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61.
Superchiral Pd3L6 Coordination Complex and Its Reversible Structural Conversion into Pd3L3Cl6 Metallocycles 下载免费PDF全文
Dr. Ondřej Jurček Pia Bonakdarzadeh Dr. Elina Kalenius Dr. Juha Matti Linnanto Dr. Michael Groessl Dr. Richard Knochenmuss Prof. Janne A. Ihalainen Prof. Kari Rissanen 《Angewandte Chemie (International ed. in English)》2015,54(51):15462-15467
Large, non‐symmetrical, inherently chiral bispyridyl ligand L derived from natural ursodeoxycholic bile acid was used for square–planar coordination of tetravalent PdII, yielding the cationic single enantiomer of superchiral coordination complex 1 Pd3 L 6 containing 60 well‐defined chiral centers in its flower‐like structure. Complex 1 can readily be transformed by addition of chloride into a smaller enantiomerically pure cyclic trimer 2 Pd3 L 3Cl6 containing 30 chiral centers. This transformation is reversible and can be restored by the addition of silver cations. Furthermore, a mixture of two constitutional isomers of trimer, 2 and 2′ , and dimer, 3 and 3′ , can be obtained directly from L by its coordination to trans‐ or cis‐N‐pyridyl‐coordinating PdII. These intriguing, water‐resistant, stable supramolecular assemblies have been thoroughly described by 1H DOSY NMR, mass spectrometry, circular dichroism, molecular modelling, and drift tube ion‐mobility mass spectrometry. 相似文献
62.
Chatelet B Payet E Perraud O Dimitrov-Raytchev P Chapellet LL Dufaud V Martinez A Dutasta JP 《Organic letters》2011,13(14):3706-3709
Hemicryptophanes are host molecules with many applications as supramolecular catalysts or in ion selective recognition. A very convenient and efficient modular approach for the synthesis of hemicryptophane-tren (tren, tris(2-aminoethyl)-amine) derivatives has been developed. For instance, hemicryptophane 1 was synthesized at the gram scale in four steps from vanillyl alcohol compared to the previous seven-step procedure. The size, shape, and functionalities of the molecular cavity were also easily modified. 相似文献
63.
Machado ME Fontanive FC de Oliveira JV Caramão EB Zini CA 《Analytical and bioanalytical chemistry》2011,401(8):2433-2444
The determination of organic sulfur compounds (OSC) in coal is of great interest. Technically and operationally these compounds
are not easily removed and promote corrosion of equipment. Environmentally, the burning of sulfur compounds leads to the emission
of SO
x
gases, which are major contributors to acid rain. Health-wise, it is well known that these compounds have mutagenic and carcinogenic
properties. Bitumen can be extracted from coal by different techniques, and use of gas chromatography coupled to mass spectrometric
detection enables identification of compounds present in coal extracts. The OSC from three different bitumens were tentatively
identified by use of three different extraction techniques: accelerated solvent extraction (ASE), ultrasonic extraction (UE),
and supercritical-fluid extraction (SFE). Results obtained from one-dimensional gas chromatography (1D GC) coupled to quadrupole
mass spectrometric detection (GC–qMS) and from two-dimensional gas chromatography with time-of-flight mass spectrometric detection
(GC × GC–TOFMS) were compared. By use of 2D GC, a greater number of OSC were found in ASE bitumen than in SFE and UE bitumens.
No OSC were identified with 1D GC–qMS, although some benzothiophenes and dibenzothiophenes were detected by use of EIM and
SIM modes. GC × GC–TOFMS applied to investigation of OSC in bitumens resulted in analytical improvement, as more OSC classes
and compounds were identified (thiols, sulfides, thiophenes, naphthothiophenes, benzothiophenes, and benzonaphthothiophenes).
The roof-tile effect was observed for OSC and PAH in all bitumens. Several co-elutions among analytes and with matrix interferents
were solved by use of GC×GC. 相似文献
64.
A GC-μECD and a GC×GC-μECD method were developed for the analysis of pesticides in sediments. For 1D-GC, instrumental LOD and LOQ were found in the range from 0.60 to 2.31μgL(-1) and 1.83 to 5.62μgL(-1), respectively. For GC×GC method development two sets of columns were tested (DB-5/DB-17ms, and HP-50+/DB-1ms), and the best results were obtained with the set of columns DB-5/DB-17ms. Instrumental LOD and LOQ were found in the range from 0.08 to 1.07μgL(-1) and 0.25 to 3.23μgL(-1), respectively. The LOD for the GC×GC was about 36% lower than those obtained for the 1D-GC. Concentrations of 21.18μgkg(-1) through 1D-GC method and 3.34μgkg(-1) for GC×GC for trifloxystrobin were found in a sediment sample which was collected close to an area of rice plantation. 相似文献
65.
