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排序方式: 共有138条查询结果,搜索用时 24 毫秒
1.
In this paper, we present experimental data for SIMS analysis of residual gas elements (RGEs) with a Cameca IMS-6f ion microprobe. We considered a simple experimental technique, which provides an effective separation of the secondary ions, sputtered from the bulk of a target, and from the molecules, adsorbed on the analyzed surface from the residual atmosphere. The technique needs the sputtering yield of one monolayer (ML) per second to be applied. The method improves (in more than one order of magnitude) the detection limit for RGEs in SIMS analysis, and simultaneously, provides information about the residual atmosphere at the sample surface and in the main chamber of the experimental instrument. The method provides a calibration method for an ion gauge, and can be used for SIMS analysis with a gas (O2) flooding. 相似文献
2.
B. Ritzer M.A. Villegas J.M. Fernández Navarro 《Journal of Sol-Gel Science and Technology》1997,8(1-3):917-921
The darkening of silica sol-gel glasses doped with 0.05 mol% silver was studied. Six sols were prepared from TEOS and silver
nitrate. Different additives were used, to influence the chemical and physical states of silver: oxidizing or reducing agents
(H2O2, As2O5), colloid stabilizer (sodium citrate) and network modifiers (Li2O, CaO). Sols were gelified at 60°C and densified at 600°C. The samples without additives and those prepared with H2O2 at room temperature even if they were protected from light. With increased temperature, the darkening became samples were
heated above, 400°C, reversible bleaching took place. This darkening-bleaching is of thermal nature (“thermochromic effect”)
and seems to be determined by a reversible aggregation-disaggregation of tiny silver particles. The presence of sodium citrate,
as an additive delayed the darkening effect and the presence of CaO delayed it even further. Lithium oxide inhibited it totally. 相似文献
3.
Carlos Cativiela Maria D. Diaz De Villegas Jos A. Mayoral Alberto Avenoza Miguel A. Roy 《Journal of heterocyclic chemistry》1988,25(3):851-855
3(5)-Carbomethoxy-4-hetarylpyrazoles 3 can be obtained by the aromatization of the corresponding cis-3-benzamido-3-carbomethoxy-4-hetaryl-Δ1-pyrazolines 2 obtained by 1,3-dipolar cycloaddition of diazo-methane with methyl Z-2-benzamido-3-hetarylpropenoates 1. An explanation, based on FMO theory, for the different reactivity of the dipolarophiles with diazomethane is given. 相似文献
4.
C. Cativiela M. D. Diaz De Villegas E. Melndez 《Journal of heterocyclic chemistry》1985,22(6):1655-1657
Several Z-2-methyl(or phenyl)-4-[α-arylethylidene]-5(4H)-oxazolones 3Z, 4Z were prepared. The results obtained were compared by diazomethane insertion and condensation procedure. In order to synthesize E-2-phenyl-4-[α-arylethylidene]-5(4H)-oxazolones 4E hydrogen bromide isomerization in dry benzene was used. 相似文献
5.
Villanueva J Villegas V Querol E Avilés FX Serrano L 《Journal of mass spectrometry : JMS》2002,37(9):974-984
In the post-genomic era, several projects focused on the massive experimental resolution of the three-dimensional structures of all the proteins of different organisms have been initiated. Simultaneously, significant progress has been made in the ab initio prediction of protein three-dimensional structure. One of the keys to the success of such a prediction is the use of local information (i.e. secondary structure). Here we describe a new limited proteolysis methodology, based on the use of unspecific exoproteases coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), to map quickly secondary structure elements of a protein from both ends, the N- and C-termini. We show that the proteolytic patterns (mass spectra series) obtained can be interpreted in the light of the conformation and local stability of the analyzed proteins, a direct correlation being observed between the predicted and the experimentally derived protein secondary structure. Further, this methodology can be easily applied to check rapidly the folding state of a protein and characterize mutational effects on protein conformation and stability. Moreover, given global stability information, this methodology allows one to locate the protein regions of increased or decreased conformational stability. All of this can be done with a small fraction of the amount of protein required by most of the other methods for conformational analysis. Thus limited exoproteolysis, together with MALDI-TOF MS, can be a useful tool to achieve quickly the elucidation of protein structure and stability. 相似文献
6.
