全文获取类型
收费全文 | 429227篇 |
免费 | 6236篇 |
国内免费 | 2249篇 |
专业分类
电工技术 | 8406篇 |
技术理论 | 5篇 |
综合类 | 1308篇 |
化学工业 | 66446篇 |
金属工艺 | 17625篇 |
机械仪表 | 12862篇 |
建筑科学 | 10798篇 |
矿业工程 | 2832篇 |
能源动力 | 10068篇 |
轻工业 | 39479篇 |
水利工程 | 4817篇 |
石油天然气 | 9115篇 |
武器工业 | 249篇 |
无线电 | 46848篇 |
一般工业技术 | 82623篇 |
冶金工业 | 79523篇 |
原子能技术 | 9654篇 |
自动化技术 | 35054篇 |
出版年
2021年 | 3849篇 |
2019年 | 3440篇 |
2018年 | 5535篇 |
2017年 | 5577篇 |
2016年 | 6024篇 |
2015年 | 4369篇 |
2014年 | 7117篇 |
2013年 | 19113篇 |
2012年 | 11832篇 |
2011年 | 15996篇 |
2010年 | 12829篇 |
2009年 | 14020篇 |
2008年 | 14833篇 |
2007年 | 15033篇 |
2006年 | 13088篇 |
2005年 | 11737篇 |
2004年 | 10828篇 |
2003年 | 10338篇 |
2002年 | 10029篇 |
2001年 | 10125篇 |
2000年 | 9708篇 |
1999年 | 9837篇 |
1998年 | 22651篇 |
1997年 | 16482篇 |
1996年 | 12785篇 |
1995年 | 9491篇 |
1994年 | 8680篇 |
1993年 | 8457篇 |
1992年 | 6628篇 |
1991年 | 6296篇 |
1990年 | 6190篇 |
1989年 | 6229篇 |
1988年 | 5874篇 |
1987年 | 5053篇 |
1986年 | 4995篇 |
1985年 | 5704篇 |
1984年 | 5455篇 |
1983年 | 5050篇 |
1982年 | 4472篇 |
1981年 | 4749篇 |
1980年 | 4342篇 |
1979年 | 4629篇 |
1978年 | 4523篇 |
1977年 | 4865篇 |
1976年 | 6456篇 |
1975年 | 3987篇 |
1974年 | 3754篇 |
1973年 | 3798篇 |
1972年 | 3182篇 |
1971年 | 2893篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
The effect of cycling the external conditions on the timber quality and drying time during seasoning has been studied for red beech (Nothofagus fusca), a difficult-to-dry New Zealand hardwood, inalaboratorybatchdryer. Intermittent drying at anair temperature of 45°C and a wet-bulb depression of 10°C takes longer to yield a given moisture content than continuous drying under the same conditions, but produces timber without honeycomb or severe case-hardening as observed in continuous drying. The experiments also indicate that the timber can tolerate a higher air temperature (55°C) in intermittent drying at the same wet-bulb depression with less case-hardening and without showing honeycomb compared with continuous drying at 45°C, having a similar total drying time. Intermittent drying at a slightly higher dry-bulb temperature (60°C) and a much higher wet-bulb depression (18°C) gives a similar degree of case-hardening to that found in samples dried continuously at a dry-bulb temperature of 45°C. 相似文献
995.
The improved understanding of adsorption chemistry which has arisen from the development of new surface analytical techniques during the last twenty years has had a major effect on the understanding of catalytic reaction mechanisms. However, there are many other areas of technology where Interfacial chemistry has a determining role but where the understanding is much less developed. In this paper examples are presented of the role of interfacial chemistry in adhesion. In particular, It Is shown that modification of a surface to the extent of just a few atomic layers in depth can have dramatic effects on the performance of adhesive bonds, particularly when exposed to hostile environmental conditions. These examples will be used to highlight a need for greater fundamental understanding of the interfacial chemistry of adhesion and also other technologies where interface effects are dominant. 相似文献
996.
997.
998.
The nature of ultrafast energy dissipation in poly(n-hexylsilyne), a prototypical σ-delocalized alkysilicon network polymer, is explored. This disordered silicon backbone material exhibits strong near-UV to visible band-edge absorption and a high quantum yield of visible emission. The time evolution of the emission band is studied over four decades of time using time-resolved luminescence as a probe. The data indicate that while there is an ‘intrinsic’ Stokes shift after photoexcitation due to kinetic energy relaxation (<10ps), thermalization within a dense band of vibronic states via intramolecular phonon-assisted hopping on a nanosecond timescale is the dominant mechanism for excited-state decay. The data can be understood in terms of theoretical predictions for energy relaxation in disordered materials. 相似文献
999.
It has been known for some time that crystal-field matrix elements (i.e., matrix elements of sums over spherical harmonics involving the coordinates of the individual electrons) are often unexpectedly proportional to one another in the f shell. To see whether similar relations hold for more complicated operators than those provided by the crystal field, we examined the matrix elements of the three-electron scalar operators ti for all configurations fN, as calculated by W. T. Carnall on the basis of the computer program of Hannah Crosswhite. These operators are widely used to take configuration interaction into account, and we found a surprising number of proportionalities that go beyond what would be expected on a straightforward application of the Wigner-Eckart theorem, as applied to the irreducible representations of the classic groups SO(7), G2 and SO(3) used by Racah in defining the f-electron states. A listing of such relations is provided. 相似文献
1000.
We have studied theoretically and experimentally the fluorescence enhancement in fluoroborate glasses, doped with the ion Eu3+, containing small silver particles. The model developed shows that the gain coefficient has quenching and enhancement regions. The absorption peak of the metallic particles occurs at 425 nm, which is not in resonance with the 5L6 level of the ion Eu3+. For this reason it is not possible to make a complete comparison between theoretical and experimental results, but the structure of the absorption spectra allows us to check some crucial aspects of the problem, such as energy transfer, enhancement of the local field and the high absorption by the particle system. Results of electronic microscopy have revealed non-uniformity of the particle distribution with average radii of approximately 20 Å and 35 Å and a measured localized mean filling factor of 0.02. 相似文献