全文获取类型
收费全文 | 433861篇 |
免费 | 3784篇 |
国内免费 | 651篇 |
专业分类
电工技术 | 7515篇 |
综合类 | 454篇 |
化学工业 | 67452篇 |
金属工艺 | 21935篇 |
机械仪表 | 15550篇 |
建筑科学 | 9081篇 |
矿业工程 | 3452篇 |
能源动力 | 7988篇 |
轻工业 | 32911篇 |
水利工程 | 5596篇 |
石油天然气 | 12611篇 |
武器工业 | 42篇 |
无线电 | 41691篇 |
一般工业技术 | 90642篇 |
冶金工业 | 72816篇 |
原子能技术 | 11894篇 |
自动化技术 | 36666篇 |
出版年
2021年 | 3256篇 |
2019年 | 3189篇 |
2018年 | 11868篇 |
2017年 | 12254篇 |
2016年 | 9851篇 |
2015年 | 3936篇 |
2014年 | 6248篇 |
2013年 | 15369篇 |
2012年 | 11414篇 |
2011年 | 18672篇 |
2010年 | 16057篇 |
2009年 | 16039篇 |
2008年 | 16563篇 |
2007年 | 18218篇 |
2006年 | 10214篇 |
2005年 | 11581篇 |
2004年 | 10222篇 |
2003年 | 9830篇 |
2002年 | 9059篇 |
2001年 | 8477篇 |
2000年 | 8251篇 |
1999年 | 7977篇 |
1998年 | 18573篇 |
1997年 | 13270篇 |
1996年 | 10159篇 |
1995年 | 7858篇 |
1994年 | 7032篇 |
1993年 | 7002篇 |
1992年 | 5535篇 |
1991年 | 5321篇 |
1990年 | 5604篇 |
1989年 | 5398篇 |
1988年 | 5228篇 |
1987年 | 4716篇 |
1986年 | 4826篇 |
1985年 | 5295篇 |
1984年 | 5049篇 |
1983年 | 4693篇 |
1982年 | 4414篇 |
1981年 | 4626篇 |
1980年 | 4418篇 |
1979年 | 4520篇 |
1978年 | 4671篇 |
1977年 | 4957篇 |
1976年 | 6433篇 |
1975年 | 4225篇 |
1974年 | 4161篇 |
1973年 | 4292篇 |
1972年 | 3772篇 |
1971年 | 3439篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
I. Kashif H. Farouk S. A. Aly A. M. Sanad M. H. El-Kottamy E. E. Assem 《Journal of Materials Science: Materials in Electronics》1992,3(3):144-146
The effect of the addition of Fe2O3 and heat treatment duration on the magnetic susceptibility of vanadium borophosphate glass were studied. The magnetic susceptibility of glass samples was found to increase with increasing Fe2O3 content, which may be explained by the formation of the FeO6 group and the change of Fe2+ to Fe3+ which has higher paramagnetic properties. No detectable changes in the magnetic susceptibility with heat treatment for the samples containing 0.0, 0.5 and 1.0 mol% Fe2O3 was observed. The magnetic susceptibility for the heat treated samples containing 2.5, 5.0 and 7.5 mol% Fe2O3 decreases sharply with increasing duration of heat treatment up to 6 h and then remains almost constant. The sharp decrease in magnetic susceptibility of 2.5 mol% Fe2O3 is attributed to the increase in the number of ferrous ions. The sharp decrease for samples containing 5.0 and 7.5 mol% Fe2O3 is attributed to the increase in the number of Fe3+ in tetrahedral co-ordination. The rate of crystallization owing to the heat treatment was calculated and was found to increase with increasing iron oxide content. The geometry of crystallization was found to be in three-, two-and one-dimension(s) for samples containing 2.5, 5.0 and 7.5 mol% Fe2O3, respectively. 相似文献
992.
993.
Li Z.-M. Landheer D. Veilleux M. Conn D.R. Surridge R. Xu J.M. McDonald R.I. 《Photonics Technology Letters, IEEE》1992,4(5):473-476
The authors have developed a 2-D device simulator for heterostructure metal-semiconductor-metal (MSM) photodetectors. They have incorporated a model of multilayer optics into the simulator and used it to analyze the temporal response of a resonant-cavity enhanced heterostructure with a confining buffer layer and a distributed Bragg reflector (DBR). The authors show that through fine tuning the layer thicknesses, optical resonance enhancement of the light absorption can be obtained 相似文献
994.
Translated from Izmeritel'naya Tekhnika, No. 7, pp. 8–9, July, 1992. 相似文献
995.
996.
Results of ballistic tests for obstacles made of combined materials in relation to striker shape are presented in the form of penetration curves. It is established that striker shape affects not only quantitative indices, but also the qualitative nature of these curves.Translated from Problemy Prochnosti, No. 1, pp. 60–62, January, 1992. 相似文献
997.
The authors provide a convergence analysis for the Kohonen learning algorithm (KLA) with respect to vector quantizer (VQ) optimality criteria and introduce a stochastic relaxation technique which produces the global minimum but is computationally expensive. By incorporating the principles of the stochastic approach into the KLA, a deterministic VQ design algorithm, the soft competition scheme (SCS), is introduced. Experimental results are presented where the SCS consistently provided better codebooks than the generalized Lloyd algorithm (GLA), even when the same computation time was used for both algorithms. The SCS may therefore prove to be a valuable alternative to the GLA for VQ design 相似文献
998.
999.
1000.