全文获取类型
收费全文 | 11522篇 |
免费 | 1107篇 |
国内免费 | 259篇 |
专业分类
化学 | 9997篇 |
晶体学 | 23篇 |
力学 | 28篇 |
综合类 | 12篇 |
数学 | 27篇 |
物理学 | 2801篇 |
出版年
2023年 | 100篇 |
2022年 | 210篇 |
2021年 | 241篇 |
2020年 | 375篇 |
2019年 | 294篇 |
2018年 | 276篇 |
2017年 | 251篇 |
2016年 | 440篇 |
2015年 | 406篇 |
2014年 | 478篇 |
2013年 | 768篇 |
2012年 | 486篇 |
2011年 | 557篇 |
2010年 | 459篇 |
2009年 | 528篇 |
2008年 | 480篇 |
2007年 | 552篇 |
2006年 | 483篇 |
2005年 | 425篇 |
2004年 | 357篇 |
2003年 | 405篇 |
2002年 | 1223篇 |
2001年 | 205篇 |
2000年 | 158篇 |
1999年 | 172篇 |
1998年 | 175篇 |
1997年 | 116篇 |
1996年 | 115篇 |
1995年 | 129篇 |
1994年 | 60篇 |
1993年 | 57篇 |
1992年 | 42篇 |
1991年 | 42篇 |
1990年 | 30篇 |
1988年 | 25篇 |
1987年 | 25篇 |
1985年 | 92篇 |
1984年 | 117篇 |
1983年 | 106篇 |
1982年 | 150篇 |
1981年 | 113篇 |
1980年 | 97篇 |
1979年 | 100篇 |
1978年 | 106篇 |
1977年 | 144篇 |
1976年 | 118篇 |
1975年 | 129篇 |
1974年 | 165篇 |
1973年 | 133篇 |
1972年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
The reaction pathway for the Ca3Al2O6 formation up to 1300°C, from mechanochemically treated mixtures of amorphous aluminum hydroxide and CaCO3, was studied in situ by differential thermal analysis, constant heating rate dilatometry and time-resolved neutron powder diffraction. The experiment was carried out, in an open system, on a sample with the nominal Ca3Al2O6 stoichiometry. The results obtained by neutron diffractometry and thermal analysis were in good agreement with the data obtained by scanning electron microscopy and X-ray diffraction on heat-treated and-quenched samples. The synthesis path implied the formation of cryptocrystalline Al2O3, crystalline CaO, CaAl2O4 and Ca12Al14O33 as transitory phases. Finally the nucleation and growth of the single phase Ca3Al2O6 took place at 1300°C and exhibited porous structure due to CO2 and H2O release. 相似文献
44.
Inés CarrancoJosé Luis D?&#x;az Oscar JiménezRodolfo Lavilla 《Tetrahedron letters》2003,44(46):8449-8452
The Lewis acid-catalyzed interaction of dihydropyridines with ethyl glyoxalate and primary aliphatic amines yields, depending on the reaction conditions, bicyclic aminals or rearranged tetrahydropyridines in one-pot multicomponent reactions. 相似文献
45.
《Tetrahedron letters》2003,44(40):7411-7415
The first total synthesis of two E type I phytoprostanes from furan, azelaic acid monomethyl ester and rac-1,2-epoxybutane is described. The key features of our synthetic strategy encompass an enzymatic kinetic resolution of a hydroxycyclopentenone, a Co-salen hydrolytic kinetic resolution of a terminal epoxide and a tandem conjugate addition/diastereoselective protonation sequence to construct the protected phytoprostanes. Mild cleavage of the silyl protective groups followed by enzymatic ester hydrolysis afforded the free E-type phytoprostanes. 相似文献
46.
The use of reagent concentration has resulted in increased rates for all stages of the REM resin synthesis of tertiary amines. These increases in rate translate into faster reaction times, higher yields and lower reagent consumption. Of the methods examined, the most successful was the use of perfluorous solvents, either alone or with a small amount of organic co-solvent. 相似文献
47.
48.
Taking both the heterogeneous catalytic processes, including the surface formation of particles with excited internal degrees of freedom, and the processes of multicomponent diffusion and heat transfer in the MESOX apparatus fully into account makes it possible to obtain a recombination coefficient and an accommodation coefficient of the oxygen-atoms-on-quartz recombination energy which are in good agreement with the experimental data. The heterogeneous catalysis model constructed can be used effectively for predicting the heat fluxes to the surface of reentry vehicles on their entry into the Earth’s atmosphere. 相似文献
49.
G. I. Nikishin L. L. Sokova V. D. Makhaev N. I. Kapustina 《Russian Chemical Bulletin》2008,57(1):118-123
The solid-phase oxidation of cinnamic, 4-methoxy- and 3,4-dimethoxycinnamic acids with Ce(NH4)2(NO3)6—MHal system leads to β-halostyrenes. Similar procedure in the absence of a metal halide results in a cleavage of the C=C
bond giving the corresponding benzaldehydes.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 114–118, January, 2008. 相似文献
50.