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   2056篇
  免费   31篇
  国内免费   25篇
化学   1041篇
晶体学   9篇
力学   150篇
数学   385篇
物理学   527篇
  2021年   22篇
  2020年   26篇
  2019年   31篇
  2018年   38篇
  2017年   28篇
  2016年   35篇
  2015年   30篇
  2014年   45篇
  2013年   68篇
  2012年   66篇
  2011年   90篇
  2010年   46篇
  2009年   41篇
  2008年   97篇
  2007年   83篇
  2006年   83篇
  2005年   75篇
  2004年   64篇
  2003年   52篇
  2002年   54篇
  2001年   34篇
  2000年   40篇
  1999年   26篇
  1997年   22篇
  1996年   36篇
  1995年   22篇
  1994年   40篇
  1993年   32篇
  1992年   31篇
  1991年   24篇
  1990年   31篇
  1989年   32篇
  1988年   30篇
  1987年   33篇
  1986年   26篇
  1983年   22篇
  1982年   26篇
  1980年   25篇
  1979年   31篇
  1977年   34篇
  1976年   40篇
  1975年   31篇
  1974年   24篇
  1973年   26篇
  1972年   25篇
  1971年   23篇
  1970年   21篇
  1969年   20篇
  1968年   24篇
  1967年   27篇
排序方式: 共有2112条查询结果,搜索用时 15 毫秒
1.
Journal of Algebraic Combinatorics - The well-known Worpitzky identity $$\begin{aligned} (x+1)^n = \sum \limits _{k=0}^{n-1} A_{n,k} {{x+n-k} \atopwithdelims (){n}} \end{aligned}$$ provides a...  相似文献   
2.
Sadagov  A. Yu.  Goidina  T. A.  Aseev  V. A.  Nikonorov  N. V.  Fedorov  Yu. K.  Chugunova  M. M.  Levin  A. D. 《Optics and Spectroscopy》2020,128(10):1658-1666
Optics and Spectroscopy - The results of development of fluorescence calibration standards based on phosphate matrix glass activated with ions of rare-earth metals are presented. The calibration...  相似文献   
3.
Cyanine dyes are broadly used for fluorescence imaging and other photonic applications. 3,3′-Diethylthiacyanine (THIA) is a cyanine dye composed of two identical aromatic heterocyclic moieties linked with a single methine, –CH. The torsional degrees of freedom around the methine bonds provide routes for non-radiative decay, responsible for the inherently low fluorescence quantum yields. Using transient absorption spectroscopy, we determined that upon photoexcitation, the excited state relaxes along two parallel pathways producing three excited-state transients that undergo internal conversion to the ground state. The media viscosity impedes the molecular modes of ring rotation and preferentially affects one of the pathways of non-radiative decay, exerting a dominant effect on the emission properties of THIA. Concurrently, the polarity affects the energy of the transients involved in the decay pathways and further modulates the kinetics of non-radiative deactivation.  相似文献   
4.
5.
Research on Chemical Intermediates - Several types of modified zeolite BETA38 with different iron loading were prepared. Prepared materials were characterized using different techniques (XRD, XRF,...  相似文献   
6.
Physics of Atomic Nuclei - The Ignitor tokamak nuclear fusion research project is one of the most ambitious initiatives undertaken under the long-term scientific cooperation program between the...  相似文献   
7.
8.
9.
Herein, we establish the preparation, characterization, and reactivity of a new diphosphine ligand, 1,2-bis(di(3-dicyclohexylboraneyl)propylphosphino)ethane (P2BCy4), a scaffold that contains four pendant boranes. An entryway into the coordination chemistry of P2BCy4 is established by using nickel, providing the octaboraneyl complex [Ni(P2BCy4)2]—this species contains a boron-rich secondary coordination sphere that reacts readily with Lewis bases. In the case of 4,4′-bipyridine, an air-sensitive coordination polymer is obtained. Characterization of this material by solid-state NMR and EPR spectroscopy reveals the presence of a charge-transfer polymer, which forms as a function of intramolecular Ni→4,4′-bpy electron transfer (ET), providing an array of oxidized nickel sites and reduced 4,4′-bpy radical anion sites. Notably, the related intermolecular reaction between the model fragments [Ni(dnppe)2] (dnppe=1,2-bis(di-n-propylphosphino)ethane) and a bis(boraneyl)-protected 4,4′-bpy, provides no ET. Overall, the P2BCy4 fragment provides a unique opportunity for Lewis base activation, in one case allowing for the facile construction of monomers for incorporation into redox-active macromolecules.  相似文献   
10.

Improving the germination of economically important crops and the condition of young plants is a major challenge currently facing agricultural practice. Pea (Pisum sativum L.) is one of the four most important cultivated legumes, along with groundnut (Arachis hypogaea L.), soybean (Glycine max L.) and beans (Phaseolus vulgaris L.). Due to the high protein content (23–33%), there is an interest in growing this crop as a source of protein for humans and animals. In this study, we focused on the effect of Cold Atmospheric Pressure Plasma (CAPP) on the decontamination and germination of pea seeds, on young seedling growth and production parameters, and on increasing their resistance and mechanical strength. We can state that germination increased by 10 to 25% after plasma treatment, and the most significant decontamination effect was detected when using non-thermal plasma generated in the ambient air (A-variants) and in the nitrogen atmosphere (N-variants). The increased in situ activity of peroxidases (POX) in the cell walls of A-variants and N-variants is also closely related to the increase in the mechanical strength of the cell walls and thus contributes to the higher resistance of these seedlings. This is also illustrated by the differences in lignin deposition among the different variants after CAPP treatment. To our knowledge, this is the first study concerning the influence of CAPP on the lignification of root tissues and on increasing the strength and resistance of plants.

  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