全文获取类型
收费全文 | 4275篇 |
免费 | 123篇 |
国内免费 | 18篇 |
专业分类
化学 | 3346篇 |
晶体学 | 63篇 |
力学 | 37篇 |
综合类 | 1篇 |
数学 | 290篇 |
物理学 | 679篇 |
出版年
2022年 | 30篇 |
2021年 | 36篇 |
2020年 | 58篇 |
2019年 | 60篇 |
2018年 | 32篇 |
2017年 | 30篇 |
2016年 | 84篇 |
2015年 | 74篇 |
2014年 | 123篇 |
2013年 | 258篇 |
2012年 | 194篇 |
2011年 | 232篇 |
2010年 | 153篇 |
2009年 | 140篇 |
2008年 | 228篇 |
2007年 | 229篇 |
2006年 | 252篇 |
2005年 | 252篇 |
2004年 | 217篇 |
2003年 | 184篇 |
2002年 | 187篇 |
2001年 | 90篇 |
2000年 | 93篇 |
1999年 | 53篇 |
1998年 | 53篇 |
1997年 | 43篇 |
1996年 | 62篇 |
1995年 | 41篇 |
1994年 | 43篇 |
1993年 | 29篇 |
1992年 | 53篇 |
1991年 | 39篇 |
1990年 | 31篇 |
1989年 | 32篇 |
1988年 | 47篇 |
1987年 | 24篇 |
1986年 | 29篇 |
1985年 | 56篇 |
1984年 | 59篇 |
1983年 | 45篇 |
1982年 | 51篇 |
1981年 | 61篇 |
1980年 | 40篇 |
1979年 | 52篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 24篇 |
1975年 | 24篇 |
1974年 | 26篇 |
1973年 | 28篇 |
排序方式: 共有4416条查询结果,搜索用时 0 毫秒
1.
A new family of positive photosensitive polyimide (PPI) systems composed of solvent soluble polyimides (Pls) with cyclobutane (CBDA) structures and diazonaphthoquinone compounds (DNQ) has been prepared. Heat and catalytic imidizations were carried out to obtain CBDA Pls; the former was better than the latter in controlling the molecular weight of the Pl. The ? OH groups in the Pls were easily acetylated during catalytic imidization, so ? COOH groups were selected as weak acidic groups in the Pls. The ? COOH groups were also effective in giving the Pls an alkaline solubility. Therefore, Pls having ? COOH groups were superior to those having ? OH groups for PPI systems. The photosensitive properties of various PPl systems containing ? COOH were found to vary with the fraction of ? COOH groups in the Pls, the content of DNQ in the systems, and the molecular weight of the Pls. 相似文献
2.
Three new cytotoxic polyacetylenes, PQ-1 (1), PQ-2 (2) and PQ-3 (3), have been isolated from Panax quinquefolium. The structures of these acetylenes were determined by analyses of their 1H-1H and 1H-13C COSY spectra. All these compounds exhibited strong cytotoxic activities against leukemia cells (L 1210) in tissue culture. 相似文献
3.
4.
5.
Makoto Sakata Takafumi Itsubo Yutakata Moritomo Yasuo Ohishi 《Journal of Physics and Chemistry of Solids》2004,65(12):1973-1976
The experimental and analytical method of the high-pressure powder experiment at BL10XU, SPring-8, is described. There is no doubt that BL10XU must be one of the most appropriate beam lines for high pressure X-ray diffraction experiment taking advantage of third generation synchrotron source. As an example of the advanced charge density study under high pressure, the structural change of Cs2Au2Br6 by applying pressure is studied by Rietveld/MEM analysis. It reveals that the structural change of Cs2Au2Br6 by applying pressure occurs basically at electron level, such as valence state change and chemical bonding, which may be called the electronic phase transition. 相似文献
6.
Edison Munaf Toyohide Takeuchi Hiroki Haraguchi 《Fresenius' Journal of Analytical Chemistry》1992,342(1-2):154-156
Summary A continuous flow analysis is described for the determination of total mercury by cold vapor atomic absorption spectrometry. Organic mercury compounds such as methylmercury(II) chloride, ethylmercury(II) chloride and phenylmercury(II) chloride were decomposed by potassium peroxodisulphate with addition of ferric chloride as catalytic reagent. The reducing reagent used was tin(II) chloride in sodium hydroxide solution. With 1,000 mg Fe/l added in the decomposition process, we found that methylmercury(II) chloride and ethylmercury(II) chloride gave response signals similar to those of mercury(II) chloride. The proposed method was applied to the analysis of total mercury in waste water.
Permanent address: Department of Chemistry, Faculty of Mathematics and Natural Sciences, Andalas University, Padang, West Sumatra, Indonesia 相似文献
7.
8.
13C NMR studies showed that the population of the norcaradiene form of the title systems containing p-CH3O, H, and p-CF3 on the 7-aryl group increases in this order. The result is consistent with the prediction from the π-acceptor strength of the aryl group estimated by INDO calculations. 相似文献
9.
10.
Makoto Kume Atsunori Hirano Bungo Ochiai Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3666-3673
A spiro orthoester with an exomethylene group (exoSOE) was radically copolymerized with acrylonitrile or vinyl acetate at several feed ratios to obtain the corresponding copolymers having spiro orthoester moieties in the side chain. The obtained copolymers could be crosslinked via the double ring‐opening polymerization of the spiro orthoester moieties in their side chain by a treatment with BF3OEt2. The volume changes upon the crosslinking of the copolymers were evaluated by density measurements with a micromeritics gas pycnometer. The copolymers experienced less than 1% volume expansion instead of volume shrinkage during typical cationic crosslinking, regardless of the copolymer compositions. Negligible shrinkage was observed during the thermal cationic crosslinking of a film cast from a nitrobenzene solution of the copolymers containing a benzylthiophenium salt as a thermally latent cationic initiator. The constantly low volume changes during the crosslinking of the copolymers from exoSOE probably depended on the almost zero volume change during the cationic polymerizations of spiro orthoester derivatives. This indicates that exoSOE is an effective monomer for crosslinkable polymers without volume changes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3666–3673, 2006 相似文献