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311.
Erel Y Axelrod T Veron A Mahrer Y Katsafados P Dayan U 《Environmental science & technology》2002,36(15):3230-3233
A high-temporal resolution collection technique was applied to refine aerosol sampling in Jerusalem, Israel. Using stable lead isotopes, lead concentrations, synoptic data, and atmospheric modeling, we demonstrate that lead detected in the atmosphere of Jerusalem is not only anthropogenic lead of local origin but also lead emitted in other countries. Fifty-seven percent of the collected samples contained a nontrivial fraction of foreign atmospheric lead and had 206Pb/207Pb values which deviated from the local petrol-lead value (206Pb/207Pb = 1.113) by more than two standard deviations (0.016). Foreign 206Pb/207Pb values were recorded in Jerusalem on several occasions. The synoptic conditions on these dates and reported values of the isotopic composition of lead emitted in various countries around Israel suggest that the foreign lead was transported to Jerusalem from Egypt, Turkey, and East Europe. The average concentration of foreign atmospheric lead in Jerusalem was 23 +/- 17 ng/m3, similar to the average concentration of local atmospheric lead, 21 +/- 18 ng/ m3. Hence, the load of foreign atmospheric lead is similar to the load of local atmospheric lead in Jerusalem. 相似文献
312.
MacPherson Jacqueline; Sternhagen Scott; Miller Tara; Devitt Mary; Petros Thomas V.; Beckwith Bill 《Canadian Metallurgical Quarterly》1996,4(4):438
The present study examined the effects of caffeine, impulsivity, and gender on specific components of text processing as indicated by measures of reading time and recall. High- and low-impulsive male and female participants received 0, 2, or 4 mg of caffeine per kilogram of body weight. Participants read 3 narrative and 3 expository passages from a computer terminal at their own rate. Immediately after reading each story participants recalled the passage. Participants given caffeine took longer to read the passages and recalled more idea units than participants given a placebo. The effects of caffeine on reading time and recall were not specific to any component of text processing but resulted in a general slowing of reading time and improvement in recall. The effects of caffeine were influenced by both gender and impulsivity. Additionally, results suggest that manipulations that increase encoding difficulty may result in enhanced recall. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
313.
We conduct a numerical study of mixing in a transverse momentum micromixer. Good values for actuation frequencies can be determined using simple kinematic arguments, and evolution strategies are introduced for the optimization of mixing by adjusting the control parameters in micromixer devices. It is shown that the chosen optimization algorithm can identify, in an automated fashion, effective actuation parameters. We find that optimal frequencies for increasing number of transverse channels are superposable despite the non-linear nature of the mixing process. 相似文献
314.
Asymptotically optimal cooperative wireless networks with reduced signaling complexity 总被引:1,自引:0,他引:1
Petros Elia Frederique Oggier P. Vijay Kumar 《Selected Areas in Communications, IEEE Journal on》2007,25(2):258-267
This paper considers an orthogonal amplify-and-forward (OAF) protocol for cooperative relay communication over Rayleigh-fading channels in which the intermediate relays are permitted to linearly transform the received signal and where the source and relays transmit for equal time durations. The diversity-multiplexing gain (D-MG) tradeoff of the equivalent space-time channel associated to this protocol is determined and a cyclic-division-algebra-based D-MG optimal code constructed. The transmission or signaling alphabet of this code is the union of the QAM constellation and a rotated version of QAM. The size of this signaling alphabet is small in comparison with prior D-MG optimal constructions in the literature and is independent of the number of participating nodes in the network 相似文献
315.
With the development of real-time ray tracing in recent years, it is now very interesting to ask if real-time performance
can be achieved for high-quality rendering algorithms based on ray tracing. In this paper, we propose a pipelined architecture
to implement reverse photon mapping. Our architecture can use real-time ray tracing to generate photon points and camera points,
so the main challenge is how to implement the gathering phase that computes the final image. Traditionally, the gathering
phase of photon mapping has only allowed coarse-grain parallelism, and this situation has been a source of inefficiency, cache
thrashing, and limited throughput. To avail fine-grain pipelining and data parallelism, we arrange computations so that photons
can be processed independently, similar to the way that triangles are efficiently processed in traditional real-time graphics
hardware. We employ several techniques to improve cache behavior and to reduce communication overhead. Simulations show that
the bandwidth requirements of this architecture are within the capacity of current and future hardware, and this suggests
that photon mapping may be a good choice for real-time performance in the future. 相似文献
316.
317.
