全文获取类型
收费全文 | 494335篇 |
免费 | 8705篇 |
国内免费 | 2634篇 |
专业分类
电工技术 | 9196篇 |
技术理论 | 5篇 |
综合类 | 1356篇 |
化学工业 | 77424篇 |
金属工艺 | 18120篇 |
机械仪表 | 14242篇 |
建筑科学 | 13012篇 |
矿业工程 | 2205篇 |
能源动力 | 12211篇 |
轻工业 | 52129篇 |
水利工程 | 4839篇 |
石油天然气 | 7738篇 |
武器工业 | 253篇 |
无线电 | 56368篇 |
一般工业技术 | 90874篇 |
冶金工业 | 92670篇 |
原子能技术 | 8342篇 |
自动化技术 | 44690篇 |
出版年
2021年 | 4480篇 |
2020年 | 3323篇 |
2019年 | 4034篇 |
2018年 | 6425篇 |
2017年 | 6361篇 |
2016年 | 7018篇 |
2015年 | 5380篇 |
2014年 | 8374篇 |
2013年 | 23325篇 |
2012年 | 14422篇 |
2011年 | 19232篇 |
2010年 | 15215篇 |
2009年 | 16486篇 |
2008年 | 17581篇 |
2007年 | 17657篇 |
2006年 | 15714篇 |
2005年 | 13973篇 |
2004年 | 12972篇 |
2003年 | 12488篇 |
2002年 | 12048篇 |
2001年 | 12301篇 |
2000年 | 11337篇 |
1999年 | 11798篇 |
1998年 | 28142篇 |
1997年 | 20160篇 |
1996年 | 15278篇 |
1995年 | 11494篇 |
1994年 | 10255篇 |
1993年 | 10074篇 |
1992年 | 7379篇 |
1991年 | 7017篇 |
1990年 | 6918篇 |
1989年 | 6661篇 |
1988年 | 6393篇 |
1987年 | 5313篇 |
1986年 | 5228篇 |
1985年 | 6189篇 |
1984年 | 5791篇 |
1983年 | 5313篇 |
1982年 | 4807篇 |
1981年 | 5070篇 |
1980年 | 4659篇 |
1979年 | 4673篇 |
1978年 | 4432篇 |
1977年 | 4980篇 |
1976年 | 6587篇 |
1975年 | 3844篇 |
1974年 | 3632篇 |
1973年 | 3724篇 |
1972年 | 3025篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
201.
Arden L. Bement 《Metallurgical and Materials Transactions B》1987,18(1):5-17
The field of materials science and engineering is advancing at a revolutionary pace. It is now generally recognized as being
among the key emerging technological fields propelling our world societies into the twenty-first century. The driving forces
for this revolutionary pace are at once social, economic, political, and technological. For example, relatively recent changes
in United States federal policies in environmental control, hazardous waste management, and energy conservation along with
heightened international trade competition have resulted in major changes in material processing and use patterns. These changing
patterns are creating new requirements for material developments, substitutions, and associated processes. This paper traces
the emergence of materials policy and technological developments through four sub-periods of history: the birth and development
of engineering in the United States (1825–1900), the evolution of a national research infrastructure (1900–1945), the evolution
of a national science policy (1945–1973), and the intensification of global interdependency (1973-present). Future trends
in materials developments and future policy requirements are outlined.
Technical Resources, of TRW, Inc., began his professional career in 1954 as a research metallurgist and reactor project engineer
with General Electric Co. at the Hanford Atomic Products Operation in Richland, WA. In 1965 he joined Battelle Memorial Institute
as a manager of the metallurgy research department and three years later became manager of the fuels and materials department.
In 1970 Dr. Bement joined the faculty of Massachusetts Institute of Technology as professor of nuclear materials. From 1974
to 1976 he served as a member of the U.S.-U.S.S.R. Bilateral Exchange Program in Magnetohydrodynamics and was the organizer
and principal investigator of the M.I.T. Fusion Technology Program. In 1976 Dr. Bement became Director of the Materials Sciences
Office of the Defense Advanced Research Projects Agency and in 1979 was appointed Deputy Under-Secretary of Defense for Research
and Engineering. Dr. Bement has co-authored one book, edited three books, and authored over 90 articles on materials science,
energy, and defense technology. He is a Fellow of the American Nuclear Society, the American Society for Metals, and the American
Institute of Chemists. In addition, he is a member of the American Institute for Mining, Metallurgical and Petroleum Engineers,
and the American Society for Testing and Materials. He has received outstanding achievement awards from the Colorado Engineering
Council in 1954, the Defense Advanced Research Projects Agency in 1977, and the Colorado School of Mines in 1984. In 1980
he was awarded the Distinguished Civilian Service Medal by the Secretary of Defense. He is a member of the National Academy
of Engineering. Dr. Bement is chairman of the National Materials Advisory Board and a member of the Board of Army Science
and Technology, the Board on Engineering Sciences, the Board on Assessment of National Bureau of Standards Programs, and the
Board on Science and Technology for International Development of the National Research Council. Dr. Bement received an Engineer
of Metallurgy (E. Met.) degree in 1954 from the Colorado School of Mines. He received an M.S. in Metallurgical Engineering
from the University of Idaho in 1959, and a Ph.D. from the University of Michigan in 1963. He is a Lt. Colonel (ret.) in the
U.S. Army Corps of Engineers. Dr. Bement and his family reside in Mayfield Village, OH. 相似文献
202.
