全文获取类型
收费全文 | 75854篇 |
免费 | 8810篇 |
国内免费 | 5193篇 |
专业分类
电工技术 | 8053篇 |
技术理论 | 6篇 |
综合类 | 8508篇 |
化学工业 | 6479篇 |
金属工艺 | 2537篇 |
机械仪表 | 4991篇 |
建筑科学 | 8634篇 |
矿业工程 | 3557篇 |
能源动力 | 2272篇 |
轻工业 | 3334篇 |
水利工程 | 2666篇 |
石油天然气 | 3285篇 |
武器工业 | 1043篇 |
无线电 | 8418篇 |
一般工业技术 | 6737篇 |
冶金工业 | 3111篇 |
原子能技术 | 923篇 |
自动化技术 | 15303篇 |
出版年
2024年 | 365篇 |
2023年 | 984篇 |
2022年 | 1906篇 |
2021年 | 2271篇 |
2020年 | 2550篇 |
2019年 | 2210篇 |
2018年 | 2004篇 |
2017年 | 2647篇 |
2016年 | 3021篇 |
2015年 | 3194篇 |
2014年 | 5117篇 |
2013年 | 4815篇 |
2012年 | 5680篇 |
2011年 | 5755篇 |
2010年 | 4495篇 |
2009年 | 4675篇 |
2008年 | 4326篇 |
2007年 | 5192篇 |
2006年 | 4698篇 |
2005年 | 3869篇 |
2004年 | 3193篇 |
2003年 | 2968篇 |
2002年 | 2538篇 |
2001年 | 2288篇 |
2000年 | 1813篇 |
1999年 | 1392篇 |
1998年 | 1079篇 |
1997年 | 920篇 |
1996年 | 692篇 |
1995年 | 621篇 |
1994年 | 513篇 |
1993年 | 369篇 |
1992年 | 274篇 |
1991年 | 263篇 |
1990年 | 216篇 |
1989年 | 164篇 |
1988年 | 116篇 |
1987年 | 100篇 |
1986年 | 72篇 |
1985年 | 75篇 |
1984年 | 57篇 |
1983年 | 37篇 |
1982年 | 42篇 |
1981年 | 38篇 |
1980年 | 34篇 |
1979年 | 30篇 |
1978年 | 17篇 |
1977年 | 15篇 |
1959年 | 18篇 |
1956年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
1.
Jean-Claude Malela-Majika Sandile Charles Shongwe Olatunde Adebayo Adeoti 《Quality and Reliability Engineering International》2021,37(8):3314-3322
The sensitivity of a monitoring scheme depends on many factors including the variance of the charting statistic which is very important in the computation of the control limits. This paper discusses the computation of the variance of the recently proposed hybrid homogeneously weighted moving average (HHWMA) scheme which was based on an incorrect assumption. The correct variance is used to evaluate the run-length characteristics of the HHWMA scheme. It is observed that the incorrect variance has a significant impact on the sensitivity (or performance) of the HHWMA scheme. 相似文献
2.
Computer-Supported Collaborative Learning (CSCL) is concerned with how Information and Communication Technology (ICT) might facilitate learning in groups which can be co-located or distributed over a network of computers such as Internet. CSCL supports effective learning by means of communication of ideas and information among learners, collaborative access of essential documents, and feedback from instructors and peers on learning activities. As the cloud technologies are increasingly becoming popular and collaborative learning is evolving, new directions for development of collaborative learning tools deployed on cloud are proposed. Development of such learning tools requires access to substantial data stored in the cloud. Ensuring efficient access to such data is hindered by the high latencies of wide-area networks underlying the cloud infrastructures. To improve learners’ experience by accelerating data access, important files can be replicated so a group of learners can access data from nearby locations. Since a cloud environment is highly dynamic, resource availability, network latency, and learner requests may change. In this paper, we present the advantages of collaborative learning and focus on the importance of data replication in the design of such a dynamic cloud-based system that a collaborative learning portal uses. To this end, we introduce a highly distributed replication technique that determines optimal data locations to improve access performance by minimizing replication overhead (access and update). The problem is formulated using dynamic programming. Experimental results demonstrate the usefulness of the proposed collaborative learning system used by institutions in geographically distributed locations. 相似文献
3.
We study a two-agent scheduling problem in a two-machine permutation flowshop with learning effects. The objective is to minimize the total completion time of the jobs from one agent, given that the maximum tardiness of the jobs from the other agent cannot exceed a bound. We provide a branch-and-bound algorithm for the problem. In addition, we present several genetic algorithms to obtain near-optimal solutions. Computational results indicate that the algorithms perform well in either solving the problem or efficiently generating near-optimal solutions. 相似文献
4.
