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排序方式: 共有145条查询结果,搜索用时 15 毫秒
51.
用从头算MOLECULE—EPSCF程序计算得到MgHe~+的基电子态~2∑4s和三个激发电子态~2∑3p、~2∏3p、~2∑3s以及BeHe~+的基电子态~2∑3s和二个激发电子态~2∏2p、~2△3d的势能曲线,并在此基础上利用自编的程序计算不态—态间光谱跃迁的Franck—Condon因子。MgHe~+的~2∏3p、~2∑3s都有一个很深的势阱,~2∑4s有一个非常浅的势阱,~2∑3p没有势阱。BeHe~+的~2∏2p、~2△3d各有一个很深的势阱,基电子态~2∑3s有一个非常浅的势阱。 相似文献
52.
Tomasi C. Scavini M. Speghini A. Bettinelli M. Riccardi M. P. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):151-164
The devitrification of glassy PbGeO3 was studied and interpreted by means of isothermal and non-isothermal Johnson-Mehl-Avrami equations. In the case of the non-isothermal
approach, several approximated equations proposed by various authors were considered in order to obtain both the activation
energy E
a and the Avrami morphological coefficient n of the crystallisation process. A critical discussion of the Avrami coefficient on the basis of experimental morphological
evidence is also presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
53.
Raphael Beumer Pau BayónPiergiuliano Bugada Sylvie Ducki Nicola MongelliFederico Riccardi Sirtori Joachim Telser Cesare Gennari 《Tetrahedron》2003,59(44):8803-8820
The synthesis of a number of novel simplified eleutheside analogs with potent tubulin-assembling and microtubule-stabilizing properties is described, using ring closing metathesis as the key-step for obtaining the 6-10 fused bicyclic ring system. The RCM precursors were synthesized starting from aldehyde 3 [prepared in 6 steps on a multigram scale from R-(−)-carvone in 30% overall yield] via multiple stereoselective Brown allylations. Second generation RCM catalyst 13 gave the desired ring closed 10-membered carbocycles as single Z stereoisomers in good yields. The RCM stereochemical course (100% Z) likely reflects thermodynamic control. The crucial role of the protecting groups of the homoallylic and allylic substituents for the efficiency of the RCM reactions is discussed. These simplified analogs of the natural product (lacking inter alia the C-4/C-7 ether bridge) retain potent microtubule-stabilizing activity. However, the cytotoxicity tests did not parallel the potent tubulin-assembling and microtubule-stabilizing properties: limited cytotoxicity was observed against three common tumor cell lines (human ovarian carcinoma and human colon carcinoma cell lines, IC50 in the μM range given in Table 2), three orders of magnitude less than paclitaxel (IC50 in the nM range). 相似文献
54.
S. Zanini M. Müller C. Riccardi M. Orlandi 《Plasma Chemistry and Plasma Processing》2007,27(4):446-457
Polyethylene glycol (PEG) chains with different lengths were covalently bonded to polypropylene membranes by means of RF plasma
polymerisation of acrylic acid (pp-Aac) followed by mono-amino PEG attachment in liquid phase. Two reactor configurations
were tested for the plasma deposition of ppAAc in order to obtain high retention of carboxylic groups in the deposited thin
films. A best configuration was assessed evaluating the membrane surface modifications by means of water droplet adsorption
time and contact angles measurements, attenuated total reflection (ATR) spectroscopy and X-ray photoelectron spectroscopy
(XPS) analysis. PEG chains were covalently bonded to the best plasma modified membranes and the resulting anti-fouling properties
were evaluated. 相似文献
55.
Range K Riccardi D Cui Q Elstner M York DM 《Physical chemistry chemical physics : PCCP》2005,7(16):3070-3079
Benchmark calculations of proton affinities and gas-phase basicities of molecules most relevant to biological phosphoryl transfer reactions are presented and compared with available experimental results. The accuracy of proton affinity and gas-phase basicity results obtained from several multi-level model chemistries (CBS-QB3, G3B3, and G3MP2B3) and density-functional quantum models (PBE0, B1B95, and B3LYP) are assessed and compared. From these data, a set of empirical bond enthalpy, entropy, and free energy corrections are introduced that considerably improve the accuracy and predictive capability of the methods. These corrections are applied to the prediction of proton affinity and gas-phase basicity values of important biological phosphates and phosphoranes for which experimental data does not currently exist. Comparison is made with results from semiempirical quantum models that are commonly employed in hybrid quantum mechanical/molecular mechanical simulations. Data suggest that the design of improved semiempirical quantum models with increased accuracy for relative proton affinity values is necessary to obtain quantitative accuracy for phosphoryl transfer reactions in solution, enzymes, and ribozymes. 相似文献
56.
