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   1150篇
  免费   34篇
  国内免费   6篇
电工技术   97篇
综合类   1篇
化学工业   234篇
金属工艺   29篇
机械仪表   42篇
建筑科学   29篇
能源动力   53篇
轻工业   116篇
水利工程   2篇
无线电   79篇
一般工业技术   252篇
冶金工业   116篇
原子能技术   32篇
自动化技术   108篇
  2023年   4篇
  2022年   11篇
  2021年   23篇
  2020年   12篇
  2019年   21篇
  2018年   20篇
  2017年   16篇
  2016年   31篇
  2015年   16篇
  2014年   22篇
  2013年   56篇
  2012年   45篇
  2011年   71篇
  2010年   54篇
  2009年   45篇
  2008年   43篇
  2007年   58篇
  2006年   54篇
  2005年   44篇
  2004年   40篇
  2003年   28篇
  2002年   33篇
  2001年   19篇
  2000年   18篇
  1999年   23篇
  1998年   47篇
  1997年   33篇
  1996年   35篇
  1995年   25篇
  1994年   11篇
  1993年   24篇
  1992年   8篇
  1991年   13篇
  1990年   15篇
  1989年   9篇
  1988年   18篇
  1987年   7篇
  1986年   8篇
  1985年   16篇
  1984年   17篇
  1983年   12篇
  1982年   10篇
  1981年   8篇
  1980年   11篇
  1979年   12篇
  1978年   5篇
  1977年   5篇
  1976年   10篇
  1975年   6篇
  1974年   5篇
排序方式: 共有1190条查询结果,搜索用时 13 毫秒
991.
The Meissen and the Kakiemon-style Arita wares were investigated by PIXE and EPMA. Both porcelain matrices were characterized by high purity ceramics, which are white in tone and translucent due to small amounts of an iron oxide inclusion. From overglazed red, green and gilt parts, enrichment of Fe, Cu, and Au, respectively, was commonly found from the above two wares. There is a resemblance between these two wares in main chemical constituents but there is a difference in impurities or minor elements.  相似文献   
992.
以面向实际应用为目的,提出了一种考虑输电网络损耗及线路过负荷约束的火力发电机起停计划方法。首先用动态规划法建立一个不含约束条件的初始解,然后运用启发式方法对初始解进行修正使之逐个满足各约束条件得到运行可能解,并通过修改各发电机的起动优先顺序使此过程反复进行直至得到(准)最佳解。在此过程中引入最优潮流计算考虑输电网络损耗及线路过负荷等网络因素对发电机起停计划的影响成为可能,并提出一种调节发电机出力和改变发电机起停计划相结合的消除线路过负荷的方法。在一个8机44母线的测试系统上对提案方法进行了各种条件下的试算,验证了所提出的方法对解决考虑网络因素影响的发电机起停计划问题有效性。计算结果还表明:不仅线路过负荷起停计划问题的有效性。计算结果还表明:不公线路过负荷约束,网络损耗也对发电机起停 计划有较大影响。  相似文献   
993.
±800 kV长串绝缘子污闪特性及绝缘子选择研究   总被引:1,自引:0,他引:1  
对±800 kV直流输电线路上可能用到的几种典型大吨位绝缘子的污闪特性进行了系统的人工污秽试验研究。针对线路中可能用到的V型串及双I串并联结构,通过试验分析了它们对绝缘子串污闪电压的影响。结果表明,大吨位绝缘子的直流污闪电压与串长之间仍存在较好的线性关系,V型绝缘子串的污闪特性与I型串基本一致,可以直接使用I型串的试验结果,但并联绝缘子串间距对绝缘子串污闪特性存在显著影响,且串长不同时,并联绝缘子串间距对其污闪电压的影响效果不同。基于上述试验结果,并考虑了现场等值盐密与试验盐密的校正关系,给出了±800 kV特高压直流输电工程外绝缘参数计算和线路绝缘子选型的方法。  相似文献   
994.
In mechanical structures such as information precision machinery, the switching from a Velocity Servo controller to a Position Servo controller is often utilized. The author has already proposed a unified design method for both the servo controllers on the basis of a single time‐varying criterion function. Its effectiveness has been verified by numerical calculations. This letter demonstrates the effectiveness of the method experimentally. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.  相似文献   
995.
