全文获取类型
收费全文 | 269787篇 |
免费 | 4537篇 |
国内免费 | 1825篇 |
专业分类
电工技术 | 5499篇 |
技术理论 | 5篇 |
综合类 | 1175篇 |
化学工业 | 43666篇 |
金属工艺 | 11148篇 |
机械仪表 | 7880篇 |
建筑科学 | 7094篇 |
矿业工程 | 1678篇 |
能源动力 | 5795篇 |
轻工业 | 26381篇 |
水利工程 | 2971篇 |
石油天然气 | 6023篇 |
武器工业 | 244篇 |
无线电 | 28270篇 |
一般工业技术 | 50670篇 |
冶金工业 | 48906篇 |
原子能技术 | 5727篇 |
自动化技术 | 23017篇 |
出版年
2021年 | 2602篇 |
2019年 | 2235篇 |
2018年 | 3547篇 |
2017年 | 3516篇 |
2016年 | 3856篇 |
2015年 | 2947篇 |
2014年 | 4793篇 |
2013年 | 11907篇 |
2012年 | 8023篇 |
2011年 | 11410篇 |
2010年 | 8455篇 |
2009年 | 9087篇 |
2008年 | 9841篇 |
2007年 | 9975篇 |
2006年 | 8822篇 |
2005年 | 7689篇 |
2004年 | 6927篇 |
2003年 | 6465篇 |
2002年 | 6435篇 |
2001年 | 6473篇 |
2000年 | 6061篇 |
1999年 | 6040篇 |
1998年 | 13081篇 |
1997年 | 9683篇 |
1996年 | 7421篇 |
1995年 | 5668篇 |
1994年 | 5205篇 |
1993年 | 5061篇 |
1992年 | 4071篇 |
1991年 | 3823篇 |
1990年 | 3903篇 |
1989年 | 3865篇 |
1988年 | 3617篇 |
1987年 | 3110篇 |
1986年 | 3136篇 |
1985年 | 3502篇 |
1984年 | 3408篇 |
1983年 | 3159篇 |
1982年 | 2752篇 |
1981年 | 2969篇 |
1980年 | 2694篇 |
1979年 | 2889篇 |
1978年 | 2809篇 |
1977年 | 2890篇 |
1976年 | 3733篇 |
1975年 | 2493篇 |
1974年 | 2330篇 |
1973年 | 2352篇 |
1972年 | 2021篇 |
1971年 | 1798篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
This report deals with direct observations of microcrack linkage at the crack tip prior to macroscopic crack initiation. It is shown that this process is directly linked to the inclusion distribution in the material and can be considered in terms of an R curve to describe microcrack development. 相似文献
152.
K.L. Johnson J.A. Greenwood J.G. Higginson 《International Journal of Mechanical Sciences》1985,27(6):383-396
A complete solution in closed form to the elastic contact of a one-dimensional sinusoidal surface with a flat surface was presented by Westergaard in 1939. This paper is concerned with the elastic contact of a two-dimensional sinusoidal surface with a flat. In this case the stress distribution within the elastic solids is three-dimensional. As the load is increased the contact areas change in shape from being circular to square and finally leave a circular region of no contact when the waves are almost squashed flat. The problem is solved in general using a numerical method due to Kalker, but asymptotic solutions in closed form have been found for light loads and also for heavy loads at which contact is almost complete. The variation of the mean separation with load, which determines the volume of the space trapped between the two surfaces, is also found. 相似文献
153.
Behaviour of a series of lubricant oils and the effect of a non stoichiometric inorganic compound, as solid extreme pressure additive, on rolling fatigue life are studied using the rolling four-ball accelerated service simulation test proposed by Barwell and Scott. The results show, in all tested cases, the remarkable efficacy of this type of additive. The Total Acidity Number (tan) was found to increase with performance time for the case of the base lubricant, while for the oils with additives, it remained at its constant low value. This led to a proposal of a possible mechanism of the additive performance in the rolling process. 相似文献
154.
155.
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
156.
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
157.
D. C. Peets R. Liang C. Stock W. J. L. Buyers Z. Tun L. Taillefer R. J. Birgeneau D. A. Bonn W. N. Hardy 《Journal of Superconductivity and Novel Magnetism》2002,15(6):531-534
We have grown cubic centimeter-size crystals of YBa2Cu3O x suitable for neutron studies, by a top-seeded melt-growth technique. Growth conditions were optimized with an eye toward maximizing phase purity. It was found that the addition of 2% Y2BaCuO5 and 0.5% Pt (by mass) were required to prevent melt loss and to obtain the highest crystallinity. A neutron diffraction study on a mosaic of six such crystals found that the final Y2BaCuO5 concentration was 5%, while other impurity phases comprised less than 1% by volume. The oxygen content was set to x = 6.5, the crystals were detwinned, and then carefully annealed to give the well-ordered ortho-II phase. The neutron study determined that 70% of the mosaic's volume was in the majority orthorhomic domain. The neutron (006) and (110) rocking curve widths were ~1° per crystal and ~2.2° for the mosaic, and the oxygen chain correlation lengths were >100 Å in the a- and b-directions and ~50 Å in the c-direction. 相似文献
158.
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
159.
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
160.