全文获取类型
收费全文 | 9771篇 |
免费 | 840篇 |
国内免费 | 43篇 |
专业分类
电工技术 | 135篇 |
综合类 | 14篇 |
化学工业 | 2139篇 |
金属工艺 | 243篇 |
机械仪表 | 388篇 |
建筑科学 | 230篇 |
矿业工程 | 4篇 |
能源动力 | 401篇 |
轻工业 | 741篇 |
水利工程 | 31篇 |
石油天然气 | 5篇 |
无线电 | 1755篇 |
一般工业技术 | 1975篇 |
冶金工业 | 1339篇 |
原子能技术 | 125篇 |
自动化技术 | 1129篇 |
出版年
2024年 | 13篇 |
2023年 | 91篇 |
2022年 | 151篇 |
2021年 | 226篇 |
2020年 | 187篇 |
2019年 | 233篇 |
2018年 | 312篇 |
2017年 | 248篇 |
2016年 | 364篇 |
2015年 | 306篇 |
2014年 | 412篇 |
2013年 | 666篇 |
2012年 | 499篇 |
2011年 | 652篇 |
2010年 | 512篇 |
2009年 | 525篇 |
2008年 | 509篇 |
2007年 | 409篇 |
2006年 | 378篇 |
2005年 | 316篇 |
2004年 | 303篇 |
2003年 | 265篇 |
2002年 | 245篇 |
2001年 | 221篇 |
2000年 | 196篇 |
1999年 | 226篇 |
1998年 | 511篇 |
1997年 | 339篇 |
1996年 | 253篇 |
1995年 | 167篇 |
1994年 | 147篇 |
1993年 | 109篇 |
1992年 | 63篇 |
1991年 | 62篇 |
1990年 | 66篇 |
1989年 | 62篇 |
1988年 | 45篇 |
1987年 | 51篇 |
1986年 | 54篇 |
1985年 | 34篇 |
1984年 | 27篇 |
1983年 | 28篇 |
1982年 | 8篇 |
1981年 | 22篇 |
1980年 | 23篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 23篇 |
1976年 | 34篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
In polyolefin processes the melt index (MI) is the most important control variable indicating product quality. Because of
the difficulty in the on-line measurement of MI, a lot of MI estimation and correlation methods have been proposed. In this
work a new dynamic MI estimation scheme is developed based on system identification techniques. The empirical MI estimation
equation proposed in the present study is derived from the 1
st
-order dynamic models. Effectiveness of the present estimation scheme was illustrated by numerical simulations based on plant
operation data including grade change operations in high density polyethylene (HDPE) processes. From the comparisons with
other estimation methods it was found that the proposed estimation scheme showed better performance in MI predictions. The
virtual sensor model developed based on the estimation scheme was combined with the virtual on-line analyzer (VOA) to give
a quality control system to be implemented in the actual HDPE plant. From the application of the present control system, significant
reduction of transition time and the amount of off-spec during grade changes was achieved 相似文献
22.
A new torque estimator for switched reluctance motor (SRM) drives based on 2-D rotary regression analysis is presented in this paper. The proposed torque estimator is composed of a bicubic regressive polynomial as a function of rotor position and input current. The regressive coefficients can be computed offline or online from the torque characteristics acquired either experimentally or from numerical computation. Furthermore, a torque estimation method by taking mutual coupling into consideration is proposed. It can be seen that the estimated and experimentally obtained self-coupling and mutual-coupling torque characteristics are in good agreement with each other. In addition, the dynamic torque waveforms with and without the mutual coupling, estimated by the proposed estimator, are found to be virtually the same as those obtained from the bicubic spline interpolation for SRM drives with single-pulse voltage, hysteresis current chopping, as well as with voltage pulse width modulation control. The success of all the case studies being reported is a good validation of the usefulness and accuracy of the proposed real-time torque estimator that, as described in this paper, can be used to quickly estimate the instantaneous output torque of SRM drives. 相似文献
23.
