全文获取类型
收费全文 | 4345篇 |
免费 | 145篇 |
国内免费 | 11篇 |
专业分类
化学 | 2389篇 |
晶体学 | 42篇 |
力学 | 128篇 |
数学 | 465篇 |
物理学 | 1477篇 |
出版年
2022年 | 62篇 |
2021年 | 69篇 |
2020年 | 81篇 |
2019年 | 85篇 |
2018年 | 91篇 |
2017年 | 63篇 |
2016年 | 123篇 |
2015年 | 93篇 |
2014年 | 117篇 |
2013年 | 264篇 |
2012年 | 243篇 |
2011年 | 279篇 |
2010年 | 168篇 |
2009年 | 154篇 |
2008年 | 217篇 |
2007年 | 213篇 |
2006年 | 226篇 |
2005年 | 189篇 |
2004年 | 129篇 |
2003年 | 115篇 |
2002年 | 101篇 |
2001年 | 75篇 |
2000年 | 75篇 |
1999年 | 54篇 |
1998年 | 42篇 |
1997年 | 40篇 |
1996年 | 50篇 |
1995年 | 49篇 |
1994年 | 43篇 |
1993年 | 57篇 |
1992年 | 47篇 |
1991年 | 35篇 |
1990年 | 49篇 |
1989年 | 41篇 |
1988年 | 40篇 |
1987年 | 39篇 |
1986年 | 29篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 40篇 |
1982年 | 37篇 |
1981年 | 37篇 |
1980年 | 41篇 |
1979年 | 33篇 |
1978年 | 38篇 |
1977年 | 33篇 |
1976年 | 37篇 |
1975年 | 31篇 |
1974年 | 35篇 |
1973年 | 37篇 |
排序方式: 共有4501条查询结果,搜索用时 31 毫秒
111.
A method for quantitative separation of antimony(III) by sorption on polyether based polyurethane foam and its spectrophotometric determination has been described. The method involves formation of a pink-red complex of antimony(III) with iodide (0.045M) and dithizone (2.3 x 10(-5)M) in 0.25-0.75M H(2)SO(4) medium, sorption of the complex on polyurethane foam (within 45 min) at room temperature followed by its elution with acidified acetone (acetone containing 0.008% H(2)SO(4)) and spectrophotometric measurement at 507.2 nm ( = 2.56 x 10(4) l mol cm). The method obeys Beer's law from 0.1 to 6.0 mug antimony(III). Tolerance limits of other ions are Co (100 mug), Ni (100 mug), Fe (10 mug), Cu (0.5 mug), Sn (20 mug), Zn (100 mug), As (100 mug), Mn (200 mug), Pb (50 mug), Ti (100 mug), V (50 mug), etc. Interference by iron and copper have been eliminated by treating with KOH prior to the extraction of antimony. The method has been standardized with glass samples spiked with known amounts of antimony and applied to the determination of antimony in various glasses. 相似文献
112.
A vesicle-forming chiral cationic surfactant (1R,2S)-(-)-N-dodecyl-N-methyl-ephedrinium bromide was evaluated as a pseudo-stationary phase in micellar electrokinetic chromatography (MEKC) for enantioseparation of eight non-steroidal anti-inflammatory drugs e.g., carprofen, flurbiprofen, fenoprofen, ibuprofen, indoprofen, ketoprofen, naproxen and suprofen by capillary electrophoresis. The effects of varying experimental conditions such as pH and concentration of surfactant in the running buffer on the enantiomer separation of the drugs are reported. A mixture of five of the above drugs was separated and each enantiomeric pair was also separated simultaneously in a single run by use of the surfactant. The strong electrostatic interactions between the analytes and the vesicles seemed to have a major role in the enantiomeric separation of the profens. 相似文献
113.
[reaction: see text] N-Aromatic secondary amides can be transformed into O-aromatic esters in high yield via N-nitrosamide intermediates. The amides can be generated in situ from the corresponding aromatic amines or nitro compounds, and phenols can easily be made from the esters. The reaction can be modified by addition of methyl methacrylate or toluene at 0 degrees C to give polymerization or deamination, respectively. The rearrangement mechanism may involve radical formation and recombination. 相似文献
114.
