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141.
A. E. Brouwer 《Journal of Graph Theory》1983,7(4):455-461
We show the uniqueness of the strongly regular graph with parameters ν = 77, k = 16, λ = O, μ = 4 embedding it in the Higman-Sims graph as a second subconstituent, and indicate the existence of a sporadic geometry. 相似文献
142.
143.
Permentier HP Jurva U Barroso B Bruins AP 《Rapid communications in mass spectrometry : RCM》2003,17(14):1585-1592
An on-line electrochemistry/electrospray mass spectrometry system (EC/MS) is described that allows fast analysis of the oxidation products of peptides. A range of peptides was oxidized in an electrochemical cell by application of a potential ramp from 0 to 1.5 V during passage of the sample. Electrochemical oxidation of peptides was found to occur readily when tyrosine was present. Tyrosine was found to be oxidized between 0.5 and 1.0 V to various oxidation products, including peptide fragments formed by hydrolysis at the C-terminal side of tyrosine. The results confirm earlier knowledge on the mechanisms and reaction products of chemical and electrochemical peptide oxidation. Methionine residues are also readily oxidized, but do not induce peptide cleavage. At potentials higher than about 1.1 V, additional oxidation products were observed in some peptides, including loss of 28 Da from the C-terminus and dimerization. The tyrosine-specific cleavage reaction suggests a possible use of the EC/MS system as an on-line protein digestion and peptide mapping system. In addition, the system can be used to distinguish phosphorylated from unphosphorylated tyrosine residues. Four forms of the ZAP-70 peptide ALGADDSYYTAR with both, either or neither tyrosine phosphorylated were subjected to a 0-1.5 V potential ramp. Oxidation of, and cleavage adjacent to, tyrosine was observed exclusively at unphosphorylated tyrosine residues. 相似文献
144.
Ageeth A. Bol Rick van Beek Joke Ferwerda Andries Meijerink 《Journal of Physics and Chemistry of Solids》2003,64(2):247-252
The temperature dependence of the luminescence properties of nanocrystalline CdS/Mn2+ particles is investigated. In addition to an orange Mn2+ emission around 585 nm a red defect related emission around 700 nm is observed. The temperature quenching of both emissions is similar (Tq≈100 K). For the defect emission the reduction in the lifetime follows the temperature dependence of the intensity. For the Mn2+ emission however, the intensity decreases more rapidly than the lifetime with increasing temperature. To explain these observations a model is proposed in which the Mn2+ ions are excited via an intermediate state involving shallowly trapped (≈40 meV) charge carriers. 相似文献
145.
L. E. J. Brouwer 《Mathematische Annalen》1909,67(2):246-267
Ohne Zusammenfassung 相似文献
146.
Brouwer DH 《Journal of the American Chemical Society》2008,130(20):6306-6307
An NMR structure refinement method for the NMR crystallography of zeolites is presented and demonstrated to give an NMR-determined crystal structure for the zeolite Sigma-2 that is in very good agreement with the single-crystal X-ray diffraction structure. The Si coordinates of the zeolite framework were solved from 29Si double-quantum NMR data obtained at a low magnetic field strength (7.0 T) and the Si and O coordinates were subsequently refined using the principal components of 29Si chemical shift tensors experimentally measured at an ultrahigh-field (21.1 T) and calculated using ab initio quantum chemical methods. 相似文献
147.
According to random-matrix theory, interference effects in the conductance of a ballistic chaotic quantum dot should vanish proportional to (tau(phi)/tau(D))(p) when the dephasing time tau(phi) becomes small compared to the mean dwell time tau(D). Aleiner and Larkin have predicted that the power law crosses over to an exponential suppression proportional to exp((-tau(E)/tau(phi)) when tau(phi) drops below the Ehrenfest time tau(E). We report the first observation of this crossover in a computer simulation of universal conductance fluctuations. Their theory also predicts an exponential suppression proportional to exp((-tau(E)/tau(D)) in the absence of dephasing--which is not observed. We show that the effective random-matrix theory proposed previously for quantum dots without dephasing explains both observations. 相似文献
148.
