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   868篇
  免费   29篇
  国内免费   7篇
电工技术   4篇
综合类   2篇
化学工业   188篇
金属工艺   31篇
机械仪表   19篇
建筑科学   35篇
能源动力   58篇
轻工业   60篇
水利工程   14篇
石油天然气   8篇
无线电   85篇
一般工业技术   183篇
冶金工业   107篇
原子能技术   12篇
自动化技术   98篇
  2024年   3篇
  2023年   11篇
  2022年   21篇
  2021年   34篇
  2020年   25篇
  2019年   21篇
  2018年   29篇
  2017年   28篇
  2016年   38篇
  2015年   19篇
  2014年   38篇
  2013年   65篇
  2012年   42篇
  2011年   56篇
  2010年   47篇
  2009年   38篇
  2008年   48篇
  2007年   42篇
  2006年   31篇
  2005年   21篇
  2004年   18篇
  2003年   17篇
  2002年   18篇
  2001年   13篇
  2000年   10篇
  1999年   6篇
  1998年   28篇
  1997年   12篇
  1996年   22篇
  1995年   10篇
  1994年   7篇
  1993年   13篇
  1992年   6篇
  1991年   8篇
  1989年   5篇
  1988年   4篇
  1987年   4篇
  1986年   3篇
  1985年   4篇
  1984年   5篇
  1983年   6篇
  1982年   6篇
  1981年   3篇
  1980年   2篇
  1978年   3篇
  1977年   2篇
  1976年   4篇
  1975年   2篇
  1966年   1篇
  1965年   1篇
排序方式: 共有904条查询结果,搜索用时 15 毫秒
11.
The paper addresses the adaptive behaviour of parallel fuzzy proportional plus fuzzy integral plus fuzzy derivative (FP+FI+FD) controller. The parallel FP+FI+FD controller is actually a non-linear adaptive controller whose gain changes continuously with output of the process under control. Two non-stationary processes, whose characteristics change with time, are considered for simulation study. Simulation is performed using software LabVIEW TM . The set-point tracking response of parallel FP+FI+FD is compared with conventional parallel proportional plus integral plus derivative (PID) controller, tuned with the Ziegler-Nichols (Z-N) tuning technique. Simulation results show that conventional PID controller fails to track the set-point and becomes unstable as the process changes its characteristic with time. But the parallel FP+FI+FD controller shows considerably much better set-point tracking response and does not deviate from steady state. Also, a huge spike is observed in the output of PID controller as the reference set-point and process parameters are changed, while the FP+FI+FD controller gives spike free control signal.  相似文献   
12.
Cell division cycle 25A (Cdc25A) is a dual-specificity phosphatase that is overexpressed in several cancer cells and promotes tumorigenesis. In normal cells, Cdc25A expression is regulated tightly, but the changes in expression patterns in cancer cells that lead to tumorigenesis are unknown. In this study, we showed that ubiquitin-specific protease 29 (USP29) stabilized Cdc25A protein expression in cancer cell lines by protecting it from ubiquitin-mediated proteasomal degradation. The presence of USP29 effectively blocked polyubiquitination of Cdc25A and extended its half-life. CRISPR-Cas9-mediated knockdown of USP29 in HeLa cells resulted in cell cycle arrest at the G0/G1 phase. We also showed that USP29 knockdown hampered Cdc25A-mediated cell proliferation, migration, and invasion of cancer cells in vitro. Moreover, NSG nude mice transplanted with USP29-depleted cells significantly reduced the size of the tumors, whereas the reconstitution of Cdc25A in USP29-depleted cells significantly increased the tumor size. Altogether, our results implied that USP29 promoted cell cycle progression and oncogenic transformation by regulating protein turnover of Cdc25A.  相似文献   
13.
Laboratory incubations were conducted to determine the ammonia (NH3) loss from urea as affected by the addition of coarse and ground (fine) pyrites at 1:1, 1:2 and 1:5 urea: pyrite (w/w) ratios and methods of application (surfaceapplication, incorporation and placement). Coarse pyrites (>-2mm) were not effective in reducing NH3 loss from urea when surface applied even at the highest ratio of pyrite (15.9% vs 18.7% without pyrite). Ground pyrites (0.1–0.25 mm), in 1:1 ratio, had about 5% less NH3 loss than the urea alone treatment. Higher ratios of pyrites reduced NH3 loss much more. Ammonia losses were the most with surface-applied urea (18.9%) and the least (13.5%) when placed (2.5 cm) below the soil surface. Addition of ground pyrite to surface-applied urea (1:1 ratio) decreased the loss to 13.2%. Urea+pyrite placed below the soil surface had the least loss (9.8%). Results indicate that combined application of urea and fine pyrite could reduce NH3 loss.  相似文献   
14.
