全文获取类型
收费全文 | 533996篇 |
免费 | 48555篇 |
国内免费 | 25498篇 |
专业分类
电工技术 | 34786篇 |
技术理论 | 76篇 |
综合类 | 58763篇 |
化学工业 | 74666篇 |
金属工艺 | 26906篇 |
机械仪表 | 28601篇 |
建筑科学 | 65413篇 |
矿业工程 | 26871篇 |
能源动力 | 17511篇 |
轻工业 | 37258篇 |
水利工程 | 23342篇 |
石油天然气 | 23772篇 |
武器工业 | 5717篇 |
无线电 | 39899篇 |
一般工业技术 | 45017篇 |
冶金工业 | 30338篇 |
原子能技术 | 5002篇 |
自动化技术 | 64111篇 |
出版年
2024年 | 1053篇 |
2023年 | 6382篇 |
2022年 | 11691篇 |
2021年 | 16847篇 |
2020年 | 14921篇 |
2019年 | 12261篇 |
2018年 | 11970篇 |
2017年 | 14862篇 |
2016年 | 18389篇 |
2015年 | 20392篇 |
2014年 | 33576篇 |
2013年 | 30737篇 |
2012年 | 36426篇 |
2011年 | 38645篇 |
2010年 | 29851篇 |
2009年 | 30682篇 |
2008年 | 28492篇 |
2007年 | 36481篇 |
2006年 | 34336篇 |
2005年 | 29815篇 |
2004年 | 24704篇 |
2003年 | 22178篇 |
2002年 | 18165篇 |
2001年 | 15097篇 |
2000年 | 12933篇 |
1999年 | 10101篇 |
1998年 | 7606篇 |
1997年 | 6657篇 |
1996年 | 5716篇 |
1995年 | 4936篇 |
1994年 | 4316篇 |
1993年 | 3209篇 |
1992年 | 2779篇 |
1991年 | 2052篇 |
1990年 | 1818篇 |
1989年 | 1619篇 |
1988年 | 1133篇 |
1987年 | 791篇 |
1986年 | 622篇 |
1985年 | 581篇 |
1984年 | 541篇 |
1983年 | 390篇 |
1982年 | 330篇 |
1981年 | 277篇 |
1980年 | 252篇 |
1979年 | 156篇 |
1978年 | 92篇 |
1977年 | 110篇 |
1962年 | 95篇 |
1959年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 718 毫秒
991.
通过对滨南油区注水现状的调查,发现存在的主要问题是水井套管损坏严重和部分水井欠注。文章全面地介绍了套管损坏井治理和攻欠增注工艺技术在现状的应用。 相似文献
992.
美国21世纪前期的军事战略重点将是争夺外空优势,夺取制天权和制信息权。分析了美国夺取外空优势的原因,及其为夺取外空优势在国家政策、航天发展和技术准备等方面采取的措施。 相似文献
993.
实施油气回收的必要性和技术方案的探讨 总被引:8,自引:0,他引:8
郝保良 《石油化工管理干部学院学报》2002,(2):41-42,69
简要介绍油气回收技术;从环保和增加经济效益的角度,以福建炼化公司的实际情况为例提出了油气回收的方案,并对实行该方案的必要性和经济效益做了分析;希望增强炼化企业对油气回收问题的重视,达到安全生产、改善环境和节约能源的目的。 相似文献
994.
995.
996.
C Brito L Niklitschek L H Molina I Molina 《International Journal of Dairy Technology》2002,55(1):32-39
This study was performed to obtain an adequate tool for predicting the yield of Chilean Gouda cheese. The theoretical yields were calculated by applying equations derived from technical references to industrial cheese production and were compared with their own actual yields, thus selecting those equations showing the best correlation with the actual yield.
The manufacturing and ripening of the cheese were controlled through the chemical composition of milk, whey and cheese, and the weight of the product before and after ripening was recorded.
The actual and theoretical yield values derived from each formula were compared using the mean yield graphs. Furthermore, the global concordance coefficient ( W ) of Kendall and Smith was also applied, showing the lack of significant discrepancy between actual and theoretical yield values [ P > 0.01 ( W = 27; W ≥ 18.48)] for either 3- or 30-day cheeses. Out of the 11 formulae used to measure the yield of cheese, six showing a good correlation between the yields were selected through the comparison of error sums and Pearson correlation analysis. However, two formulae showed the best yield results for practical use. 相似文献
The manufacturing and ripening of the cheese were controlled through the chemical composition of milk, whey and cheese, and the weight of the product before and after ripening was recorded.
The actual and theoretical yield values derived from each formula were compared using the mean yield graphs. Furthermore, the global concordance coefficient ( W ) of Kendall and Smith was also applied, showing the lack of significant discrepancy between actual and theoretical yield values [ P > 0.01 ( W = 27; W ≥ 18.48)] for either 3- or 30-day cheeses. Out of the 11 formulae used to measure the yield of cheese, six showing a good correlation between the yields were selected through the comparison of error sums and Pearson correlation analysis. However, two formulae showed the best yield results for practical use. 相似文献
997.
小浪底水库投入运用后,黄河下游水沙条件的变化,使游荡性河道整治出现了新情况,新问题。下一步治理应注意积极修建新布点工程,完成具有关键性导流作用的续建工程,确定适应新情况的设计治导线,积极开展新结构试验和观测研究。 相似文献
998.
999.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene. 相似文献
1000.