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排序方式: 共有1494条查询结果,搜索用时 46 毫秒
1.
Somnath Karmakar 《Polycyclic Aromatic Compounds》2019,39(2):159-171
Eigensolutions of {X( = C,B,N),Y( = C,B,N)}-cyclacene graphs with next nearest neighbor (nnn) interactions have been obtained in analytical forms by adapting n-fold rotational symmetry followed by two-fold rotational symmetry (or a plane of symmetry). Expressions of eigensolution indicate the subspectral relationship among such cyclacenes with an even number of hexagonal rings e.g., eigenvalues of {X,Y}-di-cyclacene are found in the eigenspectra of all such even cyclacenes. Total π-electron energies and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps are calculated using the analytical expressions obtained and are found to vary negligibly with the variation of nnn interactions in such cyclacenes. Total π-electron energy is found to increase due to increase in restriction intensity of nnn interactions, whereas the HOMO–LUMO gap of polyacenecs having the even number of hexagonal rings and with one electron at each site (atom) decreases with increase in the restriction intensity since such systems contain degenerate half-filled HOMO (bonding or nonbonding) that are much more vulnerable for perturbations imposed through nnn interactions. 相似文献
2.
In this study, we have proposed an automated classification approach to identify meaningful patterns in wind field data. Utilizing an extensive simulated wind database, we have demonstrated that the proposed approach can identify low‐level jets, near‐uniform profiles, and other patterns in a reliable manner. We have studied the dependence of these wind profile patterns on locations (eg, offshore vs onshore), seasons, and diurnal cycles. Furthermore, we have found that the probability distributions of some of the patterns depend on the underlying planetary boundary layer schemes in a significant way. The future potential of the proposed approach in wind resource assessment and, more generally, in mesoscale model parameterization improvement is touched upon in this paper. 相似文献
3.
Mostofa Shamim Somnath Sinhamahapatra Jahangir Hossain Sayan Lahiri Kausik Dana 《Ceramics International》2018,44(2):1868-1874
The mechanistic pathway of MgO-Al2O3 reaction in solid state to form MgAl2O4 spinel was investigated to correlate the kinetic parameters with ratio of reactants (MgO:Al2O3) and with the presence of a doping agent, TiO2. The time-temperature-expansion data of oxide compacts was analyzed using several model free analyses and model based (linear and non-linear) kinetic algorithms. These indicated that spinel formation process can be best described by single step with n-dimensional Avrami equation for every MgO:Al2O3 ratio, irrespective of titania dopant. The activation energy (Ea) of the process was proportional to % spinel formed in each system and validated with quantitative XRD analysis. The higher value of Avrami coefficient (n) in 90 wt% Al2O3 compositions has been explained with geometric considerations of powder packing. Incorporations of 1% TiO2 in the MgO: Al2O3 oxide compact did not markedly affect the reaction model, frequency factor and Activation energy. 相似文献
4.
We recently reported that epidermal immunization using the PowderJet particle delivery device with plasmid vector pcDNA1/EDIM6 encoding rotavirus VP6 of murine strain EDIM induced high levels of serum rotavirus IgG but failed to protect mice against EDIM infection (Choi, A. H., Knowlton, D. R., McNeal, M. M., and Ward, R. L. (1997) Virology 232, 129-138.). This was extended to determine whether pcDNA1/EDIM4 or pcDNA1/EDIM7, which encode either rotavirus VP4 or VP7, the rotavirus neutralization proteins, could also induce rotavirus-specific antibody responses and if these responses resulted in protection. Titers of rotavirus serum IgG increased with the first dose in mice immunized with pcDNA1/EDIM7, but little or no serum rotavirus IgG was detected in mice immunized with pcDNA1/EDIM4. In vitro assays with these plasmids in rabbit reticulocyte lysates showed that VP4 was expressed but the amount was considerably lower than VP6 or VP7. To improve expression of VP4 and induction of rotavirus-specific humoral responses, the coding region of VP4 was cloned into the high-expression plasmid WRG7054 as a fusion protein containing the 22-amino-acid secretory signal peptide of tissue plasminogen activator (tPA) at its N terminus. In vitro expression of tPA::VP4 was significantly higher than unmodified VP4, and mice inoculated with WRG7054/EDIM4 generated high titers of rotavirus IgG. The coding sequence of VP7 without the first 162 nucleotides was also cloned into WRG7054, but no difference was observed between titers of serum rotavirus IgG in mice immunized with this plasmid (WRG7054/EDIM7Delta1-162) and pcDNA1/EDIM7. The rotavirus-specific IgG titers in all immune sera were predominantly IgG1 indicating induction of Th 2-type responses. None of the mice immunized with any of the VP4 or VP7 plasmids developed serum or fecal rotavirus IgA or neutralizing antibody to EDIM. When immunized mice were challenged with EDIM virus, there was no significant reduction in viral shedding relative to unimmunized controls. Therefore epidermal immunization with VP4 or VP7 alone elicited rotavirus IgG responses but did not protect against homologous rotavirus challenge. 相似文献
5.
