全文获取类型
收费全文 | 7341篇 |
免费 | 128篇 |
国内免费 | 502篇 |
专业分类
化学 | 4858篇 |
力学 | 202篇 |
综合类 | 13篇 |
数学 | 1674篇 |
物理学 | 1224篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 2篇 |
2011年 | 69篇 |
2010年 | 71篇 |
2009年 | 29篇 |
2008年 | 129篇 |
2007年 | 430篇 |
2006年 | 622篇 |
2005年 | 794篇 |
2004年 | 524篇 |
2003年 | 269篇 |
2002年 | 538篇 |
2001年 | 714篇 |
2000年 | 638篇 |
1999年 | 676篇 |
1998年 | 570篇 |
1997年 | 362篇 |
1996年 | 349篇 |
1995年 | 391篇 |
1994年 | 315篇 |
1993年 | 181篇 |
1992年 | 76篇 |
1991年 | 32篇 |
1990年 | 57篇 |
1989年 | 46篇 |
1988年 | 35篇 |
1984年 | 1篇 |
排序方式: 共有7971条查询结果,搜索用时 15 毫秒
1.
2.
Synthesis catalytic performance of bimetallic NiMo- NiW-ZSM/MCM composites for production of liquid biofuels 《燃料化学学报》2017,45(7):805-816
This work presents a synthesis of bimetallic NiMo and NiW modified ZSM-5/MCM-41 composites and their heterogeneous catalytic conversion of crude palm oil( CPO) to biofuels. The ZSM-5/MCM-41 composites were synthesized through a self-assembly of cetyltrimethylammonium bromide( CTAB) surfactant with silica-alumina from ZSM-5 zeolite,prepared from natural kaolin by the hydrothermal technique. Subsequently,the synthesized composites were deposited with bimetallic NiMo and NiW by impregnation method. The obtained catalysts presented a micro-mesoporous structure,confirmed by XRD,SEM,TEM,EDX,NH_3-TPD,XRF and N_2 adsorption-desorption measurements. The results of CPO conversion demonstrate that the catalytic activity of the synthesized catalysts decreases in the series of NiMo-ZSM-5/MCM-41 NiW-ZSM-5/MCM-41 Ni-ZSM-5/MCM-41 Mo-ZSM-5/MCM-41 W-ZSM-5/MCM-41 NiMo-ZSM-5 NiW-ZSM-5 ZSM-5/MCM-41 ZSM-5 MCM-41. It was found that the bimetallic NiMo-and NiW-ZSM-5/MCM-41 catalysts give higher yields of liquid hydrocarbons than other catalysts at a given conversion. Types of hydrocarbon in liquid products,identified by simulated distillation gas chromatography-flame ionization detector( SimDis GC-FID),are gasoline( 150-200 ℃; C5-12),kerosene( 250-300 ℃; C5-20) and diesel( 350 ℃; C7-20).Moreover,the conversion of CPO to biofuel products using the NiMo-and NiW-ZSM-5/MCM-41 catalysts offers no statistically significant difference( P 0.05) at 95% confidence level,evaluated by SPSS analysis. 相似文献
3.
A DECAGONAL QUASICRYSTAL WITH AN ARC-SHAPED CRACK 总被引:2,自引:0,他引:2
Wang Xu Zhong Zheng 《Acta Mechanica Solida Sinica》2003,16(1):8-15
A decagonal quasicrystal,which is weakened by an arc-shaped crack penetratingthrough the solid in the period direction,and which is subjected to remote uniform phonon stresses,is investigated by applying the complex variable method which is just developed by the authors.It is found that the phonon and phason stresses near the crack tips exhibit inverse square rootsingularities.The four complex stress functions characterizing the phonon and phason fields arederived.Explicit expressions for the phonon and phason stress intensity factors,crack openingdisplacements and energy release rate are also presented. 相似文献
4.
Guanghui Ma State Key Laboratory of Biochemical Engineering Institute of Process Engineering Chinese Academy of Sciences Beijing P. R. China Tel: -- ghma@home.ipe.ac.cn 《中国颗粒学报》2003,1(3)
1.IntroductionPolymerparticleshavebeenusedinvariousfields.Besidestraditionalapplicationssuchaspaint,ink,andpaperindustries,muchattentionhasinrecentyearsbeenpaidtofineapplications,e.g.,carrierforenzyme(Omietal.,1997),separationmedia(Okubo&Hatorri,1993;Inomataetal.,1995;Ugelstadetal.,1992)forprotein,DNAandcell,andcarrierfordruginDrugDeliverySystem(DDS)(Paulettietal.,1997;Russell-Jones,2000).Controlofpolymerparticlesizeisespeciallyimportantinsuchfineapplications.Forexample,whenporouspartic… 相似文献
5.
