全文获取类型
收费全文 | 27668篇 |
免费 | 2462篇 |
国内免费 | 2098篇 |
专业分类
电工技术 | 387篇 |
技术理论 | 1篇 |
综合类 | 2125篇 |
化学工业 | 5888篇 |
金属工艺 | 4522篇 |
机械仪表 | 857篇 |
建筑科学 | 1026篇 |
矿业工程 | 446篇 |
能源动力 | 801篇 |
轻工业 | 3888篇 |
水利工程 | 405篇 |
石油天然气 | 640篇 |
武器工业 | 287篇 |
无线电 | 1689篇 |
一般工业技术 | 6119篇 |
冶金工业 | 1946篇 |
原子能技术 | 297篇 |
自动化技术 | 904篇 |
出版年
2024年 | 90篇 |
2023年 | 540篇 |
2022年 | 720篇 |
2021年 | 1044篇 |
2020年 | 989篇 |
2019年 | 962篇 |
2018年 | 799篇 |
2017年 | 1014篇 |
2016年 | 1016篇 |
2015年 | 992篇 |
2014年 | 1368篇 |
2013年 | 1805篇 |
2012年 | 1576篇 |
2011年 | 1934篇 |
2010年 | 1460篇 |
2009年 | 1570篇 |
2008年 | 1399篇 |
2007年 | 1643篇 |
2006年 | 1499篇 |
2005年 | 1250篇 |
2004年 | 1204篇 |
2003年 | 962篇 |
2002年 | 876篇 |
2001年 | 726篇 |
2000年 | 702篇 |
1999年 | 521篇 |
1998年 | 490篇 |
1997年 | 446篇 |
1996年 | 355篇 |
1995年 | 303篇 |
1994年 | 262篇 |
1993年 | 249篇 |
1992年 | 243篇 |
1991年 | 209篇 |
1990年 | 244篇 |
1989年 | 180篇 |
1988年 | 129篇 |
1987年 | 61篇 |
1986年 | 62篇 |
1985年 | 67篇 |
1984年 | 66篇 |
1983年 | 37篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1975年 | 10篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
61.
枪械振动测试包含刚体线位移和角位移六维运动参数.其测试方法是,将光电传感器光源与被测体固结在一起,通过求解光源在三个投影屏上随着被测体运动变化的数学模型而实现的.该传感器由激光器、投影屏、光电探测器件及处理电路、数据采集、数据处理等部分组成.并以固结在被测体上的三个激光器的交点为基点,建立其线位移数学模型;以方向余弦法来确定被测体的角位移,建立其角位移数学模型. 相似文献
62.
63.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
64.
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
65.
66.
The effect of ductile crack growth on the near tip stress field in two different specimen geometries has been investigated. For homogeneous specimens it is observed that the peak stress level increases with ductile crack growth. The effect is most pronounced up to about 1 mm of crack growth. For low and intermediate hardening there is a significant effect of specimen size on the stress level. In case of mismatch in yield stress, the simulations show that the increase in stress level in the material with the lower yield stress is of a similar magnitude as is the case for stationary cracks. In case of ductile crack growth deviation from the original crack plane occurs, the highest stresses are still found close to the interface, and not in front of the current crack tip. 相似文献
67.
Omar Snchez Estrella Asp María C Martí Marlene Roeckel 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(11):1261-1267
Most of the kinetic studies on nitrification have been performed in diluted salts medium. In this work, the ammonia oxidation rate (AOR) was determined by respirometry at different ammonia (0.01 and 33.5 mg N‐NH3 L?1), nitrite (0–450 mg N‐NO2? L?1) and nitrate (0 and 275 mg N‐NO3? L?1) concentrations in a saline medium at 30 °C and pH 7.5. Sodium azide was used to uncouple the ammonia and nitrite oxidation, so as to measure independently the AOR. It was determined that ammonia causes substrate inhibition and that nitrite and nitrate exhibit product inhibition upon the AOR. The effects of ammonia, nitrite and nitrate were represented by the Andrews equation (maximal ammonia oxidation rate, rAOMAX, = 43.2 [mg N‐NH3 (g VSSAO h)?1]; half saturation constant, KSAO, = 0.11 mg N‐NH3 L?1; inhibition constant KIAO, = 7.65 mg N‐NH3 L?1), by the non‐competitive inhibition model (inhibition constant, KINI, = 176 mg N‐NO2? L?1) and by the partially competitive inhibition model (inhibition constant, KINA, = 3.3 mg N‐NO3? L?1; α factor = 0.24), respectively. The rAOMAX value is smaller, and the KSAO value larger, than the values reported in diluted salts medium; the KIAO value is comparable to those reported. Process simulations with the kinetic model in batch nitrifying reactors showed that the inhibitory effects of nitrite and nitrate are significant for initial ammonia concentrations larger than 100 mg N‐NH4+ L?1. Copyright © 2005 Society of Chemical Industry 相似文献
68.
Yu Shichang Wu Shenqing Gong Youjun Gong Yuansheng Lian Mingsheng Ye Gang Cheng Yijun 《中国稀土学报(英文版)》2006,24(1):120-120
Grain growth behavior of 5Cr21Mn9Ni4NRE steel was experimentally studied at various solid solution treatment temperatures and holding for different times. The experimental results show that the 5Cr21Mn9Ni4NRE steel has the feature of sharp austenite grain coarsening after solid solution treatment at the temperature above 1150 ℃. RE added in the steel has the benefit to restrain grain growth and increase grain growth activation energy. 相似文献
69.
提出了用三角函数表示的一类用于油田开发指标预测的增长曲线共6条,从而进一步完善和丰富了现有的增长曲线法。提出和推导了它们的Np-t、Qt-t、Qt-Np关系式、(Np/NRmax)Qtmax准数计算式以及参数求解式。其特片研究表明,它们特征相近;(Np/NRamx)Qtmax变化范围为0-0.36785,属于峰值产量出现在油田开发初期的情况,其Qt-Np关系为一不对称的拱形曲线。提出了求取曲线参数的过原点重复线性回归法。双河油田的实例表明该方法有一定实用价值。 相似文献
70.
I.H. Song 《Thin solid films》2007,515(19):7598-7602
This paper is a report on the effect of a single perpendicular grain boundary on the hot-carrier and high current stability in high performance polycrystalline silicon (poly-Si) thin film transistors (TFTs). Under a hot carrier stress condition (Vg = Vth + 1 V, Vd = 12 V), the poly-Si TFT with a single grain boundary is superior to the poly-Si without any grain boundary because of the smaller free carriers available for electric conduction. The shift of transconductance in poly-Si TFT with a single grain boundary is less than 5% after hot carrier stress during a period of 1000 s. The shift of transconductance is about 25% in the case of the poly-Si TFTs without a grain boundary in the channel. On high current stress, the poly-Si TFT without the grain boundary is less degraded than the poly-Si TFT with the grain boundary because the concentrated electric field near the drain junction is lower. 相似文献