A kinetic spectrophotometric method for the determination of hydrocortisone acetate based on its condensation with isonicotinic acid hydrazide is proposed. The method is applied to the determination of hydrocortisone acetate in a commercially available pharmaceutical preparation, presented as a pomade, that also contains another corticosteroid and additional active compounds. The operating procedure involves dissolving the pomade in chloroform and the addition of the reagent solution directly to the cuvette, in this way avoiding the previous extraction of analytes from the insoluble pomade matrix required by the alternative HPLC procedure. Calibration is performed by partial least-squares regression, using absorbance or first derivative spectra values recorded each minute during the first 30 min of reaction. Use of first derivative spectra overcomes possible scattered light problems produced by excipients precipitating, and produced slightly better results than absorbance data. The relative standard deviation obtained for 11 replicates analysed on different days was approx. 1.5%. The proposed method improves both accuracy and precision of the classical initial rate method and the precision of the HPLC procedure. 相似文献
7.
Hydrolysis of 1,10-phenanthrolinopyrrole ethyl ester leads to the acid derivative which is unstable at room-temperature releasing CO(2) and forming 1,10-phenanthrolinopyrrole (php). The ligand reacts with ruthenium(II) to form a series of complexes of the general formula [Ru(php)(n)(bpy)(3-n)](2+), where bpy = 2,2'-bipyridine and n = 1-3. The photochemical properties reveal that the complexes have longer-lived excited states than the standard complex, [Ru(bpy)(3)](2+). Their emission lifetimes range from 9.04 micros (n = 1) to 35.5 micros (n = 3) at 77 K compared to 7.57 micros for the standard. Similarly, at room-temperature, emission lifetimes range from 1.20 micros (n = 1) to 1.70 micros (n = 3) relative to the standard (0.56 micros). The emission quantum yields also have higher values than the standard [Ru(bpy)(3)](2+) under similar conditions. The temperature-dependent studies for the complexes establish the distribution among the radiative, nonradiative, and (3)MLCT to (3)d-d decay channels and are in agreement with the energy gap law. 相似文献
8.
Olivares-Rivas W Fillous L Villegas JC 《Journal of colloid and interface science》2001,233(2):313-319
We revised the classical Stern equation for ion exchange at charged membranes using the statistical mechanics concept of chemical potential and ion activity in nonhomogeneous systems. Our proposed equation does not require an iterative procedure to obtain the self-regulated surface charge at the membranes. We predict significant differences with the classical results. When compared with experimental results, our approach not only gives a better fit but also predicts dissociation constants that are physically more reasonable than those from the classical approach. Copyright 2001 Academic Press. 相似文献
9.
Singlet ground-state geometry optimization of the monomer, four dimers, and the trimer of [Pt(bph)(CO)(2)], where bph = biphenyl dianion, was performed at the B3LYP level of density functional theory (DFT) with a mixed basis set (6-311G** on C, O, and H atoms; the Stuttgart/Dresden (SDD) effective core potential (ECP) on the Pt core; [6s5p3d] on the Pt valence shell). The aggregation was based on Pt[bond]Pt binding as well as on pi[bond]pi and electrostatic interactions. The lowest-lying triplet-state geometries of the monomer, one dimer, and the trimer of the complex were also optimized using the above theory. Significant shortening of the Pt[bond]Pt bond was recorded in the triplet state compared to the singlet one. A number of low-energy singlet and triplet allowed excited states were calculated using time-dependent density functional theory (TDDFT) and analyzed with respect to absorption, excitation, and emission spectra collected under various conditions. Simulated spectra of the monomer and dimer based on the singlet excited states were correlated with the absorption spectrum. The emission in concentrated solution was due to the triplet dimer, and the emitting states were (3)MLCT and Pt-centered states. 相似文献
10.