全文获取类型
收费全文 | 299208篇 |
免费 | 5227篇 |
国内免费 | 997篇 |
专业分类
电工技术 | 5430篇 |
综合类 | 252篇 |
化学工业 | 46473篇 |
金属工艺 | 11429篇 |
机械仪表 | 10643篇 |
建筑科学 | 7113篇 |
矿业工程 | 903篇 |
能源动力 | 9248篇 |
轻工业 | 24818篇 |
水利工程 | 2421篇 |
石油天然气 | 3308篇 |
武器工业 | 17篇 |
无线电 | 41430篇 |
一般工业技术 | 59659篇 |
冶金工业 | 52026篇 |
原子能技术 | 5642篇 |
自动化技术 | 24620篇 |
出版年
2022年 | 2344篇 |
2021年 | 3677篇 |
2020年 | 2625篇 |
2019年 | 3086篇 |
2018年 | 4683篇 |
2017年 | 4690篇 |
2016年 | 5130篇 |
2015年 | 3473篇 |
2014年 | 5981篇 |
2013年 | 14376篇 |
2012年 | 9398篇 |
2011年 | 12299篇 |
2010年 | 9588篇 |
2009年 | 10643篇 |
2008年 | 11011篇 |
2007年 | 10254篇 |
2006年 | 9183篇 |
2005年 | 8056篇 |
2004年 | 7684篇 |
2003年 | 7910篇 |
2002年 | 7241篇 |
2001年 | 7511篇 |
2000年 | 6845篇 |
1999年 | 7198篇 |
1998年 | 17857篇 |
1997年 | 12281篇 |
1996年 | 9485篇 |
1995年 | 7090篇 |
1994年 | 6282篇 |
1993年 | 6180篇 |
1992年 | 4375篇 |
1991年 | 4259篇 |
1990年 | 4087篇 |
1989年 | 3851篇 |
1988年 | 3733篇 |
1987年 | 3171篇 |
1986年 | 3046篇 |
1985年 | 3304篇 |
1984年 | 3004篇 |
1983年 | 2878篇 |
1982年 | 2668篇 |
1981年 | 2572篇 |
1980年 | 2490篇 |
1979年 | 2328篇 |
1978年 | 2133篇 |
1977年 | 2638篇 |
1976年 | 3611篇 |
1975年 | 1782篇 |
1974年 | 1744篇 |
1973年 | 1682篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
The reduction of calcium sulfate to produce calcium sulfide is a part of the cyclic process for converting sulfur dioxide
to elemental sulfur that is described in Part I. The kinetics of the hydrogen reduction of nickel-catalyzed calcium-sulfate
pellets were investigated using a thermogravimetric analysis (TGA) technique at reaction temperatures between 1023 and 1088
K and hydrogen partial pressures between 12.9 and 86.1 kPa. The reactivity of nickel-catalyzed calcium-sulfate pellets was
demonstrated by the conversion of 70 pct fresh nickel-catalyzed calcium sulfate to calcium sulfide in 20 minutes at 1073 K
under a hydrogen partial pressure of 86.1 kPa. Furthermore, the reactivity remained relatively intact after ten cycles of
reactions and regenerations. This observed characteristic of the pellets is important because the solids must be reusable
for repeated cycles to avoid generating secondary pollutants. The nucleation and growth rate expression was found to be useful
in describing the kinetics of the reaction, which had an activation energy of about 167 kJ/mol (∼40 kcal/mol) in all reaction
cycles except for the first regenerated samples that were lower at 146 kJ/mol (35 kcal/mol). The reaction order with respect
to hydrogen partial pressure was 0.22 in all cycles with the exception of the first regenerated sample for which it was 0.37. 相似文献
152.
153.
Determination of the relative amounts of free and complexed manganese ions in aqueous solution by nuclear magnetic resonance. 总被引:1,自引:0,他引:1
The ratio of the transverse relaxation rate to the longitudinal relaxation rate of water protons (T1/T2) at 90 MHz can be used to determine the relative amounts of free Mn2+ ions (the hexaquo ion) and chelated manganese ions when both species are present in the same aqueous solution. This technique is demonstrated for simple aqueous solutions containing known concentrations of both the free Mn2+ ion and a manganese(III) porphyrin. The accuracy of the method is found to be +/- 7.3% for the solutions considered in this report. The determinations of the relative amounts of the free Mn2+ ion and the manganese(III) porphyrin by this T1/T2 method are shown to agree well with those determined by nuclear magnetic resonance dispersion profiles. The theoretical basis of this ratio method as well as the scope and limitations in its application to aqueous solutions containing both free Mn2+ ions and chelated manganese species other than manganese(III) porphyrins are also discussed. This work demonstrates a unique use of NMR as a means for the quantitative analysis of manganese in which the effects of the metal ion on the solvent, and not the metal itself, are observed. 相似文献
154.
