全文获取类型
收费全文 | 27576篇 |
免费 | 4294篇 |
国内免费 | 2675篇 |
专业分类
化学 | 19048篇 |
晶体学 | 362篇 |
力学 | 1653篇 |
综合类 | 138篇 |
数学 | 3151篇 |
物理学 | 10193篇 |
出版年
2024年 | 78篇 |
2023年 | 563篇 |
2022年 | 1042篇 |
2021年 | 1011篇 |
2020年 | 1117篇 |
2019年 | 1077篇 |
2018年 | 920篇 |
2017年 | 814篇 |
2016年 | 1319篇 |
2015年 | 1268篇 |
2014年 | 1479篇 |
2013年 | 1950篇 |
2012年 | 2575篇 |
2011年 | 2565篇 |
2010年 | 1719篇 |
2009年 | 1609篇 |
2008年 | 1777篇 |
2007年 | 1640篇 |
2006年 | 1438篇 |
2005年 | 1223篇 |
2004年 | 885篇 |
2003年 | 679篇 |
2002年 | 654篇 |
2001年 | 487篇 |
2000年 | 474篇 |
1999年 | 546篇 |
1998年 | 447篇 |
1997年 | 443篇 |
1996年 | 459篇 |
1995年 | 361篇 |
1994年 | 311篇 |
1993年 | 242篇 |
1992年 | 245篇 |
1991年 | 204篇 |
1990年 | 176篇 |
1989年 | 147篇 |
1988年 | 101篇 |
1987年 | 110篇 |
1986年 | 88篇 |
1985年 | 84篇 |
1984年 | 48篇 |
1983年 | 45篇 |
1982年 | 36篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Shaobin Pan Zhe Zhang Qixiang Feng Jin Zhao Shahid Aziz Liwen Dou Jing Li Luyao Huang Huijiao Yan Xiao Wang Jia Li Daijie Wang 《Journal of separation science》2023,46(10):2300042
Cyperus rotundus L. has been extensively used in ancient medication for the treatment of different disorders worldwide, in which sesquiterpenes are the most representative components. In this study, sesquiterpenes were effectively purified by two-dimensional counter-current chromatography in combination with continuous injection and inner-recycling mode with a solvent system of n-hexane/ethyl acetate/methanol/water (1:0.2:1:0.2, v/v/v/v). For one-dimension separation, continuous injection mode was used with three times injection and the inner-recycling mode was adopted for the separation of two mixtures for two-dimensional separation. Finally, four sesquiterpenoids, including scariodione ( 1 ), cyperenoic acid ( 2 ), scariodione ( 3 ), and α-cyperone ( 4 ), were obtained with purities over 98%. Mass spectrometry and nuclear magnetic resonance were applied to identify their structures. The results from the anti-inflammation effect with zebrafish demonstrated that cyperenoic acid exhibited stronger anti-inflammation activity. Molecular docking results suggested that cyperenoic acid possessed lower binding energies –9.4545 kcal/mol with 1CX2 to form formed hydrogen bond interaction with ARG120. In general, all the obtained findings proved that the strong anti-inflammation capacity of cyperenoic acid can have the potential of being adopted for treating diseases resulting from inflammation. 相似文献
992.
Hui Xie Yanyan Niu Ying Deng Hui Cheng Chengxiang Ruan Guangjiu Li Wei Sun 《中国化学会会志》2021,68(1):114-120
In this paper, an electrochemical aptamer sensor was proposed for the highly sensitive detection of mercury ion (Hg2+). Carbon nanofiber (CNF) was prepared by electrospinning and high‐temperature carbonization, which was used for the loading of platinum nanoparticles (PtNPs) by the hydrothermal method. The Pt@CNF nanocomposite was modified on the surface of carbon ionic liquid electrode (CILE) to obtain Pt@CNF/CILE, which was further decorated by gold nanoparticles (AuNPs) through electrodeposition to get Au/Pt@CNF/CILE. Self‐assembling of the thiol‐based aptamer was further realized by the formation of Au‐S bond to get an electrochemical aptamer sensor (Aptamer/Au/Pt@CNF/CILE). Due to the specific binding of aptamer probe to Hg2+ with the formation of T‐Hg2+‐T structure, a highly sensitive quantitative detection of Hg2+ could be achieved by recording the changes of current signal after reacting with Hg2+ within the concentration range from 1.0 × 10?15 mol/L to 1.0 × 10?6 mol/L and the detection limit of 3.33 × 10?16 mol/L (3σ). Real water samples were successfully analyzed by this method. 相似文献
993.
