全文获取类型
收费全文 | 5422篇 |
免费 | 200篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 77篇 |
综合类 | 8篇 |
化学工业 | 1056篇 |
金属工艺 | 166篇 |
机械仪表 | 126篇 |
建筑科学 | 60篇 |
矿业工程 | 17篇 |
能源动力 | 341篇 |
轻工业 | 247篇 |
水利工程 | 40篇 |
石油天然气 | 27篇 |
无线电 | 730篇 |
一般工业技术 | 1267篇 |
冶金工业 | 737篇 |
原子能技术 | 36篇 |
自动化技术 | 715篇 |
出版年
2023年 | 78篇 |
2022年 | 110篇 |
2021年 | 195篇 |
2020年 | 164篇 |
2019年 | 132篇 |
2018年 | 178篇 |
2017年 | 170篇 |
2016年 | 205篇 |
2015年 | 119篇 |
2014年 | 219篇 |
2013年 | 447篇 |
2012年 | 243篇 |
2011年 | 267篇 |
2010年 | 229篇 |
2009年 | 290篇 |
2008年 | 199篇 |
2007年 | 159篇 |
2006年 | 149篇 |
2005年 | 127篇 |
2004年 | 111篇 |
2003年 | 108篇 |
2002年 | 97篇 |
2001年 | 72篇 |
2000年 | 72篇 |
1999年 | 79篇 |
1998年 | 151篇 |
1997年 | 115篇 |
1996年 | 122篇 |
1995年 | 84篇 |
1994年 | 85篇 |
1993年 | 86篇 |
1992年 | 60篇 |
1991年 | 72篇 |
1990年 | 70篇 |
1989年 | 47篇 |
1988年 | 48篇 |
1987年 | 46篇 |
1986年 | 43篇 |
1985年 | 49篇 |
1984年 | 34篇 |
1983年 | 26篇 |
1982年 | 27篇 |
1981年 | 35篇 |
1980年 | 21篇 |
1979年 | 31篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 33篇 |
1975年 | 15篇 |
1973年 | 13篇 |
排序方式: 共有5650条查询结果,搜索用时 15 毫秒
161.
Group III-V compound B-Sb films were synthesized from B/Sb/…/B multilayer films deposited by electron gun evaporation onto
silicon substrate and subjecting the above multilayer to rapid thermal annealing at 773 K for 3 min. The films were characterized
by XRD, TEM, XPS and optical studies. XPS studies indicated the ratio of B: Sb ∼ 1. XRD and electron diffraction patterns
indicated the reflections from (100), (111), (102) and (112) planes of zinc blende BSb. Band gap evaluated from optical studies
was ∼ 0·51 eV. Refractive index of the films varied between 1·65 and 2·18 with increasing energy of incident photon and plasma
frequency (ωp) was estimated to be ∼2·378×10−14 s−1. The effective mass was computed to be ∼ 0·0845 me. 相似文献
162.
Gullo L.J. Azarian M.H. Das D. Schenkelberg F. Tiku S. 《Components and Packaging Technologies, IEEE Transactions on》2006,29(2):425-428
A reliability capability assessment process can assist OEMs and system integrators in assessing prospective suppliers for their ability to design and manufacture reliable products before they are delivered for use, and on an ongoing basis, help a company in identifying shortcomings in its reliability program, which can be rectified by subsequent improvement actions. The assessment can also help to establish reliability management practices for use by designers, suppliers, customers, and independent authorities. The assessment method may be used to evaluate the reliability capability of all types of electronics-related industries that perform activities influencing the reliability of a product. It can produce increased customer satisfaction, provide competitive opportunities, and shorten the product development cycle. In summary, a reliability capability assessment can be used for: 1) specifying or planning reliability practices if product development is implemented internally; 2) evaluating reliability practices to determine the extent to which a supplier is capable of providing a product that meets the reliability requirements/needs; and 3) improving reliability practices if the current reliability practices have been evaluated and improvement is desired or required. 相似文献
163.
