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141.
For the first time, the equilibrium composition of chemical dissociation-recombination reaction is simulated from first-principles, only. Furthermore, beyond the conventional ab initio Born-Oppenheimer quantum chemistry the effects from the thermal and quantum equilibrium dynamics of nuclei are consistently included, as well as, the nonadiabatic coupling between the electrons and the nuclei. This has been accomplished by the path integral Monte Carlo simulations for full NVT quantum statistics of the H(3)(+) ion. The molecular total energy, partition function, free energy, entropy, and heat capacity are evaluated in a large temperature range: from below room temperature to temperatures relevant for planetary atmospheric physics. Temperature and density dependent reaction balance of the molecular ion and its fragments above 4000 K is presented, and also the density dependence of thermal ionization above 10,000 K is demonstrated. 相似文献
142.
Suni NM Lindfors P Laine O Ostman P Ojanperä I Kotiaho T Kauppila TJ Kostiainen R 《Analytica chimica acta》2011,699(1):73-80
We have studied the matrix effect within direct analysis of benzodiazepines and opioids from urine with desorption electrospray ionization-mass spectrometry (DESI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). The urine matrix was found to affect the ionization mechanism of the opioids in DAPPI-MS favoring proton transfer over charge exchange reaction. The sensitivity for the drugs in solvent matrix was at the same level with DESI-MS and DAPPI-MS (LODs 0.05–6 μg mL−1) but the decrease in sensitivity due to the urine matrix was higher with DESI (typically 20–160-fold) than with DAPPI (typically 2–15-fold) indicating better matrix tolerance of DAPPI over DESI. Also in MS/MS mode, DAPPI provided better sensitivity than DESI for the drugs in urine. The feasibility of DAPPI-MS/MS was then studied in screening the same drugs from five authentic, forensic post mortem urine samples. A reference measurement with gas chromatography-mass spectrometry (GC–MS) (including pretreatment) revealed 16 findings from the samples, whereas with DAPPI-MS/MS after sample pretreatment, 15 findings were made. Sample pretreatment was found necessary, since only eight findings were made from the same samples untreated. 相似文献
143.
Multi-centered nature of adsorption as well as adsorbate-adsorbate interactions is addressed. A discussed reaction mechanism includes adsorption of a bulky molecule A, which requires several sites for adsorption, and two successive reaction steps of Eley type. Numerical treatment is performed for a special case of this mechanism. 相似文献
144.
Lasse-Pekka Tiainen P?ivi M?ki-Arvela Ahmad Kalantar Neyestanaki Tapio Salmi Dmitry Yu. Murzin 《Reaction Kinetics and Catalysis Letters》2003,78(2):251-257
Selective hydrogenation of citral was investigated at 70 °C over Ru/Al2O3. Activity changes in a series of consecutive experiments were described by a mathematical model, which included reaction
kinetics and deactivation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
145.
Siltanen S Lokki T Kiminki S Savioja L 《The Journal of the Acoustical Society of America》2007,122(3):1624
An integral equation generalizing a variety of known geometrical room acoustics modeling algorithms is presented. The formulation of the room acoustic rendering equation is adopted from computer graphics. Based on the room acoustic rendering equation, an acoustic radiance transfer method, which can handle both diffuse and nondiffuse reflections, is derived. In a case study, the method is used to predict several acoustic parameters of a room model. The results are compared to measured data of the actual room and to the results given by other acoustics prediction software. It is concluded that the method can predict most acoustic parameters reliably and provides results as accurate as current commercial room acoustic prediction software. Although the presented acoustic radiance transfer method relies on geometrical acoustics, it can be extended to model diffraction and transmission through materials in future. 相似文献
146.
Influence of polymer-pore interactions on translocation 总被引:1,自引:0,他引:1
We investigate the influence of polymer-pore interactions on the translocation dynamics using Langevin dynamics simulations. An attractive interaction can greatly improve the translocation probability. At the same time, it also increases the translocation time slowly for a weak attraction while an exponential dependence is observed for a strong attraction. For fixed driving force and chain length the histogram of translocation time has a transition from Gaussian distribution to long-tailed distribution with increasing attraction. Under a weak driving force and a strong attractive force, both the translocation time and the residence time in the pore show a nonmonotonic behavior as a function of the chain length. Our simulations results are in good agreement with recent experimental data. 相似文献
147.