It is the aim of this paper to examine the effects of conditioning time on the flotation of hematite using three technical grade fatty acid reagents as providing additional evidence on their mechanism of interaction with the hematite surface. Various mechanisms have been postulated as occurring as conditioning time is increased. Both physical (e.g. conditioning time and power input) and chemical (nature, dispersion and solubility of the adsorbing species) contribute to the mechanisms of attachment of collector. In this paper, the mechanism of attachment of oleate to hematite can be readily explained by chemisorption, but the mechanism of attachment of lauric acid appears to be physical adsorption at neutral pH. The flotation of hematite with a mixture of tallow-type fatty acids (palmitic, stearic and oleic acids) is very sensitive to conditioning time, and suggests that, even though flotation is very effective at short conditioning times, it is very susceptible to the presence of fines and their associated high surface areas. It is therefore obvious that both the physical and chemical conditions contribute to the mechanisms of adsorption of fatty acids on iron-containing oxide minerals and must be understood in order to optimise the flotation of these minerals in an industrial situation. 相似文献
5.
《Planning》2019,(2)
2017年,美国心脏病学会和美国心脏协会提出将高血压诊断标准降为130/80 mm Hg (1 mm Hg=0. 133 kPa),这与其他指南有所不同。降压治疗的核心目标在于靶器官的保护,近年来降压治疗与脑小血管病预防的相关问题日益受到临床重视。目前研究结果表明,降压治疗对腔隙性卒中患者的二级预防以及白质病变进展的预防可能有一定积极意义,但确切的降压目标值并未确定。血压与临床结局可能呈现J型关系,血压过低或过高可能均有害,而取得最大获益的降压目标有待进一步探索。 相似文献
6.
This article presents a new approach for solving the Optimal Control Problem (OCP) of linear time-delay systems with a quadratic cost functional. The proposed method can also be used for designing optimal control time-delay systems with disturbance. In this study, the Variational Iteration Method (VIM) is employed to convert the original Time-Delay Optimal Control Problem (TDOCP) into a sequence of nonhomogeneous linear two-point boundary value problems (TPBVPs). The optimal control law obtained consists of an accurate linear feedback term and a nonlinear compensation term which is the limit of an adjoint vector sequence. The feedback term is determined by solving Riccati matrix differential equation. By using the finite-step iteration of a nonlinear compensation sequence, we can obtain a suboptimal control law. Finally, Illustrative examples are included to demonstrate the validity and applicability of the technique. 相似文献
7.
8.
Many models of spoken word recognition posit the existence of lexical and sublexical representations, with excitatory and inhibitory mechanisms used to affect the activation levels of such representations. Bottom-up evidence provides excitatory input, and inhibition from phonetically similar representations leads to lexical competition. In such a system, long words should produce stronger lexical activation than short words, for 2 reasons: Long words provide more bottom-up evidence than short words, and short words are subject to greater inhibition due to the existence of more similar words. Four experiments provide evidence for this view. In addition, reaction-time-based partitioning of the data shows that long words generate greater activation that is available both earlier and for a longer time than is the case for short words. As a result, lexical influences on phoneme identification are extremely robust for long words but are quite fragile and condition-dependent for short words. Models of word recognition must consider words of all lengths to capture the true dynamics of lexical activation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
基于承包商预期收益不变的不平衡报价模型 总被引:1,自引:0,他引:1
在招标实践中,通常采用最低价中标原则,使得投标人不得不压低其投标价格。基于承包商预期收益不变的不平衡报价模型,是在“工程量清单报价”的条件下,考虑到施工中工程量的变化及施工顺序的影响,体现了资金的时间价值,在保持承包商预期收益不变的前提下,通过调整各分项工程的单价,来降低工程报价,以增加中标机会而建立的。所建立的模型简单,易于操作,并配以具体的工程实例,通过计算机求得其最优解,可供承包商投标报价时参考。 相似文献
10.
针对不同地质目标的叠前时间偏移成像解释评价 总被引:3,自引:0,他引:3
随着计算机硬件和地震勘探成像技术的发展,叠前时间偏移正逐步替代常规的NMO加DMO加叠后时间偏移成为地震数据成像处理方法的主流。但对于不同的地质目标,叠前时间偏移的成像效果是否优于常规NMO加DMO加叠后时间偏移的成像效果呢?为此,从地震数据成像处理方法、处理流程和处理参数等方面进行了讨论,并基于某地区三维数据常规处理结果和叠前时间偏移处理结果,针对不同地质目标进行了剖析与评价。认为:叠前时间偏移成像的垂向分辨率较常规处理明显降低,但对于空间波阻抗变化明显的河流和断层,叠前时间偏移成像的空间分辨率要高于常规处理;对于小于1/4波长的叠置薄储层,叠前时间偏移成像的垂向和空间分辨率低于常规处理结果。 相似文献