全文获取类型
收费全文 | 19691篇 |
免费 | 3306篇 |
国内免费 | 2333篇 |
专业分类
化学 | 13718篇 |
晶体学 | 177篇 |
力学 | 1129篇 |
综合类 | 118篇 |
数学 | 2718篇 |
物理学 | 7470篇 |
出版年
2024年 | 86篇 |
2023年 | 429篇 |
2022年 | 644篇 |
2021年 | 719篇 |
2020年 | 850篇 |
2019年 | 772篇 |
2018年 | 696篇 |
2017年 | 660篇 |
2016年 | 985篇 |
2015年 | 959篇 |
2014年 | 1093篇 |
2013年 | 1462篇 |
2012年 | 1686篇 |
2011年 | 1760篇 |
2010年 | 1231篇 |
2009年 | 1099篇 |
2008年 | 1253篇 |
2007年 | 1107篇 |
2006年 | 981篇 |
2005年 | 886篇 |
2004年 | 707篇 |
2003年 | 616篇 |
2002年 | 690篇 |
2001年 | 543篇 |
2000年 | 439篇 |
1999年 | 429篇 |
1998年 | 342篇 |
1997年 | 312篇 |
1996年 | 332篇 |
1995年 | 293篇 |
1994年 | 233篇 |
1993年 | 164篇 |
1992年 | 166篇 |
1991年 | 160篇 |
1990年 | 123篇 |
1989年 | 95篇 |
1988年 | 54篇 |
1987年 | 56篇 |
1986年 | 72篇 |
1985年 | 48篇 |
1984年 | 32篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
131.
Chang Peng Yuxue Liu Xiaojia Guo Wujun Liu Qing Li Zongbao K. Zhao 《Tetrahedron letters》2018,59(42):3810-3815
Selective carboxylation of substituted phenols is realized in the presence of bicarbonate under ambient pressure by engineered Escherichia coli whole-cells expressing various hydroxybenzoate decarboxylases, leading to their corresponding ortho-hydroxybenzoates. This process may be further developed as an efficient route to upgrade lignin-derived phenolic compounds as valuable building blocks. 相似文献
132.
Isonitrile group has been identified in many natural products.Due to the broad reactivity of N≡C triple bond,these natural products have valuable pharmaceutical potentials.This review summarizes the current biosynthetic pathways and the corresponding enzymes that are responsible for isonitrile-containing natural product generation.Based on the strategies utilized,two fundamentally distinctive approaches are discussed.In addition,recent progress in elucidating isonitrile group formation mechanisms is also presented. 相似文献
133.
Synthesis of the titanium silicalite TS-1 was first reported by Taramasso et al[1]in 1983. TS-1 has received considerable interest during the last decade because of its unique catalytic properties in oxidation reactions involving H2O2 as the oxidant. It is accepted that the extraframework Ti species in TS-1 favor the decomposition of H2O2and should be avoided. But in the present study, it was observed that there was a kind of Ti species inactive in both the oxidation reaction and the decomposition of H2O2. 相似文献
134.
微量元素与儿童健康 总被引:7,自引:0,他引:7
郭蔷蔷 《广东微量元素科学》1998,5(8):71-72
论述了常见微量元素与儿童健康的关系,并简要地介绍了部分常见微量元素对人体的作用。提出了一些微量元素缺少或过量的药物治疗方法。 相似文献
135.
136.
采用密度泛函理论和MP2方法研究了3-甲基环状乙撑磷酸二酯(MEP)与甲醇的反应途径:(Ⅰ)CH3O-+MEP;(Ⅱ)CH3OH+MEP;(Ⅲ)CH3O-+HMEP(MEP的质子化形式);(Ⅳ)CH3OH+HMEP.在B3LYP/6-31++G(d,p)水平上优化了四条反应途径的反应物、中间体、过渡态及产物的几何构型,并在同水平上进行了自然电荷分析,然后在MP2/6-311++G(3df,2p)水平上计算了各驻点的单点能.采用极化连续介质模型(PCM)研究了各途径在苯、甲醇和水溶液中的溶剂化效应.计算结果表明,溶剂效应使途径(Ⅰ)的自由能垒降低,而使途径(Ⅱ)和(Ⅳ)的决速步骤的自由能垒升高.在气相和苯溶剂中途径(Ⅳ)是反应的优势途径,在甲醇和水溶剂中途径(Ⅰ)则成为最优.研究结果进一步表明实验条件下途径(Ⅱ)与(Ⅳ)对总醇解反应的贡献相当. 相似文献
137.
138.
139.
Xiaoli He Sen Lin Xuan Guo Lude Lu Xin Wang Xujie Yang 《Frontiers of Chemistry in China》2008,3(4):413-417
Three tetraorganodistannoxanes containing silicon were synthesized and their catalytic properties in esterification and acetalization
were observed via the reactions of acetic acid with isoamyl alcohol and butyraldehyde with glycol. The factors affecting the reaction, such
as the catalyst dosage, reaction time and solvent, etc. were discussed. The results show that the three tetraorganodistannoxanes
displayed similar good catalytic activities compared to dichlorotetrabutyldistannoxane in esterification and acetalization.
When the dosage of [ClBu2SnOSn-(CH2SiMe3)2Cl]2 was 1.5% based on the mass of reactant, the yield of isoamyl acetate was 91.8% and the yield of butyraldehyde glycol acetal
94.2%. The different alkyl and bridging groups on Sn sites in the structure of tetraorganodistannoxanes showed some influence
on the catalytic activities of these compounds.
__________
Translated from Chinese Journal of Applied Chemistry, 2007, 24 (11): 1265–1272 相似文献
140.
Guo P Zhu G Song H Chen X Zhang S 《Physical chemistry chemical physics : PCCP》2011,13(39):17818-17824
Graphene nanosheets (GNSs) loading graphene-encapsulated iron microspheres (GEIMs) were fabricated by heat treatment of graphene oxide nanosheets (GONs) with ferric trichloride (FeCl(3)). The special pentagon-hexagonal graphene shells have been produced by precipitation of carbon from metal carbide solutions, thanks to the high reactivity of GONs and ferric nanoparticles dispersing homogeneously between graphene layers. The morphology, structure and elemental composition of GEIMs were investigated by scanning electron microscope, X-ray diffraction and electron energy disperse spectroscope, respectively. The formation mechanism of GEIMs was proposed. Hollow graphene microspheres (HGMs) on the GNSs were obtained with the removal of ferric species in GEIMs. When used as the anode materials for lithium-ion batteries, the almost graphitic HGMs exhibit stable voltage platform at ca. 0.2 V, excellent cycle capability and higher reversible capacity of about 440 mAh g(-1) after 50 cycles and possess great potential application in lithium-ion batteries. 相似文献