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   8050篇
  免费   119篇
  国内免费   2篇
电工技术   54篇
综合类   8篇
化学工业   657篇
金属工艺   155篇
机械仪表   82篇
建筑科学   169篇
能源动力   61篇
轻工业   304篇
水利工程   9篇
石油天然气   7篇
无线电   342篇
一般工业技术   592篇
冶金工业   5330篇
原子能技术   75篇
自动化技术   326篇
  2022年   28篇
  2021年   47篇
  2020年   29篇
  2019年   50篇
  2018年   61篇
  2017年   49篇
  2016年   66篇
  2015年   47篇
  2014年   76篇
  2013年   139篇
  2012年   105篇
  2011年   140篇
  2010年   99篇
  2009年   96篇
  2008年   95篇
  2007年   110篇
  2006年   109篇
  2005年   86篇
  2004年   97篇
  2003年   88篇
  2002年   86篇
  2001年   59篇
  2000年   94篇
  1999年   255篇
  1998年   1582篇
  1997年   890篇
  1996年   634篇
  1995年   336篇
  1994年   303篇
  1993年   319篇
  1992年   76篇
  1991年   113篇
  1990年   94篇
  1989年   126篇
  1988年   109篇
  1987年   104篇
  1986年   96篇
  1985年   83篇
  1984年   37篇
  1983年   39篇
  1982年   43篇
  1981年   50篇
  1980年   86篇
  1979年   34篇
  1978年   46篇
  1977年   179篇
  1976年   347篇
  1975年   33篇
  1974年   35篇
  1973年   27篇
排序方式: 共有8171条查询结果,搜索用时 12 毫秒
31.
32.
    
Ohne ZusammenfassungMitteilung aus dem Chemischen Laboratorium der Auslandsfleischbeschaustelle Bentheim.  相似文献   
33.
New Knowledge on Degradation of Starch by Hypochlorite. Part 5. Ageing of Pastes from Oxidized Starch . In order to obtain information on storability of pastes from hypochlorite-oxidized potato starches the changes of viscosity and retrogradation as a function of the degree of oxidation were analized. Apart from a comparison of these results with the pastes of starch dextrines the influence of adding formaldehyde and toluene was investigated.  相似文献   
34.
In the present research, we test the assumption that emotional mimicry and contagion are moderated by group membership. We report two studies using facial electromyography (EMG; Study 1), Facial Action Coding System (FACS; Study 2), and self-reported emotions (Study 2) as dependent measures. As predicted, both studies show that ingroup anger and fear displays were mimicked to a greater extent than outgroup displays of these emotions. The self-report data in Study 2 further showed specific divergent reactions to outgroup anger and fear displays. Outgroup anger evoked fear, and outgroup fear evoked aversion. Interestingly, mimicry increased liking for ingroup models but not for outgroup models. The findings are discussed in terms of the social functions of emotions in group contexts. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
35.
This paper uses four case studies to emphasize the fact that field engineering decisions cannot be made without a full understanding of all the technical problems involved. Two of the studies are taken from conventional design-bid-build projects and two are taken from design-build projects in which the ability to strongly influence design in the interest of construction efficiency places a new and increased emphasis on construction and field engineering skills. The cases also show that field engineering decisions frequently address new and unexpected realities, changed conditions, and transient loads, and thus they require high levels of understanding, technical analysis, and creative thought. We emphasize the need for universities and construction engineering programs to develop graduates who are capable of integrating design and construction considerations throughout the project delivery process. We also urge programs to continue to focus strongly on field engineering as the foundation for success in an increasingly complex and technically driven construction industry.  相似文献   
36.
