全文获取类型
收费全文 | 223020篇 |
免费 | 19711篇 |
国内免费 | 9770篇 |
专业分类
电工技术 | 15193篇 |
技术理论 | 30篇 |
综合类 | 22471篇 |
化学工业 | 27459篇 |
金属工艺 | 9898篇 |
机械仪表 | 12073篇 |
建筑科学 | 30815篇 |
矿业工程 | 12713篇 |
能源动力 | 8713篇 |
轻工业 | 15874篇 |
水利工程 | 10642篇 |
石油天然气 | 11853篇 |
武器工业 | 3322篇 |
无线电 | 14336篇 |
一般工业技术 | 16645篇 |
冶金工业 | 11537篇 |
原子能技术 | 1751篇 |
自动化技术 | 27176篇 |
出版年
2024年 | 763篇 |
2023年 | 2779篇 |
2022年 | 5312篇 |
2021年 | 7330篇 |
2020年 | 6931篇 |
2019年 | 5272篇 |
2018年 | 4949篇 |
2017年 | 6190篇 |
2016年 | 7716篇 |
2015年 | 8405篇 |
2014年 | 15195篇 |
2013年 | 13428篇 |
2012年 | 16046篇 |
2011年 | 17874篇 |
2010年 | 13125篇 |
2009年 | 13332篇 |
2008年 | 12214篇 |
2007年 | 14841篇 |
2006年 | 13508篇 |
2005年 | 11884篇 |
2004年 | 9965篇 |
2003年 | 8573篇 |
2002年 | 6984篇 |
2001年 | 5750篇 |
2000年 | 4930篇 |
1999年 | 3918篇 |
1998年 | 2854篇 |
1997年 | 2448篇 |
1996年 | 2010篇 |
1995年 | 1689篇 |
1994年 | 1427篇 |
1993年 | 1002篇 |
1992年 | 808篇 |
1991年 | 557篇 |
1990年 | 485篇 |
1989年 | 463篇 |
1988年 | 252篇 |
1987年 | 193篇 |
1986年 | 163篇 |
1985年 | 195篇 |
1984年 | 144篇 |
1983年 | 115篇 |
1982年 | 66篇 |
1981年 | 77篇 |
1980年 | 86篇 |
1979年 | 37篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1975年 | 16篇 |
1959年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
991.
We performed the first-principles calculation to investigate the electronic structure and polarization behaviors in PbTiO3/SrTiO3 (PST) superlattices. The DOS (density of state) profiles show that there are strong hybridizations of atom Ti–O and Pb–O which play very important roles on ferroelectricity of the PbTiO3/SrTiO3 superlattices. Comparing to the corresponding paraelectric phase, we find the electrons of the PT (PbTiO3) layers occupy lower energy states and electrons of the ST (SrTiO3) layer occupy higher energy states. It is shown that the polarizations of the superlattices decrease with proportion of SrTiO3 increasing. The constant polarization of local layer indicates that PST superlattices with small modulation lengthen can be approximately considered as a single ferroelectric material. Furthermore, according to electrostatic model, we find that directions of internal electric fields in PT and ST layers are opposite. In PST superlattices, internal electric field in PT layer leads to the loss of polarization of this layer, but the polarization of ST layer is induced by internal electric field of this layer. Compared to the value of the polarization in bulk PbTiO3, polarization of PST is smaller. 相似文献
992.
系统介绍了舞钢开发的针状铁素体型X70宽厚板的设计思路、工艺特点和实物水平;采用电炉 炉外精炼 连铸 TMCP工艺生产的X70宽厚板满足西气东输专用技术条件的要求,并批量应用在西气东输主干线工程中。 相似文献
993.
The forming behaviour at high temperature of a modified 9%Cr‐1%Mo (P91) ferritic steel containing B and Ti for elevated temperature service was investigated. The microstructure of the as‐received material is mainly martensite at room temperature, but special etching revealed prior austenite grains of about 25 μm in size. Torsion tests were conducted at temperatures in the range 850 to 1250 °C to simulate the hot rolling process under comparable conditions of temperature, strain rate and strain. The deformation data obtained from these tests were correlated with the Garofalo equation with a stress exponent of 4.6 and an activation energy of 315 kJ/mol. This equation was used to predict the formability behaviour for the rolling process and also to determine the maximum forming efficiency and stability of the steel. A temperature of 1200 °C is recommended to conduct the forming process. 相似文献
994.
