全文获取类型
收费全文 | 65279篇 |
免费 | 5617篇 |
国内免费 | 2859篇 |
专业分类
电工技术 | 3412篇 |
技术理论 | 2篇 |
综合类 | 3404篇 |
化学工业 | 13121篇 |
金属工艺 | 1970篇 |
机械仪表 | 2314篇 |
建筑科学 | 3823篇 |
矿业工程 | 6041篇 |
能源动力 | 5603篇 |
轻工业 | 4727篇 |
水利工程 | 346篇 |
石油天然气 | 17988篇 |
武器工业 | 297篇 |
无线电 | 1330篇 |
一般工业技术 | 3324篇 |
冶金工业 | 3489篇 |
原子能技术 | 645篇 |
自动化技术 | 1919篇 |
出版年
2024年 | 218篇 |
2023年 | 844篇 |
2022年 | 1717篇 |
2021年 | 2289篇 |
2020年 | 2420篇 |
2019年 | 1999篇 |
2018年 | 1769篇 |
2017年 | 1863篇 |
2016年 | 2374篇 |
2015年 | 2278篇 |
2014年 | 4051篇 |
2013年 | 3884篇 |
2012年 | 5062篇 |
2011年 | 5175篇 |
2010年 | 3476篇 |
2009年 | 3386篇 |
2008年 | 2879篇 |
2007年 | 3660篇 |
2006年 | 3924篇 |
2005年 | 3245篇 |
2004年 | 2781篇 |
2003年 | 2454篇 |
2002年 | 2098篇 |
2001年 | 1910篇 |
2000年 | 1623篇 |
1999年 | 1304篇 |
1998年 | 992篇 |
1997年 | 853篇 |
1996年 | 676篇 |
1995年 | 565篇 |
1994年 | 450篇 |
1993年 | 328篇 |
1992年 | 263篇 |
1991年 | 208篇 |
1990年 | 180篇 |
1989年 | 160篇 |
1988年 | 64篇 |
1987年 | 48篇 |
1986年 | 43篇 |
1985年 | 33篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1981年 | 61篇 |
1980年 | 36篇 |
1979年 | 7篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1973年 | 5篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
181.
182.
Identifying the Cost-To-Serve (CTS) of customers is one of the most challenging problems in Supply Chain Management because of the diversity in their business activities. For the particular case of the industrial gas business, we are interested in predicting the cost to deliver bulk (liquefied) gas to new customers using a multifactor linear regression model. Developing a single model, i.e. analyzing the observations all at once, produces poor prediction results. Therefore prior to the regression analysis, a new supervised learning technique is used to group customers who are similar in some sense. Classes of customers are represented by hyper-boxes and a linear regression model is subsequently built within each class. The combination of data classification and regression is proven to increase the accuracy of the prediction.Two Mixed-Integer-Linear Programming (MILP) models are developed for data classification purposes. Although we are dealing with a supervised learning method, classes are not predefined in our case. Rather, we input a continuous “classification” attribute that is optimally discretized by the MILP’s in order to minimize the number of misclassifications. Therefore our data classification model offers a broader range of applications. A number of illustrative examples are used to prove the effectiveness of the proposed approach. 相似文献
183.
