全文获取类型
收费全文 | 1392篇 |
免费 | 223篇 |
国内免费 | 134篇 |
专业分类
化学 | 1050篇 |
晶体学 | 13篇 |
力学 | 42篇 |
综合类 | 3篇 |
数学 | 89篇 |
物理学 | 552篇 |
出版年
2024年 | 5篇 |
2023年 | 39篇 |
2022年 | 59篇 |
2021年 | 55篇 |
2020年 | 86篇 |
2019年 | 76篇 |
2018年 | 58篇 |
2017年 | 50篇 |
2016年 | 69篇 |
2015年 | 78篇 |
2014年 | 86篇 |
2013年 | 93篇 |
2012年 | 129篇 |
2011年 | 125篇 |
2010年 | 85篇 |
2009年 | 65篇 |
2008年 | 85篇 |
2007年 | 83篇 |
2006年 | 58篇 |
2005年 | 53篇 |
2004年 | 39篇 |
2003年 | 29篇 |
2002年 | 28篇 |
2001年 | 19篇 |
2000年 | 11篇 |
1999年 | 22篇 |
1998年 | 20篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1749条查询结果,搜索用时 0 毫秒
51.
52.
针对传统的文本编程效率低下、智能相机只允许本地监视以及监视界面固定等问题,自主研发了一套集图形化编程、任务运行、数据监控等功能于一体的智能相机管理系统;分析了智能相机管理系统在编程、运行与监视过程中的功能需求,并进行系统结构的划分和设计;构建图形化图像处理单元、可视化编程界面以实现图形化编程功能;采用网络通讯方式,实现智能相机配置过程的同步、远程监控以及与其他设备的数据交互;讨论了系统中的数据管理模型;最后,通过应用实例验证该系统在工业生产中的可行性。验证结果表明,该系统能缩短开发时间,降低用户开发成本,并能对生产线上的智能相机进行有效的管理。 相似文献
53.
54.
W. B. Dou T. Shen Z. L. Sun 《International Journal of Infrared and Millimeter Waves》1994,15(7):1247-1253
The scattering of a Gaussian beam by a ferrite cylinder is analyzed using two methods. The spatial pictures in the amplitude of the total Gaussian beam near the cylinder resulting from the two methods are both clarified and compared. The scattering by a ferrite cylinder coating a dielectric sleeve is also presented. 相似文献
55.
Yaping Chen Dr. Kun Rui Prof. Jixin Zhu Prof. Shi Xue Dou Dr. Wenping Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(3):703-713
Developing clean and sustainable energies as alternatives to fossil fuels is in strong demand within modern society. The oxygen evolution reaction (OER) is the efficiency-limiting process in plenty of key renewable energy systems, such as electrochemical water splitting and rechargeable metal–air batteries. In this regard, ongoing efforts have been devoted to seeking high-performance electrocatalysts for enhanced energy conversion efficiency. Apart from traditional precious-metal-based catalysts, nickel-based compounds are the most promising earth-abundant OER catalysts, attracting ever-increasing interest due to high activity and stability. In this review, the recent progress on nickel-based oxide and (oxy)hydroxide composites for water oxidation catalysis in terms of materials design/synthesis and electrochemical performance is summarized. Some underlying mechanisms to profoundly understand the catalytic active sites are also highlighted. In addition, the future research trends and perspectives on the development of Ni-based OER electrocatalysts are discussed. 相似文献
56.
Yandong Dou Kenry Dr. Jiang Liu Jianze Jiang Prof. Qing Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(28):6896-6901
o-Alkenylation of unprotected phenols has been developed by direct C−H functionalization catalyzed by PdII. This work features phenol group as a directing group and realizes highly site-selective C−H bond functionalization of phenols to achieve the corresponding products in moderate to excellent yields at 60 °C. The advantages of this reaction include unprecedented C−H functionalization using phenol as a directing group, high regioselectivity, good substrate scope, mild reaction conditions, and high efficiency. To the best of our knowledge, this is the first example of a regioselective C−H alkenylation of unprotected phenols utilizing phenolic hydroxyl group as a directing group. The alkenylation of unprotected tyrosine and intramolecular cyclization are also successfully carried out under this catalytic system in good yields. Furthermore, this novel method enables a late-stage modification of complex phenol-containing bioactive molecules toward a diversity-oriented drug discovery. 相似文献
57.
58.
Kai Xu Zhenchang Tang Yan Zhang Wanshu Li Haiou Li Lihui Wang Liming Liu Honghang Wang Feng Chi Xiaowen Zhang 《Current Applied Physics》2019,19(10):1076-1081
Germanium dioxide (GeO2) aqueous solutions are facilely prepared and the corresponding anode buffer layers (ABLs) with solution process are demonstrated. Atomic force microscopy, X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements show that solution-processed GeO2 behaves superior film morphology and enhanced work function. Using GeO2 as ABL of organic light-emitting diodes (OLEDs), the visible device with tris(8-hydroxy-quinolinato)aluminium as emitter gives maximum luminous efficiency of 6.5 cd/A and power efficiency of 3.5 lm/W, the ultraviolet device with 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole as emitter exhibits short-wavelength emission with peak of 376 nm, full-width at half-maximum of 42 nm, maximum radiance of 3.36 mW/cm2 and external quantum efficiency of 1.5%. The performances are almost comparable to the counterparts with poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) as ABL. The current, impedance, phase and capacitance as a function of voltage characteristics elucidate that the GeO2 ABL formed from appropriate concentration of GeO2 aqueous solution favors hole injection enhancement and accordingly promoting device performance. 相似文献
59.
Science China Chemistry - 相似文献
60.
Zheng Yang Xiaowen Zhao Yuqiao Ding Qin Yang 《Journal of Macromolecular Science: Physics》2019,58(1):113-127
A series of phenolic epoxy resin (PEP) modified polyurethane foams (PUF) were prepared via an in-situ polymerization, one step process. It was found that the epoxy modified PUF foam exhibited a perforated network structure with larger cell size, higher open cell porosity and enhanced ovality compared with pure PUF. With increasing content of PEP, the tensile strength, elongation at break and low temperature modulus of PUF decreased. A single Tg was observed for PEP modified PUF, indicating that the two component phases of the polyurethane-epoxy were miscible. With increasing PEP content, the Tg of PUF shifted slightly to higher temperature, tan δmax dropped to lower values, and the retention value of the storage modulus at ?20 and ?10?°C increased. For pure PUF, the cell walls degraded and the structure became disordered after aging under heat and stress, while for PUF/20wt%PEP, the degradation degree was obviously reduced, and an orientation of the cells along the stress direction and a density increase was observed. During aging at 200?°C, the retention of the mechanical properties of PUF/20wt% PEP was much higher than that of pure PUF, and it showed superior stability under heat and stress, attributed to incorporation of the thermally resistant oxazolidone rings and benzene rings in the PU backbones, the highly cross-linked networks of the polyurethane-epoxy systems and the obvious orientation of the cells under stress. 相似文献