全文获取类型
收费全文 | 1177篇 |
免费 | 61篇 |
国内免费 | 59篇 |
专业分类
化学 | 858篇 |
晶体学 | 8篇 |
力学 | 34篇 |
综合类 | 1篇 |
数学 | 132篇 |
物理学 | 264篇 |
出版年
2023年 | 27篇 |
2022年 | 38篇 |
2021年 | 41篇 |
2020年 | 42篇 |
2019年 | 42篇 |
2018年 | 29篇 |
2017年 | 33篇 |
2016年 | 36篇 |
2015年 | 47篇 |
2014年 | 49篇 |
2013年 | 54篇 |
2012年 | 55篇 |
2011年 | 75篇 |
2010年 | 50篇 |
2009年 | 45篇 |
2008年 | 46篇 |
2007年 | 67篇 |
2006年 | 55篇 |
2005年 | 51篇 |
2004年 | 38篇 |
2003年 | 33篇 |
2002年 | 39篇 |
2001年 | 23篇 |
2000年 | 24篇 |
1999年 | 25篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1911年 | 2篇 |
1910年 | 3篇 |
1905年 | 2篇 |
1904年 | 2篇 |
1902年 | 2篇 |
排序方式: 共有1297条查询结果,搜索用时 15 毫秒
31.
The iodine/DMAP-mediated intramolecular tandem C–C/C–O bond forming reaction of malonate bearing alkene moiety proceeded to give bicyclic lactones with good diastereoselectivity in good yield. The mechanistic investigation was also discussed on the basis of various control experimental results. 相似文献
32.
Synthesis of a new insoluble polymer-supported chiral alcohol auxiliary and its first application to nucleophilic addition to ketenes 总被引:2,自引:0,他引:2
Akkari R Calmes M Mai N Rolland M Martinez J 《The Journal of organic chemistry》2001,66(17):5859-5865
The preparation of a new optically active alcohol with a carboxylic function that allowed its attachment to an amine-functionalized insoluble polymer is described. Its first use as a polymer supported chiral auxiliary is demonstrated by asymmetric transformation of two racemic aryl propionic acids via ketene formation (95-96% ee). 相似文献
33.
Matrix solid-phase dispersion extraction and high-performance liquid chromatographic determination of residual sulfonamides in chicken. 总被引:6,自引:0,他引:6
Simultaneous determination of the six sulfonamides (SAs) sulfadiazine, sulfadimidine, sulfamonomethoxine, sulfamethoxazole, sulfadimethoxine and sulfaquinoxaline in chicken using matrix solid-phase dispersion (MSPD) with neutral aluminium oxide as an MSPD sorbent and high-performance liquid chromatography (HPLC) is presented. In the present MSPD, six SAs could be isolated by only one step, elution with a 70% (v/v) aqueous ethanol solution, without the sorbent conditioning and the sorbent-tissue matrix washing. For the HPLC determination, a LiChrospher 100 RP-8 and a mixture of 1% acetic acid solution (pH 3.0, in water)-acetonitrile-N,N-dimethylformamide (78:22:5, v/v/v) as the mobile phase with a photodiode array detector were used. Average recoveries were greater than 87.6% with relative standard deviations between 0.5 and 8.6%. The total time and amount of solvent required for the analysis of one sample were <1.5 h and <12 ml, respectively. 相似文献
34.
Thuan Nguyen Ngoc Ngan Nguyen Thi Kuo Ping-Chung Trinh Nguyen Thi Nu Thien Le Trung Mai Dam Sao Tuan Nguyen Ngoc Tan Le Van Thang Tran Dinh 《Chemistry of Natural Compounds》2021,57(6):1104-1106
Chemistry of Natural Compounds - 相似文献
35.
Rapid one-step synthesis, characterization and functionalization of silica coated gold nanoparticles
Newaz Mohammed Bahadur Shun WatanabeTakeshi Furusawa Masahide Sato Fumio KurayamaIqbal Ahmed Siddiquey Yoshio KobayashiNoboru Suzuki 《Colloids and surfaces. A, Physicochemical and engineering aspects》2011,392(1):137-144
This paper describes a rapid, simple and one-step method for preparing silica coated gold (Au@SiO2) nanoparticles with fine tunable silica shell thickness and surface functionalization of the prepared particles with different groups. Monodispersed Au nanoparticles with a mean particle size of 16 nm were prepared by citrate reduction method. Silica coating was carried out by mixing the as prepared Au solution, tetraethoxysilane (TEOS) and ammonia followed by microwave (MW) irradiation. Although there are several ways of coating Au nanoparticles with silica in the literature, each of these needs pre-coating step as well as long reaction duration. The present method is especially useful for giving the opportunity to cover the colloidal Au particles with uniform silica shell within very short time and forgoes the use of a silane coupling agent or pre-coating step before silica coating. Au@SiO2 nanoparticles with wide range of silica shell thickness (5-105 nm) were prepared within 5 min of MW irradiation by changing the concentration of TEOS only. The size uniformity and monodispersity were found to be better compared to the particles prepared by conventional methods, which were confirmed by dynamic light scattering and transmission electron microscopic techniques. The prepared Au@SiO2 nanoparticles were further functionalized with amino, carboxylate, alkyl groups to facilitate the rapid translation of the nanoparticles to a wide range of end applications. The functional groups were identified by XPS, and zeta potential measurements. 相似文献
36.
