全文获取类型
收费全文 | 405篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 273篇 |
晶体学 | 2篇 |
力学 | 7篇 |
综合类 | 3篇 |
数学 | 30篇 |
物理学 | 112篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 41篇 |
2020年 | 19篇 |
2019年 | 25篇 |
2018年 | 14篇 |
2017年 | 8篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 26篇 |
2013年 | 37篇 |
2012年 | 23篇 |
2011年 | 20篇 |
2010年 | 17篇 |
2009年 | 23篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有427条查询结果,搜索用时 62 毫秒
41.
Fluorotricyanomethane is prepared from potassium tricyanomethanide and perchlorylfluoride. The crystal structure of this compound (orthorhombic, space group P212121, with a=6.270, b=6.734, c=11.776 Å) has been determined by X-ray analysis. The results are discussed in relation to those of (NC)3C? X (X=? CH3, ? Cl, ? Br or ? CN). 相似文献
42.
Abid OU Nawaz M Ibad MF Khera RA Iaroshenko V Langer P 《Organic & biomolecular chemistry》2011,9(7):2185-2191
Aryl-substituted pyridines and pyrimidines were prepared by [4+2] cycloadditions of alkynyl-substituted pyridines and -pyrimidines with electron-rich dienes. The reactions proceed by formation of a bridged cycloadduct and subsequent thermal extrusion of ethylene. The pyridine moiety plays a crucial role for the success of the reaction. 相似文献
43.
Umar Hayat Philip N. Bartlett George H. Dodd Michael H. Lewis 《Journal of polymer science. Part A, Polymer chemistry》1988,26(1):201-206
The surface compositions of various polymeric films, grown electrochemically on platinum foils, have been investigated by energy-dispersive x-ray analysis in conjunction with scanning electron microscopy (SEM/EDS). Comparison of the relative area ratios of peaks for the C and N Kemission lines show that the EDS may be used to study the surface composition of polymers. The evidence presented strongly suggests that there is limited structural degradation and the elemental composition is not changed under the electron beam at relatively low accelerating voltages. This technique statistically samples the repeat units of the polymer. For samples grown in both aqueous and nonaqueous solutions. SEM/EDS provides evidence for extensive contamination with oxygen. 相似文献
44.
ViqarUddin Ahmad MuhammadAthar Abbasi Muhammad Zubair Naheed Fatima Umar Farooq M.Iqbal Choudhary 《Helvetica chimica acta》2004,87(1):67-72
Phytochemical investigation of Symplocos racemosa resulted in the isolation of two new glycosides, symploracemoside ( 1 ) and symplomoside ( 2 ), which are structurally related to the reported benzoylsalireposide ( 3 ) and salireposide ( 4 ). The structure elucidation of the isolated compounds was based primarily on 1D‐ and 2D‐NMR analysis, including COSY, NOESY, HMQC, and HMBC correlations. These glycosides showed inhibitory activity against snake‐venom phosphodiesterase I. 相似文献
45.
Farooq U Khan A Ahmad VU;Azhar-Ul-Haq Khan SS Farooq R Pervez A Shah MM 《Magnetic resonance in chemistry : MRC》2007,45(9):766-769
Two new tricyclic trans-clerodane diterpenoids trivially named as ballotenic acid A (1) and ballodiolic acid A (2) have been isolated from ethyl acetate fraction of Otostegia limbata. The structure assignments are based on (1)H and (13)C NMR spectra, 2D NMR (HMQC, HMBC, COSY, NOESY and NOE) techniques and comparison with the literature data. 相似文献
46.
Monodispersed PEG-coated ZnS (P-ZnS) nanoparticles (NPs) were synthesized by facile microwave process and utilized as efficient electron mediators for the fabrication of highly sensitive hydrazine chemical sensor. The detailed morphological and structural properties revealed the monodispersity and good crystallinity for synthesized P-ZnS NPs. A high-sensitivity of ∼89.3 μA cm−2 μM and low limit of detection of 1.07 μM, based on S/N ratio, were obtained for the fabrication of hydrazine chemical sensor based on P-ZnS NPs. To the best of our knowledge, this is the first report which demonstrates the utilization of P-ZnS NPs for the fabrication of efficient hydrazine chemical sensor. By this work, it could be concluded that simply synthesized ZnS NPs can be used as efficient electron mediators for the fabrication of effective hydrazine chemical sensors. 相似文献
47.
Summary Isonicotinic acid hydrazide reacts with 2,3,5-triphenyltetrazolium chloride in acidic medium in presence of excess of thallium(III) to give a pink-coloured formazan having maximum absorption at 480 nm. This colour reaction is used to determine isonicotinic acid hydrazide in urine and blood. The reaction is specific for isonicotinic acid hydrazide, and the visual limit of identification is1
g per ml.
Zusammenfassung Isonikotinsäurehydrazid reagiert mit 2,3,5-Triphenyltetrazoliumchlorid in saurem Milieu bei Gegenwart von überschüssigem Thallium(III) unter Bildung eines rosa gefärbten Formazans mit dem Absorptionsmaximum bei 480 nm. Diese Farbreaktion wird zur Bestimmung von Isonikotinsäurehydrazid in Harn und Blut verwendet. Sie ist spezifisch. Ihre Erfassungsgrenze beträgt 1g/ml.
Résumé L'hydrazide de l'acide isonicotinique réagit avec le chlorure de triphényl-2,3,5 tétrazolium, en milieu acide en présence d'un excès de thallium-III, en donnant un formazan coloré en rose dont le maximum d'absorption se situe à 480 nm. On utilise cette réaction colorée pour doser l'hydrazide de l'acide isonicotinique dans l'urine et dans le sang. La réaction est spécifique et la limite d'identification visuelle est de 1g par ml.相似文献
48.
49.
Saira Jabeen Shaukat Saeed Bakhtiar Muhammad Sagheer Gul Muhammad Farooq 《International Journal of Polymer Analysis and Characterization》2016,21(2):163-174
In this study, blends of chitosan (Cs) and bisphenol-F-diglycidyl ether (3.80 × 10?3 to 3.80 × 10?2 mol) were cast by the solution route. FT-IR results suggested that chitosan was cross-linked at terminal amino groups through diepoxide linkage. The chitosan films became less flexible and stiffer upon reaction with epoxy. Blending improved percentage elongation (31%) and toughness (10 MPa), whereas Young’s modulus (145 MPa) and tensile strength (45 MPa) were decreased. Extent of weight loss in Cs/BPFDGE was lower (15%) than that of original precursors (chitosan 33%). Moreover, blending of chitosan with BPFDGE increased water absorption properties due to generation of hydrophilic ?OH groups. 相似文献
50.
Akbar Ali Mukhtar Ahmad Majid Niaz Akhtar Saleem Farooq Shaukat Ghulam Mustafa M. Atif W. A. Farooq 《Russian Journal of Applied Chemistry》2016,89(4):517-534
Nanobiotechnology has opened a new and exciting opportunities for exploring urea biosensor based on magnetic nanoparticles (NPs) mainly Fe3O4 and Co3O4. These NPs have been extensively exploited to develop biosensors with stability, selectivity, reproducibility and fast response time. This review gives an overview of the development of urea biosensor based on Fe3O4 and Co3O4 for in vitro diagnostic applications along with significant improvements over the last few decades. Additionally, effort has been made to elaborate properties of magnetic nanoparticles (MNPs) in biosensing aspects. It also gives details of recent developments in hybrid nanobiocomposite based urea biosensor. 相似文献