Eric R. MacamAuthor VitaeBryan M. BlackburnAuthor Vitae Eric D. WachsmanAuthor Vitae 《Sensors and actuators. B, Chemical》2011,158(1):304-312
The intent of this work is to look at the effects of varying the La2CuO4 electrode area and the asymmetry between the sensing and counter electrode in a solid state potentiometric sensor with respect to NOx sensitivity. NO2 sensitivity was observed at 500-600 °C with a maximum sensitivity of ∼22 mV/decade [NO2] observed at 500 °C for the sensor with a La2CuO4 electrode area of ∼30 mm2. The relationship between NO2 sensitivity and area is nearly parabolic at 500 °C, decreases linearly with increasing electrode area at 600 °C, and was a mixture of parabolic and linear behavior 550 °C. NO sensitivity varied non-linearly with electrode area with a minima (maximum sensitivity) of ∼−22 mV/decade [NO] at 450 °C for the sensor with a La2CuO4 electrode area of 16 mm2. The behavior at 400 °C was similar to that of 450 °C, but with smaller sensitivities due to a saturation effect. At 500 °C, NO sensitivity decreases linearly with area.We also used electrochemical impedance spectroscopy (EIS) to investigate the electrochemical processes that are affected when the sensing electrode area is changed. Changes in impedance with exposure to NOx were attributed to either changes in La2CuO4 conductivity due to gas adsorption (high frequency impedance) or electrocatalysis occurring at the electrode/electrolyte interface (total electrode impedance). NO2 caused a decrease in high frequency impedance while NO caused an increase. In contrast, NO2 and NO both caused a decrease in the total electrode impedance. The effect of area on both the potentiometric and impedance responses show relationships that can be explained through the mechanistic contributions included in differential electrode equilibria. 相似文献
184.
Chander ShekharAuthor VitaeK.I. GnanasekarAuthor Vitae E. PrabhuAuthor VitaeV. JayaramanAuthor Vitae T. GnanasekaranAuthor Vitae 《Sensors and actuators. B, Chemical》2011,155(1):19-27
Indium oxide (In2O3) doped with 0.5-5 at.% of Ba was examined for their response towards trace levels of NOx in the ambient. Crystallographic phase studies, electrical conductivity and sensor studies for NOx with cross interference for hydrogen, petroleum gas (PG) and ammonia were carried out. Bulk compositions with x ≤ 1 at.% of Ba exhibited high response towards NOx with extremely low cross interference for hydrogen, PG and ammonia, offering high selectivity. Thin films of 0.5 at.% Ba doped In2O3 were deposited using pulsed laser deposition technique using an excimer laser (KrF) operating at a wavelength of (λ) 248 nm with a fluence of ∼3 J/cm2 and pulsed at 10 Hz. Thin film sensors exhibited better response towards 3 ppm NOx quite reliably and reproducibly and offer the potential to develop NOx sensors (Threshold limit value of NO2 and NO is 3 and 25 ppm, respectively). 相似文献
185.
Mika HarbeckAuthor Vitae Zafer ?enAuthor Vitae Zafer Ziya ÖztürkAuthor Vitae 《Sensors and actuators. B, Chemical》2011,156(2):673-679
Vic-dioximes, a class of organic chemical compounds, are proposed and characterized for the first time as sensitive materials for volatile organic compound sensing with sorption based chemical gas sensors. Their peculiar sensing properties described in this work originate in the oxime functional group which is a powerful H bond donor interacting strongly but reversibly with H bond acceptors. These specific interactions result in a high preferential enrichment of analyte molecules with H bonding acceptor capabilities in the sensitive material. Accordingly, sensitivity and selectivity for these compounds of vic-dioxime based sensors are high. The advantageous sensing properties are demonstrated in this work with quartz crystal microbalance sensors using 11 selected volatile organic compounds and a set of vic-dioximes varied in their substituents. Vic-dioximes with short alkylthiol substituents were found highly sensitive to such H bond acceptors as organic amines, alcohols, and esters with partition coefficients up to 26,000. At the same time they showed low affinity for aromatic compounds and chlorocarbons. Vic-dioximes are considered powerful sensing materials and interesting for practical use in chemical gas sensor arrays. 相似文献
186.