Crozatier V. Das B.K. Baili G. Gorju G. Bretenaker F. Le Gouet J.-L. Lorgere I. Sohler W. 《Photonics Technology Letters, IEEE》2006,18(14):1527-1529
A frequency agile extended cavity diode laser using an integrated Bragg reflector in a Ti : Fe : LiNbO/sub 3/ waveguide is developed and characterized. The laser emits up to 7 mW in the 1.5-/spl mu/m telecommunication window. The emission spectrum exhibits a 18-kHz linewidth, >40-dB sidemode suppression ratio, and a wavelength stability of /spl plusmn/1 pm over hours. Very fast mode hop-free frequency tuning is achieved through the electrooptic effect, with a tuning slope of 55.5 MHz/V. 相似文献
164.
Das J. Oprins H. Ji H. Sarua A. Ruythooren W. Derluyn J. Kuball M. Germain M. Borghs G. 《Electron Devices, IEEE Transactions on》2006,53(11):2696-2702
AlGaN/GaN high electron mobility transistors (HEMT) on sapphire substrates have been studied for their potential application in RF power applications; however, the low thermal conductivity of the sapphire substrate is a major drawback. Aiming at RF system-in-a-package, the authors propose a flip-chip-integration approach, where the generated heat is dissipated to an AlN carrier substrate. Different flip-chip-bump designs are compared, using thermal simulations, electrical measurements, micro-Raman spectroscopy, and infrared thermography. The authors show that a novel bump design, where bumps are placed directly onto both source and drain ohmic contacts, improves the thermal performance of the HEMT 相似文献
165.
Yonghe Liu Sajal K. Das 《Communications Magazine, IEEE》2006,44(11):142-147
Conventional wireless sensor networks rely mostly on simple scalar data (such as temperature or humidity) and specialize in single-purpose applications. Taking a fundamental departure, in this article we motivate information-rich wireless video sensor networks that emulate the compound eyes found in certain arthropods. Although constrained by scarce resources, sensor nodes can only serve extremely low-resolution video streams; the availability of vast amount of such streams due to deployment redundance can suffice for the need of information hungry applications. Unfortunately, the unique characteristics of wireless video sensor networks will introduce novel uncertainty-driven challenges in the information-intensive and yet resource-constrained environment. Correspondingly, we describe key research problems in the areas of networking, security, sensor design, and video-data analysis 相似文献
166.
The fabrication of silicon based micromechanical sensors often requires bulk silicon etching after aluminum metallization. All wet silicon etchants including ordinary undoped tetramethyl ammonium hydroxide (TMAH)-water solution attack the overlaying aluminum metal interconnect during the anisotropic etching of (100) silicon. This paper presents a TMAH-water based etching recipe to achieve high silicon etch rate, a smooth etched surface and almost total protection of the exposed aluminum metallization. The etch rate measurements of (100) silicon, silicon dioxide and aluminum along with the morphology studies of etched surfaces are performed on both n-type and p-type silicon wafers at different concentrations (2, 5, 10 and 15%) for undoped TMAH treated at various temperatures as well as for TMAH solution doped separately and simultaneously with silicic acid and ammonium peroxodisulphate (AP). It is established through a detailed study that 5% TMAH-water solution dual doped with 38 gm/l silicic acid and 7 gm/l AP yields a reasonably high (100) silicon etch rate of 70 μm/h at 80 °C, very small etch rates of SiO2 and pure aluminum (around 80 Å/h and 50 Å/h, respectively), and a smooth surface (±7 nm) at a bath temperature of 80 °C. The etchant has been successfully used for fabricating several MEMS structures like piezoresistive accelerometer, vaporizing liquid micro-thruster and flow sensor. In all cases, the bulk micromachining is carried out after the formation of aluminum interconnects which is found to remain unaffected during the prolonged etching process at 80 °C. The TMAH based etchant may be attractive in industry due to its compatibility with standard CMOS process. 相似文献
167.
