全文获取类型
收费全文 | 1870篇 |
免费 | 79篇 |
国内免费 | 53篇 |
专业分类
化学 | 993篇 |
晶体学 | 14篇 |
力学 | 109篇 |
综合类 | 16篇 |
数学 | 409篇 |
物理学 | 461篇 |
出版年
2023年 | 15篇 |
2022年 | 27篇 |
2021年 | 28篇 |
2020年 | 47篇 |
2019年 | 41篇 |
2018年 | 49篇 |
2017年 | 50篇 |
2016年 | 75篇 |
2015年 | 68篇 |
2014年 | 84篇 |
2013年 | 148篇 |
2012年 | 116篇 |
2011年 | 119篇 |
2010年 | 131篇 |
2009年 | 90篇 |
2008年 | 91篇 |
2007年 | 97篇 |
2006年 | 74篇 |
2005年 | 66篇 |
2004年 | 46篇 |
2003年 | 40篇 |
2002年 | 79篇 |
2001年 | 61篇 |
2000年 | 39篇 |
1999年 | 30篇 |
1998年 | 30篇 |
1997年 | 25篇 |
1996年 | 25篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 13篇 |
1982年 | 5篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1964年 | 8篇 |
排序方式: 共有2002条查询结果,搜索用时 15 毫秒
941.
Aslıhan Gökaltun Cemil Aydoğan Bekir Çelebi Adil Denizli Ali Tuncel 《Chromatographia》2014,77(5-6):459-469
A new reactive capillary monolith as an alternative to the commonly employed glycidyl methacrylate-based stationary phases in capillary electrochromatography (CEC) applications was synthesized and post-functionalized with charge-bearing groups. For this purpose, a hydrophilic capillary monolith with reactive 3-chloro-2-hydroxypropyl moiety was first obtained by the copolymerization of a new methacrylate-based monomer, 3-chloro-2-hydroxypropyl methacrylate (HPMA-Cl), with a methacrylic crosslinking agent, ethylene glycol dimethacrylate (EDMA). The presence of 3-chloro-2-hydroxypropyl functionality in poly(HPMA-Cl-co-EDMA) monolith allowed the synthesis of monoliths carrying strongly ionizable anionic, cationic or neutral groups such as sulfonic acid, quaternary ammonium or octadecyl, respectively, via simple and single-stage reactions. In the present study, a reactive poly(HPMA-Cl-co-EDMA) capillary monolith was functionalized with sodium bisulfite (NaHSO3) to have a strongly ionizable sulfonic acid group on the monolith. The resulting monolith providing cathodic electroosmotic flow in CEC was successfully used for the separation of phenol derivatives. The theoretical plate numbers up to 63,000 plates/column were achieved. The results showed that a new promising, reactive support that could be functionalized with different chromatographic ligands for different chromatographic applications was obtained in the study. 相似文献
942.
943.
İsa Doğan Atik B. Özen F. Tıhmınlıoğlu 《Journal of Thermal Analysis and Calorimetry》2008,94(3):687-693
The novel film structure of corn-zein coated on polypropylene (PP) synthetic film for packaging industry was developed to
examine the feasibility of resulting coated films as an alternative water barrier performance for food packaging. The effects
of coating formulation (solvent, corn-zein, plasticizer concentration and plasticizer type) on final properties of films were
observed. Corn-zein is the most important protein of corn and has good film forming property. Composites structures of PP
films coated with corn-zein were obtained through a simple solvent casting method. Polyethylene glycol (PEG) and glycerol
(GLY) were used as plasticizer to increase film flexibility. Statistical analysis based on full factorial design was performed
to observe coating formulation effects. The high water vapour barriers were obtained for films coated with coating formulation
consisting of higher amounts of corn-zein plasticized by GLY. The lower glass transition temperatures (T
g) of films were obtained by plasticization of films and T
g decreased by increasing plasticizer content. The statistical analysis defined the key parameters of coating formulation that
had major effects on the final properties of coated PP films as corn-zein, plasticizer concentration and plasticizer type.
In conclusion, corn-zein coatings could have potential as an alternative to conventional synthetic polymers used in composite
multilayer structures for food packaging applications. 相似文献
944.
该文以聚苯胺/石墨烯复合材料为涂覆材料,制备了一种涂覆型阴离子交换固定相。首先以苯胺和石墨烯为原料制备聚苯胺/石墨烯复合材料,并通过物理吸附涂覆在聚苯乙烯-二乙烯苯微球表面;然后以聚苯胺中的氮原子为反应位点,通过季铵化制备一系列具有不同交换容量的涂覆型阴离子交换固定相。通过扫描电镜(SEM)、傅里叶红外光谱(FT-IR)和元素分析(EA)对该涂覆型阴离子交换固定相进行表征,结果表明聚苯胺/石墨烯成功地涂覆在微球表面且发生了季铵化。通过分离常规阴离子和有机酸,对自制阴离子交换色谱柱的色谱性能进行评价。结果显示,8次季铵化的聚苯胺/石墨烯涂覆聚苯乙烯-二乙烯苯阴离子交换色谱柱对常规阴离子和有机酸呈现良好的分离效果。 相似文献
945.
Russian Journal of Electrochemistry - A rapid, simple, sensitive, precise and specific square wave voltammetric method was developed for the simultaneous determination of Thiocolchicoside (TC) and... 相似文献
946.
