全文获取类型
收费全文 | 5351篇 |
免费 | 747篇 |
国内免费 | 296篇 |
专业分类
化学 | 1704篇 |
晶体学 | 24篇 |
力学 | 1225篇 |
综合类 | 85篇 |
数学 | 1687篇 |
物理学 | 1669篇 |
出版年
2024年 | 3篇 |
2023年 | 55篇 |
2022年 | 139篇 |
2021年 | 138篇 |
2020年 | 149篇 |
2019年 | 114篇 |
2018年 | 121篇 |
2017年 | 210篇 |
2016年 | 218篇 |
2015年 | 176篇 |
2014年 | 254篇 |
2013年 | 412篇 |
2012年 | 253篇 |
2011年 | 283篇 |
2010年 | 253篇 |
2009年 | 231篇 |
2008年 | 284篇 |
2007年 | 311篇 |
2006年 | 322篇 |
2005年 | 247篇 |
2004年 | 230篇 |
2003年 | 243篇 |
2002年 | 213篇 |
2001年 | 175篇 |
2000年 | 178篇 |
1999年 | 176篇 |
1998年 | 150篇 |
1997年 | 126篇 |
1996年 | 111篇 |
1995年 | 89篇 |
1994年 | 69篇 |
1993年 | 74篇 |
1992年 | 56篇 |
1991年 | 39篇 |
1990年 | 42篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 25篇 |
1985年 | 31篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1974年 | 3篇 |
排序方式: 共有6394条查询结果,搜索用时 15 毫秒
1.
Shi-Tao Han Hong-Ying Duan Lan-Yun Chen Dr. Tian-Guang Zhan Dr. Li-Juan Liu Li-Chun Kong Prof. Kang-Da Zhang 《化学:亚洲杂志》2021,16(23):3886-3889
A photo-switchable hetero-complementary quadruple H-bonding array, which consists of an azobenzene-derived ureidopyrimidinone (UPy) module ( Azo-UPy ) and a nonphotoactive diamidonaphthyridine (DAN) derivative ( Napy-1 ), is constructed based on a reversible photo-locking approach. Upon UV (390 nm)/Vis (460 nm) light irradiations, photo-switchable quadruple H-bonded dimerization between Azo-UPy and Napy-1 can be achieved with exhibiting 4.8×104-fold differences in binding strength (ON/OFF ratios). Furthermore, smart polymeric gels with unique photo-controlled macroscopic self-assembly behavior can be fabricated by introducing such quadruple H-bonding array as photo-regulable noncovalent interfacial connections. 相似文献
2.
关于一类二次哈密尔顿系统在二次扰动下的极限环个数问题 总被引:2,自引:0,他引:2
本文研究了一类具有两个鞍点和一个中心的通用二次哈密尔顿向量场在二次扰动下的三参数开折,证明极限环的最小上界为2。 相似文献
3.
Second-order random wave solutions for interfacial internal waves in N-layer density-stratified fluid
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper studies the random internal wave equations describing the density interface displacements and the velocity potentials of N-layer stratified fluid contained between two rigid walls at the top and bottom. The density interface displacements and the velocity potentials were solved to the second-order by an expansion approach used by Longuet-Higgins (1963) and Dean (1979) in the study of random surface waves and by Song (2004) in the study of second- order random wave solutions for internal waves in a two-layer fluid. The obtained results indicate that the first-order solutions are a linear superposition of many wave components with different amplitudes, wave numbers and frequencies, and that the amplitudes of first-order wave components with the same wave numbers and frequencies between the adjacent density interfaces are modulated by each other. They also show that the second-order solutions consist of two parts: the first one is the first-order solutions, and the second one is the solutions of the second-order asymptotic equations, which describe the second-order nonlinear modification and the second-order wave-wave interactions not only among the wave components on same density interfaces but also among the wave components between the adjacent density interfaces. Both the first-order and second-order solutions depend on the density and depth of each layer. It is also deduced that the results of the present work include those derived by Song (2004) for second-order random wave solutions for internal waves in a two-layer fluid as a particular case. 相似文献
4.
5.
6.
带干扰的多险种风险模型 总被引:2,自引:0,他引:2
由于保险公司风险经营规模不断扩大,用单一险种的模型来描述风险过程存在局限性,本文讨论了带干扰多险种风险模型,应用鞅论方法,得出伦德伯格不等式和最终破产概率公式。 相似文献
7.
A. D. Matveev 《Journal of Applied Mechanics and Technical Physics》2003,44(5):721-726
Modified three-dimensional formulations of bending problems of homogeneous elastic plates and beams are considered. Modification of the known three-dimensional formulations reduces to using additional constraints imposed on displacement functions. An advantage of the formulations proposed is that complex fixing conditions of plates and beams can be taken into account. 相似文献
8.
9.
An analytical solution of a linearized problem of the emission of periodic internal waves by part of a plane which oscillates with a small amplitude in an arbitrary direction in a viscous exponentially stratified fluid is constructed. Solutions of the dispersion equation are given for all positions of the emitting surface (arbitrary, vertical, horizontal, and critical when one of the beam propagation directions is collinear with the emitting surface). The possibility of transition to the case of a uniform fluid, which is important for applications, is analyzed. 相似文献
10.
Zi‐Niu Wu 《国际流体数值方法杂志》2005,48(5):541-564
The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. In this paper we consider the influence of the refined interfaces on the steady state errors for second‐order three‐point difference approximations of flow equations. Since the various characteristic components of the Euler equations should behave similarly on such grids with regard to refinement‐induced errors, it is sufficient enough to conduct the analysis on a scalar model problem. The error we consider is a global error, different to local truncation error, and reflects the interaction between multiple interfaces. The steady state error will be compared to the errors on smooth refinement grids and on uniform grids. The conclusion seems to support the numerical findings of Yamaleev and Carpenter (J. Comput. Phys. 2002; 181: 280–316) that refinement does not necessarily reduce the numerical error. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献