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151.
152.
Experimental test of a robust formation controller for marine unmanned surface vessels 总被引:1,自引:0,他引:1
Daniel Schoerling Chris Van Kleeck Farbod Fahimi Charles Robert Koch Alfons Ams Peter Löber 《Autonomous Robots》2010,28(2):213-230
Experiments with two formation controllers for marine unmanned surface vessels are reported. The formation controllers are
designed using the nonlinear robust model-based sliding mode approach. The marine vehicles can operate in arbitrary formation
configurations by using two leader-follower control schemes. For the design of these controller schemes 3 degrees of freedom
(DOFs) of surge, sway, and yaw are assumed in the planar motion of the marine surface vessels. Each vessel only has two actuators;
therefore, the vessels are underactuated and the lack of a kinematic constraint puts them into the holonomic system category.
In this work, the position of a control point on the vessel is controlled, and the orientation dynamics is not directly controlled.
Therefore, there is a potential for an oscillatory yaw motion to occur. It is shown that the orientation dynamics, as the
internal dynamics of this underactuated system, is stable, i.e., the follower vehicle does not oscillate about its control
point during the formation maneuvers. The proposed formation controller relies only on the state information obtained from
the immediate neighbors of the vessel and the vessel itself. The effectiveness and robustness of formation control laws in
the presence of parameter uncertainty and environmental disturbances are demonstrated by using both simulations and field
experiments. The experiments were performed in a natural environment on a lake using a small test boat, and show robust performance
to parameter uncertainty and disturbance. This paper reports the first experimental verification of the above mentioned approach,
whose unique features are the use of a control point, the zero-dynamic stability analysis, the use of leader-follower method
and a nonlinear robust control approach. 相似文献
153.
Benjamin Van Roy 《Discrete Event Dynamic Systems》2010,20(3):307-324
We study approaches that fit a linear combination of basis functions to the continuation value function of an optimal stopping
problem and then employ a greedy policy based on the resulting approximation. We argue that computing weights to maximize
expected payoff of the greedy policy or to minimize expected squared-error with respect to an invariant measure is intractable.
On the other hand, certain versions of approximate value iteration lead to policies competitive with those that would result
from optimizing the latter objective. 相似文献
154.
F. Foscarini G. Bellocchi R. Confalonieri Cristian Savini G. Van den Eede 《Environmental Modelling & Software》2010,25(10):1256-1260
This work addresses the sensitivity analysis on the settings of fuzzy inference systems where multiple, yet dissimilar inputs are aggregated and resolved into a single output. The JAVA platform-independent development environment DANA (Data Analysis aNd Assessment) includes components for computation of fuzzy-logic based rules guiding the fuzzification–aggregation–defuzzification process by alternative membership functions (of an input to belong to fuzzy sets) and weighing systems, and unlimited aggregation levels. The integration of the library for sensitivity analysis SimLab within DANA is illustrated using the Morris screening method to determine the relative importance ranking of fuzzy settings (lower and upper limits, weights) on the final defuzzified output. The assumptions about the settings of the analysis are also discussed using an illustrative example where sensitivity analysis is applied to the fuzzy inference system designed to evaluate analytical methods in the domain of genetically modified organisms. 相似文献
155.
156.
Tim Van Gestel Feng Han Doris Sebold Hans Peter Buchkremer Detlev St?ver 《Microsystem Technologies》2011,17(2):233-242
A solid oxide fuel cell (SOFC) with a thin-film yttria-stabilized zirconia (YSZ) electrolyte was developed and tested. This
novel SOFC shows a similar multilayer set-up as other current anode-supported SOFCs and is composed of a Ni/8YSZ anode, a
gas-tight 8YSZ electrolyte layer, a dense Sr-diffusion barrier layer and a LSCF cathode. To increase the power density and
lower the SOFC operating temperature, the thickness of the electrolyte layer was reduced from around 10 μm in current cells
to 1 μm, using a nanoparticle deposition method. By using the novel 1 μm electrolyte layer, the current density of our SOFC
progressed to 2.7, 2.1 and 1.6 A/cm2 at operation temperatures of 800, 700 and 650°C, respectively, and out-performs all similar cells reported to date in the
literature. An important consideration is also that cost-effective dip-coating and spin-coating methods are applied for the
fabrication of the thin-film electrolyte. Processing of 1 μm layers on the very porous anode substrate material was initially
experienced as very difficult and therefore 8YSZ nanoparticle coatings were developed and optimized on porous 8YSZ model substrates
and transferred afterwards to regular anode substrates. In this paper, the preparation of the novel SOFC is shown and its
morphology is illustrated with high resolution SEM pictures. Further, the performance in a standard SOFC test is demonstrated. 相似文献
157.
