全文获取类型
收费全文 | 182篇 |
免费 | 4篇 |
专业分类
化学 | 155篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 13篇 |
物理学 | 16篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 2篇 |
2013年 | 10篇 |
2012年 | 9篇 |
2011年 | 18篇 |
2010年 | 10篇 |
2009年 | 17篇 |
2008年 | 7篇 |
2007年 | 12篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有186条查询结果,搜索用时 15 毫秒
51.
52.
The dinuclear μ-oxomolybdenum(V) complexes [Mo2O3(PyS)4] (1), [Mo2O3(PySe)4] (2) and [Mo2O3(4-CF3-PymS)4] (3) were obtained by similar reactions of the [MoO2Cl2(DME)] precursor with the corresponding heterocyclic bidentate (N,X) ligands, X = S, Se, where PyS, PySe and 4-CF3-PymS are the anions of pyridine-2-thione, pyridine-2-selenolato and 4-trifluoromethyl-2-pyrimidinthiol, respectively. All compounds were characterized by elemental analysis, IR, NMR, EI-MS spectroscopy and X-ray diffraction. The crystal structures of 1–3 all include the common [Mo2O3]4+ core. Compounds 1 and 2 are isostructural. The catalytic oxo-transfer properties of the molybdenum(V) compounds 1 and 2 were studied by the use of PPh3 in DMSO with a considerably higher catalytic activity for the thionato containing complex 1 than for its selenolato containing analogue 2. 相似文献
53.
Torres CV Domínguez MJ Carbonari JL Sabini MC Sabini LI Zanon SM 《Natural product communications》2011,6(7):993-994
Baccharis articulata is native of América and traditionally used for the treatment of digestive disorders and urinary infections. Cytotoxicity of aqueous extracts of B. articulata was investigated in Vero cells. As the maximal non cytotoxic concentration has been established, this concentration has been used to evaluate antiviral and virucidal activities against Herpes suis virus type 1, member of the same subfamily of Herpes simplex virus. Aqueous extracts of B. articulata exhibited more than 95% of virucidal activity. These findings support their potential application as a disinfectant or antiseptic with low toxicity and provide a valuable knowledge to ethnopharmacology properties of Baccharis articulata. 相似文献
54.
Avijit Maiti Jessica Stubbe Dr. Nicolás I. Neuman Dr. Pankaj Kalita Prakash Duari Prof. Dr. Carola Schulzke Prof. Dr. Vadapalli Chandrasekhar Prof. Dr. Biprajit Sarkar Dr. Anukul Jana 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(17):6795-6800
Diradicals have been of tremendous interest for over a century ever since the first reports of p- and m-phenylene-bridged diphenylmethylradicals in 1904 by Thiele and 1915 by Schlenk. Reported here are the first examples of cyclic(alkyl)(amino)carbene (CAAC) analogues of Thiele's hydrocarbon, a Kekulé diradical, and Schlenk's hydrocarbon, a non-Kekulé diradical, without using CAAC as a precursor. The CAAC analogue of Thiele's hydrocarbon has a singlet ground state, whereas the CAAC analogue of Schlenk's hydrocarbon contains two unpaired electrons. The latter forms a dimer, by an intermolecular double head-to-tail dimerization. This straightforward synthetic methodology is modular and can be extended for the generation of redox-active organic compounds. 相似文献
55.
Carola Pickhardt J. S. Becker Hans-Joachim Dietze 《Analytical and bioanalytical chemistry》2000,368(2-3):173-181
Because multielement trace analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is often limited by the lack of suitable reference materials with a similar matrix composition, a novel quantification strategy using solution calibration was developed. For mass spectrometric multielement determination in geological samples a quadrupole-based LA-ICP-MS is coupled with an ultrasonic nebulizer (USN). In order to arrange matrix matching the standard solutions are nebulized with a USN during solution calibration and simultaneously a blank target (e.g. lithium borate) is ablated with a focused laser beam. The homogeneous geological samples were measured using the same experimental arrangement where a 2% nitric acid is simultaneously nebulized with the USN. Homogeneous targets were prepared from inhomogeneous geological samples by powdering, homogenizing and fusing with a lithium borate mixture in a muffle furnace at 1050?°C. Furthermore, a homogeneous geological glass was also investigated. The quantification of analytical results was performed by external calibration using calibration curves measured on standard solutions. In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS, measured concentrations in homogeneous geological targets were also corrected with relative sensitivity coefficients (RSCs) determined using one standard solution only. The analytical results of LA-ICP-MS on various geological samples are in good agreement with the reference values and the results of other trace analytical methods. The relative standard deviation (RSD) for trace element determination (N = 6) is between 2 and 10%. 相似文献
56.
Gandolfi-Donadío L Gallo-Rodriguez C de Lederkremer RM 《The Journal of organic chemistry》2003,68(18):6928-6934
The galactofuran is a crucial constituent of the cell wall of mycobacteria. An efficient synthesis of the two trisaccharide units of the galactan is described. The strategy relies on the use of substituted d-galactono-1,4-lactones as precursors for the internal and the reducing galactofuranoses. Dec-9-enyl beta-d-Galf-(1-->6)-beta-d-Galf-(1-->5)-beta-d-Galf (2) and dec-9-enyl beta-d-Galf-(1-->5)-beta-d-Galf-(1-->6)-beta-d-Galf (9) so far reported as convenient substrates for the galactofuranosyl transferase, and possibly useful for immunological studies, were obtained by the trichloroacetimidate method of glycosylation. 相似文献
57.