Surface modification by poly(ethylene glycol) (PEGylation) has been acknowledged as a powerful strategy in minimizing non-specific reactions for biomedical devices. Once applied into manufacture of drug/gene delivery systems, PEGylation has demonstrated to significantly improve their biocompatibility and stealthiness in physiological environment. Nonetheless, reluctant cell membrane affinities thus cellular uptake efficiencies owing to PEGylation brought up further issues that are imperative to be resolved. Pertain to this PEGylation dilemma, we attempted to introduce peptide (GPLGVRG) linkage between block copolymer of PEG-poly{N'-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} PAsp(DET), wherein the cationic PAsp(DET) could self-assemble with pDNA into nanoscaled complex core. Noteworthy was the peptide linkage whose amino acids sequence could be specifically recognized and degraded by matrix metalloproteinases (MMPs) (overexpressed in extracellular milieu of tumors). Therefore, our subsequent studies validated facile detachment of PEGylation from the aforementioned polyplex micelles upon treatment of MMPs, which elicited improved cytomembrane affinities and cellular uptake efficiencies. In addition, promoted escape from endosome entrapment was also confirmed through direct endosome membrane destabilization by PAsp(DET), which was further elucidated to be attributable to dePEGylation as well as elevated charged density of PAsp(DET) in acidic endosomes. These benefits from dePEGylation eventually contributed to promoted gene expression at the affected cells and potent tumor growth suppression based on anti-angiogenic approach. Therefore, our developed strategy has provided a facile approach in overcoming the dilemma of PEGylation, which could be informative in design of drug/gene delivery systems. 相似文献
994.
六方最密堆积和立方最密堆积是金属晶体中最常见的结构,其正四面体空隙和正八面体空隙的分布是学生学习的难点.本文将揭示密置双层-最密堆积-离子晶体结构中空隙的分布规律,进而将典型离子晶体结构与最密堆积中的空隙分布相关联.这对学生掌握空隙分布的规律性,理解金属和离子晶体结构,提升晶体结构的学习效果大有帮助. 相似文献
995.
Xing Wei Meng‐Jiao Zhu Zhe Cheng Mengjeu Lee Hong Yan Changsheng Lu Jing‐Juan Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(10):3194-3198
The aggregation‐induced electrochemiluminescence (AIECL) of carboranyl carbazoles in aqueous media was investigated for the first time. Quantum yields, morphologies, and particle sizes were observed to determine the electrochemiluminescence (ECL) performance of these aggregated organic dots (ODs). All compounds exhibit much higher ECL stability and intensity than the carborane‐free compound, demonstrating the essential role of the carboranyl motif. Moreover, the results of cyclic voltammetry (CV) suggest that oxidation/reduction reactions take place at the carboranyl motif. The excited states of ODs were proposed to be generated by the mechanism of surface state transitions. More importantly, these compounds show a reductive–oxidative mechanism in contrast to other organic materials that show oxidative–reductive mechanisms. Our experiments and data have established the relation between AIE organic structures and ECL properties that has a strong potential for biological and diagnostic applications. 相似文献
996.
Lu Yuan Ming Kang Guanjun Chang Xiangmeng Lv Simin Shen Rong Sun 《无机化学与普通化学杂志》2019,645(21):1240-1246
Due to the unique size effects, nanomaterials in infrared absorption have attracted much attention for their strong absorption in the infrared region. To achieve the infrared multi‐band absorption, we propose to synthesize a core‐shell structure nanomaterial consisting of NaYF4:Yb3+, Er3+ core and a layer of SiO2 as shell. A series of NaYF4:Yb3+, Er3+ nanocrystals were synthesized through hydrothermal method by adjusting the ratio of citric acid(CA)‐to‐NaOH, and the effects of CA concentration, and NaOH concentration were studied in detail. NaYF4:Yb3+, Er3+@SiO2 nanoparticles were synthesized by sol‐gel method using TEOS as silica source. The results show that the core‐shell NaYF4:Yb3+, Er3+@SiO2 nanoparticles were successfully synthesized. Up‐conversion spectra of these nanoparticles were recorded with 980 nm laser excitation under room temperature. There are no changes of the emission centers of nanoparticles before or after silica coating, but the emission intensities of nanoparticles after silica coating are weakened. Furthermore, the property of infrared multi‐band absorption was tested through ultraviolet‐visible‐near infrared spectrophotometer and infrared absorption spectra. The results illustrate that the multi‐band infrared absorption nanomaterial was successfully synthesized. 相似文献
997.