The characterization of aortic valve interstitial cells (VICs) cultured under optimal conditions is essential for understanding the molecular mechanisms underlying aortic valve stenosis. Here, we propose 2% hypoxia as an optimum VIC culture condition. Leaflets harvested from patients with aortic valve regurgitation were digested using collagenase and VICs were cultured under the 2% hypoxic condition. A significant increase in VIC growth was observed in 2% hypoxia (hypo-VICs), compared to normoxia (normo-VICs). RNA-sequencing revealed that downregulation of oxidative stress-marker genes (such as superoxide dismutase) and upregulation of cell cycle accelerators (such as cyclins) occurred in hypo-VICs. Accumulation of reactive oxygen species was observed in normo-VICs, indicating that low oxygen tension can avoid oxidative stress with cell-cycle arrest. Further mRNA quantifications revealed significant upregulation of several mesenchymal and hematopoietic progenitor markers, including CD34, in hypo-VICs. The stemness of hypo-VICs was confirmed using osteoblast differentiation assays, indicating that hypoxic culture is beneficial for maintaining growth and stemness, as well as for avoiding senescence via oxidative stress. The availability of hypoxic culture was also demonstrated in the molecular screening using proteomics. Therefore, hypoxic culture can be helpful for the identification of therapeutic targets and the evaluation of VIC molecular functions in vitro.  相似文献   
996.
Nanoporous polyethersulfone (PES) membranes are widely used in dialysis systems due to their permeability and diffusion characteristics. However, PES membranes lack blood compatibility, which influences their permeability performance when employed in blood contact devices. Parylene film was deposited on a PES membrane surface and the membrane permeability and blood compatibility were investigated by long‐term blood diffusion testing. After 28 days of testing, 90% of a bare PES membrane was covered with platelets, while the parylene film coated PES membrane had improved biocompatibility with a platelet coverage of only 20–30%. The permeability of the bare PES membrane significantly declined during the first 7 days of the blood diffusion and became stable after 8 days. In contrast, the permeability of the parylene film coated PES membrane exhibited more consistent performance during the entire test. Thus, parylene film coating on PES membrane has potential for application in hemodialysis systems. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40024.  相似文献   
997.
Stable intermediates are formed during both CO and CO2 hydrogenations on Rh/MgO at 190-220°C. The intermediates consist of at least four species, each of which is consecutively and irreversibly converted at a similar rate, forming the final product of CH4 by reaction with H2  相似文献   
998.
Carbonization properties of pitches synthesized from some aromatic hydrocarbons by the aid of were studied under atmospheric 1.1 and 3.1 MPa pressures. The highest coke yields obtained under atmospheric pressure and 3.1 MPa were 64% and 85%, respectively, both of which were observed with anthracene pitch. Pyrene pitch exhibited a low coke yield of 37% under atmospheric pressure, but as high as 85% under 3.1 MPa.The pitches were revealed with 1H-NMR and FD-MS to consist essentially of oligomers of starting aromatic rings such as dimers, trimers, and tetramers. The oligomers carried significant amounts of naphthenic hydrogens, which provide their low softening point and enable the development of an anisotropic flow texture when the pitch was carbonized. The carbonization scheme is discussed in relation to the coke yield.  相似文献   
999.
The superiority of Ti plate as the substrate of dye-sensitized solar cells   总被引:4,自引:0,他引:4  
The photovoltaic properties of dye-sensitized solar cells (DSCs) based on several types of substrates, FTO, Ti and stainless steel, were investigated. The sheet resistances of the substrates were correlated to the photovoltaic properties. The efficiency of the DSC using Ti substrate was higher than that of the DSCs using stainless steel and FTO. For the large-size DSCs based on FTO, the metal track is an important component to retain the decrease in cell performance due to the relatively high sheet resistance of FTO. To minimize the internal resistance of DSCs, the Ti sheet was used as a support of nano-crystalline TiO2 due to the low sheet resistance. Although the IPCE of DSCs based on Ti substrate was lower than that of DSCs based on FTO in the range from 400 to 500 nm, the DSC based on Ti substrate showed the higher IPCE in red region due to the light reflecting on Ti substrate. The efficiency of 3.2% for the DSC based on Ti substrate was obtained with a Jsc , Voc 0.75 V, and FF 0.610. This result shows that the Ti plate has superiority for producing the large DSCs without metal track and reduces the cost of DSCs.  相似文献   
1000.
An initial efficiency of 14.1% (Jsc=13.6 mA/cm2, Voc=1.392 V, FF=74.3%) has been achieved for a-Si/transparent interlayer/poly Si solar cell (total area of 1 cm2). Both a-Si and crystalline Si films were fabricated by plasma chemical deposition at low temperature. The short circuit current was enhanced by the introduction of a transparent intermediate layer. An initial aperture efficiency of 11.7% has been achieved for 910×455 mm2 a-Si/poly Si integrated solar cell submodule, where the laser-scribing techniques were applied for series interconnections. The results of our first run of 266 submodules in our pilot plant showed the average efficiency of 11.2%, which is applicable for mass production.  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