全文获取类型
收费全文 | 25084篇 |
免费 | 2847篇 |
国内免费 | 1327篇 |
专业分类
电工技术 | 1520篇 |
综合类 | 2434篇 |
化学工业 | 3115篇 |
金属工艺 | 795篇 |
机械仪表 | 1196篇 |
建筑科学 | 2995篇 |
矿业工程 | 1364篇 |
能源动力 | 847篇 |
轻工业 | 1017篇 |
水利工程 | 1457篇 |
石油天然气 | 1592篇 |
武器工业 | 372篇 |
无线电 | 2406篇 |
一般工业技术 | 1638篇 |
冶金工业 | 1784篇 |
原子能技术 | 259篇 |
自动化技术 | 4467篇 |
出版年
2024年 | 72篇 |
2023年 | 287篇 |
2022年 | 524篇 |
2021年 | 651篇 |
2020年 | 703篇 |
2019年 | 672篇 |
2018年 | 623篇 |
2017年 | 851篇 |
2016年 | 1022篇 |
2015年 | 1047篇 |
2014年 | 1506篇 |
2013年 | 1373篇 |
2012年 | 1614篇 |
2011年 | 1837篇 |
2010年 | 1350篇 |
2009年 | 1431篇 |
2008年 | 1353篇 |
2007年 | 1594篇 |
2006年 | 1521篇 |
2005年 | 1238篇 |
2004年 | 1054篇 |
2003年 | 996篇 |
2002年 | 840篇 |
2001年 | 763篇 |
2000年 | 579篇 |
1999年 | 454篇 |
1998年 | 338篇 |
1997年 | 255篇 |
1996年 | 218篇 |
1995年 | 224篇 |
1994年 | 186篇 |
1993年 | 122篇 |
1992年 | 107篇 |
1991年 | 84篇 |
1990年 | 95篇 |
1989年 | 52篇 |
1988年 | 51篇 |
1987年 | 45篇 |
1986年 | 35篇 |
1985年 | 140篇 |
1984年 | 240篇 |
1983年 | 283篇 |
1982年 | 202篇 |
1981年 | 313篇 |
1980年 | 117篇 |
1979年 | 41篇 |
1978年 | 39篇 |
1977年 | 13篇 |
1975年 | 22篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
93.
对液压胀形轧辊(即国外的VC轧辊)辊套热装后的弹性变形进行了有限元分析,给出了确定油槽最小深度的计算公式。本文的有限元计算结果与实验结果吻合,某些结论可为液压胀形轧辊的结构设计提供理论依据。 相似文献
94.
A roll-coating experimental system is used to study the effect of pre-wetting on dynamic contact angles, the interfacial displacement depth, and the associated phenomenon of air entrainment. The system consists of a roll, which is horizontally rotating in a liquid pool. The dynamic contact angle is recorded by a macrophotography system. The test liquids are glycerol solutions with viscosities in the range 104 < μ < 748 mPa · s. The value of (μV/ρg)0.5 is taken as the characteristic length to be used in the dimensionless relationships which correlate experimental measurements. The effect of base layer entry angle into the liquid pool on the dynamic contact angles and other flow parameters is studied. Comparison is made with measurements in dry tape-coating and other pre-wet roll–coating systems. 相似文献
95.
Electric dipoles radiate an electromagnetic field into their surroundings. The electric and magnetic fields from a point source or from linear dipoles have components parallel to a spherical surface but also a radial component. In most investigations on radiated fields, only the part of the electric field that is parallel to a spherical surface is taken into account. The argument is that only that component contributes to the radiated energy. Here we show that the phase front in the lower half space is not a spherical surface and hence, the radial components contribute to radiated energy. We show differences in radiation patterns for point electric dipoles and linear dipoles, either modeled as perfectly conducting wires or as resistively loaded wires. Our primary interest lies with improving image resolution through processing of Ground-Penetrating Radar data. Here the emphasis lies with understanding the radiation characteristics of linear dipoles that can be incorporated with image processing algorithms. The model uses a thin-wire approximation for the transmitter antenna. The solution to the discrete system of equations is solved, incorporating interaction between the interface, using a CGFFT scheme including symmetrization and a newly developed preconditioning operator. We look at the electric and magnetic fields as well as the time-averaged Poynting vector radiation patterns in the E-plane and H-plane of the transmitting antenna. The results show that the radial component of the radiated electric and magnetic field is not negligible, even at distances more than seven wavelengths away from the antennas. 相似文献
96.
97.
本文着重介绍武汉钢铁公司近年来研制开发的第二代高强度低合金钢—高强韧性WDL系列钢的综合性能及应用情况。该钢具有优异的焊接性能和低温韧性,板厚≤50mm钢板焊前不预热或稍加预热而不产生焊接裂纹,是制造大型压力容器(特别是低温和常温球罐)、水电站压力钢管和水轮机蜗壳、高寒地区使用的大型工程机械、大跨度桥梁及海上采油平台等装备的理想用材。 相似文献
98.
首先对OFDM的发展以及应用做了简要的介绍,然后讨论了当前OFDM研究过程中的两个关键技术问题,最后展望了OFDM的未来发展。 相似文献
99.
节流式差压流量计的发展和现状 总被引:2,自引:0,他引:2
文章介绍节流式差压流量计的特点及标准化进程,煤气流量测量中存在的难点以及正在试图解决的途径。 相似文献
100.
Titipong Issariyakul Mangesh G. KulkarniAjay K. Dalai Narendra N. Bakhshi 《Fuel Processing Technology》2007
Transesterification of waste fryer grease (WFG) containing 5–6 wt.% free fatty acid (FFA) was carried out with methanol, ethanol, and mixtures of methanol/ethanol maintaining the oil to alcohol molar ratio of 1:6, and initially with KOH as a catalyst. Mixtures of methanol and ethanol were used for transesterification in order to use the better solvent property of ethanol and rapid equilibrium using methanol. Formation of soap by reaction of FFA present in WFG with KOH instigated difficulty in the separation of glycerol from biodiesel ester. To untangle this problem, two-stage (acid and alkali catalyzed) method was used for biodiesel synthesis. More than 90% ester was obtained when two-stage method was used compared to ∼ 50% ester in single stage alkaline catalyst. In the case of mixed alcohol, a relatively smaller amount of ethyl esters was formed along with methyl esters. Acid value, viscosity, and cetane number of all the esters prepared from WFG were within the range of the ASTM standard. Esters obtained from WFG showed good performance as a lubricity additive. 相似文献