全文获取类型
收费全文 | 28160篇 |
免费 | 950篇 |
国内免费 | 924篇 |
专业分类
化学 | 7205篇 |
晶体学 | 966篇 |
力学 | 834篇 |
综合类 | 134篇 |
数学 | 15168篇 |
物理学 | 5727篇 |
出版年
2023年 | 119篇 |
2022年 | 286篇 |
2021年 | 267篇 |
2020年 | 277篇 |
2019年 | 556篇 |
2018年 | 527篇 |
2017年 | 422篇 |
2016年 | 479篇 |
2015年 | 451篇 |
2014年 | 851篇 |
2013年 | 1711篇 |
2012年 | 806篇 |
2011年 | 2004篇 |
2010年 | 1806篇 |
2009年 | 1841篇 |
2008年 | 1847篇 |
2007年 | 1789篇 |
2006年 | 1455篇 |
2005年 | 1174篇 |
2004年 | 980篇 |
2003年 | 829篇 |
2002年 | 840篇 |
2001年 | 568篇 |
2000年 | 585篇 |
1999年 | 533篇 |
1998年 | 538篇 |
1997年 | 409篇 |
1996年 | 438篇 |
1995年 | 393篇 |
1994年 | 382篇 |
1993年 | 292篇 |
1992年 | 297篇 |
1991年 | 218篇 |
1990年 | 209篇 |
1989年 | 200篇 |
1988年 | 128篇 |
1987年 | 151篇 |
1985年 | 578篇 |
1984年 | 392篇 |
1983年 | 298篇 |
1982年 | 306篇 |
1981年 | 274篇 |
1980年 | 226篇 |
1979年 | 191篇 |
1978年 | 184篇 |
1977年 | 176篇 |
1976年 | 173篇 |
1975年 | 123篇 |
1974年 | 154篇 |
1973年 | 157篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
In this paper, we establish some new nonlinear integral inequalities of the Gronwall–Bellman–Ou-Iang-type in two variables. These on the one hand generalizes and on the other hand furnish a handy tool for the study of qualitative as well as quantitative properties of solutions of differential equations. We illustrate this by applying our new results to certain boundary value problem. 相似文献
142.
Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr2O3 using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and b (Δc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr2O3). A second phase, namely θ-(Al,Cr)2O3, was revealed by XRD in the sample containing 9.60 wt% Cr2O3. The structure of mullites was refined by the Rietveld method, location of Cr3+ was performed by the EPR spectroscopy. At low chromium doping level (Cr2O3 content less than ∼5 wt%) Cr3+ ions were substituted for Al3+ in the AlO6 octahedra of the mullite structure (M1 site). For higher doping level, Cr3+ ions were additionally substituted for Al3+ in the AlO6 octahedra of the second phase [θ-(Al,Cr)2O3 at 1400 °C, or α-(Al,Cr)2O3 at 1600 °C] which segregated in the system. Substitution of Cr3+ for Al3+ on M1 site in the mullite structure resulted in increase of average distances in (M1)O6 octahedron and decrease of average distances in T*O4 tetrahedron, while average distances in TO4 tetrahedron stayed almost constant. 相似文献
143.
144.
本文介绍非线性方程转化直线性方程和多元线性回归法来分析近代物理实验中塞曼效应分裂干涉圆环多处选点测量的处理过程。 相似文献
145.
A simple microscopic model of charge ordering in the NaxCoO2 system is presented. The model takes into account the interplane interactions between the ordered Na ions and d electrons from the CoO2 layers as well as the nearest-neighbor intraplane Coulomb interactions between d electrons. It is shown that a driving force of charge ordering in the CoO2 layers is the interplane interaction that alone is able to describe various types of inhomogeneous charge ordering (e.g., the striped phases) as well as to predict correctly the conducting properties of the system. 相似文献
146.
Gianluigi Luppi Rodrigo J. Corrêa Angelo C. Pinto Quirinus B. Broxterman Claudia Tomasini 《Tetrahedron》2006,62(51):12017-12024
The first total synthesis of (R)-convolutamydine A has been achieved by the organocatalytic addition of acetone to 4,6-dibromoisatin. The absolute configuration was determined by single crystal X-ray diffraction. DFT studies were used to model the transition states for the aldol reaction and equilibrium geometries of the post-aldol reaction intermediates. The DFT study revealed that the aldol bond forming reaction was considerably endothermic. 相似文献
147.
Common fixed-point results are established for a new class of noncommuting selfmaps. We apply them to obtain several invariant approximation results which unify, extend, and complement well-known results. 相似文献
148.
Nicola Fusco Michele Gori Francesco Maggi 《NoDEA : Nonlinear Differential Equations and Applications》2006,13(4):425-433
An approximation theorem for families of weakly coercive convex functions by means of countably many smooth families of convex
functions is proved. As a consequence, the classical “three-fold” lower semicontinuity theorem for integral functionals of
the Calculus of Variations by James Serrin is unified in one single statement. 相似文献
149.
由于混凝土材料理化特性的差异,高强混凝土的弯压极限应变明显地小于普通混凝土,依据试验结果分析了高强混凝土的弯压极限应变变化规律,并给出了它的计算公式. 相似文献
150.