A. M. Brouwer R. D. Mout P. H. Maassen van den Brink H. J. van Ramesdonk J. W. Verhoeven
J. M. Warman
S. A. Jonker 《Chemical physics letters》1991,180(6):556-562Three bridged electron donor—acceptor systems are investigated containing a 4-cyano-1-ethenylnaphthalene electron-acceptor and piperidine (compound 1), phenylpiperazine (2) and 4-methoxyphenylpiperazine (3) electron-donating groups. In the intramolecular charge-transfer states of 1 and 2, the extent of charge separation is similar, but in compound 3 the positive charge is shifted towards the more powerful arylamine donor site, which results in a significantly greater dipole moment. Optical absorption spectra of model radical cations demonstrate that the predominant charge localization on the trialkyl nitrogen in 2 and on the aryl nitrogen in 3 are a consequence of the bistable nature of the piperazine donors. 相似文献
149.
Most multivariate calibration methods require selection of tuning parameters, such as partial least squares (PLS) or the Tikhonov regularization variant ridge regression (RR). Tuning parameter values determine the direction and magnitude of respective model vectors thereby setting the resultant predication abilities of the model vectors. Simultaneously, tuning parameter values establish the corresponding bias/variance and the underlying selectivity/sensitivity tradeoffs. Selection of the final tuning parameter is often accomplished through some form of cross-validation and the resultant root mean square error of cross-validation (RMSECV) values are evaluated. However, selection of a “good” tuning parameter with this one model evaluation merit is almost impossible. Including additional model merits assists tuning parameter selection to provide better balanced models as well as allowing for a reasonable comparison between calibration methods. Using multiple merits requires decisions to be made on how to combine and weight the merits into an information criterion. An abundance of options are possible. Presented in this paper is the sum of ranking differences (SRD) to ensemble a collection of model evaluation merits varying across tuning parameters. It is shown that the SRD consensus ranking of model tuning parameters allows automatic selection of the final model, or a collection of models if so desired. Essentially, the user’s preference for the degree of balance between bias and variance ultimately decides the merits used in SRD and hence, the tuning parameter values ranked lowest by SRD for automatic selection. The SRD process is also shown to allow simultaneous comparison of different calibration methods for a particular data set in conjunction with tuning parameter selection. Because SRD evaluates consistency across multiple merits, decisions on how to combine and weight merits are avoided. To demonstrate the utility of SRD, a near infrared spectral data set and a quantitative structure activity relationship (QSAR) data set are evaluated using PLS and RR. 相似文献
150.
Bovee TF Helsdingen RJ Hamers AR Brouwer BA Nielen MW 《Analytical and bioanalytical chemistry》2011,401(3):873-882
Sensitive and robust bioassays for glucocorticoids are very useful for the pharmaceutical industry, environmental scientists
and veterinary control. Here, a recombinant yeast cell was constructed that expresses the human glucocorticoid receptor alpha
and a green fluorescent reporter protein in response to glucocorticoids. Both the receptor construct and the reporter construct
were stably integrated into the yeast genome. The correct and specific functioning of this yeast glucocorticoid bioassay was
studied by exposures to cortisol and other related compounds and critically compared to a GR-CALUX bioassay based on a human
bone cell. Although less sensitive, the new yeast glucocorticoid bioassay showed sensitivity towards all (gluco)corticoids
tested, with the following order in relative potencies: budesonide >> corticosterone > dexamethasone > cortisol = betamethasone
> prednisolone > aldosterone. Hormone representatives for other hormone nuclear receptors, like 17β-estradiol for the oestrogen
receptor, 5α-dihydrotestosterone for the androgen receptor and progesterone for the progesterone receptor, showed no clear
agonistic responses, whilst some polychlorinated biphenyls were clearly able to interfere with the GR activity. 相似文献