全文获取类型
收费全文 | 13875篇 |
免费 | 893篇 |
国内免费 | 41篇 |
专业分类
电工技术 | 203篇 |
综合类 | 26篇 |
化学工业 | 3253篇 |
金属工艺 | 284篇 |
机械仪表 | 331篇 |
建筑科学 | 496篇 |
矿业工程 | 44篇 |
能源动力 | 399篇 |
轻工业 | 720篇 |
水利工程 | 100篇 |
石油天然气 | 50篇 |
无线电 | 1689篇 |
一般工业技术 | 3222篇 |
冶金工业 | 1412篇 |
原子能技术 | 107篇 |
自动化技术 | 2473篇 |
出版年
2023年 | 224篇 |
2022年 | 395篇 |
2021年 | 688篇 |
2020年 | 498篇 |
2019年 | 426篇 |
2018年 | 519篇 |
2017年 | 436篇 |
2016年 | 618篇 |
2015年 | 464篇 |
2014年 | 656篇 |
2013年 | 892篇 |
2012年 | 807篇 |
2011年 | 918篇 |
2010年 | 640篇 |
2009年 | 622篇 |
2008年 | 642篇 |
2007年 | 601篇 |
2006年 | 465篇 |
2005年 | 378篇 |
2004年 | 323篇 |
2003年 | 288篇 |
2002年 | 266篇 |
2001年 | 204篇 |
2000年 | 166篇 |
1999年 | 179篇 |
1998年 | 394篇 |
1997年 | 249篇 |
1996年 | 186篇 |
1995年 | 158篇 |
1994年 | 120篇 |
1993年 | 160篇 |
1992年 | 90篇 |
1991年 | 87篇 |
1990年 | 74篇 |
1989年 | 71篇 |
1988年 | 65篇 |
1987年 | 61篇 |
1986年 | 56篇 |
1985年 | 63篇 |
1984年 | 62篇 |
1983年 | 47篇 |
1982年 | 40篇 |
1981年 | 39篇 |
1980年 | 34篇 |
1979年 | 30篇 |
1978年 | 40篇 |
1977年 | 36篇 |
1976年 | 66篇 |
1975年 | 34篇 |
1971年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
31.
Vladimir Rozenshtein Alexander Berg Haim Levanon Uwe Krueger Dietmar Stehlik Yuri Kandrashkin Art Van Der Est 《Israel journal of chemistry》2003,43(3-4):373-381
Light-induced spin-polarized transient EPR spectra are reported for several water-soluble copper porphyrins. The spectra are assigned to the doublet ground state, with emissive spin polarization resulting from photoexcitation and subsequent electronic relaxation. In contrast to other systems for which polarization of a doublet ground state has been observed, the exchange interactions in the copper porphyrins are strong and the geometry is fixed. It is proposed that intersystem crossing from the photoexcited trip-doublet to the trip-quartet state can lead to net polarization of the spin system and that this polarization is maintained during electronic decay, possibly via charge-transfer and exciplex states. The intensity of the observed spin polarization is essentially independent of the molecular orientation in the external field, but is strongly dependent on the nature of the charged peripheral groups. Possible reasons for this behavior are discussed. 相似文献
32.
Peter V. Sushko Alexander L. ShlugerKatsuro Hayashi Masahiro HiranoHideo Hosono 《Thin solid films》2003,445(2):161-167
Recently it has been discovered that a nano-porous main group oxide 12CaO·7Al2O3 (C12A7) can be converted from a wide-gap insulator to a good transparent conductor. Using ab initio modelling we explain good conductivity of this material by very small barriers for hopping of localised electrons between neighbouring positive cages. We show that optical absorption of C12A7 in infrared region and at energies higher than 2.7 eV is due to inter-cage and intra-cage electron transitions, respectively. The proposed mechanisms can be useful in further search for conducting transparent media. 相似文献
33.
Decreasing carboxyl retention in deposits from the glow region of an acrylic acid plasma was measured by X-ray photoelectron spectroscopy and chemical derivatisation as the collection distance from the monomer vapour inlet was increased. Volatilisation of plasma polymerised acrylic acid was detected after trifluoroethanol derivatisation; this is correlated with evaporation of low molecular weight components observed previously. 相似文献
34.
The aim of this paper is to give a general quantitative requirement which the loop gain must satisfy in order to stabilize a given unstable (possibly nonlinear and time-varying) plant, namely that the gain must exceed one. 相似文献
35.
In this work, wavelet basis and source coding are jointly optimized, while specifying the source coding strategy as entropy-constrained lattice vector quantizer (ECLVQ). The presented approach differs from previous works in which the choice of wavelet basis is quasioptimal, but the quantizer set is optimally chosen 相似文献
36.
37.
E. Ech-chamikh M. Azizan E.L. Ameziane A. Bennouna M. Brunel T.T.A. Nguyen 《Solar Energy Materials & Solar Cells》1993,31(2)
Hydro-oxygenated carbon (C : H,O) and silicon (Si : H,O) layers are deposited by RF sputtering of graphite and silicon targets in a mixture of argon, hydrogen and oxygen gases. C : H,O/Si : H,O/C : H,O/Si : H,O... multilayers are obtained by sequential deposition of C : H,O and Si : H,O layers. Infrared (IR) spectroscopy, Grazing Incidence X-ray Diffraction (GIXD) and X-ray Photoelectron Spectroscopy (XPS) techniques have been used to analyse the formed multilayers. The IR spectra made on as deposited structures show the presence of Si---C, Si---O, C---O, Si---H, C---H and C=C bonds. This result indicates an interfacial reactivity between Si : H,O and C : H,O layers. The latter result is confirmed by the XPS measurements. After an annealing at 850°c for two hours under argon atmosphere (10-3 mbar), the concentration of the Si---C bonds is increased by a factor two while the Si---H and C---H bonds disappear complet The GIXD measurements show that the multilayers are amorphous when annealed below 750°C, and they are crystallized with the formation of the α-SiC phase if the heat treatment is made at 850°C. The mean size of the microcrystallites is 50 Å about. 相似文献
38.
39.
40.