全文获取类型
收费全文 | 1094篇 |
免费 | 55篇 |
国内免费 | 6篇 |
专业分类
化学 | 919篇 |
晶体学 | 9篇 |
力学 | 11篇 |
数学 | 116篇 |
物理学 | 100篇 |
出版年
2023年 | 12篇 |
2022年 | 37篇 |
2021年 | 44篇 |
2020年 | 22篇 |
2019年 | 24篇 |
2018年 | 25篇 |
2017年 | 8篇 |
2016年 | 41篇 |
2015年 | 49篇 |
2014年 | 43篇 |
2013年 | 73篇 |
2012年 | 85篇 |
2011年 | 109篇 |
2010年 | 46篇 |
2009年 | 57篇 |
2008年 | 95篇 |
2007年 | 66篇 |
2006年 | 46篇 |
2005年 | 74篇 |
2004年 | 52篇 |
2003年 | 29篇 |
2002年 | 31篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1155条查询结果,搜索用时 15 毫秒
51.
Sonia Degeratu P. Rotaru S. Rizescu N. G. Bîzdoacă 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1255-1262
The study concerns an experimental model using a SMA spring actuator for improving the whole performance of a barrier structure. The study is, specifically, focused on the thermal analysis of the SMA spring material and on determination of the SMA spring working time periods at different values of the activating electric current inducing different phase changing speeds. 相似文献
52.
Parthasarathy Saravanan Suparna Gupta Arpita DattaGupta Sonia Gupta Vinod K. Singh 《合成通讯》2013,43(15):2695-2699
The cleavage of α-hydroxy tert-butyldimethylsilyl ether to diol takes place efficiently with LAH. It has been proposed that the reaction proceeds via intramolecular hydride transfer from the alkoxy aluminium hydride. In order to substantiate this, reduction of TBDMS ether with LAH in a variety of substrates was studied. 相似文献
53.
Roberta Del Sole Anna Scardino Maria Rosaria Lazzoi Lucia Mergola Sonia Scorrano Giuseppe Vasapollo 《Mikrochimica acta》2013,180(15-16):1401-1409
A molecularly imprinted polymer (MIP) for the specific retention of neopterin has been developed. A set of 6 polymers was prepared by radical polymerization under different experimental condition using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as crosslinker, with the aim to understand their influence on the efficiency of the MIP. The performance of each MIP was tested in batch experiments via their binding capacity. The MIP prepared in the presence of nickel ions in dimethylsulfoxide-acetonitrile mixture (P4) exhibited the highest binding capacity for neopterin (260 μmol per gram of polymer). A selectivity study with two other pteridines demonstrated the polymer P4 also to possess the best selectivity. Figure
A molecularly imprinted polymer for the specific retention of neopterin was developed. A set of 6 polymers was prepared under different experimental condition. The performance of each MIP was tested through their binding capacity. The MIP P4 prepared in the presence of nickel ions exhibited the highest binding capacity 相似文献
54.
The reactions of 2,2,2-trichloro-1-phenylethanone with various oxygen, carbon and sulfur nucleophiles were investigated with a view of widening the use of trichloroethanones as acylating agents. 相似文献
55.
Dr. Sunyoung Lee Dr. Sonia Diab Pierre Queval Dr. Muriel Sebban Dr. Isabelle Chataigner Prof. Serge R. Piettre 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(22):7181-7192
Non‐stabilized azomethine ylide 4 a reacts smoothly at room temperature with a variety of uncomplexed aromatic heterocycles and carbocycles on the condition that the ring contains at least one or two electron‐withdrawing substituents, respectively. Aromatic substrates, including pyridine and benzene derivatives, participate as 2 π components in [3+2] cycloaddition reactions and interact with one, two, or three equivalent(s) of the ylide, depending on their structure and substitution pattern. Thus, this process affords highly functionalized polycyclic structures that contain between one and three pyrrolidinyl ring(s) in useful yields. These results indicate that the site selectivity of the cycloaddition reactions strongly depends on both the nature and the positions of the substituents. In most cases, the second 1,3‐dipolar reaction occurs on the opposite face to the one that contains the first pyrrolidinyl ring. DFT calculations on model compounds indicate that a concerted mechanism features a low activation barrier. 相似文献
56.
