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   2264篇
  免费   252篇
  国内免费   199篇
化学   1702篇
晶体学   27篇
力学   100篇
综合类   14篇
数学   224篇
物理学   648篇
  2023年   39篇
  2022年   42篇
  2021年   65篇
  2020年   80篇
  2019年   97篇
  2018年   69篇
  2017年   55篇
  2016年   91篇
  2015年   83篇
  2014年   112篇
  2013年   152篇
  2012年   188篇
  2011年   202篇
  2010年   127篇
  2009年   110篇
  2008年   143篇
  2007年   137篇
  2006年   122篇
  2005年   121篇
  2004年   70篇
  2003年   56篇
  2002年   76篇
  2001年   50篇
  2000年   36篇
  1999年   35篇
  1998年   30篇
  1997年   30篇
  1996年   32篇
  1995年   32篇
  1994年   21篇
  1993年   18篇
  1992年   30篇
  1991年   12篇
  1990年   23篇
  1989年   17篇
  1988年   15篇
  1987年   15篇
  1986年   8篇
  1985年   13篇
  1984年   14篇
  1983年   9篇
  1982年   6篇
  1981年   7篇
  1980年   4篇
  1979年   5篇
  1978年   4篇
  1975年   3篇
  1962年   1篇
  1961年   1篇
  1954年   1篇
排序方式: 共有2715条查询结果,搜索用时 15 毫秒
151.
Three model drugs with different function groups were chosen to dialyze with dextran-graft-poly(N-isopropylacrylamide).Only ibuprofen could induce the formation of drug loaded micelles,which was confirmed with dynamic light scattering and transmission electron microscope.Hydrogen-bonding between the amide groups of poly(N-isopropylacrylamide) and the carboxyl groups of ibuprofen was driving force for the drug-loaded micelle.It was also found that the diameter of the ibuprofen-loaded micelles changed reversibly against temperature.  相似文献   
152.
153.
The electrochemiluminescence (ECL) of luminol on indium tin oxide (ITO) glass was high even under a low potential around 0.4-0.5 V, which was quite different from other electrodes such as platinum. ITO nanoparticles were synthesized and used in the research on ITO glass in the ECL process. A static interaction between ITO and luminol is confirmed from UV-vis and fluorescence spectra. Then the ECL enhancement can be supposed to originate from the adsorption of luminol on ITO, which facilitated luminol’s oxidization to the excited state, giving out ECL. On the other hand, ITO can catalyze the generation of reactive oxygen species (ROSs), similar to some other nanomaterials, which also favored the ECL enhancement of luminol.  相似文献   
154.
Based on the kernel formula proposed by Carroll and Kodama, we derive the dispersionless Hirota equations of the universal Whitham hierarchy. We also verify the associativity equations in this hierarchy from the dispersionless Hirota equations and give a realization of the associative algebra with the structure constants expressed in terms of residue formulas.  相似文献   
155.
Arsenic (As) and antimony (Sb) show similar chemical properties and often present together in sulfide ores. Currently, phenomenon of co-contamination of As and Sb at some sites of the world has been increasingly emerged. The present study was conducted to explore the potential of Pteris cretica L. (Cretan brake fern), an arsenic (As) hyperaccumulator, to simultaneously accumulate As and Sb under hydroponic conditions. Arsenic was imposed at medium and high levels of 5 mg L− 1 and 20 mg L− 1, while Sb was imposed either single or co-presence with As at medium and high levels of 10 mg L− 1 and 20 mg L− 1, with no As and Sb addition as the control. The single and interactive effects of As and Sb on their uptake and subcellular distributions were analyzed. Cretan brake fern could accumulate high concentrations of As and Sb, with the highest concentrations of As and Sb been recorded as 1677.2 mg kg− 1 and 1516.5 mg kg− 1 in the fronds, respectively. Arsenic and Sb were found mainly in cytosol, while less in cell wall and cytoplasmic organelles. Sb uptake by Cretan brake fern was enhanced with increasing As levels, which was accompanied with an increase of Sb but a decrease of As in cytosol fractions. Arsenic uptake was slightly enhanced whereas suppressed when Sb was co-present in a medium and high level, respectively; however, in both conditions, As was found to be decreased in cytosol of the above ground parts as fronds and stems of Cretan brake fern. The results demonstrate Cretan brake fern can simultaneously hyperaccumulate As and Sb, thus is valued in phytoremediation of As and Sb co-contamination.  相似文献   
156.
We propose a scheme to eliminate the effect of non-nearest-neighbor qubits in preparing cluster state with double-dot molecules. As the interaction Hamiltonians between qubits are Ising-model and mutually commute, we can get positive and negative effective interactions between qubits to cancel the effect of non-nearest-neighbor qubits by properly changing the electron charge states of each quantum dot molecule. The total time for the present multi-step cluster state preparation scheme is only doubled for one-dimensional qubit chain and tripled for two-dimensional qubit array comparing with the time of previous protocol leaving out the non-nearest-neighbor interactions.  相似文献   
157.
We prove that any proper holomorphic mapping from to is necessarily a totally geodesic isometric embedding with respect to their Bergman metrics and therefore is the standard linear embedding up to their automorphisms. The proof of the main result in this paper will be achieved by a differential-geometric study of a special class of complex geodesic curves on the bounded symmetric domains with respect to their Bergman metrics. Received: 31 October 2000; in final form: 2 July 2001/ Published online: 4 April 2002  相似文献   
158.
159.
We demonstrate that base and sugar protons within a DNA oligomer can be assigned unambiguously following site-specific 15N,13C isotope incorporation at levels as low as 1% enrichment. This simple and cost-effective methodology is demonstrated on the d(GGGTTCAGG) DNA sequence, which forms a dimeric G-quadruplex containing G.G.G.G tetrads sandwiched between G.(C-A) triads.  相似文献   
160.
Brenier A  Tu C  Li J  Zhu Z  Wu B 《Optics letters》2002,27(4):240-242
We exploited Nd(3+) laser emission at 1061.9 nm ((4)F(3/2)?(4)I(11/2) channel) in a self-chi((2)) active GdAl(3)(BO(3))(4):Nd(3+) laser crystal. UV radiation was obtained from a 1.8% yield from self-sum-frequency mixing: 1/pump + 1/1061.9 = 1/UV, during pumping in the Nd(3+) (4)G(5/2)-(2)G(7/2) levels near 588 nm. The UV tunability had a range of 378-382 nm. We have demonstrated, for the first time to our knowledge, generation of coherent IR radiation from a self-difference-frequency mixing laser: 1/pump - 1/1061.9 = 1/IR. We got a 0.5% yield and tunability in the 1305-1365-nm range.  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