全文获取类型
收费全文 | 4079篇 |
免费 | 573篇 |
国内免费 | 361篇 |
专业分类
化学 | 2719篇 |
晶体学 | 28篇 |
力学 | 197篇 |
综合类 | 20篇 |
数学 | 493篇 |
物理学 | 1556篇 |
出版年
2023年 | 56篇 |
2022年 | 120篇 |
2021年 | 108篇 |
2020年 | 140篇 |
2019年 | 99篇 |
2018年 | 101篇 |
2017年 | 98篇 |
2016年 | 136篇 |
2015年 | 141篇 |
2014年 | 171篇 |
2013年 | 252篇 |
2012年 | 352篇 |
2011年 | 319篇 |
2010年 | 247篇 |
2009年 | 220篇 |
2008年 | 279篇 |
2007年 | 231篇 |
2006年 | 210篇 |
2005年 | 172篇 |
2004年 | 139篇 |
2003年 | 125篇 |
2002年 | 108篇 |
2001年 | 90篇 |
2000年 | 102篇 |
1999年 | 75篇 |
1998年 | 69篇 |
1997年 | 57篇 |
1996年 | 76篇 |
1995年 | 61篇 |
1994年 | 62篇 |
1993年 | 55篇 |
1992年 | 55篇 |
1991年 | 37篇 |
1990年 | 29篇 |
1989年 | 43篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 42篇 |
1985年 | 30篇 |
1984年 | 36篇 |
1983年 | 26篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1973年 | 9篇 |
排序方式: 共有5013条查询结果,搜索用时 0 毫秒
991.
An experimental investigation of swirl atomizer sprays 总被引:1,自引:0,他引:1
In our previous studies (Chu et al. in Heat Mass Transf 43(11):1213–1224, 2007), a theoretical model of swirl atomizers was successfully established. From the analysis, the equations for the droplet size,
velocity components, the boundary layer thickness and the spray cone angle were deduced based on the fundamental governing
equations. The purpose of this study is to further compare the experimental result with the theoretical one already gained
by a satisfactory embodiment of series of experiments. The aim is to corroborate the analytical results of the influence of
atomizer construction and controlled pressure difference on typical swirl chambers. The results provide the droplet diameter
as a function of pressure difference, swirl atomizer geometry, flow rate, spray cone angle. The experimental outputs also
show a good confirmation of theoretical results and can also be used for further optimization on existing swirl chambers.
Based on the results obtained, an optimization methodology on characteristics of swirl atomizers is proposed with the adjustment
of individual design parameter and the matching flow number. 相似文献
992.
993.
Nano-porous Composites Based on Heteropolyacid Functionalized Ionic Liquid: Synthesis,Characterization, and Catalytic Performance in Esterification 下载免费PDF全文
Functionalized ionic liquid samples (bmim-PW12) were synthesized by 1-butyl-3-methyl-imidazolium bromide (bmimBr) and 12-phosphotungstic heteropolyacid (PW12). The sam-ples were annealed at 100-450 oC and were characterized by Fourier transform infrared spec-troscopy, X-ray diffraction, scanning electron microscope, thermal gravity-DTG, brunauer emmett teller, and NH3-temperature programmed desorption. The results showed that the bmim-PW12 samples were crystal and maintained intact Keggin structure. The organic parts of those samples were partly decomposed at a temperature more than 350 oC. The sample annealed at 400 oC exhibited nano-porous structure, strong acidity, and excellent catalytic activity on the esterification of n-butanol with acetic acid. The higher ester yield was ob-tained when the mass ratio of catalyst over the reactants amount was 5% for bmim-PW12 catalyst annealed at 400 oC. 相似文献
994.
H. Jory D. Wagner M. Blank S. Chu K. Felch 《International Journal of Infrared and Millimeter Waves》2001,22(10):1395-1407
A microwave system is described which allows testing of the quasi-optical mode converter in a gyrotron, which is completely assembled except for the attachment of the electron gun. Test results are presented for a TE6,2,1 gyrotron, and a similar design for a TE28,7,1 gyrotron is shown. 相似文献
995.