Organotin complexes of Schiff bases (derived from the condensation of hydrazides with salicylaldehyde derivatives) were prepared and their characterization was done using several spectroscopic techniques like FTIR, NMR (1H, 13C, and 119Sn) and mass spectrometry. The spectroscopic data of the ligands and their corresponding complexes revealed that the Schiff bases chelated to the tin metal in a tridentate manner through –ONO atoms (oxygen atom of the hydroxyl group of the salicylaldehydic derivatives, the nitrogen atom of azomethine group, and the oxygen atom of enolic group present in the carboxylic acid hydrazides). Around tin atom pentacoordinated geometry was exhibited. The synthesized ligands and their complexes have been assessed for their biological potency (antibacterial, antifungal and antioxidant using Ciprofloxacin, Fluconazole and Ascorbic acid as reference compounds) and few of the compounds showed optimistic activity. The ligands having electron withdrawing group attached showed greater antimicrobial activity as compared to the other ligands. The complexes showed the better activity than the ligands. The general trend followed by the complexes was diphenyl ?> ?dibutyl ?> ?dimethyl substituted complexes. Compound 11 was the most active against microbes. The antioxidant activity increased with electron donating group. The phenyl substituted complexes showed better activity as compared to the dibutyl and dimethyl substituted complexes. Compound 20 was the best antioxidant. 相似文献
57.
Norma Ruiz-Torres Antonio Flores-Naveda Enrique Díaz Barriga-Castro Neymar Camposeco-Montejo Sonia Ramírez-Barrn Fernando Borrego-Escalante Guillermo Nio-Medina Agustín Hernndez-Jurez Carlos Garza-Alonso Pablo Rodríguez-Salinas Josu I. García-Lpez 《Molecules (Basel, Switzerland)》2021,26(7)
The objective of this study was to determine the oxidative stress and the physiological and antioxidant responses of coriander plants (Coriandrum sativum) grown for 58 days in soil with zinc oxide nanoparticles (ZnO NPs) and zinc sulfate (ZnSO4) at concentrations of 0, 100, 200, 300, and 400 mg of Zn/kg of soil. The results revealed that all Zn compounds increased the total chlorophyll content (CHLt) by at least 45%, compared to the control group; however, with 400 mg/kg of ZnSO4, chlorophyll accumulation decreased by 34.6%. Zn determination by induction-plasma-coupled atomic emission spectrometry (ICP–AES) showed that Zn absorption in roots and shoots occurred in plants exposed to ZnSO4 at all concentrations, which resulted in high levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Only at 400 mg/kg of ZnSO4, a 78.6% decrease in the MDA levels was observed. According to the results, the ZnSO4 treatments were more effective than the ZnO NPs to increase the antioxidant activity of catalase (CAT), ascorbate peroxidase (APX), and peroxidases (POD). The results corroborate that phytotoxicity was higher in plants subjected to ZnSO4 compared to treatments with ZnO NPs, which suggests that the toxicity was due to Zn accumulation in the tissues by absorbing dissolved Zn++ ions. 相似文献
58.
Quentin Vanbellingen Paul Servin Anaïs Coinaud Sonia Mallet-Ladeira Rgis Laurent Anne-Marie Caminade 《Molecules (Basel, Switzerland)》2021,26(8)
Pyridine, pyridine imine, and bipyridine imine ligands functionalized by a phenol have been synthesized and characterized, in many cases by X-ray diffraction. Several of these N-, N,N-, and N,N,N,-ligands have been grafted onto the surface of phosphorhydrazone dendrimers, from generation 1 to generation 3. The complexation ability of these monomers and dendrimers towards palladium(II) has been assayed. The corresponding complexes have been either isolated or prepared in situ. In both cases, the monomeric and dendritic complexes have been tested as catalysts in Heck couplings and in Sonogashira couplings. In some cases, a positive dendritic effect has been observed, that is, an increase of the catalytic efficiency proportional to the dendrimer generation. 相似文献
59.
Del Sordo Filho Giovanni Torrecilha Jefferson Koyaishi Scapin Marcos Antônio Oliveira Sonia Maria Barros da Silva Paulo Sergio Cardoso 《Journal of Radioanalytical and Nuclear Chemistry》2021,329(1):61-70
Journal of Radioanalytical and Nuclear Chemistry - This study has evaluated chemical, radiological composition and determined the cation exchange capacity (CEC) for three commercially available... 相似文献
60.