全文获取类型
收费全文 | 2269篇 |
免费 | 48篇 |
国内免费 | 4篇 |
专业分类
化学 | 1518篇 |
晶体学 | 21篇 |
力学 | 18篇 |
数学 | 109篇 |
物理学 | 655篇 |
出版年
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2018年 | 24篇 |
2017年 | 15篇 |
2016年 | 32篇 |
2015年 | 30篇 |
2014年 | 25篇 |
2013年 | 88篇 |
2012年 | 84篇 |
2011年 | 97篇 |
2010年 | 61篇 |
2009年 | 61篇 |
2008年 | 138篇 |
2007年 | 137篇 |
2006年 | 124篇 |
2005年 | 135篇 |
2004年 | 125篇 |
2003年 | 105篇 |
2002年 | 107篇 |
2001年 | 63篇 |
2000年 | 51篇 |
1999年 | 27篇 |
1998年 | 24篇 |
1997年 | 27篇 |
1996年 | 38篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 27篇 |
1991年 | 25篇 |
1990年 | 25篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1986年 | 21篇 |
1985年 | 36篇 |
1984年 | 50篇 |
1983年 | 24篇 |
1982年 | 29篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 37篇 |
1978年 | 25篇 |
1977年 | 27篇 |
1976年 | 22篇 |
1975年 | 16篇 |
1973年 | 15篇 |
1972年 | 11篇 |
1969年 | 11篇 |
排序方式: 共有2321条查询结果,搜索用时 15 毫秒
71.
Yoko Kuwae Nobuo Kushibiki 《Journal of polymer science. Part A, Polymer chemistry》1989,27(12):3969-3975
The microstructure of the polymer formed by the hydrosilation of styrene with poly(hydrogenmethylsiloxane) was studied by 1H- and 13C-NMR spectra. Two modes of addition in hydrosilation were found to occur randomly without the influence of the adjacent monomer unit by statistical analysis of sequence distribution of 29Si-NMR spectrum. 相似文献
72.
Kamoda S Nomura C Kinoshita M Nishiura S Ishikawa R Kakehi K Kawasaki N Hayakawa T 《Journal of chromatography. A》2004,1050(2):211-216
Carbohydrate chains in glycoprotein pharmaceuticals have important roles for the expression of their biological activities. Therefore, development of an assessment method for the carbohydrate chains is an important parameter for quality control of glycoprotein pharmaceuticals such as newly developed therapeutic antibodies. In this report, we applied capillary electrophoresis with laser-induced fluorescence detection to the analysis of carbohydrate chains after releasing with glycoamidase followed by derivatization with 3-aminobenzoic acid. We found that four major oligosaccharides present in antibody pharmaceuticals were successfully separated with good resolution. The present method showed good precision in both migration times and relative peak areas, and gave comparable accuracy with that using a derivatization method with 8-aminopyrene-1,3,6-trisulfonate. 相似文献
73.
M. Ishikawa G. Izawa T. Omori Y. Muramatsu K. Yoshihara 《Journal of Radioanalytical and Nuclear Chemistry》1985,91(1):163-171
Particle-induced X-ray emission (PIXE) was applied to evaluate the loss of volatile elements such as iodine in biological samples. The analytical quality of the method is comparable or better than spectrophotometry, which is currently believed to be the most reliable for iodine determination. The temperature dependence of volatility loss of trace iodine was characteristic, and the feature was divided into three temperature regions. The first one, ranging from room temperature to 200 °C, showed only a slight loss below 20% on drying; the second stage, between 200 °C and 350 °C, where carbonizing processes became prominent, showed a remarkable loss up to 50%; the last one, beyond 350 °C, was accompanied by a considerable loss of iodine (more than 80%) with ashing. Even in the analysis using low temperature ashing with oxygen plasma, the loss of iodine observed was considerable (nearly 80%). The significance of these findings by PIXE in trace analysis is noted to improve analytical quality of volatile elements, such as iodine in biological, medical and also environmental fields. 相似文献
74.
