全文获取类型
收费全文 | 40699篇 |
免费 | 4103篇 |
国内免费 | 2804篇 |
专业分类
电工技术 | 2400篇 |
技术理论 | 1篇 |
综合类 | 3831篇 |
化学工业 | 6205篇 |
金属工艺 | 3102篇 |
机械仪表 | 1764篇 |
建筑科学 | 2808篇 |
矿业工程 | 1910篇 |
能源动力 | 1793篇 |
轻工业 | 3296篇 |
水利工程 | 1189篇 |
石油天然气 | 2478篇 |
武器工业 | 575篇 |
无线电 | 4151篇 |
一般工业技术 | 4403篇 |
冶金工业 | 2947篇 |
原子能技术 | 1015篇 |
自动化技术 | 3738篇 |
出版年
2024年 | 166篇 |
2023年 | 539篇 |
2022年 | 1082篇 |
2021年 | 1305篇 |
2020年 | 1487篇 |
2019年 | 1240篇 |
2018年 | 1247篇 |
2017年 | 1602篇 |
2016年 | 1724篇 |
2015年 | 1741篇 |
2014年 | 2607篇 |
2013年 | 2844篇 |
2012年 | 3155篇 |
2011年 | 3201篇 |
2010年 | 2374篇 |
2009年 | 2314篇 |
2008年 | 2089篇 |
2007年 | 2582篇 |
2006年 | 2161篇 |
2005年 | 1874篇 |
2004年 | 1613篇 |
2003年 | 1395篇 |
2002年 | 1179篇 |
2001年 | 1023篇 |
2000年 | 865篇 |
1999年 | 705篇 |
1998年 | 606篇 |
1997年 | 517篇 |
1996年 | 480篇 |
1995年 | 401篇 |
1994年 | 302篇 |
1993年 | 230篇 |
1992年 | 216篇 |
1991年 | 166篇 |
1990年 | 144篇 |
1989年 | 100篇 |
1988年 | 67篇 |
1987年 | 45篇 |
1986年 | 43篇 |
1985年 | 35篇 |
1984年 | 30篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 9篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Cs-K混合蒸气中Cs(8D)+K(4S)碰撞能量转移 总被引:3,自引:3,他引:0
在Cs-K混合蒸气中,两步激发Cs原子到8D态,观察了Cs(8D) K(4S)→Cs(5D) K(4P)碰撞能量合并逆过程(REP,reverse energy pooling)。应用双调制技术探测K(4P)原子发射的荧光,基态K原子密度用光学吸收方法测量。得到了REP速率系数,讨论了其它过程对速率系数的影响. 相似文献
2.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
3.
Shuichi Yamamoto Teruaki Morihiro Koichi Ariyoshi Turkan Aktas 《Drying Technology》2005,23(6):1319-1330
As the surface properties of the drying materials are very important not only for the drying rate but also for the quality change during drying, the effects of surface concentration on the drying behavior of liquid foods (sugar solutions) were investigated by isothermal drying experiments and by numerical calculation experiments. The isothermal drying experiments with gelled sugar solution systems (sucrose and maltodextrin) were carried out at various relative humidity (RH) values (RH = 0 to 84%). Separate experiments were carried out for determination of the desorption isotherms.
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
4.
Industry widely uses rotary valves and blow tanks for the pneumatic conveying of products, each having their pros and cons depending on the specific application. This article shows the differing results obtained when low-velocity conveying a product through a common pipeline using both a drop-through rotary valve and a bottom-discharge blow tank feeder. A number of issues arise in the rotary valve system, the main one being rotary valve air leakage. A blow tank system, on the other hand, does not leak, as it is an enclosed system. The experimental results show dramatic differences in product throughput. Further exploration leads to a novel modification being made to the rotary valve system in an attempt to increase its capacity. The result of this modification shows a slight increase in output tonnage, but still significantly less than that obtained from the blow tank. 相似文献
5.
6.
7.
Results of metal testing in impact tension–compression and indentation are analyzed. As the analysis of these data demonstrates, the strength of metals increases greatly with strain rates and at moderate indentation rates. At high indentation rates, a decrease in the specific energy (per unit volume of a displaced material) necessary for the formation of a conical cavity was observed. The account of the effects of viscosity, temperature increase upon plastic deformation and its localization can be used to explain the above phenomena. 相似文献
8.
In various medium‐to‐large‐scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat‐release rate and smoke‐production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi‐directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
9.
本文采用 2只扩散杯 ,一只选择渗透率较大的滤膜 ,使2 2 2 Rn和2 2 0 Rn能很容易的进入。另一只选择渗透率较小的滤膜 ,该滤膜只允许2 2 2 Rn进入 ,半衰期较短的2 2 0 Rn被阻挡在外面。通过不同滤膜扩散率的差异 ,改变探测器的空气交换率 ,从而达到同时测量2 2 2 Rn和2 2 0 Rn的目的 相似文献
10.
RLL码的计算机辅助设计 总被引:1,自引:1,他引:0
本文着重讨论计算机辅助设计RLL码的具体实现问题.该过程首先根据RLL码两个参数d,k确定一个编码率p/q,然后构造出RLL码的高阶状态转换-输出符号矩阵并求相应的近似特征向量.最后通过状态分裂和状态归并过程,即可得到一个满足d,k约束的编码输出表.其中状态转换-输出符号矩阵为实现计算机辅助设计RLL码提供了有效的数据结构,而且要优化RLL码编码器,就必须有选择地进行状态分裂. 相似文献