Tapio Saarinen Sanna Haavisto Anni Sorvari Juha Salmela Jukka Seppälä 《Cellulose (London, England)》2014,21(3):1261-1275
Rheology of microfibrillated cellulose (MFC) water suspensions was characterized with a rotational rheometer, augmented with optical coherence tomography (OCT). To the best of the authors’ knowledge, this is the first time the behavior of MFC in the rheometer gap was characterized by this real-time imaging method. Two concentrations, 0.5 and 1 wt% were used, the latter also with 10?3 and 10?2 M NaCl. The aim was to follow the structure of the suspensions in a rotational rheometer during the measurements and observe wall depletion and other factors that can interfere with the rheological results. The stepped flow measurements were performed using a transparent cylindrical measuring system and combining the optical information to rheological parameters. OCT allows imaging in radial direction from the outer geometry boundary to the inner geometry boundary making both the shear rate profile and the structure of the suspension visible through the rheometer gap. Yield stress and maximum wall stress were determined by start-up of steady shear and logarithmic stress ramp methods and they both reflected in the stepped flow measurements. Above yield stress, floc size was inversely proportional to shear rate. Below the yield stress, flocs adhered to each other and the observed apparent constant shear stress was controlled by flow in the depleted boundary layer. With higher ionic strength (10?2 M NaCl), the combination of yield stress and wall depletion favored the formation of vertical, cylindrical, rotating floc structures (rollers) coupled with a thicker water layer originating at the suspension—inner cylinder boundary at low shear rates. 相似文献
148.
Cross‐Linked Proteins with Gold Nanoclusters: A Dual‐Purpose pH‐Responsive Material for Controllable Cell Imaging and Antibiotic Delivery
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Pengchang Liu Hui Wang J. Kalervo Hiltunen Zhijun Chen Jiacong Shen 《Particle & Particle Systems Characterization》2015,32(7):749-755
This report describes the development of a facile method for the synthesis of cross‐linked proteins with gold nanoclusters (CP‐GNC). The synthesis reaction is completed within 15 min at 97 °C. The synthesized CP‐GNC are characterized by using UV–vis absorption, fluorescence, X‐ray photoelectron spectroscopy, and transmission electron microscopy. CP‐GNC are approximately 100 nm in diameter and 700 nm in length, whereas AuNCs within the nanorods are approximately 6 nm in size. These materials are highly fluorescent with quantum yield of 7.2% and can be absorbed onto and release from bacterial cells in a pH‐dependent and reversible manner. The recent data show that CP‐GNC can be a useful, new tool with potential applications in fluorescent cell imaging and antibiotic targeting. 相似文献
149.
A novel synthetic route has been developed for the preparation of 1-carboxymethyl-1,4,4-trimethylpiperazinium diiodide and 4-carboxymethyl-1,1-dimethylpiperazinium iodide salts. These quaternary piperazinium acids have potential, for example, in the development of novel water-soluble prodrugs or polymer derivatives. 相似文献
150.
Pekka Keski‐Rahkonen Markus Haapala Ville Saarela Sami Franssila Tapio Kotiaho Risto Kostiainen Seppo Auriola 《Rapid communications in mass spectrometry : RCM》2009,23(20):3313-3322
When a standard atmospheric pressure chemical ionization (APCI) or atmospheric pressure photoionization (APPI) ion source is used without applying the corona discharge or photoirradiation, atmospheric pressure thermospray ionization (APTSI) of various compounds can be achieved. Although largely ignored, this phenomenon has recently gained interest as an alternative ionization technique. In this study, this technique is performed for the first time on a miniaturized scale using a microchip nebulizer. Sample ionization with the presented microchip‐APTSI (µAPTSI) is achieved by applying only heat and gas flow to a nebulizer chip, without any other methods to promote gas‐phase ionization. To evaluate the performance of the described µAPTSI setup, ionization efficiency for a set of test compounds was monitored as the microchip positioning, temperature, nebulizer gas flow rate, sample solution composition, and solvent flow rate were varied. The µAPTSI mass spectra of the test compounds were also compared to those obtained with ESI and APCI. The µAPTSI produces ESI‐like spectra with low background noise, favoring the formation of protonated or deprotonated molecules of compounds that are ionizable in solution. Multiple charging of peptides without in‐source fragmentation was also observed. Unlike ESI, however, the µAPTSI source can tolerate the presence of mobile phase additives like trifluoroacetic acid (TFA) without significant ion suppression. The µAPTSI source can be used with standard mass spectrometer ion source hardware, being a unique alternative to the present interfacing techniques. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献