全文获取类型
收费全文 | 60950篇 |
免费 | 6733篇 |
国内免费 | 2314篇 |
专业分类
电工技术 | 4806篇 |
综合类 | 5019篇 |
化学工业 | 11250篇 |
金属工艺 | 6308篇 |
机械仪表 | 3272篇 |
建筑科学 | 6162篇 |
矿业工程 | 1124篇 |
能源动力 | 8754篇 |
轻工业 | 2893篇 |
水利工程 | 668篇 |
石油天然气 | 2594篇 |
武器工业 | 464篇 |
无线电 | 2671篇 |
一般工业技术 | 6824篇 |
冶金工业 | 3792篇 |
原子能技术 | 1575篇 |
自动化技术 | 1821篇 |
出版年
2024年 | 201篇 |
2023年 | 739篇 |
2022年 | 1561篇 |
2021年 | 1806篇 |
2020年 | 1931篇 |
2019年 | 1527篇 |
2018年 | 1402篇 |
2017年 | 1759篇 |
2016年 | 2084篇 |
2015年 | 2122篇 |
2014年 | 3561篇 |
2013年 | 3835篇 |
2012年 | 4332篇 |
2011年 | 4712篇 |
2010年 | 3383篇 |
2009年 | 3536篇 |
2008年 | 2861篇 |
2007年 | 3930篇 |
2006年 | 3626篇 |
2005年 | 3120篇 |
2004年 | 2717篇 |
2003年 | 2465篇 |
2002年 | 2213篇 |
2001年 | 1805篇 |
2000年 | 1536篇 |
1999年 | 1237篇 |
1998年 | 1001篇 |
1997年 | 893篇 |
1996年 | 749篇 |
1995年 | 651篇 |
1994年 | 536篇 |
1993年 | 439篇 |
1992年 | 368篇 |
1991年 | 246篇 |
1990年 | 195篇 |
1989年 | 208篇 |
1988年 | 135篇 |
1987年 | 101篇 |
1986年 | 77篇 |
1985年 | 68篇 |
1984年 | 79篇 |
1983年 | 62篇 |
1982年 | 62篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1975年 | 5篇 |
1959年 | 28篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
沈阳太平洋广场空调冷热源方案比较 总被引:4,自引:1,他引:3
对一幢11.5万m^2的四星级综合建筑的空调冷热源不同的蓄冷和取冷比较了四种方案,论证了其中直燃型溴化锂吸收式冷热水机组供冷供暖、小型燃油锅炉供蒸汽的方案最为合理。 相似文献
172.
173.
Y. Kraftmakher 《International Journal of Thermophysics》1994,15(5):983-991
Relaxation phenomena due to equilibration of point defects in metals are reviewed. The relaxation effect in specific heat observed in tungsten and platinum confirms that in both cases the nonlinear increase in the high-temperature specific heat has to be attributed to point-defect formation. Relaxation phenomena observed by measurements of electrical resistivity and positron annihilation are also considered. The comparison of the data seems to be favorable for the conclusion that all the phenomena are of one origin. 相似文献
174.
We present a method that is useful in the estimate and assessment of heat capacity data. The approach is based on an analysis of the logarithmic average of the phonon frequencies. In this quantity, that may be easily derived from experimental data on the vibrational entropy, the influence of atomic masses can be exactly accounted for even in polyatomic solids. Our method is applied to Li2O, Na2O, K2O, Rb2O, and Cs2O. In particular, literature data for K2O are critically examined. 相似文献
175.
176.
Ricardo Garcia-Padron Dan Loyd Stefan Sjökvist 《Subsurface Sensing Technologies and Applications》2002,3(2):125-150
One promising method of locating buried objects, such as land mines, is to use optical systems for detecting contrasts in surface temperature. With enhanced knowledge about the interacting physical processes behind these temperature contrasts, it is possible to improve detection precision. In such a context, moisture movement in the soil and moisture evaporation from the surface have been found to be of particular interest. This study was based on indoor experiments on wet and dry sand exposed to radiation from a solar panel. Simulations of heat and moisture transfer conducted with a one-dimensional model are also presented for the experiments. The calculations were successful in accurately predicting surface temperatures for both wet and dry sand, making it possible to predict surface temperatures under different conditions. These findings will contribute to increasing the probability of successful detection of buried objects under real conditions using optical methods. 相似文献
177.
L. Z. Jin 《Journal of Materials Engineering and Performance》1994,3(6):734-739
Chloride-induced stress-corrosion cracking (SCC) is one of the failure modes of stainless steels. Highly alloyed austenitic
stainless steels S32654, S31254, and N08028, and duplex grades S32750 and S31803 possess much improved resistance to SCC compared
with S30400 and S31600 steels. With the development of a database, SSData, experimental data collected from calcium chloride
tests, autoclave tests, and drop evaporation tests were evaluated. Stress-corrosion cracking data generated by autoclave tests
agreed well with the practical service conditions and can be used to discriminate alloys for SCC resistance in sodium chloride
solution. Drop evaporation test data can be used in situations where evaporation may occur and cyclic loading may be involved.
The SCC resistance of alloys under each method increased with increasing molybdenum equivalent Mo + 0.25Cr + 0.1Ni. For a
given alloy, the testing result depends on the stress state and environment; different test methods can give different ranking
orders concerning SCC resistance. The performance of duplex stainless steels in a chloride-containing environment at higher
temperatures was not as good as expected when dynamic loading was involved. 相似文献
178.
The heat affect zone (HAZ) is in many cases considered to be the most critical part of a weldment. In this paper, the effect of crack size and weld metal mismatch on the HAZ cleavage toughness of wide plate specimens with X-groove has been investigated by the J-Q-M theories and a simple micromechanism for cleavage fracture. Two crack sizes have been studied (a/w = 0.1 and 0.3). In the analyses, the HAZ yield strength is assumed to be higher than the base metal. For each crack size, weld metal local overmatch and local evenmatch with respect to the HAZ are considered. For a given global strain, the results indicate that weld metal overmatch and evenmatch yield the same crack tip loading in terms of J-integral for a/w = 0.3. For a/w = 0.1, overmatch gives lower crack tip loading than evenmatch. For a given crack tip loading, weld metal local evenmatch in general results in less effective crack tip loading than the overmatch. Overmatch is detrimental to HAZ toughness, but this detrimental effect becomes less significant when the crack size decreases. 相似文献
179.
Mao Ze yu Chen Chang zhi Department of Hydraulic Engineering Tsinghua University Beijing P.R.China 《水动力学研究与进展(B辑)》1999,(3)
1. INTRODUCTIONThesimulationofstreamwatertemperatureissignificantlyimportantforthestudyofnumericalmodelingofrivericeprocesses[1] .Historically,themathematicalmodelingofthetransportandfateofheatinawaterbodyhasbeenthesubjectofextensivestudyforvariousre… 相似文献
180.
石玉泓 《机械工程与自动化》2004,(4):82-83
随着国有企业改革的不断深化,市场竞争愈加激烈,针对机械行业的现状,从3个方面探讨了强化管理机制,推进机械制造企业可持续快速发展的途径. 相似文献