Metallic magnesium (Mg) and its alloys are highly suitable for medical applications as biocompatible and biodegradable implant materials. Magnesium has mechanical properties similar to bone, stimulates bone regeneration, is an essential non-toxic element for the human body and degrades completely within the body environment. In consequence, magnesium is a promising candidate as implant material for orthopaedic applications. Protocols using the guideline of current ISO standards should be carefully evaluated when applying them for the characterization of the cytotoxic potential of degradable magnesium materials. For as-cast material we recommend using 10 times more extraction medium than recommended by the ISO standards to obtain reasonable results for reliable cytotoxicity rankings of degradable materials in vitro. In addition primary isolated human osteoblasts or mesenchymal stem cells should be used to test magnesium materials.  相似文献   
37.
Electron beam x-ray tomography is an imaging technique, which can provide cross-sectional images of an object of interest with about 1 mm spatial resolution at frame rates of up to 10,000 frames per second. As a non-intrusive method it is especially suited for studying multiphase flows. For this purpose we devised an experimental limited-angle scan setup which utilizes linear beam deflection to generate radiographic projections. This setup was employed in the study of gas–liquid flow in an experimental flow loop operated at different liquid and gas flow rates. Electron-beam tomography images were compared with image data of a wire-mesh sensor. The latter is a fast but intrusive imaging device which is commonly used in gas–liquid flow imaging and achieves comparable frame rates but at lower spatial resolution. As a novelty we implemented a dual-plane limited-angle electron beam x-ray tomography which allows us to gain information about the phase velocities using cross-correlation data analysis.  相似文献   
38.
This paper presents the design and test of asymmetric quasioptical resonators for gyrotron applications, where most of the diffraction output coupling comes from the smaller of two mirrors. A computer code based on scalar diffraction theory is used to calculate the resonator losses and the electric field near the mirrors. Resonators with mirror separations approaching confocal have reduced side lobes in the diffraction patterns, which should allow for better power transmission and focusing. Cold tests have been performed at 94 and 141 GHz to measure the quality factor of the asymmetric resonators as a function of mirror separation and mirror misalignment. Typical resonator parameters include 65 cm mirror separation, 1-3% output coupling and 85% of the losses from the small mirror. A half-symmetric resonator with one flat and one curved mirror has also been investigated. The calculated values of Q are in reasonably good agreement with the cold test measurements.  相似文献   
39.
A macropipelined CISC microprocessor was implemented in a 0.75-μm CMOS 3.3-V technology. The 1.3-million-transistor custom chip measures 1.62×1.46 cm2 and dissipates 16.3 W. The 100-MHz parts were benchmarked at 50 SPEC marks. The on-chip clocking system and several high-performance logic and circuit techniques are described. Macroinstruction handling, micropipeline management, and control store structures highlight the design architecture. The hierarchical array organization and fast tag comparison technique of the primary cache are discussed. Power estimation procedures are outlined, and the results are compared to measurements. Physical design and verification methods, and CAD tools are also described. After extensive functional verification efforts are described, chip and system test results are presented  相似文献   
40.
We report the results of an experimental study of molecular-beam epitaxy of ZnSe-based laser heterostructures with a new structure of the active region, which contains a fractional-monolayer CdSe recombination region in an expanded ZnSe quantum well and a waveguide based on a variably-strained, short-period superlattice are reported. Growth of a fractional-monolayer CdSe region with a nominal thickness of 2–3 ML, i.e., less than the critical thickness, on a ZnSe surface (Δa/a∼7%) leads to the formation of self-organized, pseudomorphic, CdSe-enriched islands with lateral dimensions ∼10–30 nm and density ∼2×1010 cm−2, which serve as efficient centers of carrier localization, giving rise to effective spatial separation of defective regions and regions of radiative recombination and, as a result, a higher quantum efficiency. Laser structures for optical pumping in the (Zn, Mg) (S, Se) system with a record-low threshold power density (less than 4 kW/cm2 at 300 K) and continuous-wave laser diodes in the system (Be, Mg, Zn) Se with a 2.5 to 2.8-ML-thick, fractional-monolayer CdSe active region have been obtained. The laser structures and diodes have an improved degradation resistance. Fiz. Tekh. Poluprovodn. 33, 1115–1119 (September 1999)  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