全文获取类型
收费全文 | 4345篇 |
免费 | 301篇 |
国内免费 | 205篇 |
专业分类
化学 | 842篇 |
晶体学 | 20篇 |
力学 | 604篇 |
综合类 | 20篇 |
数学 | 540篇 |
物理学 | 674篇 |
综合类 | 2151篇 |
出版年
2023年 | 43篇 |
2022年 | 59篇 |
2021年 | 53篇 |
2020年 | 74篇 |
2019年 | 213篇 |
2018年 | 84篇 |
2017年 | 109篇 |
2016年 | 113篇 |
2015年 | 107篇 |
2014年 | 163篇 |
2013年 | 171篇 |
2012年 | 156篇 |
2011年 | 216篇 |
2010年 | 166篇 |
2009年 | 226篇 |
2008年 | 193篇 |
2007年 | 263篇 |
2006年 | 239篇 |
2005年 | 203篇 |
2004年 | 189篇 |
2003年 | 182篇 |
2002年 | 210篇 |
2001年 | 138篇 |
2000年 | 118篇 |
1999年 | 122篇 |
1998年 | 92篇 |
1997年 | 79篇 |
1996年 | 86篇 |
1995年 | 90篇 |
1994年 | 68篇 |
1993年 | 57篇 |
1992年 | 57篇 |
1991年 | 62篇 |
1990年 | 62篇 |
1989年 | 53篇 |
1988年 | 40篇 |
1987年 | 25篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 38篇 |
1978年 | 14篇 |
1977年 | 22篇 |
1976年 | 13篇 |
1975年 | 15篇 |
1974年 | 16篇 |
1973年 | 19篇 |
排序方式: 共有4851条查询结果,搜索用时 187 毫秒
1.
2.
Alexander Krasnosel'skii Dmitrii Rachinskii 《NoDEA : Nonlinear Differential Equations and Applications》2002,9(1):93-115
We consider autonomous systems with a nonlinear part depending on a parameter and study Hopf bifurcations at infinity. The
nonlinear part consists of the nonlinear functional term and the Prandtl--Ishlinskii hysteresis term. The linear part of the
system has a special form such that the close-loop system can be considered as a hysteresis perturbation of a quasilinear
Hamiltonian system. The Hamiltonian system has a continuum of arbitrarily large cycles for each value of the parameter. We
present sufficient conditions for the existence of bifurcation points for the non-Hamiltonian system with hysteresis. These
bifurcation points are determined by simple characteristics of the hysteresis nonlinearity. 相似文献
3.
4.
The interaction between multiple incompressible air jets has been studied numerically and experimentally. The numerical predictions have been first validated using experimental data for a single jet configuration. The spreading features of five unequal jets in the configuration of one larger central jet surrounded by four smaller equi‐distant jets, have been studied, for different lateral spacing ratios of 1.5, 2.0 and 2.5 and a central jet Reynolds number of 1.24×105 (corresponding to a Mach number of 0.16). Flow of five equal jets has also been simulated, for the sake of comparison. The jet interactions commence at an axial distance of about 3–4 diameters and complete by an axial distance of about 10 diameters for the lowest spacing ratio of 1.5. For larger spacing ratios, the length required for the start and completion of jet interaction increase. Peripheral jets bend more towards the central jet and merge at a smaller distance, when their sizes are smaller than that of the central jet. The entrainment ratio for multiple jets is higher than that for a single jet. Excellent agreement is observed between the experimental data and theoretical predictions for both mean flow field and turbulent quantities, at regions away from the jet inlet. The potential core length and initial jet development, however, are not predicted very accurately due to differences in the assumed and actual velocity profiles at the jet inlet. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
5.
We show that, contrary to earlier reports, application of the one-parameter variational technique to the classical (image) model for H in front of an Al surface leads to energy shifts for the ground state which are very close to those obtained numerically with a more sophisticated model of the system. 相似文献
6.
The first aim in the present paper is to give an integral representation for Beppo Levi functions on R
n. Our integral representation is an extension of Sobolev's integral representation given for infinitely differentiable functions with compact support. As applications, continuity and differentiability properties of Beppo Levi functions are studied.Our second aim in this paper is to study the existence of limits at infinity for Beppo Levi functions. We also consider the existence of fine-type limits at infinity with respect to Bessel capacities, which yields the radial limit result at infinity. 相似文献
7.
8.
新的基团法估算沸点下蒸发焓 总被引:5,自引:0,他引:5
提出了估算沸点下蒸发焓的含基团重量分率的基团法和估算式,拟合团贡献值,对385种有机物的计算平均偏差约为1.5%。所提出的新方法明显优于3种对应状态和用蒸发熵的基团法。 相似文献
9.
针形锂电池CR425的研制 总被引:1,自引:0,他引:1
采用Li—MnO2电池材料和工艺制造CR425锂电池.重点对正极活性物质的加工制备及电池组装工艺进行了试验和改进.通过XRD试验测试了热处理前后电解二氧化锰(EMD)的结构,对制备的电池在不同温度下进行恒电流和恒电阻放电,并对贮存1周、3个月和6个月电池的开路电压、短路电流、内阻及放电容量进行了测试.结果表明,电池性能完全满足CR425锂电池的技术要求,可作为夜间钓鱼时的发光浮标或商务通用笔夜间使用时的照明电源. 相似文献
10.
一类平面七次多项式系统赤道环的稳定性与极限环分支 总被引:2,自引:0,他引:2
本文研究一类平面七次多项式系统赤道环的稳定性和极限环分支,给出了系统的前12个奇点量公式,可积性条件及在赤道附近存在3个极限环的条件,较为精细地指出了极限环的存在位置。 相似文献