全文获取类型
收费全文 | 26428篇 |
免费 | 5203篇 |
国内免费 | 3732篇 |
专业分类
化学 | 19403篇 |
晶体学 | 374篇 |
力学 | 1798篇 |
综合类 | 276篇 |
数学 | 2834篇 |
物理学 | 10678篇 |
出版年
2024年 | 56篇 |
2023年 | 614篇 |
2022年 | 736篇 |
2021年 | 1037篇 |
2020年 | 1301篇 |
2019年 | 1147篇 |
2018年 | 987篇 |
2017年 | 888篇 |
2016年 | 1316篇 |
2015年 | 1396篇 |
2014年 | 1644篇 |
2013年 | 1976篇 |
2012年 | 2525篇 |
2011年 | 2567篇 |
2010年 | 1736篇 |
2009年 | 1684篇 |
2008年 | 1898篇 |
2007年 | 1596篇 |
2006年 | 1558篇 |
2005年 | 1259篇 |
2004年 | 976篇 |
2003年 | 782篇 |
2002年 | 777篇 |
2001年 | 618篇 |
2000年 | 534篇 |
1999年 | 559篇 |
1998年 | 410篇 |
1997年 | 364篇 |
1996年 | 399篇 |
1995年 | 330篇 |
1994年 | 309篇 |
1993年 | 237篇 |
1992年 | 218篇 |
1991年 | 172篇 |
1990年 | 151篇 |
1989年 | 131篇 |
1988年 | 121篇 |
1987年 | 81篇 |
1986年 | 77篇 |
1985年 | 57篇 |
1984年 | 41篇 |
1983年 | 29篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1971年 | 2篇 |
1966年 | 3篇 |
1957年 | 6篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
991.
Solid-liquid phase transfer catalytic elimination reaction for the preparation of acyclic and cyclic ketene acetals has been developed. 相似文献
992.
Zhijie Fang Zhe Su Wenjing Qin Hao Li Bing Fang Wei Du Qiong Wu Bo Peng Peng Li Haidong Yu Lin Li Wei Huang 《中国化学快报》2021,31(11):2903-2908
H2S is an essential gas signal molecule in cells, and viscosity is a key internal environmental parameter. Recent studies have shown that H2S acts as a cytoarchitecture agent and gas transmitter in many tissues, e.g., as a regulator of neuroendocrine in the brain for mediating vascular tone in blood vessels. Mitochondrial viscosity is an important parameter for judging whether mitochondrial function is normal. It has been reported that oxidative stress and mitochondrial dysfunction are connected with Parkinson’s disease (PD), and the protective role of H2S in PD models has been extensively demonstrated. Herein, Mito-HS, a new two-photon fluorescent probe was demonstrated to detect cross-talk between the two channels of mitochondrial viscosity and H2S content. Moreover, this probe could detect the relative amount of and changes in mitochondrial H2S in situ due to the reduced mitochondrial targeting ability after reaction with H2S. The results show that H2S in mitochondria is inversely related to viscosity. The PD model has a lower H2S in mitochondria and a higher mitochondrial viscosity than did the normal. This result is important for our deep understanding of PD and its causes. 相似文献
993.
Dual template method to prepare hierarchical porous carbon nanofibers for high-power supercapacitors
Qiang Wang Qi Cao Xianyou Wang Bo Jing Hao Kuang Ling Zhou 《Journal of Solid State Electrochemistry》2013,17(10):2731-2739
Hierarchical porous carbon nanofibers serving as electrode materials are prepared through carbonization and hydrofluoric acid treatment of polyacrylonitrile-based electrospinning involving dual templates. The hierarchical porous structures are synergistically tailored by varying template contents in the spinning solution. The carbon nanofibers prepared from the electrospinning of polyacrylonitrile containing 15/15 wt.% polymethylmethacrylate/tetraethyl orthosilicate exhibit the largest specific surface area (699 m2 g?1) and microporous volume (0.196 cm3 g?1). In 6 M KOH electrolyte, a symmetrical supercapacitor equipped with the hierarchical porous carbon nanofibers demonstrates its high-end specific capacitance of 170 F g?1, superior rate capability, and high-power density output up to 14.7 kW kg?1. Cycling evolution indicates capacitance fading is only 5.8 % of initial capacitance at a current density of 1 A g?1 even after 8,000 cycles. The excellent electrochemical performances of the carbon nanofiber are mainly ascribed to the optimized pore size distributions of both micropores and mesopores and the unique hierarchical pore structures possessed by abundant micropores. 相似文献
994.
