全文获取类型
收费全文 | 61890篇 |
免费 | 4791篇 |
国内免费 | 2727篇 |
专业分类
电工技术 | 3278篇 |
技术理论 | 6篇 |
综合类 | 4098篇 |
化学工业 | 10472篇 |
金属工艺 | 3859篇 |
机械仪表 | 3804篇 |
建筑科学 | 4664篇 |
矿业工程 | 2196篇 |
能源动力 | 1954篇 |
轻工业 | 3495篇 |
水利工程 | 1067篇 |
石油天然气 | 4537篇 |
武器工业 | 464篇 |
无线电 | 6455篇 |
一般工业技术 | 7233篇 |
冶金工业 | 3433篇 |
原子能技术 | 720篇 |
自动化技术 | 7673篇 |
出版年
2024年 | 248篇 |
2023年 | 989篇 |
2022年 | 1706篇 |
2021年 | 2434篇 |
2020年 | 1828篇 |
2019年 | 1648篇 |
2018年 | 1836篇 |
2017年 | 2033篇 |
2016年 | 1819篇 |
2015年 | 2343篇 |
2014年 | 2987篇 |
2013年 | 3467篇 |
2012年 | 3653篇 |
2011年 | 4013篇 |
2010年 | 3675篇 |
2009年 | 3294篇 |
2008年 | 3260篇 |
2007年 | 3209篇 |
2006年 | 3190篇 |
2005年 | 2766篇 |
2004年 | 2042篇 |
2003年 | 2145篇 |
2002年 | 2503篇 |
2001年 | 2102篇 |
2000年 | 1631篇 |
1999年 | 1716篇 |
1998年 | 1252篇 |
1997年 | 1067篇 |
1996年 | 1107篇 |
1995年 | 848篇 |
1994年 | 633篇 |
1993年 | 470篇 |
1992年 | 365篇 |
1991年 | 274篇 |
1990年 | 206篇 |
1989年 | 166篇 |
1988年 | 153篇 |
1987年 | 88篇 |
1986年 | 69篇 |
1985年 | 37篇 |
1984年 | 38篇 |
1983年 | 27篇 |
1982年 | 25篇 |
1981年 | 14篇 |
1980年 | 22篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
鉴于目前电信的声讯系统中竞争的激烈性,它们急需要提高自身的系统集成度及高可用性,保证以最小的投资获得最丰厚的回报,由此出现了CompactPCI的系列产品,它不仅可以大大提高系统的集成度,同时对于系统的高可用性也进行了充分的考虑。本文将就声讯系统中基于CompactPCI的应用进行分析。 相似文献
52.
53.
The change of foot length and width with age has been reported in a few anthropometric studies in the literature. However, the relationship with body height rarely is reported, and the dynamic effect of weightbearing on foot size has not been documented. In this series, 2829 children 3 to 18 years of age of equal gender distribution were included in the study. The foot length and width on weightbearing and nonweightbearing were measured with a special precision electronic caliper. The foot length and width were found to increase linearly from the age of 3 years until 12 years in girls and 15 years in boys. This was followed by a phase during which the increase plateaued. The foot length and width increased significantly on weightbearing at all ages in both genders with a mean of 2.1 to 4.4 mm or 3.1% to 4.8%, respectively. The foot length and width also were found to correlate significantly with the body height in both genders, with a correlation coefficient of 0.96 to 0.98. No significant differences were found between the sizes of the dominant and nondominant foot in either gender. 相似文献
54.
介绍了靶场测量雷达新一代引导接收机。它是一种模拟/数字混合型锁相接收机,可对USB(UnifyS-Band)信号进行谱线识别和谱线跟踪,其捕捉范围和跟踪范围可达±180kHz。它能提供目标角误差信号、目标强度信息和目标速度信息。 相似文献
55.
