全文获取类型
收费全文 | 102736篇 |
免费 | 8493篇 |
国内免费 | 4125篇 |
学科分类
工业技术 | 115354篇 |
出版年
2024年 | 325篇 |
2023年 | 1752篇 |
2022年 | 2892篇 |
2021年 | 4218篇 |
2020年 | 3228篇 |
2019年 | 2796篇 |
2018年 | 3233篇 |
2017年 | 3575篇 |
2016年 | 2970篇 |
2015年 | 3979篇 |
2014年 | 5059篇 |
2013年 | 5986篇 |
2012年 | 6319篇 |
2011年 | 6896篇 |
2010年 | 5925篇 |
2009年 | 5705篇 |
2008年 | 5570篇 |
2007年 | 5228篇 |
2006年 | 5378篇 |
2005年 | 4729篇 |
2004年 | 3135篇 |
2003年 | 2931篇 |
2002年 | 2676篇 |
2001年 | 2352篇 |
2000年 | 2523篇 |
1999年 | 2796篇 |
1998年 | 2371篇 |
1997年 | 1938篇 |
1996年 | 1861篇 |
1995年 | 1590篇 |
1994年 | 1251篇 |
1993年 | 948篇 |
1992年 | 758篇 |
1991年 | 562篇 |
1990年 | 448篇 |
1989年 | 358篇 |
1988年 | 298篇 |
1987年 | 186篇 |
1986年 | 130篇 |
1985年 | 119篇 |
1984年 | 76篇 |
1983年 | 52篇 |
1982年 | 62篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 19篇 |
1978年 | 9篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 407 毫秒
991.
聚醋酸乙烯乳液缩醛化的改性研究 总被引:4,自引:1,他引:4
本文介绍了为提高聚醋酸乙烯乳液稳定性、耐水性和防冻性而进行缩醛化改性的原理,并确定了最佳工艺条件即甲醛与聚乙烯醇的配比为0.45~0.50。 相似文献
992.
993.
994.
(接上期第 2 3页 )3 膜分离Doraietal[16] 通过超滤除去低相对分子质量级份 ,使聚醚多元醇 ,尤其是聚四氢呋喃多元醇 ,具有较窄的分布 (Mw∶Mn=1 .2~ 1 .8)。该方法通过对多分散的熔融聚合物实施物理分级 ,达到降低相对分子质量分布的目的 ,可使最终产物的相对分子质量为 40 0~ 40 0 0 ,分散度为 1 .2~ 1 .8。该方法首先需要准备 1套交叉流动的膜分离系统 ,采用渗透膜或半渗透膜 ,膜的一边是滞留物 ,另一边是超滤液。然后 ,在起始聚合物的熔点以上 ,分解温度以下 ,且温度不大于膜的熔融和分解温度 ,将起始聚合物熔融 ,并流入该系统中… 相似文献
995.
996.
重点对地表水质预测模型的几种人工智能方法进行了评述,具体说明了BP神经网络水质预测模型、地表水COD灰色预测模型、时间数列预测方法及WASP5模型系统等方法的原理和特点.并提出地表水质预测模型WASP5与GIS系统集成的趋势,建立水质自动监测系统是我国水质现状和社会发展的需要,并分析了发展水质自动检测系统的方法及可行性. 相似文献
997.
998.
This paper focuses on the design of a low order robust stabilizer for the tracking/disturbance rejection problem based on the internal model principle in the time-varying setting and its application to the hydraulic pressure tracking with varying frequency. The problem of this kind known as output regulation generally consists of two major parts: internal model unit construction and stabilizer design. While the construction of the time-varying internal model unit is non-trivial by itself and a very recent research outcome enables its synthesis for a class of linear time-varying systems, the effective stabilization of the augmented system (internal model unit and plant) for practical applications remains a challenge. This is due to the need to stabilize the high order time-varying augmented system using a low order stabilizer in a robust fashion and with desirable transient performance. While directly applying the stabilization approaches for a general LTV system will result in a high order stabilizer, a new method is proposed in this paper that overcomes this bottleneck by taking advantage of the unique structure of the internal model based control system. Instead of using a dynamic stabilizer with high order, this approach uses a sequence of time-varying gains that are directly injected into the internal model unit. A critical issue addressed is how to avoid the non-convex optimization associated with the time-varying gain synthesis and then convert the stabilizer design into a series of Linear Matrix Inequalities (LMIs). The proposed control approach is then demonstrated on an electrohydraulic system. 相似文献
999.
A bridge crane is a complicated nonlinear underactuated mechatronic system, for which high-speed positioning and anti-swing control is the kernel objective. Existing methods for varying cable length cranes require either linearizations or approximations, when performing analysis, and they usually assume small load swing; moreover, the ranges of the tracking errors cannot be guaranteed during the overall process. Motivated by these facts, we present a new tracking scheme for cranes with load horizontal transportation and lowering control, which achieves simultaneous load swing suppression and elimination. To the best of our knowledge, the proposed method yields the first feedback closed-loop control result not needing linearization or approximation operations to the original nonlinear crane dynamics with cable length variation, while relaxing the common assumption imposed on load swing associated with existing methods. It can also guarantee that the tracking errors are always within a priori set bounds and converge to zero rapidly. Lyapunov-like analysis is implemented to support the theoretical derivations. We carry out hardware experiments to illustrate the superior control performance of the new method. 相似文献
1000.
In the present paper, we investigate the output-controllability and optimal output control problems of a state-dependent switched Boolean control network. By using the semi-tensor product, the algebraic form of the system is obtained. Then, output-controllability problems of the system are discussed and some necessary and sufficient conditions are given. Next, the Mayer-type optimal output control issue is considered and an algorithm is provided to find out the control sequence. At last, an example is given to show the effectiveness of the main results. 相似文献