Becker JS Boulyga SF Pickhardt C Becker J Buddrus S Przybylski M 《Analytical and bioanalytical chemistry》2003,375(4):561-566
Inductively coupled plasma mass spectrometry (ICP-MS) is used for phosphorus determination in protein samples. A small amount of solid protein sample (down to 1 micro g) or digest (1-10 micro L) protein solution was denatured in nitric acid and hydrogen peroxide by closed-microvessel microwave digestion. Phosphorus determination was performed with an optimized analytical method using a double-focusing sector field inductively coupled plasma mass spectrometer (ICP-SFMS) and quadrupole-based ICP-MS (ICP-QMS). For quality control of phosphorus determination a certified reference material (CRM), single cell proteins (BCR 273) with a high phosphorus content of 26.8+/-0.4 mg g(-1), was analyzed. For studies on phosphorus determination in proteins while reducing the sample amount as low as possible the homogeneity of CRM BCR 273 was investigated. Relative standard deviation and measurement accuracy in ICP-QMS was within 2%, 3.5%, 11% and 12% when using CRM BCR 273 sample weights of 40 mg, 5 mg, 1 mg and 0.3 mg, respectively. The lowest possible sample weight for an accurate phosphorus analysis in protein samples by ICP-MS is discussed. The analytical method developed was applied for the analysis of homogeneous protein samples in very low amounts [1-100 micro g of solid protein sample, e.g. beta-casein or down to 1 micro L of protein or digest in solution (e.g., tau protein)]. A further reduction of the diluted protein solution volume was achieved by the application of flow injection in ICP-SFMS, which is discussed with reference to real protein digests after protein separation using 2D gel electrophoresis.The detection limits for phosphorus in biological samples were determined by ICP-SFMS down to the ng g(-1) level. The present work discusses the figure of merit for the determination of phosphorus in a small amount of protein sample with ICP-SFMS in comparison to ICP-QMS. 相似文献
58.
Carola W. N. Damen Hilde Rosing Jan H. M. Schellens Jos H. Beijnen 《Analytical and bioanalytical chemistry》2009,394(4):1171-1182
A sensitive, specific and efficient high-performance liquid chromatography-tandem mass spectrometry assay for the simultaneous
determination of vincristine and actinomycin-D in human dried blood spots is presented. Dried blood spots were punched out
of a collection paper with a 0.25-in.-diameter punch. The analytes were extracted from the punched-out disc using sonication
during 15 min in a mixture of acetonitrile–methanol–water (1:1:1, v/v/v) containing the internal standard vinorelbine. Twenty-microlitre volumes were injected onto the HPLC system. Separation was
achieved on a 50 × 2.1 mm ID Xbridge C18 column using elution with 1 mM ammonium acetate–acetonitrile (70:30, v/v) adjusted to pH 10.5 with ammonia and run in a gradient with methanol at a flow rate of 0.4 mL/min. HPLC run time was 6 min.
The assay quantifies vincristine from 1 to 100 ng/mL and actinomycine-D from 2 to 250 ng/mL using a blood sample obtained
by a simple finger prick. Validation results demonstrate that vincristine and actinomycin-D can be accurately and precisely
quantified in human dried blood spots with the presented method. The assay can now be used to support clinical pharmacologic
studies with vincristine and actinomycin-D. 相似文献
59.
Lisa M. S. Stiegler Dr. Stefanie Klein Prof. Dr. Carola Kryschi Prof. Dr. Winfried Neuhuber Prof. Dr. Andreas Hirsch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(5):1655-1669
A new series of shell-by-shell (SbS)-functionalized Al2O3 nanoparticles (NPs) containing a perylene core in the organic interlayer as a fluorescence marker is introduced. Initially, the NPs were functionalized with both, a fluorescent perylene phosphonic acid derivative, together with the lipophilic hexadecylphosphonic acid or the fluorophilic (1 H,1 H,2 H,2H-perfluorodecyl)phosphonic acid. The lipophilic first-shell functionalized NPs were further implemented with amphiphiles built of aliphatic chains and polar head-groups. However, the fluorophilic NPs were combined with amphiphiles consisting of fluorocarbon tails and polar head-groups. Depending on the nature of the combined phosphonic acids and the amphiphiles, tuning of the perylene fluorescence can be accomplished due variations of supramolecular organization with the shell interface. Because the SbS-functionalized NPs dispose excellent dispersibility in water and in biological media, two sorts of NPs with different surface properties were tested with respect to biological fluorescent imaging applications. Depending on the agglomeration of the NPs, the cellular uptake differs. The uptake of larger agglomerates is facilitated by endocytosis, whereas individualized NPs cross directly the cellular membrane. Also, the larger agglomerates were preferentially incorporated by all tested cells. 相似文献
60.
A method for the enantioselective separation of all-E-astaxanthin (3,3'-dihydroxy-beta,beta-carotene-4,4'-dione), an important colorant in the feed industry, was developed. Different chiral stationary phases (CSPs) such as Pirkle phases (R,R Ulmo and l-leucine), modified polysaccharides and a beta-cyclodextrin have been investigated on their separation performance of astaxanthin enantiomers. Direct resolution was only achieved employing the Chiralcel OD-RH (cellulose-tris-3,5-dimethylphenyl-carbamate) under reversed phase conditions. The chiral separation of the enantiomeric forms of astaxanthin produced in microalgae and yeasts was reported. The yeast Xanthophyllomyces sp. produces astaxanthin predominantly in the R,R configuration, whereas in the green microalgae Scenedesmus sp. astaxanthin is built primarily in the S,S form. The separation method for the identification of astaxanthin enantiomers is of great interest since astaxanthin is used as functional food additive in human nutrition. Moreover the method may be used as a food chain indicator in farmed salmon. 相似文献