首页 | 官方网站   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   259篇
  免费   4篇
工业技术   263篇
  2021年   3篇
  2018年   3篇
  2017年   3篇
  2016年   2篇
  2015年   2篇
  2014年   5篇
  2013年   7篇
  2012年   5篇
  2011年   8篇
  2010年   6篇
  2009年   5篇
  2008年   10篇
  2007年   4篇
  2006年   8篇
  2005年   5篇
  2004年   7篇
  2003年   7篇
  2002年   4篇
  2001年   5篇
  2000年   7篇
  1999年   6篇
  1998年   18篇
  1997年   7篇
  1996年   10篇
  1995年   5篇
  1994年   8篇
  1993年   7篇
  1992年   3篇
  1990年   2篇
  1989年   5篇
  1988年   3篇
  1987年   2篇
  1986年   8篇
  1984年   5篇
  1983年   3篇
  1982年   9篇
  1981年   2篇
  1979年   5篇
  1977年   3篇
  1976年   6篇
  1975年   2篇
  1974年   4篇
  1973年   4篇
  1972年   2篇
  1971年   3篇
  1970年   2篇
  1969年   2篇
  1966年   4篇
  1964年   3篇
  1963年   2篇
排序方式: 共有263条查询结果,搜索用时 15 毫秒
51.
The nanostructured solid solution Mn0.5Ce0.5O2 is synthesized to develop effective noble metal free catalysts for the detoxification of technogenic contaminants. Its chemical and phase compositions and textural characteristics are studied by differential thermal analysis, X-ray diffraction analysis, laser mass spectrometry, and low-temperature nitrogen adsorption. The activity of the solid solution in the oxidation of carbon monoxide is determined by the flow method within a temperature range of 20–300°C at atmospheric pressure, a gas hourly space velocity of 1800 h−1 for the following gas mixture composition, vol %: CO, 3.6; O2, 8.0; N2, balance. The activity of Mn0.5Ce0.5O2 is shown to be appreciably higher than the activity of MnOx and CeO2, and the temperature of 100% conversion is 92, 120, and 210°C, respectively. Using the solid solution as a support and the technique of impregnation, we synthesize the nanostructured catalysts Cu/Mn0.5Ce0.5O2 and Ag/Mn0.5Ce0.5O2, which manifest high activity in the oxidation of carbon monoxide: the temperature of 100% conversion is 77 and 85°C, respectively. The new catalysts could be of interest for the purification of industrial and motor vehicle wastes.  相似文献   
52.
Illicit trade in tobacco products presents a threat to public health because it undermines the use of tax and price policies, which are among the most effective mechanisms for reducing tobacco consumption. Parties to the WHO Framework Convention on Tobacco Control (FCTC) are in the final stages of negotiating a protocol aimed at strengthening international cooperation in the fight against illicit tobacco trade. While an effective multilateral response to illicit tobacco trade would make a significant contribution to global tobacco control, achieving this through the FCTC forum is challenging. First, while illicit tobacco trade is a health problem, the expertise, experience and capacity needed to combat illicit trade are not traditionally found in health agencies. The development of links with other agencies, both domestic and international, is critical to ensure both an effective response and an efficient use of limited governmental and non-governmental resources. Second, in many parts of the world, the tobacco industry cooperates closely with governments in the combating of illicit trade. This cooperation poses risks for tobacco control, particularly if relationships and norms of cooperation spill over into other areas of FCTC implementation. An examination of the industry's positioning suggests that it sees an opportunity to portray itself as 'legitimate' and 'responsible', a friend of governments, and a way to integrate itself into FCTC processes. This paper makes suggestions for moving forward in this challenging area towards ensuring that the approach taken actually reduces illicit tobacco trade, strengthens tobacco tax policies and does not operate to undermine the FCTC.  相似文献   
53.
Three studies, 2 conducted in Israel and 1 conducted in Bosnia and Herzegovina, demonstrated that affirming a positive aspect of the self can increase one's willingness to acknowledge in-group responsibility for wrongdoing against others, express feelings of group-based guilt, and consequently provide greater support for reparation policies. By contrast, affirming one's group, although similarly boosting feelings of pride, failed to increase willingness to acknowledge and redress in-group wrongdoing. Studies 2 and 3 demonstrated the mediating role of group-based guilt. That is, increased acknowledgment of in-group responsibility for out-group victimization produced increased feelings of guilt, which in turn increased support for reparation policies to the victimized group. Theoretical and applied implications are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
54.
