首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1990篇
  免费   377篇
  国内免费   559篇
化学   1200篇
晶体学   11篇
力学   155篇
综合类   19篇
数学   811篇
物理学   730篇
  2024年   5篇
  2023年   57篇
  2022年   89篇
  2021年   86篇
  2020年   121篇
  2019年   87篇
  2018年   83篇
  2017年   56篇
  2016年   55篇
  2015年   69篇
  2014年   127篇
  2013年   254篇
  2012年   255篇
  2011年   234篇
  2010年   194篇
  2009年   204篇
  2008年   169篇
  2007年   189篇
  2006年   181篇
  2005年   105篇
  2004年   51篇
  2003年   45篇
  2002年   51篇
  2001年   43篇
  2000年   21篇
  1999年   21篇
  1998年   10篇
  1997年   9篇
  1996年   12篇
  1995年   10篇
  1994年   13篇
  1993年   4篇
  1992年   4篇
  1991年   4篇
  1990年   1篇
  1985年   1篇
  1979年   1篇
  1959年   1篇
  1957年   3篇
  1936年   1篇
排序方式: 共有2926条查询结果,搜索用时 31 毫秒
21.
《分析论及其应用》2015,(4):394-406
The self-affine measure μM,Dassociated with an iterated function system{φd(x)=M~(-1)(x + d)}_(d∈D) is uniquely determined. It only depends upon an expanding matrix M and a finite digit set D. In the present paper we give some sufficient conditions for finite and infinite families of orthogonal exponentials. Such research is necessary to further understanding the non-spectral and spectral of μM,D. As an application,we show that the L~2(μM,D) space has infinite families of orthogonal exponentials on the generalized three Sierpinski gasket. We then consider the spectra of a class of self-affine measures which extends several known conclusions in a simple manner.  相似文献   
22.
Flower-like TiO2 materials, with their advantages of high specific surface area, developed pore structure, and high photocatalytic activity, have been widely used in environmental management and air purification, sterilization, and surface self-cleaning, among other areas. This paper summarizes several methods used to fabricate the flower-like TiO2 nanostructures, such as the hydrothermal, solvothermal, microemulsion, sol–gel, hydrolysis, and electrodeposition oxidation methods. In addition, the morphologies, properties, and performance of different flower-like TiO2 structures are discussed. Meanwhile, the application progresses of different flower-like TiO2 structures are also analyzed.  相似文献   
23.
Research on Chemical Intermediates - A new mononuclear Zn(II) complex, [Zn(L 2 )2]·CH3OH (HL 2  = 1-(2-{[(E)-3,5-dichloro-2-hydroxybenzylidene]amino}phenyl)ethanone oxime),...  相似文献   
24.
Ma  Guofu  Li  Jindan  Sun  Kanjun  Peng  Hui  Feng  Enke  Lei  Ziqiang 《Journal of Solid State Electrochemistry》2017,21(2):525-535
Journal of Solid State Electrochemistry - Nitrogen-doped porous activated carbons have been fabricated through a simple and efficient carbonization method at 700 °C with the waste...  相似文献   
25.
结合Plinio等人([Plinio D,Duane G S,Temarn R,Time-dependent attractor for the oscillon equation,Discrete Contin Dyn Syst,2011,29(1):141-167.])提出的时间依赖全局吸引子概念,运用压缩函数的方法,证明了带有时间依赖系数的非自治Plate方程时间依赖拉回吸引子在空间H~4(Ω)∩H~2_0(Ω)×H~2_0(Ω)中的存在性.  相似文献   
26.
Recent studies demonstrate that resource competition is an essential component of T-cell proliferation in HIV progression, which can contribute instructively to the disease development. In this paper, we formulate an age-structured within-host HIV model, in the form of a hyperbolic partial differential equation (PDE) for infected target cells coupled with two ordinary differential equations for uninfected T-cells and the virions, to explore the effects of both the T-cell competition and viral shedding variations on the viral dynamics. The basic reproduction number is derived for a general viral production rate which determines the local stability of the infection-free equilibrium. Two special forms of viral production rates, which are extensively investigated in previous literature, the delayed exponential distribution and a step function rate, are further investigated, where the original system can be reduced into systems of delay differential equations. It is confirmed that there exists a unique positive equilibrium for two special viral production rates when the basic reproduction number is greater than one. However, the model exhibits the phenomenon of backward bifurcation, where two positive steady states coexist with the infection-free equilibrium when the basic reproduction number is less than one.  相似文献   
27.