O. Onay  O.M. Kockar  T.R. Tyagi 《Fuel》2006,85(3):382-392
This paper discusses the maximisation of the yields of useful bio-oils generated from seeds and nut-shells both by extraction and by hydropyrolysis. The formation and the composition of the bio-oils are also discussed.Powdered (<0.25 mm diameter) Rapeseed, Linseed and Safflower seed and Hazel nut and Walnut shells, that is, fresh precursors of liptinite, have been characterised by their elemental analyses, infra-red and NMR spectra. Bio-oils obtained both by extraction and by slow hydropyrolysis to 520 °C at moderate pressure in the presence of ammonium dioxydithiomolybdate have been compared by the same analyses and by gas chromatography. Consistent with previous work [Hardy JA. A greener future with biodiesel. Green Chem 2001 G56-G57], extraction of the seeds with organic solvents, including Diesel oil, gave yields of up to 40% together with an uninteresting residue. However, subsequent saponification of the residues gave further yields of oil. Hydropyrolysis removed oxygen from the seeds as water and as oxides of carbon to generate bio-oil in yields of up to 75%. Whereas little oil could be extracted from the nut-shells, hydropyrolysis gave oil yields of ∼40%. Some char was also formed, suggesting that optimisation of the hydropyrolysis might give even larger yields of oil.  相似文献   
15.
Experimental profiles of a single penetrant (water) across the membrane have been established at different downstream pressures during steady state pervaporation. The profiles ofacetic acid-water binary penetrant system across the membrane were also measured at different downstream pressures, temperatures and compositions during steady state pervaporation. A stack of identical pre-characterized symmetric aromatic polyamide membranes was used for the profile study. The theoretical prediction of concentration polarization from mathematical equations has been confirmed by the experimental profile data for a binary penetrant system.  相似文献   
16.
Formation of nanocrystalline calcia from calcite has been studied in situ via transmission electron microscopy. The crystallographic transformation occurred via two mechanisms: the first is by distortion of the cleaved rhombohedron of calcite, formed by {104} planes in hexagonal coordinates, into a cube. This produced a microstructure of oriented, elongated nanocrystals of calcia with planar boundaries. In the second mechanism, the micrometer-sized parent calcite particles broke up into nano-sized grains as the decomposition began, leading to irregularly shaped, randomly oriented nanocrystals of calcia.  相似文献   
17.
In this report, a free space frequency‐time‐domain technique is presented for characterizing the electrical properties and thickness of the sample using multiple reflections and fabry‐perot resonance phenomenon. The retrieval of constitutive electromagnetic parameters of the sample has been carried out by comparing the measured reflection coefficient data from the sample at two different incident angles. The relative permittivity as well as relative permeability along with the thickness of different samples viz., beryllia, silicon, and plexiglass have been evaluated with high accuracy in the frequency range 1 to 15 GHz. The method is also experimentally validated by successfully reconstructing the unknown material properties of two different samples. The unique advantage of this method lies in non‐requirement of any prior knowledge of the sample's thickness for measuring the complex relative dielectric constant as well as relative permeability of the sample. To determine the electromagnetic properties of the sample, the sole knowledge of reflection coefficient data are needed. Moreover, the method does not involve any additional measurement for the reference calibration. The simple, cost‐effective proposed scheme is quite useful in many applications like accurate determination of signal strength in indoor wireless communication, through wall imaging, food industry, and so on.  相似文献   
18.
For the purpose of developing collaborative support in design studio environments, we have carried out ethnographic fieldwork in professional and academic product design studios. Our intention was to understand design practices beyond the productivity point of view and take into account the experiential, inspirational and aesthetical aspects of design practices. Using examples from our fieldwork, we develop our results around three broad themes by which design professionals support communication and collaboration: (1) use of artefacts, (2) use of space and (3) designerly practices. We use the results of our fieldwork for drawing implications for designing technologies for the design studio culture.  相似文献   
19.
This paper presents research that investigated algorithms for high-precision identification of contextual information in location-aware engineering applications. The primary contribution of the presented work is the design and implementation of a dynamic user-viewpoint tracking scheme in which mobile users’ spatial context is defined not only by their position (i.e., location), but also by their three-dimensional head orientation (i.e., line of sight). This allows the identification of objects and artifacts visible in a mobile user’s field of view with much higher accuracy than was possible by tracking position alone. For outdoor applications, a georeferencing based algorithm has been developed using the Global Positioning System (GPS) and magnetic orientation tracking devices [5] to track a user’s dynamic viewpoint. For indoor applications, this study explored the applicability of wireless technologies, in particular Indoor GPS, for dynamic user position tracking in situations where GPS is unavailable. The objectives of this paper are to describe the details of the three-stage-algorithm that has been designed and implemented, and to demonstrate the extent to which positioning technologies such as GPS and Indoor GPS can be used together with high-precision orientation trackers to accurately interpret the fully-qualified spatial context of a mobile user in challenging environments such as those found on construction sites. The obtained results highlight the potential of using location-aware technologies for rapidly identifying and retrieving contextual information in engineering applications.  相似文献   
20.
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