全文获取类型
收费全文 | 79017篇 |
免费 | 21002篇 |
国内免费 | 1109篇 |
专业分类
电工技术 | 15571篇 |
综合类 | 1367篇 |
化学工业 | 22483篇 |
金属工艺 | 1174篇 |
机械仪表 | 2910篇 |
建筑科学 | 2680篇 |
矿业工程 | 480篇 |
能源动力 | 2567篇 |
轻工业 | 7666篇 |
水利工程 | 524篇 |
石油天然气 | 205篇 |
武器工业 | 95篇 |
无线电 | 12768篇 |
一般工业技术 | 17663篇 |
冶金工业 | 3020篇 |
原子能技术 | 154篇 |
自动化技术 | 9801篇 |
出版年
2024年 | 112篇 |
2023年 | 356篇 |
2022年 | 587篇 |
2021年 | 1190篇 |
2020年 | 3713篇 |
2019年 | 6088篇 |
2018年 | 5498篇 |
2017年 | 6418篇 |
2016年 | 6230篇 |
2015年 | 6168篇 |
2014年 | 6635篇 |
2013年 | 6656篇 |
2012年 | 6378篇 |
2011年 | 6190篇 |
2010年 | 4887篇 |
2009年 | 4314篇 |
2008年 | 4410篇 |
2007年 | 4339篇 |
2006年 | 4098篇 |
2005年 | 3279篇 |
2004年 | 2786篇 |
2003年 | 2540篇 |
2002年 | 2304篇 |
2001年 | 1977篇 |
2000年 | 1768篇 |
1999年 | 1069篇 |
1998年 | 273篇 |
1997年 | 212篇 |
1996年 | 166篇 |
1995年 | 128篇 |
1994年 | 106篇 |
1993年 | 67篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A Facile Preparative Route of Nanoscale Perovskites over Mesoporous Metal Oxide Films and Their Applications to Photosensitizers and Light Emitters 下载免费PDF全文
《Advanced functional materials》2018,28(39)
By two‐step sequential Pb2+ adsorption and reaction with methylammonium‐iodide (MAI) or ‐bromide (MABr) at a low concentration level of 0.06–0.10 m over mesoporous TiO2 or ZrO2 film, a well‐defined nanoscale CH3NH3PbI3 (MAPbI3) photosensitizer or CH3NH3PbBr3 (MAPbBr3) light emitter could be prepared in situ, respectively in a reproducible and atom‐economical way. The as‐prepared nanoscale perovskites are compared with their thin film counterparts in terms of light absorption/emission, crystallinity, surface morphology, and energy‐conversion efficiency. The nanoscale perovskite‐decorated films display more transparency than the bulky film due to the much lower amount deposited, while blueshifted and overwhelmingly brighter photoluminescence is observed in the “nano” relative to the “bulk” due to quantum size confinement. Transmission electron microscopy images also clearly show that a few nanometer‐sized perovskite dots are deposited homogeneously over the surface of TiO2‐ or ZrO2‐particulate film in the course of the current preparative route. When the nano‐MAPbI3 is tested as a photosensitizer in a solid‐state dye‐sensitized solar cell configuration with a very thin ( ≈ 650 nm) TiO2 mesoporous film, it has a promising initial power conversion efficiency of 6.23%, which outperformed the result of 2.28% from a typical organic molecular dye coded as MK‐2. 相似文献
992.
Walid M. Ibrahim Najah Abu Ali Hossam S. Hassanein Abd‐Elhamid M. Taha 《Wireless Communications and Mobile Computing》2016,16(18):3316-3331
Deployments over large geographical areas in the Internet of Things (IoT) pose a major challenge for single‐hop localization techniques, giving rise to applications of multi‐hop localizations. And while many proposals have been made on implementations for multi‐hop localization, a close understanding of its characteristics is yet to be established. Such an understanding is necessary, and is inevitable in extending the reliability of location based services in IoT. In this paper, we study the characteristics of multi‐hop localization and propose a new solution to enhance the performance of multi‐hop localization techniques. We first examine popular assumptions made in simulating multi‐hop localization techniques, and offer rectifications facilitating more realistic simulation models. We identify the introduced errors to follow the Gaussian distribution, and the estimated distance follows the Rayleigh distribution. We next use our simulation model to characterize the effect of the number of hops on localization in both dense and sparse deployments. We find that, contrary to common belief, it is better to use long hops in sparse deployments, while short hops are better in dense deployments – despite the traffic overhead. Finally, we propose a new solution that decreases and manages the overhead generated during the localization process. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
993.
