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   1805篇
  免费   217篇
  国内免费   174篇
化学   412篇
晶体学   2篇
力学   116篇
综合类   47篇
数学   1269篇
物理学   350篇
  2024年   4篇
  2023年   19篇
  2022年   47篇
  2021年   33篇
  2020年   54篇
  2019年   55篇
  2018年   47篇
  2017年   62篇
  2016年   81篇
  2015年   46篇
  2014年   75篇
  2013年   132篇
  2012年   113篇
  2011年   116篇
  2010年   84篇
  2009年   134篇
  2008年   104篇
  2007年   131篇
  2006年   102篇
  2005年   87篇
  2004年   84篇
  2003年   72篇
  2002年   81篇
  2001年   70篇
  2000年   70篇
  1999年   55篇
  1998年   49篇
  1997年   36篇
  1996年   28篇
  1995年   21篇
  1994年   14篇
  1993年   8篇
  1992年   9篇
  1991年   5篇
  1990年   6篇
  1989年   4篇
  1988年   5篇
  1987年   3篇
  1986年   8篇
  1985年   4篇
  1984年   5篇
  1983年   5篇
  1982年   3篇
  1981年   5篇
  1979年   4篇
  1977年   6篇
  1971年   1篇
  1970年   1篇
  1969年   1篇
  1959年   2篇
排序方式: 共有2196条查询结果,搜索用时 10 毫秒
11.
T Singh  R Chaubey 《Pramana》2006,67(3):415-428
A self-consistent system of gravitational field with a binary mixture of perfect fluid and dark energy given by a cosmological constant has been considered in Bianchi Type-V universe. The perfect fluid is chosen to be obeying either the equation of state p=γρ with γ ε |0,1| or a van der Waals equation of state. The role of A-term in the evolution of the Bianchi Type-V universe has been studied.  相似文献   
12.
In the present paper the oscillatory properties of the solutions of parabolic equations with nonlinear neutral terms are investigated. Our approach is to reduce the multi-dimensional problem to a one-dimensional problem for delay differential inequalities.  相似文献   
13.
组合原则回溯   总被引:1,自引:1,他引:0  
曹肇基 《大学物理》1998,17(9):29-31,47
从组合原则产生的背景和关键入手,分析和叙述了里兹的组合原则在光谱学上的重要意义,同时,也阐述了它与玻尔氢原子理论之间的关系。  相似文献   
14.
The interaction between heparin and neutral red was investigated by molecular spectroscopic methods. The change of all spectra suggested that positively charged neutral red had interacted with negatively charged heparin. The study of influence factors indicated that electrostatic force and hydrophobic bond might be involved in the interaction. The total binding number per disaccharide unit and intrinsic binding constant were obtained using Scatchard model.  相似文献   
15.
Using ClO2 as chemiluminescence (CL) oxidant, a novel homogeneous CL system in neutral and near neutral aqueous solution is proposed in this paper. ClO2 could oxidize sulfite in pH 5.0–8.5 acetate buffer to produce CL emission, and pipemidic acid could sensitize the CL system. The ClO2–SO32−–pipemidic acid reaction was used as a model CL system and explored the possibility of highly active and eco-friendly ClO2 being used as CL oxidant in neutral and near neutral aqueous solution. Combined with flow-injection analysis, the proposed CL system was applied to the automated dissolution testing of pipemidic acid tablet. Compared with the common strong acidic or strong basic CL system, this proposed CL owns its advantages.  相似文献   
16.
17.
The differential equations and the boundary conditions for the nonequilibrium binary distribution function of an unsymmetrical binary electrolyte are derived from the Ebeling-Falkenhagen continuity equation. The connection between the Onsager reciprocal relation and the binary distribution functions is shown. Further, Feistel's result for thec logc contribution to the conductance is extended to unsymmetrical binary electrolytes. The reason for the difference between Feistel's and Chen'sc logc term is explained, and the significance of Onsager's reciprocal relation for the calculation ofc logc and higher-concentration contributions of the conductance is discussed.  相似文献   
18.
Through the sol–gel process, using the so-called neutral amine route, spherical particles of 1:1 zirconia–titania were synthesized from zirconium(IV) and titanium(IV) butoxides as well as 1,12-diaminododecane as precursor species. The obtained product exhibited a hexagonal structure, as determinated by X-ray diffraction data. The obtained material was also characterized by thermogravimetry, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, and surface area measurements. Despite the release of template molecules on heating, the spherical morphology was retained up to about 1200°C, at which the disruption of the spheres took place.  相似文献   
19.
An electrochemical quartz crystal microbalance (EQCM) is employed for monitoring the growth of poly(neutral red) films on platinum in the electrolytic solution containing 5.0 mmol dm−3 neutral red, 0.3 mol dm−3 H2SO4, and 0.5 mol dm−3 Na2SO4. The in situ measurement of the frequency changes of the EQCM reveals that both the adsorption/desorption of neutral red and the formation of poly(neutral red) film can be observed together with anion sorption/desorption during the redox transformation of the polymer, and that the polymerization rate of neutral red increases slowly before the 11th cycle and then increases quickly with increasing number of potential cycles. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 3, pp. 284–289. The text was submitted by the authors in English.  相似文献   
20.
The widespread occurrence of the neutral loss of one to six amino acid residues as neutral fragments from doubly protonated tryptic peptides is documented for 23 peptides with individual sequences. Neutral loss of amino acids from the N-terminus of doubly charged tryptic peptides results in doubly charged y-ions, forming a ladder-like series with the ions [M + 2H](2+) = y(max) (2+), y(max - 1) (2+), y(max - 2) (2+), etc. An internal residue such as histidine, proline, lysine or arginine appears to favor this type of fragmentation, although it was sometimes also observed for peptides without this structure. For doubly protonated non-tryptic peptides with one of these residues at or near the N-terminus, we observed neutral loss from the C-terminus, resulting in a doubly charged b-type ion ladder. The analyses were performed by Q-TOF tandem mass spectrometry, facilitating the recognition of neutral loss ladders by their 2+ charge state and the conversion of the observed mass differences into reliable sequence information. It is shown that the neutral loss of amino acid residues requires low collision offset values, a simple mechanistic explanation based on established fragmentation rules is proposed and the utility of this neutral loss fragmentation pathway as an additional source for dependable peptide sequence information is documented.  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