全文获取类型
收费全文 | 16319篇 |
免费 | 1501篇 |
国内免费 | 835篇 |
专业分类
电工技术 | 831篇 |
技术理论 | 1篇 |
综合类 | 881篇 |
化学工业 | 2482篇 |
金属工艺 | 1008篇 |
机械仪表 | 869篇 |
建筑科学 | 1044篇 |
矿业工程 | 289篇 |
能源动力 | 495篇 |
轻工业 | 1592篇 |
水利工程 | 337篇 |
石油天然气 | 550篇 |
武器工业 | 106篇 |
无线电 | 1669篇 |
一般工业技术 | 2187篇 |
冶金工业 | 1791篇 |
原子能技术 | 169篇 |
自动化技术 | 2354篇 |
出版年
2024年 | 81篇 |
2023年 | 280篇 |
2022年 | 657篇 |
2021年 | 936篇 |
2020年 | 637篇 |
2019年 | 473篇 |
2018年 | 519篇 |
2017年 | 617篇 |
2016年 | 538篇 |
2015年 | 689篇 |
2014年 | 908篇 |
2013年 | 1023篇 |
2012年 | 1128篇 |
2011年 | 1215篇 |
2010年 | 1003篇 |
2009年 | 960篇 |
2008年 | 890篇 |
2007年 | 803篇 |
2006年 | 731篇 |
2005年 | 590篇 |
2004年 | 416篇 |
2003年 | 347篇 |
2002年 | 327篇 |
2001年 | 307篇 |
2000年 | 242篇 |
1999年 | 242篇 |
1998年 | 497篇 |
1997年 | 375篇 |
1996年 | 257篇 |
1995年 | 164篇 |
1994年 | 131篇 |
1993年 | 125篇 |
1992年 | 55篇 |
1991年 | 37篇 |
1990年 | 53篇 |
1989年 | 40篇 |
1988年 | 28篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 18篇 |
1981年 | 40篇 |
1980年 | 21篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 28篇 |
1976年 | 32篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
952.
在电磁轴承中为了提高功率放大器的效率,一般采用PWM开关功率放大器。功率放大器控制电磁轴承中电磁铁线圈的电流,以获得轴承悬浮所需要的吸力。因此,电磁线圈电流的控制精度和速度将直接影响电磁轴承的悬浮特性。功放设计中,以电流型PWM控制器UC3842为控制核心,产生控制模拟开关通断时间的PWM信号;采用新型的高侧电流传感器AD628检测电磁线圈中的电流,并进行放大作为反馈信号,所设计的PWM开关功放应用于磁悬浮轴承中,其控制精度和速度达到了磁轴承悬浮的应用要求。 相似文献
953.
模糊神经网络在UV-LIGA工艺优化中的应用 总被引:3,自引:9,他引:3
将模糊神经网络理论和算法应用于负性光刻胶(SU-8)加工高分辨率和高深宽比微结构的工艺研究,在正交试验的基础上对网络进行训练,建立了光刻图形质量与前烘时间、前烘温度、曝光量、后烘时间之间的预测模型。该模型采用五层前向模糊神经网络,学习算法为梯度下降法。进行了实验,实验结果表明,前烘温度与前烘时间对光刻质量影响最大。对120~340 μm厚的光刻胶,前烘温度取95℃,前烘时间100 min时,图形的相对线宽差最小;超声搅拌能缩短显影时间,显著改善图形质量,试验结果与计算结果十分吻合。将模糊神经网络应用于UV-LIGA工艺中,能实现光刻加工微结构的工艺参数优化。 相似文献
954.
955.
956.
