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   955篇
  免费   93篇
  国内免费   11篇
电工技术   26篇
综合类   1篇
化学工业   352篇
金属工艺   36篇
机械仪表   12篇
建筑科学   17篇
能源动力   34篇
轻工业   156篇
水利工程   12篇
石油天然气   14篇
无线电   74篇
一般工业技术   193篇
冶金工业   20篇
原子能技术   7篇
自动化技术   105篇
  2024年   1篇
  2023年   23篇
  2022年   70篇
  2021年   86篇
  2020年   57篇
  2019年   81篇
  2018年   75篇
  2017年   85篇
  2016年   75篇
  2015年   52篇
  2014年   75篇
  2013年   87篇
  2012年   52篇
  2011年   57篇
  2010年   36篇
  2009年   37篇
  2008年   16篇
  2007年   13篇
  2006年   12篇
  2005年   15篇
  2004年   5篇
  2003年   4篇
  2002年   1篇
  2001年   5篇
  2000年   3篇
  1999年   6篇
  1997年   2篇
  1996年   5篇
  1995年   2篇
  1994年   1篇
  1992年   2篇
  1991年   1篇
  1990年   2篇
  1988年   2篇
  1987年   1篇
  1986年   3篇
  1984年   1篇
  1983年   3篇
  1982年   2篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有1059条查询结果,搜索用时 93 毫秒
141.
Due to rapid development of Internet technology and electronic business, fraudulent activities have increased. One of the ways to cope with damages of them is fraud detection. In this field, there is a need for methods accurate and fast. Therefore, a novel and efficient feature extraction method based on social network analysis called FEMBSNA is proposed for fraud detection in banking accounts. In this method, in order to increase accuracy and control runtime in the first step, features based on network level are considered using social network analysis and extracted feature is combined with other features based on user level in the next phase. To evaluate our feature extraction method, we use PCK-means method as a basic method to learn. The results show using the proposed feature extraction as a pre-processing step in fraud detection improves the accuracy remarkably while it controls runtime in comparison with other methods.  相似文献   
142.
Heat transport across vertical interfaces of heterogeneous 2D materials is usually governed by the weak Van der Waals interactions of the surface‐terminating atoms. Such interactions play a significant role in thermal transport across transition metal carbide and nitride (MXene) atomic layers due to their hydrophilic nature and variations in surface terminations. Here, the metallicity of atomically thin Ti3C2Tz MXene, which is also verified by scanning tunneling spectroscopy for the first time, is exploited to develop a self‐heating/self‐sensing platform to carry out direct‐current annealing experiments in high (<10?8 bar) vacuum, while simultaneously evaluating the interfacial heat transport across a Ti3C2Tz/SiO2 interface. At room temperature, the thermal boundary conductance (TBC) of this interface is found, on average, to increase from 10 to 27 MW m?2 K?1 upon current annealing up to the breakdown limit. In situ heating X‐ray diffraction and X‐ray photo‐electron spectroscopy reveal that the TBC values are mainly affected by interlayer and interface spacing due to the removal of absorbents, while the effect of surface termination is negligible. This study provides key insights into understanding energy transport in MXene nanostructures and other 2D material systems.  相似文献   
143.
The fundamental nature of charge transport in highly ordered organic semiconductors is under constant debate. At cryogenic temperatures, effects within the semiconductor such as traps or the interaction of charge carriers with the insulating substrate (dipolar disorder or Fröhlich polarons) are known to limit carrier motion. In comparison, at elevated temperatures, where charge carrier mobility often also decreases as function of temperature, phonon scattering or dynamic disorder are frequently discussed mechanisms, but the exact microscopic cause that limits carrier motion is debated. Here, the mobility in the temperature range between 200 and 420 K as function of carrier density is explored in highly ordered perylene‐diimide from 3 to 9 nm thin films. It is observed that above room temperature increasing the gate electric field or decreasing the semiconducting film thickness leads to a suppression of the charge carrier mobility. Via X‐ray diffraction measurements at various temperatures and electric fields, changes of the thin film structure are excluded as cause for the observed mobility decrease. The experimental findings point toward scattering sites or traps at the semiconductor–dielectric interface, or in the dielectric as limiting factor for carrier mobility, whose role is usually neglected at elevated temperatures.  相似文献   
144.
145.
In this paper, according to the fifth-order Taylor expansion of the objective function and the modified secant equation suggested by Li and Fukushima, a new modified secant equation is presented. Also, a new modification of the scaled memoryless BFGS preconditioned conjugate gradient algorithm is suggested which is the idea to compute the scaling parameter based on a two-point approximation of our new modified secant equation. A remarkable feature of the proposed method is that it possesses a globally convergent even without convexity assumption on the objective function. Numerical results show that the proposed new modification of scaled conjugate gradient is efficient.  相似文献   
146.
A novel approach for synthesis of copper oxide nanoparticles is reported by separation of nucleation and growth. The nano-material was characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and UV–Vis diffuse reflectance spectroscopy, transmission electron microscopy, atomic force microscopy, and Brunauer–Emmett–Teller analyses. Optical analysis of mono-dispersed nanostructure copper oxide by UV–Vis diffused reflectance spectroscopy showed the band gap value of 1.47 eV with a blue-shift in the optical band gap due to quantum confinement effect. The dynamic light scattering and zeta potential results showed fairly narrow size distribution and colloidal stability. The results showed that nano-particles were mono-dispersed spheres of 8 nm with no aggregation. Cell viability of treated murine fibroblast cell line (L-929) treated by different concentrations of nanoparticles showed significant viability up to 96% at concentrations 15 and 30 μg ml?1. The nanoparticles exhibited outstanding and stable antibacterial activity against Staphylococcus aureus ATCC 6538 at 30 µg ml?1. The viability and reactive oxygen species (ROS) generation in the L-929 cell line indicated that the nanoparticles were not toxic at the concentrations which were effective on bacteria. ROS analysis using DCFH-DA probe on L-929 were exposed to 7.5–60 μg ml?1 of copper oxide nanoparticles in 6 h revealed ROS generation was decreased dramatically compare to the untreated cells and positive control.  相似文献   
147.
148.
Photocatalytic degradation under visible light irradiation is an important task of using solar energy for the removal of environmental pollutants. N-F/TiO2 nanoparticles were synthesized in one-pot sol–gel condition using tetra-isopropyl-orthotitanate as the TiO2 precursor and NH4F as the N-F doping source. Diffuse reflectance spectroscopy (DRS) analysis of the material has shown a reduction of band gap energy and shifting absorption edge to the visible wavelengths. A fluidized-spouted bed reactor equipped with the light source was designed and constructed for the oxidation process of VOC from the high airflow rate under Hg lamp irradiation using synthesized N-F/TiO2 nanoparticles. Acetaldehyde was used as the air pollutant model molecule of VOC in this process. The effluent acetaldehyde concentration was analyzed continuously along the time by an online Gas Chromatography (GC) from the start up to reaching steady conditions. The results have revealed significant enhancement of acetaldehyde removal by the N-F/TiO2 sample fabricated with an equal weight ratio of NH4F/Ti. After steady conditions, almost 100% removal of acetaldehyde was observed in the spouted bed reactor from a high airflow stream of 5?L/min polluted with 1000?ppm acetaldehyde at room-temperature conditions, under 80?W Hg with 500 Lux intensity.  相似文献   
149.
Aims: Recently, salinomycin (SAL) has been reported to inhibit proliferation and induce apoptosis in various tumors. The aim of this study was to deliver SAL to orthotopic model of pancreatic cancer by the aid of poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs).

