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   9941篇
  免费   432篇
  国内免费   17篇
电工技术   132篇
综合类   18篇
化学工业   2246篇
金属工艺   367篇
机械仪表   452篇
建筑科学   143篇
矿业工程   3篇
能源动力   381篇
轻工业   979篇
水利工程   36篇
石油天然气   7篇
武器工业   1篇
无线电   1694篇
一般工业技术   2318篇
冶金工业   600篇
原子能技术   84篇
自动化技术   929篇
  2024年   139篇
  2023年   158篇
  2022年   202篇
  2021年   352篇
  2020年   285篇
  2019年   305篇
  2018年   327篇
  2017年   360篇
  2016年   442篇
  2015年   370篇
  2014年   485篇
  2013年   666篇
  2012年   687篇
  2011年   879篇
  2010年   618篇
  2009年   584篇
  2008年   466篇
  2007年   409篇
  2006年   336篇
  2005年   270篇
  2004年   269篇
  2003年   228篇
  2002年   172篇
  2001年   158篇
  2000年   163篇
  1999年   140篇
  1998年   235篇
  1997年   135篇
  1996年   109篇
  1995年   60篇
  1994年   64篇
  1993年   47篇
  1992年   37篇
  1991年   24篇
  1990年   23篇
  1989年   24篇
  1988年   16篇
  1987年   10篇
  1986年   15篇
  1985年   7篇
  1984年   10篇
  1983年   11篇
  1981年   6篇
  1980年   7篇
  1979年   6篇
  1977年   7篇
  1976年   9篇
  1974年   7篇
  1971年   7篇
  1970年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Vitamins are non‐toxic compounds that perform a variety of biological functions and also available in a large quantity. Other than the usage as food supplements, few attempts have been made to use them as functional materials. In this study, we report that vitamin B6, pyridoxal 5′‐phosphate (PLP), is a multi‐functional molecule for oxide surface chemistry. PLP‐immobilized surfaces exhibit superhydrophilicity and even hemophilicity, enhancing proliferation, migration, and differentiation of mammalian cells. Unlike existing molecules used so far in surface modification, PLP has an intrinsic chemical reactivity toward biomacromolecules due to the presence of the aldehyde group. In fact, RGD peptide is covalently tethered onto PLP surfaces directly in one step without any chemical activation. Furthermore, PLP‐functionalized implant device showed rapid bone healing. As vitamin B6 is a FDA approved molecule for human usage, the surface chemistry of vitamin B6 potentially allows a fast route for surface functionalized medical devices into clinic.  相似文献   
102.
Anodic dissolution and the electrochemical migration characteristics of eutectic Sn-Pb solder alloy in deaerated 0.001% NaCl and Na2SO4 solutions were investigated using anodic polarization and water drop tests. Anodic polarization results revealed that a Pb-rich phase was preferentially ionized in deaerated 0.001% NaCl solution and an Sn-rich phase was predominantly ionized in deaerated 0.001% Na2SO4 solution, which coincides well with the composition of the dendrites formed during water drop tests. X-ray diffraction and photoelectron spectroscopy results showed that the surface oxide film formed on pure Sn in deaerated 0.001% NaCl solution is more stable than that formed on pure Sn in deaerated 0.001% Na2SO4 solution. The surface oxide film formed on pure Pb in deaerated 0.001% Na2SO4 solution is more stable than that formed on pure Sn in deaerated 0.001% NaCl solution. Therefore, the quality of the surface film of eutectic Sn-Pb solder in a chemical environment seems to be critical not only for corrosion resistance, but also for electrochemical migration resistance.  相似文献   
103.
In this brief, we present a 60-W power amplifier that is linearized using an RF predistorter for multicarrier wideband code-division multiple-access (WCDMA) applications. The proposed RF predistorter is fully composed of RF or analog circuits, and it has a moderate memory effect compensation capability using a delayed third-order intermodulation (IM3) component path. It also includes the IM5 generation circuits and a compact IM3 generator that is capable of autocanceling for the fundamental component. The proposed RF predistorter was implemented and applied to a 60-W high-power WCDMA amplifier. For a four-carrier downlink WCDMA signal, the RF predistorter improved the adjacent channel leakage power ratio at a 5-MHz offset by 6.19 dB at an average output power of 48 dBm. The total efficiency of the system is as high as 13.6% at the same output power level. At an output power level of 60 W, the linearized power amplifier complies with the linearity specification of the WCDMA system.  相似文献   
104.
