全文获取类型
收费全文 | 261459篇 |
免费 | 20208篇 |
国内免费 | 13253篇 |
专业分类
电工技术 | 16749篇 |
技术理论 | 51篇 |
综合类 | 36331篇 |
化学工业 | 28346篇 |
金属工艺 | 9641篇 |
机械仪表 | 14025篇 |
建筑科学 | 37771篇 |
矿业工程 | 14915篇 |
能源动力 | 7861篇 |
轻工业 | 14509篇 |
水利工程 | 14034篇 |
石油天然气 | 11235篇 |
武器工业 | 2503篇 |
无线电 | 16813篇 |
一般工业技术 | 18274篇 |
冶金工业 | 15425篇 |
原子能技术 | 2608篇 |
自动化技术 | 33829篇 |
出版年
2024年 | 804篇 |
2023年 | 2475篇 |
2022年 | 4762篇 |
2021年 | 5722篇 |
2020年 | 6081篇 |
2019年 | 5122篇 |
2018年 | 4829篇 |
2017年 | 5885篇 |
2016年 | 6993篇 |
2015年 | 7825篇 |
2014年 | 14503篇 |
2013年 | 13141篇 |
2012年 | 17202篇 |
2011年 | 18321篇 |
2010年 | 14585篇 |
2009年 | 15239篇 |
2008年 | 14237篇 |
2007年 | 18744篇 |
2006年 | 17792篇 |
2005年 | 15587篇 |
2004年 | 13270篇 |
2003年 | 11996篇 |
2002年 | 9871篇 |
2001年 | 8346篇 |
2000年 | 7040篇 |
1999年 | 5764篇 |
1998年 | 4355篇 |
1997年 | 3819篇 |
1996年 | 3550篇 |
1995年 | 2998篇 |
1994年 | 2679篇 |
1993年 | 2010篇 |
1992年 | 1781篇 |
1991年 | 1324篇 |
1990年 | 1161篇 |
1989年 | 1021篇 |
1988年 | 819篇 |
1987年 | 563篇 |
1986年 | 425篇 |
1985年 | 350篇 |
1984年 | 329篇 |
1983年 | 240篇 |
1982年 | 214篇 |
1981年 | 165篇 |
1980年 | 130篇 |
1979年 | 110篇 |
1978年 | 62篇 |
1977年 | 72篇 |
1976年 | 56篇 |
1975年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
U. Reimer
H. -J. Schek
《Data & Knowledge Engineering》1989,4(4):321-352The first part of this paper introduces the basic constructs of a frame representation model and gives a formal definition for them. Subsequently the nested relational model (NF2) is described as an extension of the classical relational model to support relation-valued attributes. In the second part of this paper both models are compared with each other and a mapping of frame representation structures to NF2 structures is specified. The structural similarities between frames and NF2 relations are made clear and it is shown that their main difference is due to the type polymorphism introduced by the concept hierarchy of the frame model. This causes type collisions to occur in the strictly typed NF2 model when frames are directly mapped to NF2 structures. Two solutions to this problem are suggested and compared. The paper concludes with a reformulation of query operations of the frame model in terms of NF2 algebra operations. 相似文献
102.
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
103.
[Correction Notice: An erratum for this article was reported in Vol 20(2) of Canadian Journal of Behavioural Science Revue canadienne des Sciences du comportement (see record 2007-09831-001). The abstract accompanying the original article was incorrect; the correct abstract (in French) is presented in the erratum.] We know little about individuals who are declared unfit to stand trial and/or not guilty by reason of insanity. The few existing studies are characterized by methodological weaknesses, notably by short follow-up periods and a lack of external validity. The present investigation, which aims to evaluate and explain readmissions that occurred during a seven- to nine-year period, corrects only some of these weaknesses. Sixty-one per cent of the subjects were rehospitalized during the period of study. It proved difficult to identify the factors associated with readmission. However, males with a diagnosis of schizophrenia and who had committed violent crimes were found the most likely to be readmitted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
105.
对耐火材料——棕刚玉粉的质量分析控制,提出了用实用性的检测方法测定其Al2O3含量。通过与国家标准分析方法的对比试验,证实快速实用分析方法测定棕刚玉粉中Al2O3含量是可行的。 相似文献
106.
Makris Angela P.; Rush Craig R.; Frederich Robert C.; Taylor Alisia C.; Kelly Thomas H. 《Canadian Metallurgical Quarterly》2007,15(2):123
Modafinil is indicated for the management of excessive daytime sleepiness; however, recent studies have examined a broad range of potential uses. Given that clinical uses of modafinil may be expanding, this study compared modafinil and d-amphetamine effects on subjective and performance measures. Across 11 sessions, 11 healthy adults were tested after oral doses of placebo (5 sessions), modafinil (1.75 mg/kg, 3.50 mg/kg, or 7.00 mg/kg), and d-amphetamine (0.035 mg/kg, 0.070 mg/kg, 0.140 mg/kg) under double-blind, randomized conditions. Assessments of cognitive performance and subjective effects were completed before drug administration, 30 min after drug administration, and at hourly intervals after drug administration for 5 hr. Modafinil increased ratings on the Amphetamine and Morphine Benzedrine Group scales of the Addiction Research Center Inventory (ARCI) and increased ratings on the Vigor and Total Positive scales of the Profile of Mood States. d-Amphetamine increased visual analog ratings of feeling stimulated and liking the drug and increased ratings on the Morphine Benzedrine Group scale of the ARCI. Both medications significantly reduced visual analog scale ratings of feeling sleepy, and modafinil decreased ratings on the ARCI Pentobarbital-Chlorpromazine-Alcohol Group scale. Both medications sustained performance that deteriorated across time on the Sternberg Number Recognition Test. Modafinil also enhanced performance rate on the Digit-Symbol Substitution Task above baseline levels and increased response rate on the Repeated Acquisition of Response Sequences Task. These results suggest that modafinil engenders alerting effects and increases performance in healthy non-sleep-deprived individuals comparable with that of d-amphetamine. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
Excel在大学物理实验中的应用 总被引:1,自引:0,他引:1
利用Excel的强大功能,对实验数据进行处理、分析,对实验过程及实验结果的监控。 相似文献
108.
文章介绍了包钢炼钢厂生产管理信息系统中成本分析子系统的可行性分析以及具体的数据归集流程,详细介绍了该系统的开发环境以及该系统的模块和数据库的结构、功能及其具体的设计思想;简要介绍了Oraele Develop数据库开发应用的一些特点. 相似文献
109.
钢铁企业的氧气厂要深入了解本企业的用氧情况及周边市场的需要,据此确定拟新增空分装置的设计参数,选定最适宜的空分流程。探讨了空分流程选择时要考虑的几个方面。介绍了一种对空分装置的投资和长期运行费用之间进行经济性分析的定量计算公式,并得出了四点结论。 相似文献
110.
基于PLC的焦炉集气管压力专家控制系统 总被引:4,自引:1,他引:3
舒雄鹰 《计算机测量与控制》2003,11(8):583-584,592
通过对焦炉煤气集气管压力系统的分析研究,提出基于专家系统的集气管压力协调控制方案,使得系统在传统PID控制的基础上,能够按照系统实际运行状况智能选择控制策略。全部系统基于西门子S7系列PLC构成,并采用PROFIBUS电缆组成总线型网络。 相似文献