Four new coordination polymers, [Cd(3-TPTP)Cl]2 (3-HTPTP = 4′-(3-tetrazolylphenyl)2,2′:6′2′′-terpyridine, 1), {[Cd(3-TPTP)(pBDC)0.5]?4H2O}n (pH2BDC = 1,4-benzenedicarboxylic acid, 2), {[Mn(3-TPTP)(mBDC)0.5]?5H2O}n (mH2BDC = 1,3-benzenedicarboxylic acid, 3), and [Pb(3-TPTP)(H2O)2]?OH (4), were obtained. Compounds 1–3 are composed of binuclear [M2(3-TPTP)2] ring as building unit. In 1, the binuclear rings pack into a 3-D supramolecular framework via various hydrogen bonds. In 2 and 3, the binuclear rings are connected by mBDC2? and pBDC2?, respectively, resulting in two types of 1-D chains. In 4, the mononuclear [Pb(3-TPTP)] units are connected by Pb?N weak interactions, giving a chiral 1-D coordination chain, which is further connected by O–H?N interaction to form a chiral 3-D supramolecular framework. The phase purity of 1–4 and luminescence properties of 1, 2, and 4 were also investigated. 相似文献
995.
Qingxiang Zhou Zhenwen Zheng Junping Xiao Huili Fan Xiuyi Yan 《Analytical and bioanalytical chemistry》2016,408(19):5211-5220
996.
Fengyang Deng Bin Xu Yong Gao Zheng Liu Duanguang Yang Huaming Li 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3767-3774
In this study, a series of linear poly(triazole)s (PTAs) were successfully synthesized by the metal‐ and solvent‐free, thermal click polymerization of diazide and dialkyne (A2 + B2) monomers. All click polymerizations proceeded smoothly at 80 °C in an open atmosphere without protection from oxygen and moisture. After being polymerized for 36 h, the crude polymer was further fractionated into three fractions using a multistep precipitation method. By selectively choosing precipitating agents, this process produced poly(triazole) fractions with low polydispersity index (<1.30). The resulting PTAs are soluble in common organic solvents and stable at a temperature up to 320 °C. Furthermore, the methyl benzoate moieties in the main chain can serve as useful building blocks for further postpolymerization functionalization, yielding 1,2,4‐triazole derivatives. This functionalization strategy offers potential for the development of novel triazole‐based materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
997.
Zhaojie Gu Lijun Deng Hao Luo Xia Guo Haohao Li Zhencai Cao Xunshan Liu Xinwei Li Hongyan Huang Yingzi Tan Yong Pei Songting Tan 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3848-3858
A series of novel low band gap polymers containing conjugated side chains with 4,7‐dithien‐5‐yl‐2,1,3‐benzodiathiazole and different electron‐withdrawing end groups of aldehyde ( PT‐DTBTCHO ), 2‐ethylhexyl cyanoacetate ( PT‐DTBTCN ), 1,3‐diethyl‐2‐thiobarbituric acid ( PT‐DTBTDT ), and electron‐donating end group of 2‐methylthiophene ( PT‐DTBTMT ) have been designed and synthesized. All polymers exhibit good solubility in common organic solvents, film‐forming ability, and thermal stability. These conjugated polymers show the broad ultraviolet‐visible absorption and the narrow optical band gaps in the range of 1.65–1.90 eV. Through changing the end group of conjugated side chains, the photophysical properties and energy levels of the polymers were tuned effectively. Bulk heterojunction solar cells based on the blend of these polymers and (6,6)‐phenyl‐C61‐butyric acid methyl ester (PC61BM) reached the best power conversion efficiency (PCE) of 2.72%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
998.
Bergman cyclization has shown great promise in constructing conjugated polymers.However,the application of this reaction in polymer science is still limited due to the harsh reaction condition and ill-defined structure of the achieved polymers.To this end,the cycloaromatization polymerization of enediynes catalyzed by a series of transition metal catalysts is investigated in this work,by taking advantage of the coordination chemistry of the enediyne with the transition metal complexes.According to the nuclear magnetic resonance (NMR),Fourier transform infrared (FTIR),ultraviolet-visble (UV-Vis) spectroscopies and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis,the cycloaromatization polymerization of enediynes proceeds under milder conditions and in a more controlled manner in the presence of palladium(Ⅱ) complexes,giving structurally regulated conjugated polymers in high yields. 相似文献
999.
A novel approach was developed to improve the solubility of non-soluble compounds by introducing solubilising molecules peripherally through hydrogen-bond-mediated assembly. The solubilisation process can be reversed by adding competing hydrogen bonding moieties and removing the solubilising molecules. This method may potentially facilitate device fabrication. 相似文献
1000.