全文获取类型
收费全文 | 105711篇 |
免费 | 10597篇 |
国内免费 | 6101篇 |
专业分类
电工技术 | 7832篇 |
技术理论 | 6篇 |
综合类 | 8320篇 |
化学工业 | 16129篇 |
金属工艺 | 5920篇 |
机械仪表 | 6992篇 |
建筑科学 | 8843篇 |
矿业工程 | 2839篇 |
能源动力 | 3146篇 |
轻工业 | 7220篇 |
水利工程 | 2254篇 |
石油天然气 | 5697篇 |
武器工业 | 1031篇 |
无线电 | 12725篇 |
一般工业技术 | 12177篇 |
冶金工业 | 4144篇 |
原子能技术 | 1370篇 |
自动化技术 | 15764篇 |
出版年
2024年 | 550篇 |
2023年 | 1752篇 |
2022年 | 3308篇 |
2021年 | 4577篇 |
2020年 | 3465篇 |
2019年 | 2796篇 |
2018年 | 2964篇 |
2017年 | 3420篇 |
2016年 | 3135篇 |
2015年 | 4205篇 |
2014年 | 5334篇 |
2013年 | 6331篇 |
2012年 | 7203篇 |
2011年 | 7650篇 |
2010年 | 6815篇 |
2009年 | 6623篇 |
2008年 | 6692篇 |
2007年 | 6125篇 |
2006年 | 6041篇 |
2005年 | 4905篇 |
2004年 | 3577篇 |
2003年 | 3477篇 |
2002年 | 4019篇 |
2001年 | 3530篇 |
2000年 | 2716篇 |
1999年 | 2392篇 |
1998年 | 1641篇 |
1997年 | 1393篇 |
1996年 | 1291篇 |
1995年 | 1018篇 |
1994年 | 847篇 |
1993年 | 635篇 |
1992年 | 475篇 |
1991年 | 348篇 |
1990年 | 259篇 |
1989年 | 232篇 |
1988年 | 213篇 |
1987年 | 136篇 |
1986年 | 77篇 |
1985年 | 60篇 |
1984年 | 40篇 |
1983年 | 26篇 |
1982年 | 37篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1976年 | 2篇 |
1971年 | 2篇 |
1959年 | 5篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
21.
Lili Hao Jiaxiang Li Peng Wang Zongliang Wang Zhenxu Wu Yu Wang Zixue Jiao Min Guo Tongfei Shi Qigang Wang Yoshihiro Ito Yen Wei Peibiao Zhang 《Advanced functional materials》2021,31(15):2009661
The degradation behavior of implants is significantly important for bone repair. However, it is still unprocurable to spatiotemporally regulate the degradation of the implants to match bone ingrowth. In this paper, a magneto-controlled biodegradation model is established to explore the degradation behavior of magnetic scaffolds in a magnetothermal microenvironment generated by an alternating magnetic field (AMF). The results demonstrate that the scaffolds can be heated by magnetic nanoparticles (NPs) under AMF, which dramatically accelerated scaffold degradation. Especially, magnetic NPs modified by oleic acid with a better interface compatibility exhibit a greater heating efficiency to further facilitate the degradation. Furthermore, the molecular dynamics simulations reveal that the enhanced motion correlation between magnetic NPs and polymer matrix can accelerate the energy transfer. As a proof-of-concept, the feasibility of magneto-controlled degradation for implants is demonstrated, and an optimizing strategy for better heating efficiency of nanomaterials is provided, which may have great instructive significance for clinical medicine. 相似文献
22.
Wireless Networks - TCP latency is critical to the performance of Web services. However, packet loss greatly impairs the TCP performance due to its poor loss recovery mechanisms. Recent work FUSO... 相似文献
23.
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
24.
25.
Nan Wu Xiaodong Li Mu Zhang Yi Ren Qi Zhu Haijun Peng Hongqiang Ru Xudong Sun 《Journal of the European Ceramic Society》2021,41(4):2898-2907
Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd2O3-MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd2O3-MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3?6 μm wavelength range, due mainly to its extremely fine-grain size of Gd2O3 and MgO (93 and 78 nm, respectively) and high density. 相似文献
26.
27.
World Wide Web - Rule mechanism has been widely used in many areas, such as databases, artificial intelligent and pervasive computing. In a rule mechanism, rule activation decides which rules are... 相似文献
28.
29.
30.
Xian Suo Xili Cui Lifeng Yang Nan Xu Yuqi Huang Yi He Sheng Dai Huabin Xing 《Advanced materials (Deerfield Beach, Fla.)》2020,32(29):1907601
The design of highly stable and efficient porous materials is essential for developing breakthrough hydrocarbon separation methods based on physisorption to replace currently used energy-intensive distillation/absorption technologies. Efforts to develop advanced porous materials such as zeolites, coordination frameworks, and organic polymers have met with limited success. Here, a new class of ionic ultramicroporous polymers (IUPs) with high-density inorganic anions and narrowly distributed ultramicroporosity is reported, which are synthesized by a facile free-radical polymerization using branched and amphiphilic ionic compounds as reactive monomers. A covalent and ionic dual-crosslinking strategy is proposed to manipulate the pore structure of amorphous polymers at the ultramicroporous scale. The IUPs exhibit exceptional selectivity (286.1–474.4) for separating acetylene from ethylene along with high thermal and water stability, collaboratively demonstrated by gas adsorption isotherms and experimental breakthrough curves. Modeling studies unveil the specific binding sites for acetylene capture as well as the interconnected ultramicroporosity for size sieving. The porosity-engineering protocol used in this work can also be extended to the design of other ultramicroporous materials for the challenging separation of other key gas constituents. 相似文献