全文获取类型
收费全文 | 96320篇 |
免费 | 9285篇 |
国内免费 | 15139篇 |
专业分类
化学 | 73034篇 |
晶体学 | 2732篇 |
力学 | 1692篇 |
综合类 | 669篇 |
数学 | 19542篇 |
物理学 | 23075篇 |
出版年
2024年 | 165篇 |
2023年 | 1444篇 |
2022年 | 1659篇 |
2021年 | 2597篇 |
2020年 | 3084篇 |
2019年 | 3041篇 |
2018年 | 2624篇 |
2017年 | 3022篇 |
2016年 | 3337篇 |
2015年 | 3113篇 |
2014年 | 4281篇 |
2013年 | 8109篇 |
2012年 | 5625篇 |
2011年 | 6772篇 |
2010年 | 5670篇 |
2009年 | 6636篇 |
2008年 | 6787篇 |
2007年 | 6678篇 |
2006年 | 5986篇 |
2005年 | 5125篇 |
2004年 | 4806篇 |
2003年 | 3983篇 |
2002年 | 3776篇 |
2001年 | 2776篇 |
2000年 | 2628篇 |
1999年 | 2279篇 |
1998年 | 1912篇 |
1997年 | 1623篇 |
1996年 | 1537篇 |
1995年 | 1503篇 |
1994年 | 1364篇 |
1993年 | 1075篇 |
1992年 | 960篇 |
1991年 | 711篇 |
1990年 | 516篇 |
1989年 | 502篇 |
1988年 | 412篇 |
1987年 | 309篇 |
1986年 | 267篇 |
1985年 | 321篇 |
1984年 | 263篇 |
1983年 | 124篇 |
1982年 | 228篇 |
1981年 | 243篇 |
1980年 | 172篇 |
1979年 | 159篇 |
1978年 | 124篇 |
1977年 | 128篇 |
1976年 | 102篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献
102.
GAO Jing ZHOU Xiaohua CHEN Xun Chongqing University Chemical Engineering Department Chongqing China 《Chinese Journal of Reactive Polymers》2006,(2)
1. INTRODUCTION In the process of coking plant, about 30%~35% sulfur is transformed to H2S and some other sulfide, which form impurity in coal gas together with NH3 and HCN. Only 0.1% H2S containing in air can lead to die, so it is very important to carry on desulphurization and decyanation with coal gas [1~3]. Currently desulphurization and decyanation craft technique have Dry Oxidation Technology, Wet Oxidation Technology and Liquid Absorption Technology [2] three main kinds. The… 相似文献
103.
Electron spin resonance spectra of Mn2+ in diluted solid solutions of MnO2 in Y2O3 have been studied at room temperature for Mn concentrations between 0.20 and 2.00 mol%. Isolated Mn2+ ions in sites with two different symmetries were observed, as well as Mn2+ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Mn2+ ions decreases with increasing manganese concentration. The results are consistent with the assumption that the manganese ions occupy preferentially the C2 symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Mn2+ ions of 0.53 nm, of the same order as that of Mn2+ ions in CaO. 相似文献
104.
H.S RagabA Shehap M.S Abo EllilW.H Osman F.H Abd El-Kader 《Journal of Physics and Chemistry of Solids》2002,63(10):1839-1847
Ternary-phase ceramic system of Li2O Al2O3 4SiO2 doped with CuO, FeO and TiO2 has been prepared and subjected to dc electrical conductivity and thermally stimulated depolarization current (TSDC) measurements as a function of temperature (30-250 °C) and field strength. The electrical conductivity results are explained by assuming both ionic and electronic conduction mechanisms coexist with different contributions over the whole temperature range of experiments. TSDC spectra have been found to be characterized by a broad intense relaxation peak, which can be attributed to an ionic charge polarization. The broad relaxation transitions are apparently a result of the nonuniform nature of this process. Activation energies are calculated for both dc electrical conductivity and TSDC according to Arrhenius equation and initial rise method, respectively. 相似文献
105.
We obtain a solution of the DGLAP equation for the gluon at low x first by expanding the gluon in a Taylor series and then using the method of characteristics. We test its validity by comparing
it with that of Glück, Reya and Vogt. The convergence criteria of the approximation used are also discussed. We also calculate
εF
2(x,Q)2/ε In Q
2 using its approximate relations with the gluon distribution at low x. The predictions are then compared with the HERA data. 相似文献
106.
107.
108.
新生MnO2对酸性媒介黑T的吸附 总被引:4,自引:0,他引:4
以化学法合成的新生MnO2为吸附剂,对水中酸性媒介黑T(染料之一)进行了吸附脱色研究,并探讨了影响吸附的因素。结果表明,酸性媒介黑T的脱色率达95%。且PH是影响染料脱色的主要因素。 相似文献
109.
110.
Michel Hébert 《Archive for Mathematical Logic》1991,31(2):133-143
Summary We give a syntactic characterization of (finitary) theories whose categories of models are closed under the formation of connected limits (respectively the formation of pullbacks and substructures) in the category of all structures. They are also those theories whose consistent extensions by new atomic facts admit in each component an initial structure (respectively an initial term structure), and also thoseT for whichM(T) is locally finitely multi-presentable in a canonical way. We also show that these two properties of theories are nonuniform. 相似文献