全文获取类型
收费全文 | 3992篇 |
免费 | 530篇 |
国内免费 | 426篇 |
专业分类
电工技术 | 218篇 |
综合类 | 315篇 |
化学工业 | 265篇 |
金属工艺 | 186篇 |
机械仪表 | 201篇 |
建筑科学 | 170篇 |
矿业工程 | 98篇 |
能源动力 | 66篇 |
轻工业 | 189篇 |
水利工程 | 56篇 |
石油天然气 | 31篇 |
武器工业 | 36篇 |
无线电 | 867篇 |
一般工业技术 | 424篇 |
冶金工业 | 126篇 |
原子能技术 | 63篇 |
自动化技术 | 1637篇 |
出版年
2024年 | 10篇 |
2023年 | 53篇 |
2022年 | 77篇 |
2021年 | 98篇 |
2020年 | 111篇 |
2019年 | 118篇 |
2018年 | 109篇 |
2017年 | 138篇 |
2016年 | 157篇 |
2015年 | 176篇 |
2014年 | 240篇 |
2013年 | 292篇 |
2012年 | 352篇 |
2011年 | 316篇 |
2010年 | 237篇 |
2009年 | 257篇 |
2008年 | 298篇 |
2007年 | 297篇 |
2006年 | 271篇 |
2005年 | 214篇 |
2004年 | 181篇 |
2003年 | 165篇 |
2002年 | 105篇 |
2001年 | 111篇 |
2000年 | 119篇 |
1999年 | 70篇 |
1998年 | 63篇 |
1997年 | 61篇 |
1996年 | 48篇 |
1995年 | 37篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 25篇 |
1991年 | 16篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1972年 | 2篇 |
1955年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有4948条查询结果,搜索用时 15 毫秒
1.
利用猪毛、风化煤和腐植酸钠的水解液为增效剂制备了一种增效过磷酸钙,探讨了增效过磷酸钙的增效机制及其对玉米生长的影响。结果表明,蒸馏水浸提条件下,增效过磷酸钙能减缓水溶磷的释放,具备较高的pH值缓冲性。与普通过磷酸钙相比,增效过磷酸钙处理的玉米生物量平均增加了41.9%,吸磷量和吸钙量分别增加了61.7%和27.8%,根系活力增加了24.3%。该研究结果对过磷酸钙生产的技术改进具有指导意义。 相似文献
2.
The pharmacy service requires that some pharmacies are always available and shifts have to be organized: a shift corresponds to a subset of pharmacies that must be open 24 hours a day on a particular week. Under the requirement that each pharmacy belongs to exactly one shift and the assumption that users minimize the distance to the closest open pharmacy during each shift, we want to determine a partition of the pharmacies into a given number of shifts, such that the total distance covered by users is minimized. It may be also required that shift cardinalities are balanced. We discuss different versions and the related computational complexity, showing that the problem is NP-hard in general. A set packing formulation is presented and solved by branch-and-price, together with a fast solution technique based on a tabu search. They have been applied to real and random instances showing that (i) the set packing formulation is very tight and often exhibits no integrality gap; (ii) the branch-and-price solves problems of practical relevance to optimality in a reasonable amount of time (order of minutes); (iii) the tabu search finds optimal or near-optimal solutions in order of seconds. 相似文献
3.
Journal of Computer Science and Technology - New non-volatile memory (NVM) technologies are expected to replace main memory DRAM (dynamic random access memory) in the near future. NAND flash... 相似文献
4.
Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk. 相似文献
5.
提出了一种基于光纤环的光缓存器的结构,对结合半导体光放大器作光开关的此结构的物理模型进行了详细描述,并根据此模型分析了其增益、噪声、信噪比等方面的特性. 相似文献
6.
7.
8.
9.
本文对分布式数据库的设计方法、分割与分配技术作了一些探讨,并就分布式数据库的发展方向进行了初步分析。 相似文献
10.
Jean‐Marc Aldric Philippe Thonart 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1401-1408
BACKGROUND: In the framework of biological processes used for waste gas treatment, the impact of the inoculum size on the start‐up performance needs to be better evaluated. Moreover, only a few studies have investigated the behaviour of elimination capacity and biomass viability in a two‐phase partitioning bioreactor (TPPB) used for waste gas treatment. Lastly, the impact of ethanol as a co‐substrate remains misunderstood. RESULTS: Firstly, no benefit of inoculation with a high cellular density (>1.5 g L?1) was observed in terms of start‐up performance. Secondly, the TPPB was monitored for 38 days to characterise its behaviour under several operational conditions. The removal efficiency remained above 63% for an inlet concentration of 7 g isopropylbenzene (IPB) m?3 and at some time points reached 92% during an intermittent loading phase (10 h day?1), corresponding to a mean elimination capacity of 4 × 10?3 g L?1 min?1 (240 g m?3 h?1) for a mean IPB inlet load of 6.19 × 10?3 g L?1 min?1 (390 g m?3 h?1). Under continuous IPB loading, the performance of the TPPB declined, but the period of biomass acclimatisation to this operational condition was shorter than 5 days. The biomass grew to approximately 10 g L?1 but the cellular viability changed greatly during the experiment, suggesting an endorespiration phenomenon in the bioreactor. It was also shown that simultaneous degradation of IPB and ethanol occurred, suggesting that ethanol improves the biodegradation process without causing oxygen depletion. CONCLUSION: A water/silicone oil TPPB with ethanol as co‐substrate allowed the removal of a high inlet load of IPB during an experiment lasting 38 days. Copyright © 2008 Society of Chemical Industry 相似文献