全文获取类型
收费全文 | 71219篇 |
免费 | 5815篇 |
国内免费 | 4658篇 |
专业分类
化学 | 26769篇 |
晶体学 | 184篇 |
力学 | 3776篇 |
综合类 | 1258篇 |
数学 | 31393篇 |
物理学 | 18312篇 |
出版年
2023年 | 623篇 |
2022年 | 786篇 |
2021年 | 1896篇 |
2020年 | 1540篇 |
2019年 | 1653篇 |
2018年 | 1318篇 |
2017年 | 1561篇 |
2016年 | 2035篇 |
2015年 | 1833篇 |
2014年 | 2960篇 |
2013年 | 4686篇 |
2012年 | 3171篇 |
2011年 | 3703篇 |
2010年 | 3367篇 |
2009年 | 4360篇 |
2008年 | 4585篇 |
2007年 | 4805篇 |
2006年 | 3882篇 |
2005年 | 3024篇 |
2004年 | 2606篇 |
2003年 | 2646篇 |
2002年 | 4912篇 |
2001年 | 2176篇 |
2000年 | 1789篇 |
1999年 | 1510篇 |
1998年 | 1441篇 |
1997年 | 1183篇 |
1996年 | 1039篇 |
1995年 | 897篇 |
1994年 | 866篇 |
1993年 | 807篇 |
1992年 | 756篇 |
1991年 | 519篇 |
1990年 | 470篇 |
1989年 | 386篇 |
1988年 | 425篇 |
1987年 | 339篇 |
1986年 | 343篇 |
1985年 | 511篇 |
1984年 | 397篇 |
1983年 | 216篇 |
1982年 | 421篇 |
1981年 | 582篇 |
1980年 | 515篇 |
1979年 | 539篇 |
1978年 | 432篇 |
1977年 | 336篇 |
1976年 | 299篇 |
1974年 | 94篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Recent Progress in the $L_p$ Theory for Elliptic and Parabolic Equations with Discontinuous Coefficients 下载免费PDF全文
Hongjie Dong 《分析论及其应用》2020,36(2):161-199
In this paper, we review some results over the last 10-15 years on elliptic and parabolic equations with discontinuous coefficients. We begin with an approach given by N. V. Krylov to parabolic equations in the whole space with $\rm{VMO}_x$ coefficients. We then discuss some subsequent development including elliptic and parabolic equations with coefficients which are allowed to be merely measurable in one or two space directions, weighted $L_p$estimates with Muckenhoupt ($A_p$) weights, non-local elliptic and parabolic equations, as well as fully nonlinear elliptic and parabolic equations. 相似文献
62.
《中国化学快报》2020,31(7):1919-1922
A novel BODIPY (boradiazaindacene) dye denoted as BODIPY-DT containing terpyridine unit has been designed and characterized. The dye is found to be selective and visual solvatochromic sensor toward DMF among test organic solvents. The sensing process displays time-controllable, dynamic signal outputs in the emission colors including red, purple, yellow and even white emission colors. It is presented that selective free radical oxidation reaction happens during the recognition process. 相似文献
63.
64.
ABSTRACT Multicolour emissive carbon dots (CDs) are widely investigated by virtue of their merits on fluorescent properties. Method on heteroatom doping assisted with various solvents has been proved efficient in achieving multiple-colour-emissive CDs, especially long-wavelength emission. Herein, a synthesis of multicolour-emissive CDs by controlled surface function is reported. By tuning the thermal-pyrolysis temperature and molar ratio of reactants, optimal emission of the resulted CDs gradually shifts from blue to yellow light with the assistance of different solvents. According to the emissive relationship dependent on excitation, fluorescence lifetimes, and FT-IR of these CDs, the different surface states participated with S and N elements on the surface of carbogenic core govern fluorescent colours of the CDs. In terms of the applications, blue CDs (B-CDs) exhibits high sensitivity for ion detections of Ag+ and Fe3+, which is further illustrated to have different quenching mechanisms each other because that these ions have the affinity interaction with different surface groups of the CDs. Moreover, blue and yellow CDs solutions are mixed with PVP water solution to fabricate white-light CDs/PVP film, which exhibits stable fluorescence with a CIE coordinate of (0.32, 0.33) and endows these CDs as potentially fluorescent nanomaterial in the solid state lighting field. 相似文献
65.
Dario Tamascelli 《Entropy (Basel, Switzerland)》2020,22(11)
The chain mapping of structured environments is a most powerful tool for the simulation of open quantum system dynamics. Once the environmental bosonic or fermionic degrees of freedom are unitarily rearranged into a one dimensional structure, the full power of Density Matrix Renormalization Group (DMRG) can be exploited. Beside resulting in efficient and numerically exact simulations of open quantum systems dynamics, chain mapping provides an unique perspective on the environment: the interaction between the system and the environment creates perturbations that travel along the one dimensional environment at a finite speed, thus providing a natural notion of light-, or causal-, cone. In this work we investigate the transport of excitations in a chain-mapped bosonic environment. In particular, we explore the relation between the environmental spectral density shape, parameters and temperature, and the dynamics of excitations along the corresponding linear chains of quantum harmonic oscillators. Our analysis unveils fundamental features of the environment evolution, such as localization, percolation and the onset of stationary currents. 相似文献
66.
67.
68.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献
69.
A. Othman Almatroud Amina-Aicha Khennaoui Adel Ouannas Giuseppe Grassi M. Mossa Al-sawalha Ahlem Gasri 《Entropy (Basel, Switzerland)》2020,22(12)
This article proposes a new fractional-order discrete-time chaotic system, without equilibria, included two quadratic nonlinearities terms. The dynamics of this system were experimentally investigated via bifurcation diagrams and largest Lyapunov exponent. Besides, some chaotic tests such as the 0–1 test and approximate entropy (ApEn) were included to detect the performance of our numerical results. Furthermore, a valid control method of stabilization is introduced to regulate the proposed system in such a way as to force all its states to adaptively tend toward the equilibrium point at zero. All theoretical findings in this work have been verified numerically using MATLAB software package. 相似文献
70.
Juan Luis García Guirao Jaume Llibre Wei Gao 《Journal of Difference Equations and Applications》2020,26(2):203-208
The objective of this work is to present sufficient conditions for having positive topological entropy for continuous self-maps defined on a closed surface by using the action of this map on the homological groups of the closed surface. 相似文献