全文获取类型
收费全文 | 534666篇 |
免费 | 6509篇 |
国内免费 | 1600篇 |
学科分类
工业技术 | 542775篇 |
出版年
2021年 | 3842篇 |
2020年 | 2891篇 |
2019年 | 3639篇 |
2018年 | 12944篇 |
2017年 | 13519篇 |
2016年 | 10487篇 |
2015年 | 4659篇 |
2014年 | 7482篇 |
2013年 | 21345篇 |
2012年 | 13865篇 |
2011年 | 23068篇 |
2010年 | 19420篇 |
2009年 | 20279篇 |
2008年 | 20963篇 |
2007年 | 22644篇 |
2006年 | 14009篇 |
2005年 | 15487篇 |
2004年 | 13711篇 |
2003年 | 13495篇 |
2002年 | 11955篇 |
2001年 | 11901篇 |
2000年 | 11300篇 |
1999年 | 11752篇 |
1998年 | 29047篇 |
1997年 | 20406篇 |
1996年 | 15801篇 |
1995年 | 12152篇 |
1994年 | 10833篇 |
1993年 | 10725篇 |
1992年 | 7978篇 |
1991年 | 7595篇 |
1990年 | 7320篇 |
1989年 | 6891篇 |
1988年 | 6660篇 |
1987年 | 5777篇 |
1986年 | 5610篇 |
1985年 | 6379篇 |
1984年 | 5902篇 |
1983年 | 5475篇 |
1982年 | 5135篇 |
1981年 | 5006篇 |
1980年 | 4806篇 |
1979年 | 4580篇 |
1978年 | 4261篇 |
1977年 | 5138篇 |
1976年 | 6704篇 |
1975年 | 3812篇 |
1974年 | 3734篇 |
1973年 | 3713篇 |
1972年 | 3104篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Wireless Personal Communications - In recent years, the emergence of Internet of things and cyber-physical system provide a proactive and efficacious solution to enable remote monitoring, machine... 相似文献
32.
Multimedia Tools and Applications - In this paper, a hashing based watermarking technique for the protection and authentication of document image is proposed. Message Digest 5 (MD5) hashing is... 相似文献
33.
Heiba Zein K. Mohamed Mohamed Bakr Farag Noura M. Badawi Ali 《Journal of Materials Science: Materials in Electronics》2022,33(13):10388-10398
Journal of Materials Science: Materials in Electronics - Nano Mn0.95M0.05S (M ≡ Cu, Mg) samples were produced using molten salt solid state reaction method. Rietveld analysis of X-ray... 相似文献
34.
Radiochemistry - Magnetically modified waste bark of the Aegle marmelos tree was prepared by using green synthesis method and was used in a batch system for U(VI) removal from aqueous solution. The... 相似文献
35.
Laís D. Silva Fernanda C. Puosso Viviane O. Soares Oscar Peitl Filho Simone do R.F. Sabino Francisco C. Serbena Murilo C. Crovace Edgar D. Zanotto 《Ceramics International》2021,47(13):18720-18731
Bioactive glasses and glass-ceramics (GCs) effectively regenerate bone tissue, however most GCs show improved mechanical properties. In this work, we developed and tested a rarely studied bioactive glass composition (24.4K2O-26.9CaO-46.1SiO2-2.6P2O5 mol%, identified as 45S5-K) with different particle sizes and heating rates to obtain a sintered GC that combines good fracture strength, low elastic modulus, and bioactivity. We analyzed the influence of the sintering processing conditions in the elastic modulus, Vickers microhardness, density, and crystal phase formation in the GC. The best GC shows improved properties compared with its parent glass. This glass achieves a good densification degree with a two-step viscous flow sintering approach and the resulting GC shows as high bioactivity as that of the standard 45S5 Bioglass®. Furthermore, the GC elastic modulus (56 GPa) is relatively low, minimizing stress shielding. Therefore, we unveiled the glass sintering behavior with concurrent crystallization of this complex bioactive glass composition and developed a potential GC for bone regeneration. 相似文献
36.
This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al2O3)-doped V2O5 ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V2O5 phase formation with increasing strain on the doping of Al2O3 in place of V2O5 in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO5] polyhedra converts into [VO4] polyhedra on the doping of Al2O3 into V2O5. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability. 相似文献
37.
Belov M. I. Anashin D. V. Kabdin N. E. Storchevoy V. F. Sudnik Yu. A. 《Russian Engineering Research》2022,42(11):1110-1116
Russian Engineering Research - The stability of robot-mower motion in a specific direction is considered. The direction is regulated by means of an angular sensor and a programmable controller... 相似文献
38.
Precipitation of calcium deficient hydroxyapatite nanoparticles in an environmentally benign manner by using only dilute solutions of calcium hydroxide and phosphoric acid without pH adjustment and addition of other chemicals, and water, being the only by-product was investigated by using continuous flow Vortex Reactor (VR) and Semi-Batch Reactor (SBR). The effect of hydrodynamics by changing the Reynolds number of the jets providing residence times of 8.4 ms to 4.37 s for VR, and by changing the stirrer speed between 100 rpm (Re = 2656) and 1000 rpm (Re = 26560) for SBR, on the particle size, particle size distribution, and morphology of the particles was investigated for both systems. It has been shown that it is possible to produce pure phase hydroxyapatite nanoparticles in the desired morphology by changing production system, without resorting to additives. While VR produced rod-like particles with the crystallite size around 4 nm, SBR produced spherical particles with the crystallite size of around 5 nm. 相似文献
39.
Belcher Calvin H. Zheng Baolong MacDonald Benjamin E. Langlois Eric D. Lehman Benjamin Pearce Charles Delaney Robert Apelian Diran Lavernia Enrique J. Monson Todd C. 《Journal of Materials Science》2022,57(9):5518-5532
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic... 相似文献
40.
Mohammed Amin Salih Venkatachalam K. Hubálovský S. Trojovský P. Prabu P. 《Mobile Networks and Applications》2022,27(3):1050-1059
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via... 相似文献