全文获取类型
收费全文 | 15868篇 |
免费 | 2651篇 |
国内免费 | 3235篇 |
专业分类
化学 | 12749篇 |
晶体学 | 194篇 |
力学 | 871篇 |
综合类 | 264篇 |
数学 | 2043篇 |
物理学 | 5633篇 |
出版年
2024年 | 11篇 |
2023年 | 293篇 |
2022年 | 401篇 |
2021年 | 507篇 |
2020年 | 650篇 |
2019年 | 718篇 |
2018年 | 546篇 |
2017年 | 577篇 |
2016年 | 807篇 |
2015年 | 835篇 |
2014年 | 899篇 |
2013年 | 1254篇 |
2012年 | 1238篇 |
2011年 | 1320篇 |
2010年 | 1096篇 |
2009年 | 973篇 |
2008年 | 1162篇 |
2007年 | 985篇 |
2006年 | 921篇 |
2005年 | 855篇 |
2004年 | 726篇 |
2003年 | 699篇 |
2002年 | 882篇 |
2001年 | 755篇 |
2000年 | 547篇 |
1999年 | 408篇 |
1998年 | 275篇 |
1997年 | 181篇 |
1996年 | 194篇 |
1995年 | 145篇 |
1994年 | 156篇 |
1993年 | 112篇 |
1992年 | 94篇 |
1991年 | 125篇 |
1990年 | 106篇 |
1989年 | 51篇 |
1988年 | 53篇 |
1987年 | 35篇 |
1986年 | 40篇 |
1985年 | 44篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1957年 | 3篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
991.
Amphiphilic diblock copolymer polystyrene-block-poly(ethylene oxide) (PS-PEO) assembled into nonequilibrium bicontinuous structures or mixture of vesicles, bilayers and nanorods upon rapid micellization induced by rapid addition of selective solvent (water) into the PS-PEO solutions in a common solvent (dimethyl formamide) with different concentrations. These kinetically trapped assemblies were unstable and slowly evolved into thermodynamically favorable spheres and vesicles. The addition of non-ionic surfactant Pluronic P123 upon rapid micellization generated novel nanocages and flower-like vesicles. The nanocages spontaneously transformed into tubules capped with vesicles. These novel assemblies are beyond the classic phase diagram of block copolymer self-assemblies, especially for those primarily based on thermodynamics. 相似文献
992.
Ren‐Qi Wang Katharina Druckenmüller Gereon Elbers Klaus Guenther Jean‐Philippe Croué 《Journal of mass spectrometry : JMS》2014,49(2):154-160
The composition and physiochemical properties of aquatic‐phase natural organic matter (NOM) are most important problems for both environmental studies and water industry. Laser desorption/ionization (LDI) mass spectrometry facilitated successful examinations of NOM, as humic and fulvic acids in NOM are readily ionized by the nitrogen laser. In this study, hydrophobic NOMs (HPO NOMs) from river, reservoir and waste water were characterized by this technique. The effect of analytical variables like concentration, solvent composition and laser energy was investigated. The exact masses of small molecular NOM moieties in the range of 200–1200 m/z were determined in reflectron mode. In addition, spectra of post‐source‐decay experiments in this range showed that some compounds from different natural NOMs had the same fragmental ions. In the large mass range of 1200–15 000 Da, macromolecules and their aggregates were found in HPO NOMs from natural waters. Highly humic HPO exhibited mass peaks larger than 8000 Da. On the other hand, the waste water and reservoir water mainly had relatively smaller molecules of about 2000 Da. The LDI‐MS measurements indicated that highly humic river waters were able to form large aggregates and membrane foulants, while the HPO NOMs from waste water and reservoir water were unlikely to form large aggregates. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
993.
Xian‐Kai Wan Shang‐Fu Yuan Zhi‐Wei Lin Prof. Dr. Quan‐Ming Wang 《Angewandte Chemie (International ed. in English)》2014,53(11):2923-2926
The chirality of a gold nanocluster can be generated from either an intrinsically chiral inorganic core or an achiral inorganic core in a chiral environment. The first structural determination of a gold nanocluster containing an intrinsic chiral inorganic core is reported. The chiral gold nanocluster [Au20(PP3)4]Cl4 (PP3=tris(2‐(diphenylphosphino)ethyl)phosphine) has been prepared by the reduction of a gold(I)–tetraphosphine precursor in dichloromethane solution. Single‐crystal structural determination reveals that the cluster molecular structure has C3 symmetry. It consists of a Au20 core consolidated by four peripheral tetraphosphines. The Au20 core can be viewed as the combination of an icosahedral Au13 and a helical Y‐shaped Au7 motif. The identity of this Au20 cluster is confirmed by ESI‐MS. The chelation of multidentate phosphines enhances the stability of this Au20 cluster. 相似文献
994.
Tunable Oxygen Activation for Catalytic Organic Oxidation: Schottky Junction versus Plasmonic Effects 下载免费PDF全文
Ming Gong Shan Zhou Jiahua Hu Min Zhi Yang You Song Bai Prof. Jun Jiang Prof. Qun Zhang Prof. Xiaojun Wu Prof. Yujie Xiong 《Angewandte Chemie (International ed. in English)》2014,53(12):3205-3209
The charge state of the Pd surface is a critical parameter in terms of the ability of Pd nanocrystals to activate O2 to generate a species that behaves like singlet O2 both chemically and physically. Motivated by this finding, we designed a metal–semiconductor hybrid system in which Pd nanocrystals enclosed by {100} facets are deposited on TiO2 supports. Driven by the Schottky junction, the TiO2 supports can provide electrons for metal catalysts under illumination by appropriate light. Further examination by ultrafast spectroscopy revealed that the plasmonics of Pd may force a large number of electrons to undergo reverse migration from Pd to the conduction band of TiO2 under strong illumination, thus lowering the electron density of the Pd surface as a side effect. We were therefore able to rationally tailor the charge state of the metal surface and thus modulate the function of Pd nanocrystals in O2 activation and organic oxidation reactions by simply altering the intensity of light shed on Pd–TiO2 hybrid structures. 相似文献
995.
