全文获取类型
收费全文 | 4634篇 |
免费 | 108篇 |
国内免费 | 936篇 |
专业分类
化学 | 5190篇 |
晶体学 | 66篇 |
力学 | 13篇 |
综合类 | 6篇 |
数学 | 19篇 |
物理学 | 384篇 |
出版年
2024年 | 1篇 |
2023年 | 230篇 |
2022年 | 51篇 |
2021年 | 50篇 |
2020年 | 74篇 |
2019年 | 100篇 |
2018年 | 96篇 |
2017年 | 106篇 |
2016年 | 83篇 |
2015年 | 72篇 |
2014年 | 139篇 |
2013年 | 308篇 |
2012年 | 344篇 |
2011年 | 252篇 |
2010年 | 245篇 |
2009年 | 294篇 |
2008年 | 287篇 |
2007年 | 450篇 |
2006年 | 323篇 |
2005年 | 258篇 |
2004年 | 264篇 |
2003年 | 164篇 |
2002年 | 127篇 |
2001年 | 134篇 |
2000年 | 171篇 |
1999年 | 137篇 |
1998年 | 101篇 |
1997年 | 115篇 |
1996年 | 120篇 |
1995年 | 121篇 |
1994年 | 103篇 |
1993年 | 86篇 |
1992年 | 66篇 |
1991年 | 64篇 |
1990年 | 33篇 |
1989年 | 44篇 |
1988年 | 37篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有5678条查询结果,搜索用时 15 毫秒
71.
Yan-Chun Guo Jing Li Jiao-Li Ma Zhi-Ran Yu Hai-Wei Wang Wen-Juan Zhu Xin-Cheng Liao Yu-Fen Zhao 《中国化学快报》2015,26(6):755-758
Two series of thieno[2,3-d]pyrimidine derivatives were designed and synthesized, in which bioactive a-aminophosphonate subunits were introduced at the N3 position through an N–N bond connection.The in vitro cytotoxic activity of the novel compounds was tested against human esophageal carcinoma cells(EC109), human hepatocarcinoma cells(Hep G2), human gastric carcinoma cells(MGC-803),respectively, by the MTT method. The evaluation results revealed that compounds 6mb, 6mf, 6mg, 6nd and 6nh exerted the most potent inhibition against Hep G2, MGC-803 and EC109 cells, respectively. In particular, compound 6mg presented excellent inhibitory effect against Hep G2(91.2%) and MGC-803(94.4%) cells. 相似文献
72.
“Green Electrodes” Modified with Au Nanoparticles Synthesized in Glycerol,as Electrochemical Nitrite Sensor 下载免费PDF全文
Dino Gobelli N. Mariano Correa M. Fátima Barroso Fernando Moyano Patricia G. Molina 《Electroanalysis》2015,27(8):1883-1891
A new environmentally friendly Au nanoparticles (Au NPs) synthesis in glycerol by using ultraviolet irradiation and without extra‐added stabilizers is described. The synthesis proposed in this work may impact on the non‐polluting production of noble nanoparticles with simple chemicals normally found in standard laboratories. These Au NPs were used to modify a carbon paste electrode (CPE) without having to separate them from the reaction medium. This green electrode was used as an electrochemical sensor for the nitrite detection in water. At the optimum conditions the green sensor presented a linear response in the 2.0×10?7–1.5×10?5 M concentration range, a good detection sensitivity (0.268 A L mol?1), and a low detection limit of 2.0×10?7 M of nitrite. The proposed modified green CPE was used to determine nitrite in tap water samples. 相似文献
73.
74.
Francesca Deganello Avesh Kumar Tyagi 《Progress in Crystal Growth and Characterization of Materials》2018,64(2):23-61
Solution combustion synthesis (SCS) is a worldwide used methodology for the preparation of inorganic ceramic and composite materials with controlled properties for a wide number of applications, from catalysis to photocatalysis and electrocatalysis, from heavy metal removal to sensoristics and electronics. The high versatility and efficiency of this technique have led to the introduction of many variants, which allowed important optimization to the prepared materials. Moreover, its ecofriendly nature encouraged further studies about the use of sustainable precursors for the preparation of nanomaterials for energy and environment, according to the concept of circular economy. On the other hand, the large variety of expressions to define SCS and the often-contradictory definitions of the SCS parameters witnessed a scarce consciousness of the potentiality of this methodology. In this review article, the most important findings about SCS and the selection criteria for its main parameters are critically reviewed, in order to give useful guidelines to those scientists who want to use this methodology for preparing materials with improved or new functional properties. This review aims as well (i) to bring more clarity in the SCS terminology (ii) to increase the awareness of the SCS as a convenient tool for the synthesis of materials and (iii) to propose a new perspective in the SCS, with special attention to the use of ecofriendly procedures. Part of the review is also dedicated to precautions and limitations of this powerful methodology. 相似文献
75.
