全文获取类型
收费全文 | 506篇 |
免费 | 15篇 |
国内免费 | 3篇 |
专业分类
化学 | 410篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 54篇 |
物理学 | 54篇 |
出版年
2023年 | 4篇 |
2022年 | 46篇 |
2021年 | 53篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 25篇 |
2015年 | 20篇 |
2014年 | 30篇 |
2013年 | 33篇 |
2012年 | 41篇 |
2011年 | 31篇 |
2010年 | 39篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 22篇 |
2006年 | 13篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1964年 | 1篇 |
1961年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有524条查询结果,搜索用时 15 毫秒
11.
The aim of the study was to assess the antioxidant potential of goat’s milk and whey from goat’s milk fermented with selected bacteria strains from kefir grain (L. plantarum, L. fermentum, L. rhamnosus and L. acidophilus) with regard to fermented cow’s milk with the same bacteria strains. The assessment of antioxidant potential was made by ABTS, DPPH, TPC and FRAP methods. The work also assessed metabolic activity of tested lactic acid bacteria using measurement of electrical impedance changes in the growing medium. The highest values describing the antioxidant potential were found for fermented milk by L. acidophilus. It was also found that the time of cooling storage causes significantly increasing the antioxidant potential of most analyzed samples. Metabolic activity of tested lactic acid bacteria was the highest for cow’s milk. The course of curves for goat’s milk and whey from goat’s milk was similar, which confirms the differences between cow and goat milk. 相似文献
12.
Helicenophyrins: Expanded Carbaporphyrins Incorporating Aza[5]helicene and Heptacyclic S‐Shaped Aza[5]helicene Motifs 下载免费PDF全文
Dr. Bartosz Szyszko Monika Przewoźnik Dr. Michał J. Białek Dr. Agata Białońska Prof. Dr. Piotr J. Chmielewski Dr. Jakub Cichos Prof. Dr. Lechosław Latos‐Grażyński 《Angewandte Chemie (International ed. in English)》2018,57(15):4030-4034
Incorporation of phenanthrene into a hexaphyrin(1.1.1.1.1.0) frame resulted in intramolecular ring fusion, thus giving rise to chiral helicenophyrins. These molecules contain helicene and porphyrin features by incorporating either an aza[5]helicene or heptacyclic S‐shaped aza[5]helicene. 相似文献
13.
Metal(II) Ion Complexes with 5‐(Pyrazin‐2‐yl)‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thione; Synthesis,Structural Characterization,Acid‐base,and Complexing Properties in Solution 下载免费PDF全文
Aleksander Kufelnicki Jolanta Jaciubek‐Rosińska Marta Sobiesiak Agata Paneth Julia Jezierska Elzbieta Budzisz 《无机化学与普通化学杂志》2017,643(16):1067-1074
The study reports the synthesis of complexes Co(HL)Cl2 ( 1 ), Ni(HL)Cl2 ( 2 ), Cu(HL)Cl2 ( 3 ), and Zn(HL)3Cl2 ( 4 ) with the title ligand, 5‐(pyrazin‐2‐yl)‐1,2,4‐triazole‐5‐thione (HL), and their characterization by elemental analyses, ESI‐MS (m/z), FT‐IR and UV/Vis spectroscopy, as well as EPR in the case of the CuII complex. The comparative analysis of IR spectra of the metal ion complexes with HL and HL alone indicated that the metal ions in 1 , 2 , and 3 are chelated by two nitrogen atoms, N(4) of pyrazine and N(5) of triazole in the thiol tautomeric form, whereas the ZnII ion in 4 is coordinated by the non‐protonated N(2) nitrogen atom of triazole in the thione form. pH potentiometry and UV/Vis spectroscopy were used to examine CoII, NiII, and ZnII complexes in 10/90 (v/v) DMSO/water solution, whereas the CuII complex was examined in 40/60 (v/v) DMSO/water solution. Monodeprotonation of the thione triazole in solution enables the formation of the L:M = 1:1 species with CoII, NiII and ZnII, the 2:1 species with CoII and ZnII, and the 3:1 species with ZnII. A distorted tetrahedral arrangement of the CuII complex was suggested on the basis of EPR and Vis/NIR spectra. 相似文献
14.