《中国化学快报》2023,34(5):107792
In recent twenty years, aggregation-induced emission (AIE), due to its excellent application prospect, has aroused widespread interests. The development of novel and easy to make AIE luminogens (AIEgens) is an attractive subject. For this purpose, it's very important to study the structure-property relationship of AIEgens. Because azine derivatives are easy to synthesis and some of them have nice AIE properties, herein, a series of azine derivatives (ADs) were employed as models to study the influence of different functional groups, electronic effects and structures on the AIE properties of azine derivatives. The AIE mechanism were studied by single crystal analysis, density functional theory (DFT) calculations and so on. The results indicated that the o-hydroxyl aryl substituted azine compounds could show good AIE properties. Meanwhile, the AIE properties of o-hydroxyl aryl substituted azine compounds were also influenced by the electronic effects of the aryl groups in the azine compounds. The o-hydroxyl groups could form intramolecular hydrogen bond with imine group, which play key role to restrict the intramolecular rotation of the aryl groups and act as base stone for the AIE process of this kind compounds. The HOMO-LUMO energy gaps of o-hydroxyl substituted azine are smaller than other homologous compounds, which is agree with the proposed AIE mechanism. Finally, thanks to the AIE properties, the o-hydroxy-substituted azines could be used as efficient Al3+ and Cu2+ fluorescent chemosensors in different conditions. In addition, test strips based on AD10 has been prepared, which can conveniently detect Cu2+ in industrial wastewater. This research supplied a way for the design of novel easy to make AIEgens through simple azine derivatives.  相似文献   
28.
《中国化学快报》2023,34(6):107703
Aqueous zinc-ion batteries (ZIBs) has been regarded as a promising energy storage system for large-scale application due to the advantages of low cost and high safety. However, the growth of Zn dendrite, hydrogen evolution and passivation issues induce the poor electrochemical performance of ZIBs. Herein, a Na3Zr2Si2PO12 (NZSP) protection layer with high ionic conductivity of 2.94 mS/cm on Zn metal anode was fabricated by drop casting approach. The protection layer prevents Zn dendrites formation, hydrogen evolution as well as passivation, and facilitates a fast Zn2+ transport. As a result, the symmetric cells based on NZSP-coated Zn show a stable cycling over 1360 h at 0.5 mA/cm2 with 0.5 mAh/cm2 and 1000 h even at a high current density of 5 mA/cm2 with 2 mAh/cm2. Moreover, the full cells combined with V2O5-based cathode displays high capacities and high rate capability. This work offers a facile and effective approach to stabilizing Zn metal anode for enhanced ZIBs.  相似文献   
29.
《中国化学快报》2023,34(8):108088
Synthesis and functionalization of novel macrocyclic host molecules are important topics in supramolecular chemistry. In this work, the first amphiphilic [2]biphenyl-extended pillar[6]arene (AM-[2]BP-ExP6) was designed and synthesized with poly(ethylene glycol) chains as the hydrophilic tails and a rigid cavity as the hydrophobic core. Due to its amphiphilic nature, AM-[2]BP-ExP6 could self-assemble to stable fibers in water. What's more, AM-[2]BP-ExP6 could associate with quaternary ammonium modified tetraphenylethylene guest (QTPE) to form a 2:1 host-guest complex, accompanied by significant enhanced fluorescence. Interestingly, different like AM-[2]BP-ExP6, AM-[2]BP-ExP6⊃QTPE host-guest complex self-assembled into fluorescent particles with diameter about 310 nm, the obtained fluorescent particles can be further employed in living cell imaging.  相似文献   
30.
《中国化学快报》2023,34(6):108007
Water splitting by photoelectrochemical (PEC) processes to convert solar energy into hydrogen energy using semiconductors is regarded as one of the most ideal methods to solve the current energy crisis and has attracted widespread attention. Herein, Co-based metal-organic framework (Co(bpdc)(H2O)4 (Co-MOF) nanosheets as passivation layers were in-situ constructed on the surface of BiVO4 films through an uncomplicated hydrothermal method (Co-MOF/BiVO4). Under AM 1.5G illumination, synthesized Co-MOF/BiVO4 electrode exhibited a 4-fold higher photocurrent than bare BiVO4, measuring 6.0 mA/cm2 at 1.23 V vs. RHE in 1 mol/L potassium borate electrolyte (pH 9.5) solution. Moreover, the Co-MOF/BiVO4 film demonstrated a 96% charge separation efficiency, a result caused by an inhibited recombination rate of photogenerated electrons and holes by the addition of Co-MOF nanosheets. This work provides an idea for depositing inexpensive 2D Co-MOF nanosheets on the photoanode as an excellent passivation layer for solar fuel production.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号