首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   36157篇
  免费   4102篇
  国内免费   2035篇
电工技术   2873篇
技术理论   3篇
综合类   4703篇
化学工业   1904篇
金属工艺   714篇
机械仪表   1770篇
建筑科学   4460篇
矿业工程   1815篇
能源动力   1013篇
轻工业   3732篇
水利工程   2057篇
石油天然气   4098篇
武器工业   849篇
无线电   2349篇
一般工业技术   2361篇
冶金工业   1072篇
原子能技术   272篇
自动化技术   6249篇
  2024年   111篇
  2023年   539篇
  2022年   1057篇
  2021年   1278篇
  2020年   1321篇
  2019年   1077篇
  2018年   1058篇
  2017年   1132篇
  2016年   1452篇
  2015年   1517篇
  2014年   2559篇
  2013年   2230篇
  2012年   2959篇
  2011年   3028篇
  2010年   2192篇
  2009年   2270篇
  2008年   2047篇
  2007年   2458篇
  2006年   2150篇
  2005年   1892篇
  2004年   1518篇
  2003年   1268篇
  2002年   917篇
  2001年   818篇
  2000年   628篇
  1999年   540篇
  1998年   383篇
  1997年   370篇
  1996年   297篇
  1995年   252篇
  1994年   195篇
  1993年   153篇
  1992年   96篇
  1991年   93篇
  1990年   59篇
  1989年   76篇
  1988年   31篇
  1987年   28篇
  1986年   28篇
  1985年   21篇
  1984年   26篇
  1983年   28篇
  1982年   15篇
  1981年   13篇
  1979年   10篇
  1978年   9篇
  1977年   8篇
  1975年   7篇
  1963年   7篇
  1959年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
为了评估北盘江鱼类增殖放流效果,2017~2018年期间采用体外荧光、剪鳍、"T"型标三种标志方法对目标鱼类进行标志放流,通过集中捕捞方式进行回捕调查,集中捕捞时间为2017年7月、2018年8月,捕捞水域为董菁-马马崖-光照-善泥坡库区。结果表明,白甲鱼回捕率较高,为0.82%,其他鱼类均在0.5%左右,其中主要为低龄鱼类,高龄鱼类较少;董菁打邦河及各库尾水域物种丰富度较高,善泥坡高家渡码头和马马崖库区试验库尾物种多样性指数相对较低。建议在以后的增殖放流活动中,加大每年的监测频次。  相似文献   
12.
A large-scale point to point hydrogen transport is one strategy for a prospective energy import scenario for certain countries. The case for a hydrogen transport from Australia to Japan has been addressed in several studies. However, most studies lack transparency and detailed insights into the made assumptions thus a fair evaluation of different transport pathways is challenging. To address this issue, we developed a model where a large-scale point to point hydrogen transport of liquid hydrogen is compared with the transport via liquid organic hydrogen carrier (LOHC), namely via methyl cyclohexane and hydrogenated dibenzyl toluene. We analyzed, where energy is required along the different pathways, where hydrogen losses do occur and how the costs are put together. Furthermore, the influence of hydrogen feed costs is also considered. For hydrogen production costs of 5 €2018/kgH2 the total delivery costs are in the range of 6.40– 8.10 €2018/kgH2.  相似文献   
13.
李夏 《云南化工》2019,(6):162-163
结合不同改性剂掺量单因素试验,确定了采用88mm叶轮、115mm容器、圆盘锯齿式搅拌器(转速1400r/min)、175℃共混温度、改性剂掺量4.27%、单次搅拌300g的制备工艺参数。在此条件下制备的聚氨酯改性沥青具有优异的水稳定性、储存稳定性且耐老化、耐高温,拥有比普通聚合物改性沥青更高的车辙因子G*/sinδ和15℃动态模量,基本满足高模量沥青要求。  相似文献   
14.
Replacement of precious single metal catalysts with cost-effective, highly-dispersed composite catalysts for catalytic hydrothermal conversion of residue holds tremendous promise for the residue upgrading technologies. Organic metals were added to the feed as the oil-soluble precursors, and transformed into the catalytic active phases in this work. Physical properties and structures of the composite catalysts had been investigated by X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and transmission electron microscopy. The composite catalysts were found to be highly efficient in the catalytic hydrothermal conversion of both model compound and residue. Increased metal dispersion and synergistic effects of two metals played indispensable roles in such catalytic system. Results showed that under the test conditions in the article, the catalyst had the best catalytic performance when the mass ratio of molybdenum to iron was 1.5.  相似文献   
15.
