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   2588篇
  免费   94篇
  国内免费   3篇
化学   2178篇
晶体学   82篇
力学   29篇
数学   171篇
物理学   225篇
  2024年   5篇
  2023年   25篇
  2022年   87篇
  2021年   119篇
  2020年   93篇
  2019年   102篇
  2018年   62篇
  2017年   61篇
  2016年   108篇
  2015年   71篇
  2014年   87篇
  2013年   138篇
  2012年   186篇
  2011年   175篇
  2010年   120篇
  2009年   97篇
  2008年   147篇
  2007年   107篇
  2006年   117篇
  2005年   146篇
  2004年   101篇
  2003年   120篇
  2002年   73篇
  2001年   37篇
  2000年   37篇
  1999年   19篇
  1998年   18篇
  1997年   16篇
  1996年   29篇
  1995年   21篇
  1994年   23篇
  1993年   19篇
  1992年   6篇
  1991年   11篇
  1990年   4篇
  1989年   9篇
  1987年   6篇
  1986年   13篇
  1985年   6篇
  1984年   5篇
  1982年   8篇
  1981年   9篇
  1980年   3篇
  1979年   5篇
  1978年   4篇
  1977年   5篇
  1976年   4篇
  1975年   4篇
  1972年   3篇
  1971年   3篇
排序方式: 共有2685条查询结果,搜索用时 15 毫秒
21.
22.
The goal of this article is to discuss the Simple Equations Method (SEsM) for obtaining exact solutions of nonlinear partial differential equations and to show that several well-known methods for obtaining exact solutions of such equations are connected to SEsM. In more detail, we show that the Hirota method is connected to a particular case of SEsM for a specific form of the function from Step 2 of SEsM and for simple equations of the kinds of differential equations for exponential functions. We illustrate this particular case of SEsM by obtaining the three- soliton solution of the Korteweg-de Vries equation, two-soliton solution of the nonlinear Schrödinger equation, and the soliton solution of the Ishimori equation for the spin dynamics of ferromagnetic materials. Then we show that a particular case of SEsM can be used in order to reproduce the methodology of the inverse scattering transform method for the case of the Burgers equation and Korteweg-de Vries equation. This particular case is connected to use of a specific case of Step 2 of SEsM. This step is connected to: (i) representation of the solution of the solved nonlinear partial differential equation as expansion as power series containing powers of a “small” parameter ϵ; (ii) solving the differential equations arising from this representation by means of Fourier series, and (iii) transition from the obtained solution for small values of ϵ to solution for arbitrary finite values of ϵ. Finally, we show that the much-used homogeneous balance method, extended homogeneous balance method, auxiliary equation method, Jacobi elliptic function expansion method, F-expansion method, modified simple equation method, trial function method and first integral method are connected to particular cases of SEsM.  相似文献   
23.
Cellulose - In this work, we have developed methods of synthesis of cellulose nanocrystal (CNC) conjugates with chlorotriazine reactive dyes (RDs)—reactive violet, reactive-bright red and...  相似文献   
24.
Synthetic routes have been developed to a number of (thio) squaraine dyes containing the residues of CH‐acids at the central cyclobutene ring. The electronic and spatial structure as well as the chemical conversions and optical behaviour of the compounds obtained have been studied both theoretically and by X‐ray diffraction analysis, 1H NMR and electronic spectroscopy. As shown, the electronic nature and sterical characteristics of the central ring substituents give rise to some general conformational features and crystal packing regularities and also govern the spectral position of the first π–π* absorption band. The structure–property relationships established in the study provide guidance for the purposeful design of deeply coloured (thio) squaraines. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
25.
The interaction in the molten system Rb2O‐P2O5‐TiO2‐NiO was investigated at different molar ratios Rb/P = 0.5‐1.3, fixed Ti/P = 0.15, Ti/Ni = 1.0 at temperature range 1073–953 K. The conditions of formation of complex phosphates RbTi2(PO4)3, Rb2Ni0.5Ti1.5(PO4)3 and RbNiPO4 have been determined. The new phosphate Rb2Ni0.5Ti1.5(PO4)3 (space group P213, a = 9.9386(2) Å) has been obtained and investigated by the single crystal X‐ray diffraction and FTIR‐spectroscopy. It has langbeinite‐like structure, that is built up from mixed (Ni/Ti)O6‐octahedra and РО4‐tetrahedra. Rubidium atoms are located in closed cavities of 3D‐framework.  相似文献   
26.
