全文获取类型
收费全文 | 1859篇 |
免费 | 183篇 |
国内免费 | 325篇 |
专业分类
化学 | 1512篇 |
晶体学 | 36篇 |
力学 | 14篇 |
综合类 | 11篇 |
物理学 | 252篇 |
综合类 | 542篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 49篇 |
2021年 | 64篇 |
2020年 | 69篇 |
2019年 | 53篇 |
2018年 | 59篇 |
2017年 | 100篇 |
2016年 | 80篇 |
2015年 | 100篇 |
2014年 | 84篇 |
2013年 | 176篇 |
2012年 | 118篇 |
2011年 | 103篇 |
2010年 | 82篇 |
2009年 | 89篇 |
2008年 | 84篇 |
2007年 | 110篇 |
2006年 | 92篇 |
2005年 | 90篇 |
2004年 | 83篇 |
2003年 | 63篇 |
2002年 | 68篇 |
2001年 | 41篇 |
2000年 | 48篇 |
1999年 | 46篇 |
1998年 | 49篇 |
1997年 | 51篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 43篇 |
1993年 | 31篇 |
1992年 | 37篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有2367条查询结果,搜索用时 15 毫秒
111.
Tadashi Kataoka Hironori Kinoshita 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):989-992
Abstract The Chalcogeno-Morita-Baylis-Hillman reaction was achieved by the reactions of 2-(methylchalcogeno)phenyl vinyl ketones with carbonyl compounds or acetals in the presence of BF3· Et2O. This reaction proceeds via the intramolecular Michael addition of the chalcogenide group to an enone moiety followed by the aldol reaction of the resulting chalcogenonio-enolate with an aldehyde. The reactions were worked up with triethylamine or saturated aqueous NaHCO3 to give the α -methylene aldols (the Morita-Baylis-Hillman adducts). 相似文献
112.
Oguejiofo T. Ujam Kyle Devey William Henderson Brian K. Nicholson Michael R. Mucalo Corry Decker 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):1508-1525
Abstract The immobilization of the dinuclear platinum(II) sulfido complex [Pt2(μ-S)2 (PPh3)4] on solid supports has been investigated. Reaction with haloalkyl functionalized polymers [Merrifield's resin (chloromethylated polystyrene), chloropropyl silica, chloropropyl controlled pore glass, and bromopropyl polysiloxane] gives complexes immobilized through alkylation of one of the sulfide ligands, forming a μ-thiolate ligand acting as an anchor to the polymer support, akin to well-established reactions of [Pt2(μ-S)2(PPh3)4] with molecular alkylating agents. The model complex [Pt2(μ-S)(μ-SCH2SiMe3)(PPh3)4]PF6 was prepared as the first molecular silicon-containing derivative of [Pt2(μ-S)2(PPh3)4] and was fully characterized by NMR spectroscopy, electrospray ionization-mass spectrometry, and single-crystal X-ray diffraction. Immobilization of [Pt2(μ-S)2(PPh3)4] by phosphine exchange reactions was also achieved using commercial polystyrene-grafted triphenylphosphine or a new immobilized phosphine [derived by sequential functionalization of Merrifield's resin with a polyether amine and then Ph2PCH2OH]. 相似文献
113.
Arash Shokrolahi Abbas Zali 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):454-460
Abstract Sulfonated condensed polynuclear aromatic (S-COPNA) resin was found to be a highly efficient, environmentally friendly, recyclable heterogeneous catalyst for the oxidation of alkyl and aryl sulfides to the corresponding sulfoxides or sulfones, in good yields under mild reaction conditions using 30% hydrogen peroxide as an oxidant. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Synthesis of the S-COPNA resin catalyst. Spectroscopic data for compounds. 相似文献
114.
115.
