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   6252篇
  免费   748篇
  国内免费   619篇
化学   5066篇
晶体学   73篇
力学   270篇
综合类   21篇
数学   672篇
物理学   1517篇
  2024年   13篇
  2023年   151篇
  2022年   224篇
  2021年   229篇
  2020年   294篇
  2019年   306篇
  2018年   270篇
  2017年   186篇
  2016年   326篇
  2015年   291篇
  2014年   376篇
  2013年   478篇
  2012年   586篇
  2011年   559篇
  2010年   378篇
  2009年   312篇
  2008年   350篇
  2007年   315篇
  2006年   266篇
  2005年   208篇
  2004年   170篇
  2003年   168篇
  2002年   190篇
  2001年   141篇
  2000年   118篇
  1999年   133篇
  1998年   85篇
  1997年   61篇
  1996年   90篇
  1995年   72篇
  1994年   33篇
  1993年   42篇
  1992年   26篇
  1991年   32篇
  1990年   36篇
  1989年   21篇
  1988年   17篇
  1987年   17篇
  1986年   15篇
  1985年   14篇
  1984年   6篇
  1983年   5篇
  1982年   2篇
  1981年   1篇
  1980年   3篇
  1970年   1篇
  1963年   1篇
  1936年   1篇
排序方式: 共有7619条查询结果,搜索用时 15 毫秒
991.
992.
993.
Ligustri Lucidi Fructus (LLF) is the fruits of Ligustrum lucidum Ait. (Oleaceae). This review based on nearly 80 literary sources discusses the knowledge of chemistry and biological effects of this species. Several types of chemical constituents considered as the characteristic and active constituents from LLF were isolated including 40 triterpenoids, 48 iridoids, 10 flavones, 10 phenylethanoid glycosides and others. Various extracts and individual compounds derived from this species have been found to possess a variety of pharmacological effects, e.g. anti-tumour, hepatoprotective, immune regulating, antioxidative and anti-ageing effects, anti-inflammation and reducing hypercholesterolaemia effects and so on. The results of data analysis on the chemical, pharmacological characteristics of LLF support the view that this species has many therapeutic properties and indicate its potential as an effective herbal remedy. Finally, some suggestions for further research on chemical and pharmacological properties are given in this review. Theoretical basis was given for further exploiting and utilising LLF.  相似文献   
994.
We study the dissipative quantum phase transition(QPT)in a biased Tavis–Cummings model consisting of an ensemble of two-level systems(TLSs)interacting with a cavity mode,where the TLSs are pumped by a drive field.In our proposal,we use a dissipative TLS ensemble and an active cavity with effective gain.In the weak drive-field limit,the QPT can occur under the combined actions of the loss and gain of the system.Owing to the active cavity,the QPT behavior can be much differentiated even for a finite strength of the drive field on the TLS ensemble.Also,we propose to implement our scheme based on the dissipative nitrogen-vacancy(NV)centers coupled to an active optical cavity made from the gainmedium-doped silica.Furthermore,we show that the QPT can be measured by probing the transmission spectrum of the cavity embedding the ensemble of the NV centers.  相似文献   
995.
The self-assembly of inorganic nanoparticles into well-ordered structures in the absence of solvents is generally hindered by van der Waals forces, leading to random aggregates between them. To address the problem, we functionalized rigid rare-earth (RE) nanoparticles with a layer of flexible polymers by electrostatic complexation. Consequently, an ordered and solvent-free liquid crystal (LC) state of RE nanoparticles was realized. The RE nanomaterials including nanospheres, nanorods, nanodiscs, microprisms, and nanowires all show a typical nematic LC phase with one-dimensional orientational order, while their microstructures strongly depend on the particles’ shape and size. Interestingly, the solvent-free thermotropic LCs possess an extremely wide temperature range from −40 °C to 200 °C. The intrinsic ordering and fluidity endow anisotropic luminescence properties in the system of shearing-aligned RE LCs, offering potential applications in anisotropic optical micro-devices.  相似文献   
996.
A new star-shaped structure conjugated microporous polymers, poly (2,8,14-tri[4-diphenyl-benzene]-hexaazatrinaphthylene) (PTPA-HATN), was designed and in-situ electrochemically polymerized on the surfaces of FTO electrodes with a directional alignment TiO2 nanorod array to obtain TiO2/PTPA-HATN core-shell nanocomposite films. Compared with the PTPA-HATN film, the TiO2/PTPA-HATN composite film exhibits higher optical contrast and faster response time, with contrast of 57% at 783 nm, coloring time of 3.62 s and discoloring time of 2.55 s (43%, 4.63 s and 4.77 s for PTPA-HATN film, respectively). After 400 cycles, the contrast of nanocomposite film decreased by 28%, while the PTPA-HATN film basically lost its electrochromic properties. A simple three-layer EC prototype device based on TiO2/PTPA-HATN nanocomposite film constructed with hydrogel electrolyte clearly shows color changes at different voltages. On the one hand, the formation of core-shell porous nanostructure of TiO2/PTPA-HATN composite film provides a larger ion doping/de-doping interface, shortening the average diffusion length of ions. On the other hand, the large indented polymer-nanorods contact interface makes it difficult for the polymer to detach from the electrode, thus significantly improving the cyclic stability of the composite film.  相似文献   
997.
998.
New approach for the reversal tolerant anode for polymer electrolyte membrane fuel cell is suggested by using the multifunctional IrRu alloy catalyst having concurrent superior activities towards hydrogen oxidation reaction and oxygen evolution reaction to mitigate the degradation of anode under the fuel starvation condition.  相似文献   
999.
Zhao  Yu  You  Liang  Burkow  Daniel  Yuan  Sanling 《Nonlinear dynamics》2019,95(2):1529-1548
Nonlinear Dynamics - With the increasing demand for aquatic products all over the world, exploring the interactions between inshore and offshore fisheries is one of the meaningful issues to help...  相似文献   
1000.
We develop a theory for the magnon Kerr effect in a cavity magnonics system, consisting of magnons in a small yttrium iron garnet(YIG) sphere strongly coupled to cavity photons, and use it to study the bistability in this hybrid system. To have a complete picture of the bistability phenomenon, we analyze two different cases in driving the cavity magnonics system, i.e.,directly pumping the YIG sphere and the cavity, respectively. In both cases, the magnon frequency shifts due to the Kerr effect exhibit a similar bistable behavior but the corresponding critical powers are different. Moreover, we show how the bistability of the system can be demonstrated using the transmission spectrum of the cavity. Our results are valid in a wide parameter regime and generalize the theory of bistability in a cavity magnonics system.  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