In this study, new chalcone compound 1 , new phthalonitrile derivatives 2 and 3, new copper(II), manganese(III) phthalocyanines bearing chalcone groups at peripheral or nonperipheral positions were synthesized. Electrochemistry of tetra-(4-{(2 E )-3-[2-fluoro-4-(trifluoromethyl)phenyl]prop-2-enoyl}phenoxy) substituted Co(II)Pc and Mn(III)Pcs were studied with cyclic voltammetry (CV) to determine the redox properties of the phthalocyanines. According to the results, while the CuPcs 2a and 3a showed two Pc based reduction reactions and one Pc based oxidation reaction, MnPcs 2b and 3b gave two metal-based reduction reactions. All the redox processes are shifted toward positive potentials as a result of the increased electron-withdrawing ability of the trifluoromethyl substituents. 相似文献
76.
A novel synthetic approach to (±)-Z-recifeiolide 6, a 12-membered-ring lactone which can be selectively isomerized into (E)-recifeiolide, a natural antibiotic product isolated from fungus (Cephalosporium recifei) is reported. The synthesis is accomplished in five steps starting from readily available cyclooctanone and acetaldehyde based on the Lewis acid-catalyzed TMS-directed oxy-2-oxonia-Cope rearrangement. The work represents a novel strategy to assemble related macrolides. 相似文献
77.
Zheng-Wang Chen Dong-Nai Ye Min YeZhong-Gao Zhou Shen-Huan LiLiang-Xian Liu 《Tetrahedron letters》2014
A AgF/TFA-promoted highly efficient synthesis of a wide range of α-haloketones from haloalkynes is described. The reactions are conducted under convenient conditions and provide products in moderate to excellent yields, with broad substrate scope, including a variety of aromatic chloroalkynes and bromoalkynes. 相似文献
78.
Haiqin Wang 《Phosphorus, sulfur, and silicon and the related elements》2016,191(7):1009-1012
A series of aryl(arylamino)methylphosphonic acids were synthesized based on the previous work for the modification of alkylphosphonates. As key intermediates, α-aminophosphonates were synthesized with high yield by a three-component Kabachnik–Fields reaction under solvent-free conditions. The compounds were identified and characterized by infrared, 1H NMR, 13C NMR, mass spectrum, and elemental analyses. Their fungicidal activities against typical fungi occurring in the Chinese agro-ecosystems were evaluated. The results of preliminary bioassays showed that some of the title compounds exhibited moderate fungicidal activities against tomato late blight and cucumber fusarium wilt. For example, compound 3b showed 78% inhibitory activity against tomato late blight, and compound 3h possessed 86% inhibitory activity against cucumber fusarium wilt. 相似文献
79.
80.
《Journal of Coordination Chemistry》2012,65(2):315-322
Two structurally similar trinuclear complexes, [Cu(Cu(μ-Cl)2L1)2] (1) and [Cu(Cu(μ-Cl)2L2)2] (2) (HL1 = 4-chloro-2-[(2-morpholin-4-ylethylimino)methyl]phenol, HL2 = 1-[(2-piperidin-1ylethylimino)methyl]naphthalen-2-ol), have been synthesized and structurally characterized. Both complexes are bridged trinuclear compounds. The central Cu in each complex is in an octahedral environment with two phenolate and four bridging chlorides. The symmetry-related terminal Cu in each complex is square pyramidal with one phenolate oxygen, one imine nitrogen and one amine nitrogen of the Schiff-base ligand, one Cl? in the basal plane, and one bridging Cl? in the apical position. The complexes and Schiff bases were tested in vitro for their antibacterial activities. 相似文献