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531.
In this paper, we propose an algorithm to automatically detect regular subcurves in a set of digital curves. The decision criterion is based on Helmholtz Principle introduced by Desolneux, Moisan and Morel and formulated in terms of number of false alarms. We apply our algorithm to low-level computer vision. Following Gestalt Theory, good continuation is indeed, one of the most important grouping laws entering into the early perception of objects. We check this on the level lines of images, which give a contrast invariant representation of images. The result is that most objects are good continuations. This experimentally shows that contrast invariance is a very sound hypothesis for low level vision and that objects can be detected independently of contrast. The parameters of the method may be reduced to a single one – the number of false alarms – and we can show that the detection has a very weak dependency on this number. 相似文献
532.
We present for the first time an analytical approach for determining the time of firing of multicomponent nonlinear stochastic neuronal models. We apply the theory of first exit times for Markov processes to the Fitzhugh-Nagumo system with a constant mean gaussian white noise input, representing stochastic excitation and inhibition. Partial differential equations are obtained for the moments of the time to first spike. The observation that the recovery variable barely changes in the prespike trajectory leads to an accurate one-dimensional approximation. For the moments of the time to reach threshold, this leads to ordinary differential equations that may be easily solved. Several analytical approaches are explored that involve perturbation expansions for large and small values of the noise parameter. For ranges of the parameters appropriate for these asymptotic methods, the perturbation solutions are used to establish the validity of the one-dimensional approximation for both small and large values of the noise parameter. Additional verification is obtained with the excellent agreement between the mean and variance of the firing time found by numerical solution of the differential equations for the one-dimensional approximation and those obtained by simulation of the solutions of the model stochastic differential equations. Such agreement extends to intermediate values of the noise parameter. For the mean time to threshold, we find maxima at small noise values that constitute a form of stochastic resonance. We also investigate the dependence of the mean firing time on the initial values of the voltage and recovery variables when the input current has zero mean. 相似文献
533.
In this article, mid-infrared Fourier transform (Mid-FT-IR) and carbon thirteen nuclear magnetic resonance (13C NMR) spectroscopy have been used to determine possible interactions between sucrose and various alkali or alkaline earth metals in aqueous solution. In the presence of these metals, significant shifts in the absorption bands of sucrose were noted by mid-FT-IR coupled with principal component analysis (PCA). These shifts were explained on the basis of weakening of the H-bond network between sucrose and water and possible interactions between sucrose and the metal ion. Factorial maps were established and the spectral patterns obtained show that these interactions vary according to the nature of the metal ion. 13C NMR analysis showed that the carbon atoms of sucrose undergo shielding or deshielding in the presence of metal ions in aqueous solutions. Two factors were invoked to account for the variation of chemical shifts: the rupture of hydrogen bonds due to hydration of the metal ion and the possible coordination of the metal ion to the oxygen atoms of sucrose. 相似文献
534.
Merritt S Bevilacqua F Durkin AJ Cuccia DJ Lanning R Tromberg BJ Gulsen G Yu H Wang J Nalcioglu O 《Applied optics》2003,42(16):2951-2959
We report coregistration of near-infrared diffuse optical spectroscopy (DOS) and magnetic resonance imaging (MRI) for the study of animal model tumors. A combined broadband steady-state and frequency-domain apparatus was used to determine tissue oxyhemoglobin, deoxyhemoglobin, and water concentration locally in tumors. Simultaneous MRI coregistration provided structural (T2-weighted) and contrast-enhanced images of the tumor that were correlated with the optical measurements. By use of Monte Carlo simulations, the optically sampled volume was superimposed on the MR images, showing precisely which tissue structure was probed optically. DOS and MRI coregistration measurements were performed on seven rats over 20 days and were separated into three tumor tissue classifications: viable, edematous, and necrotic. A ratio of water concentration to total hemoglobin concentration, as measured optically, was performed for each tissue type and showed values for edematous tissue to be greater than viable tissue (1.2 +/- 0.49 M/microM versus 0.48 +/- 0.15 M/microM). Tissue hemoglobin oxygen saturation (StO2) also showed a large variation between tissue types: viable tissue had an optically measured StO2 value of 61 +/- 5%, whereas StO2 determined for necrotic tissue was 43 +/- 6%. 相似文献
535.
To achieve the ever increasing demand for science return, planetary exploration rovers require more autonomy to successfully perform their missions. Indeed, the communication delays are such that teleoperation is unrealistic. Although the current rovers (such as MER) demonstrate a limited navigation autonomy, and mostly rely on ground mission planning, the next generation (e.g., NASA Mars Science Laboratory and ESA Exomars) will have to regularly achieve long range autonomous navigation tasks. However, fully autonomous long range navigation in partially known planetary‐like terrains is still an open challenge for robotics. Navigating hundreds of meters without any human intervention requires the robot to be able to build adequate representations of its environment, to plan and execute trajectories according to the kind of terrain traversed, to control its motions, and to localize itself as it moves. All these activities have to be planned, scheduled, and performed according to the rover context, and controlled so that the mission is correctly fulfilled. To achieve these objectives, we have developed a temporal planner and an execution controller, which exhibit plan repair and replanning capabilities. The planner is in charge of producing plans composed of actions for navigation, science activities (moving and operating instruments), communication with Earth and with an orbiter or a lander, while managing resources (power, memory, etc.) and respecting temporal constraints (communication visibility windows, rendezvous, etc.). High level actions also need to be refined and their execution temporally and logically controlled. Finally, in such critical applications, we believe it is important to deploy a component that protects the system against dangerous or even fatal situations resulting from unexpected interactions between subsystems (e.g., move the robot while the robot arm is unstowed) and/or software components (e.g., take and store a picture in a buffer while the previous one is still being processed). In this article we review the aforementioned capabilities, which have been developed, tested, and evaluated on board our rovers (Lama and Dala). After an overview of the architecture design principle adopted, we summarize the perception, localization, and motion generation functions required by autonomous navigation, and their integration and concurrent operation in a global architecture. We then detail the decisional components: a high level temporal planner that produces the robot activity plan on board, and temporal and procedural execution controllers. We show how some failures or execution delays are being taken care of with online local repair, or replanning. © 2007 Wiley Periodicals, Inc. 相似文献
536.
