全文获取类型
收费全文 | 261299篇 |
免费 | 4005篇 |
国内免费 | 1058篇 |
专业分类
电工技术 | 4458篇 |
综合类 | 207篇 |
化学工业 | 39198篇 |
金属工艺 | 8422篇 |
机械仪表 | 7436篇 |
建筑科学 | 7208篇 |
矿业工程 | 588篇 |
能源动力 | 7515篇 |
轻工业 | 29227篇 |
水利工程 | 2217篇 |
石油天然气 | 1954篇 |
武器工业 | 5篇 |
无线电 | 33973篇 |
一般工业技术 | 47711篇 |
冶金工业 | 48111篇 |
原子能技术 | 3455篇 |
自动化技术 | 24677篇 |
出版年
2021年 | 1933篇 |
2020年 | 1447篇 |
2019年 | 1773篇 |
2018年 | 2718篇 |
2017年 | 2731篇 |
2016年 | 3044篇 |
2015年 | 2319篇 |
2014年 | 3887篇 |
2013年 | 12612篇 |
2012年 | 7094篇 |
2011年 | 10099篇 |
2010年 | 7786篇 |
2009年 | 8757篇 |
2008年 | 9317篇 |
2007年 | 9292篇 |
2006年 | 8632篇 |
2005年 | 7768篇 |
2004年 | 7486篇 |
2003年 | 7310篇 |
2002年 | 6823篇 |
2001年 | 7178篇 |
2000年 | 6477篇 |
1999年 | 6977篇 |
1998年 | 16571篇 |
1997年 | 11531篇 |
1996年 | 8737篇 |
1995年 | 6677篇 |
1994年 | 5848篇 |
1993年 | 5691篇 |
1992年 | 4106篇 |
1991年 | 3872篇 |
1990年 | 3648篇 |
1989年 | 3495篇 |
1988年 | 3367篇 |
1987年 | 2695篇 |
1986年 | 2596篇 |
1985年 | 3282篇 |
1984年 | 2934篇 |
1983年 | 2665篇 |
1982年 | 2444篇 |
1981年 | 2475篇 |
1980年 | 2280篇 |
1979年 | 2137篇 |
1978年 | 1959篇 |
1977年 | 2270篇 |
1976年 | 2815篇 |
1975年 | 1665篇 |
1974年 | 1569篇 |
1973年 | 1623篇 |
1972年 | 1198篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Mark T. Muldoon Dale V. Onisk Michael C. Brown & James W. Stave 《International Journal of Food Science & Technology》2004,39(8):851-861
Bovine spongiform encephalopathy (BSE), or ‘mad cow disease’, is one of several transmissable spongiform encephalopathies (TSEs) known to affect certain mammals and is spread through the ingestion of infected animal tissue. It is believed that the inadvertent contamination of meat and bone meal (MBM) with infected animal tissue and the subsequent use of this material as a feed supplement contributed to the spread of the disease in cattle. As a result, the use of processed animal proteins (PAPs) in animal feeds is regulated in many parts of the world. Although feed testing is the only definitive means to certify compliance, regulatory compliance often relies solely on paper certification. Recently, rapid methods have become available that can be used by regulators to determine compliance during routine inspections. We describe a rapid, immunochromatographic strip test that can detect 0.1% MBM in animal feed. The test takes 15 min to perform and large numbers of samples can be screened for PAPs simultaneously. 相似文献
992.
993.
994.
995.
We investigate a novel technique to generate the transmission signal in digital-microwave link applications. This technique is based on a photonic device that achieves both electrical modulation (QAM, PSK, ASK) and harmonic upconversion of the microwave carrier. Simulation results are provided for a seventh-harmonic 38.5-GHz transmission of a 2.5-Gbps signal through a 1-km fiber span. The impact of fiber chromatic-dispersion on the link bandwidth is also analyzed. 相似文献
996.
Volmer C. Weber J. Stephan R. Blau K. Hein M.A. 《Antennas and Propagation, IEEE Transactions on》2008,56(2):360-370
Placing the radiators of antenna arrays closer than aggravates the problem of power mismatch. Based on efficiency considerations, a general analysis of this effect is presented, putting forward a simple tool to quantify, compare, and optimize the performance of antenna arrays. This analysis is not restricted with respect to the number of radiators or the degree of compactness. In order to improve power matching, a systematic approach for the design of lossless decoupling and matching networks based on 180 directional couplers is suggested for up to eight radiators. Implications of network losses, which have not yet received appropriate attention by researchers in the past, will be analyzed and discussed by means of a manufactured three-element prototype array. 相似文献
997.
The present research was focused on the development of a new glass to produce glass–alumina FGMs. The glass formulation, belonging to the CaO–ZrO2–SiO2 system, was doped with cobalt, by adding a small molar percentage (about 0.1 mol%) of CoO, in order to obtain a blue glass, which could be useful to appreciate the final compositional gradient. The glass was accurately characterized, evaluating its thermal behaviour, its mechanical properties, and its attitude to crystallize during a thermal treatment. Subsequently, the glass was used to produce glass–alumina FGMs via percolation and the so obtained specimens were analysed in order to evaluate the effect of the glass infiltration. The possible development of new crystal phases, in particular, was tested via micro X-ray diffraction and the elastic properties gradient associated with the compositional gradient was measured via depth-sensing Vickers microindentation. 相似文献
998.
Solid solutions of the GdFeO3–GdInO3 system were prepared at 1550 °C by ceramic powder processing. The formulated composition was Gd(Fe1−xInx)O3 (GFI) with the indium contents at x = 0, 0.25, 0.5, 0.75, and 1.0. A stable phase of Gd(Fe1/3In2/3)O3 in our system was identified by X-ray diffraction and phase composition analysis. Multi-phase morphologies were observed for GFI bulks with x = 0.5 and 0.75. Dielectric and electrical properties of the GFI bulks were investigated. The addition of 25% In3+ in GdFeO3 had an obvious enhancement in polarization and led to an elevated resonance frequency. Dielectric properties of GFI bulks except GdInO3 were strongly dependent upon the test frequency, which corresponded to the response of polarization mechanism. GdInO3 displayed as a stable dielectric, which was frequency- and temperature-insensitive. GdInO3 was thermally activated and became leaky until above 600 °C. 相似文献
999.
Periklis E. Ergatis Panagiotis G. Massouros Georgia C. Athanasouli George P. Massouros 《国际能源研究杂志》2003,27(9):795-811
A time‐dependent coefficient of heat transfer is proposed for the computation of thermal power required, so that a room temperature reaches a desired value within a given time. A mathematical formulation of the room heating transient phenomenon is constructed in a dimensionless form. Using an integral approximate solution an analytical expression for this coefficient is provided and it is verified by diagrams adopted by DIN 4701. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
1000.
Material removal and surface damage of Ti3SiC2 ceramic during electrical discharge machining (EDM) were investigated. Melting and decomposition were found to be the main material removal mechanisms during the machining process. Material removal rate was enhanced acceleratively with increasing discharge current, ie, working voltage, ui, but increased deceleratively with pulse duration, te. Microcracks in the surface and loose grains in the subsurface resulted from thermal shock were confirmed, and the surface damage in Ti3SiC2 ceramic led to a degradation of both strength and reliability. 相似文献