采用简单的热解-硫化两步法成功制备了一种新型的富氮掺杂碳空心纳米笼(NC)负载双元金属硫化物纳米颗粒(CoNixSy)的复合材料 CoNixSy/NC。该策略以丁二酮肟镍为镍源,增加了活性位点,同时前驱体 ZIF-8@Ni-ZIF-67的核壳结构为空心碳纳米笼的构建提供了可能性。这种独特的负载多金属硫化物纳米颗粒的中空结构使CoNixSy/NC作为电极材料时具有更多的活性位点、更高的导电性和结构稳定性,从而使其具有较高的比容量(1 A·g-1时比容量为629.2 F·g-1),优异的循环稳定性(1 A·g-1下1 000次循环测试后容量保持率为93.4%)。当将其进一步组装成对称超级电容器后,在1 A·g-1下可提供207.2 F·g-1的比电容,1 000圈循环稳定后的容量保持率为85.36%。 相似文献
116.
A series of novel anthranilic diamides with benzyl sulfide scaffold were synthesized,in which N-pyridylpyrazole moiety generally regarded as key pharmacophore was abandoned.The target compounds were characterized by 1H NMR,13C NMR,19F NMR and HRMS.The preliminary bioassays indicated that half of the title compounds were endowed with good insecticidal activities against armyworm(Mythimna sepatara) at the concentration of 500 mg/L,Exhilaratingly,the synthesized compound 3a was also active against Tetranychus cinnabarinus at 100 mg/L.The difference in activities between the target compounds was influenced by the substituents,which provided some hints for further investigation on structure modifications. 相似文献
117.
《Green Chemistry Letters and Reviews》2013,6(1):19-26
Abstract An efficient one-pot synthesis of β-hydroxy sulfides from thiophenol and cyclic carbonates catalyzed by large-pore zeolites has been reported. Reaction of thiophenol with ethylene carbonate in the presence of the Na-X zeolite catalyst gave the highest yield of 2-(phenylthio)ethanol (100%), while reaction with propylene carbonate a highest yield of regioselective product 1-(phenylthio)propan-2-ol was obtained (97%). Enantiomerically pure 1,2-propylene carbonate gave highly regioselective and stereospecific phenylthiopropanol, demonstrating that original chirality of propylene carbonate is retained. A plausible mechanism has been proposed for zeolite-catalyzed transformation involving a chemoselective nucleophilic attack of thiophenoloxide ion onto the less-substituted carbon of cyclic carbonate. The Na-X zeolite catalyst is recyclable and provides advantages of green chemistry approach to the synthesis of β-hydroxy sulfides without the use of any solvent. 相似文献
118.
Yanjun Wang Shaoyun Chen Heng Chen Xingzhou Yuan Yongchun Zhang 《Journal of Energy Chemistry》2013,22(6):902-906
Removal of carbonyl sulfide (COS) from CO2 stream is significant for the production and utilization of food grade CO2. This study investigates the adsorption performance of Ag/NaZSM-5 as adsorbent prepared by incipient wetness impregnation for the removal of COS from a CO2 stream in a fixed-bed adsorption apparatus. Effects of various conditions on the preparation of adsorbent, adsorption and desorption were intensively examined. The results revealed that COS can be removed to below 1×10?9 from a CO2 stream (1000 ppm COS/CO2) using Ag/NaZSM-5 (10 wt% AgNO3) with an adsorption capacity of 12.86 mg-g?1. The adsorbent can be fully regenerated using hot air at 450 °C. The adsorption ability remained stable even after eight cycles of regeneration. 相似文献
119.
Biswanath Das Penagaluri Balasubramanyam Maddeboina Krishnaiah Boyapati Veeranjaneyulu Dega Sudhakar 《合成通讯》2013,43(14):2113-2121
Regio-, stereo-, and chemoselective ring opening of epoxides with thiols using Cu/MgO as a heterogeneous catalyst has efficiently been carried out to produce the corresponding β-hydroxy sulfides in excellent yields at room temperature under solvent-free conditions. The treatment of the epoxides with thiols and 50% aqueous H2O2 in the presence of the same catalyst at room temperature affords the β-hydroxy sulfoxides in excellent yields. 相似文献
120.
An improved, mild procedure for the CuI‐catalyzed coupling reactions of aryl iodides with aliphatic and aromatic thiols, using L ‐proline as the ligand, is reported. This procedure is noteworthy given its high generality and exceptional level of functional group toleration. 相似文献