I. Werbrouck M. Antrop V. Van Eetvelde C. Stal Ph. De Maeyer M. Bats J. Bourgeois M. Court-Picon Ph. Crombé J. De Reu Ph. De Smedt P.A. Finke M. Van Meirvenne J. Verniers A. Zwertvaegher 《Expert systems with applications》2011,38(7):8178-8185
This paper discusses the generation of a high precision DEM (Digital Elevation Model) based on high density airborne LiDAR (Light Detection and Ranging) data for an interdisciplinary landscape archaeological study concerning the settlement history and environment in Sandy Flanders, a region to the north of Ghent (Belgium). The objective was to create a detailed topographical surface free of artificial features and topographical artefacts, in the form of a DEM, visualizing the natural and current topography through the implementation of true ground points only. The semi-automatical removal of these features and artefacts was based on topographical vector data, visual interpretations and slope analysis. Ultimately two DEM’s were constructed (1) a TIN (Triangulated Irregular Network) model, whereby the inherent large file format restricts the usability to large scale and (2) a grid model which can be used for small-, medium- and large-scale applications. Both datasets were used as an image that is interpreted using ancillary data from historical sources. Its usefulness is illustrated in a case of field pattern and microfield topography. Starting from this DEM, the approach of this landscape historical study is mainly retrogressive, i.e. starting from the landscape structures and elements that are still present in the contemporary landscape and moving into the past. 相似文献
158.
Proteomics has long been thought to hold the promise of producing results of clinical utility which will influence patient treatment and outcomes. A recent Wellcome Trust/EBI meeting and retreat--“Perspectives in Clinical Proteomics”--brought together experts from a broad range of stakeholder groups with an interest in ensuring proteomics achieves this aim. This viewpoint presents views derived from these forums, proposing a pathway for the development of next-generation proteomic analyses in the clinical setting from selection of candidates through to their validation and ultimate demonstration of utility through health technology assessments. Although not meant to be all encompassing, important elements for proteomics researchers to consider are presented. 相似文献
159.
Triangle algebras are equationally defined structures that are equivalent with certain residuated lattices on a set of intervals, which are called interval-valued residuated lattices (IVRLs). Triangle algebras have been used to construct triangle logic (TL), a formal fuzzy logic that is sound and complete w.r.t. the class of IVRLs.In this paper, we prove that the so-called pseudo-prelinear triangle algebras are subdirect products of pseudo-linear triangle algebras. This can be compared with MTL-algebras (prelinear residuated lattices) being subdirect products of linear residuated lattices.As a consequence, we are able to prove the pseudo-chain completeness of pseudo-linear triangle logic (PTL), an axiomatic extension of TL introduced in this paper. This kind of completeness is the analogue of the chain completeness of monoidal T-norm based logic (MTL).This result also provides a better insight in the structure of triangle algebras; it enables us, amongst others, to prove properties of pseudo-prelinear triangle algebras more easily. It is known that there is a one-to-one correspondence between triangle algebras and couples (L,α), in which L is a residuated lattice and α an element in that residuated lattice. We give a schematic overview of some properties of pseudo-prelinear triangle algebras (and a number of others that can be imposed on a triangle algebra), and the according necessary and sufficient conditions on L and α. 相似文献
160.
SecondSkin estimates an appearance model for an object visible in a video sequence, without the need for complex interaction or any calibration apparatus. This model can then be transferred to other objects, allowing a non‐expert user to insert a synthetic object into a real video sequence so that its appearance matches that of an existing object, and changes appropriately throughout the sequence. As the method does not require any prior knowledge about the scene, the lighting conditions, or the camera, it is applicable to video which was not captured with this purpose in mind. However, this lack of prior knowledge precludes the recovery of separate lighting and surface reflectance information. The SecondSkin appearance model therefore combines these factors. The appearance model does require a dominant light‐source direction, which we estimate via a novel process involving a small amount of user interaction. The resulting model estimate provides exactly the information required to transfer the appearance of the original object to new geometry composited into the same video sequence. 相似文献