Methods: The NPs were physico-chemically characterized and evaluated for cytotoxicity on luciferase-transduced AsPC-1 cells in vitro as well as implanted orthotopically into the pancreas of nude mice.

Results: SAL (3.5 mg/kg every other day) blocked tumor growth by 52% compared to the control group after 3 weeks of therapy. Western blotting of tumor protein extracts indicated that SAL treatment leads to up-regulation of E-cadherin, β-catenin, and transforming growth factor beta receptor (TGFβR) expressions in AsPC-1 orthotopic tumor. Noteworthy, immunofluorescence staining of adjacent tumor sections showed that treatment with SAL NPs cause significant apoptosis in the tumor cells rather than the stroma. Further investigations also revealed that TGFβR2 over-expression was induced in stroma cells after treatment with SAL NPs.

Conclusion: These results highlight SAL-loaded PLGA NPs as a promising system for pancreatic cancer treatment, while the mechanistic questions need to be subsequently tested.  相似文献   

150.
The aim of the present research was to evaluate the impact of coating layers on release profile from enteric coated dosage forms. Capsules were coated with Eudragit FS 30D using dipping method. The drug profile was evaluated in both phosphate buffer and Hank’s solutions. Utilization X-ray imaging, gastrointestinal transmission of enteric coated capsules was traced in rats. According to the results, no release of the drug was found at pH 1.2, and the extent of release drug in pH 6.8 medium was decreased by adding the coating layers. The results indicated single-layer coated capsules in phosphate buffer were significantly higher than that in Hank’s solution. However, no significant difference was observed from capsules with three coating layers in two different dissolution media. X-ray imaging showed that enteric coated capsules were intact in the stomach and in the small intestine, while disintegrated in the colon.  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