An experimental investigation was carried out to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb2S3). A scale dynamometer was used for friction tests and particular emphases were given to the effect of applied pressure, sliding speed, and temperature on the coefficient of friction according to the relative amounts of the two solid lubricants. Results showed that the brake linings with both solid lubricants exhibited better friction stability and less speed sensitivity than the friction materials containing a single solid lubricant. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high-temperature friction test. 相似文献
24.
25.
HJ Lee HK Ha MH Kim YK Jeong PN Kim MG Lee JS Kim DJ Suh SG Lee YI Min YH Auh 《Canadian Metallurgical Quarterly》1997,169(2):517-520
OBJECTIVE: The purpose of this study was to evaluate ERCP and CT findings of ectopic drainage of the common bile duct into the duodenal bulb. CONCLUSION: Although rare, the diagnosis of ectopic drainage of the common bile duct into the duodenal bulb is important to prevent inadvertent damage during biliary tract or gastric surgery and to clarify the cause of chronic peptic ulcers. 相似文献
26.
We present a technique for in situ lens nucleus emulsification using low phaco power and high vacuum, a continuous curvilinear capsulorhexis, and hydrodelineation. Emulsification is done with the phaco tip slanted down 30 or 45 degrees. Cutting and aspiration do not cause an undesirable energy loss. This technique can be combined with the nuclear chopping or divide and conquer methods because of its ability to drill and hold the nucleus. Posterior capsular rupture is prevented because the separated epinucleus acts as a barrier between the nucleus and the cortex. The low power used minimizes the energy transfer to the corneal endothelium. This technique is particularly useful in eyes with brunescent cataract. 相似文献
27.
We examined the molecular mechanism of metronidazole resistance by constructing a lambda-Zap II phagemid expression library with genomic DNA from a metronidazole-resistance strain of Helicobacter pylori. Twenty-two clones were found to have elevated MTZ resistances in XLOLR strain of E. coli. Phagemids belonging to the twenty two clones were extracted and then retransformed into the XLOLR strain of E. coli. After MTZ selection, five clones could confer metronidazole resistance consistently. According to Southern hybridization and DNA sequencing, the five clones contained a same locus, recA. In addition, transforming the five clones into BL21 strain of E. coli produced a higher resistance to MTZ. Interestingly, electroporation of one of the five phagemid clones into two MTZ sensitive H. pylori yielded MTZ resistant strains. Comparing amino acid sequence in MTZ resistant with sensitive isolates revealed two point mutations at this locus. Above results suggest that mutation in recA may be associated with metronidazole resistance of H. pylori. 相似文献
28.
29.
Cluster analysis in industrial market segmentation through artificial neural network 总被引:6,自引:0,他引:6
Market segmentation has commonly applied cluster analysis. This study intends to make the comparison of conventional two-stage method with proposed two-stage method through the simulated data. The proposed two-stage method is the combination of self-organizing feature maps and K-means method. The simulation results show that the proposed scheme is better than the conventional two-stage method based on the rate of misclassification. 相似文献
30.
Buffer analysis has traditionally relied heavily on the use of traffic models with short range (exponentially decaying) autocorrelation, e.g. Poisson and Markov modulated Poisson processes. Recent literature has suggested the presence of traffic with slowly (hyperbolically) decaying autocorrelation functions; these sources collectively and individually seem to be exhibiting the phenomenon of long range dependence (LRD). Furthermore, it has been claimed that this sort of traffic may exhibit behaviour, when buffered, that is advantageous in that a smaller buffer may be required than would be the case with non-LRD traffic. This phenomenon has been named the crossover effect, and the authors quantify its relevance to ATM networking, using simulation studies of a homogenous mix of chaotic sources. These show that there is a crossover effect, but the key finding is that this effect is much nearer to a buffer length of zero than was predicted by previous theoretical studies, actually occurring at a value so low that it has no practical significance 相似文献