全文获取类型
收费全文 | 1307篇 |
免费 | 47篇 |
国内免费 | 10篇 |
专业分类
化学 | 760篇 |
晶体学 | 17篇 |
力学 | 42篇 |
综合类 | 1篇 |
数学 | 267篇 |
物理学 | 277篇 |
出版年
2023年 | 13篇 |
2022年 | 41篇 |
2021年 | 35篇 |
2020年 | 35篇 |
2019年 | 34篇 |
2018年 | 39篇 |
2017年 | 35篇 |
2016年 | 68篇 |
2015年 | 48篇 |
2014年 | 53篇 |
2013年 | 134篇 |
2012年 | 75篇 |
2011年 | 100篇 |
2010年 | 85篇 |
2009年 | 53篇 |
2008年 | 62篇 |
2007年 | 58篇 |
2006年 | 38篇 |
2005年 | 44篇 |
2004年 | 41篇 |
2003年 | 18篇 |
2002年 | 16篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1959年 | 5篇 |
排序方式: 共有1364条查询结果,搜索用时 15 毫秒
31.
32.
L. R. G. Valadon Mohamed Osman Rosemary S. Mummery 《Photochemistry and photobiology》1979,29(3):605-607
Abstract— Ten minutes of red irradiation (R) increased carotenogenesis in Verticillium agoricinum and this effect was reversed by 10min of far-red (FR) irradiation indicating that phytochrome is involved. A far-red minus red difference spectrum of a crude extract shows a peak at 670 nm and a dip at 750 nm wavelength, values slightly larger than higher plant phytochrome. indicating the presence of phytochrome. 相似文献
33.
Craig NC Brickey TW Lingenfelter PT Osmani AS Rathore MO Pearson A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(7):1571-1583
Infrared and Raman spectra were recorded for cis-3,4-difluorocyclobutene (cDFCB) and trans-3,4-difluorocyclobutene-d4. Unscaled density functional theory (DFT) calculations of frequencies and intensities at the B3LYP/6-311++G(d,p) level supported the complete assignment of the vibrational fundamentals. The previous assignment of fundamentals of trans-3,4-difluorocyclobutene was revised. An unusual blue shift occurs for the methylenic CH-stretching frequencies of cis-3,4-difluorocyclobutene in going from the gas phase to the liquid phase. This hydrogen bond effect is related to similar observations recently reported and interpreted. The blue shift does not occur for the vinylic CH bonds of the cis isomer and does not occur for either type of CH bond in the trans isomer. 相似文献
34.
Liao YC Subramani HJ Franses EI Basaran OA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):9926-9930
Surfactants are routinely used to control the breakup of drops and jets in many applications such as inkjet printing, crop spraying, and DNA or protein microarraying. The breakup of surfactant-free drops and jets has been extensively studied. By contrast, little is known about the closely related problem of interface rupture when surfactants are present. Solutions of a nonionic surfactant, pentaethylene glycol monododecyl ether, or C12E5, in water and in 90 wt % glycerol/water are used to show the effects of surfactant and viscosity on the deformation and breakup dynamics of stretching liquid bridges. Equilibrium surface tensions for both solutions can be fitted with the Langmuir-Szyskowski equation. All experiments have been done at 24 degrees C. The critical micelle concentrations for C12E5 are 0.04 and 0.4 mM in water and the glycerol/water solution, respectively. With high-speed imaging, the dynamic shapes of bridges held captive between two rods of 3.15 mm diameter are captured and analyzed with a time resolution of 0.1-1 ms. The bridge lengths are 3.15 mm initially and about 5-7 mm at pinch-off. Breakup occurs after stretching for about 0.2-0.3 s, depending on the solution viscosity and the surfactant concentration. When the liquid bridges break up, the volume of the sessile drop left on the bottom rod is about 3 times larger than that of the pendant drop left on the top rod. This asymmetry is due to gravity and is influenced by the equilibrium surface tensions. Surfactant-containing low-viscosity water bridges are shown to break up faster than surfactant-free ones because of the effect of gravity. With or without surfactant, water bridges form satellite drops. Surfactant-containing high-viscosity glycerol/water bridges break up more slowly than surfactant-free ones because of strong viscous effects. Moreover, the shapes of the sessile drops close to breakup exhibit a "pear-like" tip; whether a satellite forms depends on the surface age of the bridge before stretching commences. These unexpected effects arising from the addition of surfactants are due to the capillary pressure reduction and Marangoni flows linked to dynamic surface tension. 相似文献
35.
Ligia Bicudo de Almeida Marilene De Vuono Camargo Penteado George Britton Peter Uebelhart Murat Acemoglu Conrad Hans Eugster 《Helvetica chimica acta》1988,71(1):31-32
The 5,6:5′,6′-diepoxy-5,6:5′,6;-tetrahydro-β,β-carotene, isolated from tubers of a white-fleshed variety of sweet potato (Ipomoea batatas LAM .) has been assigned the (5R,6S,5′R,6′S)-chirality on the basis of its HPLC, UV/VIS, and CD data. 相似文献
36.
Murat Acemoglu Roland Prewo Jost Hans Bieri Conrad Hans Eugster 《Helvetica chimica acta》1984,67(1):175-183
Synthesis and X-Ray Structure of (6′RS,8′RS,2E)- and (6′RS,8′SR,2E)-3-Methyl-3-(2′,2′,6′-trimethyl-7′-oxabicyclo[4.3.0]non-9′-en-8′-yl)-2-propenal ([(5RS,8RS)- and (5RS,8SR)-5,8-Epoxy-5,8-dihydro-ionylidene]acetaldehyde) To check our previous spectroscopic assignments of the structures of trans- and cis-substituted furanoid end groups of carotenoid-5,8-epoxides, we now have synthesized the title compounds. An X-ray structure determination of a single crystal of the trans-isomer (±)- -10A is in agreement with the 1 H-NMR spectroscopic arguments: isomers with Δδ (H? C(7), H? C(8)) = 0.15–0.22 ppm and J > 1.4 for H? C(7) belong to the cis-series; Δδ in trans-compounds is < 0.07 ppm, and H? C(7) appears as a broad singulett. 相似文献
37.
38.
39.
In this paper we establish some new dynamic inequalities on time scales which contain in particular generalizations of integral and discrete inequalities due to Hardy, Littlewood, P′olya, D'Apuzzo, Sbordone and Popoli. We also apply these inequalities to prove a higher integrability theorem for decreasing functions on time scales. 相似文献
40.
A series of new ionic binuclear Pd(II) complexes supported by water‐soluble bis(α‐diimine) ligands were prepared and employed as catalysts for the palladium‐catalyzed Suzuki reaction in aqueous media. The binuclear nature of the complexes increased the reaction rate, while electronic and steric modification of the ligand frameworks had a remarkable influence upon the catalytic activity of the palladium complexes. The catalysts were shown to be homogeneous through mercury poisoning experiments and complexes could be recycled more than 10 times without loss of catalytic activity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献