全文获取类型
收费全文 | 357555篇 |
免费 | 28006篇 |
国内免费 | 15705篇 |
专业分类
电工技术 | 20938篇 |
技术理论 | 45篇 |
综合类 | 25392篇 |
化学工业 | 59745篇 |
金属工艺 | 20805篇 |
机械仪表 | 22483篇 |
建筑科学 | 27648篇 |
矿业工程 | 11702篇 |
能源动力 | 9700篇 |
轻工业 | 24017篇 |
水利工程 | 6759篇 |
石油天然气 | 23456篇 |
武器工业 | 2796篇 |
无线电 | 38805篇 |
一般工业技术 | 39343篇 |
冶金工业 | 18540篇 |
原子能技术 | 3624篇 |
自动化技术 | 45468篇 |
出版年
2024年 | 1457篇 |
2023年 | 5573篇 |
2022年 | 9878篇 |
2021年 | 13839篇 |
2020年 | 10455篇 |
2019年 | 8550篇 |
2018年 | 9861篇 |
2017年 | 11074篇 |
2016年 | 10142篇 |
2015年 | 13887篇 |
2014年 | 17470篇 |
2013年 | 20925篇 |
2012年 | 22730篇 |
2011年 | 25199篇 |
2010年 | 22263篇 |
2009年 | 21077篇 |
2008年 | 20674篇 |
2007年 | 19707篇 |
2006年 | 20075篇 |
2005年 | 17672篇 |
2004年 | 11967篇 |
2003年 | 10698篇 |
2002年 | 9899篇 |
2001年 | 8812篇 |
2000年 | 8767篇 |
1999年 | 9407篇 |
1998年 | 7186篇 |
1997年 | 6141篇 |
1996年 | 5814篇 |
1995年 | 4792篇 |
1994年 | 3893篇 |
1993年 | 2622篇 |
1992年 | 2075篇 |
1991年 | 1573篇 |
1990年 | 1234篇 |
1989年 | 997篇 |
1988年 | 830篇 |
1987年 | 524篇 |
1986年 | 410篇 |
1985年 | 258篇 |
1984年 | 206篇 |
1983年 | 164篇 |
1982年 | 128篇 |
1981年 | 76篇 |
1980年 | 96篇 |
1979年 | 43篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 28篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
食品安全.在2005年中仍然纷纷扰扰:食品与家庭每个成员的健康息息相关,而维护全家人的健康,则是女主人义不容辞的责任。我们一起来听听.于她们而言.2005年最关心的食品安全问题是什么?[编者按] 相似文献
952.
The performance of second-order statistics (SOS)-based semiblind channel estimation in long-code direct-sequence code-division multiple-access systems is analyzed. The covariance matrix of second-order statistics estimates is obtained in the large system limit and is used to analyze the large-sample performance of two SOS-based semiblind channel estimation algorithms. A notion of blind estimation efficiency is also defined and is examined via simulation results. 相似文献
953.
InAs channel field-effect transistors of 1-μm gate length were grown by molecular beam epitaxy and observed to operate at channel electric fields (20 kV/cm) higher than previously demonstrated and several times greater than the threshold for impact ionization in bulk InAs. Voltage gains on the order of 10 were observed with transconductances as high as 414 mS/mm and output conductances as low as 33 mS/mm. These voltage gains are comparable to those of GaAs-based devices and are the highest observed for InAs channel devices. The results demonstrate the potential for practical room-temperature operation of InAs FETs 相似文献
954.
Ilexonin A, a new drug in improving the blood circulation and microcirculation, is extracted from Ilicis pubescentis. The preventive and therapeutic effects of Ilexonin A on chemical salpingitis induced tubal obstruction (CSTO) with morphological and hemorheological change in rats was studied. Results showed that Ilexonin A was effective in treating (CSTO by oppositing the degeneration and necrosis of epithelium, inhibiting the hyperplasia of connective tissue, and reducing the infiltration of inflammatory cells. The improvement of morphology was more significant in treated groups than that in controls (P < 0.05-0.01). The indices concerning model rat's hemorheology were also analysed between treated groups and controls. It indicated that Ilexonin A could improve the viscosity of blood and aggregation of red blood cells. It is suggested Ilexonin A could promote the absorption of inflammatory substances as a result of improving hemorheology. 相似文献
955.
新型氮系阻燃剂——三嗪衍生物的合成 总被引:6,自引:0,他引:6
合成了两种三嗪衍生物,并将其与多聚磷酸铵复配用于聚丙烯阻燃试验,结果表明,这两种阻燃剂具有良好的阻燃作用。 相似文献
956.
957.
金属表面柴油机油沉积物的反射红外光谱法研究 总被引:1,自引:1,他引:0
利用镜反射红外光谱法研究了CC级柴油机油中添加剂对成漆板板面漆膜组成的影响:考察了成漆板漆膜组成与Cat.1H2活塞环台漆膜组成的相关性。试验结果对柴油机油的研制和应用有一定指导作用。 相似文献
958.
Hsueh-Jyh Li Yung-Deh Wang Long-Huai Wang 《Antennas and Propagation, IEEE Transactions on》1996,44(4):444-452
In this paper, how the statistical properties of the matching scores are affected by the carrier frequency, the aspect variation, the range resolution, and the target complexity are studied. The statistical parameters (mean and standard deviation) of the matching scores among range profiles of independent objects are derived, and their values are used as references to determine the threshold values for target identification. It is found that the range profile obtained at a certain carrier frequency can also be used as the feature vector for radars operated at shifted frequencies if the range resolution is fine enough or the target is simple. It is also found that a radar with higher range resolution can tolerate more aspect variation, yielding a significant advantage in saving memory space for establishing the data base. The results obtained can have several applications such as target identification, data association in multiple target tracking, and target direction determination when widely-spaced high-resolution radars are employed 相似文献
959.
两种新型热释光剂量计 总被引:1,自引:0,他引:1
报告两种可报告於年代测定实验室的热释光剂量计,它们是TLD-QF301和TLD-FF301。给出它们对各类辐射响应的特征,分别以实验数据图表明了各自的适用范围。 相似文献
960.
本文阐述了氧化锆增韧陶瓷(ZTC)的相变增韧机理,并探讨了热处理工艺对ZTC的相变及显微组织的影响规律。 相似文献