全文获取类型
收费全文 | 21178篇 |
免费 | 2936篇 |
国内免费 | 1889篇 |
专业分类
化学 | 15782篇 |
晶体学 | 238篇 |
力学 | 943篇 |
综合类 | 97篇 |
数学 | 1796篇 |
物理学 | 7147篇 |
出版年
2024年 | 59篇 |
2023年 | 311篇 |
2022年 | 647篇 |
2021年 | 691篇 |
2020年 | 765篇 |
2019年 | 751篇 |
2018年 | 659篇 |
2017年 | 547篇 |
2016年 | 954篇 |
2015年 | 897篇 |
2014年 | 1102篇 |
2013年 | 1543篇 |
2012年 | 1894篇 |
2011年 | 1884篇 |
2010年 | 1227篇 |
2009年 | 1206篇 |
2008年 | 1440篇 |
2007年 | 1307篇 |
2006年 | 1188篇 |
2005年 | 1067篇 |
2004年 | 860篇 |
2003年 | 733篇 |
2002年 | 763篇 |
2001年 | 515篇 |
2000年 | 397篇 |
1999年 | 386篇 |
1998年 | 307篇 |
1997年 | 257篇 |
1996年 | 253篇 |
1995年 | 216篇 |
1994年 | 190篇 |
1993年 | 162篇 |
1992年 | 140篇 |
1991年 | 126篇 |
1990年 | 100篇 |
1989年 | 80篇 |
1988年 | 45篇 |
1987年 | 40篇 |
1986年 | 48篇 |
1985年 | 48篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Yu. A. Mitropol’skii Nguyen Dong Anh Nguyen Dyk Tynh 《Ukrainian Mathematical Journal》1998,50(11):1731-1737
We construct the second approximation for random oscillations described by the Van der Pol equation which are under the action
of a broadband random process.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 11, pp. 1517–1521, November, 1998. 相似文献
62.
63.
64.
65.
Sang Kyu Lee Min Ju Cho Jung‐Il Jin Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2007,45(3):531-542
New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene‐based chromophore. The 2‐(3‐cyano‐4‐(2‐{4‐[hexyl‐(6‐hydroxy‐hexyl)‐amino]‐phenyl}‐vinyl)‐5‐oxo‐1‐{4‐[4‐(3‐oxo‐3‐phenyl‐propenyl)‐ phenoxy]‐butyl}‐1,5‐dihydro‐pyrrol‐2‐ylidene)‐malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (λ = 330–360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531–542, 2007 相似文献
66.
67.
Sang Hyun Kwon Yoshio Okamoto Chiyo Yamamoto Wonjo Cheong Myeonghee Moon Jung Hag Park 《Analytical sciences》2006,22(12):1525-1529
Porous zirconia particles are very robust material and have received considerable attention as a stationary phase support for HPLC. We prepared cellulose dimethylphenylcarbamate-bonded carbon-clad zirconia (CDMPCCZ) as a chiral stationary phase (CSP) for separation of enantiomers of a set of 14 racemic compounds in normal phase (NP) and reversed-phase (RP) liquid chromatography. Retention and enantioselectivity on CDMPCCZ were compared to those on CDMPC-coated zirconia (CDMPCZ) to see how the change in immobilization method of the chiral selector affects the retention and chiral selectivity. In NPLC, retention was longer and the number of resolved racemates was smaller on CDMPCCZ than on CDMPCZ. However, chiral selectivity factors for some resolved racemates were better on CDMPCCZ than on CDMPCZ. The longer retention on CDMPCCZ is likely due to strong, non-chiral discriminating interactions with the carbon layer on CDMPCZ. In RPLC only two racemates were resolved on CDMPCCZ, but retention times were shorter than, and resolutions were comparable to, those in NPLC, indicating a potential for improving chromatographic performance of the CDMPCCZ column in RPLC with optimized column preparation and separation conditions. 相似文献
68.
This article studies the inshore-offshore fishery model with impulsive diffusion. The existence and global asymptotic stability of both the trivial periodic solution and the positive periodic solution are obtained. The complexity of this system is also analyzed. Moreover, the optimal harvesting policy are given for the inshore subpopulation, which includes the maximum sustainable yield and the corresponding harvesting effort. 相似文献
69.
Chan Sik Cho Jun Ho KimHeung-Jin Choi Tae-Jeong KimSang Chul Shim 《Tetrahedron letters》2003,44(14):2975-2977
Anilines react with epoxides in dioxane at 180°C in the presence of a catalytic amount of a ruthenium catalyst along with tin(II) chloride to afford 2-substituted indoles in moderate to good yields. 相似文献
70.
Monodisperse polyaniline nanoparticles (PAPSSA) were synthesized from an oxidative dispersion polymerization using poly(sodium 4-styrenesulfonate) (PSSA) as both a polymeric stabilizer and a dopant agent due to its acidity. The nanoparticles were being stabilized with two different molecular weight of PSSA. Size effect of PAPSSA particles were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The d.c. electrical conductivity of composite films on the glass substrate was measured by a four-probe method. It was found that the electrical properties of the composite films are affected by the content of nano-sized polyaniline and different molecular weights of stabilizer in the poly(vinyl alcohol) (PVA) matrix. 相似文献