全文获取类型
收费全文 | 37829篇 |
免费 | 4736篇 |
国内免费 | 2535篇 |
专业分类
电工技术 | 5649篇 |
技术理论 | 1篇 |
综合类 | 2718篇 |
化学工业 | 4465篇 |
金属工艺 | 2810篇 |
机械仪表 | 3676篇 |
建筑科学 | 562篇 |
矿业工程 | 2026篇 |
能源动力 | 656篇 |
轻工业 | 1691篇 |
水利工程 | 190篇 |
石油天然气 | 1549篇 |
武器工业 | 451篇 |
无线电 | 6213篇 |
一般工业技术 | 6822篇 |
冶金工业 | 1626篇 |
原子能技术 | 1160篇 |
自动化技术 | 2835篇 |
出版年
2024年 | 202篇 |
2023年 | 849篇 |
2022年 | 1265篇 |
2021年 | 1483篇 |
2020年 | 1469篇 |
2019年 | 1289篇 |
2018年 | 1355篇 |
2017年 | 1633篇 |
2016年 | 1791篇 |
2015年 | 1797篇 |
2014年 | 2238篇 |
2013年 | 2413篇 |
2012年 | 2664篇 |
2011年 | 2880篇 |
2010年 | 2000篇 |
2009年 | 2115篇 |
2008年 | 1957篇 |
2007年 | 2329篇 |
2006年 | 2070篇 |
2005年 | 1724篇 |
2004年 | 1511篇 |
2003年 | 1342篇 |
2002年 | 1022篇 |
2001年 | 825篇 |
2000年 | 832篇 |
1999年 | 676篇 |
1998年 | 554篇 |
1997年 | 518篇 |
1996年 | 447篇 |
1995年 | 325篇 |
1994年 | 315篇 |
1993年 | 247篇 |
1992年 | 187篇 |
1991年 | 152篇 |
1990年 | 120篇 |
1989年 | 114篇 |
1988年 | 74篇 |
1987年 | 52篇 |
1986年 | 45篇 |
1985年 | 42篇 |
1984年 | 51篇 |
1983年 | 36篇 |
1982年 | 45篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1959年 | 5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.
高灵敏度热释电摄象管红外电视系统 总被引:1,自引:0,他引:1
针对热释电摄象管(PEV)在传统的对称斩波模式下存在的各种问题,设计了一种新的非对称斩波模式PEV红外电视系统.通过提高PEV摄象机的温度响应率R_i和采用高去噪声信号处理系统,大大改善了PEV红外成象系统的性能. 相似文献
62.
Backscattered electron (BSE) images of heat-cured concretes show alite grains surrounded by inner C-S-H gel of two distinct grey levels (referred to as two-tone inner C-S-H gel). The lighter rim forms at elevated temperature whereas the darker rim develops during subsequent exposure to moisture at 20 °C. This microstructural feature can potentially be used as an indicator to assess the curing history of a concrete. However, microstructural examinations of room-temperature concretes containing silica fume or which have been exposed to severe conditions (external sulfate, carbonation) also show distinct rims of two-tone inner C-S-H gel.The chemical compositions of the rims were determined by EDX microanalysis in the scanning electron microscope (SEM). Our results show that for heat-cured samples, the different grey levels of the two-tone inner C-S-H are caused by relative differences in microporosity and water content and not by ones in chemical composition. However, in silica-fume blended concrete, sulfate attacked or carbonated specimens the different grey levels of the two-tone inner C-S-H gel were associated with significant differences in chemical composition. This difference allows two-tone inner C-S-H gel arising from heat curing to be distinguished from that arising from these other causes. 相似文献
63.
红外热成象技术可以有效地用于股骨头坏死疾病的诊断和针刺治疗效果的评价,效果优于其它常规方法。 相似文献
64.
薄膜磁头磁轭制备工艺研究 总被引:1,自引:1,他引:0
本文重点讨论了用不同的工艺方法来制备薄膜磁头中的关键元件-磁轭。采用多次光刻的方法克服湿法工艺中磁性膜NiFe层的侧向钻蚀问题,从而实现对磁轭几何尺寸的精确控制,并对几种工艺方法的优缺点作了比较详细的分析。 相似文献
65.
反散射成像法是数字辐射成像的主要方法之一,介绍了获得反散射数字图像的实验装置,并着重分析了针对此装置获得的反散性图像的处理方法。 相似文献
66.
67.
68.
Nuclear magnetic resonance (n.m.r.) studies of 19F nuclei in a random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T2 components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T1 appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T1 were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals. 相似文献
69.
70.
Christine H. Setchell 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(3):175-182
Magnetic separation technology has a broad range of potential applications in both small and large scale biotechnology. This review considers a selection of magnetic techniques and their possible uses. 相似文献