全文获取类型
收费全文 | 3276篇 |
免费 | 203篇 |
国内免费 | 43篇 |
专业分类
化学 | 2329篇 |
晶体学 | 39篇 |
力学 | 136篇 |
综合类 | 3篇 |
数学 | 393篇 |
物理学 | 622篇 |
出版年
2024年 | 34篇 |
2023年 | 65篇 |
2022年 | 192篇 |
2021年 | 314篇 |
2020年 | 197篇 |
2019年 | 179篇 |
2018年 | 160篇 |
2017年 | 134篇 |
2016年 | 214篇 |
2015年 | 139篇 |
2014年 | 152篇 |
2013年 | 263篇 |
2012年 | 235篇 |
2011年 | 259篇 |
2010年 | 151篇 |
2009年 | 121篇 |
2008年 | 137篇 |
2007年 | 120篇 |
2006年 | 88篇 |
2005年 | 74篇 |
2004年 | 41篇 |
2003年 | 44篇 |
2002年 | 38篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1960年 | 1篇 |
排序方式: 共有3522条查询结果,搜索用时 15 毫秒
991.
992.
Muhammad A. Rashid Bettina Appel Vahuni Karapetyan Helmut Reinke Peter Langer 《Tetrahedron》2008,64(22):5416-5425
Functionalized 1-azaxanthones (5-oxo-5H-[1]-benzopyrano[2,3-b]pyridines) were prepared by TMSOTf-mediated condensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-cyanochromones and subsequent base-mediated domino ‘retro-Michael/nitrile-addition/heterocyclization’ reaction. 相似文献
993.
994.
Muhammad Taher Abuelmaatti 《International Journal of Infrared and Millimeter Waves》2007,28(10):849-858
A mathematical model for the relationship between the output voltage and incident radiation of the infrared semiconductor
mercury-cadmium-telluride (MCT) detector is presented. The model, basically a sine-series function, can easily yield closed-form
expressions for the harmonic and intermodulation performance of the MCT detector with large-amplitude multisinusoidal incident
radiation. The special case of two-tone equal-amplitude incident radiation is considered in detail. The results show that
the second-order harmonic and intermodulation products are always higher than the third-order components. Moreover, the results
show that the second-order intermodulation is always dominant. 相似文献
995.
Muhammad Taher Abuelmaatti 《International Journal of Infrared and Millimeter Waves》2007,28(9):741-749
A mathematical model for the temperature dependence of the bolometer semiconductor resistance is presented. The model, basically
a sine-series function, can easily yield closed-form expressions for the harmonic and intermodulation performance of the acquired
interferogram voltage with large-amplitude multisinusoidal variations in the incident radiation. The special case of two-tone
equal-amplitude incident radiation is considered in detail. The results show that the intermodulation components are always
higher than the harmonic components of the same order. The results also show that the second-order intermodulation is always
dominant and is higher than the second-harmonic component by about 6 dB. Moreover, the results show that for relatively small
incident amplitudes of the incident radiation the ratio between the second- and third-harmonic components is almost equal
to the ratio between the second-harmonic component and the fundamental. The results also show that the ratio between the amplitudes
of the second- and third-order intermodulation components is almost equal to the ratio between the amplitudes of the second-order
intermodulation component and the fundamental. 相似文献
996.
Tahir MN Théato P Müller WE Schröder HC Borejko A Faiss S Janshoff A Huth J Tremel W 《Chemical communications (Cambridge, England)》2005,(44):5533-5535
Silicatein immobilised on self-assembled polymer layers using a histidine-tag chelating anchor group retains its hydrolytical activity for the formation of biosilica, and catalyses the formation of layered arrangements of biotitania and biozirconia. 相似文献
997.
Ferheen S Ahmed E Afza N Malik A Shah MR Nawaz SA Choudhary MI 《Chemical & pharmaceutical bulletin》2005,53(5):570-572
Haloxylines A (1) and B (2), new piperidine alkaloids, have been isolated from the chloroform soluble fraction of Haloxylon salicornicum and their structures elucidated by spectroscopic techniques including 2D-NMR. Both the compounds displayed antifungal and cholinesterase enzymes inhibitory potentials. 相似文献
998.
Muhammad?I.?SalehEmail author E.?Kusrini R.?Adnan Ismail?A.?Rahman B.?Saad A.?Usman H.?-K.?Fun B.?M.?Yamin 《Journal of chemical crystallography》2005,35(6):469-475
[Bis-picrate(pentaethylene glycol)]praseodymium(III) picrate, [Pr(pic)2⋅(EO5]+[pic]−, was successfully obtained from the reaction of praseodymium nitrate hexahydrate, picric acid and pentaethylene glycol in acetonitrile–methanol as solvent. The crystal system is monoclinic with space group P21/c, a = 18.91419(11) Å, b = 9.0470(6) Å, c = 24.1209(14) Å and α = γ = 90∘, β = 109.07(1)∘, V = 3880.3(4) Å3 and Z = 4. The Pr atom is coordinated to the flexible and open EO5 ring via all the six oxygen atoms and two picrate ligands, one via phenoxo oxygen atom and the other one with both phenoxo and nitro oxygen atoms in a bidentate manner resulting a 9-coordinate tricapped trigonal prismatic geometry. The two picrate ligands coordinated to the Pr atom are at the opposite sides of the hexadentate EO5 ring with phenyl fragments almost perpendicular with dihedral angle of 89.7(3)∘. Thermal analysis results show that the complex is stable up to 100∘C when it began to slowly decompose and followed by an explosive decomposition at 290∘C. 相似文献
999.
The response of the transmission spectrum of cascaded long period gratings (LPGs) to the deposition of nanostructured coatings by use of the Langmuir-Blodgett technique is investigated. The phase of the interference fringes within the LPGs' attenuation bands is shown to be highly sensitive to the optical thickness of the coating, for thicknesses of the order of 100 nm. 相似文献
1000.
Abbasi MA Ahmad VU Zubair M Nawaz SA Lodhi MA Farooq U Choudhary MI 《Natural product research》2005,19(5):509-515
Phytochemical investigation of Symplocos racemosa resulted in the isolation of a new ethyl substituted glycoside, 1-ethyl brachiose-3'-acetate (1) along with four known compounds ketochaulmoogric acid (2), nonaeicosanol (3), triacontyl palmitate (4) and methyl triacontanoate (5). The substitution of ethyl group on 1 was natural because during the course of extraction and purification ethanol was not used. The structural elucidation of the isolated compounds was based primarily on 1D- and 2D-NMR analysis, including COSY, HMQC, and HMBC correlations. The glycoside 1 and triacontyl palmitate (4) displayed the inhibitory potential against lipoxygenase and urease enzyme, respectively. 相似文献