Haitham Z. Azazi Sayed M. Ahmed Azza E. Lashine 《International Journal of Electronics》2018,105(1):30-41
This article presents a single-stage three-phase power factor correction (PFC) circuit for AC-to-DC converter using a single-switch boost regulator, leading to improve the input power factor (PF), reducing the input current harmonics and decreasing the number of required active switches. A novel PFC control strategy which is characterised as a simple and low-cost control circuit was adopted, for achieving a good dynamic performance, unity input PF, and minimising the harmonic contents of the input current, at which it can be applied to low/medium power converters. A detailed analytical, simulation and experimental studies were therefore conducted. The effectiveness of the proposed controller algorithm is validated by the simulation results, which were carried out using MATLAB/SIMULINK environment. The proposed system is built and tested in the laboratory using DSP-DS1104 digital control board for an inductive load. The results revealed that the total harmonic distortion in the supply current was very low. Finally, a good agreement between simulation and experimental results was achieved. 相似文献
994.
Fluorinated Polyimide as a Novel High‐Voltage Binder for High‐Capacity Cathode of Lithium‐Ion Batteries 下载免费PDF全文
An increase in the energy density of lithium‐ion batteries has long been a competitive advantage for advanced wireless devices and long‐driving electric vehicles. Li‐rich layered oxide, xLi2MnO3?(1?x)LiMn1?y?zNiyCozO2, is a promising high‐capacity cathode material for high‐energy batteries, whose capacity increases by increasing charge voltage to above 4.6 V versus Li. Li‐rich layered oxide cathode however suffers from a rapid capacity fade during the high‐voltage cycling because of instable cathode–electrolyte interface, and the occurrence of metal dissolution, particle cracking, and structural degradation, particularly, at elevated temperatures. Herein, this study reports the development of fluorinated polyimide as a novel high‐voltage binder, which mitigates the cathode degradation problems through superior binding ability to conventional polyvinylidenefluoride binder and the formation of robust surface structure at the cathode. A full‐cell consisting of fluorinated polyimide binder‐assisted Li‐rich layered oxide cathode and conventional electrolyte without any electrolyte additive exhibits significantly improved capacity retention to 89% at the 100th cycle and discharge capacity to 223–198 mA h g?1 even under the harsh condition of 55 °C and high charge voltage of 4.7 V, in contrast to a rapid performance fade of the cathode coated with polyvinylidenefluoride binder. 相似文献
995.
Metal–Organic Framework Derived Narrow Bandgap Cobalt Carbide Sensitized Titanium Dioxide Nanocage for Superior Photo‐Electrochemical Water Oxidation Performance 下载免费PDF全文
Despite recent progress in photo‐electrochemical (PEC) water oxidation systems for TiO2‐based photoanodes, PEC performance improvement is still seriously hampered due to poor carrier transport efficiency and sluggish surface water oxidation kinetics of pristine TiO2. Herein, for the first time a brand new metal–organic framework (MOF)‐derived Co3C nanosheet with narrow bandgap energy is demonstrated, to effectively sensitize TiO2 hollow cages as a heterostructure photoanode for PEC water oxidation. It is found that MOF‐derived Co3C nanosheet with narrow bandgap characteristic can simultaneously accelerate the surface water oxidation kinetics and extend the light harvesting range of pristine TiO2. Meanwhile, a uniquely matched type‐II heterojunction constructed between MOF‐derived Co3C and TiO2 results in an evidently spontaneous e?/h+ separation. MOF‐derived Co3C/TiO2 heterostructure photoanodes bring about drastically improved PEC water oxidation performance. Specifically, MOF‐derived Co3C‐3/TiO2 photoanode with an optimized content of Co3C achieves the highest photocurrent density and charge separation efficiency of 2.6 mA cm?2 and 92.6% at 1.23 V versus reversible hydrogen electrode, corresponding to 201% and 152% improvement compared with pristine TiO2 nanocages. The ingeniously prepared MOF‐derived Co3C carbide with narrow bandgap energy as a cocatalyst paves new way to construct potentially high performance solar‐energy conversion system. 相似文献
996.