PP/organoclay nanocomposites were prepared using different processing aids (EMCA and PPG), and their effects on the thermal and mechanical properties were evaluated by WAXD, TEM, SEM, DSC, and mechanical tests. This study helps to clarify the effects of processing aids on the organoclay surface and on the intercalation and exfoliation processes. Nanocomposites with elongated intercalated and partially exfoliated structures were obtained, mainly when C‐15A was used. The results for the mechanical properties showed that the processing aids increased the impact strength significantly (up to three times that of neat PP) but reduced the flexural modulus of PP nanocomposites. PPG, which is polar promoted wetting MMT surface, thus increasing its interlayer distance, mainly for PP/C‐20A nanocomposites. However, it reduced the interfacial adhesion between the clay and the matrix. Nanocomposites impact strength was improved, especially when the C‐15A organoclay was used, while were achieved better results with the C‐20A organoclay when EMCA was used. The larger the amount of processing aid added, the higher the impact strength, but the lower the flexural modulus of the nanocomposites. PPG caused debonding of the clay particles and increased the number of microvoids, generating more mechanisms to aid in the energy dissipation of the systems. EMCA promoted debonding of clay particles with the formation of fibrils, indicating stronger interactions between the clay and matrix. A slight nucleation effect for PP crystallization was observed, mainly when EMCA was used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   
55.
Five studies examined hypothesis generation and discounting in causal attribution from the perspective of regulatory focus theory (E. T. Higgins, 1997, 1998). According to this theory, a promotion focus is associated with generating more and simultaneously endorsing multiple hypotheses, whereas a prevention focus is associated with generating only a few hypotheses and selecting 1 hypothesis from a given set. Five studies confirmed these predictions for both situationally induced and chronic individual differences in regulatory focus. In Studies 1, 2, and 3, individuals in a promotion focus generated more hypotheses than individuals in a prevention focus. In Studies 4 and 5, individuals in a promotion focus discounted explanations in light of alternatives less than individuals in a prevention focus. Study 5 also found that in a promotion focus, person explanations were generalized across situations less than in a prevention focus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
The properties of polypropylene (PP) nanocomposites are dependent on the quaternary ammonium salt in the montmorillonite (MMT). A nanocomposite with C-15A, which has a high cation exchange capacity (CEC), exhibits an increase in its impact properties, while one prepared with C-20A, which has a low CEC, shows an increase in the flexural modulus. In order to obtain enhancements in both properties, PP nanocomposites were prepared using a combination of 1:1 of C-15A/C-20A. X-ray, TEM, thermal properties, dynamical mechanical analysis (DMA), and mechanical tests were used to evaluate the properties of this novel mixture. Nanocomposites of partially exfoliated morphology were obtained, especially when 5 wt% of poly(propylene-graft-maleic anhydride) (PP-g-MA) was used. The mechanical tests showed that the use of a 1:1 mixture of C-15A/C-20A caused a simultaneous gain of approximately 12% in flexural modulus and a five times higher impact strength. In addition, the dispersion of the clay was more homogeneous, with the absence of agglomerated structures that were present when either the individual C-15A or C-20A was used. The DMA results showed that while the organoclay improved the modulus of PP, the Tg was decreased slightly.  相似文献   
57.
Six experiments examined whether novelty versus familiarity influences global versus local processing styles. Novelty and familiarity were manipulated by either framing a task as new versus familiar or by asking participants to reflect upon novel versus familiar events prior to the task (i.e., procedural priming). In Experiments 1–3, global perception was enhanced after novelty priming or framing, whereas familiarity priming facilitated local perception relative to a control group. In Experiment 4, participants used more inclusive categories under novelty priming and narrower categories under familiarity priming. In Experiments 5–6, participants construed actions and products more abstractly when these were framed as novel as compared to familiar. These results support the construal level theory (N. Liberman & Y. Trope, 2008; Y. Trope & N. Liberman, 2003) contention that having less direct experience is associated with using higher construal levels. Implications of the findings for research on mood, processing styles, stereotypes, and consumer research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
58.
Four light-cured calcium hydroxide and three chemically cured resin-based lining materials were compared for hydoxil ion (OH-) release. Results indicated that the chemically cured calcium hydroxide cements were capable of OH- release for a longer period than the light-cured resin bases. Alkaliner (a chemically cured liner) produced and maintained the highest alkaline environment in the long-term, whereas calcium fluoride liner and Basic-L (both resin-based) showed the lowest values of OH- ion release.  相似文献   
59.
Thermally reversible poly(N-isopropylacrylamide) (PIPAAm) was covalently grafted onto tissue culture dishes to allow detachment of cultured cells upon temperature change from physiological to room temperature. In addition the grafted polymer matrix was used to entrap biomolecules such as growth factors either to be released by diffusion early in cell cultures, or remain entrapped and be reversibly exposed to cell receptors. Experiments with model proteins trypsin and insulin show that amount loaded and released depends upon the PIPAAm grafting density. Dishes grafted with 2.5 microgram/cm2 PIPAAm released approximately four times more model protein over 4 h than dishes grafted with 1.8 microgram/cm2. This in vitro drug delivery system can be used to deliver factors to the basal side of cells early in cell culture by providing high local concentrations without high bulk concentration. Cultures of human retinal pigmented epithelium showed higher growth rate on insulin loaded dishes than on controls containing a similar bulk solution concentration. These cultures retained the ability to detach singly or as confluent sheets from the loaded surfaces.  相似文献   
60.
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-23

京公网安备 11010802026262号