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   3175篇
  免费   115篇
  国内免费   16篇
电工技术   63篇
综合类   1篇
化学工业   627篇
金属工艺   69篇
机械仪表   75篇
建筑科学   69篇
矿业工程   6篇
能源动力   176篇
轻工业   204篇
水利工程   31篇
石油天然气   16篇
无线电   513篇
一般工业技术   697篇
冶金工业   294篇
原子能技术   32篇
自动化技术   433篇
  2023年   32篇
  2022年   74篇
  2021年   130篇
  2020年   86篇
  2019年   105篇
  2018年   132篇
  2017年   111篇
  2016年   128篇
  2015年   68篇
  2014年   105篇
  2013年   247篇
  2012年   130篇
  2011年   149篇
  2010年   132篇
  2009年   154篇
  2008年   125篇
  2007年   117篇
  2006年   95篇
  2005年   67篇
  2004年   49篇
  2003年   52篇
  2002年   68篇
  2001年   48篇
  2000年   36篇
  1999年   53篇
  1998年   69篇
  1997年   56篇
  1996年   60篇
  1995年   42篇
  1994年   39篇
  1993年   36篇
  1992年   37篇
  1991年   33篇
  1990年   18篇
  1989年   33篇
  1988年   33篇
  1987年   33篇
  1986年   26篇
  1985年   28篇
  1984年   29篇
  1983年   31篇
  1982年   26篇
  1981年   29篇
  1980年   25篇
  1979年   13篇
  1978年   21篇
  1977年   13篇
  1976年   21篇
  1975年   17篇
  1974年   14篇
排序方式: 共有3306条查询结果,搜索用时 15 毫秒
31.
The growth of metallic (predominantly Sn) whiskers from pure metallic platings has been studied for over 50 years. While the phenomenon of Sn whiskering has been studied for decades, very little is known about the mechanical properties of these materials. This can be attributed to the difficulty in handling, gripping, and testing such fine-diameter and high-aspect-ratio whiskers. We report on the stress–strain behavior of Sn whiskers inside a dual-beam focused ion beam (FIB) with a scanning electron microscope (SEM). Lift-out of the whiskers was conducted in situ in the FIB, and the whiskers were tested using a microelectromechanical system tensile testing stage. Using this technique, the whiskers had minimum exposure to ambient air and were not handled by hand. SEM images after fracture enabled reliable calculation of the whisker cross-sectional area. Tests on two different whiskers revealed relatively high tensile strengths of 720 MPa and 880 MPa, respectively, and a limited strain to failure of ~2% to 3%. For both whiskers, the Young’s modulus was between 42 GPa and 45 GPa. It is interesting to note that the whiskers were quite strong and had limited ductility. These findings are intriguing and provide a basis for further work to understand the effect of Sn whisker mechanical properties on short circuits in electronics.  相似文献   
32.
In contrast with the conventional split loop digital phase lock loop, a new loop is presented in this paper that differs from the earlier version principally by design aspects. It incorporates an additional phase modulation input along with its frequency modulation input in the digital controlled oscillator. It is capable of eliminating the deleterious effects of rounding and truncation error with faster signal accusation. Higher loop stability is also achievable using the new split loop digital phase lock loop. Furthermore, radio frequency filtering is done using an In phase and Quadrature phase (IQ) voltage controlled oscillator to avoid interaction between the loop filter and the radio frequency filter. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
33.
Currently, the problem size that can be solved in reasonable time using the Method of Moments is limited by the amount of memory installed in the computer. This paper offers a new development that not only breaks this memory constraint, but also maintains the efficiency of running the problem in-core. In this paper, highly efficient parallel matrix-filling schemes are presented for parallel in-core and parallel out-of-core integral-equation solvers with subdomain RWG basis functions. The parallel methodology for matrix filling is quite different when using a subdomain basis as opposed to using a higher-order basis. The parallel in-core solver uses memory, which is often expensive and limited in size. The parallel out-of-core solver is introduced to extend the capability of MoM to solve larger problems that can be as large as the amount of storage on the hard disk. Numerical results on several typical computer platforms show that the parallel matrix-filling schemes and matrix-equation solvers introduced here are highly efficient and achieve theoretical predictions. The implementation of these advancements with the widely used RWG basis functions creates a powerful tool for efficient computational electromagnetics solution of complex real-world problems.  相似文献   
34.
Mobile ad-hoc networks (MANET) operate like self organizing entity. The mobile nodes are operate in a host as well as in a router and dynamic topology. In MANET every network node operates autonomously. It has limited resources like power, bandwidth and storage capacity. Selection of a propagation model plays the vital role of application possibilities in MANET. In this paper, calculations have been performed for three propagation models: Two-ray ground, COST 231 and Okumura–Hata model. The paper shows the impact of these propagation models based on Ad-hoc on-demand distance vector (AODV) protocol at 1.5 GHz frequency, varying transmitted power and number of nodes. This paper also studies effects of the propagation models with the conclusion of choosing the most accurate propagation model. Okumura–Hata propagation model shows better results at 1.5 GHz frequency as compared to COST 231 and Two-ray ground model in open space using Network Simulator (NS 2.35). Two-ray ground propagation model shows better results with varying transmitted power and number of nodes as compared to COST 231 and Okumura–Hata model.  相似文献   
35.
