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   4678篇
  免费   573篇
  国内免费   568篇
化学   2711篇
晶体学   43篇
力学   344篇
综合类   20篇
数学   1006篇
物理学   1695篇
  2024年   4篇
  2023年   390篇
  2022年   321篇
  2021年   332篇
  2020年   434篇
  2019年   200篇
  2018年   207篇
  2017年   274篇
  2016年   294篇
  2015年   288篇
  2014年   327篇
  2013年   328篇
  2012年   420篇
  2011年   356篇
  2010年   305篇
  2009年   226篇
  2008年   136篇
  2007年   170篇
  2006年   158篇
  2005年   111篇
  2004年   51篇
  2003年   90篇
  2002年   72篇
  2001年   127篇
  2000年   59篇
  1999年   98篇
  1998年   15篇
  1997年   7篇
  1996年   3篇
  1995年   3篇
  1994年   1篇
  1993年   2篇
  1991年   1篇
  1990年   2篇
  1986年   2篇
  1985年   4篇
  1971年   1篇
排序方式: 共有5819条查询结果,搜索用时 93 毫秒
1.
Atopic dermatitis is characterized by leukocyte migration into the skin dermis and typically driven by excessive chemokine production at the site of inflammation. Conventional topical formulations such as gels, creams, and ointments are insufficient for this treatment because of low penetration of drug molecules into the targeted skin tissues. Herein, using a simple, green, sustainable strategy, we have developed novel primary zein nanoparticles embedded in curcumin (Cur) and coated with silk sericin (ZHSCs) for the topical delivery of Cur to penetrate into the dermis and exercise anti-dermatitis effects on the lesion with minimal side-effects. Transdermal delivery experiments and porcine skin fluorescence imaging indicated that ZHSCs facilitate the penetration of Cur across the epidermis layer of skin to reach deep-seated sites. Notably, ZHSCs = 1:0.25 (zein-to-silk sericin mass ratios of 1:0.25) markedly elevated the skin permeability and cumulative turnover of Cur transferred, which were provided a greater than a 3.8-fold increase relative to free Cur. The special nanoparticles of ZHS = 1:0.25 possessed the deepest localization depth and experience a transition of the particle structure and core-shell separation after penetrating into the dermis of skin. In a cell model of dermatitis induced by tumor necrosis factor α/interferon γ co-stimulation, compared with free Cur, Cur-loaded ZHS nanoparticles down-regulated the generation of inflammatory cytokines and chemokines in keratinocytes through suppression of the nuclear translocation of NF-κBp65 and hence exerted an anti-dermatitis effect. This strategy may provide new avenues and direction for the demanding issues of valid topical delivery systems.  相似文献   
2.
Liquid-liquid-solid systems are becoming increasingly common in everyday life with many possible applications. Here, we focus on a special case of such liquid-liquid-solid systems, namely, capillary suspensions. These capillary suspensions originate from particles that form a network based on capillary forces and are typically composed of solids in a bulk liquid with an added secondary liquid. The structure of particle networks based on capillary bridges possesses unique properties compared with networks formed via other attractive interactions where these differences are inherently related to the properties of the capillary bridges, such as bridge breaking and coalescence between adjacent bridges. Thus, to tailor the mechanical properties of capillary suspensions to specific requirements, it is important to understand the influences on different length scales ranging from the dynamics of the bridges with varying external stimuli to the often heterogeneous network structure.  相似文献   
3.
Copper-catalyzed divergent annulations between α-diketones and alkynyl α-diketones have been achieved, delivering a series of highly functionalized and biologically important cis-hexahydro-2Hcyclopenta[b]furan(HCPF) and 2-hydroxydihydrofuran-3(2H)-one(HDFO) products with high levels of stereoselectivity under identical conditions. The protocol features the use of earth-abundant copper catalyst, mild conditions, shortening synthetic routes in constructing different molecular frameworks, and reduc...  相似文献   
4.
