全文获取类型
收费全文 | 365305篇 |
免费 | 42731篇 |
国内免费 | 28254篇 |
专业分类
电工技术 | 31047篇 |
技术理论 | 16篇 |
综合类 | 41343篇 |
化学工业 | 33241篇 |
金属工艺 | 13292篇 |
机械仪表 | 28448篇 |
建筑科学 | 39610篇 |
矿业工程 | 14219篇 |
能源动力 | 15277篇 |
轻工业 | 20105篇 |
水利工程 | 18396篇 |
石油天然气 | 20255篇 |
武器工业 | 4696篇 |
无线电 | 27788篇 |
一般工业技术 | 33786篇 |
冶金工业 | 14173篇 |
原子能技术 | 4404篇 |
自动化技术 | 76194篇 |
出版年
2024年 | 1808篇 |
2023年 | 5171篇 |
2022年 | 10195篇 |
2021年 | 11694篇 |
2020年 | 12528篇 |
2019年 | 10721篇 |
2018年 | 10248篇 |
2017年 | 12748篇 |
2016年 | 14868篇 |
2015年 | 15480篇 |
2014年 | 23031篇 |
2013年 | 23706篇 |
2012年 | 26963篇 |
2011年 | 29205篇 |
2010年 | 21966篇 |
2009年 | 22548篇 |
2008年 | 21642篇 |
2007年 | 25427篇 |
2006年 | 22216篇 |
2005年 | 19001篇 |
2004年 | 15747篇 |
2003年 | 13713篇 |
2002年 | 11092篇 |
2001年 | 9200篇 |
2000年 | 7868篇 |
1999年 | 6423篇 |
1998年 | 5357篇 |
1997年 | 4535篇 |
1996年 | 3845篇 |
1995年 | 3258篇 |
1994年 | 2782篇 |
1993年 | 2020篇 |
1992年 | 1750篇 |
1991年 | 1372篇 |
1990年 | 1091篇 |
1989年 | 943篇 |
1988年 | 700篇 |
1987年 | 496篇 |
1986年 | 391篇 |
1985年 | 368篇 |
1984年 | 396篇 |
1983年 | 324篇 |
1982年 | 303篇 |
1981年 | 161篇 |
1980年 | 172篇 |
1979年 | 140篇 |
1978年 | 79篇 |
1977年 | 67篇 |
1976年 | 51篇 |
1959年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
We present an optimization-based unsupervised approach to automatic document summarization. In the proposed approach, text summarization is modeled as a Boolean programming problem. This model generally attempts to optimize three properties, namely, (1) relevance: summary should contain informative textual units that are relevant to the user; (2) redundancy: summaries should not contain multiple textual units that convey the same information; and (3) length: summary is bounded in length. The approach proposed in this paper is applicable to both tasks: single- and multi-document summarization. In both tasks, documents are split into sentences in preprocessing. We select some salient sentences from document(s) to generate a summary. Finally, the summary is generated by threading all the selected sentences in the order that they appear in the original document(s). We implemented our model on multi-document summarization task. When comparing our methods to several existing summarization methods on an open DUC2005 and DUC2007 data sets, we found that our method improves the summarization results significantly. This is because, first, when extracting summary sentences, this method not only focuses on the relevance scores of sentences to the whole sentence collection, but also the topic representative of sentences. Second, when generating a summary, this method also deals with the problem of repetition of information. The methods were evaluated using ROUGE-1, ROUGE-2 and ROUGE-SU4 metrics. In this paper, we also demonstrate that the summarization result depends on the similarity measure. Results of the experiment showed that combination of symmetric and asymmetric similarity measures yields better result than their use separately. 相似文献
92.
In this paper, a model taking into account the effects of carrier loss mechanisms has been developed. The model simulates the photovoltaic properties of the graphene/n-type silicon Schottky barrier solar cells (G/n-Si_SBSC), and it can reproduce the experimentally determined parameters of the G/n-Si_SBSC. To overcome the low efficiencies of G/n-Si_SBSC, their performances have been optimized by modifying the work function of graphene and Si properties, accounted for variation of its thickness and doping level. The obtained results show that the work function of graphene has the major impact on the device performance. Also, the temperature dependence of the G/n-Si_SBSC performance is investigated. 相似文献
93.
94.
This work is devoted to the stress–strain state of isotropic double curved shell with defect system. The construction is weakened by two non-through thickness (internal) cracks of different length and by a circular hole located between cracks. In this study we use the line-spring model. Within the framework of this model cracks are modeled as mathematical cuts of shell’s middle surface. This leads to a two-dimensional problem. The problem is reduced to a system of eight boundary integral equations. To ensure the uniqueness of solution an additional equation is added. In the numerical solution of the problem special quadrature formulas for singular integrals of Cauchy type and the finite difference method are applied. The influence of defects on each other for double curved shell has been investigated. The given theoretical results can be used for the calculation of structural elements with holes, cracks on the strength and fracture toughness in various branches of engineering. 相似文献
95.
96.
ARIMA is seldom used in supply chains in practice. There are several reasons, not the least of which is the small sample size of available data, which restricts the usage of the model. Keeping in mind this restriction, we discuss in this paper a state-space ARIMA model with a single source of error and show how it can be efficiently used in the supply-chain context, especially in cases when only two seasonal cycles of data are available. We propose a new order selection algorithm for the model and compare its performance with the conventional ARIMA on real data. We show that the proposed model performs well in terms of both accuracy and computational time in comparison with other ARIMA implementations, which makes it efficient in the supply-chain context. 相似文献
97.
98.
In this paper, an adaptive control approach is designed for compensating the faults in the actuators of chaotic systems and maintaining the acceptable system stability. We propose a state‐feedback model reference adaptive control scheme for unknown chaotic multi‐input systems. Only the dimensions of the chaotic systems are required to be known. Based on Lyapunov stability theory, new adaptive control laws are synthesized to accommodate actuator failures and system nonlinearities. An illustrative example is studied. The simulation results show the effectiveness of the design method. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
99.
为了成功预测竹林山煤矿综放高瓦斯矿井大采高工作面煤层瓦斯涌出量,以主采3号煤层为主要研究对象,针对3号煤层以往开采情况,通过布设测点测量其煤层瓦斯含量和了解相邻矿井瓦斯含量,采用分源预测法、回归法及统计法等预测方法得到了3号煤层瓦斯含量的分布规律,并绘制了3号煤层的瓦斯含量等值线图。对矿井不同生产时期的瓦斯含量进行预测,得到了生产前期、中期及后期采区的最大绝对瓦斯涌出量和最大相对瓦斯涌出量,说明了竹林山煤矿各个时期均属于高瓦斯矿井。 相似文献
100.
This paper deals with the application of wavelet transforms for the detection, classification and location of faults on transmission lines. A Global Positioning System clock is used to synchronize sampling of voltage and current signals at both the ends of the transmission line. The detail coefficients of current signals of both the ends are utilized to calculate fault indices. These fault indices are compared with threshold values to detect and classify the faults. Artificial Neural Networks are employed to locate the fault, which make use of approximate decompositions of the voltages and currents of local end. The proposed algorithm is tested successfully for different locations and types of faults. 相似文献