全文获取类型
收费全文 | 132064篇 |
免费 | 12709篇 |
国内免费 | 7557篇 |
专业分类
电工技术 | 10071篇 |
技术理论 | 6篇 |
综合类 | 10253篇 |
化学工业 | 19613篇 |
金属工艺 | 8163篇 |
机械仪表 | 8985篇 |
建筑科学 | 9869篇 |
矿业工程 | 3509篇 |
能源动力 | 4001篇 |
轻工业 | 9268篇 |
水利工程 | 3048篇 |
石油天然气 | 6024篇 |
武器工业 | 1496篇 |
无线电 | 16291篇 |
一般工业技术 | 15151篇 |
冶金工业 | 5802篇 |
原子能技术 | 1673篇 |
自动化技术 | 19107篇 |
出版年
2024年 | 502篇 |
2023年 | 1722篇 |
2022年 | 3509篇 |
2021年 | 5037篇 |
2020年 | 3716篇 |
2019年 | 3097篇 |
2018年 | 3413篇 |
2017年 | 4032篇 |
2016年 | 3930篇 |
2015年 | 5397篇 |
2014年 | 6809篇 |
2013年 | 8085篇 |
2012年 | 9535篇 |
2011年 | 10202篇 |
2010年 | 9513篇 |
2009年 | 8980篇 |
2008年 | 8888篇 |
2007年 | 8304篇 |
2006年 | 7882篇 |
2005年 | 6593篇 |
2004年 | 5012篇 |
2003年 | 4700篇 |
2002年 | 5092篇 |
2001年 | 4345篇 |
2000年 | 3038篇 |
1999年 | 2397篇 |
1998年 | 1636篇 |
1997年 | 1395篇 |
1996年 | 1204篇 |
1995年 | 1015篇 |
1994年 | 834篇 |
1993年 | 611篇 |
1992年 | 439篇 |
1991年 | 350篇 |
1990年 | 262篇 |
1989年 | 217篇 |
1988年 | 170篇 |
1987年 | 114篇 |
1986年 | 83篇 |
1985年 | 52篇 |
1984年 | 44篇 |
1983年 | 32篇 |
1982年 | 32篇 |
1981年 | 31篇 |
1980年 | 24篇 |
1979年 | 12篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1959年 | 9篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Jin‐Hong Kim 《Polymer Engineering and Science》2008,48(1):97-101
Polyetherimide (PEI) substrate for next‐generation high density optical data storage is fabricated and characterized. Cover‐layer incident or first‐surface recording configurations do not require optical properties of the substrate, which are the prerequisite conditions for the conventional material of polycarbonate (PC). Instead of the optical properties, good mechanical properties with a sufficient transcribability are required. Even though PEI has higher glass transition temperature than that of PC, a microscopic transcribability of PEI is comparable with PC by laminating a thermal insulation layer on the backside of a stamper to retard the heat flow. A macroscopic warpage of PEI substrate is smaller than that of PC substrates, which reduces tilt and servo burden. The lowest critical speed coupled with the flutter of PEI substrate is larger than that of PC substrate because of the mechanical properties of PEI. POLYM. ENG. SCI., 48:97–101, 2008. © 2007 Society of Plastics Engineers 相似文献
82.
介绍了一种带USB接口的光的155Mb/s码型发生器。伪随机码和其他格式的码型由PC产生通过USB接口进入双口RAM,再经串并变换后由光发射模块发射。该系统可方便地设定各种格式的码型,并同时具备光接口和电接口,可广泛应用于光通信各种实验中,具有重要的实用价值。 相似文献
83.
Synthesis of 21R AlN polytypoids was investigated using Al and ultrafine SiO2 powder in a flowing nitrogen atmosphere by means of thermal gravity (TG), differential scanning calorimeter (DSC), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) linked with energy dispersive spectrometer (EDS). The results showed that the formation mechanism of AlN polytypoids was different from that in reaction sintering process using Si3N4, AlN, Al2O3 and other sintering additive as raw materials. It was suggested that firstly Al reduce SiO2 into Si and is also nitrided into AlN, then AlN, Al2O3 and SiO2 dissolve into silicon liquid until the AlN polytypoids precipitate in saturated liquid in a flowing nitrogen atmosphere at lower than 1700 °C. 相似文献
84.
An experimental investigation was carried out to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb2S3). A scale dynamometer was used for friction tests and particular emphases were given to the effect of applied pressure, sliding speed, and temperature on the coefficient of friction according to the relative amounts of the two solid lubricants. Results showed that the brake linings with both solid lubricants exhibited better friction stability and less speed sensitivity than the friction materials containing a single solid lubricant. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high-temperature friction test. 相似文献
85.
Yawei Li Shaobai Sang Shengli Jin Chunyan Yang Nan Li 《Journal of Materials Science》2006,41(18):5815-5819
Synthesis of Mg-α-Sialon has been investigated by the mixture of silicon, aluminum and magnesia powders in a flowing nitrogen atmosphere in the range of 1300–1600 °C, when Mg-α-Sialon is designed with a chemical formulation of Mg
x
Si12−3x
Al3x
O
x
N16−x
in present work. The results showed that Mg-α-sialon initially occurred at 1400 °C and basically increased with elevated temperatures. For the samples of x = 0.6, 0.8 and 1.0 the products mainly consisted of Mg-α-Sialon with small amounts of Si, AlN and 21R AlN-polytypoid phases at 1600° C. However, in final products of x = 1.2, 1.4 and 1.6 only a little of Mg-α-Sialon formed and a great amount of Si remained in these samples at all the fired temperatures. Fortunately, the content of Mg-α-Sialon in these samples were obviously increased by adding a small amount of α-Si3N4 as seeds before nitridation. 相似文献
86.
Guo Haitao Qiao Weihong Ba Yan Li Zongshi Jin Kun Peng Qinji 《Petroleum Science and Technology》2006,24(1):51-60
The GC/MS and NMR analysis of the reaction products of naphthalene with 1-bromohexane were reported. The products obtained were suggested to have six isomers of linear hexylnaphthalene and the structure of each isomer was determined by GC/MS and NMR spectra. For the first time, the unique chemical shift data were obtained. The content of each isomer calculated by 1H NMR and 13C NMR spectra was consistent with that by GC/MS spectra, which confirmed the accuracy of NMR data. 相似文献
87.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献
88.
89.
微地震相分析在河流储层精细描述中的应用 总被引:1,自引:1,他引:0
传统地震相分析满足不了目前油田勘探开发的需要。神经网络微地震相分析将神经网络应用于高质量三维地震数据体中,可对单一反射同相轴进行波形信号分析和训练,建立模型地震道,并对实际地震道分类,进而得到在平面和剖面上精度较高的微地震相分布。采用该方法并结合测井资料,在研究区块中建立的微地震相分布图能够清晰地表现出该区块的沉积微相特征,且较好地解释了工区内2口井的产能差异,表明神经网络微地震相分析是可靠和有效的。 相似文献
90.
马勇 《金属材料与冶金工程》2003,31(1):21-24
通过煤种,入窑球冷态强度和还原过程强度,以及钛精矿与煤灰混合物的软化温度等分析探讨了钛精矿预热球团回转窑直接还原产生结圈的可能性,获得了可以避免结圈的结论。 相似文献