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   1452篇
  免费   66篇
  国内免费   3篇
电工技术   90篇
综合类   4篇
化学工业   432篇
金属工艺   55篇
机械仪表   23篇
建筑科学   23篇
矿业工程   1篇
能源动力   90篇
轻工业   108篇
水利工程   4篇
石油天然气   3篇
无线电   73篇
一般工业技术   357篇
冶金工业   68篇
原子能技术   45篇
自动化技术   145篇
  2023年   8篇
  2022年   20篇
  2021年   37篇
  2020年   16篇
  2019年   38篇
  2018年   41篇
  2017年   34篇
  2016年   50篇
  2015年   38篇
  2014年   37篇
  2013年   77篇
  2012年   83篇
  2011年   113篇
  2010年   69篇
  2009年   88篇
  2008年   81篇
  2007年   72篇
  2006年   46篇
  2005年   51篇
  2004年   59篇
  2003年   45篇
  2002年   35篇
  2001年   33篇
  2000年   21篇
  1999年   28篇
  1998年   32篇
  1997年   36篇
  1996年   27篇
  1995年   14篇
  1994年   16篇
  1993年   18篇
  1992年   18篇
  1991年   25篇
  1990年   12篇
  1989年   16篇
  1988年   5篇
  1987年   8篇
  1986年   8篇
  1985年   9篇
  1984年   9篇
  1983年   6篇
  1982年   9篇
  1981年   4篇
  1980年   7篇
  1979年   5篇
  1978年   3篇
  1976年   2篇
  1975年   5篇
  1973年   2篇
  1968年   2篇
排序方式: 共有1521条查询结果,搜索用时 15 毫秒
991.
The poorly crystallized steel rusts have been prepared by hydrolysis of aqueous solutions dissolving Fe(III) and different metal ions such as Ti(IV), Cr(III), Ni(II) and Cu(II) at varied atomic ratios in metal/(Fe+metal). The precipitates formed by the hydrolysis were frozen with liquid N2 to inhibit crystallization and particle growth. The rusts produced were poorly crystalline and nanosized particles with sizes of 4-10 nm and the rust formed without adding metal ions was assigned to ferrihydrite. The crystallite size decreased from 1.1 to 0.7 nm with increasing the added metal ions. It was shown by extended X-ray fine structure and Mössbauer spectroscopy that the short-range structure of poorly crystalline rusts was disturbed by adding Ti(IV).  相似文献   
992.
Metallurgical and Materials Transactions A - Age-hardened Cu-Ti alloys are widely used as conductive materials in small electrical devices, so it is important for them to have suitable mechanical...  相似文献   
993.
Organic electrolytes with negatively chargeable functional groups such as benzoic acid (BA, weak acid), benzenesulfonic acid (BSA, strong acid), and p‐aminobenzoic acid (p‐ABA, ampholyte) were concentrated through polyethylene (PE) films photografted with 2‐(dimethylamino)ethyl methacrylate (DMAEMA) by electrotransport. The permeabilities of DMAEMA‐grafted PE (PE‐g‐PDMAEMA) films to BA and BSA were considerably increased by the application of direct current at pH 6. BA and BSA could be selectively permeated from the respective binary BA/phenyl‐1,2‐ethandiol (PhED, neutral) and BSA/PhED mixtures by making use of the difference in their permeabilities. In addition, BSA was selectively permeated from the binary BSA/BA mixtures. The organic electrolytes mentioned above were transported against their concentration gradient toward the anode side and their degrees of concentration went up to 90% by the continuous application of direct current. The degrees of concentration for organic electrolytes obtained by electrotransport in this study were slightly higher than those obtained by the uphill transport using the pH difference across the PE‐g‐PDMAEMA film, and the concentration time was considerably shortened. It was made clear that the electrotransport through the PE‐g‐PDMAEMA films is one of the effective techniques to selectively separate or concentrate organic electrolytes with negatively chargeable functional groups. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2535–2544, 2003  相似文献   
994.
Different novel copolymers, ABA‐type block copolymers composed of polyamide4 as outer segments and polyoxyethylene as an inner segment and AB‐ and ABA‐type block copolyamides containing polyamide4 and another hydrophilic polyamide derived from a bicyclic lactam, were synthesized by the anionic ring‐opening polymerization of 2‐pyrrolidone using the corresponding acyllactam‐type macromolecular activators. The degradation rate of both block copolymers containing polyamide4 segments in a composted soil was found to decrease with increasing content of the second segments, although they were also hydrophilic and/or biodegradable. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3492–3498, 2004  相似文献   
995.
We have proposed that the co‐occurrence frequency image (CFI) based on the co‐occurrence frequency histogram of the gray value of an image can be used in a new scheme for image feature extraction. This paper proposes new enhancement filters to achieve sharpening and smoothing of images. These filters are very similar in result but quite different in process from those which have been used previously. Thus, we show the possibility of a new paradigm for basic image enhancement filters making use of the CFI. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(1): 36–42, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20699  相似文献   
996.
When malathion was incubated in aqueous extracts obtained from 17 vegetables and fruits at pH 7.4 and 37 °C for 4 h, asparagus extract exhibited the highest malathion degradation. The degradation effects of the extracts ranged from 100% (asparagus) to 0.5% (papaya). The highest malathion‐degradation effects obtained from extracts of asparagus at different growing stages incubated at pH 7.4 and 37 °C for 1 h was 94.4 ± 0.45% (stem length, 5–10 cm), followed by 88.0 ± 0.31% (10–15 cm), 85.1 ± 0.94 (15–20 cm), 82.2 ± 0.52 (20–25 cm), 81.2 ± 1.4% (pre‐emergent), 67.3 ± 0.67% (>25 cm), and 42.7 ± 2.1% (fern). The protein content in an asparagus extract from different growing stages was not consistent with the degradation activity of malathion. Results of time course studies on malathion degradation in asparagus extracts from different growing stages yielded half‐life times of malathion degradation ranging from 51.7 min (fern stage) to 17.3 min (stem length, 5–10 cm). Formation of α‐ and β‐malathion mono acids from malathion was detected in an incubated sample by gas chromatography/mass spectrometry. The results support the presence of carboxylesterases in asparagus extracts. Copyright © 2006 Society of Chemical Industry  相似文献   
997.
The focus in this study is on the effect of residual stress on the delamination crack initiation from the interface edge between thin films, Cu/TiN, where the stress is intensified by the free edge effect. The delamination tests, where the mechanical stress is applied on the interface, show that the specimen with the thinner Cu film has an apparently higher strength at the interface edge. The residual stress in the films is then evaluated by curvature measurement of film/substrate coupon and the influence on the delamination is analyzed. The residual stress increases with the increase of film thickness and remarkably intensifies the stress near the edge. By superimposing the contributions of the applied load and the residual stress, a good agreement is obtained in the normal stress intensity near the interface edge at the delamination independent of the Cu thickness. This signifies that the combination of intensified stresses due to the applied load and the residual stress governs the crack initiation at the interface edge, and the toughness at the interface edge is evaluated by the stress intensity factor on the basis of the fracture mechanics concept.  相似文献   
998.
999.
1000.
With the number of known roles played by Ras proteins increasing rapidly, finding answers to how the diverse cellular responses are triggered is becoming increasingly pertinent. Although our understanding of the control of specificity of signal transduction is still small, the combination of biochemical, structural and genetic analyses is starting to reveal how the cell-specific responses to Ras activation are controlled.  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