岩样自然伽玛能谱的数据库管理系统 总被引:3,自引:0,他引:3
本文阐述了岩样自然伽玛能谱数据库管理系统的功能、结构、特点以及它在研究自然伽玛能谱与岩性参数间关系中的应用,为自然伽玛能谱测井的资料解释奠定了理论基础。 相似文献
56.
57.
58.
PURPOSE: Nitric oxide (NO) is generated in mammalian tissue by the conversion of L-arginine to L-citrulline. The reaction is catalyzed by nitric oxide synthase (NOS). NO has been suggested to have a dual role in tumor biology with both antitumor and tumor promoter activity. Furthermore, it has been proposed that NO contributes to interleukin-2-induced antitumor activity. Since interleukin-2 is used in the treatment of renal cell carcinoma (RCC) it was of interest to study the NOS activity in the human kidney and in RCC and its correlation to tumor grade. Furthermore, the effect of cytokine treatment on NOS activity and the effect of NO donor application was studied in cultured cells. MATERIALS AND METHODS: The effect of cytokine treatment on NOS activity and the effect of NO donor application on cell proliferation was studied in cultured human proximal tubular cells and in RCC cell lines HN4 and HN51. NOS activity was measured by the L-arginine to L-citrulline conversion assay. RESULTS: Calcium-dependent NOS activity was found in all non-malignant kidney tissues (486+/-63 pmol. min(-1) g(-1) tissue). The activity was significantly lower in RCC (24+/-6 pmol. min(-1) g(-1) tissue) and correlated with tumor grade; thus high grade tumors showed lower activity than low grade tumors. Calcium-independent NOS activity was not detected in non-malignant kidney tissue or in RCC tissue. In cultured proximal tubular cells and RCC cell lines HN4 and HN51, cytokine treatment induced a marked increase in NOS activity and NO exerted cytostatic effects on these cell lines. Conclusions: The NOS activity was higher in non-malignant kidney tissue than in RCC tissue and was inversely correlated with tumor grade. Furthermore, cytokine treatment induced a marked increase in NOS activity and NO exerted cytostatic effects on cultured proximal tubular cells and RCC cell lines. 相似文献
59.
Chemical reactions between aluminum and fly ash during synthesis and reheating of Al-fly ash composite 总被引:5,自引:0,他引:5
Thermodynamic analysis indicates that there is the possibility of chemical reactions between aluminum melt and cenosphere
fly ash particles. These particles contain alumina, silica, and iron oxide, which, during solidification processing of aluminum-fly
ash composites or during holding of such composites at temperatures above the melting temperature of aluminum, are likely
to undergo chemical reduction. These chemical reactions between the fly ash and molten aluminum have been studied by metallographic
examination, differential thermal analysis (DTA), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX)
and X-ray analysis after holding the aluminum-fly ash composites for different periods above the liquidus temperature. The
experiments indicate that there is progressive reduction of silica and mullite in the fly ash, and formation of alumina with
holding time of composites at a temperature of 850 °C. The walls of the cenosphere fly ash particles progressively disintegrate
into discrete particles as the reaction progresses. The rate of chemical reaction was high at the start of holding the composite
at a temperature of 850 °C, and then the rate significantly decreased with time. The reaction was almost complete after 10
hours. 相似文献
60.
Li Xi Zuoyan Peng Wei Fan Kui Guo Gu Jianmin Muyu Zhao Wu Guoqiang 《Materials Science and Engineering: B》1996,40(2-3):147-152
SrMgxTi1 - xO3 nanocrystals (x = 0.1–0.6) were synthesized by the stearic acid gel method. Powder samples were characterized by X-ray diffraction and X-ray photoelectron (XP) spectroscopy. The results showed that the lattice parameter a and the O 1s XP spectrum changed not only with the Mg content x but also with the grain size d of the samples. The conductivity of a thick film specimen fabricated on an aluminium oxide wafer was investigated in a nitrogen—oxygen atmosphere. 相似文献