全文获取类型
收费全文 | 120396篇 |
免费 | 12248篇 |
国内免费 | 6719篇 |
专业分类
电工技术 | 8213篇 |
技术理论 | 5篇 |
综合类 | 9168篇 |
化学工业 | 19075篇 |
金属工艺 | 7000篇 |
机械仪表 | 7760篇 |
建筑科学 | 9368篇 |
矿业工程 | 3976篇 |
能源动力 | 3405篇 |
轻工业 | 9902篇 |
水利工程 | 2463篇 |
石油天然气 | 6376篇 |
武器工业 | 1222篇 |
无线电 | 14462篇 |
一般工业技术 | 13133篇 |
冶金工业 | 5043篇 |
原子能技术 | 1158篇 |
自动化技术 | 17634篇 |
出版年
2024年 | 786篇 |
2023年 | 2514篇 |
2022年 | 4615篇 |
2021年 | 6100篇 |
2020年 | 4424篇 |
2019年 | 3660篇 |
2018年 | 3936篇 |
2017年 | 4255篇 |
2016年 | 3778篇 |
2015年 | 5296篇 |
2014年 | 6364篇 |
2013年 | 7220篇 |
2012年 | 8488篇 |
2011年 | 8997篇 |
2010年 | 7606篇 |
2009年 | 7315篇 |
2008年 | 7003篇 |
2007年 | 6581篇 |
2006年 | 6524篇 |
2005年 | 5382篇 |
2004年 | 3888篇 |
2003年 | 3410篇 |
2002年 | 3387篇 |
2001年 | 2911篇 |
2000年 | 2502篇 |
1999年 | 2356篇 |
1998年 | 1877篇 |
1997年 | 1577篇 |
1996年 | 1385篇 |
1995年 | 1166篇 |
1994年 | 1008篇 |
1993年 | 703篇 |
1992年 | 528篇 |
1991年 | 438篇 |
1990年 | 312篇 |
1989年 | 247篇 |
1988年 | 220篇 |
1987年 | 148篇 |
1986年 | 121篇 |
1985年 | 70篇 |
1984年 | 36篇 |
1983年 | 25篇 |
1982年 | 46篇 |
1981年 | 25篇 |
1980年 | 43篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Electromigration reliability of interconnect under bidirectional current stress has been studied in a wide frequency range (mHz to 200 MHz). Experimental results show that the AC lifetime rises with the stress current frequency. The current density exponent and the activation energy of AC lifetime are found to be twice that of DC lifetime. Pure AC current stress failure at extremely high current density is believed to result from thermal migration of metal at hot/cold transition points 相似文献
62.
When melting processes are associated with an exothermic heat of mixing, unique coupled transport phenomena take place. In
this article, a mathematical model has been developed to simulate these unique coupled heat and mass transfer events. The
model was based on the control-volume finite difference approach and on an enthalpy method. In order to verify the mathematical
model, a low-temperature physical model was established consisting of ice and sulfuric acid solutions. In this physical model,
both temperature and velocity measurements were carried out. The model predictions were compared with experimental measurements,
and they were found to be in good agreement. The model was also applied to a high-temperature system, namely, the melting
of silicon metal in liquid high carbon iron. The predictions distinguished two periods present in the entire melting process.
In the first period, the silicon was heated up. The second period, i.e., free melting period, occurred in tandem with the exothermic reaction, and consequently, the melting process was greatly
accelerated. As was the case with the low-temperature physical model, as with the high-temperature system, good agreement
was obtained between the predicted results and the experimental measurements. 相似文献
63.
中国的三种非同步轨道卫星移动通信系统星座方案 总被引:6,自引:1,他引:5
本文介绍基于我国的三种非同步轨道卫星移动通信系统星座方案:低、中轨系统各有24和18颗星,轨道高度分别为1326和8035km,两系统各以5°和30°的仰角对我国的覆盖率为99.78%和99.96%;椭圆轨道系统12颗星,近、远地点分别为427和2906km,以7°和15°仰角对我国北纬20°以上地区覆盖率分别为97.90%和89.61%,若增加4颗中轨卫星,以15°仰角对我国的覆盖率为99.99%。 相似文献
64.
65.
苯并口恶嗪-环氧化合物-胺类催化剂体系开环聚合反应的研究 总被引:9,自引:0,他引:9
采用TLC,GPC,1H-NMR及IR等分析方法,对苯并恶嗪-环氧化合物-胺类催化剂体系的聚合反应进行了研究,表征了产物结构,并探讨了聚合反应机理,结果表明,苯并恶唪-环氧化合物体系在胺类催化剂如苄胺,咪唑的作用下,能发生开环聚合反应,生成低分子量的聚合物。 相似文献
66.
Cluster analysis in industrial market segmentation through artificial neural network 总被引:6,自引:0,他引:6
Market segmentation has commonly applied cluster analysis. This study intends to make the comparison of conventional two-stage method with proposed two-stage method through the simulated data. The proposed two-stage method is the combination of self-organizing feature maps and K-means method. The simulation results show that the proposed scheme is better than the conventional two-stage method based on the rate of misclassification. 相似文献
67.
介绍了一种采用改进型的CLS3700数控测井系统对微电阻率扫描仪数据采集与控制接口的设计及实现方法。基于CLS3700数控测井仪和FMS仪采用89C51单片机设计出通信接口,解决了微电阻率方法。基于CLS3700数控测井仪和FMS仪采用89C51单片机设备出通信接口电路,解决了微电阻主扫描仪现现场实时处理中的瓶颈问题。 相似文献
68.
69.
70.
Z Ma S Ramanadham K Kempe Z Hu J Ladenson J Turk 《Canadian Metallurgical Quarterly》1996,1308(2):151-163
We prepared polymers having a phospholipid polar group, poly [omega-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate(BMA)], as new biomedical materials and evaluated their blood compatibility with attention to protein adsorption and platelet adhesion. The total amount of proteins adsorbed on the polymer surface from human plasma was determined, and the distribution of adsorbed proteins on the plasma-contacting surface was analyzed. The amount of proteins adsorbed on every poly (MAPC-co-BMA) was small compared with that observed on polymers without the phospholipid polar group. However, there was no significant difference in the amount of adsorbed proteins on the poly(MAPC-co-BMA) even when the methylene chain length between the phospholipid polar group and the backbone in the MAPC moiety was altered. Platelet adhesion on the polymer surface from a platelet suspension in a buffered solution was evaluated with and without plasma treatment on the surface. When a rabbit platelet suspension was brought into contact with the poly(BMA) surface after treatment with plasma, many platelets adhered and aggregated. However, a reduced amount of platelet adhered on the poly(BMA) was found in the case of direct contact with the platelet suspension. On the other hand, the poly(MAPC-co-BMA)s could inhibit platelet adhesion under both conditions. Based on these results, it can be concluded that the proteins adsorbed on the surface play an important role in determining the platelet adhesion and suppression of the protein adsorption on the surface, which is one of the most significant ways of inhibiting platelet adhesion. 相似文献