全文获取类型
收费全文 | 24573篇 |
免费 | 1091篇 |
国内免费 | 678篇 |
专业分类
电工技术 | 2022篇 |
技术理论 | 5篇 |
综合类 | 2395篇 |
化学工业 | 2518篇 |
金属工艺 | 654篇 |
机械仪表 | 1150篇 |
建筑科学 | 4462篇 |
矿业工程 | 1484篇 |
能源动力 | 687篇 |
轻工业 | 1342篇 |
水利工程 | 1343篇 |
石油天然气 | 1750篇 |
武器工业 | 169篇 |
无线电 | 970篇 |
一般工业技术 | 941篇 |
冶金工业 | 1994篇 |
原子能技术 | 95篇 |
自动化技术 | 2361篇 |
出版年
2024年 | 18篇 |
2023年 | 81篇 |
2022年 | 267篇 |
2021年 | 270篇 |
2020年 | 347篇 |
2019年 | 224篇 |
2018年 | 252篇 |
2017年 | 312篇 |
2016年 | 386篇 |
2015年 | 490篇 |
2014年 | 1446篇 |
2013年 | 943篇 |
2012年 | 1665篇 |
2011年 | 1804篇 |
2010年 | 1569篇 |
2009年 | 1852篇 |
2008年 | 1498篇 |
2007年 | 2045篇 |
2006年 | 1854篇 |
2005年 | 1676篇 |
2004年 | 1440篇 |
2003年 | 1274篇 |
2002年 | 1083篇 |
2001年 | 856篇 |
2000年 | 710篇 |
1999年 | 506篇 |
1998年 | 345篇 |
1997年 | 283篇 |
1996年 | 221篇 |
1995年 | 183篇 |
1994年 | 119篇 |
1993年 | 64篇 |
1992年 | 49篇 |
1991年 | 43篇 |
1990年 | 27篇 |
1989年 | 31篇 |
1988年 | 31篇 |
1987年 | 8篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1979年 | 3篇 |
1966年 | 3篇 |
1961年 | 3篇 |
1959年 | 4篇 |
1958年 | 6篇 |
1957年 | 4篇 |
1956年 | 3篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
本文分析了乌兰矿投产前期采矿现状及存在的主要问题,针对该矿所处蒙古国经济落后、投资风险大的现实状况,为避免生产中断、规避投资风险,早日回收前期投资考虑,采取了双斜坡道开拓、全尾胶结充填、高端壁空场嗣后充填采矿、多中段组合式连续开采等系列技术应对方案。大大降低了一次性投资规模及投资风险,前期投资得以快速回笼的同时,矿山产能也充分释放,确保了矿山的持续稳定,取得了较好的经济和社会效益。为海外地下近地表矿体开采矿山规避投资风险提供了很好的技术方案借鉴。 相似文献
2.
3.
一个完整枪支(弹药)库室的安全防范由管理要求、物防要求、技防要求及人防要求完美的结合而成,其中技防要求是需要根据枪支(弹药)库室现场实体情况采取的一项电子技术手段,是起到安全预报警的最佳方式。本文就枪支(弹药)库室安全防范在技防要求方面按现行GA 1016-2012标准在检测中存在的问题做一些探讨、建议,以期为需要枪支(弹药)库室的建设单位、施工单位提供参考。 相似文献
4.
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
5.
Based on the multi-item Food Choice Questionnaire (FCQ) originally developed by Steptoe and colleagues (1995), the current study developed a single-item FCQ that provides an acceptable balance between practical needs and psychometric concerns. Studies 1 (N = 1851) and 2 (2a (N = 3290), 2b (N = 4723), 2c (N = 270)) showed that the single-item FCQ scale has good convergent and discriminant validity. Generally, the results showed the highest correlations with the related multi-item dimensions (>0.40). Study 2 refined the scale. Only the items for convenience (Study 2a), sensory appeal (Study 2b) and mood (Study 2c) needed to be revised (as Study 1 showed a correlation between the multi-item and the single-item below the threshold of 0.60). The results also showed comparable predictive validity. Both methods revealed similar association patterns between food motives and consumption behaviours (Fisher’s z tests revealed agreements of 86.2% for Study 1, 92.9% for Study 2a and 100% for Studies 2b and 2c). Study 3 (N = 6062) showed an example of the added value of a context-specific application for the single-item FCQ. Different motives were shown to be relevant across contexts, and the context-specific motives had additional explained variance beyond the general multi-item FCQ. Studies 2b and 3 also showed the performance of the single-item FCQ in an international context. In sum, the results indicate that the single-item FCQ can be used as a flexible and short substitute for the multi-item FCQ. The study also discusses the conditions that should be considered when using the single-item scale. 相似文献
6.
Clustering is a solution for classifying enormous data when there is not any early knowledge about classes. With emerging new concepts like cloud computing and big data and their vast applications in recent years, research works have been increased on unsupervised solutions like clustering algorithms to extract knowledge from this avalanche of data. Clustering time-series data has been used in diverse scientific areas to discover patterns which empower data analysts to extract valuable information from complex and massive datasets. In case of huge datasets, using supervised classification solutions is almost impossible, while clustering can solve this problem using un-supervised approaches. In this research work, the focus is on time-series data, which is one of the popular data types in clustering problems and is broadly used from gene expression data in biology to stock market analysis in finance. This review will expose four main components of time-series clustering and is aimed to represent an updated investigation on the trend of improvements in efficiency, quality and complexity of clustering time-series approaches during the last decade and enlighten new paths for future works. 相似文献
7.
针对水利工程开发方案优选具有多目标、多层次等特点,建立灰局势决策模型并应用变异系数法确定评价指标权重。利用该模型对灌区改建扩建规划方案进行优选,结果表明这是一种有效的方法。 相似文献
8.
为了满足市场的需要,中石化天津分公司炼油厂根据FCCU自身特点采取了一系列提高柴汽比的措施,包括:调节反应系统和分馏的操作条件及采用MGD技术,以提高柴油产率。实施后,FCCU的柴汽比从0.5提高到0.9,创造了良好的经济效益。 相似文献
9.
10.
热镀锌板(卷)工程设计中的环境保护问题 总被引:1,自引:0,他引:1
对热镀锌板(卷)的生产工艺、主要生产设备进行了简要介绍,并就其污染源(工序)、生产过程中产生的污染物及其控制措施进行了评述,同时就设计和生产中宜注意的几个环保问题进行了分析。 相似文献