基于DFT-BS方法,在不同泛函方法和基组下计算[CuIIGdIII{pyCO(OEt)py C(OH)(OEt)py}3]2+及3d-Gd异金属配合物的磁耦合常数,结果表明,PBE0/TZVP(Gd为SARC-DKH-TZVP)水平可用于描述其磁学性质。顺磁中心CuII、GdIII与桥联配位氧原子间存在较强的轨道相互作用,其磁轨道主要由GdIII的4fz3、4fz(x2-y2)轨道、CuII的3dx2-y2轨道和桥联配位原子O的p轨道组成。顺磁中心CuII离子以自旋离域作用为主,GdIII离子以自旋极化作用为主,顺磁中心CuII自旋离域作用对桥联氧原子的影响大于顺磁中心GdIII的自旋极化作用。在同结构3d-Gd配合物中,随着MII离子未成对电子的增加,顺磁中心间自旋密度平方差越大,顺磁中心MII和GdIII之间的反铁磁性贡献越大,其磁耦合常数越小。 相似文献
998.
Hongyu Zhang Changlong Hao Aihua Qu Maozhong Sun Liguang Xu Chuanlai Xu Hua Kuang 《Angewandte Chemie (International ed. in English)》2020,59(18):7131-7138
The accumulation and deposition of β‐amyloid (Aβ) plaques in the brain is considered a potential pathogenic mechanism underlying Alzheimer's disease (AD). Chiral l/d ‐FexCuySe nanoparticles (NPs) were fabricated that interfer with the self‐assembly of Aβ42 monomers and trigger the Aβ42 fibrils in dense structures to become looser monomers under 808 nm near‐infrared (NIR) illumination. d ‐FexCuySe NPs have a much higher affinity for Aβ42 fibrils than l ‐FexCuySe NPs and chiral Cu2?xSe NPs. The chiral FexCuySe NPs also generate more reactive oxygen species (ROS) than chiral Cu2?xSe NPs under NIR‐light irradiation. In living MN9D cells, d ‐NPs attenuate the adhesion of Aβ42 to membranes and neuron loss after NIR treatment within 10 min without the photothermal effect. In‐vivo experiments showed that d ‐FexCuySe NPs provide an efficient protection against neuronal damage induced by the deposition of Aβ42 and alleviate symptoms in a mouse model of AD, leading to the recovery of cognitive competence. 相似文献
999.
Niankun Guo Hui Xue Amurisana Bao Zihong Wang Jing Sun Tianshan Song Xin Ge Wei Zhang Keke Huang Feng He Qin Wang 《Angewandte Chemie (International ed. in English)》2020,59(33):13778-13784
Vacancy defects of catalysts have been extensively studied and proven to be beneficial to various electrocatalytic reactions. Herein, an ultra‐stable three‐dimensional PtCu nanowire network (NNW) with ultrafine size, self‐supporting rigid structure, and Cu vacancy defects has been developed. The vacancy defect‐rich PtCu NNW exhibits an outstanding performance for the oxygen reduction reaction (ORR), with a mass activity 14.1 times higher than for the commercial Pt/C catalyst (20 %.wt, JM), which is currently the best performance. The mass activity of the PtCu NNW for methanol oxidation reaction (MOR) is 17.8 times higher than for the commercial Pt/C catalyst. Density‐functional theory (DFT) calculations indicate that the introduction of Cu vacancies enhances the adsorption capacity of Pt atoms to the HO* intermediate and simultaneously weakens the adsorption for the O* intermediate. This work presents a facile strategy to assemble efficient electrocatalysts with abundant vacancy defects, at the same time, provides an insight into the ORR mechanism in acidic solution. 相似文献
1000.
Chencheng Dai Yuanmiao Sun Gao Chen Adrian C. Fisher Zhichuan J. Xu 《Angewandte Chemie (International ed. in English)》2020,59(24):9418-9422
Nitrates are widely used as fertilizer and oxidizing agents. Commercial nitrate production from nitrogen involves high‐temperature‐high‐pressure multi‐step processes. Therefore, an alternative nitrate production method under ambient environment is of importance. Herein, an electrochemical nitrogen oxidation reaction (NOR) approach is developed to produce nitrate catalyzed by ZnFexCo2?xO4 spinel oxides. Theoretical and experimental results show Fe aids the formation of the first N?O bond on the *N site, while high oxidation state Co assists in stabilizing the absorbed OH? for the generation of the second and third N?O bonds. Owing to the concerted catalysis, the ZnFe0.4Co1.6O4 oxide demonstrates the highest nitrate production rate of 130±12 μmol h?1 gMO?1 at an applied potential of 1.6 V versus the reversible hydrogen electrode (RHE). 相似文献