The molecular hybridization approach has been used to develop compounds with improved efficacy by combining two or more pharmacophores of bioactive scaffolds. In this context, hybridization of various relevant pharmacophores with phenothiazine derivatives has resulted in pertinent compounds with diverse biological activities, interacting with specific or multiple targets. In fact, the development of new drugs or drug candidates based on phenothiazine system has been a promising approach due to the diverse activities associated with this tricyclic system, traditionally present in compounds with antipsychotic, antihistaminic and antimuscarinic effects. Actually, the pharmacological actions of phenothiazine hybrids include promising antibacterial, antifungal, anticancer, anti-inflammatory, antimalarial, analgesic and multi-drug resistance reversal properties. The present review summarizes the progress in the development of phenothiazine hybrids and their biological activity.  相似文献   
27.
Crystallography Reports - Fluoride crystals K2(Ta0.9I0.1)F7 (sp. gr. Р21/c) complementary to the K2TaF7 and K2NbF7 fluoride family have been obtained by hydrothermal synthesis. Their...  相似文献   
28.
Wheat allergens are responsible for symptoms in 60–70% of bakers with work-related allergy, and knowledge, at the molecular level, of this disorder is progressively accumulating. The aim of the present study is to investigate the panel of wheat IgE positivity in allergic Italian bakers, evaluating a possible contribution of novel wheat allergens included in the water/salt soluble fraction. The water/salt-soluble wheat flour proteins from the Italian wheat cultivar Bolero were separated by using 1-DE and 2-DE gel electrophoresis. IgE-binding proteins were detected using the pooled sera of 26 wheat allergic bakers by immunoblotting and directly recognized in Coomassie stained gel. After a preparative electrophoretic step, two enriched fractions were furtherly separated in 2-DE allowing for detection, by Coomassie, of three different proteins in the range of 21–27 kDa that were recognized by the pooled baker’s IgE. Recovered spots were analyzed by nanoHPLC Chip tandem mass spectrometry (MS/MS). The immunodetected spots in 2D were subjected to mass spectrometry (MS) analysis identifying two new allergenic proteins: a glucose/ribitol dehydrogenase and a 16.9 kDa class I heat shock protein 1. Mass spectrometer testing of flour proteins of the wheat cultivars utilized by allergic bakers improves the identification of until now unknown occupational wheat allergens.  相似文献   
29.
Crystals of new indium iodate (K0.6Na0.4Ba)In[IO3]6 were prepared by the hydrothermal synthesis. The unit-cell parameters are a = 11.3984(3) Å, с = 11.3817(3) Å, sp. gr. R3?. The chemical formula of the compound was derived from the structure determination and refinement with anisotropic displacement parameters to R = 0.0284. In the structure the InO6 octahedra share vertices with six umbrella-like [IO3]–groups typical of iodates and form isolated 3?-symmetric charged \(\rm{In[IO_{3}]_6^{3-}}\) clusters. Large Ba, K, and Na cations occupy a common site on a threefold axis due to the isomorphous substitution and compensate the charge of the clusters. The new structure extends the family of the recently discovered alkali-metal and barium iodates containing Ti and Zr atoms in octahedral sites. The iodate K2Ge[IO3]6 containing Ge atoms in the centers of octahedra is the parent compound of this structural family.  相似文献   
30.
Implicit Runge-Kutta (RK) methods are in common use when addressing stiff initial value problems (IVP). They usually share the property of A-stability that is of crucial importance in solving the latter type of IVP. Radau IIA family of implicit RK methods is among the preferred ones. Especially its fifth-order representative named RADAU5 has received a lot of attention for use with lax accuracies. Here, we try the lesser possible perturbation of its coefficients. Then, we derive a trigonometric fitted modification that is intended to be applied in periodic IVPs. Numerical tests over a variety of problems with oscillatory solutions justify our effort.  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