Y. G. Wang H. Q. Ye K. H. Kuo X. J. Feng S. Z. Long G. L. Lao 《Journal of Materials Science》1991,26(23):6325-6330
The microstructures of unhydrated calcium aluminosulphate Ca4Al6SO16 and Ca3SrAl6SO16 have been studied by high-resolution electron microscopy (HREM). The results showed that twinning and twinned slabs could be introduced taking the [1 1 2] direction as the twin axis so that it seems to be coincident with the law of twinning formed in body-centred cubic structures. A previously reported superlattice with a repeat period twice that of the fundamental structure along the 〈1 1 0〉 direction has also been found in both matrix and twin variants. The close intergrowth of Ca3SrAl6SO16 and another phase, possibly Sr3Al2O6 existing as an inclusion between these two twin variants, was determined and clearly revealed by electron diffraction and HREM images. The coherent interphase boundaries and orientation relationship between them can also be deduced. 相似文献
155.
Gyeong-Ho Kim 《Computer Methods in Applied Mechanics and Engineering》2008,198(2):234-244
A continuum-based modeling of coupled electrostatics-structure interactions is presented for the frequency computations of MEMS devices. The present general formulation of electrostatics accounting for free space is validated first by specializing it to one-dimensional uniform motion of conducting surfaces and comparing the resulting electrostatics to conventional lumped models. The general coupled electrostatics-structure interactions are then applied for the prediction of resonant frequencies of MEMS devices due to bias-voltage changes and temperature variations. Comparisons of predicted resonant frequencies obtained by the present coupled electrostatics-structure interaction models with experimental results available in the literature demonstrate that the proposed continuum-based interaction modeling yields high-confidence predictions of resonant frequencies of MEMS devices. 相似文献
156.
Troya A. Maharatna K. Krstic M. Grass E. Jagdhold U. Kraemer R. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(2):672-686
In this paper, we propose low-power designs for the synchronizer and channel estimator units of the Inner Receiver in wireless local area network systems. The objective of the work is the optimization, with respect to power, area, and latency, of both the signal processing algorithms themselves and their implementation. Novel circuit design strategies have been employed to realize optimal hardware and power efficient architectures for the fast Fourier transform, arc tangent computation unit, numerically controlled oscillator, and the decimation filters. The use of multiple clock domains and clock gating reduces the power consumption further. These blocks have been integrated into an experimental digital baseband processor for the IEEE 802.11a standard implemented in the 0.25mum- 5-metal layer BiCMOS technology from Institute for High Performance Microelectronics. 相似文献
157.
Ploennigs J. Neugebauer M. Kabitzsch K. 《Industrial Informatics, IEEE Transactions on》2008,4(2):71-79
Network performance engineering can verify the design and dimensioning of large-scale control networks like CSMA-based building automation networks. It combines performance analysis with diagnosis methods to evaluate the network utilization and to detect design errors before installation and can therewith save the expenses of overdimensioning and redesign. This paper will develop a diagnosis model based on fault trees that is able to use the huge amount of performance analysis results to identify design errors and analyze their coherences. This enables not only a fast tracing back of fault causes and the derivation of solutions; it can also visualize the fault coherence to the user and help him to understand his design. Additional consulting tools implement best practice strategies, to support the user in parameterization. 相似文献
158.
本文详细探讨了使用无线网络分析器调试ZigBee协议系统的基本方法,从而便于更好地确保网络的可靠性. 相似文献
159.
A 0.9 V 92 dB Double-Sampled Switched-RC Delta-Sigma Audio ADC 总被引:1,自引:0,他引:1
Min Gyu Kim Gil-Cho Ahn Hanumolu P.K. Sang-Hyeon Lee Sang-Ho Kim Seung-Bin You Jae-Whui Kim Temes G.C. Un-Ku Moon 《Solid-State Circuits, IEEE Journal of》2008,43(5):1195-1206
A 0.9 V third-order double-sampled delta-sigma audio ADC is presented. A new method using a combination of a switched-RC technique and a floating switched-capacitor double-sampling configuration enabled low-voltage operation without clock boosting or bootstrapping. A three-level quantizer with simple dynamic element matching was used to improve linearity. The prototype IC implemented in a 0.13 CMOS process achieves 92 dB DR, 91 dB SNR and 89 dB SNDR in a 24 kHz audio signal bandwidth, while consuming 1.5 mW from a 0.9 V supply. The prototype operates from 0.65 V to 1.5 V supply with minimal performance degradation. 相似文献
160.
Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability. 相似文献