Ho Wai Wong-Lam 《电子产品世界》2006,(11):44-46
ExpressCard模块是由PCMCIA推出的一种更薄、更快、更轻的抽屉式插卡,用以取代现有的PC卡和CardBus模块,主要用于笔记本计算机后继市场中的功能性升级和扩展.同样,ExpressCard模块最初旨在服务于笔记本计算机后继市场(图1a). 相似文献
168.
Y. L. Saraswathi S. Das D. P. Mondal 《Metallurgical and Materials Transactions A》2005,36(8):2259-2262
The erosion-corrsosion behavior of SiC particle-reinforced Al-Si alloy has been studied in NaOH slurry simulating the mining
atmosphere. The study was performed at two different sand concentrations, namely, 20 and 30 wt pct, and at a speed of 900
rpm. It is depicted that the wear rates decreased with increasing sand content, indicating that corrosion is the dominating
mode of material removal. Further composite exhibited lower wear resistance than the laloys irrespective of the sand concentration.
Scanning electron microscope (SEM) observations indicated the dissolution of dendrites of Al due to severe corrosion, leaving
behind the network of Si. This ultimately results in the falling of Si particles from the matrix, leaving behind voids. This
also results in the formation of voids around the SiC particles and leads to pullout of SiC particles from the matrix during
the wear process. 相似文献
169.
U. S. Mohanty B. C. Tripathy S. C. Das V. N. Misra 《Metallurgical and Materials Transactions B》2005,36(6):737-741
The effect of thiourea on the cathodic current efficiency (CE), deposit quality, crystallographic orientations, surface morphology,
and polarization behavior of the cathode was investigated during nickel electrodeposition from acidic sulfate solutions for
2 hours at 60 °C. A slight decrease of 3 to 4 pct in the CE was observed, when the concentration of thiourea was increased
from 2 to 40 mg dm−3. The nickel deposit quality deteriorated significantly at higher thiourea concentrations; the surface morphology deteriorated
and the contamination of the nickel deposits increased. The presence of thiourea affected the peak intensities of the crystal
planes. Cyclic voltammetric studies on nickel deposition at 25 °C revealed depolarization behavior of the cathode at lower
thiourea concentrations, ≤10 mg dm−3; however, a mixed behavior is observed at higher thiourea concentrations. These changes were also observed in the exchange
current density (i
0) values. 相似文献
170.
Reda M. Bakeer Mark A. Shutt Jianqiang Zhong Sankar C. Das Mark Morvant 《Canadian Metallurgical Quarterly》2005,10(2):228-237
A large number of pile-supported bridge approach slabs in southeastern Louisiana were examined to identify the factors that affect their long-term performance. Design drawings and subsoil conditions at these sites as well as their traffic and maintenance records were compiled, and seven representative test sites were selected for thorough field investigation that included inspection of the approach slabs, bridge decks, bridge abutments, and roadway pavement. Field evaluation included walking profiler, falling-weight deflectometer (FWD), laser profiler, geodetic survey, soil borings, cone penetrometer, and nondestructive testing. Measurements made with the walking profiler agreed well with the geodetic survey. The FWD and nondestructive testing were effectively used to detect voids under the approach slab. Results of the study indicated that the current empirical methodology used by the Louisiana Department of Transportation and Development for design of pile-supported approach slabs yields inconsistent field performance. It was concluded that this inconsistent performance is primarily due to the differences in roadway embankment design and construction and in subsoil conditions, which in turn affect the negative skin friction (downdrag) loads imparted on the piles. Impact of other variables such as ramp type, speed limit, traffic volume, and so on was found to be insignificant. Results of the field study were used to develop a new rating system for approach slabs (IRIS) based on International Roughness Index (IRI) measurements obtained with the laser profiler. 相似文献