全文获取类型
收费全文 | 180561篇 |
免费 | 8847篇 |
国内免费 | 5791篇 |
专业分类
化学 | 81786篇 |
晶体学 | 2645篇 |
力学 | 11873篇 |
综合类 | 330篇 |
数学 | 33479篇 |
物理学 | 65086篇 |
出版年
2024年 | 185篇 |
2023年 | 1206篇 |
2022年 | 2301篇 |
2021年 | 2388篇 |
2020年 | 2402篇 |
2019年 | 2315篇 |
2018年 | 11668篇 |
2017年 | 12547篇 |
2016年 | 7359篇 |
2015年 | 3866篇 |
2014年 | 3675篇 |
2013年 | 5004篇 |
2012年 | 10560篇 |
2011年 | 19644篇 |
2010年 | 12136篇 |
2009年 | 12044篇 |
2008年 | 16032篇 |
2007年 | 19425篇 |
2006年 | 4067篇 |
2005年 | 10741篇 |
2004年 | 6385篇 |
2003年 | 5793篇 |
2002年 | 3426篇 |
2001年 | 2291篇 |
2000年 | 2042篇 |
1999年 | 1713篇 |
1998年 | 1309篇 |
1997年 | 1254篇 |
1996年 | 1358篇 |
1995年 | 1137篇 |
1994年 | 992篇 |
1993年 | 814篇 |
1992年 | 745篇 |
1991年 | 697篇 |
1990年 | 616篇 |
1989年 | 491篇 |
1988年 | 409篇 |
1987年 | 369篇 |
1986年 | 341篇 |
1985年 | 353篇 |
1984年 | 290篇 |
1983年 | 251篇 |
1982年 | 208篇 |
1981年 | 195篇 |
1980年 | 168篇 |
1979年 | 170篇 |
1978年 | 174篇 |
1976年 | 135篇 |
1975年 | 123篇 |
1973年 | 144篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The mechanism of transition of a Bose gas to the superfluid state via thermal fluctuations under the condition of external cooling at a temperature above the transition point is considered. The probability of formation of such critical fluctuations (instantons) is calculated; it is found that this probability increases as the system approaches the transition temperature. It is shown that the evolution of an individual instanton is impossible without the formation of vortices in its superfluid part. 相似文献
102.
The spectrum and the spatial distribution of the emission of scattered particles upon bombardment of Be, Ti, Ta, and W with H and He ions were studied. The quantum yield and the velocity and angular distributions of the scattered excited particles were measured. Computer simulation of the scattering of H ions and He ions from the metals under study was performed with the use of the program TRIM-95. Agreement is observed between the calculated and experimentally measured angular distributions of the scattered particles. 相似文献
103.
Chin‐Ping Yang Ruei‐Shin Chen Kuei‐Hung Chen 《Journal of polymer science. Part A, Polymer chemistry》2003,41(7):922-938
To investigate the position and amount of the CF3 group affecting the coloration of polyimides (PIs), we prepared 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]hexafluoropropane ( 2 ) with four CF3 groups with 2‐chloro‐5‐nitrobenzotrifluoride and 2,2‐bis(4‐hydroxyphenol)hexafluoropropane. A series of soluble and light‐colored fluorinated PIs ( 5 ) were synthesized from 2 and various aromatic dianhydrides ( 3a – 3f ). 5a – 5f had inherent viscosities ranging from 0.80 to 1.19 dL/g and were soluble in amide polar solvents and even in less polar solvents. The glass‐transition temperatures of 5 were 221–265 °C, and the 10% weight‐loss temperatures were above 493 °C. Their films had cutoff wavelengths between 343 and 390 nm, b* values (a yellowness index) ranging from 5 to 41, dielectric constants of 2.68–3.01 (1 MHz), and moisture absorptions of 0.03–0.29 wt %. In a comparison of the PI series 6 – 8 based on 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane, and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane, we found that the CF3 group close to the imide group was more effective in lowering the color; this means that CF3 of 5 , 7 , and 8f was more effective than that of 6c . The color intensity of the four PI series was lowered in the following order: 5 > 7 > 6 > 8 . The PI 5f , synthesized from diamine 2 and 4,4′‐hexafluoroisopropylidenediphthalic anhydride, had six CF3 groups in a repeated segment, so it exhibited the lightest color among the four series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 922–938, 2003 相似文献
104.
105.
106.
A. P. Katchalov 《Journal of Mathematical Sciences》2005,127(6):2374-2388
Relationships between Gaussian beams and geometry are considered in the paper. We show that the main properties of the Gaussian beam solutions are determined by the natural geometry related to the problem under consideration. The geometry is determined by the Hamilton-Jacobi equation and the corresponding Hamiltonian. In particular, we find a geometric interpretation of the Riccati equation for the quadratic form of the phase function corresponding to a Gaussian beam in the case of Finsler geometry. Bibliography: 2 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 297, 2003, pp. 66–92. 相似文献
107.
The numerical prediction of the fields of inelastic strains (the linear invariant of the tensor of inelastic strains) in thermoset polyester/marble filler composite plates is discussed. A uniformly distributed load is applied to the plates, which lie on a steel base. The strain fields are predicted by means of the boundary element method by using creep test data for the composites and the polyester matrix itself. Identical creep tests were performed for two ages of the materials (1 month and 13 years), which allowed evaluating the aging effect. The study is carried out in two stages. At the first stage, the application of the generalized Maxwell-Gurevich equation to the thermoset matrix/mineral filler composite is demonstrated. The model parameters determined from the experimental creep data is used for the second stage, where the state of inelastic strains in the plates is predicted by applying the boundary element method. The influence of composite formulation (filler content) and physical aging of the polyester matrix on the state of inelastic strains in the plates is shown.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 145–156, March–April, 2005. 相似文献
108.
109.
本文提出从高分辨电子显微像中,利用光学、全息和部分相干等方法,提取传递函数,制作相位和振幅滤波器,实现解卷,提高高分辨电子显微像的分辨率. 相似文献
110.
Z.J. Yang T.H. Johansen H. Bratsberg G. Helgesen A.T. Skjeltorp 《Physica C: Superconductivity and its Applications》1989,160(5-6):461-465
Based on a dipole-dipole interaction model, we discuss the levitation force and related vibration problems to understand the effects of flux pinning in type-II superconductors, and the applications of levitation in superconducting systems. 相似文献