全文获取类型
收费全文 | 5204篇 |
免费 | 471篇 |
国内免费 | 123篇 |
专业分类
电工技术 | 169篇 |
综合类 | 305篇 |
化学工业 | 756篇 |
金属工艺 | 208篇 |
机械仪表 | 314篇 |
建筑科学 | 941篇 |
矿业工程 | 70篇 |
能源动力 | 246篇 |
轻工业 | 224篇 |
水利工程 | 84篇 |
石油天然气 | 106篇 |
武器工业 | 13篇 |
无线电 | 501篇 |
一般工业技术 | 939篇 |
冶金工业 | 188篇 |
原子能技术 | 163篇 |
自动化技术 | 571篇 |
出版年
2024年 | 6篇 |
2023年 | 33篇 |
2022年 | 103篇 |
2021年 | 133篇 |
2020年 | 107篇 |
2019年 | 103篇 |
2018年 | 87篇 |
2017年 | 134篇 |
2016年 | 194篇 |
2015年 | 221篇 |
2014年 | 291篇 |
2013年 | 273篇 |
2012年 | 274篇 |
2011年 | 398篇 |
2010年 | 261篇 |
2009年 | 321篇 |
2008年 | 299篇 |
2007年 | 349篇 |
2006年 | 334篇 |
2005年 | 271篇 |
2004年 | 234篇 |
2003年 | 217篇 |
2002年 | 217篇 |
2001年 | 176篇 |
2000年 | 156篇 |
1999年 | 152篇 |
1998年 | 52篇 |
1997年 | 73篇 |
1996年 | 57篇 |
1995年 | 36篇 |
1994年 | 37篇 |
1993年 | 30篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有5798条查询结果,搜索用时 171 毫秒
281.
选取新疆额尔齐斯河流域富蕴、阿勒泰、哈巴河气象站1962—2013年实测逐月降水与气温资料,采用复Morlet小波分析法、R/S分析法及相关水文统计方法对流域气温变化特征及变化趋势进行了分析。结果表明:额尔齐斯河流域内3个气象站年降水量、年平均气温均呈现出上升趋势,同时流域年降水量呈现出多个时间尺度的相对丰枯交替特征,富蕴、阿勒泰、哈巴河气象站主震荡周期分别为22 a,18 a,22 a;赫斯特指数表明未来额尔齐斯河流域内年平均气温总体上继续保持上升趋势,且其未来年份年平均气温上升趋势的变化程度为:富蕴>哈巴河>阿勒泰。 相似文献
282.
283.
在叙述典型的制冷冷凝器的类型、结构及其优缺点基础上,着重介绍了一种新研究开发成功的全新型的水与空气组合式冷凝器及其优点、特点和适用范围。 相似文献
284.
285.
《Measurement》2016
This research was conducted with the aim of analyzing two of the main metrological characteristics of any measurement system: Repeatability and Reproducibility. Both of these features play an important role in the analysis of the measurements and they can give us a lot of information about who and what influences any measuring system. The analysis of Repeatability and Reproducibility is generally carried out through the use of the study Gage R&R. This study permits to understand which are the decisive factors in a measurement system, and, definitively, if the process is stable, that is under statistical control or out of statistical control. 相似文献
286.
《中国工程学刊》2012,35(1):51-62
This article presents research efforts made to assist a Fortune 500 glassmaker in reducing the variability of its automated visual inspection systems in assessing product quality. Through interviewing line workers, engineers and managers, and direct observations of the inspection process possible causes leading to large variability observed in the inspection process were identified. Responding to these findings, solutions related to equipment setup, job changes, and operational procedures were suggested in order to minimize the inspection process variations as well as to improve the replicability of the inspection stations. Additionally, a unique statistical experiment was conducted to analyze how three factors (namely, operator, defect size, and threshold value used) would affect the mean of the defective ratio. A robust design aiming at controlling these variations was then given to optimize the system's performance. 相似文献
287.
Ya‐Ping Xue Zhi‐Qiang Liu Ming Xu Ya‐Jun Wang Yu‐Guo Zheng 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2011,86(3):391-397
BACKGROUND: (R)‐(‐)‐Mandelic acid (R‐MA) is an important intermediate and chiral regent with broad uses. An efficient method for the separation of R‐MA from the bioreaction mixture with high yield is of great importance, thus, the main objective of this work is to investigate the recovery of R‐MA using an ion‐exchange process. RESULTS: The equilibrium isotherms for the separation of R‐MA by resin HZ202 were obtained in the pH range 5.0–9.0 and temperature range 25–35 °C. The equilibrium data are well fitted by the Langmuir isotherm. Batch kinetic experiments showed that the mobility of R‐MA? in solution was rapid and the R‐MA?/OH? ion‐exchange process reached equilibrium after about 60 min. Adsorption kinetics were analyzed by a linear driving force mass‐transfer model, yielding good prediction of the kinetic behavior. In fixed bed column experiments, the breakthrough curves of R‐MA from the solution on resin HZ202 were determined at different flow rates and R‐MA was eluted with different concentrations of HCl. A favorable breakthrough curve and optimal eluant concentration were obtained. The results were used for the separation of R‐MA biosynthesized from (R,S)‐mandelonitrile with nitrilase, and separation was successfully achieved with above 90% recovery yield. CONCLUSION: Resin HZ202 presents favorable behavior for the recovery of R‐MA, in terms of capacity, kinetics, affinity, and susceptibility to regeneration. The results of this study provide an efficient method for R‐MA recovery from bioreaction mixture and could potentially be used in industry. Copyright © 2010 Society of Chemical Industry 相似文献
288.
Toppino Thomas C.; Cohen Michael S.; Davis Meghan L.; Moors Amy C. 《Canadian Metallurgical Quarterly》2009,35(5):1352
The authors clarify the source of a conflict between previous findings related to metacognitive control over the distribution of practice. In a study by L. Son (2004), learners were initially presented pairs of Graduate Record Examination (GRE) vocabulary words and their common synonyms for 1 s, after which they chose to study the pair again immediately (massed practice), later (spaced practice), or not at all (done). Learners chose spaced practice less as pair difficulty increased. A. S. Benjamin and R. D. Bird (2006), using different materials and procedures and a longer presentation duration (5 s), concluded just the opposite. The authors adopted Son’s materials and procedures and replicated her findings with a 1-s stimulus duration. However, the declining choice of spacing as item difficulty increased largely reflected learners’ failure to fully perceive items with brief presentations. With longer presentations, ensuring full perception, the choice of spaced practice increased with greater pair difficulty, in agreement with Benjamin and Bird. Theoretical implications are discussed in the context of discrepancy-reduction and proximal-learning perspectives. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
289.
290.