全文获取类型
收费全文 | 89015篇 |
免费 | 7878篇 |
国内免费 | 4072篇 |
专业分类
电工技术 | 5102篇 |
技术理论 | 8篇 |
综合类 | 6122篇 |
化学工业 | 14845篇 |
金属工艺 | 5253篇 |
机械仪表 | 5565篇 |
建筑科学 | 6463篇 |
矿业工程 | 3016篇 |
能源动力 | 2793篇 |
轻工业 | 6500篇 |
水利工程 | 1594篇 |
石油天然气 | 5225篇 |
武器工业 | 686篇 |
无线电 | 9889篇 |
一般工业技术 | 10718篇 |
冶金工业 | 4613篇 |
原子能技术 | 1102篇 |
自动化技术 | 11471篇 |
出版年
2024年 | 275篇 |
2023年 | 1371篇 |
2022年 | 2267篇 |
2021年 | 3595篇 |
2020年 | 2716篇 |
2019年 | 2393篇 |
2018年 | 2657篇 |
2017年 | 2889篇 |
2016年 | 2642篇 |
2015年 | 3564篇 |
2014年 | 4515篇 |
2013年 | 5386篇 |
2012年 | 5720篇 |
2011年 | 6033篇 |
2010年 | 5499篇 |
2009年 | 4958篇 |
2008年 | 4875篇 |
2007年 | 4647篇 |
2006年 | 4794篇 |
2005年 | 4125篇 |
2004年 | 2813篇 |
2003年 | 2846篇 |
2002年 | 3262篇 |
2001年 | 2745篇 |
2000年 | 2271篇 |
1999年 | 2317篇 |
1998年 | 1726篇 |
1997年 | 1455篇 |
1996年 | 1366篇 |
1995年 | 1207篇 |
1994年 | 958篇 |
1993年 | 627篇 |
1992年 | 531篇 |
1991年 | 430篇 |
1990年 | 326篇 |
1989年 | 270篇 |
1988年 | 230篇 |
1987年 | 138篇 |
1986年 | 115篇 |
1985年 | 80篇 |
1984年 | 61篇 |
1983年 | 40篇 |
1982年 | 47篇 |
1981年 | 38篇 |
1980年 | 39篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
我国是煤炭资源大国,煤层气储量规模相当可观,但煤储层又具有低孔、低渗的不足,照搬国外或常规石油天然气的开采程序和方法已被证实是走不通的。应结合实际,根据不同地质条件、不同煤阶的开采程序,进行孔隙特征研究。煤孔隙特征、连通性和吸附能力对煤层气开采影响尤为重要,为研究煤孔隙结构特征随煤变质程度的变化关系及其吸附能力的响应特点,采取不同地区不同变质程度煤样,进行压汞测试和等温吸附实验。实验结果表明,煤孔隙度和平均孔径均随变质程度增加呈现降低—升高—降低的趋势;煤中孔隙连通性随煤变质程度增加逐渐变差;随煤变质程度增加,其最大吸附能力也呈现降低—升高—降低的总体趋势。 相似文献
92.
在煤矿测量工作中,贯通测量是其中重要工作之一,确保贯通点的误差在设定的范围内,决定了贯通测量的成败。本文将马脊梁煤矿副立井与王村回风立井的贯通作为研究对象,选择使用井下控制测量、竖井联系测量及陀螺定向技术等,设定了贯通测量的方案,开展了误差预计,通过对比预计结果和要求,保证了贯通测量设计的可行性。 相似文献
93.
A novel dual-rotation bobbin tool friction stir welding (DBT-FSW) was developed, in which the upper shoulder (US) and lower shoulder (LS) have different rotational speeds. This process was tried to weld 3.2 mm thick aluminum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formability. Experimental results show that compared to conventional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process. 相似文献
94.
正据《亚洲橡胶》(www. rubberasia. com)2018年9月25日报道,缅甸联邦共和国加入天然橡胶生产国协会(ANRPC),使ANRPC成员国数量增加至13个。ANRPC所有成员国的天然橡胶总产量达到世界天然橡胶总产量的90. 5%。2017年6月至2018年6月,缅甸天然橡胶产量为24. 2万t,橡胶树开割面积仅为31. 1万hm~2。缅甸 相似文献
95.
96.
97.
Carbohydrates and their conjugates play important roles in many biological processes including fertilization, differentiation, development, immune response, and infection. Their activities are largely dependent on the properties of terminal mono‐ or disaccharides. Galactose, mannose, fucose, glucose, sialic acid, etc., are commonly used as powerful scaffolds installed on drug molecules for targeting specific tissues including brain, liver, and cancers, and as epitopes for enhancing the targeting of various vaccines. This review focuses on the influence of their structural variations, including changes in sugar type, substituent groups and their positions, as well as length of linker portion, on the targeting of drugs or their efficacy. Particular attention is paid to the targeting properties of mono‐ and disaccharides applied in drug design and discovery. 相似文献
99.
Microsystem Technologies - Recently, nonlinear system identification has received increasingly more attention due to its promising applications in engineering fields. It has become a challenging... 相似文献
100.
Xiangrong Ma Rui Dang Ning Yang Xiao Li Ya zhang Ying Gong Zhipan Liu Wei Guo Yuanyuan Zhang Chunyan Li 《International Journal of Hydrogen Energy》2021,46(44):22842-22851
The high cost of noble metal catalysts has been a great bottleneck for the catalyst industry. Using the noble metal at a single-atom level for catalytic applications could dramatically decrease the cost. The impacts of single Pt atoms on the photocatalytic performance of Ag3VO4 have been investigated and reported. In this report, single Pt atoms were anchored on the surface of Ag3VO4 (AVO) as a cocatalyst, and the resultant composite photocatalyst has been studied for photocatalytic H2 production from water driven by visible light. The as-prepared AVO particles are hollow nanospheres in the monoclinic phase with a bandgap of 2.20 eV. The light absorption edge of AVO/Pt is slightly red-shifted compared to that of the pristine AVO, indicating more visible light absorption of AVO/Pt. The XPS peaks of Ag, V, and Pt exhibit a significant shift after AVO and Pt get into contact, suggesting the strong interaction between the surface Ag and V atoms, and single Pt atoms. After 3-h illumination, the photocatalytic H2 evolution amount from AVO/Pt is improved up to 1400 μmol, which is 2.8 times that on the bare AVO. Such efficient photocatalytic H2 evolution on AVO/Pt is still maintained after five reaction cycles. The better photocatalytic performance of AVO/Pt has been attributed to the more efficient visible light utilization and the lower interfacial charge transfer resistance, as demonstrated in the DRS and EIS spectra. The presence of the surface Pt atoms also leads to a higher amount of reactive radicals, which could efficiently promote the surface redox reactions. 相似文献