Wireless sensor networks (WSNs) are constrained by limited node (device) energy, low network bandwidth, high communication overhead and latency. Data aggregation alleviates the constraints of WSN. In this paper, we propose a multi-agent based homogeneous temporal data aggregation and routing scheme based on fish bone structure of WSN nodes by employing a set of static and mobile agents. The primary components of fishbone structure are backbone and ribs connected to both sides of a backbone. A backbone connects a sink node and one of the sensor nodes on the boundary of WSN through intermediate sensor nodes. Our aggregation scheme operates in the following steps. (1) Backbone creation and identifying master centers (or nodes) on it by using a mobile agent based on parameters such as Euclidean distance, residual energy, backbone angle and connectivity. (2) Selection of local centers (or nodes) along the rib of a backbone connecting a master center by using a mobile agent. (3) Local aggregation process at local centers by considering nodes along and besides the rib, and delivering to a connected master center. (4) Master aggregation process along the backbone from boundary sensor node to the sink node by using a mobile agent generated by a boundary sensor node. The mobile agent aggregates data at visited master centers and delivers to the sink node. (5) Maintenance of fish bone structure of WSN nodes. The performance of the scheme is simulated in various WSN scenarios to evaluate the effectiveness of the approach by analyzing the performance parameters such as master center selection time, local center selection time, aggregation time, aggregation ratio, number of local and master centers involved in the aggregation process, number of isolated nodes, network lifetime and aggregation energy. We observed that our scheme outperforms zonal based aggregation scheme.  相似文献   
36.
37.
Colloidal silver is observed to affect the transmittance of p-type Cd1−y Zn y Te (CZT) single-crystal substrate material at room temperature. The optical transmittance spectra have been analyzed in the near-infrared (NIR) and mid-infrared (MIR) regions. The transmittance characteristics of CZT showed significant reduction in absorption due to split-off valance band transitions in the NIR region and intervalence band absorption in the MIR region upon coating CZT substrates with silver paste. This reduction in absorption has been explained to be due to the compensation of the acceptor defects (native and foreign). Silver atoms incorporated from the silver coating help in compensation of these defects. A similar effect on transmittance characteristics of mercury cadmium telluride (MCT) epilayers grown on CZT substrates after coating silver paste on the CZT substrate side was also observed. An improvement in the transmittance of CZT substrates after the application of silver paste was observed. A similar improvement in transmittance is usually achieved by annealing the substrates in a Cd/Zn atmosphere. The results are explained by considering the formation of neutral complexes of acceptors (cadmium vacancies) and the interstitial silver. This study also points to the important conclusion that silver paste on CZT should be applied with caution for measurement purposes since it diffuses even at room temperature and modifies the optical characteristics.  相似文献   
38.
Ultra thin HfAlOx high-k gate dielectric has been deposited directly on Si1−xGex by RF sputter deposition. The interfacial chemical structure and energy-band discontinuities were studied by using X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (TOF-SIMS) and electrical measurements. It is found that the sputtered deposited HfAlOx gate dielectric on SiGe exhibits excellent electrical properties with low interface state density, hysteresis voltage, and frequency dispersion. The effective valence and conduction band offsets between HfAlOx (Eg = 6.2 eV) and Si1−xGex (Eg = 1.04 eV) were found to be 3.11 eV and 2.05 eV, respectively. In addition, the charge trapping properties of HfAlOx/SiGe gate stacks were characterized by constant voltage stressing (CVS).  相似文献   
39.
This article presents a new current mode single-input-multiple-output nth order universal filter. The proposed circuit employs (n + 1) number multiple output second generation current conveyors and n number grounded capacitors only. Presented circuits can realize current mode low pass, high pass, band pass, notch and all pass responses simultaneously at different high output impedance terminals. The current mode filter circuit provides low input impedance by selecting the proper value of bias current and also has high output impedance, which is suitable for cascading. The circuit offers some important features such as resistor less realization, no passive component matching constraints, low sensitivity, electronic tunability and active-C realization. The functionality of the proposed filter circuit is tested with the PSPICE simulation, which is found to agree well with the proposed theory.  相似文献   
40.
In a MOSFET, a nonuniform, graded vertical dopant profile in the polysilicon gate causes a potential drop at the polysilicon/oxide interface. In this paper, the effect of this potential drop on the gate leakage current has been evaluated for the first time. The extent of variations of this affected gate leakage current with gate oxide thickness, gate length, and gate and drain bias conditions have been assessed with device simulation for an nMOS at 0.13 /spl mu/m low-voltage process. The results provide a guideline to the severity of this effect from the point of view of device and circuit operation and standby power consumption.  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