全文获取类型
收费全文 | 2518篇 |
免费 | 42篇 |
国内免费 | 3篇 |
专业分类
化学 | 1429篇 |
晶体学 | 15篇 |
力学 | 71篇 |
综合类 | 1篇 |
数学 | 368篇 |
物理学 | 679篇 |
出版年
2021年 | 19篇 |
2020年 | 15篇 |
2019年 | 24篇 |
2018年 | 21篇 |
2016年 | 46篇 |
2015年 | 29篇 |
2014年 | 39篇 |
2013年 | 107篇 |
2012年 | 87篇 |
2011年 | 88篇 |
2010年 | 41篇 |
2009年 | 26篇 |
2008年 | 94篇 |
2007年 | 91篇 |
2006年 | 87篇 |
2005年 | 108篇 |
2004年 | 79篇 |
2003年 | 94篇 |
2002年 | 75篇 |
2001年 | 69篇 |
2000年 | 61篇 |
1999年 | 53篇 |
1998年 | 28篇 |
1997年 | 44篇 |
1996年 | 55篇 |
1995年 | 40篇 |
1994年 | 34篇 |
1993年 | 36篇 |
1992年 | 46篇 |
1991年 | 33篇 |
1990年 | 56篇 |
1989年 | 44篇 |
1988年 | 41篇 |
1987年 | 25篇 |
1986年 | 32篇 |
1985年 | 46篇 |
1984年 | 44篇 |
1983年 | 37篇 |
1982年 | 46篇 |
1981年 | 38篇 |
1980年 | 36篇 |
1979年 | 30篇 |
1978年 | 38篇 |
1977年 | 34篇 |
1976年 | 26篇 |
1975年 | 32篇 |
1974年 | 31篇 |
1973年 | 38篇 |
1972年 | 14篇 |
1969年 | 15篇 |
排序方式: 共有2563条查询结果,搜索用时 15 毫秒
61.
62.
Philip J. Hammond C. Dennis Hall 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):351-353
Abstract Cis-1-alkyl (or aryl)-2,5-dimethyl-3-phospholens isomerize to the trans-isomers in deuteriochloroform and the isomerization is probably due to small quantities of phosgene in the solvent. 相似文献
63.
64.
Mainly through the extensive investigations of Nakagawa and coworkers, nickel peroxide has emerged as a powerful oxidant for organic compounds. For example, it has been used for the oxidation of alcohols to aldehydes or carboxylic acids,2,3 allylic hydroxyl (selectively) to the carbonyl group,4 α-ketols to α-diketones,5 α-glycols, α-ketols, α-hydroxyl and α-keto acids to cleavage products,6 aldehydes to amides or nitriles in the presence of ammonia,7 phenols to quinones,8,9 certain Schiff bases to benzoxazoles,10 amines to azo compounds or nitriles,11,12 diarylamines to hydrazines,13 carbazoles to dimers and trimers,14 hydrazones to diazo compounds,15,16 1-aminobenzotriazole to benzyne,17 N-substituted hydroxylamines to azoxy compounds,18 phenylacetonitrile to dimeric products,19 a thiouracil to a uracil derivative,20 thiols to disulfides and sulfides to sulfones,21 N-substituted phenothiazines to sulfoxides and sulfones,21 haloforms to hexahaloethanes.23 相似文献
65.
Abstract Polymer chain diffusion in the nematic mesophase was studied using a model main chain liquid crystalline (LC) polyether based on 2,2′-dimethyl-4,4′-dihydroxyazoxybenzene and mixed alkane spacers. A side chain LC polymethacrylate containing an azobenzene mesogenic group was also investigated. Tracer diffusion coefficients were determined as a function of temperature by an ion-beam depth profiling technique, forward recoil spectrometry. The results confirm that main chain LC polymer chain dynamics are dramatically affected by phase transitions and sample geometry. This behaviour is in marked contrast to the side chain LC polymer which exhibited no phase dependence on the part of the tracer diffusion coefficient. 相似文献
66.
