487篇 |
1998年 | 373篇 |
1997年 | 374篇 |
1996年 | 327篇 |
1995年 | 306篇 |
1994年 | 296篇 |
1993年 | 192篇 |
1992年 | 183篇 |
1991年 | 152篇 |
1990年 | 123篇 |
1989年 | 92篇 |
1988年 | 73篇 |
1987年 | 48篇 |
1986年 | 25篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1963年 | 4篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In this paper we have studied the control of linear systems with algebraic-equation constraint. A pole-assignment controller with two-layer structure for such constrained systems has been presented. The objective of the controller is to assign the desired poles to constrained system and simultaneously force the corresponding closed-loop system to satisfy the constraint. The conditions for the existence of pole-assignment controller are discussed in different cases. The implementation algorithm of pole-assignment controller is also presented. An example is given to illustrate the validity of the method in this paper. 相似文献
52.
This paper finds the appropriate pi-coefficients for a parameter estimation adaptive system and uses them to analyze the stability of two estimation algorithms. The estimation error dynamics of the system are modeled by a linear time-invariant subsystem and a nonlinear time-varying update law in a feedback loop. Then the so-called max-p problems are formulated and solved to obtain the pi-coefficients for the linear subsystem and nonlinear update low. For the investigated system, the quantitative results show that the least-squares update algorithm has larger stability range than that of the gradient algorithm, and the σ-modification scheme gives larger stability ranges for both algorithms. 相似文献
53.
The high-temperature crystallization of poly(p-phenylene terephthalamide) (PPTA) from dilute organic solutions was achieved through the introduction of a non-solvent, or precipitating agent, at the desired crystallization temperature. The morphology and crystal structure were examined for crystals produced from PPTA polymer with two different molecular weights (Mw = 46000 and 3430 g mol−1), using transmission electron microscopy. For the high-molecular-weight polymer, ribbon-like crystals were produced, while the low-molecular-weight polymer yielded small needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weight polymer, the molecular axes were parallel to the ribbon axes in a chain-extended type structure. A hypothesis for the orientation of the low-molecular-weight PPTA in the small platelets, is also given. 相似文献
54.
55.
H. Safiri M. Ahmadi G.A. Jullien W.C. Miller 《The Journal of VLSI Signal Processing》2002,31(2):91-100
A new algorithm based on Genetic Programming (GP) for the problem of optimization of Multiple constant Multiplication (MCM) by Common Subexpression Elimination(CSE) is developed. This method is used for hardware optimization for DSP systems. A solution based on Genetic Programming is shown in this paper. The performance of the technique is demonstrated in one- and multi-dimensional digital filters with constant coefficients. 相似文献
56.
57.
Label printing finds many applications in industry. However, this task is still labor intensive in many printing factories. Since each template can only accommodate a fixed number of labels, an important task is to work out the compositions of templates by allocating suitable labels to each template in order to fulfill the order requirements effectively. The template design could be rather arbitrary, which usually ends up with a lot of excessive printed labels. Enhancing the template design will significantly improve the efficiency of the printing process, and, at the same time, reduce the waste of resources. This motivates the study of more automatic design methods. In this paper, the problem is first formulated as a nonlinear integer programming problem. The main variables in the formulation are the compositions and the printing frequencies of templates. For practical purpose, each type of label is confined to one template only which allows automated packing and handling. The structure of the problems is carefully analyzed and a new algorithm is proposed. Numerical results show that the proposed method is a simple but effective way of generating good template designs. 相似文献
58.
59.
在氧化铝生产过程中,熟料折合比是烧结法一项重要的综合性指标,本文通过对熟料折合比的定义、计算公式的剖析,分析了生产过程中影响熟料折合比的主要因素,对有效降低熟料折合比的措施进行了探讨。 相似文献
60.
The viscometric, turbidimetric and potentiometric properties of copolymers of acrylamide (AM) with 2-acrylamido-2-methylpropanedimethylammonium chloride (AMPDAC) were studied in aqueous solutions. The AMPDAC polymers exhibit poor salt tolerance and large, negative viscosity/temperature coefficients. Furthermore, the polymers were found to be sensitive to changes in pH. The AMPDAC polymers undergo phase separation in the presence of dianions as a function of temperature and AMPDAC composition. 相似文献