F Javier Álvarez‐Hornos Carmen Gabaldón Vicente Martínez‐Soria Paula Marzal Josep‐Manuel Penya‐roja 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):643-653
BACKGROUND: Two peat biofilters were used for the removal of toluene from air for one year. One biofilter was fed with pure toluene and the other received 1:1 (by weight) ethyl acetate:toluene mixture. RESULTS: The biofilters were operated under continuous loading: the toluene inlet load (IL) at which 80% removal occurred was 116 g m?3 h?1 at 57 s gas residence time. Maximum elimination capacity of 360 g m?3 h?1 was obtained at an IL of 745 g m?3 h?1. The elimination of toluene was inhibited by the presence of ethyl acetate. Intermittent loading, with pollutants supplied for 16 h/day, 5 days/week, did not significantly affect the removal efficiency (RE). Biomass was fully activated in 2 h after night closures, but 6 h were required to recover RE after weekend closures. Live cell density remained relatively constant over the operational period, while the dead cell fraction increased. Finally, a 15 day starvation period was applied and operation then re‐started. Performance was restored with similar re‐acclimatization period to that after weekend closures, and a reduction in dead cell fraction was observed. CONCLUSION: This study demonstrates the capacity of the system to handle intermittent loading conditions that are common in industrial practices, including long‐term starvation. Copyright © 2008 Society of Chemical Industry 相似文献
995.
疏水缔合型聚丙烯酰胺的合成与性能评价 总被引:1,自引:0,他引:1
为了提高高相对分子质量的聚丙烯酰胺的抗温抗盐性能,利用自制的两亲表面活性单体与丙烯酰胺共聚合成了疏水缔合型聚丙烯酰胺并进行室内评价。结果表明,在高温、高盐、高钙条件下,合成的疏水缔合型聚丙烯酰胺具有良好的增粘性和较强的热稳定性;克服了疏水缔合型聚合物在盐水中溶解性差的问题,可用各种矿化度的盐水和油田产出污水配制;具有良好的无机盐增粘性能和抗温性能。 相似文献
996.
使用自粘性防水卷材对带钢副框的铝合金门窗窗边进行粘接,以防止雨水通过副框与墙体之间的缝隙渗漏到室内,重点介绍了详细的施工措施。 相似文献
997.
998.
A parametric interpolator with confined chord errors, acceleration and deceleration for NC machining 总被引:6,自引:0,他引:6
Tsehaw Yong Author Vitae Author Vitae 《Computer aided design》2003,35(13):1249-1259
Parametric interpolation has many advantages over linear interpolation in machining curves. Real time parametric interpolation research so far has addressed achieving a uniform feed rate, confined chord errors and jerk limited trajectory planning. However, simultaneous consideration of confined chord errors that respect the acceleration and deceleration capabilities of the machine has not been attempted. In this paper, the offline detection of feed rate sensitive corners is proposed. The velocity profile in these zones is planned so that chord errors are satisfied while simultaneously accommodating the machine's acceleration and deceleration limits. Outside the zone of the feed rate sensitive corners, the feed rate is planned using the Taylor approximation. Simulation results indicate that the offline detection of feed rate sensitive corners improves parametric interpolation. For real time interpolation, the parametric curve information can be augmented with the detected feed rate sensitive corners that are stored in 2×2 matrices. 相似文献
999.
1000.
稠油热采注汽管道由于长期在高温、高压下运行,极易发生各种损伤,如腐蚀、裂纹、材料退化等,极易造成管道承压能力降低,发生失效事故。如何检测出潜在危险性缺陷,判断注汽管道能否继续使用,是保证注汽管道安全运行的关键问题。探讨了高温压力管道在线检测技术发展现状及其应用范围。 相似文献