全文获取类型
收费全文 | 179244篇 |
免费 | 15647篇 |
国内免费 | 8436篇 |
专业分类
电工技术 | 11377篇 |
技术理论 | 13篇 |
综合类 | 11645篇 |
化学工业 | 29313篇 |
金属工艺 | 9917篇 |
机械仪表 | 11251篇 |
建筑科学 | 13708篇 |
矿业工程 | 5432篇 |
能源动力 | 5293篇 |
轻工业 | 12437篇 |
水利工程 | 3271篇 |
石油天然气 | 10719篇 |
武器工业 | 1403篇 |
无线电 | 21529篇 |
一般工业技术 | 21509篇 |
冶金工业 | 8737篇 |
原子能技术 | 1922篇 |
自动化技术 | 23851篇 |
出版年
2024年 | 900篇 |
2023年 | 3414篇 |
2022年 | 6340篇 |
2021年 | 8499篇 |
2020年 | 6399篇 |
2019年 | 5060篇 |
2018年 | 5724篇 |
2017年 | 6394篇 |
2016年 | 5704篇 |
2015年 | 7583篇 |
2014年 | 9393篇 |
2013年 | 11250篇 |
2012年 | 12244篇 |
2011年 | 12874篇 |
2010年 | 10991篇 |
2009年 | 10374篇 |
2008年 | 9900篇 |
2007年 | 9122篇 |
2006年 | 9298篇 |
2005年 | 7965篇 |
2004年 | 5312篇 |
2003年 | 4468篇 |
2002年 | 4003篇 |
2001年 | 3605篇 |
2000年 | 3533篇 |
1999年 | 4147篇 |
1998年 | 3453篇 |
1997年 | 2932篇 |
1996年 | 2741篇 |
1995年 | 2213篇 |
1994年 | 1798篇 |
1993年 | 1297篇 |
1992年 | 1044篇 |
1991年 | 785篇 |
1990年 | 567篇 |
1989年 | 465篇 |
1988年 | 367篇 |
1987年 | 252篇 |
1986年 | 209篇 |
1985年 | 129篇 |
1984年 | 116篇 |
1983年 | 86篇 |
1982年 | 86篇 |
1981年 | 68篇 |
1980年 | 62篇 |
1979年 | 29篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
通过3种不同的碱来制备2,4-二氯-5-氟苯甲酰乙酸甲酯,优选得到了其最佳缩合剂甲醇钠;同时应用正交设计实验,研究了原料配比、反应时间、反应温度对收率的影响,在优选条件下收率为78.5%。 相似文献
94.
本文采用茜素络合酮比色法和氟离子选择电极法对饲料磷酸氢钙进行氟的测定实验对比,得出常用的氟离子选择电极法完全可以代替经典的蒸馏比色法的结论。 相似文献
95.
The coal filter cake is a product of fine coal after floatation which has an ash content of 7-13%, water content of 30±2%, and a particle size of less than 1 mm. The ash content was measured by the intensity of the single backscattered gamma-ray, and its accuracy is mainly dependent on the energy of the gamma-ray. The 238Pu low energy photon source is selected in this work. The energy of its gamma-ray is 15 keV, which can result not only in the best sensitivity, but also in the lowest contribution to the environment radiation. The root mean square deviation of the ash measurement is±0.33% (±1σ). 相似文献
96.
With the “orthogonal experimental design” (OED), the dependence of conductivity and transparency of tin oxide films and open circuit voltage Voc of SIS solar cells on the spray deposition process factors was studied. The OED technique was found to be a powerful method for realizing the best factor combination. Using OED, curves were obtained which clearly depict the effects of each factor on the SIS characteristics. The results of the experiments also illustrate exactly which variation in fabrication technique most affects the sheet resistance, Voc, and film transparency. Under the optimal combination of conditions, a thin film doped with NH4F was obtained, with about 90% transmission and a sheet resistance of about 80 Ω/□, along with an SIS structure with a Voc of about 0.61 V. 相似文献
97.
Yung-Chung Chang Wei-Tzen Yang Chun-Chang Liu 《Power Systems, IEEE Transactions on》1994,9(3):1665-1671
A method is proposed which avoids many limitations associated with traditional B-coefficient loss coefficient calculation. The proposed method, unlike the traditional B-coefficient method, is very fast and can handle line outages. The method utilizes network sensitivity factors which are established from DC load flow solutions, Line outage distribution factors (ODFs) are formulated using changes in network power generations to simulate the outaged line from the network. The method avoids the use of complicated reference frame transformations based upon Kron's tenser analysis. The necessity of data normalization used in least squares and the evaluation of the slope of &thetas;j versus PGn is not necessary with the proposed method. Using IEEE standard 14-bus and 30-bus systems, the method's results are compared against results obtained from an AC load flow program (LFED). The method's solution speed is compared to that of the LFED method, the base case database method and the conventional B-coefficient method based on Ajn-factor. The proposed method is easy to implement and, when compared to other methods, has exhibited good accuracy and rapid execution times. The method is well suited to online dispatch applications 相似文献
98.
99.
100.
本文提出采用高分子有机材料配合,生产石膏制品防水防潮剂的生产方法和工艺。该剂还可以应用到氧化镁系列板材,同时提出开发珠光或彩色防水防潮剂,能达到满足的装饰效果,值提开发推广。 相似文献