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   1912篇
  免费   307篇
  国内免费   153篇
化学   1319篇
晶体学   25篇
力学   139篇
综合类   12篇
数学   173篇
物理学   704篇
  2024年   5篇
  2023年   33篇
  2022年   57篇
  2021年   73篇
  2020年   70篇
  2019年   54篇
  2018年   70篇
  2017年   66篇
  2016年   92篇
  2015年   109篇
  2014年   116篇
  2013年   151篇
  2012年   183篇
  2011年   197篇
  2010年   112篇
  2009年   123篇
  2008年   125篇
  2007年   120篇
  2006年   100篇
  2005年   75篇
  2004年   40篇
  2003年   33篇
  2002年   35篇
  2001年   31篇
  2000年   36篇
  1999年   30篇
  1998年   24篇
  1997年   24篇
  1996年   32篇
  1995年   15篇
  1994年   18篇
  1993年   12篇
  1992年   7篇
  1991年   15篇
  1990年   24篇
  1989年   16篇
  1988年   11篇
  1987年   11篇
  1986年   7篇
  1985年   2篇
  1981年   2篇
  1976年   2篇
  1957年   1篇
  1942年   1篇
  1941年   1篇
  1936年   4篇
  1930年   2篇
  1929年   1篇
  1927年   1篇
  1923年   1篇
排序方式: 共有2372条查询结果,搜索用时 15 毫秒
991.
We report a novel approach to continuous and scalable production of core-shell droplets and polymer capsules in microfluidic devices. The described method is also useful in the synthesis of polymer particles with nonspherical shapes. We used capillary instability-driven break-up of a liquid jet formed by two immiscible fluids. Precise control of emulsification of each liquid allowed for the production of highly monodisperse core-shell droplets with a predetermined diameter of cores and thickness of shells. We also achieved control over the number of cores per droplet and the location of cores in the droplet. We carried out fast throughput photopolymerization of the monomeric shells and obtained polymer particles with various shapes and morphologies, including spheres, truncated spheres and, hemispheres, and single and multicore capsules.  相似文献   
992.
Continuous microfluidic reactors for polymer particles   总被引:4,自引:0,他引:4  
This article provides an overview of our work in the area of the synthesis of polymer particles in continuous microfluidic reactors. The method includes (a) the generation of highly monodisperse monomer droplets in a microfluidic flow-focusing device and (b) in-situ solidification of these droplets by means of photopolymerization. We discuss the effect of monomer properties on the emulsification process, the effect of the polymerization rate on the production of high-quality particles, the role of the material of the microfluidic device in droplet formation, and the synthesis of particles with different shapes and compositions. We also demonstrate the production of highly ordered arrays of polymer particles achieved by photopolymerization of the dynamic lattices of monomer droplets in microfluidic channels. The article is concluded with a summary of future research directions in the production of polymer colloids in microfluidic reactors.  相似文献   
993.
Peng H  Liang C  He D  Nie L  Yao S 《Talanta》2000,52(3):441-448
A new bulk acoustic wave (BAW) sensor modified with a molecularly imprinted polymer (MIP) was fabricated and applied for the determination of pyrimethamine. This sensor exhibited high selectivity and sensitive response to pyrimethamine. Factors such as pH and the amount of coating influencing sensor properties, were investigated in detail and optimized. The calibration curve was linear in the range 6.0x10(-7)-1.0x10(-4) M. The determination limit was 2.0x10(-7) M. In harsh chemical environments such as high temperature, organic solvents, bases, acids, etc., the sensor still exhibited long-term stability. The proposed method has been satisfactorily applied for the determination of pyrimethamine in serum and urine media.  相似文献   
994.
The electron impact mass spectra of several cyclic esters with helical structures have been studied. Their fragmentation pathways were proposed and confirmed by mass-analyzed ion kinetic energy (MIKE) and high-resolution data. In general, the dominant fragmentation pathways in the spectra of these compounds originate from a alpha-cleavage with loss of a hydrogen or methyl group. The difference between hydrogen and methyl group loss greatly affects the subsequent fragmentations. Although, due to their helicity, these cyclic esters are optically active no stereo-related fragmentation pathway was observed. Copyright 2000 John Wiley & Sons, Ltd.  相似文献   
995.