SL Romney GY Ho PR Palan J Basu AS Kadish S Klein M Mikhail RJ Hagan CJ Chang RD Burk 《Canadian Metallurgical Quarterly》1997,65(3):483-492
OBJECTIVES: The age-dependence of the development of ventricular arrhythmias was studied in German shepherd dogs with inherited ventricular arrhythmias and sudden death. BACKGROUND: A colony of German shepherd dogs has been established that exhibit inherited ventricular arrhythmias and sudden death. The incidence of arrhythmias increases with age. Because ventricular tachycardia is associated with bradycardia, it was hypothesized that the increased incidence of arrhythmias was related to age-dependent slowing of heart rate. METHODS: Arrhythmia counts and RR intervals were measured from serial ambulatory ECG recordings obtained in 71 dogs (1-48 weeks). In addition, 19 dogs were challenged with phenylephrine (10 micrograms/kg i.v.) at 15, 28, and 45 weeks of age, 10 dogs were challenged with epinephrine (1 microgram/kg i.v.) at 3, 5, 7, 9, 11, 18, and 28 weeks of age, and 10 dogs were challenged at 28 weeks with epinephrine (2.5 micrograms/kg i.v.), before and after propranolol (0.5 mg/kg i.v.). RESULTS: The incidence and severity of ventricular arrhythmias increased between 7 and 28 weeks of age and decreased between 28 and 44 weeks of age. The age-dependent increase in the incidence of ventricular tachycardia was associated with age-dependent reductions in sinus rate. Baroreflex-mediated slowing of the heart rate unmasked arrhythmias in young animals that did not spontaneously display arrthythmias and exacerbated existing arrhythmias in older animals. However, the magnitude of baroreflex-induced bradycardia was similar from 7-18 weeks of age, yet the incidence of arrhythmias increased progressively. Moreover, the waning of ventricular arrhythmias in older animals was not associated with more rapid sinus rates. CONCLUSION: The risk for sudden death in dogs with inherited ventricular arrhythmias increases with age in part because of age-dependent slowing of heart rate and in part because of other heart-rate-independent factors. The correspondence between the development of ventricular tachycardia and sinus pauses is consistent with the hypothesis that ventricular arrhythmias are initiated by early afterdepolarization-induced triggered activity. 相似文献
6.
This paper describes the results of experiments designed to quantify the cooling rate of corium by an overlying water pool. The experiments are intended to provide fundamental information on the ability of water to ingress into cracks and fissures that form in the debris during quench, thereby augmenting the otherwise conduction-limited heat transfer process. This information is being used to assess the effectiveness of a water pool in thermally stabilizing a molten-core/concrete interaction and cooling of ex-vessel core debris. The experiments involved corium inventories of 75 kg with a melt depth of 15 cm and diameter of 30 cm. The corium was composed of UO2/ZrO2/concrete to simulate mixtures of molten reactor core components and either siliceous or limestone/common sand (LCS) concrete. Initial melt temperatures were of the order of 2100 °C. The heat transfer rate from the corium was determined through measurements of the vapor production rate from the water pool. The melt was quenched at atmospheric pressure for the first two tests and at 4 bar for the two subsequent tests. Preliminary data analysis indicates that the overall heat transfer rate exceeded the conduction-limited rate for the three melts containing 8 wt.% concrete, but not for the fourth, which had 23 wt.% concrete. Also, the quench rate of the 8 wt.% concrete melts did not vary appreciably with pressure. 相似文献
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9.
Dhyanjyoti Deka Deepu S. Joseph Somnath Ghosh Michael J. Mills 《Metallurgical and Materials Transactions A》2006,37(5):1371-1388
This paper develops an experimentally validated computational model based on crystal plasticity for the analysis of two-phase
α/β Ti-6242 polycrystalline alloys. A rate-dependent elastic-crystal plasticity model is incorporated in this model to accommodate
anisotropy in material behavior and tension-compression asymmetry inherent to this alloy. A combination of microtesting, orientation
imaging microscopy, computational simulations, and minimization process, involving genetic algorithms, is implemented in this
study for careful characterization and calibration of the material parameters. Size effects are considered in this analysis
through a simple scaling process. A homogenized equivalent model of the primary α with transformed β colonies is developed
for incorporation in the Ti-6242 FE model. The polycrystalline Ti-6242 computational model incorporates accurate phase volume
fractions, as well as statistically equivalent orientation distributions to those observed in the orientation imaging microscopy
scans. The effects of orientation, misorientations, and microtexture distributions are investigated through simulations by
this computational model. The model is used to simulate constant strain rate and creep tests in compression and tension, and
the results are compared with experiments. The effects of microstructure and creep-induced load-shedding on the localization
of microstructural stresses and strains are studied for potential crack initiation criteria. 相似文献
10.
Nano-crystal embedded PbO-P2O5 glass has been prepared and characterized by XRD and TEM measurements. The ultrasonic velocity and attenuation measured within
the temperature range 80–300 K show significant structure and interesting feature with the presence of nano-crystalline region.
The glass samples were prepared by melt-quench method and nano-crystals of different sizes were produced by heat treatment
of the glasses for different durations of heating. All the processes were carried out at or above glass transition temperature.
A theoretical model that takes account of the effects of thermally activated relaxation, anharmonicity as well as microscopic
elastic inhomogeneities arising out of fluctuations has been successfully applied to interpret the variation of ultrasonic
velocity and attenuation data. An interesting outcome of this application has been to propose a method for the determination
of the size of nano-crystals from the ultrasonic attenuation data. 相似文献