全文获取类型
收费全文 | 96048篇 |
免费 | 8857篇 |
国内免费 | 5304篇 |
专业分类
电工技术 | 6527篇 |
技术理论 | 4篇 |
综合类 | 7427篇 |
化学工业 | 14934篇 |
金属工艺 | 5484篇 |
机械仪表 | 6026篇 |
建筑科学 | 7924篇 |
矿业工程 | 2474篇 |
能源动力 | 2693篇 |
轻工业 | 9115篇 |
水利工程 | 2068篇 |
石油天然气 | 4577篇 |
武器工业 | 988篇 |
无线电 | 11020篇 |
一般工业技术 | 10388篇 |
冶金工业 | 4120篇 |
原子能技术 | 1160篇 |
自动化技术 | 13280篇 |
出版年
2024年 | 361篇 |
2023年 | 1427篇 |
2022年 | 2815篇 |
2021年 | 3830篇 |
2020年 | 2920篇 |
2019年 | 2320篇 |
2018年 | 2642篇 |
2017年 | 2956篇 |
2016年 | 2720篇 |
2015年 | 3987篇 |
2014年 | 4949篇 |
2013年 | 6049篇 |
2012年 | 6989篇 |
2011年 | 7544篇 |
2010年 | 6716篇 |
2009年 | 6451篇 |
2008年 | 6509篇 |
2007年 | 6085篇 |
2006年 | 5613篇 |
2005年 | 4665篇 |
2004年 | 3331篇 |
2003年 | 2832篇 |
2002年 | 2740篇 |
2001年 | 2333篇 |
2000年 | 1953篇 |
1999年 | 1724篇 |
1998年 | 1417篇 |
1997年 | 1165篇 |
1996年 | 1068篇 |
1995年 | 896篇 |
1994年 | 676篇 |
1993年 | 590篇 |
1992年 | 394篇 |
1991年 | 325篇 |
1990年 | 300篇 |
1989年 | 198篇 |
1988年 | 152篇 |
1987年 | 108篇 |
1986年 | 92篇 |
1985年 | 60篇 |
1984年 | 53篇 |
1983年 | 34篇 |
1982年 | 36篇 |
1981年 | 29篇 |
1980年 | 40篇 |
1979年 | 15篇 |
1977年 | 12篇 |
1976年 | 16篇 |
1973年 | 11篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
Telecommunication Systems - Machine to Machine technology has a broad application prospect in the 5G network, but there is a bottleneck in the energy consumption of intelligent devices powered by... 相似文献
12.
Xueru Chen Yin Zhang Dashui Yuan Wu Huang Jing Ding Hui Wan Wei-Lin Dai Guofeng Guan 《材料科学技术学报》2021,71(12):211-220
Porous g-C3N4 nanosheets (PCN) were prepared by the nickel-assisted one-step thermal polymerization method.Hydrogen (H2) which was produced by the reaction between nickel (Ni) foam and ammonia (NH3) defined the structure and properties of PCN.During the formation of PCN,the participation of H2 not only enhanced the spacing between layers but also boosted the specific surface area that more active sites were exposed.Additionally,H2 promoted pores formation in the nanosheets,which was beneficial to the transfer of photons through lamellar structure and improved the absorption efficiency of visible light.Remarkably,the obtained PCN possessed better Cr(Ⅵ) photocatalytic reduction efficiency than pure g-C3N4.The reaction rate constant (k) of PCN (0.013 min-1) was approximately twice that of bare g-C3N4 (0.007 min-1).Furthermore,the effects of original pH and concentration of Cr(Ⅵ)-containing solution on removal efficiency of Cr(Ⅵ) were explored.A possible photocatalytic mechanism was proposed based on the experiments of radical scavengers and photoelectrochemical characterizations. 相似文献
13.
Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl3) and hexamethyldisilazane (HN(SiMe3)2) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl3 and HN(SiMe3)2 to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl3 and HN(SiMe3)2 alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl3 with more heat released compared to that for the introduction of HN(SiMe3)2. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions. 相似文献
14.
石油和天然气行业不断关注增材制造技术在航空航天和汽车行业的应用发展。研发了利用增材制造技术的超高膨胀封隔器,该封隔器的支承环系统由增材制造。增材制造设计大幅减少了支承系统的构件数量,同时显著提高了膨胀能力和额定压力。密封元件系统与增材制造支承环安装在一起,提供了极端膨胀比、零挤压间隙和对不规则孔的良好适应性。分析和测试结果表明:直径膨胀比高达111%,与常规封隔器相比,提高50%以上; 至少涵盖5种线重的套管(外径相同); 在148.89 ℃的温度下,密封元件能够保持压力68.95 MPa。介绍了增材制造技术、增材制造支承环概念、增材制造材料力学性能、密封元件系统优化和测试情况,以期给我国的完井作业提供借鉴。 相似文献
15.
16.
Science China Technological Sciences - Accurate modelling of lithium ion batteries is crucial for battery management in electric vehicles. Recent studies have revealed the fractional order nature... 相似文献
17.
18.
19.
反应堆屏蔽计算中经常出现厚屏蔽、小探测器问题,常规蒙特卡罗方法难以有效解决。基于自动重要抽样(AIS)方法,本文提出了小探测器自动重要抽样(SDAIS)方法,并针对小探测器问题,优化了AIS方法的虚粒子赌分裂算法。该方法在自主开发的蒙特卡罗屏蔽程序MCShield上进行了实现。使用NUREG/CR-6115 PWR基准题验证该方法的正确性和计算效率。结果表明,SDAIS方法可有效地解决厚屏蔽小探测器问题,相比AIS方法及传统的重要性方法,计算效率提升1~2个量级。 相似文献
20.
Qi Yang Qilong Wu Yang Liu Shuiping Luo Xiaotong Wu Xixia Zhao Haiyuan Zou Baihua Long Wen Chen Yujia Liao Lanxi Li Pei Kang Shen Lele Duan Zewei Quan 《Advanced materials (Deerfield Beach, Fla.)》2020,32(36):2002822
Engineering novel Sn-based bimetallic materials could provide intriguing catalytic properties to boost the electrochemical CO2 reduction. Herein, the first synthesis of homogeneous Sn1−xBix alloy nanoparticles (x up to 0.20) with native Bi-doped amorphous SnOx shells for efficient CO2 reduction is reported. The Bi-SnOx nanoshells boost the production of formate with high Faradaic efficiencies (>90%) over a wide potential window (−0.67 to −0.92 V vs RHE) with low overpotentials, outperforming current tin oxide catalysts. The state-of-the-art Bi-SnOx nanoshells derived from Sn0.80Bi0.20 alloy nanoparticles exhibit a great partial current density of 74.6 mA cm−2 and high Faradaic efficiency of 95.8%. The detailed electrocatalytic analyses and corresponding density functional theory calculations simultaneously reveal that the incorporation of Bi atoms into Sn species facilitates formate production by suppressing the formation of H2 and CO. 相似文献