Kong WM Chik Z Ramachandra M Subramaniam U Aziddin RE Mohamed Z 《Molecules (Basel, Switzerland)》2011,16(9):7344-7356
The extract from Mitragyna speciosa has been widely used as an opium substitute, mainly due to its morphine-like pharmacological effects. This study investigated the effects of M. speciosa alkaloid extract (MSE) on human recombinant cytochrome P450 (CYP) enzyme activities using a modified Crespi method. As compared with the liquid chromatography-mass spectrometry method, this method has shown to be a fast and cost-effective way to perform CYP inhibition studies. The results indicated that MSE has the most potent inhibitory effect on CYP3A4 and CYP2D6, with apparent half-maximal inhibitory concentration (IC(50)) values of 0.78 μg/mL and 0.636 μg/mL, respectively. In addition, moderate inhibition was observed for CYP1A2, with an IC(50) of 39 μg/mL, and weak inhibition was detected for CYP2C19. The IC(50) of CYP2C19 could not be determined, however, because inhibition was <50%. Competitive inhibition was found for the MSE-treated CYP2D6 inhibition assay, whereas non-competitive inhibition was shown in inhibition assays using CYP3A4, CYP1A2 and CYP2C19. Quinidine (CYP2D6), ketoconazole (CYP3A4), tranylcypromine (CYP2C19) and furafylline (CYP1A2) were ACCESSused as positive controls throughout the experiments. This study shows that MSE may contribute to an herb-drug interaction if administered concomitantly with drugs that are substrates for CYP3A4, CYP2D6 and CYP1A2. 相似文献
66.
Kalenius E Beyeh NK Jänis J Rissanen K 《Chemical communications (Cambridge, England)》2011,47(9):2649-2651
Pyrogallarene shows concentration-dependent instability in dilute solutions resulting in elimination of two ketene molecules and formation of pyrogallarene lactones. This unexpected phenomenon, which is not observed with resorcinarenes, highlights the significance of the four hydroxyl groups at 2-position for the molecular characteristics of pyrogallarenes. 相似文献
67.
Kirsi S. Mikkonen Leena Pitk?nen Ville Liljestr?m Elina Mabasa Bergstr?m Ritva Serimaa Lennart Salmén Maija Tenkanen 《Cellulose (London, England)》2012,19(2):467-480
The chemical structure of rye arabinoxylan (rAX) was systematically modified, exploiting selective enzymes to mimic different
naturally occurring xylans, i.e., its degree of substitution (DS) was decreased using α-l-arabinofuranosidase, and a controlled decrease in the degree of polymerization (DP) was performed using endo-1,4-β-d-xylanase. The arabinose to xylose ratio was decreased from 0.45 to 0.27 and the weight-average molar mass was decreased from
184,000 to 49,000 g/mol. The resulting samples were used to prepare films, as such, and with 15% (wt. − %) softwood-derived
microfibrillated cellulose (MFC) to obtain novel plant-derived biocomposite materials. The enzymatic tailoring of rAX increased
the crystallinity of films, evidenced by X-ray diffraction studies, and the addition of MFC to the debranched, low DS rAX
induced the formation of ordered structures visible with polarizing optical microscopy. MFC decreased the moisture uptake
of films and increased the relative humidity of softening of the films, detected with moisture scanning dynamic mechanical
analysis. For the first time, the chemical structure of xylan was proven to significantly affect the reinforcement potential
of nano-sized cellulose, as the tensile strength of films from high DP rAXs, but not that of low DP rAXs, clearly increased
with the addition of MFC. At the same time, MFC only increased the Young’s modulus of films from rAX with high arabinose content,
regardless of DP. 相似文献
68.
Electrochemical DNA biosensors are promising tools for the fast, inexpensive and simple in vitro analysis for the determination of free radicals and antioxidants. High concentrations of antioxidants in such compounds as
phenolic acids and plant extracts, act as free radical terminators which reduce the effect of the oxidative dam-age on DNA.
The electrochemical behavior of three representative phenolic acids, caffeic acid, gallic acid and trolox were studied by
cyclic voltammetry. Moreover, the determination of the above antioxidants under the optimized conditions (scan rate, deposition
potential and time) using differential pulse voltammetry was also investigated. In vitro studies focused on their antioxidative effect were performed by adsorptive transfer stripping voltammetry and dsDNA biosensor.
Using Fenton’s system, with FeSO4 and H2O2 was chosen as a strong oxidative system. This biosensor was applied as a screening antioxidant test in order to estimate
the antioxidant capacity of aqueous herb extracts.
相似文献
69.
Christian Klemps Dipl.‐Chem. Elina Payet Lionel Magna Dr. Lucien Saussine Dr. Xavier F. Le Goff Dr. Pascal Le Floch Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(33):8259-8268
Chromium(III) complexes bearing R′N(CH2PR2)2 (PCNCP) ligands have been prepared. Upon activation with methylaluminoxane, these complexes proved to be effective in the selective tri‐ and tetramerization of ethylene. The formation of either 1‐hexene or 1‐octene was found to be highly dependent on the steric bulk of the substituents R on the phosphine moieties. This observation was rationalized by using density functional theory calculations on selected steps of the metallacyclic mechanism of the ethylene oligomerization reaction. 相似文献
70.
In order to utilise wood and wood fibres in advanced materials, a better understanding of the mechanical material characteristics
and the interactions among the components is necessary. For this purpose, FTIR was explored together with mechanical loading
as a means of studying the molecular responses to the loading of spruce wood and cellulose paper material. A linear shift
of absorption bands was detected as the loading was applied. In relation to the applied stress these shifts were higher under
moist conditions than under dry ones but they were similar with regard to the strains applied. There were no shifts detected
in bands related to lignin or the hemicelluloses. The results are interpreted as reflecting a parallel arrangement of the
load bearing component, the cellulose ordered structure, and the moisture accessible regions in the cellulose microfibril
structure. This therefore represents an equal strain loaded system. 相似文献