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   2757篇
  免费   540篇
  国内免费   288篇
化学   2188篇
晶体学   36篇
力学   154篇
综合类   13篇
数学   239篇
物理学   955篇
  2024年   5篇
  2023年   61篇
  2022年   67篇
  2021年   109篇
  2020年   153篇
  2019年   153篇
  2018年   134篇
  2017年   116篇
  2016年   167篇
  2015年   171篇
  2014年   171篇
  2013年   253篇
  2012年   271篇
  2011年   278篇
  2010年   170篇
  2009年   142篇
  2008年   206篇
  2007年   145篇
  2006年   140篇
  2005年   102篇
  2004年   88篇
  2003年   75篇
  2002年   58篇
  2001年   47篇
  2000年   38篇
  1999年   45篇
  1998年   27篇
  1997年   21篇
  1996年   28篇
  1995年   22篇
  1994年   25篇
  1993年   14篇
  1992年   14篇
  1991年   9篇
  1990年   20篇
  1989年   10篇
  1988年   10篇
  1987年   4篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   2篇
  1980年   1篇
排序方式: 共有3585条查询结果,搜索用时 15 毫秒
981.
We study anomalous heat conduction and anomalous diffusion in low-dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is sigma(2)(t)=2Dt(alpha) (01) implies an anomalous heat conduction with a divergent thermal conductivity (beta>0), and more interestingly, a subdiffusion (alpha<1) implies an anomalous heat conduction with a convergent thermal conductivity (beta<0), consequently, the system is a thermal insulator in the thermodynamic limit. Existing numerical data support our theoretical prediction.  相似文献   
982.
工质热物理性质的计算方法及程序设计   总被引:4,自引:0,他引:4  
文中就工质物性计算程序中常用的公式法和数据库法进行了讨论 ,并着重介绍了公式法的应用原理和编程方法。以低温工质为例 ,介绍了程序计算模块和界面模块各自的特点和相互关系 ,并分别采用 Fortran和 VC+ +两种语言混合编程的方法 ,实现了程序模块间的连接。此方法为DOS和 Windows不同平台间程序的移植提供了借鉴思路  相似文献   
983.
Yao G  Jiao S  Wang LV 《Optics letters》2000,25(10):734-736
A frequency-swept ultrasonic beam was focused into a biological tissue sample to modulate the laser light passing through the ultrasonic beam inside the tissue. Parallel detection of the speckle field formed by the transmitted laser light was implemented with the source-synchronous-illumination lock-in technique to improve the signal-to-noise ratio. The ultrasound-modulated laser light reflects the local optical and mechanical properties in the ultrasonic beam and can be used for tomographic imaging of the tissue. Sweeping the ultrasonic frequency provides spatial resolution along the ultrasonic axis, which is scalable with the frequency span of the sweep. Two-dimensional images of biological tissue with buried objects were successfully obtained experimentally.  相似文献   
984.
PP can be included in the cavities of cyclodextrin (CD). The crystalline inclusion complex between β-CD and lowmolecular weight polypropylene (PP) was obtained and investigated. α-CD and γ-CD did not form crystalline inclusioncomplexes with PP. The FTIR spectra, TGA, X-ray diffraction spectra were studied, ~1H-NMR spectra and ~(13)C CP/MAS NMR spectra were used to characterize the crystalline inclusion complexes.  相似文献   
985.
Highly enantioselective aziridination of chalcones catalyzed by a novel backbone 1,8-bisoxazolidinylanthracene (AnBOX) and CuOTf with up to >99% ee and the opposite enantioselectivity compared with the ligands of Evans are described.  相似文献   
986.
987.
Cavity-enhanced spectroscopy in optical fibers   总被引:3,自引:0,他引:3  
Gupta M  Jiao H  O'Keefe A 《Optics letters》2002,27(21):1878-1880
Cavity-enhanced methods have been extended to fiber optics by use of fiber Bragg gratings (FBGs) as reflectors. High-finesse fiber cavities were fabricated from FBGs made in both germanium/boron-co-doped photosensitive fiber and hydrogen-loaded Corning SMF-28 fiber. Optical losses in these cavities were determined from the measured Fabry-Perot transmission spectra and cavity ring-down spectroscopy. For a 10-m-long single-mode fiber cavity, ring-down times in excess of 2 ms were observed at 1563.6 nm, and individual laser pulses were resolved. An evanescent-wave access block was produced within a fiber cavity, and an enhanced sensitivity to optical loss was observed as the external medium's refractive index was altered.  相似文献   
988.
Bhalotra SR  Kung HL  Jiao Y  Miller DA 《Optics letters》2002,27(13):1147-1149
We present a method of spectral discrimination that employs time-domain processing instead of the typical frequency-domain analysis and implement the method in a Michelson interferometer with a nonlinear mirror scan. The technique yields one analog output value per scan instead of a complete interferogram by directly filtering a measured scan with a reference function in the time domain. Such a procedure drastically reduces data-processing requirements downstream. Additionally, using prerecorded interferograms as references eliminates the need to compensate for scan nonlinearities, which broadens the field of usable components for implementation in miniaturized sensing systems. With our efficient use of known spectral signatures, we demonstrate real-time discrimination of 633- and 663-nm laser sources with a mirror scan length of 1 microm , compared with the Rayleigh criterion of 7 microm.  相似文献   
989.
990.
大孔吸附树脂对肿瘤坏死因子吸附性能的研究   总被引:1,自引:0,他引:1  
选用NK-110、碳化树脂和MET-10043种大孔吸附树脂,通过对树脂吸附量的测定,吸附动力学曲线和吸附等温线的描述等方法,研究了3种大孔吸附树脂对血浆中TNFα的吸附性能,结果表明NK-110和MET-1004对TNFα的吸附量较高,其中又以MET-1004的吸附速率最快  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