Health risk assessment on dietary exposure to polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China 总被引:5,自引:0,他引:5
Zhonghuan Xia Xiaoli Duan Di Liu Shu Tao Bin Lu Xinxin Hu 《The Science of the total environment》2010,408(22):5331-10242
Twenty-five kinds of seven categories of foods were sampled in December 2008 and the concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined. The highest level of total PAHs was detected in pork (195.30 ng/g) whereas the lowest concentration was found in milk (8.73 ng/g). The median values of B[a]P equivalent (B[a]Peq) daily exposure doses for children, adolescents, adults and seniors of male were estimated to be 392.42, 511.01, 571.56 and 532.56 ng/d, respectively, whereas those for the above population groups of female were found to be 355.16, 440.51, 487.64 and 444.85 ng/d, respectively. The incremental lifetime cancer risk (ILCR) values at the 22.1th, 26.1th, 12.7th, 24.9th, 22.7th, 27.0th, 12.9th, and 25.5th percentiles for male children, male adolescents, male adults, male seniors, female children, female adolescents, female adults and female seniors, respectively, were larger than 10− 6, indicating high potential carcinogenic risk, and were larger than 10− 4 at the 74.5th, 78.7th, 60.6th, 77.4th, 75.3th, 79.5th, 60.8th and 77.9th percentiles for the above groups, respectively, which implied significant cancer risk. Sensitivity analysis found that the two variables of oral cancer slope factor of benzo(a) pyrene (SF) and the daily dietary PAH exposure level (ED) had the greater impact than that of body weight (BW) on the ILCR. 相似文献
957.
C. La Tessa L. Di Fino M. Larosa K. Lee D. Mancusi D. Matthiä L. Narici V. Zaconte 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(21-22):3549-3557
The ALTEA-Space detector has been calibrated by testing its response to several monochromatic beams. These measurements provided energy-deposition spectra in silicon of 100, 600 and 1000 MeV/nucleon 12C and 200 and 600 MeV/nucleon 48Ti. The results have been compared to three Monte Carlo transport codes, namely PHITS, GEANT4 and FLUKA. Median, full width at half maximum (FWHM) and interquartile range (IQR) have been calculated for all datasets to characterize location, width and asymmetry of the energy-deposition spectra. Particular attention has been devoted to the influence of δ rays on the shape of the energy-deposition spectrum, both with the help of analytical calculations and Monte Carlo simulations. The two approaches proved that, in this range of projectile charge, projectile energy and detector size, the leakage of secondary electrons might introduce a difference between the energy-loss and energy-deposition spectrum, in particular by changing the location, width and symmetry of the distribution. The overall agreement between the Monte Carlo predictions and the measurements is fair and makes PHITS, FLUKA and GEANT4 all possible candidates for simulating ALTEA-Space experiment. 相似文献
958.
G.M. Polli L. Reccia A. Cucchiaro A. della Corte A. Di Zenobio L. Muzzi A. Pizzuto G. Ramogida S. Turtú R. Villari M. Nannini C. Portafaix L. Zani P. Barabaschi 《Fusion Engineering and Design》2009,84(7-11):1531-1538
In the framework of the Broader Approach Agreement, Europe is involved in the design activities for the Japanese Tokamak JT-60SA, investigating, among several issues, the operation of the superconducting TF magnets and their subsystems, aimed at the reactor conceptual design definition. In particular, one of the main critical aspects to study is the heating of the conductor due to both direct component of energy deposited by neutrons and by secondary gamma generated during plasma operation, and heat generated by the radiation on casing and transferred to the winding pack. Indeed, the operating temperature and the relevant temperature margin (i.e. the operating safety margin) of the magnet will depend strongly on the heat loads and on the capability of the coolant to remove it. Furthermore, the heat power to the conductor will depend on several aspects, namely the thickness of insulating material, the mass flow rate of helium flowing in the conductors and its thermodynamic properties at operating conditions, and the layout of the superconductors constituting the winding. Moreover, a crucial aspect in the final design will be the presence and position of the casing cooling channels. In this paper a 2D sensitivity analysis of heat transfer from casing to winding pack with respect to cooling channels number and position is presented, based on the reference layout of the magnet. As a result, we evaluated the optimum number and positioning of cooling channels needed, as a trade-off between magnet operating limits and available cryogenic power and if, at limit, they could be even neglected in normal operation, keeping dwell-time within reasonable values. 相似文献
959.
在蒙特卡罗模拟光子运输的过程中,截面一直是一个比较棘手的问题,本文用曲线拟合的最小二乘法来拟合137CS源发出的射线与NaI晶体发生相互作用时其光电截面、康普顿散射截面、总吸收系数,并模拟了137CS源在NaI探测器中的沉积谱. 相似文献
960.