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   405篇
  免费   4篇
  国内免费   3篇
电工技术   34篇
化学工业   73篇
金属工艺   6篇
机械仪表   4篇
建筑科学   4篇
能源动力   33篇
轻工业   8篇
无线电   66篇
一般工业技术   55篇
冶金工业   98篇
原子能技术   11篇
自动化技术   20篇
  2023年   2篇
  2022年   3篇
  2021年   6篇
  2020年   3篇
  2019年   3篇
  2017年   4篇
  2016年   3篇
  2015年   3篇
  2014年   7篇
  2013年   6篇
  2012年   8篇
  2011年   10篇
  2010年   11篇
  2009年   12篇
  2008年   13篇
  2007年   11篇
  2006年   17篇
  2005年   10篇
  2004年   12篇
  2003年   10篇
  2002年   9篇
  2001年   7篇
  2000年   8篇
  1999年   17篇
  1998年   43篇
  1997年   29篇
  1996年   10篇
  1995年   13篇
  1994年   13篇
  1993年   11篇
  1992年   5篇
  1991年   7篇
  1990年   6篇
  1988年   4篇
  1987年   3篇
  1986年   4篇
  1985年   3篇
  1984年   8篇
  1983年   5篇
  1982年   3篇
  1981年   6篇
  1980年   5篇
  1979年   5篇
  1978年   4篇
  1977年   5篇
  1976年   6篇
  1975年   2篇
  1974年   3篇
  1973年   5篇
  1972年   3篇
排序方式: 共有412条查询结果,搜索用时 15 毫秒
1.
The use of field robots can greatly decrease the amount of time, effort, and associated risk compared to if human workers were to carryout certain tasks such as disaster response. However, transportability and reliability remain two main issues for most current robot systems. To address the issue of transportability, we have developed a lightweight modularizable platform named AeroArm. To address the issue of reliability, we utilize a multimodal sensing approach, combining the use of multiple sensors and sensor types, and the use of different detection algorithms, as well as active continuous closed‐loop feedback to accurately estimate the state of the robot with respect to the environment. We used Challenge 2 of the 2017 Mohammed Bin Zayed International Robotics Competition as an example outdoor manipulation task, demonstrating the capabilities of our robot system and approach in achieving reliable performance in the fields, and ranked fifth place internationally in the competition.  相似文献   
2.
3.
Infrared (IR) detecting elements were prepared using positive temperature coefficient (PTC) thermistors with large temperature coefficients of resistivity (α). Their compositions were denoted as Ba1−x Sr x Nb0.003Ti0.997O3 + 1 mol % TiO2 + 0.07 mol %MnO (x=0, 0.2), and their temperature coefficients of resistivity were 78 and 50% K−1, respectively. Their IR sensing properties were measured under the self-regulating heating conditions, and were compared with those of a detector with small α (18 % K−1). It was shown that large α was effective for controlling the element temperature by self-regulating heating and for improving sensitivity. The responsivity,R v of the element withx=0.2 was 980 VW−1, and was as large as those of pyroelectric detectors. Expressions which normalize the sensitivity and the thermal time constant were derived. From these expressions, criteria for improving some IR sensing properties were obtained.  相似文献   
4.
The objectives of this study were 1) to evaluate interleukin-8 concentrations in cervical secretions in predicting preterm delivery, microbial invasion of the amniotic cavity and histologic chorioamnionitis in patients with preterm labor and intact membranes and 2) to compare the diagnostic value of interleukin-8 with fetal fibronectin determinations in predicting preterm delivery, microbial invasion of the amniotic cavity and histologic chorioamnionitis in patients with preterm labor and intact membranes. Interleukin-8 and fetal fibronectin were assayed in cervical secretions in 106 patients with singleton pregnancies and intact membranes admitted for preterm labor. Amniotic fluid obtained by amniocentesis was cultured and placentas (No = 43) analyzed for the presence of chorioamnionitis. The prevalence of pregnancies delivered preterm was 46.2% (49/106) and 15.09% (16/106) of amniotic fluid cultures were positive. Interleukin-8 levels in cervical secretions were significantly increased in patients who delivered preterm (p < or = 0.0001), in presence of positive amniotic fluid culture (p = 0.0016) and histological chorioamnionitis (p = 0.008) than in patients with negative findings. Receiver-operator characteristics curve analysis showed that an interleukin-8 value > 450 pg/ml is comparable to that of a fetal fibronectin value > 50 ng/ml in predicting preterm delivery (p = 0.247). Among patients who delivered preterm interleukin-8 concentrations > 860 pg/ml predicted a positive amniotic fluid culture with a sensitivity of 81.2% and a specificity 66.6%. Further, in patients who delivered preterm and had a negative amniotic fluid culture, IL-8 concentrations > 480 pg/ml predicted histological chorioamnionitis with a sensitivity 78.5% and specificity 61.5%. A positive fetal fibronectin > 50 ng/ml was not predictve of either a positive amniotic fluid culture or the presence of histological chorioamnionitis. In conclusion, increased concentrations of interleukin-8 and fetal fibronectin are associated with impending delivery and their diagnostic value seems comparable. However, interleukin-8 concentrations identify patients at risk of a positive amniotic fluid culture and the presence of histological chorioamnionitis. Measurement of interleukin-8 in cervical secretion is a non-invasive method to identify patients at risk for both preterm delivery and intrauterine infection.  相似文献   
5.
