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   447篇
  免费   20篇
电工技术   4篇
综合类   3篇
化学工业   110篇
金属工艺   2篇
机械仪表   4篇
建筑科学   22篇
矿业工程   3篇
能源动力   6篇
轻工业   77篇
水利工程   8篇
无线电   12篇
一般工业技术   61篇
冶金工业   115篇
自动化技术   40篇
  2023年   1篇
  2022年   9篇
  2021年   25篇
  2020年   7篇
  2019年   11篇
  2018年   11篇
  2017年   14篇
  2016年   7篇
  2015年   16篇
  2014年   4篇
  2013年   27篇
  2012年   21篇
  2011年   35篇
  2010年   24篇
  2009年   21篇
  2008年   42篇
  2007年   32篇
  2006年   23篇
  2005年   16篇
  2004年   10篇
  2003年   15篇
  2002年   14篇
  2001年   8篇
  2000年   7篇
  1999年   12篇
  1998年   3篇
  1997年   4篇
  1996年   8篇
  1995年   5篇
  1994年   2篇
  1993年   6篇
  1992年   5篇
  1990年   3篇
  1989年   3篇
  1988年   4篇
  1987年   2篇
  1985年   2篇
  1984年   4篇
  1983年   1篇
  1981年   1篇
  1980年   1篇
  1966年   1篇
排序方式: 共有467条查询结果,搜索用时 15 毫秒
121.
The effect of H2 and C2H2 addition on particle formation in the pyrolysis of C3O2/Ar mixtures was studied behind reflected shock waves. An existing reaction mechanism for the pyrolysis of highly-diluted C3O2 in argon was expanded to conditions with higher C3O2 concentrations (up to 33 volume%) at elevated pressures and high temperatures and was validated against experimental data. The simulations for the gas-phase chemistry were performed with the program CHEMKIN. The heterogeneous particle formation was modeled by post-processing using the program PREDICI relying on the Galerkin method. It was found that in C3O2/H2/Ar pyrolysis, the induction times and rate constants of particle formation do not differ significantly from those of pure C3O2/Ar pyrolysis. However, the presence of H2 reduced the particle volume fraction, the mean diameter of particles, the particle number density, and the maximum temperature rise of the mixture. Hydrocarbon-bonded hydrogen in C3O2/C2H2/Ar pyrolysis caused significantly increased induction times for particle formation, decreased particle volume fractions, and decreased temperature rises. The different reaction channels for carbon particle formation were identified in view of the role of hydrogen. An alternating reaction channel including C2 species played an important role in forming polycyclic aromatic hydrocarbons (PAH) in the mixtures.  相似文献   
122.
Whey protein beverages reduced blood pressure in young men and women in a six week controlled intervention. There were no differences in systolic blood pressure (SBP), diastolic blood pressure (DBP), or mean arterial pressure (MAP) observed between groups consuming 28 g per day of either hydrolyzed or non-hydrolyzed whey protein in a beverage. However, in young adults with elevated DBP and SBP, whey beverage consumption significantly decreased SBP, DBP, and MAP by 8.0, 8.6, and 6.4 mm Hg, respectively (P ≤ 0.001 for all comparisons). In subjects with elevated SBP only, SBP significantly decreased by 3.8 mm Hg (P ≤ 0.04) after the whey beverage intervention. Subjects with normal blood pressure had no change in SBP, DBP, and MAP. Whey beverages also significantly decreased total and low-density lipoprotein cholesterol concentrations (P ≤ 0.001 and 0.05, respectively). Whey protein beverages may be useful for the dietary treatment of prehypertension and/or stage 1 hypertension.  相似文献   
123.
It is often argued that the internet poses a threat to traditional forms of authority. Within studies of religion online claims have also been made that the internet is affecting religious authority online, but little substantive work has backed up these claims. This paper argues for an approach to authority within online studies which looks separately at authority: roles, structures, beliefs/ideologies and texts. This approach is applied to a thematic analysis of 100 religious blogs and demonstrates that religious bloggers use their blogs to frame authority in ways that may more often affirm than challenge traditional sources of authority.  相似文献   
124.
In mobile devices there exist several in-built sensor units and sources which provide data for context reasoning. More context sources can be attached via wireless network connections. Usually, the mobile devices and the context sources are battery powered and their computational and space resources are limited. This sets special requirements for the context recognition algorithms. In this paper, several classification and automatic feature selection algorithms are compared in the context recognition domain. The main goal of this study is to investigate how much advantage can be achieved by using sophisticated and complex classification methods compared with a simple method that can easily be implemented in mobile devices. The main result is that even a simple linear classification algorithm can achieve a reasonably good accuracy if the features calculated from raw data are selected in a suitable way. Usually context recognition algorithms are fitted to a particular problem instance in an off-line manner and modifying methods for on-line learning is difficult or impossible. An on-line version of the Minimum-distance classifier is presented in this paper and it is justified that it leads to considerably higher classification accuracies compared with the static off-line version of the algorithm. Moreover, we report superior performance for the Minimum-distance classifier compared to other classifiers from the view point of computational load and power consumption of a smart phone.  相似文献   
125.