将TiNi基记忆合金薄膜与光纤相结合可制成智能化、集成化且成本经济的微机电系统和微传感器件.本文采用磁控溅射法在二氧化硅光纤基底上制备TiNi记忆合金薄膜,系统讨论了溅射工艺参数以及后续退火处理对薄膜质量的影响.采用自研制光纤镀膜掩膜装置在直径为125μm的光纤圆周表面上形成均匀薄膜.实验表明:在靶基距、背底真空度、Ar气流量和溅射时间一定的条件下,溅射功率存在最佳值;溅射压强较大时,薄膜沉积速率较低,但薄膜表面粗糙度较小.进行退火处理后,薄膜形成较良好的晶体结构,Ti49.09Ni50.91薄膜中马氏体B19′相和奥氏体B2相共存,但以B19′为主.根据本文研究结果,在玻璃光纤基底上制备高质量的TiNi基记忆合金薄膜是可实现的,本工作为下一步研制微机电系统和微型传感器做了基础准备.  相似文献   
5.
Liang  Guiming  Huang  Yunbao  Li  Haiyan  Lin  Jingliang 《Nonlinear dynamics》2021,105(4):3393-3407
Nonlinear Dynamics - The modal truncation is usually used in the dynamic response analysis of flexible multibody systems, in which, appropriate selection of modal shapes is very critical to achieve...  相似文献   
6.
An iterative formula for the Green polynomial is given using the vertex operator realization of the Hall-Littlewood function. Based on this, (1) a general combinatorial formula of the Green polynomial is given; (2) several compact formulas are given for Green's polynomials associated with upper partitions of length ≤3 and the diagonal lengths ≤3; (3) a Murnaghan-Nakayama type formula for the Green polynomial is obtained; and (4) an iterative formula is derived for the bitrace of the finite general linear group G and the Iwahori-Hecke algebra of type A on the permutation module of G by its Borel subgroup.  相似文献   
7.
Set-Valued and Variational Analysis - This paper is concerned with second-order optimality conditions for the mathematical program with semidefinite cone complementarity constraints. To achieve...  相似文献   
8.
Fluorescence probes in the NIR-IIa region show drastically improved imaging owing to the reduced photon scattering and autofluorescence in biological tissues. Now, NIR-IIa polymer dots (Pdots) are developed with a dual fluorescence enhancement mechanism. First, the aggregation induced emission of phenothiazine was used to reduce the nonradiative decay pathways of the polymers in condensed states. Second, fluorescence quenching was minimized by different levels of steric hindrance to further boost the fluorescence. The resulting Pdots displayed a fluorescence QY of ca. 1.7 % in aqueous solution, suggesting an enhancement of ca. 21 times in comparison with the original polymer in tetrahydrofuran (THF) solution. Small-animal imaging by using the NIR-IIa Pdots exhibited a remarkable improvement in penetration depth and signal to background ratio, as confirmed by through-skull and through-scalp fluorescent imaging of the cerebral vasculature of live mice.  相似文献   
9.
Using first principles density functional theory, we predict a monolayer B2Si structure with space group Pmm2 in the present work. This structure is confirmed to be dynamically stable. Based on the plane wave pseudopotential approach, the charge density, electron localization function, density of states, energy band, phonon property and thermal conductivity of Pmm2-B2Si are systematically studied. It is interesting that the sp2 hybridization and coordination bond of Si are found in Pmm2-B2Si, which is the most important factor for its structural stability. The density of states and energy band analysis reveals that Pmm2-B2Si is metallic because of the partial occupied Si 3pz and B 2pz states. Moreover, the acoustic-optical coupling is important for phonon transport in Pmm2-B2Si, and the contribution of optical modes to the lattice thermal conductivity along the [100] and [010] directions is 13% and 12%, respectively. This study gives a fundamental understanding of the structural, electronic and phonon properties in Pmm2-B2Si.  相似文献   
10.
Journal of Solid State Electrochemistry - Polyaniline/diazonium salt/TiO2 nanotube arrays (PANI/DZ/TiO2 NAs), as a supercapacitor electrode material, are fabricated by two-step anodic oxidation of...  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