We deal with the mathematical model of the incremental degradation of the internal coating (e.g. a polymeric material) of a metallic pipe in which a fluid flows relatively fast. The fluid drags solid impurities so that longitudinal scratches, inaccessible to any direct inspection procedure, are produced on the coating. Time evolution of this kind of defects can be reconstructed from the knowledge of a sequence of temperature maps of the external surface. The time-varying orthogonal section of this damaged interface is determined as a function of time and polar angle through the identification of a suitable effective heat transfer coefficient by means of Thin Plate Approximation.  相似文献   
16.
This article theoretically and empirically analyzes backtesting portfolio value-at-risk (VaR) with estimation risk in an intrinsically multi-variate framework. It particularly takes into account the estimation of portfolio weights in forecasting portfolio VaR and its impact on backtesting. It shows that the estimation risk from estimating portfolio weights and that from estimating the multi-variate dynamic model make the existing methods in a univariate framework inapplicable. It proposes a general theory to quantify estimation risk applicable to the present problem and suggests practitioners a simple but effective way to implement valid inference to overcome the effect of estimation risk in backtesting portfolio VaR. In particular, we apply our theory to the efficient mean-variance-skewness portfolio for a multi-variate generalized autoregressive conditional heteroscedasticity model with multi-variate general hyperbolic distributed innovations. Some Monte Carlo simulations and an empirical application demonstrate the merits of our method.  相似文献   
17.
盘瑶  赵华 《日用化学工业》2018,48(6):314-321
概述了化妆品人体功效评价实验设计的概念、基本要素和基本原则,介绍了常用实验设计类型和实验设计要点,提供了人体功效评价实验方案设计的思路,有助于提高研究者制定实验设计方案的水平。  相似文献   
18.
目的: 建立快速灵敏的LC-MS/MS法测定人血浆中阿莫西林浓度,并用于两种阿莫西林胶囊的一致性评价。方法: 采用岛津公司LCMS-8060型LC-MS/MS仪,以MRM模式测定阿莫西林(m/z 366.00/114.00)的浓度,d4-阿莫西林作内标(m/z 370.10/114.05),离子源为ESI源。色谱柱选用Waters ACQUITY BEH C18(2.1×50 mm,1.7 μm),梯度洗脱。血浆样本加入内标,经甲醇沉淀蛋白后取上清液进样检测。结果: 所建方法经验证,其线性、准确度、精密度、最低定量限、提取回收率、特异性、基质效应、稳定性等各项指标均符合CFDA的指导原则及最新核查标准要求,并较文献报道中的方法有处理简单、灵敏度高、色谱峰形好的优点。结论: 所建方法快速、灵敏,适用于人血浆中阿莫西林浓度的检测。用于一致性评价的样本实测,两种制剂生物等效。  相似文献   
19.
The network reconfiguration is an important stage of restoring a power system after a complete blackout or a local outage. Reasonable planning of the network reconfiguration procedure is essential for rapidly restoring the power system concerned. An approach for evaluating the importance of a line is first proposed based on the line contraction concept. Then, the interpretative structural modeling (ISM) is employed to analyze the relationship among the factors having impacts on the network reconfiguration. The security and speediness of restoring generating units are considered with priority, and a method is next proposed to select the generating unit to be restored by maximizing the restoration benefit with both the generation capacity of the restored generating unit and the importance of the line in the restoration path considered. Both the start-up sequence of generating units and the related restoration paths are optimized together in the proposed method, and in this way the shortcomings of separately solving these two issues in the existing methods are avoided. Finally, the New England 10-unit 39-bus power system and the Guangdong power system in South China are employed to demonstrate the basic features of the proposed method.  相似文献   
20.
兰建国 《现代矿业》2020,36(7):13-16
为深入贯彻生态文明思想,促进矿产资源全面节约和高效利用,对招远市展开了金矿矿产资源开发利用水平调查评价,对2018年度数据进行整理和实地核查后,进行了单个矿山评价和多矿山评价,包括矿种评价、地区评价、行业评价。招远市16个矿山实际数据和基准值指标对比显示,单个矿山评价和多矿山评价的达标率均为100%。在此基础上,分析了金矿矿产资源资源开发利用水平调查评价的意义和存在问题。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号