全文获取类型
收费全文 | 2768篇 |
免费 | 520篇 |
国内免费 | 411篇 |
专业分类
化学 | 2086篇 |
晶体学 | 17篇 |
力学 | 162篇 |
综合类 | 23篇 |
数学 | 311篇 |
物理学 | 1100篇 |
出版年
2024年 | 9篇 |
2023年 | 60篇 |
2022年 | 89篇 |
2021年 | 71篇 |
2020年 | 117篇 |
2019年 | 119篇 |
2018年 | 122篇 |
2017年 | 104篇 |
2016年 | 149篇 |
2015年 | 124篇 |
2014年 | 178篇 |
2013年 | 190篇 |
2012年 | 225篇 |
2011年 | 235篇 |
2010年 | 177篇 |
2009年 | 171篇 |
2008年 | 210篇 |
2007年 | 153篇 |
2006年 | 160篇 |
2005年 | 160篇 |
2004年 | 109篇 |
2003年 | 101篇 |
2002年 | 109篇 |
2001年 | 76篇 |
2000年 | 58篇 |
1999年 | 64篇 |
1998年 | 49篇 |
1997年 | 29篇 |
1996年 | 36篇 |
1995年 | 41篇 |
1994年 | 39篇 |
1993年 | 36篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有3699条查询结果,搜索用时 78 毫秒
21.
22.
本文论述常用燃烧室的柴油机燃用纯酒精的技术可行性。以L195型柴油机采用高压喷射、火花助燃进行燃用纯酒精试验为依据,分析其主要性能和指标。从理论上探讨混合气形成、着火、功率、热效率和使用性能的特点与影响因素。 相似文献
23.
Mei-Qin Zhan 《Mathematical Methods in the Applied Sciences》1994,17(8):613-641
We study here the Landau–Maxwell system in its classical form. We prove the local existence of weak solution with initial data of unrestricted size. The main tools consist of an approximation method and a regularity result for velocity averages of solutions of some general linear transport equations. 相似文献
24.
25.
Yonggang Shangguan Li Zhao Liyang Tao Qiang Zheng 《Journal of Polymer Science.Polymer Physics》2007,45(13):1704-1712
The effects of preparation method, composition, and thermal condition on formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X‐ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α‐iPP and β‐iPP can simultaneity form in the melt‐blended samples, whereas only α‐iPP exists in the solution‐blended samples. The results show that the formation of β‐iPP in the melt‐blended samples is related to the crystallization temperature and the β‐iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β‐iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β‐iPP in iPP/EPR. Furthermore, it was found that the amount of β‐iPP in melt‐blended iPP/EPR samples is dependent on the composition and the maximum amount of β‐iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β‐crystallization of iPP. However, only α‐iPP can be observed in solution‐blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase‐separation happens in both melt‐blended and solution‐blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β‐iPP. It is suggested that the origin of formation of β‐iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007 相似文献
26.
Chunlin Li Yilu Fu Guozhu Bian Tiandou Hu Yaning Xie Jing ZhanDepartment of Chemical Physics University of Science and Technology of China Hefei China Institute of High Energy Physics Chinese Academy of Sciences Beijing China 《天然气化学杂志》2003,12(3)
The Ni/CeO2-ZrO2-Al2O3 catalyst with different Al2O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and Al2O3 is stronger than that between NiO and CeO2-ZrO2.The addition of Al2O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess Al2O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity. 相似文献
27.
本文针对空间光学系统轻型特点,设计了一个二元光学折/衍混合红外反射式望远系统。采用了离轴式格里高利(Gregorian)结构形式,消除了望远系统中的中心遮拦问题。用衍射光学元件校正系统象差,使反射面为球面,二元光学表面尺寸比施密特(Schmidt)校正板(位于入瞳处)缩小于3~4倍,光学设计运用OSLO软件,光学系统的通光孔径φ=120mm,焦距f=-1000mm,波长λ=4.3μm,视场2ω=2°×6°(子午×弧矢),分辨率Res=0.05mm,MTF≥0.4(空间频率fre≤10cl/mm). 相似文献
28.
从双包层光纤激光器的速率方程出发,得到了光纤中泵浦光与激光的功率分布、输出功率与泵浦功率的关系、腔镜反射率及光纤长度对输出功率的影响。研究结果表明:输出激光功率与光纤长度及后腔镜反射率有很强的依赖关系,存在一个输出功率最大的最佳光纤长度。后腔镜反射率越大,输出激光功率越小;当光纤长度较短时,在输出端放置反射镜使泵浦光高反射,可以提高输出功率和效率。通过对端面泵浦掺Yb3+双包层光纤激光器进行理论分析和实验研究,得到输出激光的中心波长为1088.3nm,斜率效率为33.7%,最大输出功率为1.75W。 相似文献
29.
Further study of the viscoelastic phase separation of cyanate ester modified with poly(ether imide) 总被引:1,自引:0,他引:1
Guozhu Zhan Yingfeng Yu Xiaolin Tang Qingsheng Tao Shanjun Li 《Journal of Polymer Science.Polymer Physics》2006,44(3):517-523
In this study, the viscoelastic phase separation process was studied further by time‐resolved light scattering, differential scanning calorimetry, and scanning electron microscopy in the system of poly(ether imide)‐modified bisphenol‐A dicyanate. It was observed that the evolution time of phase structure and relaxation time of diffusion flow of the bisphenol‐A dicyanate were similar with the phase diagram of curing conversion versus content of PEI. The results suggested that the viscoelastic phase separation was affected by the curing conversion of the system at the onset point of phase separation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 517–523, 2006 相似文献
30.