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   1979篇
  免费   62篇
  国内免费   9篇
化学   1508篇
晶体学   6篇
力学   45篇
数学   319篇
物理学   172篇
  2023年   21篇
  2022年   105篇
  2021年   92篇
  2020年   75篇
  2019年   56篇
  2018年   40篇
  2017年   33篇
  2016年   63篇
  2015年   74篇
  2014年   47篇
  2013年   116篇
  2012年   124篇
  2011年   157篇
  2010年   87篇
  2009年   80篇
  2008年   133篇
  2007年   143篇
  2006年   108篇
  2005年   105篇
  2004年   84篇
  2003年   78篇
  2002年   76篇
  2001年   21篇
  2000年   13篇
  1999年   11篇
  1998年   3篇
  1997年   10篇
  1996年   14篇
  1995年   11篇
  1994年   7篇
  1993年   5篇
  1992年   2篇
  1991年   2篇
  1990年   9篇
  1989年   3篇
  1988年   7篇
  1987年   2篇
  1986年   2篇
  1985年   5篇
  1984年   5篇
  1983年   2篇
  1982年   5篇
  1981年   3篇
  1980年   1篇
  1979年   2篇
  1978年   3篇
  1977年   1篇
  1975年   1篇
  1969年   1篇
  1968年   1篇
排序方式: 共有2050条查询结果,搜索用时 15 毫秒
991.
992.
993.
Zirconium phosphate nanoparticles from water-in-oil microemulsions   总被引:1,自引:0,他引:1  
Non-ionic water-in-oil (w/o) microemulsions of pentaoxyethylenenonylphenyl ether (Igepal-CO520)/cyclohexane/water at 25 °C have been used as reaction vessels to obtain zirconium hydrogen phosphate nanoparticles.  相似文献   
994.

Background  

It has recently been demonstrated that the fate of adult cells is not restricted to their tissues of origin. In particular, it has been shown that bone marrow stem cells can give rise to cells of different tissues, including neural cells, hepatocytes and myocytes, expanding their differentiation potential.  相似文献   
995.
The aim of this paper is to discuss the main ideas of the Talagrand proof of the Parisi Ansatz for the free-energy of Mean Field Spin Glasses with a physicist's approach. We consider the case of the spherical p-spin model, which has the following advantages: (1) the Parisi Ansatz takes the simple “one step replica symmetry breaking form,” (2) the replica free-energy as a function of the order parameters is simple enough to allow for numerical maximization with arbitrary precision. We present the essential ideas of the proof, we stress its connections with the theory of effective potentials for glassy systems, and we reduce the technically more difficult part of the Talagrand's analysis to an explicit evaluation of the solution of a variational problem.  相似文献   
996.
Solid-state NMR techniques are used to study the effect of theinclusion of toluene and benzene on the mobility ofp-tert-butylcalixarene. We attribute the great increase inhost mobility upon complexation to the lack of strongdirectional intermolecular interactions. The differences inthe behaviour of the host in the two complexes are explainedin terms of the steric effects of the guest methyl group.  相似文献   
997.
Poly(diethylene terephthalate‐co‐thiodiethylene terephthalate) (PDET/TDET) copolymers of various compositions were synthesized and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All the polymers showed a good thermal stability. At room temperature they appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to homopolymers. WAXD measurements indicated that cocrystallization occurs over an extended composition range and three different crystalline phases have been identified. In particular, the applicability of Wendling–Suter's equation has been checked for the PDET/TDET copolymers with TDET unit content ranging from 60 to 90 mol %. Amorphous samples were obtained after melt quenching and a decrease of Tg as the content of TDET units is increased was observed. This behavior was explained as due to the presence of flexible C? S? C bonds in the polymeric chain. Lastly, the Fox equation well described Tg‐composition data. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1562–1571, 2006  相似文献   
998.
A state‐of‐the‐art overview of N‐dopant characterizations in nano‐TiO2 second‐generation photocatalysts is provided. The related literature is very rich and sometimes offers contrasting interpretations. Here we critically discuss up‐to‐date literature results and our own findings, as retrieved by several experimental (BET, HR‐TEM, XPS, DRS, HR‐XRPD, EXAFS, electrochemical tools) and theoretical (periodic DFT) techniques. Our intent is to pull together outcomes from very different and complementary sources to make an as much as possible coherent picture of the morphological, electrochemical and electronic properties of N‐TiO2 materials. It is commonly accepted that critical issues to be considered in the design of high‐performing N‐TiO2 photocatalysts are synthetic strategy, defect concentration and chemical nature of the lattice point defects. We focus on the latter two issues, with emphasis on sol‐gel prepared materials, according to the specific area of expertise of our group. The problem of the chemical nature of guest N species into the lattice is crucial, as substitutional (Ns) or interstitial (Ni) nitrogen place their valence states just above the valence band or deeper into the band gap. Overall, we show how synergism among experimental and theoretical techniques is decisive to disentangle structural, electronic and morphological effects in complex N‐doped TiO2 matrices.  相似文献   
999.
The paper presents an optimization framework for dealing with morphing airfoils for helicopter rotor blades. With regard to the morphing strategy, a conformable camber line is considered to deal with variable flow conditions encountered in forward flight with the objective of increasing the aerodynamic performance on the advancing and retreating sides of the rotor. Another peculiarity of the method is that the optimal shape is sought to be minimally sensitive to uncertainty in the operating conditions. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
1000.
Polyelectrolyte multilayer (PEM) capsules engineered with active elements for targeting, labeling, sensing and delivery hold great promise for the controlled delivery of drugs and the development of new sensing platforms. PEM capsules composed of biodegradable polyelectrolytes are fabricated for intracellular delivery of encapsulated cargo (for example peptides, enzymes, DNA, and drugs) through gradual biodegradation of the shell components. PEM capsules with shells responsive to environmental or physical stimuli are exploited to control drug release. In the presence of appropriate triggers (e.g., pH variation or light irradiation) the pores of the multilayer shell are unlocked, leading to the controlled release of encapsulated cargos. By loading sensing elements in the capsules interior, PEM capsules sensitive to biological analytes, such as ions and metabolites, are assembled and used to detect analyte concentration changes in the surrounding environment. This Review aims to evaluate the current state of PEM capsules for drug delivery and sensing applications.  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