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   344篇
  免费   17篇
  国内免费   2篇
电工技术   6篇
化学工业   134篇
金属工艺   3篇
机械仪表   3篇
建筑科学   11篇
矿业工程   1篇
能源动力   6篇
轻工业   97篇
水利工程   1篇
无线电   16篇
一般工业技术   38篇
冶金工业   8篇
原子能技术   2篇
自动化技术   37篇
  2023年   7篇
  2022年   30篇
  2021年   42篇
  2020年   19篇
  2019年   18篇
  2018年   14篇
  2017年   7篇
  2016年   9篇
  2015年   17篇
  2014年   14篇
  2013年   24篇
  2012年   21篇
  2011年   27篇
  2010年   20篇
  2009年   13篇
  2008年   18篇
  2007年   15篇
  2006年   12篇
  2005年   6篇
  2004年   4篇
  2003年   1篇
  2002年   3篇
  1998年   2篇
  1997年   1篇
  1994年   3篇
  1993年   2篇
  1991年   2篇
  1989年   2篇
  1986年   1篇
  1985年   1篇
  1982年   1篇
  1978年   1篇
  1977年   2篇
  1973年   1篇
  1972年   1篇
  1970年   1篇
  1947年   1篇
排序方式: 共有363条查询结果,搜索用时 15 毫秒
41.
This critique analyzes the methodology used in a study of the economic burden imposed on public finances in the Czech Republic by the consumption of cigarettes. The study was prepared by a consulting firm on behalf of the Phillip Morris Company. This critique, by using economic theory and a cost-benefit methodology, refutes the conclusion of the Phillip Morris study that smoking represents an economic benefit to Czech state finances. In fact, the correction of only one among numerous errors in assumptions and calculations in the Phillip Morris study leads to the opposite conclusion: Instead of savings of $150 million per year, smoking drains at least $373 million from the state budget annually, nearly.8% of the Czech gross domestic product. The net loss to the society is even greater if all pertinent costs and benefits are calculated properly. The critique demonstrates how to craft a rigorous economic response to common industry attempts to influence public opinion in which the industry employs specious or erroneous assumptions and data.  相似文献   
42.
Transport of L -leucine into Schizosaccharomyces pombe cells from the stationary phase of growth (after preincubation for 60 min with 1% glucose) proceeds uphill, practically unidirectionally, and is mediated by at least two systems: a high-affinity system with a KT of 0·045 mmol 1?1 and Jmax of 3·3 nmol min?1 (mg dry weight)?1 and a low-affinity system with a KT of 1·25 mmol 1?1 and Jmax of 16·0 nmol min?1 (mg dry weight)?1. The high-affinity system has a pH optimum at 3.2, the accumulation ratio is highest at a cell density of 2–4 mg dry weight per ml and decreases with increasing leucine concentration. Transport of leucine by the high-affinity system is strongly inhibited by proton conductors, ammonium ions and by most amino acids, but only L -phenylalanine, L -isoleucine, L -valine and L -cysteine behave as fully competitive inhibitors. Systems of L -leucine transport in S. pombe are not constitutive. Transport activity appears only after preincubation of cells with a suitable source of energy. If cycloheximide is added during preincubation with glucose, no transport systems for leucine are synthesized. After removal of glucose, the activity of transport systems decays with a half-time of about 20 min. The presence of cyclic AMP increases the initial rate of leucine uptake only in cells preincubated with glucose and in the absence of cycloheximide.  相似文献   
43.
The presented report focuses on the testing of heterogenized methyltrioxorhenium (MTO) in indene epoxidation. A range of mesoporous materials with different SiO2/Al2O3 ratios, namely aluminosilicates type Siral and MCM-41 silica and fumed silica, were used as supports for immobilization of MTO. The tested support materials and prepared catalytic systems exhibited high surface area, well-defined regular structure and narrow pore size distribution of mesopores and therefore represent good quality catalysts for various reactions. The immobilized MTO on various supports was tested for the preparation of 1,2-epoxyindane using two forms of hydrogen peroxide as oxidation agents, namely aqueous solution of hydrogen peroxide and its anhydrous form, urea-hydrogen peroxide. The prepared catalysts were successfully used for the preparation of 1,2-epoxyindane with achieved 100 % selectivities to the desired product at high conversions of indene.  相似文献   
44.
45.
46.
Optoelectronic properties of CdS:In/Si anisotype heterojunction photodetector fabricated by depositing of polycrystalline CdS and indium doped CdS films used thermal resistive technique on clean monocrystalline p-type silicon substrates are presented. The effect of In diffusion temperature(T d)in CdS layer on the optoelectronic characteristics of these devices has been studied. Two peaks situated at 650 and 800 nm with values of 0.32 and 0.43 A/W, respectively, were observed in the responsivity plot. Other optoelectronics properties such as detectivity, photovoltaic, and response time are also presented.  相似文献   
47.
Nitric oxide (NO) affects multiple gastrointestinal functions, including mucosal inflammation and antimicrobial activity. The aim of this study was to screen the ability of probiotic bacteria to stimulate NO production in porcine intestinal epithelial cells and macrophages in the presence and absence of interferon gamma (INF-γ). Production of NO in intestinal epithelium was stimulated by individual strains of lactobacilli without INF-γ priming. While none of the tested bifidobacteria were capable of inducing NO production, most constitutively secreted NO. Most tested strains induced a significant increase in NO production compared with the control cells in the macrophage cell line 3D4/21. Results support the protective role of the individual strains of the genera Lactobacillus and Bifidobacterium and may lead to new approaches for manipulating and regulating immune responses at the mucosal surfaces of the gastrointestinal tract.  相似文献   
48.
Hydrolysis of the epoxide groups of the copolymer glycidylmethacrylate - ethylenedi-methacrylate in variously concentrated sulphuric acid solutions was studied. An approximate activation energy of hydrolysis, 41 kJ mol?1, was determined from the temperature dependences. For the sake of comparison the effect of pH on the degree of hydrolysis over the whole range of pH values was examined, and the importance of the results with respect to other reactions of the copolymer used was discussed.  相似文献   
49.
Polymeric composites were prepared by reticulate doping of poly(γ-methyl-L-glutamate) (PMLGA) and poly(γ-methyl-LD-glutamate) (PMLDGA, 1 : 1) having different conformation forms with 1,3-dimethylimidazolium-TCNQ complex salt. The heat induced α-helix to coil transition in PMLGA and α-helix to β-form and coil transition in PMLDGA were carried out in chlorobenzene and o-dichlorobenzene at temperatures between 70 and 150°C. The conductivity of polyglutamate composites thermally treated and prepared at 70°C is higher by approximately two orders of magnitude than that of thermally not treated films cast at ambient temperature. The conductivity of the most conductive reticulate-doped PMLGA film is higher by more than four orders of magnitude than that of the 1,3-dimethylimidazolium-TCNQ complex salt in pressed pellets.  相似文献   
50.
The deformation of dispersed droplets in a PS/LLDPE 95:5 blend during uniaxial elongation and after cessation of the flow was studied. The behavior of the dispersed droplets during elongation is in a good agreement with a prediction of the modified capillary number model using transient elongational viscosities. The phase structure changes after the elongation was studied in relaxation and recovery modes. The morphology was investigated using scanning electron microscopy and small‐angle X‐ray scattering. Thus the dimensions of the dispersed particles and their degree of orientation were estimated. It was shown that the SAXS as an integral method gives new additional information which is hardly accessible by SEM as a method providing local information about discrete locations in the sample. The results of both methods proved that the stress in the sample is a decisive parameter determining the morphology development after cessation of the flow.

  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