Maarouf Hayat El; Carriere Frederic; Riviere Mireille; Abousalham Abdelkarim 《Protein engineering, design & selection : PEDS》2000,13(11):811-817
Phospholipase D (PLD) is an important enzyme involved in signaltransduction, vesicle trafficking and membrane metabolism. Inthis study, large amounts of a recombinant plant PLD were secretedinto the culture medium of baculovirus-infected insect cellsand purified to homogeneity in the form of a fully active enzyme.The transient production of recombinant PLD yielded a protein(rPLDa, 88 kDa) together with a shorter form (rPLDb, 87 kDa),which accumulated in the medium. N-Terminal amino acid sequencingof the rPLDa and rPLDb showed that rPLDb resulted from proteolyticcleavage at Gly8Ile9. Immunoblotting showed that bothrPLDa and rPLDb are recognized by a polyclonal antibody previouslyraised against native soybean PLD. One-step calcium-dependentoctyl-Sepharose chromatography was used to obtain the two highlypurified forms of rPLD, as attested by gel electrophoresis,N-terminal amino acid sequence and mass spectrometry. The N-terminalregion of PLD is homologous with the C2 domains which are presentin a number of enzymes known to be involved in signal transductionand/or phospholipid metabolism. The truncated rPLDb lacks thefirst acidic amino acid in its N-terminus, which is probablyinvolved in the calcium binding site. The rPLDb was thus easilyeluted from the octyl-Sepharose column by decreasing the calciumconcentration of the buffer from 50 to 30 mM, whereas, the rPLDawas eluted after chelating calcium ions with EDTA. The purifiedrPLD yield reached a level of 10 mg per liter of serum-freeculture medium. The availability of baculovirus-derived rPLDconstitutes a valuable source of enzyme for future crystallographicstudies to determine its three-dimensional structure. 相似文献
537.
Daniel J. Lege Frederic Barlat John C. Brem 《International Journal of Mechanical Sciences》1989,31(7)
A 2008-T4 sheet sample has been characterized and its mechanical behavior and formability have been modeled. Uniaxial tensile and equal biaxial tensile stress-strain data, compressive yield strengths, crystallographic texture, earing and the forming limit curve were experimentally determined. Bulge test specimen shape and thickness profiles were also measured after various amounts of biaxial strain. A recently developed phenomenological constitutive model of anisotropic mechanical behavior was used to predict the directionality of strength, plastic strain ratio (R) and shear strain ratio (Г) values. In addition, this model was used to predict the forming limit curve for this sample. Predictions made with the recent model generally compare favorably with experimental results and with predictions made using the Taylor/Bishop and Hill theory. According to the data obtained in hydraulic bulge testing, the 2008-T4 exhibited apparent isotropic behavior. However, in cup drawing—another axisymmetric deformation mode—this material exhibited anisotropic behavior, as indicated by the formation of ears and troughs. 相似文献
538.
F. Frederic Deng 《The Annals of Regional Science》2005,39(2):353-373
Since late 1980s China's urban land use began to change from administrative allocation to public land leasing. Based on the
assumptions of fiscal decentralization and growth of private economy, this paper provides another perspective on public land
leasing in addition to the well-known efficiency of market allocation of land resource. My focus is on the endogenous evolution
of local public finance due to rent capitalization. Especially, I model a two-sector urban economy and a multi-task local
government that allocates its effort to maximize fiscal revenue. The findings indicate that complete wage capitalization under
administrative allocation of land contributes to the pressure on local governments to look for alternative revenue source.
Public land leasing helps to include private firms into local public finance and re-orient local governments' interest from
SOEs to public goods provision. A simple test on the institutional change shows the efficiency of public land leasing relative
to the old system.
I thank Rena Sivitanidou and Yongheng Deng for their helpful comments on an early version of the paper. 相似文献
539.
540.
Wojciech Knap Salman Nadar Hadley Videlier Stephane Boubanga-Tombet Dominique Coquillat Nina Dyakonova Frederic Teppe Kristoph Karpierz Jerzy ?usakowski Maciej Sakowicz Irmantas Kasalynas Dalius Seliuta Gintaras Valusis Taiichi Otsuji Yahya Meziani Abdel El Fatimy Simon Vandenbrouk Kamel Madjour Didier Th��ron Christophe Gaqui��re 《Journal of Infrared, Millimeter and Terahertz Waves》2011,32(5):618-628
Resonant frequencies of the two-dimensional plasma in field effect transistors (FETs) increase with the reduction of the channel dimensions and can reach the Terahertz (THz) range. Nonlinear properties of the plasma/electron gas in the transistor channel can be used for the rectification and detection of THz radiation. The excitation of plasma waves by sub-THz and THz radiation was demonstrated for short gate transistors at cryogenic temperatures. At room temperature plasma oscillations are usually overdamped, but the FETs can still operate as efficient broadband rectifiers/detectors in the THz range. We present a few recent experimental results on THz detection by FETs showing some new ways of improvement of FETs for THz imaging at room temperature as well as the new physical phenomena like detection in quantizing magnetic fields. We also demonstrate THz emission properties of GaN based FETs. 相似文献