J.Michael Birchall Roy Fields Robert N. Haszeldine Reginald J. McLean 《Journal of fluorine chemistry》1980,15(6):487-495
Thermolysis of hexafluorocyclopropane in the presence of ethylene, propene, vinyl chloride, and vinyl bromide gives good yields of the corresponding 1,1-difluorocyclopropanes, formed by addition of difluorocarbene to the olefin. The tetrafluoroethylene formed dimerises to octafluorocyclobutane, co-dimerises with the olefin, or survives, depending on the reaction conditions. With allene, hexafluorocyclopropane gives 1-(difluoromethylene)cyclopropane, 2,2,3,3-tetrafluorospiropentane, and products derived from tetrafluoroethylene and allene. 相似文献
115.
This article describes an integrated process for simultaneous purification of lysozyme, ovalbumin, and ovomucoid from hen egg white. The crude egg white extract was passed through a cation exchanger Streamline trade mark SP and the bound lysozyme was eluted with 5% ammonium carbonate, pH 9.0, containing 1 M NaCl after elution of avidin. This partially purified lysozyme was further purified 639-fold on dye-linked cellulose beads. Ovalbumin and ovomucoid did not bind to Streamline SP. Ovalbumin could be precipitated from this unbound fraction by 5% trichloroacetic acid, and ovomucoid was removed from the supernatant by precipitation with ethanol. The yields of lysozyme, ovomucoid, and ovalbumin were 77, 94, and 98%, respectively. All the purified proteins showed single bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis. All the steps are easily scalable, and the process described here can be used for large-scale simultaneous purification of these proteins in the pure form. 相似文献
116.
A new chelating resin was synthesised by the modification of styrene-divinylbenzene (2%) copolymer and incorporation of dithiocarbamate groups. The polydithiocarbamate resin was characterised by elemental analysis, thermal studies and IR studies. The analytical characteristics of the sorbent were established and optimum sorption conditions for Cu, Ni, Pb, Fe, As and Mn determined. The total sorption capacity of the resin was 37 mg g−1 for Ni(II), 35 mg g−1 for Cu(II), 29 mg g−1 for Fe(III) and 23 mg g−1 for Pb(II). The optimum pH for the removal of metal ions was 3-5 for Ni(II), 5 for Cu(II), 4 for Fe(III) and 4-5 for Pb(II). High sorption capacity was observed when compared with other conventional chelating polymers. The sorption kinetics was fairly rapid, as apparent from the loading half time t1/2 values, indicating a better accessibility of the chelating sites. 相似文献
117.
Ellen Herlihy Peter H. Gies Colin R. Roy Michael Jones 《Photochemistry and photobiology》1994,60(3):288-294
Abstract Quantifying individual exposure to ultraviolet radiation (UVR) is critical to understanding the etiology of a number of diseases including nonmelanotic and melanotic skin cancers. Measurements of personal exposure to solar UVR were made in Hobart, Tasmania in February (summer) 1991 for six different outdoor activities using UVR-sensitive polysulfone (PS) film attached at seven anatomical sites. Concurrent behavioral and environmental observations were also made. To date many studies have relied on subject recall to quantify past solar UVR exposures. To gain insight into the accuracy of subject recall the measured UVR exposures received by different subjects using the PS film were compared to those calculated from personal diaries and ambient solar UVB levels from a monitoring station. In general, when UVR exposure activities took place under close supervision, good correlations were obtained between the PS badges and the ambient measurements/diaries approach. Ultraviolet radiation exposures for the field study involving 94 subjects engaged in a number of outdoor activities are presented. 相似文献
118.
Santosh K. Mondal Parimal Paul Rita Roy Kamalaksha Nag 《Transition Metal Chemistry》1984,9(7):247-250
Summary Complexes of nickel(II), palladium(II), copper(II), cobalt(II), and cobalt(III) with methyl-2-(-salicylaldiminoethyl)-cyclopent-1-en-dithiocarboxylate (H2L1) and methyl-2-(-salicylaldiminoisopropyl)cyclopent-1-en-dithiocarboxylate (H2L2) have been prepared. They contain the donor sites ONNS. The metal(II) ions from neutral, monomeric square planar chelate complexes. The cobalt(III) complexes [CoL1-(H2O)2]X (X=Cl or ClO4) appear to betrans-diaqua-species. All compounds have been characterized by a number of physico-chemical methods. 相似文献
119.
Abstract —Chloride anions, when added to DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea]-treated spinach chloroplasts, change the rate of decay of the delayed light emission in the seconds region but do not change the shape or the temperature dependence of the decay. Benzoate anions, on the other hand, change both the rate and the shape of the decay of the delayed light emission. These results are consistent with a model in which the membrane potential and the structure of the reaction center affect the decay kinetics of the delayed light emission in the seconds region. 相似文献