全文获取类型
收费全文 | 223150篇 |
免费 | 19971篇 |
国内免费 | 10143篇 |
专业分类
电工技术 | 14417篇 |
技术理论 | 30篇 |
综合类 | 22601篇 |
化学工业 | 27871篇 |
金属工艺 | 9625篇 |
机械仪表 | 11551篇 |
建筑科学 | 31116篇 |
矿业工程 | 13163篇 |
能源动力 | 8333篇 |
轻工业 | 16531篇 |
水利工程 | 10662篇 |
石油天然气 | 12063篇 |
武器工业 | 3831篇 |
无线电 | 14181篇 |
一般工业技术 | 17137篇 |
冶金工业 | 11579篇 |
原子能技术 | 1757篇 |
自动化技术 | 26816篇 |
出版年
2024年 | 1045篇 |
2023年 | 2990篇 |
2022年 | 5760篇 |
2021年 | 7447篇 |
2020年 | 7244篇 |
2019年 | 5446篇 |
2018年 | 5127篇 |
2017年 | 6549篇 |
2016年 | 7870篇 |
2015年 | 8463篇 |
2014年 | 15266篇 |
2013年 | 13483篇 |
2012年 | 16031篇 |
2011年 | 17759篇 |
2010年 | 13103篇 |
2009年 | 13294篇 |
2008年 | 12139篇 |
2007年 | 14792篇 |
2006年 | 13444篇 |
2005年 | 11755篇 |
2004年 | 9774篇 |
2003年 | 8490篇 |
2002年 | 6908篇 |
2001年 | 5691篇 |
2000年 | 4850篇 |
1999年 | 3821篇 |
1998年 | 2709篇 |
1997年 | 2368篇 |
1996年 | 1936篇 |
1995年 | 1616篇 |
1994年 | 1368篇 |
1993年 | 973篇 |
1992年 | 781篇 |
1991年 | 550篇 |
1990年 | 474篇 |
1989年 | 442篇 |
1988年 | 244篇 |
1987年 | 193篇 |
1986年 | 163篇 |
1985年 | 186篇 |
1984年 | 135篇 |
1983年 | 113篇 |
1982年 | 60篇 |
1981年 | 75篇 |
1980年 | 81篇 |
1979年 | 38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 0 毫秒
31.
María P. Albano Liliana B. Garrido 《Journal of Materials Synthesis and Processing》2002,10(4):211-218
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values. 相似文献
32.
用快切装置替代备自投装置提高厂用电安全可靠性 总被引:3,自引:0,他引:3
指出目前厂用电切换装置存在的不足,分析了快切装置的基本原理以及厂用电事故下的成功快切对电厂安全生产的意义,说明了在厂用电切换中尽快应用快切装置的必要性。 相似文献
33.
34.
测定钠中杂质的手动阻塞计的研究 总被引:1,自引:1,他引:0
文章介绍了测定钠中杂质浓度的手动阻塞计的原理、装置和实验结果。为了减少测量误差,我们研究了影响准确测定阻塞温度的因素,并且找到了减少测量误差的办法。在同样的杂质饱和温度下,该阻塞计测得的高、低阻塞温度所对应的杂质浓度差是很接近的。对氧其差值为1.03ppm;对氢为0.0763ppm。 相似文献
35.
软X射线不仅能引起红细胞表面电荷的变化,同时也能导致淋巴细胞和血小板表面电荷下降,表现为照射后它们的电泳率下降。低剂量范围内,这种电荷的变化是暂时性的,照后4小时降到最低点,24小时后恢复到对照的水平。细胞电泳率的下降与辐射剂量相关。淋巴细胞是一个复杂的细胞群,正常状态下,按细胞在电场中泳动速度的快慢,可分为两个组分:快峰为T细胞,慢峰为B细胞。软X射线照射以后,T和B细胞的电泳率皆减慢,频数分布峰值下降,离散度加大。血小板成分单一,电泳率较一致。 从照射浓集的血小板再加回自身血浆中电泳率的下降较照射血浆再加到血小板中的电泳率下降大得多;受照射的血小板在磷酸缓冲液中电泳率下降较在血浆悬液中严重得多;2000 rad照后,悬浮于血浆中的血小板电泳率能恢复,而悬浮于磷酸缓冲液中则不能恢复,三个方面来看,血浆中可能存在抗辐射因子。超氧化物岐化酶能有效地预防血小板电泳率的下降,从而可阻止血小板的凝聚。 相似文献
36.
位山引黄灌区泥沙淤积原因及处理对策 总被引:7,自引:2,他引:5
位山灌区是黄河下游大型引黄灌区 ,渠系泥沙淤积严重 ,泥沙处理困难。通过采用远距离输沙、集中处理沉沙区泥沙、分散沉沙和节水减淤等技术措施 ,减少了渠系的泥沙淤积。对清淤产生的泥沙 ,采取综合开发利用的技术和管理措施 ,取得了比较可靠的效果。 相似文献
37.
Gabriel Wainer 《Software》2002,32(13):1261-1306
The features of a toolkit for modeling and simulation based on the DEVS formalism are presented. The tool is built as a set of independent software pieces running on different platforms. Not only are the main characteristics of the environment presented, a focus on its use is also considered by inclusion of application examples for a variety of problems. Many models can be defined in an automated fashion, simplifying the construction of new models and easing their verification. The use of this formal approach has allowed the development of safe and cost‐effective simulations, significantly reducing development time. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
38.
建立了挠性胶管阻尼耗能的简化模型。以此为基础分析了挠性胶管的阻尼耗能的一般规律,并得出了一些新的结论。 相似文献
39.
A nuclear microprobe with high spatial resolution and high analytical sensitivity was applied to analyze trace elements,especially lead,in vehicle exhaust of Shanghai city.The result shows that the chemical composition and its corresponding x-ray relative intensity are different among different vehicle exhausts.There are many kinds of metal elements in particles of vehicle exhaust.most are harmful to people,such as Ti,Cr,Mn,Pb,etc.We found that the lead concentration was 6820μg/g and the bromine concentration was 5300μg/g in the exhaust from Santana using leaded gasoline(SULG).which is higher than any other kinds of vehicle exhausts.We have also detected the minimum lead in the particles of unleaded gasoline and its content varies from one to another.Its mean concentration was 450μg/g and the highest reached 6210μg/g.The unleaded gasoline‘s Pb existed in the whole particle while the leaded gasoline‘s enriched in the surface of the particle and was more harmful to the human beings. 相似文献
40.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献