Agata Górska Karolina Szulc Ewa Ostrowska-Ligęza Joanna Bryś Magdalena Wirkowska-Wojdyła 《Journal of Thermal Analysis and Calorimetry》2017,128(1):177-183
Epoxy-based nanocomposites containing different concentrations (0–3%) of surface-modified graphene nanosheets (GNS) with 3-aminopropyltriethoxysilane were prepared and their thermal and mechanical properties including dynamic mechanical analysis, tensile strength, hardness, and abrasion tests were evaluated in order to have a database for thermo-mechanical properties of epoxy nanocomposites. The main aim of this study was to understand the optimum percentage of GNS which would perform the best reinforcing influence on mechanical and physical performance of an epoxy nanocomposite. The results explain how applying the analysis of variance (ANOVA) method as a useful tool in optimization of GNS concentration in preparation of high-performance epoxy-based nanocomposites. 相似文献
15.
16.
17.
18.
Magdalena Połosak Agata Piotrowska Seweryn Krajewski Aleksander Bilewicz 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(3):1867-1872
The aim of this study was to evaluate acyclic ligands which can be applied for labeling proteins such as monoclonal antibodies and their fragments with scandium radionuclides. Recently, scandium isotopes (47Sc, 44Sc) are more available and their properties are convenient for radiotherapy or PET imaging. They can be used together as “matched pair” in theranostic approach. Because proteins denaturize at temperature above 42 °C, ligands which efficiently form complexes at room temperature, are necessary for labelling such biomolecules. For complexation of scandium radionuclides open chain ligands DTPA, HBED, BAPTA, EGTA, TTHA and deferoxamine have been chosen. We found that the ligands studied (except HBED) form strong complexes within 10 min and that the radiolabelling yield varies between 96 and 99 %. The complexes were stable in isotonic NaCl, but stability of 46Sc-TTHA, 46Sc-BAPTA and 46Sc-HBED in PBS buffer was low, due to formation by Sc3+stronger complexes with phosphates than with the studied ligands. From the radiolabelling studies with n.c.a. 47Sc we can conclude that the most stable complexes are formed by the 8-dentate DTPA and EGTA ligands. 相似文献
19.
A major challenge in the area of DNA detection is the development of rapid methods that do not require polymerase chain reaction
(PCR) amplification of the genetic sample. The PCR amplification step increases the cost of the assay, the complexity of the
detection, and the quantity of DNA required for the assay. In this context, methods that are able to perform DNA analyses
with ultrasensitivity have recently been investigated with the aim of developing new PCR-free detection protocols. Functionalized
gold nanoparticles have played a central role in the development of such methods. Here, possibilities offered by functionalized
gold nanoparticle in the ultrasensitive detection of DNA are discussed. The different functionalization protocols available
for gold nanoparticles and the principal DNA detection methods that are able to detect DNA at the femtomolar to attomolar
level are presented. 相似文献
20.
Conducting polymer (CP) films, used as ion-sensing membranes under open circuit potentiometric conditions, are usually characterised with rather high detection limit, in the range of 10−4-10−5 mol dm−3. This effect is unfavourable, not only from the point of view of CP applications in potentiometry as ion sensitive membranes, but also when these materials are used as ion-to-electron transducers (solid contacts) for ion-selective electrodes. The theoretical considerations presented underline the crucial role of spontaneous processes of polymer charging/discharging—the source of observed high detection limit of sensors comprising CP layer under zero current conditions. Although the mechanism of occurring process is different from that observed for plastic, solvent polymeric based ion-selective electrodes, the ultimate result—alteration of activity of electrolyte at the membrane/solution interface leading to elevation of the detection limit—is the same.The method of estimation of parameters characterising spontaneous charge transfer processes is presented. The values obtained can be used to calculate the resulting polymer/solution interface activity of electrolyte ions, thus the detection limit of CP membrane can be theoretically predicted.A method of lowering of the detection limit of conducting polymer membranes, applying galvanostatic polarisation to compensate the spontaneous process of polymer charging/discharging, is presented.The experimental results obtained for poly(pyrrole), poly(N-methylpyrrole) and poly(3,4-ethylenedioxythiophene) are in good accordance with predictions of the presented model. 相似文献