Electrochemical Synthesis of Tetrahexahedral Rhodium Nanocrystals with Extraordinarily High Surface Energy and High Electrocatalytic Activity 下载免费PDF全文
Neng‐Fei Yu Dr. Na Tian Dr. Zhi‐You Zhou Long Huang Jing Xiao Yu‐Hua Wen Prof. Shi‐Gang Sun 《Angewandte Chemie (International ed. in English)》2014,53(20):5097-5101
Noble metal nanocrystals (NCs) enclosed with high‐index facets hold a high catalytic activity thanks to the high density of low‐coordinated step atoms that they exposed on their surface. Shape‐control synthesis of the metal NCs with high‐index facets presents a big challenge owing to the high surface energy of the NCs, and the shape control for metal Rh is even more difficult because of its extraordinarily high surface energy in comparison with Pt, Pd, and Au. The successful synthesis is presented of tetrahexahedral Rh NCs (THH Rh NCs) enclosed by {830} high‐index facets through the dynamic oxygen adsorption/desorption mediated by square‐wave potential. The results demonstrate that the THH Rh NCs exhibit greatly enhanced catalytic activity over commercial Rh black catalyst for the electrooxidation of ethanol and CO. 相似文献
996.
Copper‐Catalyzed Intermolecular Trifluoromethylazidation of Alkenes: Convenient Access to CF3‐Containing Alkyl Azides 下载免费PDF全文
Fei Wang Xiaoxu Qi Zhaoli Liang Dr. Pinhong Chen Prof. Dr. Guosheng Liu 《Angewandte Chemie (International ed. in English)》2014,53(7):1881-1886
A novel copper‐catalyzed intermolecular trifluoromethylazidation of alkenes has been developed under mild reaction conditions. A variety of CF3‐containing organoazides were directly synthesized from a wide range of olefins, including activated and unactivated alkenes, and the resulting products can be easily transformed into the corresponding CF3‐containing amine derivatives. 相似文献
997.
Mechanistic Insights into the Interface‐Directed Transformation of Thiols into Disulfides and Molecular Hydrogen by Visible‐Light Irradiation of Quantum Dots 下载免费PDF全文
Xu‐Bing Li Zhi‐Jun Li Yu‐Ji Gao Qing‐Yuan Meng Shan Yu Prof. Dr. Richard G. Weiss Prof. Dr. Chen‐Ho Tung Prof. Dr. Li‐Zhu Wu 《Angewandte Chemie (International ed. in English)》2014,53(8):2085-2089
Quantum dots (QDs) offer new and versatile ways to harvest light energy. However, there are few examples involving the utilization of QDs in organic synthesis. Visible‐light irradiation of CdSe QDs was found to result in virtually quantitative coupling of a variety of thiols to give disulfides and H2 without the need for sacrificial reagents or external oxidants. The addition of small amounts of nickel(II) salts dramatically improved the efficiency and conversion through facilitating the formation of hydrogen atoms, thereby leading to faster regeneration of the ground‐state QDs. Mechanistic studies reveal that the coupling reaction occurs on the QD surfaces rather than in solution and offer a blueprint for how these QDs may be used in other photocatalytic applications. Because no sacrificial agent or oxidant is necessary and the catalyst is reusable, this method may be useful for the formation of disulfide bonds in proteins as well as in other systems sensitive to the presence of oxidants. 相似文献
998.
Zhi Zeng Ke Tang Qianmin Ma Qianming Wang 《Journal of Sol-Gel Science and Technology》2014,69(1):231-236
Magnolol and honokiol as pharmaceutical ligands have been introduced into terbium complex systems for the first time and two hybrid organic–inorganic materials were successfully prepared. Both of them can sensitize terbium characteristic green emission effectively based on intra-molecular energy transfer channel. Moreover, they selectively recognized Cu2+ and Fe3+ through luminescence quenching effects. The photophysical properties and morphological structures were extensively investigated. 相似文献
999.
Frontispiece: New Insight into the Hydrocarbon‐Pool Chemistry of the Methanol‐to‐Olefins Conversion over Zeolite H‐ZSM‐5 from GC‐MS,Solid‐State NMR Spectroscopy,and DFT Calculations 下载免费PDF全文
1000.
The First Five‐Membered‐Heterocycle‐Fused Subphthalocyanine Analogues: Chiral Tri(benzo[b]thiopheno)subporphyrazines 下载免费PDF全文
Hong Shang Luyang Zhao Dr. Dongdong Qi Chao Chen Prof. Dr. Jianzhuang Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16266-16272
Two tri(benzo[b]thiopheno)subporphyrazine regioisomers with C3 and C1 molecular symmetry have been isolated from the cyclotrimerization of benzo[b]thiophene‐2,3‐dicarbonitrile as the first five‐membered‐heterocycle‐fused subphthalocyanine analogues. Optical resolution of both regioisomers was achieved by using a chiral HPLC technique, affording the first chiral subphthalocyanine analogues. 相似文献