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1.
In this paper we consider A(θ)-stable finite difference methods for numerical solutions of dissipative partial differential equations of parabolic type.
Combining two rational approximation methods with different orders of accuracy, where the lower order method is applied n
0 times (n
0 fixed) at each time step, we prove the existence of a second order method which is contractive for all time steps. Moreover,
we shed light on the conditions on the lower order method which are sufficient (and sometimes necessary) to obtain the optimal
order of accuracy. For the one-dimensional heat equation we construct a family of numerical methods which are contractive
in the maximum norm for all values of the discretization parameters. We also present numerical examples to illustrate our
results.
Received: May 2002 / Accepted: January 2003 相似文献
2.
The transformations of a molecule containing two adjacent epoxide rings, 2,2-bioxirane that is, were studied over various acidic aluminosilicates (HZSM-5, HY-FAU, AlMCM-41), for the first time, In the 373–473 K temperature range, in a pulse reactor, a ring-opening–ring-enlargment reaction producing furan only occured over the zeolites and it was the predominant reaction on AlMCM-41 as well. The driving force of this transformation route is water formation via elimination from 2,2-bioxirane. Suprising is the lack of the mono- or dialdehyde, the would-be products of the cleavage of the sterically more hindered C–O bonds – an acid-catalysed reaction typical for alkyl-substituted oxiranes. 相似文献
3.
The main aim of this paper is to predict NO and NO2 concentrations 4 days in advance by comparing two artificial intelligence learning methods, namely, multi-layer perceptron
and support vector machines, on two kinds of spatial embedding of the temporal time series. Hourly values of NO and NO2 concentrations, as well as meteorological variables were recorded in a cross-road monitoring station with heavy traffic in
Szeged, in order to build a model for predicting NO and NO2 concentrations several hours in advance. The prediction of NO and NO2 concentrations was performed partly on the basis of their past values, and partly on the basis of temperature, humidity and
wind speed data. Since NO can be predicted more accurately, its values were considered primarily when forecasting NO2. Time series prediction can be interpreted in a way that is suitable for artificial intelligence learning. Two effective
learning methods, namely, multi-layer perceptron and support vector regression are used to provide efficient non-linear models
for NO and NO2 time series predictions. Multi-layer perceptron is widely used to predict these time series, but support vector regression
has not yet been applied for predicting NO and NO2 concentrations. Three commonly used linear algorithms were considered as references: 1-day persistence, average of several
day persistence and linear regression. Based on the good results of the average of several day persistence, a prediction scheme
was introduced, which forms weighted averages instead of simple ones. The optimization of these weights was performed with
linear regression in linear case and with the learning methods mentioned in non-linear case. Concerning the NO predictions,
the non-linear learning methods give significantly better predictions than the reference linear methods. In the case of NO2, the improvement of the prediction is considerable, however, it is less notable than for NO. 相似文献
4.
5.
Judit Molnár Gábor J. Szebeni Boglárka Csupor-L?ffler Zsuzsanna Hajdú Thomas Szekeres Philipp Saiko Imre Ocsovszki László G. Puskás Judit Hohmann István Zupkó 《International journal of molecular sciences》2016,17(2)
Plants and plant extracts play a crucial role in the research into novel antineoplastic agents. Four sesquiterpene lactones, artecanin (1), 3β-chloro-4α,10α-dihydroxy-1α,2α-epoxy-5α,7αH-guaia-11(13)-en-12,6α-olide (2), iso-seco-tanapartholide 3-O-methyl ether (3) and 4β,15-dihydro-3-dehydrozaluzanin C (4), were isolated from two traditionally used Asteraceae species (Onopordum acanthium and Artemisia asiatica). When tested for antiproliferative action on HL-60 leukemia cells, these compounds exhibited reasonable IC50 values in the range 3.6–13.5 μM. Treatment with the tested compounds resulted in a cell cycle disturbance characterized by increases in the G1 and G2/M populations, while there was a decrease in the S phase. Additionally, 1–3 elicited increases in the hypodiploid (subG1) population. The compounds elicited concentration-dependent chromatin condensation and disruption of the membrane integrity, as revealed by Hoechst 33258–propidium staining. Treatment for 24 h resulted in significant increases in activity of caspases-3 and -9, indicating that the tested sesquiterpenes induced the mitochondrial pathway of apoptosis. The proapoptotic properties of the sesquiterpene lactones were additionally demonstrated withannexin V staining. Compounds 1 and 2 increased the Bax/Bcl-2 expression and decreased the expressions of CDK1 and cyclin B2, as determined at the mRNA level by means of RT-PCR. These experimental results indicate that sesquiterpene lactones may be regarded as potential starting structures for the development of novel anticancer agents. 相似文献
6.