Albrecht H Zbinden P Rizzi A Villetti G Riccardi B Puccini P Catinella S Imbimbo BP 《Combinatorial chemistry & high throughput screening》2004,7(8):745-756
A cell-based assay using homogeneous time-resolved fluorescence has been developed for high throughput screening of putative beta-amyloid (Abeta)production inhibitors. In this assay, total Abeta is detected by simply adding two commercially available antibody complexes. The first was a biotinylated monoclonal antibody (4G8), specifically recognizing an epitope comprising the residues 17-24 of the Abetapeptide, complexed with europium cryptate-streptavidin conjugate. The second was a polyclonal antibody (BioS-N), raised against the N-terminus of the Abeta peptide, complexed with an allophycocyanin-anti rabbit antibody conjugate. Binding of the two complexes to the Abeta peptide brought europium cryptate (fluorescence donor) and allophycocyanin (fluorescence acceptor) into close proximity, consequently a fluorescent resonance energy transfer signal was produced upon excitation at 337 nm. The resulting fluorescence signal (665 nm) was then detected using a Discovery or a ViewLux reader. Detection of Abeta by the proposed method is possible at concentrations of approximately 1 nM. The method was employed for the detection of Abeta secreted from a stable transfected human neuroglioma cell line (H4) overexpressing a mutated form of the human amyloid precursor protein (APP695NL) and developed for robotic automation. At optimized conditions, signal-to-background ratios exceeding 5 and Z' factors around 0.7 were achieved in a 384-well format. High throughput screening of 56,913 potential Abeta production inhibitors led to identification of new non-cytotoxic and cell permeable compounds with potencies in the submicromolar range. 相似文献
57.
C. Galas Umberto Sansone Maria Belli Sabrina Barbizzi Philippe Cyffroy Giovanni Paolo Fanzutti Volodya Kanivets Rita Ocone Raffaella Piani Milena Repetti Michele Riccardi Cinzia Terzoni Oleg V. Voitsekhovitch 《Accreditation and quality assurance》2002,7(5):202-208
Sampling and sample preparation/processing are known to carry large, but typically unknown uncertainty contribution to the
final analytical data and there is a lack of qualitative and quantitative data on the comparability of results achieved by
the different sampling methods.
To this end, an intercomparison programme was founded by the European Commission, in which different institutions participated
using their own ”in-situ” methods (”ANPA”, ”EDF” and ”MIDIYA”) for collection of water and suspended material in freshwater
bodies. The main criterion for this intercomparison was the agreement among the 137Cs activity concentrations in the dissolved phase (Bq l–1), those associated with the suspended particles (Bq g–1) and the concentrations of total suspended material (TSM) in the water body (mg l–1). The results show that the sampling systems provide TSM concentration results with low accuracy; on the contrary, they are
recommended for the determination of 137Cs activity concentration in the dissolved phase. Concerning the determination of radiocaesium activity concentration in the
suspended particles, the ”EDF” system provides the more reliable results.
Received: 10 December 2001 Accepted: 4 March 2002 相似文献
58.
Quantitative analysis of small molecules by desorption electrospray ionization mass spectrometry from polytetrafluoroethylene surfaces 总被引:1,自引:0,他引:1
Ifa DR Manicke NE Rusine AL Cooks RG 《Rapid communications in mass spectrometry : RCM》2008,22(4):503-510
Desorption electrospray ionization mass spectrometry (DESI-MS) is an emerging technique for ambient analysis. However, its application to routine quantitation has not been explored extensively and this is undertaken here. We present studies that utilize a particularly suitable surface, porous polytetrafluoroethylene (porous PTFE), which shows less cross contamination between samples and improved sensitivity and signal stability compared to other surfaces. Quantitative experiments for 1 microL spotted solutions of the beta-blocker propranolol, using isotopically labeled propranolol as internal standard, showed a good linear correlation (r2 > 0.996) over the range 0.01-100 microM. The inter-day precision, based on the relative standard deviation, for replicates analyzed on three different days was 13% for 0.01 microM and better than 7% for the remainder of the calibration points. The inter-day accuracy, expressed as relative error, was better than +/-7% for all calibration points along the curve. These day-to-day measurements suggest that DESI-MS can be successfully employed for routine quantitative analysis. The use of the analog atenolol as an internal standard and further considerations that should improve quantitation by DESI-MS are also presented. 相似文献
59.
Fantazzini P Bortolotti V Garavaglia C Gombia M Riccardi S Schembri P Virgili R Soresi Bordini C 《Magnetic resonance imaging》2005,23(2):359-361
The current systems are unable to control and predict the cured meat composition nondestructively and in a reasonable time for production needs. In this work, T1 and T2 maps were obtained, with a monoexponential model, on internal sections of Longissimus dorsi muscle at increasing salting times. The maps allow one to visualize the salting process nondestructively and noninvasively. The method goes beyond the simple qualitative visualization, because, for each section of the sample and in any region of the section, it is possible to obtain quantitative information on the progress of salting and to predict salt-to-moisture ratios. In addition, detailed relaxation measurements were performed on samples cored after imaging in order to define better the relaxation properties of the dry-cured meat. 相似文献