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   483篇
  免费   19篇
  国内免费   2篇
电工技术   43篇
综合类   4篇
化学工业   139篇
金属工艺   6篇
机械仪表   9篇
建筑科学   3篇
能源动力   25篇
轻工业   40篇
水利工程   1篇
石油天然气   2篇
无线电   33篇
一般工业技术   125篇
冶金工业   11篇
原子能技术   11篇
自动化技术   52篇
  2024年   1篇
  2023年   2篇
  2022年   3篇
  2021年   13篇
  2020年   3篇
  2019年   9篇
  2018年   5篇
  2017年   11篇
  2016年   12篇
  2015年   10篇
  2014年   22篇
  2013年   32篇
  2012年   26篇
  2011年   32篇
  2010年   26篇
  2009年   29篇
  2008年   37篇
  2007年   25篇
  2006年   34篇
  2005年   33篇
  2004年   17篇
  2003年   12篇
  2002年   20篇
  2001年   8篇
  2000年   6篇
  1999年   8篇
  1998年   3篇
  1997年   4篇
  1996年   6篇
  1995年   6篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   5篇
  1990年   6篇
  1989年   3篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1984年   3篇
  1983年   4篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有504条查询结果,搜索用时 0 毫秒
71.
Fabrications of micro-dot electrodes of LiCoO2 and Li4Ti5O12 on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm−2. The prepared LiCoO2 and Li4Ti5O12 micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO2 and Li4Ti5O12 micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO2 micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li+, and the Li4Ti5O12 micro-dot electrode showed sharp redox peaks at 1.5 V.  相似文献   
72.
Maleic anhydride-modified polypropylene (MAPP) is a compatibilizer used to improve the physical and mechanical properties of many wood/plastic composites (WPCs). The properties of WPCs containing MAPP differ according to the characteristics of the specific MAPP that it is used. In this study, the physical and mechanical properties, including shear viscosity, of polypropylene-based WPCs containing different types of MAPP were investigated before and after water absorption. The shear viscosity of MAPP increased with increasing molecular weight, but remained nearly constant for WPCs containing different types of MAPP. In dry conditions, the strongest WPC contained the MAPP with the highest acid value. The highest flexural modulus was observed with the WPC containing the MAPP with the highest molecular weight. In wet conditions, the WPC exhibiting the best mechanical properties contained a MAPP with a molecular weight of 58,000.  相似文献   
73.
Macroporous monoliths, composed of thermoresponsive, tertiary‐aminated, and crosslinking monomers, were prepared for continuous‐flow separation of palladium(II) ions. N ‐Isopropylacrylamide was required to form the porous structure in the monoliths, indicating that the mechanism of porous structure formation involved polymerization‐induced phase separation of the poly(N ‐isopropylacrylamide) gel. Tertiary‐aminated monoliths showed adsorption selectivity for palladium(II) ions in hydrochloric media, compared with copper(II) ions. The maximum capacities of the monoliths with tertiary amine contents of 10, 20, 30, and 70 mol % for palladium(II) ions were 0.6, 1.1, 1.3, and 2.3 mmol/g, respectively. Darcy's permeabilities of water through the macroporous monolith were 10?14 to 10?13 m2, and those were comparable to that through a commercially available membrane filter with a pore size of several micrometers. In the continuous‐flow process, the macroporous monolith with tertiary amine selectively adsorbed palladium(II) ions in the coexistence of copper(II) ions with 10 times higher concentration than the palladium(II) ions. The palladium(II) ions were eluted from the macroporous monolith, and the concentration of palladium(II) ions in the eluate was up to 45 times of that in the feed solution. The average enrichment factor and total recovery percentage of palladium(II) ions were 8.7 times and 95%, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44385.  相似文献   
74.
[Correction Notice: An erratum for this article was reported in Vol 27(3) of Health Psychology (see record 2008-08834-013). In the aforementioned article, the second sentence of the Results portion of the abstract should read: Among participants most attracted to Whites, group devaluation was associated with higher levels of nonprimary partner UAI; but was associated with lower levels of nonprimary partner UAI among those most attracted to non-Whites.] Objective: This study examined depressive mood and HIV-risk behavior in relation to perceived group devaluation and group identity. Design: Cross-sectional survey of 192 Asian gay men. Main Outcome Measures: Depressive mood assessed using the Centers for Epidemiological Studies Depression Scale (CES-D) and self-reported receptive or insertive unprotected anal intercourse (UAI) in the past 3 months. Results: Group devaluation was positively associated with depressive mood. Among participants most attracted to Whites, group devaluation was associated with higher levels of nonprimary partner UAI, among those most attracted to non-Whites. Among participants reporting higher levels of group devaluation, those with more positive personal evaluations of the Asian gay community had lower levels of total UAI compared to those with more negative personal evaluations of the Asian gay community. Conclusions: Results suggest that group devaluation is associated with higher levels of depressive mood among Asian gay men. Asian gay men most attracted to non-Whites or hold more positive evaluations of their group may be buffered from the influence of high perceived group devaluation on UAI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
Reports an error in "Perceived group devaluation, depression, and HIV-risk behavior among Asian gay men" by David H. Chae and Hirokazu Yoshikawa (Health Psychology, 2008[Mar], Vol 27[2], 140-148). In the aforementioned article, the second sentence of the Results portion of the abstract should read: Among participants most attracted to Whites, group devaluation was associated with higher levels of nonprimary partner UAI; but was associated with lower levels of nonprimary partner UAI among those most attracted to non-Whites. (The following abstract of the original article appeared in record 2008-03424-002.) Objective: This study examined depressive mood and HIV-risk behavior in relation to perceived group devaluation and group identity. Design: Cross-sectional survey of 192 Asian gay men. Main Outcome Measures: Depressive mood assessed using the Centers for Epidemiological Studies Depression Scale (CES-D) and self-reported receptive or insertive unprotected anal intercourse (UAI) in the past 3 months. Results: Group devaluation was positively associated with depressive mood. Among participants most attracted to Whites, group devaluation was associated with higher levels of nonprimary partner UAI, among those most attracted to non-Whites. Among participants reporting higher levels of group devaluation, those with more positive personal evaluations of the Asian gay community had lower levels of total UAI compared to those with more negative personal evaluations of the Asian gay community. Conclusions: Results suggest that group devaluation is associated with higher levels of depressive mood among Asian gay men. Asian gay men most attracted to non-Whites or hold more positive evaluations of their group may be buffered from the influence of high perceived group devaluation on UAI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
76.