We consider three types of near-boundary elements: curvilinear quadrangles and families of arcs and points, and their application to a two-dimensional problem of the static theory of elasticity with boundary conditions in displacements. The comparison of the theoretical and numerical aspects of the obtained solutions is performed. It is shown that the accuracy of evaluation of the components of the vector of displacements increases in the following cases: in the case of complete quantization of the near-boundary region (but not in the case of its partial quantization or quantization with overlapping), in the case where the numbers of arcs and points increase, and in the case of simultaneous application of different types of near-boundary elements (specifically, quadrangles and families of arcs). 相似文献
203.
L A Geddes 《IEEE engineering in medicine and biology magazine》2002,21(3):102-103
Poiseuille, known for his law of fluid flow, which is the analog of Ohm's law, introduced the units (mmHg) by which we measure blood pressure by using the mercury manometer, which he described in his medical school thesis in 1828. For 50 years, mean blood pressure was all that could be measured because of the long response time of the mercury manometer. It is true that the height of the mercury column displayed pulsatile oscillations, but their amplitude was much less than that of pulse pressure. It is interesting to note that the slowly responding mercury manometer was made to display first systolic then diastolic pressure by means of an ingenious device that contained two oppositely directed check valves. It took from 1828 to 1903 for high-fidelity graphic recordings of blood pressure to appear in which systolic and diastolic pressures were believable. However, systolic and diastolic pressures were measurable since 1878 when Golz and Gaule created their ingenious valved device that permitted use of the slowly responding mercury manometer to display these pressures accurately 相似文献
204.
Field R. D. Hartwig K. T. Necker C. T. Bingert J. F. Agnew S. R. 《Metallurgical and Materials Transactions A》2002,33(13):965-972
The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions
have been successfully completed on Ni-canned billets of Be at approximately 425°C. No cracking was observed in the billets,
and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed
for a singlepass extrusion, including evidence of <c> and <c+a> dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation
processing technique and the underlying physical processes which sustain the deformation.
S.R. AGNEW, formerly with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
205.
巴西的一个重要电力公司COPEL最近开发了一个水电站高级控制系统,这是在电力部门经受重大变革时期,提高水电竞争力的里程碑。 相似文献
206.
Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis
Griffiths M. Sage D. Holt R. A. Tome C. N. 《Metallurgical and Materials Transactions A》2002,33(13):859-865
X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed
in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to
extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In
both cases, for specific tensile tests, a significant contribution to the basal line braodening was observed, which was clearly
not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed
that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed
was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their
c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few,
if any, c-component dislocations present.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science and Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
207.
The precautionary principle (PP), according to one of its definitions, says that lack of certainty, given the current scientific and technological knowledge, shall not delay effective and proportionate actions to prevent hazards, taking into account cost-benefit considerations. Rather than being a single principle, a variety of statements of the PP are found in international treaties and other documents. Apart from any specific legal force of the documents, countries (e.g., France) have used these statements as a starting point for their own guidance documents and regulations for addressing specific environmental and health issues, for example regulation of genetically modified organisms. Thus, any discussion of the precautionary principle must address a complex legal and regulatory situation. We briefly review different statements of the PP and important commentary, largely from the European Union. We provide references to the original source documents (many of which are found in English on the World Wide Web). 相似文献
208.
Commault C. Dion J.-M. Sename O. Motyeian R. 《Automatic Control, IEEE Transactions on》2002,47(12):2074-2079
209.
210.
A theory is presented that explains how the visual system infers the lightness, opacity, and depth of surfaces from stereoscopic images. It is shown that the polarity and magnitude of image contrast play distinct roles in surface perception, which can be captured by 2 principles of perceptual inference. First, a contrast depth asymmetry principle articulates how the visual system computes the ordinal depth and lightness relationships from the polarity of local, binocularly matched image contrast. Second, a global transmittance anchoring principle expresses how variations in contrast magnitudes are used to infer the presence of transparent surfaces. It is argued that these principles provide a unified explanation of how the visual system computes the 3-D surface structure of opaque and transparent surfaces. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献