全文获取类型
收费全文 | 16017篇 |
免费 | 2038篇 |
国内免费 | 770篇 |
专业分类
电工技术 | 767篇 |
技术理论 | 2篇 |
综合类 | 1110篇 |
化学工业 | 2525篇 |
金属工艺 | 353篇 |
机械仪表 | 580篇 |
建筑科学 | 575篇 |
矿业工程 | 218篇 |
能源动力 | 630篇 |
轻工业 | 3467篇 |
水利工程 | 116篇 |
石油天然气 | 183篇 |
武器工业 | 119篇 |
无线电 | 2614篇 |
一般工业技术 | 2749篇 |
冶金工业 | 361篇 |
原子能技术 | 119篇 |
自动化技术 | 2337篇 |
出版年
2024年 | 143篇 |
2023年 | 587篇 |
2022年 | 611篇 |
2021年 | 823篇 |
2020年 | 793篇 |
2019年 | 705篇 |
2018年 | 642篇 |
2017年 | 715篇 |
2016年 | 683篇 |
2015年 | 690篇 |
2014年 | 1003篇 |
2013年 | 988篇 |
2012年 | 1008篇 |
2011年 | 1167篇 |
2010年 | 794篇 |
2009年 | 828篇 |
2008年 | 822篇 |
2007年 | 944篇 |
2006年 | 759篇 |
2005年 | 618篇 |
2004年 | 547篇 |
2003年 | 478篇 |
2002年 | 377篇 |
2001年 | 299篇 |
2000年 | 297篇 |
1999年 | 261篇 |
1998年 | 202篇 |
1997年 | 114篇 |
1996年 | 146篇 |
1995年 | 125篇 |
1994年 | 120篇 |
1993年 | 81篇 |
1992年 | 76篇 |
1991年 | 43篇 |
1990年 | 47篇 |
1989年 | 31篇 |
1988年 | 31篇 |
1987年 | 11篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 39篇 |
1983年 | 40篇 |
1982年 | 32篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1961年 | 5篇 |
1959年 | 4篇 |
1956年 | 3篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Vittorio Ghergia 《Sadhana》1992,17(3-4):411-430
Starting from the present state-of-the-art of discrete devices up to the realization of monolithic semiconductor integrated
prototypes, an overview of optoelectronic devices for telecommunications is given. Among discrete devices single frequency
lasers, tunable and multi-sectionDFB lasers andPIN andAPD photodiode detectors are analysed, including the use of new technologies in progress for a second generation of devices.
On the future perspective ofIBCN distribution networks, some economics of the hybrid and monolithic form of integration are attempted. Finally a short outline
of the most recent achievements in monolithic integration is presented, taking into particular consideration the activities
in this field byEEC ESPRIT andRACE programmes. 相似文献
62.
63.
P. Ravirajan S.A. Haque J.R. Durrant D.D.C. Bradley J. Nelson 《Advanced functional materials》2005,15(4):609-618
We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO2 and a conjugated polymer. Three different poly(2‐methoxy‐5‐(2′‐ethylhexoxy)‐1,4‐phenylenevinylene) (MEH‐PPV)‐based polymers and a fluorene–bithiophene copolymer are compared. We use photoluminescence quenching, time‐of‐flight mobility measurements, and optical spectroscopy to characterize the exciton‐transport, charge‐transport, and light‐harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic‐device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO2/polymer devices as a function of the fabrication route and device design. Including a dip‐coating step before spin‐coating the polymer leads to excellent polymer penetration into highly structured TiO2 networks, as was confirmed through transient optical measurements of the photoinduced charge‐transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip‐coated and PEDOT:PSS layers produced a short‐circuit current density of about 1 mA cm–2, a fill factor of 0.50, and an open‐circuit voltage of 0.86 V under simulated AM 1.5 illumination (100 mW cm–2, 1 sun). The corresponding power conversion efficiency under 1 sun was ≥ 0.4 %. 相似文献
64.
Magnetic and electric fields have been used to determine the splay (k11) and bend (k33) elastic constants in a series of polymer/monomer liquid crystal solutions using the well known Freedericksz transition technique. Measurements have been carried out as a function of concentration and temperature. The polymer used was a smectogenic polysiloxane side chain liquid crystal with both cyanobiphenyl and benzoate ester side groups. The monomeric solvent was the nematogen 4-n-pentyl-4′-cyanobiphenyl. All of the solutions studied were nematogenic up to a concentration of 40% w/w. It has been shown that k11, k33 and all decrease with increasing polymer concentration and that at high enough concentrations tends to become independent of temperature. The implications of these results are discussed in terms of the performance of the most common liquid crystal display, i.e. the twisted nematic device. 相似文献
65.
66.
67.
探讨了新型保健绿豆纤维功能饮料的生产工艺,对影响产品品质的几个主要因素进行了较为深入的探讨,提出了生产绿豆纤维功能饮料的最佳工艺条件。 相似文献
68.
在分析负离子净化空气的原理及环境状况与空气中负离子浓度的关系基础上,应用负离子功能粘胶长丝和涤纶短纤混纺纱针织物作为空调滤材,利用空调出风(冷风)使针织物滤材试样飘动,相互拍击摩擦,使空调出风中的氧气分子和水分发生有效电离,从而产生大量空气负离子。实验结果表明,负离子功能粘胶长丝和涤纶短纤混纺纱针织物都有释放空气负离子的功能;而且在同规格纱线的平针组织、双罗纹组织、蜂巢组织和畦编组织针织物中,畦编组织针织物释放的负离子量最大;空气相对湿度对功能材料释放负离子数量有明显影响,当相对湿度在65%~70%时释放的负离子量趋于最大。 相似文献
69.
Gradient-corrected density functional theory was used to investigate the adsorption of H2S on Pd(1 1 1) surface. Molecular adsorption was found to be stable with H2S binding preferentially at top sites. In addition, the adsorption of other S moieties (SH and S) was investigated. SH and S were found to be preferentially bind at the bridge and fcc sites, respectively. The reaction pathways and energy profiles for H2S decomposition giving rise to adsorbed S and H were determined. Both H2S(ad) → SH(ad) + H(ad) and SH(ad) → S(ad) + H(ad) reactions were found to have low barriers and high exothermicities. This reveals that the decomposition of H2S on Pd(1 1 1) surface is a facile process. 相似文献
70.
William Kent 《Computer Standards & Interfaces》1991,13(1-3):201-206
OSQL is the object-oriented database language developed for the Iris object-oriented database management system at Hewlett-Packard Laboratories. Its three fundamental constructs are objects, types, and functions. This paper provides an overview of the underlying concepts and some important features of OSQL. 相似文献