Mo-Y2O3阴极的热电子发射性能   总被引:2,自引:0,他引:2  
利用装管发射、电子显微分析等手段系统地研究了含3%~5%(wt)Y2O3的MoY2O3热阴极丝的电子发射性能和材料显微结构。结果表明,MoY2O3丝具有良好的热电子发射能力,与WThO2阴极相比发射效率高、工作温度低。经过与MoLa2O3丝同样的碳化处理后,用Φ026mm的MoY2O3丝作阴极的实验电子管与MoLa2O3阴极电子管相比发射性能更稳定。MoY2O3阴极丝材的显微结构为具有亚结构的纤维状组织,碳化层为粒状晶粒结构,该结构有利于Y2O3迁移和输送到阴极表面。  相似文献   
996.
Preparation and characterization of crosslinked chitosan-based nanofibers   总被引:1,自引:0,他引:1  
Crosslinked chitosan-based nanofibers were successfully prepared via electrospinning technique with heat mediated chemical crosslinking followed.The structure,morphology and mechanical property of nanofibers were characterized by attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR),scanning electron microscopy(SEM),Instron machine,respec- tively.The results showed that,nanofibers exhibited a smooth surface and regular morphology,and tensile strength of nanofibers improved with increasing of triethylene glycol dimethacrylate(TEGDMA)content.  相似文献   
997.
 本文就年轮型高压装置,对福长修的平板模型作了改进,即在式中引入了压砧的半顶角θ,计算了封垫中的压力及封垫对于压砧的支撑力,计算结果基本上和实验结果符合。就年轮型及立方六面顶型高压装置讨论了高压室和封垫的压力增量之间的匹配问题,还就卸压问题介绍了Murnaghan方程的应用。  相似文献   
998.
基于gyrator变换和矢量分解的非对称图像加密方法   总被引:1,自引:0,他引:1       下载免费PDF全文
姚丽莉  袁操今  强俊杰  冯少彤  聂守平 《物理学报》2016,65(21):214203-214203
本文结合矢量分解和gyrator变换的数学实现得到了一种新的非对称图像加密算法,它将待加密图像先通过矢量分解加密到两块纯相位板中,然后利用从gyrator变换的数学实现中推导出来的加密算法加密其中一块相位板,获得最终的实值密文.另一块相位板作为解密密钥.算法的解密密钥不同于加密密钥,实现了非对称加密,加密过程中产生的两个私钥增大了算法的安全性.数值模拟结果验证了该算法的可行性和有效性.  相似文献   
999.
Perovskite formamidinium lead triiodide (FAPbI3) is a very promising photovoltaic material. Unfortunately, perovskite FAPbI3 converts to a hexagonal phase at ambient conditions. Herein we study the electronic structure of both perovskite and hexagonal FAPbI3 films using soft X‐ray absorption near edge structure (XANES) and density functional theory. We find that the C and N 2p states of FA hybridize with the Pb, I states at the conduction band minimum in hexagonal, but not perovskite, FAPbI3. We also demonstrate that C K‐edge XANES can be used to investigate shifts in the valence band in other organic‐inorganic hybrid perovskites.

Graphical summary of the electronic structure and C K‐edge XANES in both perovskite and hexagonal FAPbI3 highlighting our findings.  相似文献   

1000.
Knowledge on the interactions between engineered nanomaterials (ENMs) and biological systems is critical both for the assessment of biological effects of ENMs and for the rational design of ENM-based products. However, probing the events that occur at the nano-bio interface remains extremely challenging due to their complex and dynamic nature. So far, the understanding of mechanisms underlying nano-bio interactions has been mainly limited by the lack of proper analytical techniques with sufficient sensitivity, selectivity and resolution for characterization of nano-bio interface events. Moreover, many classic bioanalytical methods are not suitable for direct measurement of nano-bio interface interactions. These have made establishing analytical methodologies for systematic and comprehensive study of nano-bio interface one of the most focused areas in nanobiology. In this review we have discussed some representative developments regarding analytical techniques for nano-bio interface characterization, including the improvements of traditional methods and the emergence of powerful new technologies. These developments have allowed ultrasensitive, real-time analysis of interactions between ENMs and biomolecules, transformations of ENMs in biological environment, and impacts of ENMs on living systems on molecular or cellular level.  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