Aznar F Fañanás-Mastral M Alonso J Fañanás FJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):325-332
Fischer carbene complexes react with 4-unsubstituted 1-amino-1,3-dienes to give different carbocyclization products depending on the nature of the carbene complex and on the substitution pattern of the aminodiene. Thus, the reaction of arylcarbene chromium complexes and 1-aminodienes diastereoselectively affords cyclopropane derivatives by means of a formal [2+1] carbocyclization reaction. In particular, pentacarbonyl[(2-furyl)(methoxy)methylene]chromium complex furnishes formal [4+1] carbocyclization products. Starting from beta-substituted alkenylcarbene complexes, formal [4+1] reactions occur and cyclopentenamine derivatives are diastereoselectively formed. However, when the alpha,beta-disubstituted alkenylcarbene complex pentacarbonyl[(5,6-dihydro-2H-pyran-2-yl)(methoxy)methylene]tungsten is used, the outcome of the reaction depends on the substitution on the carbon atom at the 3-position of the aminodiene, generating the [3+2] or [4+3]-cyclization products if the substituent is or is not a hydrogen atom, respectively. Finally, when the reaction is performed with alkynylcarbene complexes, benzaldehyde derivatives are obtained if the triple-bond substituent is a phenyl group or indene derivatives if the group is an alkenyl moiety. 相似文献
947.
Özlem Aksu Dönmez Abdürrezzak Bozdoğan Gönül Kunt 《Monatshefte für Chemie / Chemical Monthly》2006,137(9):1163-1168
Summary. A partial least-squares calibration (PLS) method has been developed for simultaneous quantitative determination of escin (ES) and diethylamine salicylate (DAS) in pharmaceutical preparations. The resolution of these mixtures has been accomplished without prior separation or derivatisation,
by using partial least-squares (PLS-2) regression analysis of electronic absorption spectral data. The experimental calibration
matrix was constructed with 9 samples. The concentration ranges considered were 10, 20, 30 (ES) and 40, 50, 60 (DAS) μg cm−3. The absorbances were recorded between 200 and 325 nm every 5 nm. Proposed method was compared with conventional spectrophotometric
method. The results show that PLS-2 is a simple, rapid, and accurate method applied to the determination of these compounds
in pharmaceuticals. 相似文献
948.
Le' an Hu Yao Zhang Qing‐Wen Zhang Qin Yin Xumu Zhang 《Angewandte Chemie (International ed. in English)》2020,59(13):5321-5325
A Ru‐catalyzed direct asymmetric reductive amination of ortho‐OH‐substituted diaryl and sterically hindered ketones with ammonium salts is reported. This method represents a straightforward route toward the synthesis of synthetically useful chiral primary diarylmethylamines and sterically hindered benzylamines (up to 97 % yield, 93–>99 % ee). Elaborations of the chiral amine products into bioactive compounds and a chiral ligand were demonstrated through manipulation of the removable and convertible ‐OH group. 相似文献
949.
Tadeusz Lis Petra Stachov Duan Valigura Jan Moncol 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m375-m377
The title compound {systematic name: tetrakis(μ‐3,5‐dinitrobenzoato‐κ2O:O′)bis[(3,7‐dihydro‐1,3,7‐trimethyl‐1H‐purine‐2,6‐dione‐κO2)copper(II)]}, [Cu2(C7H3N2O6)4(C8H10N4O2)2], consists of paddle‐wheel dimeric tetrakis(μ‐3,5‐dinitrobenzoato‐κ2O:O′)dicopper(II) units with O‐coordinated caffeine molecules in both apical positions. The entire dimeric molecule lies on a tetragonal inversion axis, and thus one nitrobenzoate anion with one Cu atom in a special position belong to the independent part of the molecule. The caffeine ligand bonded to the Cu atom is disordered on a local twofold non‐crystallographic axis coincident with the axis. A π–π stacking interaction is observed between the caffeine rings and adjacent symmetry‐related benzene rings of the 3,5‐dinitrobenzoate anions. 相似文献
950.
Xiaoyu Song Xinyue Wang Yusen Li Chengzhi Zheng Bowen Zhang Chong‐an Di Feng Li Chao Jin Wenbo Mi Long Chen Wenping Hu 《Angewandte Chemie (International ed. in English)》2020,59(3):1118-1123
2D conductive metal–organic frameworks (2D c‐MOFs) feature promising applications as chemiresistive sensors, electrode materials, electrocatalysts, and electronic devices. However, exploration of the spin‐polarized transport in this emerging materials and development of the relevant spintronics have not yet been implemented. In this work, layer‐by‐layer assembly was applied to fabricate highly crystalline and oriented thin films of a 2D c‐MOF, Cu3(HHTP)2, (HHTP: 2,3,6,7,10,11‐hexahydroxytriphenylene), with tunable thicknesses on the La0.67Sr0.33MnO3 (LSMO) ferromagnetic electrode. The magnetoresistance (MR) of the LSMO/Cu3(HHTP)2/Co organic spin valves (OSVs) reaches up to 25 % at 10 K. The MR can be retained with good film thickness adaptability varied from 30 to 100 nm and also at high temperatures (up to 200 K). This work demonstrates the first potential applications of 2D c‐MOFs in spintronics. 相似文献