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   639篇
  免费   9篇
  国内免费   9篇
电工技术   7篇
综合类   2篇
化学工业   73篇
金属工艺   95篇
机械仪表   4篇
建筑科学   13篇
能源动力   27篇
轻工业   11篇
水利工程   1篇
无线电   86篇
一般工业技术   123篇
冶金工业   156篇
原子能技术   1篇
自动化技术   58篇
  2023年   2篇
  2022年   2篇
  2021年   15篇
  2020年   3篇
  2019年   2篇
  2018年   3篇
  2017年   7篇
  2016年   3篇
  2014年   18篇
  2013年   33篇
  2012年   34篇
  2011年   41篇
  2010年   48篇
  2009年   35篇
  2008年   36篇
  2007年   36篇
  2006年   25篇
  2005年   14篇
  2004年   16篇
  2003年   14篇
  2002年   21篇
  2001年   16篇
  2000年   20篇
  1999年   19篇
  1998年   20篇
  1997年   32篇
  1996年   22篇
  1995年   15篇
  1994年   17篇
  1993年   14篇
  1992年   12篇
  1991年   6篇
  1990年   6篇
  1989年   8篇
  1988年   4篇
  1987年   7篇
  1986年   3篇
  1985年   5篇
  1984年   3篇
  1983年   5篇
  1982年   5篇
  1981年   4篇
  1979年   3篇
  1978年   2篇
  1977年   1篇
排序方式: 共有657条查询结果,搜索用时 156 毫秒
1.
The aim of this study is to explore whether lung cancer associated with air pollution has cell type specificity. The air quality data (SO(2), CO, O(3), NOx) from the Taiwan EPA's air quality monitoring stations were collected between 1995 and 1998. Patients with lung cancer were identified through the National Cancer Registration Program operated by the Taiwanese government. Two major pathological types (adenocarcinoma (AC) and squamous cell carcinoma (SCC)) were considered. The Pearson correlation coefficients between the air quality index and age-standardized incidence rate per 100,000 person years (ASR) of AC and SCC were calculated for both genders for three township categories characterized by different levels of air pollution. The traffic-related NOx and CO showed significant correlations with female lung cancer incidence rate, with Pearson's correlation 0.33 (P=0.03) and 0.40 (P=0.01) respectively. However, the correlation between air pollution and lung cancer was not significant for males. Significant correlation coefficients were also found between the ratio of AC/SCC and the mean concentrations of NOx (r=0.41, P=0.04) and CO (r=0.47, P=0.02) in females. Our results show that the worse the air pollution was in the area, the higher the AC rate, regardless of gender. On the other hand, SCC incidence rates did not increase with increasing air pollution. Our results show that a correlation exists between air pollution and lung adenocarcinoma incidence.  相似文献   
2.
Ozonation on the phenols present in pyrolytic aqueous phases attained from biomass thermochemical conversion was evaluated. During ozonation, the dark color of original samples was found to decrease as a function of ozonation time. The oxidation kinetics of phenols was quantified by a method based on the color changes of samples. The oxidation profiles showed different behaviors and in some cases the phenols presented a positive correlation with the relative R color parameter, except eugenol, syringol, and vanillin which were markedly different. Finally, the color changes observed seem to be associated with the changes in the overall content of phenols and with the change in the molecular weight of the heavy fractions that include lignin oligomers.  相似文献   
3.
Ultra-small-angle X-ray scattering (USAXS) is employed to quantify the average size, interparticle spacing, and volume fraction of the primary B2 precipitates in Fe-based superalloys with varying Al concentration. The results are analyzed with a model incorporating polydispersity and interference effects and verified by transmission electron microscopy (TEM) characterizations. As the Al amount increases from 4 to 10?mass pct, there is an approximately 40?pct decrease in the average interparticle spacing and?~30?pct reduction in the average particle diameter.  相似文献   
4.
Due to rapid environmental change, policymakers no longer choose foresight issues based on their own experience. Instead, they need to consider all the possible factors that will influence new technological developments and formulate an appropriate future technological development strategy to the country through the technology foresight system. For the sake of gathering more objective evidence to convince stakeholders to support the foresight issues, researchers can employ bibliometric analysis to describe current scientific development and forecast possible future development trends. Through this process, a consensus is reached about the direction of future technology development. However, we believe that bibliometric analysis can do more for technology policy formulation, such as (1) offer quantitative data as evidence to support the results of qualitative analysis; (2) review the situations of literature publication in specific technological fields to seize the current stage of technology development; and (3) help us grasp the relative advantage of foresight issues development in Taiwan and the world and develop profound strategic planning in accordance with the concept of Revealed Comparative Advantage. For those reasons, our research will revisit the role that bibliometric analysis plays for nations while choosing the foresight issues. In addition, we will analyze the development of the technology policy in Taiwan based on bibliometric analysis, and complete the foresight issues selection by processing key issue integration, key word collection related to this field, the searching and confirmation of literature, development opportunities exploration, comparative development advantage analysis and the innovation-foresight matrix construction, etc.  相似文献   
5.