[Eu(pda)2]? and [Eu(bda)2]? (pda=1,10‐phenanthroline‐2, 9‐dicarboxylic acid; bda=2,2′ bipyridine 5,5′‐dicarboxylic acid) have an achiral D2d structure in crystals. These complexes exhibit circularly polarized luminescence (CPL) in water containing chiral amino acids. In this work, induced CPL of [Eu(pda)2]? and [Eu(bda)2]? in water solutions containing a mixture of d ‐ and l ‐ amino acids were examined. Plots of glum values of the induced CPL as a function of mol‐fraction of l ‐ and d ‐ arginine reveal that [Eu(pda)2]? favors homo‐association ([Eu(pda)2]?‐(l ‐arginine)2 or [Eu(pda)2]?‐(d ‐arginine)2) over hetero‐association {[Eu(pda)2]?‐(l ‐arginine)?(d ‐arginine)}. This suggests that association of an arginine molecule induces a structural change in [Eu(pda)2]? to promote chiral selective association to another arginine, i.e., homo‐allosteric association. On the other hand, the system of [Eu(pda)2]? with histidine favors hetero‐allosteric association over homo‐association. No allosteric effect is recognized in CPL from [Eu(bda)2]?. 相似文献
37.
Chiral quaternary ammonium salts derived from cinchonidine have been applied to catalyze the stereoselective iodolactonizations of trans-5-aryl-4-pentenoic acids leading to a mixture of two regioselectively iodolactonized products with fair to excellent yield (37-98%) and moderate enantioselectivity (exo = 42.0% ee, endo = 31.0% ee) under mild conditions. This work is the first example of asymmetric iodolactonization reaction in the presence of less than a stoichiometric amount of chiral reagent. 相似文献
38.
Junpeng Xie Xiaodan Li Haojie Lai Zhijuan Zhao Jinliang Li Wanggang Zhang Weiguang Xie Yiming Liu Wenjie Mai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14882-14889
Metal–organic framework‐derived NiCo2.5S4 microrods wrapped in reduced graphene oxide (NCS@RGO) were synthesized for potassium‐ion storage. Upon coordination with organic potassium salts, NCS@RGO exhibits an ultrahigh initial reversible specific capacity (602 mAh g?1 at 50 mA g?1) and ultralong cycle life (a reversible specific capacity of 495 mAh g?1 at 200 mA g?1 after 1 900 cycles over 314 days). Furthermore, the battery demonstrates a high initial Coulombic efficiency of 78 %, outperforming most sulfides reported previously. Advanced ex situ characterization techniques, including atomic force microscopy, were used for evaluation and the results indicate that the organic potassium salt‐containing electrolyte helps to form thin and robust solid electrolyte interphase layers, which reduce the formation of byproducts during the potassiation–depotassiation process and enhance the mechanical stability of electrodes. The excellent conductivity of the RGO in the composites, and the robust interface between the electrodes and electrolytes, imbue the electrode with useful properties; including, ultrafast potassium‐ion storage with a reversible specific capacity of 402 mAh g?1 even at 2 A g?1. 相似文献
39.
C Chao Z Ren Y Zhu Z Xiao Z Liu G Xu J Mai X Li G Shen G Han 《Angewandte Chemie (International ed. in English)》2012,51(37):9283-9287
Free-standing single-crystal PbTiO(3) nanoplates were synthesized by a facile hydrothermal method. A "self-templated" crystal growth is presumed to lead to the formation of the PbTiO(3) nanoplates, which have ferroelectric single-domain structures, whose polarization areas can be manipulated by writing and reading. The nanoplates are also effective catalysts for the oxidation of carbon monoxide. 相似文献
40.
A new method for determining the size of critical nucleus of fibril formation of polypeptide chains is proposed. Based on the hypothesis that the fibril grows by addition of a nascent peptide to the preformed template, the nucleus size N(c) is defined as the number of forming template peptides above which the time to add a new monomer becomes independent of the template size. Using lattice models one can show that our method and the standard method which is based on calculation of the free energy, provide the same result for N(c). 相似文献