The industrial scale application of graphene and other functional materials in the field of electronics has been limited by inherent defects, and the lack of simple deposition methods. A simple spray deposition method is developed that uses a supersonic air jet for a commercially available reduced graphene oxide (r‐GO) suspension. The r‐GO flakes are used as received, which are pre‐annealed and pre‐hydrazine‐treated, and do not undergo any post‐treatment. A part of the considerable kinetic energy of the r‐GO flakes entrained by the supersonic jet is used in stretching the flakes upon impact with the substrate. The resulting “frozen elastic strains” heal the defects (topological defects, namely Stone‐Wales defect and C2 vacancies) in the r‐GO flakes, which is reflected in the reduced ratio of the intensities of the D and G bands in the deposited film. The defects can also be regenerated by annealing.  相似文献   
105.
The growth of the total (Cu3Sn+Cu6Sn) intermetallic compound layer in Cu-60Sn40Pb solder joints during static annealing at 50°C to 150°C was described by the equation hi=ho+Ao exp(−Qa/RT)tp with ho=0–0.3 μm, p=0.38–0.70, Ao=1.9×10−4–3.4×10−4 m/sp, and Qa=25.5–30.9 kJ/mole. These constants are within the range of those obtained by others and give values of Do and Q which are in reasonable accord with those for the diffusion coefficients in Cu3Sn and Cu6Sn5 determined in diffusion couples. The deviation of the values of the time exponent p from the ideal of 0.5 for diffusion growth may be due to inaccuracies or errors pertaining to the measured thickness (especially ho) and the complex nature of the diffusion process.  相似文献   
106.
Control of distributed generation systems - Part II: Load sharing control   总被引:1,自引:0,他引:1  
This work is concerned with the control strategy for the parallel operation of distributed generation systems (DGS) in a standalone ac power supply. The proposed control method uses only low-bandwidth data communication signals between each generation system in addition to the locally measurable feedback signals. This is achieved by combining two control methods: droop control method and average power control method. The average power method with slow update rate is used in order to overcome the sensitivity about voltage and current measurement errors. In addition, a harmonic droop scheme for sharing harmonic content of the load currents is proposed based on the voltages and currents control algorithm. Experimental and simulation studies using two parallel three-phase pulsewidth modulation (PWM) inverters are presented to show the effectiveness of the proposed control.  相似文献   
107.
Jung  J.W. Cho  K.Y. Oh  D.S. Youn  M.J. 《Electronics letters》1992,28(11):981-983
A new current control scheme with the reference voltage estimation for a voltage-fed pulsewidth modulated (PWM) inverter is presented. This scheme is simple and can provide smaller current error than predictive control with the same switching frequency when the load parameters are mismatched.<>  相似文献   
108.
We propose the S-shaped vertical probes with branch springs for the wafer-level testing of IC chips. The conventional S-shaped vertical probe requires a guide structure to prevent buckling due to the large overdrive actuation involved. However, the guide structure not only increases the cost of fabrication, but it also requires a troublesome assembly procedure. In this paper, we present the S-shaped vertical probe with branch springs on the left and right sides of the main spring to prevent buckling. This probe was designed using finite-element methods and fabricated using Ni-Co electroplating. The performances of the probe for the wafer-level testing of IC chips were measured with the probe test equipments. Compared to the identical conventional S-shaped probe, the proposed probe has the overdrive (60 μm) that is 1.2 times larger and the contact force (25 mN) that is 2.5 times larger. This new S-shaped vertical probe satisfies the design requirements for a vertical probe without the guide structure and has the potential for use as a cost-effective guide-free probe card for the wafer-level testing of IC chips.  相似文献   
109.
110.
Here, we report on the effects of channel (or active) layer thickness on the bias stress instability of InGaZnO (IGZO) thin-film transistors (TFTs). The investigation on variations of TFT characteristics under the electrical bias stress is very crucial for commercial applications. In this work, the initial electrical characteristics of the tested TFTs with different channel layer thicknesses (40, 50, and 60 nm) are performed. Various gate bias (VGS) stresses (10, 20, and 30 V) are then applied to the tested TFTs. For all VGS stresses with different channel layer thickness, the experimentally measured threshold voltage shift (ΔVth) as a function of stress time is precisely modeled with stretched-exponential function. It is indicated that the ΔVth is generated by carrier trapping but not defect creation. It is also observed that the ΔVth shows incremental behavior as the channel layer thickness increases. Thus, it is verified that the increase of total trap states (NT) and free carriers resulted in the increase of ΔVth as the channel layer thickness increases.  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