We have previously found that thymic B cells, particularly thymic CD5+ B cells, show low responsiveness to the usual B cell stimulants such as lipopolysaccharide or anti-IgM plus interleukin (IL)-4, although they proliferate and produce antibodies after direct interaction with major histocompatibility complex class II-restricted T blasts. These findings raise the possibility that a CD40-CD40 ligand (L) interaction is involved in the activation of thymic B cells. In the present study, we therefore examine this possibility using CD40L-transfected Chinese hamster ovary (CHO) cells or anti-CD40 monoclonal antibody (mAb). When B cells in the spleen and peritoneal cavity were stimulated, they proliferated and produced immunoglobulin (Ig) in the presence of CD40L-CHO cells or anti-CD40 mAb alone. However, another signal delivered by IL-10 in addition to CD40L-CHO cells or anti-CD40 mAb was found to be necessary for thymic B cells to proliferate and secrete Ig. Other interleukins acting on B cells, such as IL-4, IL-5, and IL-6, had no effect on the activation of thymic B cells, which thus have unique characteristics not found in peripheral B cells. This report discusses the physiological significance of IL-10- and CD40-driven signals in the activation of thymic B cells.  相似文献   
6.
The 35 nm gate length CMOS devices with oxynitride gate dielectric and Ni salicide have been fabricated to study the feasibility of higher performance operation. Nitrogen concentration in gate oxynitride was optimized to reduce gate current I/sub g/ and to prevent boron penetration in the pFET. The thermal budget in the middle of the line (MOL) process was reduced enough to realize shallower junction depth in the S/D extension regions and to suppress gate poly-Si depletion. Finally, the current drives of 676 /spl mu/A//spl mu/m in nFET and 272 /spl mu/A//spl mu/m in pFET at V/sub dd/=0.85 V (at I/sub off/=100 nA//spl mu/m) were achieved and they are the best values for 35 nm gate length CMOS reported to date.  相似文献   
7.
When a fault occurs on transmission or distribution systems due to lightning or overvoltage, often an arc discharge occurs at the fault point. The arc discharge, which is caused by a fault current, has a high current, high temperature, strong light emission, etc., thus it sometimes causes heavy damages to electric power equipment. The arc discharge is influenced by the conditions around the arcs, i.e., gas, insulation materials, gap length, weather, etc. Also, the arc voltage along the arc column indicates the characteristics of the arc. If the voltage waveforms of the arcs caused by the fault on transmission or distribution systems are classified, it is possible to find the location and the equipment where the fault occurred. In this paper, the arc voltage data in 6-kV class XLPE cables and 6-kV class overhead lines are analyzed and an artificial neural network method is applied to classify the arc voltage waveforms. The results obtained from the six artificial neural networks developed show that the artificial neural network method is effective for classification of arc voltage waveforms if adequate input parameters are selected.  相似文献   
8.
The authors propose a photodetector-amplifier circuit consisting of a bridge photodetector circuit and a CMOS differential amplifier, both monolithically integrated on a transparent substrate. A test circuit was fabricated using a-Si p-i-n photodiodes and poly-Si thin-film transistors on a quartz substrate. A clear effect of the differential amplifier was demonstrated in the test circuit. It is shown that the circuit performance can be controlled by changing the bias current of the differential amplifier. With a relatively low bias current on the order of 10-11 A, the circuit works digitally with output voltages either close to 0 V or VDD. The power consumption of the circuit is approximately 60 μW, which is low enough for use in two-dimensional arrays  相似文献   
9.
Catalytic behavior of silica-supported transition metals for NO reduction with propene in the presence of oxygen was investigated. While both silica and cobalt oxides did not show any activity for the selective NO reduction, impregnated CoO/SiO2 prepared from cobalt acetate showed good activity although the preparation conditions had significant effect on the activity. It was suggested that highly dispersed surface Co2+ ions on silica are responsible for the catalytic activity.  相似文献   
10.
The pre-treatment of a silica-supported gallium oxide catalyst with H2 at 823 K increased the yield of aromatics and the selectivity to aromatics in the dehydrogenation of propane over the catalyst at 823 K. Gallium oxide in the catalyst was partially reduced with H2 at 823 K. NH3 desorption and DRIFTS studies on the gallium oxide catalyst suggest that the dehydrogenation of propane over a silica-supported gallium oxide catalyst would proceed in the following way: (1) the dehydrogenation of propane to produce propene would occur on Ga sites including Gaδ+–H sites and (2) the aromatization of propene to aromatics on Ga–O–H acid sites.  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