Enhanced fatigue property of PZT thin films using LaNiO3 thin layer as bottom electrode 总被引:2,自引:0,他引:2
X.J. Meng J.L. Sun J. Yu G.S. Wang S.L. Guo J.H. Chu 《Applied Physics A: Materials Science & Processing》2001,73(3):323-325
A highly (100)-oriented metallic LaNiO3 film was prepared directly on a Si substrate by a simple metalorganic decomposition (MOD) technique using lanthanum nitrate
and nickel acetate as the starting sources. Subsequent Pb(Zr,Ti)O3 (PZT) thin films deposited on the LaNiO3-coated Si substrate were obtained by a modified sol–gel method. It was found that the PZT thin films began to form a single
perovskite phase at a low annealing temperature of 530 °C, and exhibited highly (100) orientation. A ferroelectric capacitor
of Pt/Pb(Zr,Ti)O3/LaNiO3/Si annealed at 600 °C displayed a good P-E hysteresis characteristic and was fatigue-free even after 1011 switching cycles.
Received: 25 May 2000 / Accepted: 9 August 2000 / Published online: 30 November 2000 相似文献
996.
Investigation has been carried out on the thermal performance of sintered miniature heat pipes with 3 mm outer diameter.
In the theoretical analysis, the influence of wick structure parameters is determined by using the theory of capillary limitation.
As a result, the degree of importance is found to be as follows: porosity, powder diameter and thickness of wick structure.
In the experiments, heat pipes with sintered dendritic copper powder wicks were fabricated and tested. The maximum heat transfer
rate is about 13 W with an effective heat pipe length of 20 cm. By adopting the formulae developed for both sintered spherical
powder and fiber and adjusting their proportion, the agreement between experimental results and prediction is found to be
quite good in the tested operation temperature range.
Received on 26 February 2001 相似文献
997.
Low frequency effects of surface states on 4H—SiC metal—semiconductor field effect transistor 下载免费PDF全文
The process-related surface state effect is investigated the fabrication of SiC devices, and a nonllnear model for 4H-SiC power metal-semiconductor field effect transistor (MESFET) is propose, which takes into account the surface related parameters. The frequency-and temperature-dependent transconductance dispersion is readily demonstrated in terms of the improved model. Simulation results show that larger dispersion and higher transition frequency occur in 4H-SiC MESFET than in GaAs MESFET. The advantage of this analytical model over the two-dimensional numerical simulation is the simplicity of calculations, therefore it is suitable for the processing improvement of SiC devices 相似文献
998.
Theory of the coherent-mode decomposition of laser beams is proposed. The new model for the flat-topped beams proposed by Li recently is taken as an example. The analytical expressions for the M^2-factor and mode coherence coefficients of flat-topped beams have been derived in the rectangular coordinate system, by means of which the mode correlation, mode structure, and coherent-mode decomposition of flat-topped beams can be analysed. 相似文献
999.
假定二元液态混合物分子间的相互作用势能可以表示成多体相互作用势能的和,分子间的力为短程力,相互作用势能只与分子间的相对距离有关.利用分布函数理论导出了二元液态混合物的过剩内能和内压的公式.二元液态混合物的过剩内能和内压可以表示成体积的幂级数形式,其中的系数可以用多体相互作用势和多体径向分布函数表出.讨论了单元液体的内压和过剩内能的表达式,在两种特殊情形下,过剩内能和内压的表达式分别与Egelstaff的微扰论结果及Frank的实验结果具有相同的形式.讨论了二元混合物内压和内能的两个特例,其一,在特殊情形下,给出了混合液体过剩内能的混合规则的一个证明.其二,给出的二元混合物的过剩内能和内压的表达式与Frank的实验结果具有相同的形式. 相似文献
1000.
分析了溶液的微观结构,结果表明,单个溶质粒子影响其周围的溶剂的结构,溶质粒子间的相互作用也将影响溶剂的结构,溶质对溶剂结构的影响称作溶剂的重组织.提出了二阶重组织能及二阶重组织熵等概念,可以描述在两个溶质粒子发生碰撞时对其周围溶剂结构的影响.利用二元系的集团展开理论,给出了溶剂的一阶、二阶重组织能和重组织熵的表达式.统计热力学分析给出了溶剂-溶剂径向分布函数与溶质和溶剂化学势之间的关系,给出了无限稀溶液模型是否成立的宏观判据.提出的理论可用于低密度的二元溶液. 相似文献