全文获取类型
收费全文 | 33174篇 |
免费 | 2382篇 |
国内免费 | 1204篇 |
专业分类
电工技术 | 1498篇 |
综合类 | 1922篇 |
化学工业 | 5867篇 |
金属工艺 | 1560篇 |
机械仪表 | 1896篇 |
建筑科学 | 2998篇 |
矿业工程 | 610篇 |
能源动力 | 1050篇 |
轻工业 | 2049篇 |
水利工程 | 478篇 |
石油天然气 | 1810篇 |
武器工业 | 210篇 |
无线电 | 4061篇 |
一般工业技术 | 4365篇 |
冶金工业 | 1774篇 |
原子能技术 | 433篇 |
自动化技术 | 4179篇 |
出版年
2024年 | 92篇 |
2023年 | 444篇 |
2022年 | 684篇 |
2021年 | 1074篇 |
2020年 | 841篇 |
2019年 | 721篇 |
2018年 | 792篇 |
2017年 | 931篇 |
2016年 | 853篇 |
2015年 | 1108篇 |
2014年 | 1442篇 |
2013年 | 1861篇 |
2012年 | 1962篇 |
2011年 | 2127篇 |
2010年 | 1784篇 |
2009年 | 1792篇 |
2008年 | 1744篇 |
2007年 | 1726篇 |
2006年 | 1772篇 |
2005年 | 1599篇 |
2004年 | 1100篇 |
2003年 | 987篇 |
2002年 | 979篇 |
2001年 | 830篇 |
2000年 | 909篇 |
1999年 | 978篇 |
1998年 | 966篇 |
1997年 | 783篇 |
1996年 | 779篇 |
1995年 | 639篇 |
1994年 | 499篇 |
1993年 | 455篇 |
1992年 | 311篇 |
1991年 | 228篇 |
1990年 | 230篇 |
1989年 | 161篇 |
1988年 | 130篇 |
1987年 | 92篇 |
1986年 | 73篇 |
1985年 | 52篇 |
1984年 | 45篇 |
1983年 | 31篇 |
1982年 | 32篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1973年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
水和甲醇存在下MAMS的消失反应动力学研究 总被引:1,自引:0,他引:1
通过实验研究了甲基丙烯酰胺硫酸盐(MAMS)与甲醇、水进行反应的动力学,并对该反应的机理进行了探讨。 相似文献
994.
995.
膜法富氧技术及其应用研究 总被引:12,自引:0,他引:12
介绍了作者在膜法富氧技术方面的研究进展,并将膜法与其他制氧方法进行了比较,最后讨论了膜法富氧技术目前的有关应用,着重研究了膜法富氧在有色金属冶炼,硅酸盐窑炉,化铁炉,加热炉,医疗保健和柴油机增氧等方面的典型应用。 相似文献
996.
Dajun Shen 《国际水》2013,38(4):484-496
China's rivers face major challenges arising from social and economic development, particularly associated with pollution and over-abstraction. Although these issues vary significantly across the country, China has adopted a national, unified approach to manage water resources in a river basin context. This paper assesses the legal and institutional arrangements for river basin management in terms of decentralization and centralization. It considers the appropriate roles for the different levels of government, including providing for participation and integration across these levels. It proposes strengthening institutional development and capacity building in the future. 相似文献
997.
998.
In order to improve the electrochemical performance and thermal stability of Li1.05Co1/3Ni1/3Mn1/3O2 materials,Li1.05Co0.3Ni0.35Mn0.3M0.05O2(M=Ge,Sn)cathode materials were synthesized via co-precipitation method.The structure,electrochemical performance and thermal stability were characterized by X-ray diffraction(XRD),charge/discharge cycling,cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS)and differential scanning calorimetry(DSC).ESEM showed that Sn-doped and Ge-doped slightly increased the size of grains.XRD and CV showed that Sn-doped and Ge-doped powders were homogeneous and had the better layered structure than the bare one.Sn-doped and Ge-doped improved high rate discharge capacity and cycle-life performance.The reason of the better cycling performance of the doped one was the increasing of lithium-ion diffusion rate and charge transfer rate.Sn-doped and Ge-doped also improved the mateials thermal stability. 相似文献
999.
Pressure relief to increase permeability significantly improves gas extraction efficiency from coal seams. In this paper we report results from simulations using FLAC3D code to analyze changes in coal displacement and stress after special drill slots were formed. We investigated the mechanism of pressure relief and permeability increase in a high-gas and low-permeability coal seam through the modeling of gas flow. This allows the development of the technology. Slotting across rock layers in the coal seam with a rotary type cutter was then applied in the field. The results show that pressure relief and permeability increases from slotting the coal seam can increase the transport and the fracture of the coal. This expands the range of pressure relief from the drilling and increases the exposed area of the seam. The total quantity of gas extracted from slotted bore holes was three times that seen with ordinary drilling. The concentration of gas extracted from the slotted drills was from two to three times that seen using ordinary drills. The gas flow was stable at 80%. Improved permeability and more efficient gas extraction are the result of the slotting. The roadway development rate is increased by 30–50% after gas drainage. This technology diminishes the lag between longwall production and roadway development and effectively prevents coal and gas outburst, which offers the prospect of broad application. 相似文献
1000.
Difficulties with soft coal seams having a high gas content and high stress levels can be addressed by a technology of pressure relief and permeability increase. Slotting the seam by auxiliary drilling with a water jet that breaks the coal and slots the coal seam during the process of retreat drilling achieves pressure relief and permeability increase. Improved efficiency of gas extraction from a field test, high gas coal seam was observed. Investigating the theory of pressure relief and permeability increase required analyzing the characteristics of the double power slotting process and the effects of coal pressure relief and permeability increase. The influence of confining pressure on coal physical properties was examined by using FLAC3D software code to simulate changes of coal stress within the tool destruction area. The double power joint drilling method was modeled. Field experiments were performed and the effects are analyzed. This research shows that there is an “islanding effect” in front of the joint double power drill and slotting equipment. The failure strength of the coal seam is substantially reduced within the tool destruction area. Drilling depths are increased by 72% and the diameter of the borehole is increased by 30%. The amount of powdered coal extracted from the drill head increases by 17 times when using the new method. A 30 day total flow measurement from the double power drilled and slotted bores showed that gas extraction increased by 1.3 times compared to the standard drilled bores. Gas concentrations increased from 30% to 60% and were more stable so the overall extraction efficiency increased by a factor of two times. 相似文献