Towards a GC-based microsystem for benzene and 1,3 butadiene detection: Pre-concentrator characterization 总被引:1,自引:0,他引:1
H. LahlouAuthor Vitae J.-B. SanchezAuthor VitaeX. VilanovaAuthor Vitae F. BergerAuthor VitaeX. CorreigAuthor Vitae V. FierroAuthor VitaeA. CelzardAuthor Vitae 《Sensors and actuators. B, Chemical》2011,156(2):680-688
The performance of a gas pre-concentrator/gas chromatographic column/gas sensor system was studied step by step towards benzene vapor in presence of 1,3 butadiene vapor. The pre-concentrator, based on an activated carbon of high adsorption capacity, was first characterized using a GC/FID system. By this way, the adsorption capacity of each pollutant was evaluated, first separately, then mixed with different proportions in air. It was shown that the affinity of the pre-concentrator for benzene was higher than for butadiene. Once the optimal pre-concentration parameters were adjusted, we replaced the FID detector by a metal oxide gas sensor. The use of such gas pre-concentrator allowed decreasing the detection limit of the system towards benzene in presence of butadiene by at least ten times. 相似文献
187.
S. NazarpourAuthor Vitae C. López-GándaraAuthor VitaeC. ZamaniAuthor Vitae F.M. RamosAuthor VitaeAlbert CireraAuthor Vitae 《Sensors and actuators. B, Chemical》2011,155(2):489-499
Effect of sacrificial carbon on microstructure of protective layer and sensing properties of limiting current oxygen sensors were studied. Graphite and carbon nanofiber with different concentrations were examined as sacrificial layer. Therefore, several YSZ-based electrochemical gas sensors were fabricated with dissimilarity in the diffusivity of the layer covering their measuring electrodes.Gas sensors were tested as potentiometric and amperometric devices under O2-N2 mixtures, and synthetic gases similar to the exhaust gas mixtures from combustion engines. Sensors with low diffusivity (low concentration of sacrificial material) exhibit more abrupt and O2-sensitive potentiometric responses. Indeed, less O2-linear amperometric responses and higher response times are their characteristics. Sensors with high diffusion in their layers (high concentration of sacrificial material) show a less abrupt step-drop potentiometric response but a more linear O2 dependence for the amperometric response and, in general, lower response times.Results suggest that the configuration of the diffusive layer shall be controlled in terms of the expected performance of the sensor, as an amperometric or potentiometric device. The controlling parameters are discussed and given in this study. 相似文献
188.
Yeon-Tae YuAuthor Vitae Prabir DuttaAuthor Vitae 《Sensors and actuators. B, Chemical》2011,157(2):444-449
Au/SnO2 core-shell structure nanoparticles (NPs) were synthesized using two methods, microwave and conventional precipitation. In both cases, the size of the Au core was 12-18 nm and the thickness of the SnO2 shell was 8-12 nm. The particle size of SnO2 synthesized using the microwave and precipitation method was 3-5 nm and 1-2 nm, respectively. Upon heating to 400-600 °C, both particles maintained their core-shell morphology but the smaller SnO2 particles prepared using the precipitation method were more sintered. The resistance changes in films of these particles were measured as a function of CO concentration. The Au/SnO2 particles prepared using the microwave method showed higher sensor response than those prepared using the precipitation method, even providing a significant signal at testing temperatures approaching ambient conditions, thereby affording a new class of material for gas sensing. Both sets of core-shell particles showed higher sensor response than the SnO2 nanoparticles. The role of the Au core as a catalyst in improving the adsorption and oxidation of CO gas is important for improving the low temperature response. In addition, the maintenance of the size of SnO2 in the microwave method during sintering contributed to the higher response towards CO sensing. 相似文献
189.
190.
研究了一种新型的采用打印技术的NH3传感器,探讨了打印"墨水"材料聚苯胺和聚吡咯的制备和"墨水"掺酸比例对NH3传感器敏感度的影响。为了提高传感器灵敏度,分别对传感器的直流和交流阻抗特性进行了研究。结果发现在1.5 kHz左右交流阻抗的测试条件下,传感器灵敏度要较直流阻抗测试高近1个数量级。此外还通过构建1个交流阻抗拟合模型对传感器交流阻抗变化过程作了解释。研究的采用打印技术基于聚合物的NH3传感器具有成本低,可以制作在柔性衬底上和适合大规模生产等特点,在食品加工、养殖业和医疗等领域具有广泛的应用前景。 相似文献