An irradiation experiment on uranium–plutonium–zirconium (U–Pu–Zr) alloys containing 5 wt% or less minor actinides (MAs) and rare earths was carried out in the Phénix fast reactor. The isotope compositions of the fuel alloys irradiated for 120 and 360 equivalent full-power days (EFPDs) were chemically analyzed by inductively coupled plasma–mass spectrometry after 3.3–5.3 years of cooling. The results of chemical analysis indicated that the discharged burnups of the fuel alloys irradiated for 120 and 360 EFPDs were 2.1–2.5 and 5.3–6.4 at%, respectively. The changes in the isotopic abundances of plutonium, americium, and curium during the irradiation experiment were assessed to discuss the transmutation performance of MA nuclides added to U–Pu–Zr alloy fuel. Multigroup three-dimensional diffusion and burnup calculations accurately predicted the changes in these isotopic abundances after fuel fabrication. An evaluation of the MA transmutation ratio based on the results of chemical analysis revealed that the quantity of MA elements in the U–19Pu–10Zr–5MA (wt%) alloy decreased by about 20% during the irradiation experiment for 360 EFPDs.  相似文献   
77.
Nascent mesodermal cells derived from EB5 embryonic stem (ES) cells were sorted in terms of cardiogenic potential on the basis of their expression levels of platelet-derived growth factor receptor alpha (PDGFRalpha) and fetal liver kinase 1 (Flk-1). The sorted cells were cocultured with OP9 stromal cells to induce terminal differentiation into contractile cardiac colonies. A significant number of cardiac colonies were found in the Flk-1+/PDGFRalpha+ fraction. The enrichment double-positive fraction produced approximately fivefold more cardiac colonies than the Flk-1+/PDGFRalpha- fraction and 10-fold more than the Flk-1-/PDGFRalpha+ fraction. To investigate the involvement of these markers in embryonic cardiogenesis, the cells that disseminated from the E7.5-7.75 embryos were fractionated and seeded on OP9 cells. The cardiogenic potential was markedly enhanced in the Flk-1+/PDGFRalpha+ fraction. These results suggest that some of the precursor cells coexpressing these markers are selectively involved in cardiogenic events, and that the identification of ES-cell-derived precursors with these markers will contribute to the effective production of cardiomyocytes for cell therapies.  相似文献   
78.
79.
Hirai A  Matsumoto H 《Applied optics》2006,45(22):5614-5620
A technique for the measurement of the group refractive index wavelength dependence of optical materials using a low-coherence tandem interferometer and a spectrometer is proposed. Four channeled spectra resulting from interferences of light beams from different pairs of optical paths are used for the calculation of optical path differences. The group refractive index wavelength dependence is calculated from these optical path differences generated from the sample under measurement. No a priori information of the geometric thickness of a sample is required. The wavelength dependence of the group refractive index of the samples BK7 parallel plate of 5.200 and 10.025 mm from 675 to 850 nm is experimentally measured with an accuracy of the order of 10(-5) and a repeatability of the order of 10(-9).  相似文献   
80.
A copolymer with α-D-mannose (Man) and trimethoxysilane (TMS) units was synthesized for immobilization on siliceous matrices such as a sensor cell and membrane. Immobilization of the trimethoxysilane-containing copolymer on the matrices was readily performed by incubation at high heat. The recognition of lectin by poly(Man-r-TMS) was evaluated by measurement with a quartz crystal microbalance (QCM) and adsorption on an affinity membrane, QCM results showed that the mannose-binding protein, concanavalin A, was specifically bound on a poly(Man-r-TMS)-immobilized cell with a higher binding constant than bovine serum albumin. The amount of concanavalin A adsorbed during permeation through a poly(Man-r-TMS)-immobilized membrane was higher than that through an unmodified membrane. Moreover, the concanavalin A adsorbed onto the poly(Man-r-TMS)-immobilized membrane was recoverable by permeation of a mannose derivative at high concentration.  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