全文获取类型
收费全文 | 4705篇 |
免费 | 126篇 |
国内免费 | 992篇 |
专业分类
化学 | 5221篇 |
晶体学 | 69篇 |
力学 | 21篇 |
综合类 | 34篇 |
数学 | 6篇 |
物理学 | 472篇 |
出版年
2023年 | 31篇 |
2022年 | 54篇 |
2021年 | 68篇 |
2020年 | 79篇 |
2019年 | 72篇 |
2018年 | 110篇 |
2017年 | 129篇 |
2016年 | 120篇 |
2015年 | 101篇 |
2014年 | 186篇 |
2013年 | 512篇 |
2012年 | 225篇 |
2011年 | 261篇 |
2010年 | 201篇 |
2009年 | 272篇 |
2008年 | 272篇 |
2007年 | 345篇 |
2006年 | 325篇 |
2005年 | 332篇 |
2004年 | 317篇 |
2003年 | 247篇 |
2002年 | 192篇 |
2001年 | 148篇 |
2000年 | 138篇 |
1999年 | 125篇 |
1998年 | 93篇 |
1997年 | 99篇 |
1996年 | 93篇 |
1995年 | 103篇 |
1994年 | 96篇 |
1993年 | 87篇 |
1992年 | 82篇 |
1991年 | 45篇 |
1990年 | 34篇 |
1989年 | 41篇 |
1988年 | 32篇 |
1987年 | 18篇 |
1986年 | 25篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有5823条查询结果,搜索用时 31 毫秒
71.
72.
73.
G. R. Sudhakaran R. L. Bhattacharjee J. C. Sarker L. H. Johnston 《International Journal of Infrared and Millimeter Waves》1986,7(12):1903-1911
A submillimeter laser Stark spectrum has been observed for fully deuterated Methyl Chloride (CD3Cl) with the 337 m line of the HCN laser up to Stark fields of about 54000 V/cm. The spectra were taken for both Parallel and Perpendicular Polarizations and the multiplet transitions were identified as JK=42K41K in the ground vibrational state. Three families with K=12, 13 and 14 have been identified and their zero field frequencies have been given with improved accuracy over those calculated from available molecular constants. 相似文献
74.
75.
A new salicylic-based open-chain crown ether ligand, 1,10-bis(2′-carboxylphenyl)-1,4,7,10-tetraoxadecane (BCPTD) was synthesized. Solutions of its complex with Tb3+ can emit the intrinsic fluorescence of Tb3+. The fluorescence intensity of the complex in KCl solution was enhanced by the addition of silver(I), leading to a new fluorescence enhancement phenomenon. The spectrofluorimetric determination of traces of silver(I) based on the above phenomenon was carried out. The excitation and emission wavelengths are 298 and 545 nm, respectively. Under optimal conditions, the differential value of fluorescence intensity in the absence and presence of Ag+ was proportional to the concentration of silver(I) in the range 0.5-20 μg ml−1. The method was applied to the determination of silver(I) in a standard ore sample. The analytical performance is investigated in detail by using common aromatic carboxylic acids or synthetic analogues of BCPTD as ligands to replace BCPTD. It was found that Tb-aromatic acid complexes did not result in fluorescence enhancement of Tb3+ in AgCl collosol. The phenomenon was only observed in Tb(III) with BCPTD or its open-chain crown ether analogues solutions.In addition, the enhancement of the fluorescence intensity of terbium(III) in these complexes depends on the extent of formation of the AgCl collosol. 相似文献
76.
Thin layers of cellulose I nanocrystals were spin-coated onto silicon wafers to give a flat model cellulose surface. A mild heat treatment was required to stabilize the cellulose layer. Interactions of this surface with polyelectrolyte layers and multilayers were probed by atomic force microscopy in water and dilute salt solutions. Deflection–distance curves for standard silicon nitride tips were measured for silicon, cellulose-coated silicon, and for polyelectrolytes adsorbed on the cellulose surface. Transfer of polymer to the tip was checked by running deflection–distance curves against clean silicon. Deflection–distance curves were relatively insensitive to adsorbed polyelectrolyte, but salt addition caused transfer of cationic polyelectrolyte to the tip, and swelling of the polyelectrolyte multilayers. 相似文献
77.
Investigation of Tomato Plant Defence Response to Tobacco Mosaic Virus by Determination of Methyl Salicylate with SPME-Capillary GC-MS 总被引:2,自引:0,他引:2
Headspace SPME was applied to investigation of tomato plant defence response to tobacco mosaic virus (TMV) by determination of compounds emitted from tomato plants at the extraction conditions of 25 °C and 15 min. It was found that TMV-inoculated tomato plant released large amount of methyl salicylate (MeSA) as response to TMV and MeSA concentration changed dramatically with time after inoculation. Gaseous MeSA as a signaling compound could induce in surrounding tomato plants to produce salicylic acid (SA) and synthesize and release MeSA. These results show that MeSA might be an airborne plant-signalling molecule in tomato plant response to TMV. The present method provided low detection limit of 2.0 ng L–1 and needed little sample preparation time (15 min), so the method makes it easy to find the critical times of tomato plant response to TMV by fast determination of MeSA released from tomato plant. 相似文献
78.
When promoted by samarium in DMF, aroyl chlorides react readily with acrylates to afford α,β-diaroylpropionates in good to excellent yields without pretreating or activating the metallic samarium. 相似文献
79.
80.
The core-shell structured grafted copolymer particles of polybutadiene grafted polymethyl methacrylate (PB-g-PMMA, MB) were prepared by emulsion polymerization. The MB particles were used to modify poly (vinyl chloride) (PVC) by melt blending. The mechanical properties of the PVC blends were investigated. The micro-morphology of the PVC blends was observed by scanning electron microscopy (SEM). The results indicated that the samples with the best impact strength could be obtained when the core-shell weight ratio of PB to PMMA is lower than 93:7, the mechanical properties correlated well with SEM morphologies, the addition of modifier with the ratio core to shell of 93:7 could reduce the domain size of the dispersed phase. Furthermore, the compatibility and properties of the blends were greatly enhanced and improved. The modifier particles could be well dispersed in the PVC matrix. 相似文献