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   254532篇
  免费   3172篇
  国内免费   1183篇
化学   138040篇
晶体学   3774篇
力学   10258篇
综合类   32篇
数学   28792篇
物理学   77991篇
  2020年   1928篇
  2019年   2198篇
  2018年   2622篇
  2017年   2520篇
  2016年   4111篇
  2015年   2871篇
  2014年   4217篇
  2013年   11808篇
  2012年   8630篇
  2011年   10612篇
  2010年   7004篇
  2009年   6907篇
  2008年   9549篇
  2007年   9743篇
  2006年   8841篇
  2005年   8320篇
  2004年   7476篇
  2003年   6700篇
  2002年   6667篇
  2001年   7572篇
  2000年   5696篇
  1999年   4471篇
  1998年   3729篇
  1997年   3733篇
  1996年   3466篇
  1995年   3317篇
  1994年   3119篇
  1993年   3145篇
  1992年   3424篇
  1991年   3460篇
  1990年   3274篇
  1989年   3216篇
  1988年   3260篇
  1987年   3132篇
  1986年   3010篇
  1985年   4144篇
  1984年   4323篇
  1983年   3527篇
  1982年   3882篇
  1981年   3750篇
  1980年   3631篇
  1979年   3662篇
  1978年   3863篇
  1977年   3735篇
  1976年   3916篇
  1975年   3476篇
  1974年   3599篇
  1973年   3905篇
  1972年   2381篇
  1971年   1819篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
3.
4.
5.
6.
A generic strategy based on the use of CdSe/ZnS Quantum Dots (QDs) as elemental labels for protein quantification, using immunoassays with elemental mass spectrometry (ICP-MS), detection is presented. In this strategy, streptavidin modified QDs (QDs-SA) are bioconjugated to a biotinylated secondary antibody (b-Ab2). After a multi-technique characterization of the synthesized generic platform (QDs-SA-b-Ab2) it was applied to the sequential quantification of five proteins (transferrin, complement C3, apolipoprotein A1, transthyretin and apolipoprotein A4) at different concentration levels in human serum samples. It is shown how this generic strategy does only require the appropriate unlabeled primary antibody for each protein to be detected. Therefore, it introduces a way out to the need for the cumbersome and specific bioconjugation of the QDs to the corresponding specific recognition antibody for every target analyte (protein). Results obtained were validated with those obtained using UV–vis spectrophotometry and commercial ELISA Kits.  相似文献   
7.
8.
9.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
10.
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data.  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