6.
Issues of asymptotic stabilization of a class of non-linear driftless systems are presented. In addition to the necessary and sufficient condition for the existence of a smooth time-invariant asymptotic stabilizer, sufficient condition for the existence of a quadratic-type Lyapunov function candidate is also proposed herein to alleviate the construction of stabilizing control laws. Following the deduction of the equivalence of the sufficient condition and the determination of the local definiteness of a defined scalar function, the stabilizability checking conditions are then derived in terms of system dynamics and its derivatives at the origin only. These are achieved by taking Taylor's series expansion on system dynamics. The derived conditions are shown to be consistent with those obtained by Brockett. Comparative results of Liaw and Liang are also included. Finally, examples are given to demonstrate the use of the main results.  相似文献   
7.
To improve the pervaporation performance in separating an aqueous ethanol solution, polyamide thin‐film composite (TFC) membranes (m‐tolidine‐H‐TMC/mPAN) were prepared through the interfacial polymerization reaction between trimesoyl chloride (TMC) and 2,2'‐dimethylbenzidine hydrochloride (m‐tolidine‐H) on the surface of a modified polyacrylonitrile (mPAN) membrane. The effects of the feed ethanol concentration on the pervaporation performance and the durability of m‐tolidine‐H‐TMC/mPAN TFC membranes were investigated. To choose the optimal mPAN membrane as the TFC substrate, the effect of hydrolysis time on the chemical properties and separation performance of an mPAN substrate was also studied. An appropriate hydrolysis time of 15 min was chosen to obtain the mPAN substrate due to the corresponding high permeation flux. The m‐tolidine‐H‐TMC/mPAN TFC membrane exhibited a high pervaporation performance for ethanol dehydration. A positron annihilation lifetime spectroscopy experiment was used to estimate the mean free‐volume radius of the m‐tolidine‐H‐TMC polyamide selective layer, which lay between the radii of the water and ethanol molecules. © 2013 Society of Chemical Industry  相似文献   
8.
This work studies a series of fluorescent materials, benzo[k]fluoranthene-based linear acenes, and uses these materials directly as the non-doped active layer to fabricate deep blue- to green-emissive organic light emitting diodes (OLEDs). Experimental results indicate that benzo[k]fluoranthene-based linear acenes with different substituents in pristine films have a wide range and strong intensity of the luminescence spectra. The substituents of benzo[k]fluoranthene derivatives modulate the lifetime of the excited state and PL spectra of excitonic, excimer or both emissions in the solid state. Controls of emission spectra are exploited in fabricating high-performance non-doped deep blue to green OLEDs with electroluminescence in the deep blue region (420–460 nm), green region (480–580 nm) or both (430–580 nm).  相似文献   
9.
The strain-controlled fatigue behavior of the new nickel-chromium-molybdenum superalloy, HASTELLOY® C-2000® was investigated. Low-cycle fatigue specimens were tested in strain-controlled fatigue conditions under axial strain range control at 24 °C, 204 °C and 427 °C. The results indicated that at total strain ranges below 0.8%, temperature does not significantly influence fatigue life, whereas at high total strain ranges, there is a significant drop in fatigue life at 427 °C. At room temperature and 204 °C, the cyclic stress response was cyclic hardening, followed by cyclic stability, cyclic hardening, or cyclic softening, depending on the total strain range. At 427 °C, only cyclic hardening was observed. Fractographic and metallographic analyses were also conducted. The strain-life and Holloman relation parameters are calculated. A theoretical model that predicts the life of this alloy under the tested conditions using the plastic strain energy method is also presented. The results of the theoretical model are in good agreement with the experimental results.  相似文献   
10.
An Fe41Co7Cr15Mo14C15B6Y2 bulk metallic glass with a diameter of 5 mm was prepared with the copper-mold-casting method. The corrosion resistance of this amorphous steel in sulfuric-acid solutions was determined by electrochemical measurements. The passive film formed on the surface of the alloy after immersion in the 0.5-mol/l H2SO4 solution for 1 week was analyzed by X-ray photoelectron spectroscopy (XPS). Electrochemical measurements show that the corrosion resistance of the amorphous steel in the 1 mol/l-H2SO4 solution is superior to a stainless steel (SUS 321), and is almost the same as Ti6Al4V, which shows that the amorphous steel has an excellent corrosion resistance in sulfuric-acid solutions. As the concentration of the sulfuric-acid solutions increases from 0.5 mol/l to 4 mol/l, the corrosion resistance of the amorphous steel decreases. The XPS result reveals that a bilayer structure of protective film formed on the surface of the amorphous steel in a H2SO4 solution. The compositions of the inner part of the film are MoO2, Cr2O3, CoO, and FeO, and those of the outer film are MoO3, Cr(OH)3, Co(OH)2, and Fe(OH)3.  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