Definition of the Problem Models of decision making in medical ethics have to establish themselves as being able to lead to ethically right or at least “credible” decisions. For this purpose, approaches of theoretical justification stemming from ethics are vital. However, clinical ethics is sometimes criticized for theoretical deficits. In order to address this criticism, we will try to justify ethical case discussion and ethics consultation by principlism and discourse ethics by referring to a clinical ethics project (METAP). Arguments Principlism and discourse ethics can fruitfully complement each other when used in ethical case discussion or consultation. Thereby, some theoretical as well as practical weaknesses of both approaches can be mitigated. Discourse ethics, for example, safeguards the ethical validity of moral decisions and norms for action, respectively, thus mitigating shortcomings of justification when using principlism. Conversely, principlism answers questions concerning ethical adequacy and functions particularly as a safeguard for appropriate decisions in the individual case. Conclusion By using a combination of these two approaches, a broader justification seems possible rather than by relying on principlism or discourse ethics alone. Even if some challenges persist, and even if the combined model cannot always prevent dissent, it may strengthen practical confidence in the ethical decision by its ?double“ safeguards (principles and discourse). This could render clinical ethics more ?robust“ that have been missing so far.  相似文献   
126.
One‐ and two‐dimensional diffraction gratings were fabricated on commercial polyethylene terephthalate (PET) film by two beam direct laser interference patterning (DLIP) method using a pulse laser (10 ns) with a wavelength of 266 nm. The relative diffraction efficiency of the structured specimens (at 633 nm) in transmission mode was measured and correlated with the topological characteristics of the structured PET substrates. The obtained diffraction gratings made by DLIP show better or similar diffraction efficiencies when compared with the reported efficiency of gratings made by other methods (up to 42.5% for 1 μm arrays), and can be fabricated on large areas in very short processing times (up to 18 cm2/s). POLYM. ENG. SCI., 52:1903–1908, 2012. © 2012 Society of Plastics Engineers  相似文献   
127.
LIMITATIONS OF FOLIN ASSAYS OF FOLIAR PHENOLICS IN ECOLOGICAL STUDIES   总被引:7,自引:0,他引:7  
We examined the response of the widely used Folin-Denis assay to purified tannins from 16 woody plant species and to three commercial polyphenol preparations often used as standards. The reagent's response to these chemical mixtures differed significantly among sources (tree species, commercial preparations) and sampling dates, even though the mixtures contained the same total dry weight of tannins. Response to commercial standards usually did not resemble response to actual plant tannin and produced estimates that differed from actual concentrations by as much as twofold. Species-based and seasonal differences in polyphenol composition are evidently responsible for these variable results. Reagents that depend on redox reactions, such as the Folin-Denis, do not produce reliable absolute or relative quantification of phenolics when different species or samples from different dates are compared, and use of commercial standards does not resolve this problem.  相似文献   
128.
This study was designed to investigate the DNA-methylation status of E-cadherin (CDH1) and H-cadherin (CDH13) in serum samples of cervical cancer patients and control patients with no malignant diseases and to evaluate the clinical utility of these markers. DNA-methylation status of CDH1 and CDH13 was analyzed by means of MethyLight-technology in serum samples from 49 cervical cancer patients and 40 patients with diseases other than cancer. To compare this methylation analysis with another technique, we analyzed the samples with a denaturing high performance liquid chromatography (DHPLC) PCR-method. The specificity and sensitivity of CDH1 DNA-methylation measured by MethyLight was 75% and 55%, and for CDH13 DNA-methylation 95% and 10%. We identified a specificity of 92.5% and a sensitivity of only 27% for the CDH1 DHPLC-PCR analysis. Multivariate analysis showed that serum CDH1 methylation-positive patients had a 7.8-fold risk for death (95% CI: 2.2-27.7; p = 0.001) and a 92.8-fold risk for relapse (95% CI: 3.9-2207.1; p = 0.005). We concluded that the serological detection of CDH1 and CDH13 DNA-hypermethylation is not an ideal diagnostic tool due to low diagnostic specificity and sensitivity. However, it was validated that CDH1 methylation analysis in serum samples may be of potential use as a prognostic marker for cervical cancer patients.  相似文献   
129.
This article focuses on the effect of pulp bleaching and emerging commercial compatibilizers on physical performance of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. Industrially bleached and unbleached hardwood kraft pulp fibers are treated with several additive types, and compounded with PLA to fiber content of 30 wt %. After injection molding, the produced biocomposites are evaluated by their mechanical performance and fiber–matrix adhesion. For selected materials, fiber surface and fiber properties are reflected to composite performance by analyzing the compositions, dimensions, and lignin coverage of original fibers, as well as fiber dispersion and dimensions after melt processing. As a conclusion, unbleached kraft pulp fibers provide significant improvement in physical properties of PLA/pulp fiber composites. Of the screened compatibilizers, epoxidated linseed oil has a clear positive effect on performance when bleached kraft pulp fibers are used. The improvements correspond to enhanced fiber–matrix adhesion and differences in remaining fiber length distributions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47955.  相似文献   
130.
In industrial scale catalytic volatile organic compounds (VOCs) incineration it is sometimes observed that the VOC conversions are higher than expected, based on the laboratory scale experiments at the same temperatures. One reason for this is that the construction material of the industrial scale catalytic incinerator may have an effect on the total VOC conversion. In this study, the effect of construction material on VOC removal activity is studied through laboratory experiments, by thermodynamic calculations and by flow modelling. The results showed that copper and Aluzinc decreased the light-off temperature (T50) of n-butyl acetate compared to thermal experiments. Copper and Aluzinc did not, however, further decrease the T50 when they were introduced into the reactor packed with the catalyst. The higher total VOC conversion observed in the industrial scale incinerator is presumably due to the higher temperatures at the outlet of the catalyst, which is maintained by the heat exchangers.  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