全文获取类型
收费全文 | 1355篇 |
免费 | 32篇 |
国内免费 | 273篇 |
专业分类
化学 | 1357篇 |
晶体学 | 4篇 |
力学 | 5篇 |
综合类 | 5篇 |
物理学 | 289篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 21篇 |
2021年 | 25篇 |
2020年 | 20篇 |
2019年 | 21篇 |
2018年 | 37篇 |
2017年 | 35篇 |
2016年 | 26篇 |
2015年 | 31篇 |
2014年 | 62篇 |
2013年 | 116篇 |
2012年 | 77篇 |
2011年 | 79篇 |
2010年 | 64篇 |
2009年 | 86篇 |
2008年 | 70篇 |
2007年 | 102篇 |
2006年 | 94篇 |
2005年 | 92篇 |
2004年 | 96篇 |
2003年 | 64篇 |
2002年 | 46篇 |
2001年 | 53篇 |
2000年 | 40篇 |
1999年 | 42篇 |
1998年 | 39篇 |
1997年 | 32篇 |
1996年 | 23篇 |
1995年 | 20篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1660条查询结果,搜索用时 15 毫秒
11.
12.
树脂吸附法处理水杨酸甲酯生产废水的研究 总被引:7,自引:0,他引:7
采用吸附树脂NDA—99处理水杨酸甲酯生产废水,结果表明该树脂时废水中的5磺基水杨酸及水杨酸均具有良好的吸附—脱附性能.废水经预处理和吸附处理后,CODCr由57000-59000mg/L降至6300mg/L左右,去除率接近89%.用IBV8%NaOH 3BVH2O作脱附剂,在温度为60℃、流量为IBV/h的条件下,脱附率接近100%,树脂可重复使用.高浓度脱附液经酸化、浓缩、冷却结晶,可回收5—磺基水杨酸,回收率为95%左右。纯度为78%。 相似文献
13.
The equilibrium structure of CH3F has been determined using new sets of accurate rotational constants that have been determined by taking into account all the interactions between the excited vibrational states. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD(T) level of theory with the cc-pV(5, Q)Z basis set (including corrections for the core correlation and for the effect of diffuse functions on fluorine). Finally, the experimental and ab initio structures have been combined by a least-squares analysis. The results are
, and L
e(HCH) = 110.2 (1)°, where the uncertainties shown in parentheses correspond to three standard deviations. 相似文献
14.
15.
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
16.
A background-free, fast protein staining method in polyacrylamide gel electrophoresis using an acidic dye, zincon (ZC) and a basic dye, ethyl violet (EV) is described. It is based on the counterion dye staining technique that employs two oppositely charged dyes to form an ion-pair complex in staining solution. The selective binding of free dye molecules to proteins in acidic solution produces bluish violet-colored bands. It is a rapid and end-point staining procedure, involving only fixing and staining steps that are completed in 1-1.5 h. The detection limit of this method is 8-15 ng of protein that is comparable to the sensitivity of the colloidal Coomassie Brilliant Blue G (CBBG) stain. Due to its sensitivity and speed, this stain may be more practical than any other dye-based stains for routine laboratory purposes. 相似文献
17.
Preparation of cellulose and cellulose derivative azo compounds 总被引:1,自引:0,他引:1
Maha Ibrahim 《Cellulose (London, England)》2002,9(3-4):337-349
Wood pulp and cotton linter are the most common sources of cellulose forindustrial use. Methyl cellulose (MC) and cellulose sulfate (CS) were preparedusing bleached wood pulp and cotton linter. Coloured azo compounds were alsoprepared from coupling cellulose, wood pulp, MC and CS with aromatic diazoniumsalt. The presence of electron-releasing or withdrawing substituents affectedthe electrophilic substitution reaction. The produced azo compounds werecharacterized by FT-IR methodology, as well as mass spectrometry, in which thefunctional groups and the ion fragments of the products were analyzed. 相似文献
18.
Two new esters, methyl 4‐(prenyloxy)dihydrocinnamate and methyl 4‐(geranyloxy)dihydrocinnamate, together with fourteen known compounds have been isolated from the stem bark of Zanthoxylum pistaciiflorum. The structures of two new compounds were determined through spectral analyses. Among the isolates, four compounds exhibited effective cytotoxicities against P‐388 and HT‐29 cell lines in vitro. 相似文献
19.
A. C. Bhasikuttan A. V. Sapre L. V. Shastri 《Journal of photochemistry and photobiology. A, Chemistry》1995,90(2-3):177-182
The reactions of two triphenyl methane (TPM) dyes—crystal violet (CV+) and malachite green (MG+)—with N3• and OH• radicals were studied by pulse radiolytic kinetic spectrophotometry. The rate constants for the reaction of the cationic dyes (D+) with N3• are (9.0±0.6)×109 and (3.0±0.2)×109 dm3 mol−1 s−1 respectively and those for the reaction with OH• are obtained as (8.0±0.6)×109 and (1.1±0.1)×109 dm3 mol−1 s−1 respectively. The transient spectra resulting from the oxidation of the dyes were characterized. The time-resolved spectra indicate that the reaction with OH• radicals initially generates an adduct which subsequently dissociates to form the radical dication D•2+. The D•2+ species decay by further reaction with the parent dye. 相似文献
20.
Efficient microwave-assisted glycosylations from methyl glucopyranosides are described. We have discussed the effects of microwave irradiation on this unique glycoside exchanging reaction from view points such as amount of Lewis acid promoters and acceptors, hydroxyl protecting groups of methyl glucopyranosides donors for reactivity, and neighboring effect. 相似文献