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51.
In a 2008 paper, Walmsley argued that the explanations employed in the dynamical approach to cognitive science, as exemplified
by the Haken, Kelso and Bunz model of rhythmic finger movement, and the model of infant preservative reaching developed by
Esther Thelen and her colleagues, conform to Carl Hempel and Paul Oppenheim’s deductive-nomological model of explanation (also
known as the covering law model). Although we think Walmsley’s approach is methodologically sound in that it starts with an
analysis of scientific practice rather than a general philosophical framework, we nevertheless feel that there are two problems
with his paper. First, he focuses only on the deductivenomological model and so neglects the important fact that explanations
are causal. Second, the explanations offered by the dynamical approach do not take the deductive-nomological format, because
they do not deduce the explananda from exceptionless laws. Because of these two points, Walmsley makes the dynamical explanations
in cognitive science appear problematic, while in fact they are not. 相似文献
52.
Classifying species of individual trees by intensity and structure features derived from airborne laser scanner data 总被引:3,自引:0,他引:3
Hans Ole Ørka Erik Næsset Ole Martin Bollandsås 《Remote sensing of environment》2009,113(6):1163-3342
The objective of this study was to identify candidate features derived from airborne laser scanner (ALS) data suitable to discriminate between coniferous and deciduous tree species. Both features related to structure and intensity were considered. The study was conducted on 197 Norway spruce and 180 birch trees (leaves on conditions) in a boreal forest reserve in Norway. The ALS sensor used was capable of recording multiple echoes. The point density was 6.6 m− 2. Laser echoes located within the vertical projection of the tree crowns, which were assumed to be circular and defined according to field measurements, were attributed to three categories: “first echoes of many”, “single echoes”, or “last echoes of many echoes”. They were denoted FIRST, SINGLE, and LAST, respectively. In tree species classification using ALS data features should be independent of tree heights. We found that many features were dependent on tree height and that this dependency influenced selection of candidate features. When we accounted for this dependency, it was revealed that FIRST and SINGLE echoes were located higher and LAST echoes lower in the birch crowns than in spruce crowns. The intensity features of the FIRST echoes differed more between species than corresponding features of the other echo categories. For the FIRST echoes the intensity values tended to be higher for birch than spruce. When using the various features for species classification, maximum overall classification accuracies of 77% and 73% were obtained for structural and intensity features, respectively. Combining candidate features related to structure and intensity resulted in an overall classification accuracy of 88%. 相似文献
53.
Erik Næsset 《Remote sensing of environment》2009,113(1):148-3297
Canopy height distributions were created from small-footprint airborne laser scanner (ALS) data collected over 40 field sample plots with size 1000 m2 located in mature conifer forest. ALS data were collected with two different instruments, i.e., the ALTM 1233 and ALTM 3100 laser scanners (Optech Inc.). The ALTM 1233 data were acquired at a flying altitude of 1200 m and a pulse repetition frequency (PRF) of 33 kHz. Three different acquisitions were carried out with ALTM 3100, i.e., (1) a flying altitude of 1100 m and a PRF of 50 kHz, (2) a flying altitude of 1100 m and a PRF of 100 kHz, and (3) a flying altitude of 2000 m and a PRF of 50 kHz. Height percentiles, mean and maximum height values, coefficients of variation of the heights, and canopy density at different height intervals above the ground were derived from the four different ALS datasets and for single + first and last echoes of the ALS data separately. The ALS-derived height- and density variables were assessed in pair-wise comparisons to evaluate the effects of (a) instrument, (b) flying altitude, and (c) PRF. A systematic shift in height values of up to 0.3 m between sensors when the first echoes were compared was demonstrated. Also the density-related variables differed significantly between the two instruments. Comparisons of flying altitudes and PRFs revealed upwards shifted canopy height distributions for the highest flying altitude (2000 m) and the lowest PRF (50 kHz). The distribution of echoes on different echo categories, i.e., single and multiple (first and last) echoes, differed significantly between acquisitions. The proportion of multiple echoes decreased with increasing flying altitude and PRF. Different echo categories have different properties since it is likely that single echoes tend to occur in the densest parts of the tree crowns, i.e., near the apex where the concentration of biological matter is highest and distance to the ground is largest. To assess the influence of instrument, flying altitude, and PRF on biophysical properties derived from ALS data, regression analysis was carried out to relate ALS-derived metrics to mean tree height (hL) and timber volume (V). Cross validation revealed only minor differences in precision for the different ALS acquisitions, but systematic differences between acquisitions of up to 2.5% for hL and 10.7% for V were found when comparing data from different acquisitions. 相似文献
54.