Sanghoon Kim Seung Hyun Jaeyong Lee Kyu Seong Lee Woo Lee Jin Kon Kim 《Advanced functional materials》2018,28(23)
Two types (hard and soft) of the molds are widely used in nanoimprint lithography for a high throughput over a large area, and high‐resolution parallel patterning. Although hard molds have proven excellent resolutions and can be used at high temperatures, cracks often occur in the mold in addition to the requirement of high imprinting pressure. On the other hand, though soft molds can operate at lower pressures, they give poor pattern resolution. Here, a novel hybrid mold of anodized aluminum oxide (AAO) template attached to a flexible polydimethylsiloxane (PDMS) plate is introduced. Due to the flexible nature of PDMS, various polymer nanostructures are obtained on flat and curved substrates without crack formation on the AAO mold surface. Furthermore, the hybrid mold is successfully used for roll‐to‐roll imprinting for the fabrication of high density array of various shaped polymeric nanostructures over a large area. 相似文献
997.
Hak‐Sung Jung Kyung‐Jin Cho Yeonee Seol Yasuharu Takagi Andrew Dittmore Paul A. Roche Keir C. Neuman 《Advanced functional materials》2018,28(33)
Fluorescent nanodiamonds (FNDs) are promising bioimaging probes compared with other fluorescent nanomaterials such as quantum dots, dye‐doped nanoparticles, and metallic nanoclusters, due to their remarkable optical properties and excellent biocompatibility. Nevertheless, they are prone to aggregation in physiological salt solutions, and modifying their surface to conjugate biologically active agents remains challenging. Here, inspired by the adhesive protein of marine mussels, encapsulation of FNDs within a polydopamine (PDA) shell is demonstrated. These PDA surfaces are readily modified via Michael addition or Schiff base reactions with molecules presenting thiol or nitrogen derivatives. Modification of PDA shells by thiol terminated poly(ethylene glycol) (PEG‐SH) molecules to enhance colloidal stability and biocompatibility of FNDs is described. Their use as fluorescent probes for cell imaging is demonstrated; it is found that PEGylated FNDs are taken up by HeLa cells and mouse bone marrow‐derived dendritic cells and exhibit reduced nonspecific membrane adhesion. Furthermore, functionalization with biotin‐PEG‐SH is demonstrated and long‐term high‐resolution single‐molecule fluorescence based tracking measurements of FNDs tethered via streptavidin to individual biotinylated DNA molecules are performed. This robust polydopamine encapsulation and functionalization strategy presents a facile route to develop FNDs as multifunctional labels, drug delivery vehicles, and targeting agents for biomedical applications. 相似文献
998.
999.
数字控制技术在电气传动领域应用越来越广泛,为使学生掌握以计算机为核心的数字控制技术,培养计算机应用的能力,本文主要介绍了计算机引入直流调速教学实验系统的改革尝试。 相似文献
1000.
AN EFFICIENT NUMERICAL MODELING OF THE DC RESISTIVITY LOGGING: THEORY AND APPLICATIONS 总被引:1,自引:0,他引:1
Nie Zaiping Yang Fong Nie Xiaochuen Yuan Ning Cheng Shiyuan 《电子科学学刊(英文版)》1997,14(2):169-179
The numerical solution of Green's function for the potential in 2-D arbitrary in-homogeneous media with axial symmetry has been given by use of efficient half-analytical, half-numerical hybrid method. Then the logging responses of various kinds of the DC resistivity log with axisymmetric excitation have been obtained by using surface integral equation method to match the boundary conditions on the electrodes of the logging sonde. Comparing the results with that obtained by other methods, one can see good precision and efficiency of the given method. Some applications of the numerical modeling have been also discussed. 相似文献