Philip Demokritou Tarun Gupta Petros Koutrakis 《Aerosol science and technology》2013,47(11):1061-1072
A high volume (2500 LPM) system for the condensational growth of ultrafine particles was developed and evaluated using indoor air as a test aerosol. The main features of this system are the following: (a) ultrafine particles grow condensationally to supermicron sizes using high purity deionized water as a condensing medium; (b) the supersaturation ratio is adjustable and can be precisely controlled; (c) the system can operate for a wide range of ambient air temperature and relative humidity conditions; and (d) a thermal dryer is used to return the condensationally grown particles back to their original size. Restoring the original ambient size distribution and preserving the composition of the ambient ultrafine particles is very important for inhalation studies. The system is fully automated and has computerized feedback controls. In addition, saturation of the aerosol with water vapor occurs at close to ambient temperatures to minimize particle losses of volatile components. Saturation of sample air is obtained using a direct steam-injecting, fully modulating electric humidifier. The sample air after saturation is drawn through the supersaturator, which is a refrigerant-to-air heat exchanger and is cooled down to obtain the desirable supersaturation ratio. Supersaturation ratios can be precisely adjusted, with the optimum operational level found to be in the range of 2 to 3. The performance of the system was evaluated as a function of critical operation parameters, including the supersaturation ratio as well as the saturation and supersaturation temperatures. A series of virtual and conventional impactors was used to characterize the condensational growth of ultrafine particles. This new high volume apparatus was shown to grow ambient ultrafine particles to supermicron sizes with a particle size growth of approximately 1.8 w m. Particle losses in the system were found to be minimal (about 10%). The thermal dryer was used successfully to restore the grown particles back to their original size distribution. Particle concentration, aerosol temperature, and residence time (aerosol flow) are key parameters shown to affect the performance of the thermal dryer was used successfully to restore the grown particles back to their original size distribution. Particle concentration, aerosol temperature, and residence time (aerosol flow) are key parameters shown to affect the performance of the thermal dryer. 相似文献
318.
Non-invasive pulmonary perfusion assessment in young patients with cystic fibrosis using an arterial spin labeling MR technique at 1.5 T 总被引:1,自引:1,他引:0
Schraml C Schwenzer NF Martirosian P Boss A Schick F Schäfer S Stern M Claussen CD Schäfer JF 《Magma (New York, N.Y.)》2012,25(2):155-162
Object
To assess lung perfusion in young patients with cystic fibrosis (CF) using an arterial spin labeling (ASL) technique. 相似文献319.
Kevin A. Nibur Brian P. Somerday Chris San Marchi James W. Foulk III Mohsen Dadfarnia Petros Sofronis 《Metallurgical and Materials Transactions A》2013,44(1):248-269
Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. Thresholds for crack extension under rising displacement, K THi, for crack extension under constant displacement, $ K_{\text{THi}}^{*} $ , and for crack arrest under constant displacement K THa, were identified. These values were not found to be equivalent, i.e. K THi < K THa < $ K_{\text{THi}}^{*} $ . The hydrogen assisted fracture mechanism was determined to be strain controlled for all of the alloys in this study, and the micromechanics of strain controlled fracture are used to explain the observed disparities between the different threshold measurements. K THa and K THi differ because the strain singularity of a stationary crack is stronger than that of a propagating crack; K THa must be larger than K THi to achieve equivalent crack tip strain at the same distance from the crack tip. Hydrogen interacts with deformation mechanisms, enhancing strain localization and consequently altering both the nucleation and growth stages of strain controlled fracture mechanisms. The timing of load application and hydrogen exposure, i.e., sequential for constant displacement tests and concurrent for rising displacement tests, leads to differences in the strain history relative to the environmental exposure history and promotes the disparity between $ K_{\text{THi}}^{*} $ and K THi. K THi is the only conservative measurement of fracture threshold among the methods presented here. 相似文献
320.
Jrg Schmehl Hartmut Stoll Marina Danalache Gerd Christian Grzinger Tim-Oliver Greiner Rebecca Felizitas Leibfritz Petros Martirosian Konstantin Nikolaou Stefanie Elser 《International journal of molecular sciences》2021,22(13)
Mesenchymal stem cells (MSC) are known for their vascular regeneration capacity by neoangiogenesis. Even though, several delivery approaches exist, particularly in the case of intravascular delivery, only limited number of cells reach the targeted tissue and are not able to remain on site. Applicated cells exhibit poor survival accompanied with a loss of functionality. Moreover, cell application techniques lead to cell death and impede the overall MSC function and survival. 3D cell spheroids mimic the physiological microenvironment, thus, overcoming these limitations. Therefore, in this study we aimed to evaluate and assess the feasibility of 3D MSCs spheroids for endovascular application, for treatment of ischemic peripheral vascular pathologies. Multicellular 3D MSC spheroids were generated at different cell seeding densities, labelled with ultra-small particles of iron oxide (USPIO) and investigated in vitro in terms of morphology, size distribution, mechanical stability as well as ex vivo with magnetic resonance imaging (MRI) to assess their trackability and distribution. Generated 3D spheroids were stable, viable, maintained stem cell phenotype and were easily trackable and visualized via MRI. MSC 3D spheroids are suitable candidates for endovascular delivery approaches in the context of ischemic peripheral vascular pathologies. 相似文献