Yasukawa A Ueda E Kandori K Ishikawa T 《Journal of colloid and interface science》2005,288(2):468-474
Particles of carbonated barium-calcium hydroxyapatite solid solutions (BaCaHap) with different Ba/(Ba+Ca) (X(Ba)) atomic ratios were prepared by a wet method at 100 degrees C and characterized by various means. The crystal phases and structures of the products strongly depended on the composition of the starting solution, that is, the Ba/(Ba+Ca) atomic ratio ([X(Ba)]) and H3PO4 concentration ([H3PO4]) in the solution. BaCaHap with X(Ba)0.43 could be prepared at [X(Ba)]0.7 by changing [H3PO4], but could never be obtained at [X(Ba)]=0.8-0.95 regardless of [H3PO4]. The carbonated calcium hydroxyapatite particles prepared at [X(Ba)]=0 were fine and short rod-shaped particles (ca. 14x84 nm). With increasing [X(Ba)] from 0 to 0.8, the particles obtained became large spherical agglomerates. The carbonated barium hydroxyapatite particles formed at [X(Ba)]=1 were long rod-shaped agglomerates (ca. 0.2x2 microm) of fine primary particles. The amount of CO2 adsorbed irreversibly on a series of BaCaHaps showed a minimum at (Ba+Ca)/(P+C) atomic ratio of around 1.56, which agreed well with the minimum cation/P ratio obtained for the other hydroxyapatites, as already reported. 相似文献
75.
76.
Nobuo Ishikawa Tomoya Kitazume Kunitake Chino Mohamed El-Said Mustafa 《Journal of fluorine chemistry》1981,18(4):447-457
The reactions of -2-methyl-2-pentene (1) with several - difunctional benzenes afforded eight- and nine-membered benzoheterocyclic compounds carrying perfluoroalkyl groups. Salicylic acid, salicylaldehyde, and their methyl or chloro derivatives reacted in triethylamine-acetonitrile system giving perfluoroalkylated 2H,6H-1,5-benzodioxocin-2,6-dione (8) and 4H,6H-1,5-benzodioxocin (9) compounds respectively, while phthalyl alcohol and o-hydroxyphenethyl alcohol in triethylamine-diethyl ether system gave perfluoroalkylated 1H,3H,7H-2,6- and 4H,6H,7H-1,5-benzodioxonin compounds, (10) and (11). o-Aminobenzyl alcohol and (1) in diethyl ether afforded a perfluoroalkylated benzoxazocinobenzoxazocinone compound (15). 相似文献
77.
106Ru chloro and nitrosyl-nitrato complexes in sea water were separated into several species by continuous electrophoresis on
a filter paper curtain. Biological uptake experiments were carried out on sea algae Fucus virsoides with fractionated106Ru chloro and nitrosyl-nitrato complex species in sea water. The biological uptake of106Ru chloro complex species was about 8 times higher than the uptake of106Ru nitrosyl-nitrato species. Electrophoretically most mobile electrically positively charged cationic species in both systems
also showed about 8 times higher biological uptake than the most mobile negatively charged anionic species. A close relation
of the biological uptake to the sign of the electrical charge and the electrophoretic mobility of the species is demonstrated.
The results are discussed with respect to possible danger to the biological environment as a consequence of the aging of ruthenium
species in sea water resulting from106Ru waste disposal to the sea from a nuclear reprocessing plant.
On leave of absence from the National Institute of Radiological Sciences, 9-1, 4-chome, Anagawa, Chiba-shi, Japan, on a fellowship
from The Science and Technology Agency of the Japanese Govemment. 相似文献
78.
We show that the mono-N-methylated and -ethylated derivatives of the achiral compound bisguanidinobenzene undergo spontaneous asymmetric crystallization into a chiral form with chiral space group P212121. The absolute configurations of the chiral crystals were determined by X-ray crystallography and correlated with circular dichroism (CD) spectra recorded in the solid state. The corresponding protonated and isopropylated derivatives, by contrast, afforded achiral crystals. 相似文献
79.
[structure: see text] A second generation total synthesis of the potent antitumor agent (+)-phorboxazole A (1) has been achieved. The cornerstone of this approach comprises a more convergent strategy, involving late-stage Stille union of a fully elaborated C(1-28) macrocycle with a C(29-46) side chain. The second generation synthesis entails the longest linear sequence of 24 steps, with an overall yield of 4.2%. 相似文献
80.
[reaction: see text] This paper describes a novel method to synthesize a quinoline backbone by incorporating allenyl cations into a catalytic intramolecular Friedel-Crafts reaction. The initial products were isomerized and aromatized upon treatment with acid and base, respectively, to give quinolines. The basic concept also proved to be promising for 1-benzazepine, 1-benzazocine, or isoquinoline synthesis. 相似文献