0Introduction Thefracturepropertiesofconcreteandrockmaterials,suchasfracturetoughnessKICand strengthfthavebeenofgreatinterestsformanyyearsbecauseoftheirimportantroleincontrolling thestructuralintegrityofvariousengineeringstructures[1-27].Varioustestingtec… 相似文献
6.
Hou Weijian Yu Tongxi Su Xianyue Department of Mechanics Peking University Beijing P. R. China Department of Mechanical Engineering UMIST Manchester M QD UK 《Acta Mechanica Solida Sinica》1995,8(1):32-44
A lumped masses-springs model is proposed to analyze the dynamicresponse of an elastic-plastic cantilever beam resulting from impact. The numericalresults are in good agreement with those by finite-element approaches. The simplifiedmodel can catch the most essential features of elastic-plastic response of beams; inparticular, it demonstrates the effect of elastic deformation on the distribution ofbending moment and energy dissipation, and provides valuable quatitative results. 相似文献
7.
INFLUENCE OF ASIAN DUSTS ON THE PHYSICOCHEMICAL PROPERTIES OF ATMOSPHERIC AEROSOLS IN TAIWAN DISTRICT USING THE PENGHU ISLANDS AS AN EXAMPLE 总被引:1,自引:0,他引:1
Chung-Shin Yuan* Cheng-Chung Sau Ming-Chung Chen Institute of Environmental Engineering Sun Yat-sen University Kaohsiung China 《中国颗粒学报》2004,2(4):144-152
1. Introduction In the early months of each year, Asian dusts transport frequently from Northwest China and Mongolia to the Pa-cific-Rim countries (Kagawa et al., 2001; Uno et al., 2002). It causes significant environmental effects such as ambient air quality deterioration, atmospheric visibility impairment, radiation energy reduction, mineral deposition, and acid rain neutralization (Terada et al., 2002; Zhang & An, 1999). During Asian dust periods, significant increases of atmos-pheric … 相似文献
8.
Guan Huimin Liao Zhenpeng 《Acta Mechanica Solida Sinica》1995,8(4):283-293
Wave motion in finite element models presents some characteristics different from thoseof wave motion in continuum,which leads to the errors and other special phenomena in finite elementsimulation of wave motion.The wave propagation in a 3-D finite element model is studied by utilizingthe formal solution in the paper,and the corresponding dispersion relations are derived.Then the mainproperties of wave motion in 3-D grids such as dispersion,cut-off frequency and polarization drift arediscussed.Characteristics different from those of wave motion in 2—D grids are revealed. 相似文献
9.
Shi Ling Dai Fulong Jiang Xiaolin 《Acta Mechanica Solida Sinica》1996,9(1):81-87
The etching technique of the single-lined zero-thickness specimen grating is applied tothe surface of the SiC fiber toughening Si_3N_4 ceramic composite specimen.The position of the crackand the crack length during the process of crack extension when the load is applied and gradually in-creased can be determined by recording the output voltage value of the Wheatstone bridge in which theceramic specimen with the fracture grating on is located.The crack-growth-resistance(R-curve) of thismaterialis thus obtained. 相似文献
10.
Sofiyev Abdullah Ay Zeki 《Acta Mechanica Solida Sinica》2003,16(1):81-87
The subject of this investigation is to study the buckling of orthotropic cylindricalthin shells under torsion,which is a power function of time.The dynamic stability and compati-bility equations are obtained first.These equations are subsequently reduced to a time dependentdifferential equation with variable coefficient by using Galerkin's method.Finally,the critical dy-namic and static loading,the corresponding wave numbers,the dynamic factors,critical time andcritical impulse are found analytically by applying the Ritz type variational method.Using thoseresults,the effects of the variations of the power of time in the torsion load expression,of theloading parameter,the ratio of the Young's moduli and the ratio of the radius to thickness onthe critical parameters are studied numerically.It is observed that these factors have appreciableeffects on the critical parameters of the problem in the heading. 相似文献