István Szilágyi Ottó Berkesi Mónika Sipiczki László Korecz Antal Rockenbauer István Pálinkó 《Catalysis Letters》2009,127(3-4):239-247
In order to find highly active and selective oxygen-transfer catalysts with appreciable durability, Cu(II)–histidine complexes were covalently grafted onto a chlorinated polystyrene resin as copper-containing enzyme mimics. The Cu(II)-histidine complexes and the mobile polymer were to resemble the active center and the proteomic skeleton of the enzymes, respectively. The resulting heterogenized complexes were expected to be nearly so active and more durable catalysts that are easier to recycle than their homogeneous counterparts. The substances were tested in a superoxide radical anion dismutation reaction. Control for the syntheses was exerted by protecting either the N-terminal or the C-terminal of the covalently grafted l-histidine molecules. During the preparative work generally applied methods of synthetic organic chemistry (alkylation or esterification) were used. Various anchored complexes were prepared and characterized by classical analytical methods, different forms of spectroscopy as well as molecular modeling. The covalently grafted complexes having the protected amino acids as ligands displayed remarkably high activities in the superoxide dismutase (SOD) test reaction. 相似文献
7.
8.
Parametric analysis of a two-layered axially loaded strand is performed using the recently developed p-version finite element code, which describes the geometry well and takes into account all possible inter-wire motions and frictional contact between the wires. A special nonlinear contact theory was developed based on the Hertz-theory. It is assumed that the wires have homogenous, isotropic, linear elastic material properties. The developed code is a tool for designing wire rope strands that require low computer resources and short computational time. Case studies are performed to verify and demonstrate the efficiency and applicability of the method. Design curves are presented according to the strand geometry parameters such as helix angle and ratio of the wire radius in the different layers. The optimal geometry parameters for a given strand can be determined using these design curves. 相似文献
9.
Nagy P Bakonyi G Bongers T Kádár I Fábián M Kiss I 《The Science of the total environment》2004,320(2-3):131-143
Long-term effects of Cd, Cr, Cu, Se and Zn were studied 7 years after artificially contaminating plots of an agricultural field on a calcareous chernozem soil. Effects of three to four different contamination levels (originally 10, 30, 90 and 270 mg kg−1) were studied. Nematode density was significantly reduced by 90 and 270 mg kg−1 Se as well as by 270 mg kg−1 Cr, while 90 and 270 mg kg−1 Se also reduced nematode generic richness. Maturity Index values (calculated for c-p 2–5 nematodes) consistently decreased with increasing Cr and Se concentration and to a lesser extent in Zn plots as well. Structure Index showed decreasing trends in increasing Cr, Se and (to a lesser extent) in Zn treatments, while in Cd it shows a moderate increase. Distribution of c-p groups was negatively affected by the increasing Cr and Se concentration, while in Zn plots, this decrease was not significant. Response of feeding groups to pollutions was similar to other parameters: Cr and Se caused significant changes toward the loss of variability. The proportion of the most sensitive omnivorous and predatory nematodes decreased clearly as a consequence of Cr and Se treatments. Zn pollution also resulted in a slight decrease in this group, while Cd caused an increase. Nematode diversity profiles showed a significant decrease in the plots of increased Cr and Se concentrations, while increased concentrations of Cu and Zn resulted in ambiguous effects. Besides providing evidence on the harmful effects of Cr and Se on a soil nematode assemblage, our results suggest that simultaneous analysis of Maturity Index, Structure Index and diversity profiles provide a promising tool in nematological indication of soil pollution. 相似文献
10.