Russell G. Baughman Gabriel B. Hall 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(10):975-977
Structural studies performed in this laboratory of organophosphorus pesticides continue with these related compounds. The –NO2 groups of methyl parathion (systematic name: dimethyl 4‐nitrophenyl phosphorothioate, C8H10NO5PS) and dicapthon (systematic name: 2‐chloro‐4‐nitrophenyl dimethyl phosphorothioate, C8H9ClNO5PS) make dihedral angles of 10.67 (8) and 5.8 (1)°, respectively, with the planes of their attached rings, which accompanies angular distortion at the ring C atoms to which the –NO2 groups are attached. Similar distortions are observed at the C atom to which the thiophosphate groups are attached. Significant differences in distances and angles around the phenolic O, versus the –OMe groups, explain why it is the site of hydrolysis for these compounds. A comparison of a torsion angle involving the thiophosphate group and phenolic O atom with similar pesticide structures is given and indicates steric influences on that angle. 相似文献
67.
We report on the adiabatic splitting of a Bose-Einstein condensate of 87Rb atoms by an asymmetric double-well potential located above the edge of a perpendicularly magnetized TbGdFeCo film atom chip. By controlling the barrier height and double-well asymmetry, the sensitivity of the axial splitting process is investigated through observation of the fractional atom distribution between the left and right wells. This process constitutes a novel sensor for which we infer a single shot sensitivity to gravity fields of deltag/g approximately 2 x 10(-4). From a simple analytic model, we propose improvements to chip-based gravity detectors using this demonstrated methodology. 相似文献
68.
69.
Nicky Rogge Richard Simper Marijn Verschelde Maximilian Hall 《European Journal of Operational Research》2015
This paper fills a noticeable gap in the current economic and penology literature by proposing new performance-enhancing policies based on an efficiency analysis of a sample of male prisons in England and Wales over the period 2009/10. In addition, we advance the empirical literature by integrating the managerialism of four strategic functions of prisons, employment and accommodation, capacity utilization, quality of life in prison and the rehabilitation and re-offending of prisoners. We find that by estimating multiple models focussing on these different areas some prisons are more efficient than other establishments. In terms of policy, it is therefore necessary to consider not just an overall performance metric for individual prisons, as currently undertaken annually by the UK Ministry of Justice, but to look into the administration and managerialism of their main functions in both a business and public policy perspective. Indeed, it is further necessary to view prisons together and not as single entities, so as to obtain a best practice frontier for the different operations that management undertakes in English and Welsh prisons. 相似文献
70.
Roger Hagen Lennart Salmn Bengt Stenberg 《Journal of Polymer Science.Polymer Physics》1996,34(12):1997-2006
The viscoelastic properties of various crosslinked natural rubbers, NR, were investigated by mechanical spectroscopy. The glass transition temperature, Tg, was found to be dependent on both the crosslink density and the crosslink type. Higher values of Tg were obtained for sulfur-crosslinked NR than for peroxide-crosslinked NR at the same crosslink density. The greater influence of the sulfur content on Tg may be attributed to polysulfidic crosslinks and cyclic sulfide structures favored at high sulfur contents. Sulfur-vulcanized NRs with monosulfidic crosslinks, favored at relatively high accelerator/sulfur ratios, have properties more similar to the peroxide-cured NR with simple carbon(SINGLE BOND)carbon crosslinks covalent bonds, resulting in only small shifts in Tg. A qualitative analysis of monosulfidic crosslinks and polysulfidic structures was performed with 13C solid-state NMR spectroscopy. The storage modulus, E′, in the rubbery plateau region increased with increasing crosslink density. However, the crosslink type did not influence the moduli values as much as it influenced the Tg values. Different methods of detecting the crosslink density were also discussed. © 1996 John Wiley & Sons, Inc. 相似文献