全文获取类型
收费全文 | 1334篇 |
免费 | 80篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 17篇 |
综合类 | 1篇 |
化学工业 | 293篇 |
金属工艺 | 25篇 |
机械仪表 | 25篇 |
建筑科学 | 44篇 |
矿业工程 | 1篇 |
能源动力 | 59篇 |
轻工业 | 92篇 |
水利工程 | 8篇 |
石油天然气 | 2篇 |
无线电 | 134篇 |
一般工业技术 | 269篇 |
冶金工业 | 162篇 |
原子能技术 | 12篇 |
自动化技术 | 271篇 |
出版年
2023年 | 14篇 |
2022年 | 20篇 |
2021年 | 51篇 |
2020年 | 27篇 |
2019年 | 48篇 |
2018年 | 44篇 |
2017年 | 34篇 |
2016年 | 48篇 |
2015年 | 44篇 |
2014年 | 61篇 |
2013年 | 93篇 |
2012年 | 87篇 |
2011年 | 134篇 |
2010年 | 79篇 |
2009年 | 71篇 |
2008年 | 90篇 |
2007年 | 57篇 |
2006年 | 63篇 |
2005年 | 47篇 |
2004年 | 31篇 |
2003年 | 32篇 |
2002年 | 19篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 16篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1972年 | 3篇 |
1958年 | 2篇 |
1954年 | 3篇 |
1948年 | 2篇 |
1947年 | 2篇 |
1946年 | 2篇 |
排序方式: 共有1415条查询结果,搜索用时 15 毫秒
1.
2.
Maria A. Ospina Monica Pizarro Thierry Tran Julien Ricci John Belalcazar Jorge L. Luna Luis F. Londoño Sandra Salazar Hernan Ceballos Dominique Dufour Luis A. Becerra Lopez-Lavalle 《International Journal of Food Science & Technology》2021,56(3):1343-1353
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes. 相似文献
3.
Various image processing applications exploit a model of the human visual system (HVS). One element of HVS-models describes the masking-effect, which is typically parameterized by psycho-visual experiments that employ superimposed sinusoidal stimuli. Those stimuli are oversimplified with respect to real images and can capture only very elementary masking-effects. To overcome these limitations a new psycho-visual test method is proposed. It is based on natural scenery stimuli and operates in the wavelet domain. The collected psycho-visual data is finally used to evaluate the performance of various masking models under conditions as found in real image processing applications like compression. 相似文献
4.
We study the effect of Josephson coupling between adjacent superconducting layers on the BCS energy spectrum. We find that the interference between the gap functions of two layers can lead to vanishing condensation energy for perpendicular momenta corresponding to the formation of standing waves. We therefore predict a conventional energy spectrum for large interlayer spacings, if the gap of the single layers has no nodes, and in all cases a gapless spectrum for small spacings. Within the experimental error, our numerical results account for the low-temperature dependence of the penetration depth reported in Nd1.85Ce0.15CuO4 and YBa2Cu3O6.9. 相似文献
5.
B. Dagens A. Martinez D. Make O. Le Gouezigou J.-G. Provost V. Sallet K. Merghem J.-C. Harmand A. Ramdane B. Thedrez 《Photonics Technology Letters, IEEE》2005,17(5):971-973
Among the new semiconductor materials for telecom devices, the GaInNAs-GaAs structure presents interesting properties for low-cost applications, like high differential gain and high T/sub 0/. Another key aspect of the performance is the behavior of the GaInNAs-GaAs based lasers under high bit rate direct modulation. Here, we demonstrate the dynamic capabilities of GaInNAs-GaAs three-quantum-well ridge structure through 2.5-Gb/s directly modulated laser emission and transmission on standard fiber, in the temperature range 25/spl deg/C-85/spl deg/C. Besides transmission is demonstrated up to 10 Gb/s at 25/spl deg/C on the same fiber, without penalty and bit-error-rate floor. 相似文献
6.
The reactivity of lithium with layered chalcogenides InSe and In2Se3 is studied using transmission electron microscopy (TEM), electrochemical potential spectroscopy (EPS) and Raman scattering (RS). It is found that for x(Li)≥0.1 in LixInSe, the host material decomposes with the formation of lithium selenide. The presence of Li2Se is confirmed by Raman spectroscopy. The insertion of Li into In2Se3 appears more stable with the occurrence of a superlattice formation at x(Li)≈0.25. The superstructure corresponding to the 2a×2a lattice is consistent with the EPS measurements of LixIn2Se3. 相似文献
7.
Langanay J. Brindel P. Brun E. Provost J.G. Lesterlin D. Hamaide J.P. 《Electronics letters》1994,30(19):1599-1601
The variability of optical frequency modulation with electric field in an electro-optical phase section is analysed. When configured for maximum sensitivity, the electro-optical phase section was used to compensate for the chirp of the gain section: 48 ps and 8.5 GHz wide transform-limited pulses were obtained at 5 GHz 相似文献
8.
9.
Breton M. Tremblay P. Julien C. Cyr N. Tetu M. Latrasse C. 《IEEE transactions on instrumentation and measurement》1995,44(2):162-165
The performance of 196.0-THz (1529-nm) DFB lasers frequency-locked to absorption lines of a rubidium vapor optically pumped at 384.2 THz (780.2 nm) is studied. The absorption profiles of the pumped vapor are measured under various conditions and compared with theoretical predictions. A bright resonance resulting from the cascade of two cycling transitions is characterized both experimentally and theoretically. The measured frequency stability of a DFB laser frequency-locked to this line reaches a level of 2×10-10 for an averaging time of 100 s when compared to a similar laser locked to an acetylene line 相似文献
10.
B. Raveau C. Michel M. Hervieu D. Groult A. Maignan J. Provost 《Journal of Superconductivity and Novel Magnetism》1992,5(3):203-217
Different ways to optimizeT c 's and the magnetic properties of high-T c superconductive cuprates are described and discussed. Oxygen intercalation-desintercalation phenomena and cationic substitutions (M3+ for M2+ or vice versa) lead to a variation of the hole carrier density and can have a drastic influence onT c 's, as shown for bismuth, thallium, and lead-based cuprates, as well as for La2CuO4 and “123”-type superconductors. In the former, the role of hole reservoirs for the rock salt type layers is outlined. The modification of the hybridization of orbitals can also explain the variations ofT c 's observed in some systems like Y1?x Ca x Ba2Cu3?x :Fe x O7 in which the oxidation state of copper remains constant. A critical current density enhancement can be realized by irradiating high-T c materials by high-energy heavy ions because of the peculiar columnar structure of the heavy ion-induced tracks. The effects of such columnar defects, 70 Å in diameter, on flux pinning, magnetic relaxation, and location of the irreversibility line of bismuth-based 2212 crystals irradiated by 6-GeV Pb ions are reported. We observe a strong shift of the irreversibility line toward high fields and temperatures, indicating that pinning effects must be taken into account in the vortex lattice motion. Such induced changes are accompanied by a strong enhancement of the critical current density and a significant enlargement of the irreversibility region in theH,T plane. 相似文献