全文获取类型
收费全文 | 3508篇 |
免费 | 548篇 |
国内免费 | 511篇 |
专业分类
化学 | 2260篇 |
晶体学 | 78篇 |
力学 | 442篇 |
综合类 | 40篇 |
数学 | 278篇 |
物理学 | 1469篇 |
出版年
2024年 | 8篇 |
2023年 | 57篇 |
2022年 | 139篇 |
2021年 | 118篇 |
2020年 | 123篇 |
2019年 | 98篇 |
2018年 | 119篇 |
2017年 | 159篇 |
2016年 | 158篇 |
2015年 | 166篇 |
2014年 | 200篇 |
2013年 | 319篇 |
2012年 | 211篇 |
2011年 | 238篇 |
2010年 | 160篇 |
2009年 | 207篇 |
2008年 | 213篇 |
2007年 | 185篇 |
2006年 | 212篇 |
2005年 | 190篇 |
2004年 | 176篇 |
2003年 | 139篇 |
2002年 | 103篇 |
2001年 | 106篇 |
2000年 | 89篇 |
1999年 | 72篇 |
1998年 | 73篇 |
1997年 | 79篇 |
1996年 | 68篇 |
1995年 | 68篇 |
1994年 | 47篇 |
1993年 | 48篇 |
1992年 | 33篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1973年 | 2篇 |
1959年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有4567条查询结果,搜索用时 46 毫秒
71.
Summary The influence of various parameters (concentration of the injected polymer solution, flow rate, temperature gradient, relaxation conditions) on the retention and shape of the fractogram of ultra-high molecular weight polystyrenes in thermal field-flow fractionation was investigated. Under the operating conditions adopted, reproducible oscillations in the peak shape are observed for molecular weights larger than a few millions, especially at relatively high polymer concentration. They are attributed to some hydrodynamic instabilities. The retention of ultra-high molecular weight polystyrenes at high flow rate is strongly dependent on the initial relaxation period. All of the investigated operational variables have a complex effect on the resulting shape of the fractogram. Consequently, the confirmation of the shear-induced focusing of macromolecules across the channel thickness requires further study. Experiments on reinjection of fractions collected after an initial high speed pass through the separation system leads to the conclusion that shear degradation of the ultra-high molecular weight polymers did not occur under the investigated experimental conditions even at the highest flow rates. 相似文献
73.
Karen?Glenn Andrew?van?Bommel Subhash?C.?Bhattacharya Rama?M.?PalepuEmail author 《Colloid and polymer science》2005,283(8):845-853
The mixed micelles of sodium dodecyl sulphate (SDS) with Brij35 and Brij 97 were studied separately by fluorescence measurement using pyrene as fluorescent probe. In the range of 0–1.0 mole fraction (X) of added SDS to Brij solutions, the cmc value of the mixed micelles varies from 0.085 to 8 mmol with Brij 35 and 0.04 to 8 mmol with Brij 97. The aggregation number also changes. A measure of the stability of mixed micelles is also presented. The interaction parameter 12 and the chain–chain contribution parameter (B1) are extracted from the analysis of the results. This parameter B1 is related to the standard free energy change associated with the introduction of one ionic species into a nonionic micelle coupled with the release of one nonionic species from the micelle. The clouding behaviour of Brij 97 in the presence of SDS was investigated and the associated thermodynamic parameters of clouding were generated and discussed. 相似文献
74.
Liping Heng Jin Zhai Yong Zhao Jinjie Xu Xianliang Sheng Lei Jiang 《Chemphyschem》2006,7(12):2520-2525
A light-emitting poly (distyryldimethylbenzene-co-triethylene glycol) rod-coil block copolymer was used to fabricate films with three-dimensionally ordered honeycomb structures by the breath-figure method. Photocurrent generation and photovoltaic performance are studied, and the dependence of photocurrent on applied electric field is investigated. Introducing the ordered porous structure significantly improves the photoelectric conversion behavior, because porous structures not only enhance the light-harvesting efficiency but also benefit charge separation and charge transfer. This phenomenon may have great prospects for enhancing the photovoltaic behavior of organic thin-film devices. 相似文献
75.
磷脂酰胆碱水溶液CMC的测定陈鲁生周武姜云生(山东师范大学化学系济南250014)关键词磷脂酰胆碱临界胶束浓度磷脂酰胆碱是一种天然生物两性表面活性物质,也是一种重要的生命物质,具有广泛的用途[1],由于磷脂酰胆碱的水溶性较差,所以较长时间以来对其溶液... 相似文献
76.
WANG Qin-Sun ZHU Chang-Shou YAN Bing-WenNational Laboratory of Elemento-Organic Chemistry Nankai University Tianjin China 《中国化学》1995,(2)
A computer-assisted advanced simplex method is presented for the simultaneous optimization of multifactor ( stationary phase loading, carrier gas flow rate and column temperature ) for separation of ten compounds in gas chromatography. A three factors factorial design was used. The method was based on a special polynomial established from fifteen preliminary runs, using resolution as the selection criterion, with connection to a general simplex method. Excellent agreement is found between the predicted data and the experimental results, and most of experiments required in the general simplex method can be omitted. 相似文献
77.
巯基葡聚糖凝胶分离富集光度法测定镉的研究 总被引:2,自引:0,他引:2
研究了在TritonX-100存在下,新显色剂邻羧基苯基重氮氨基偶氮苯(CDAA)与镉的显色体系,在pH10.6的Na2B4O7-NaOH体系中,显色反应灵敏度很高。络合物的最大吸收位于545nm处,其摩尔吸光系数为2.22×10^5L·mol^-1·cm^-1。镉含量在0 ̄12μg/25mL符合比耳定律。将该体系用于巯基葡聚糖凝胶分离富集-光度法测水样中微量镉,结果令人满意。 相似文献
78.
V. G. Berezkin A. A. Korolev I. V. Malyukova R. G. Mardanov 《Russian Chemical Bulletin》1997,46(12):2064-2073
The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using
a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention
depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases:
helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than
relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention
values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption
nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997. 相似文献
79.
A new method for cadmium separation and concentration with microcrystalline phenolphthalein modified by crystal violet (CV) was developed in the paper. In the presence of potassium iodide (KI) and CV, cadmium are quantitatively absorbed on microcrystalline phenolphthalein in the pH range 1.0-6.0 as the forms of water-insoluble ion-associated complexes (CdI3−)·(CV+) and (CdI42−)·(CV+)2. Effect of different parameters such as phenolphthalein amount, stirring time, the concentration of CV and KI, various salts and metal ions was studied in detail. During the present study, a significant enhancement of the extraction of cadmium was observed. Cd(II) can be completely separated from Zn(II), Fe(II), Co(II), Ni(II), Mn(II), Cr(III) and Al(III) in this microcrystalline system and well concentrated without the interference of these metal ions at high level. The possible reactive mechanism of cadmium concentration has been discussed. Analytical results obtained by this new method were very gratifying. 相似文献