Design patterns for user interface for mobile applications 总被引:1,自引:0,他引:1
The topic of this paper is a collection of user interface (UI) design patterns for mobile applications. In the paper we present the structure of the patterns collection – the patterns are suggested solutions to problems that are grouped into a set of problem areas that are further grouped into three main problem areas – a structure which is valuable both as an index to identifying patterns to use, and it gives a fairly comprehensive overview of issues when designing user interfaces for mobile applications. To show the breadth of the patterns collection we present six individual problems with connected design patterns in some detail – each coming from different problem areas. They represent important and relevant problems, and are on different levels of abstraction, thus showing how patterns may be used to present problems and solutions on different levels of detail. To show the relevance and usefulness of the patterns collection for usability professionals with a mixed background, we present some relevant findings from a validation of the patterns collection. In addition to verifying the relevance and usefulness of the patterns collection, it also shows both expected and surprising correlations between background and perceived relevance and usefulness. One important finding from the validation is an indication that the patterns collection is best suited for experienced UI developers wanting to start developing mobile UIs. Using a patterns collection for documenting design knowledge and experience has been a mixed experience, so we discuss pros and cons of this. Finally, we present related work and future research. 相似文献
55.
A k-spanner of a graph G is a spanning subgraph of G in which the distance between any pair of vertices is at most k times the distance in G. We prove that for fixed k,w, the problem of deciding if a given graph has a k-spanner of treewidth w is fixed-parameter tractable on graphs of bounded degree. In particular, this implies that finding a k-spanner that is a tree (a tree k-spanner) is fixed-parameter tractable on graphs of bounded degree. In contrast, we observe that if the graph has only one vertex of unbounded degree, then Treek-Spanner is NP-complete for k?4. 相似文献
56.
Khaled Elbassioni Erik Krohn Domagoj Matijević Julián Mestre Domagoj Ševerdija 《Algorithmica》2011,60(2):451-463
We present a 4-approximation algorithm for the problem of placing the fewest guards on a 1.5D terrain so that every point
of the terrain is seen by at least one guard. This improves on the previous best approximation factor of 5 (see King in Proceedings
of the 13th Latin American Symposium on Theoretical Informatics, pp. 629–640, 2006). Unlike most of the previous techniques, our method is based on rounding the linear programming relaxation of the corresponding
covering problem. Besides the simplicity of the analysis, which mainly relies on decomposing the constraint matrix of the
LP into totally balanced matrices, our algorithm, unlike previous work, generalizes to the weighted and partial versions of
the basic problem. 相似文献
57.
58.
Real-time path planning in dynamic virtual environments using multiagent navigation graphs 总被引:1,自引:0,他引:1
Sud A Andersen E Curtis S Lin MC Manocha D 《IEEE transactions on visualization and computer graphics》2008,14(3):526-538
We present a novel approach for efficient path planning and navigation of multiple virtual agents in complex dynamic scenes. We introduce a new data structure, Multi-agent Navigation Graph (MaNG), which is constructed using first- and second-order Voronoi diagrams. The MaNG is used to perform route planning and proximity computations for each agent in real time. Moreover, we use the path information and proximity relationships for local dynamics computation of each agent by extending a social force model [Helbing05]. We compute the MaNG using graphics hardware and present culling techniques to accelerate the computation. We also address undersampling issues and present techniques to improve the accuracy of our algorithm. Our algorithm is used for real-time multi-agent planning in pursuit-evasion, terrain exploration and crowd simulation scenarios consisting of hundreds of moving agents, each with a distinct goal. 相似文献
59.
60.
Staged self-assembly: nanomanufacture of arbitrary shapes with <Emphasis Type="Italic">O</Emphasis>(1) glues 总被引:1,自引:1,他引:0
Erik D. Demaine Martin L. Demaine Sándor P. Fekete Mashhood Ishaque Eynat Rafalin Robert T. Schweller Diane L. Souvaine 《Natural computing》2008,7(3):347-370
We introduce staged self-assembly of Wang tiles, where tiles can be added dynamically in sequence and where intermediate constructions can be stored for later
mixing. This model and its various constraints and performance measures are motivated by a practical nanofabrication scenario
through protein-based bioengineering. Staging allows us to break through the traditional lower bounds in tile self-assembly
by encoding the shape in the staging algorithm instead of the tiles. All of our results are based on the practical assumption
that only a constant number of glues, and thus only a constant number of tiles, can be engineered. Under this assumption,
traditional tile self-assembly cannot even manufacture an n × n square; in contrast, we show how staged assembly in theory enables manufacture of arbitrary shapes in a variety of precise
formulations of the model.
相似文献
Diane L. SouvaineEmail: |