全文获取类型
收费全文 | 22319篇 |
免费 | 2367篇 |
国内免费 | 2337篇 |
专业分类
化学 | 3768篇 |
晶体学 | 33篇 |
力学 | 1839篇 |
综合类 | 569篇 |
数学 | 14524篇 |
物理学 | 6290篇 |
出版年
2024年 | 29篇 |
2023年 | 182篇 |
2022年 | 396篇 |
2021年 | 418篇 |
2020年 | 481篇 |
2019年 | 472篇 |
2018年 | 492篇 |
2017年 | 672篇 |
2016年 | 726篇 |
2015年 | 576篇 |
2014年 | 1112篇 |
2013年 | 1431篇 |
2012年 | 1155篇 |
2011年 | 1368篇 |
2010年 | 1224篇 |
2009年 | 1513篇 |
2008年 | 1506篇 |
2007年 | 1584篇 |
2006年 | 1408篇 |
2005年 | 1360篇 |
2004年 | 1121篇 |
2003年 | 1004篇 |
2002年 | 877篇 |
2001年 | 790篇 |
2000年 | 735篇 |
1999年 | 627篇 |
1998年 | 588篇 |
1997年 | 534篇 |
1996年 | 407篇 |
1995年 | 331篇 |
1994年 | 279篇 |
1993年 | 198篇 |
1992年 | 183篇 |
1991年 | 133篇 |
1990年 | 161篇 |
1989年 | 105篇 |
1988年 | 102篇 |
1987年 | 86篇 |
1986年 | 74篇 |
1985年 | 89篇 |
1984年 | 69篇 |
1983年 | 46篇 |
1982年 | 70篇 |
1981年 | 62篇 |
1980年 | 39篇 |
1979年 | 38篇 |
1978年 | 30篇 |
1977年 | 26篇 |
1976年 | 31篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Veli B. Shakhmurov 《Journal of Mathematical Analysis and Applications》2007,327(2):1182-1201
The nonlocal boundary value problems for anisotropic partial differential-operator equations with a dependent coefficients are studied. The principal parts of the appropriate generated differential operators are nonself-adjoint. Several conditions for the maximal regularity and the fredholmness in Banach-valued Lp-spaces of these problems are given. These results permit us to establish that the inverse of corresponding differential operators belongs to Schatten q-class. Some spectral properties of the operators are investigated. In applications, the nonlocal BVP's for quasielliptic partial differential equations and for systems of quasielliptic equations on cylindrical domain are studied. 相似文献
92.
In this paper,the concept of the infinitesimal realization factor is extended to the parameter-dependent performance functions in closed queueing networks. Then the concepts of realization matrix (its elements are called realization factors) and performance potential are introduced,and the relations between infinitesimal realization factors and these two quantities are discussed. This provides a united framework for both IPA and non IPA approaches. Finally,another physical meaning of the service rate is given. 相似文献
93.
Fluorescence line narrowing (FLN) spectroscopy was used to study the role of the polypeptide chain in influencing the spectrum of Zn-substituted cytochrome c (Zn cyt c) and metal-free cyt c (porphyrin cyt c). For both derivatives the spectra show characteristics of relaxed fluorescence from an inhomogeneously broadened sample. Zero phonon lines and phonon wings can be clearly distinguished, and vibrational frequencies of the ground and excited states were identified. The inhomogeneous distribution width for porphyrin cyt c is slightly wider than that of Zn cyt c and a second population of molecules was apparent in the porphyrin cyt c. The phonon coupling was greater for Zn cyt c than for porphyrin cyt c, which may be due to the extra coupling to the polypeptide chain by metal ligation.This work has been done in partial fulfillment of the requirements for the Doctor of Philosophy degree. 相似文献
94.
A. Gerasimov 《Journal of statistical physics》1993,70(3-4):939-948
The analysis is carried out of the response of the center of gravity (dipole moment) of the distribution of noninteracting thermalized nonlinear oscillators to a sinusoidal driving force. Heat bath coupling is modeled by damping and noise. The driving is weak, but the frequency is resonant, so that there is a nonlinear resonance in the phase space. The response has a linear part that can be obtained from the perturbation analysis and a small nonlinear correction that is specific for the resonant structure. 相似文献
95.
96.
CLIFFORDMARTINGALESΦ-EQUIVALENCEBETWEENS(f)ANDf¥LONGRULIN;QIANTAO(InstituteofMathematics,AcademiaSinica,Beijing100080,China.)... 相似文献
97.
98.
讨论了微分方程组 dx/dt=-y(1 -ax2 n) +bx-cx2 n+ 1,dy/dt=x(1 -ax2 n) ,并且给出了其极限环存在唯一的条件 . 相似文献
99.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献
100.
既不离散也不连续的随机变量 总被引:2,自引:1,他引:1
讨论了既不离散也不连续的随机变量 ,并纠正了有关文献中关于连续型随机变量定义中的错误 . 相似文献