全文获取类型
收费全文 | 10366篇 |
免费 | 284篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 142篇 |
综合类 | 8篇 |
化学工业 | 2371篇 |
金属工艺 | 243篇 |
机械仪表 | 190篇 |
建筑科学 | 449篇 |
矿业工程 | 54篇 |
能源动力 | 303篇 |
轻工业 | 697篇 |
水利工程 | 105篇 |
石油天然气 | 106篇 |
无线电 | 653篇 |
一般工业技术 | 1781篇 |
冶金工业 | 1848篇 |
原子能技术 | 102篇 |
自动化技术 | 1612篇 |
出版年
2022年 | 109篇 |
2021年 | 152篇 |
2020年 | 122篇 |
2019年 | 116篇 |
2018年 | 160篇 |
2017年 | 160篇 |
2016年 | 202篇 |
2015年 | 176篇 |
2014年 | 255篇 |
2013年 | 722篇 |
2012年 | 392篇 |
2011年 | 498篇 |
2010年 | 369篇 |
2009年 | 404篇 |
2008年 | 450篇 |
2007年 | 397篇 |
2006年 | 388篇 |
2005年 | 330篇 |
2004年 | 302篇 |
2003年 | 257篇 |
2002年 | 264篇 |
2001年 | 178篇 |
2000年 | 171篇 |
1999年 | 169篇 |
1998年 | 233篇 |
1997年 | 195篇 |
1996年 | 175篇 |
1995年 | 146篇 |
1994年 | 154篇 |
1993年 | 144篇 |
1992年 | 130篇 |
1991年 | 111篇 |
1990年 | 112篇 |
1989年 | 144篇 |
1988年 | 101篇 |
1987年 | 119篇 |
1986年 | 122篇 |
1985年 | 135篇 |
1984年 | 158篇 |
1983年 | 116篇 |
1982年 | 117篇 |
1981年 | 95篇 |
1980年 | 91篇 |
1979年 | 99篇 |
1978年 | 82篇 |
1977年 | 102篇 |
1976年 | 98篇 |
1975年 | 87篇 |
1974年 | 92篇 |
1973年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Conventionally drought severity is assessed based on drought indices. Recently the Reconnaissance Drought Index (RDI) was
proposed to assess drought severity based on the precipitation to potential evapotranspiration ratio (P/PET). In this paper
RDI is studied as a bivariate index under a set of assumptions and simplifications. The paper presents a simple computational
procedure for estimating the P/PET ratio for selected reference periods varying from 3 to 12 months, for any return period
of drought. Alternatively, based on this procedure, the severity of any drought episode is rationally assessed. A bivariate
probability analysis is employed based on the assumption that P and PET values are normally distributed and often negatively
correlated. Examples for the application of the proposed procedure are presented using data from several meteorological stations
in Greece. It is shown that the assumption of normality of both P and PET holds for long periods at all examined stations. 相似文献
142.
George Nikolakopoulos Kostas Alexis 《International Journal of Control, Automation and Systems》2013,11(2):389-397
In this article, a switching networked attitude controller for an unmanned quadrotor over a wireless sensor network is presented. To deal with the network induced time varying delays, the quadrotor is being modeled as a switching time varying linear system, while the applied switching output feedback control scheme, is calculated based on Linear Matrix Inequalities, and is able to guarantee the stability of the quadrotor under arbitrary changes in the time delays. 相似文献
143.
Recently a power study of some popular tests for bivariate independence based on ranks has been conducted. An alternative class of tests appropriate for testing not only bivariate, but also multivariate independence is developed, and their small-sample performance is studied. The test statistics employ the familiar equation between the joint characteristic function and the product of component characteristic functions, and may be written in a closed form convenient for computer implementation. Simulations on a distribution-free version of the new test statistic show that the proposed method compares well to standard methods of testing independence via the empirical distribution function. The methods are applied to multivariate observations incorporating data from several major stock-market indices. Issues pertaining to the theoretical properties of the new test are also addressed. 相似文献
144.
Reconfigurable computing (RC) applications employing both microprocessors and FPGAs have potential for large speedup when compared with traditional (software) parallel applications. However, this potential is marred by the additional complexity of these dual-paradigm systems, making it difficult to identify performance bottlenecks and achieve desired performance. Performance analysis concepts and tools are well researched and widely available for traditional parallel applications but are lacking in RC, despite being of great importance due to the applications’ increased complexity. In this paper, we explore challenges and present new techniques in automated instrumentation, runtime measurement, and visualization of RC application behavior. We also present ideas for integration with conventional performance analysis tools to create a unified tool for RC applications as well as our initial framework for FPGA instrumentation and measurement. Results from a case study are provided using a prototype of this new tool. 相似文献
145.
Parag Chaudhuri George Papagiannakis Nadia Magnenat-Thalmann 《The Visual computer》2008,24(7-9):525-533
In this paper we present a new character animation technique in which the animation adapts itself based on the change in the user’s perspective, so that when the user moves and their point of viewing the animation changes, then the character animation adapts itself in response to that change. The resulting animation, generated in real-time, is a blend of key animations provided a priori by the animator. The blending is done with the help of efficient dual-quaternion transformation blending. The user’s point of view is tracked using either computer vision techniques or a simple user-controlled input modality, such as mouse-based input. This tracked point of view is then used to suitably select the blend of animations. We show a way to author and use such animations in both virtual as well as augmented reality scenarios and demonstrate that it significantly heightens the sense of presence for the users when they interact with such self adaptive animations of virtual characters. 相似文献
146.
Educational software games aim at increasing the students’ motivation and engagement while they learn. However, if software games are targeted to school classrooms they have to be usable and likeable by all students. Usability of virtual reality games may be a problem because these games tend to have complex user interfaces so that they are more attractive. Moreover, if the games acquire an educational content they may lose the attractiveness and appeal that they have on users who are familiar with commercial games. Consequently, likeability may also be questioned. In this paper, we address the issue of usability and likeability of a virtual reality game that is meant to teach students geography. We describe the evaluation experiments conducted, which involved three categories of students in terms of their level of game-playing expertise: novice, intermediate and expert game players. The evaluation results showed that the game was indeed usable and likeable but there was scope for usability and likeability improvement so that the educational benefits may be maximised for all categories of students. The evaluation studies reported in this paper, revealed important issues about further research on virtual reality educational games. 相似文献
147.
We address concerns about the sustainability of the open source content model by examining the effect of external appropriation, whereby the product of open source contributors’ efforts is monetized by a party that did not contribute to the project, on intended effort withdrawal (reduction in contribution level). We examine both the personality of contributors and their contextual motivations to contribute, using a scenario-based survey of Wikipedia contributors. The findings suggest that perceived justice of the open source license terms, and intrinsic motivations are both negatively related with effort withdrawal intentions. Moreover, we find that the effect of the fairness personality trait on effort withdrawal is stronger for individuals who are low in perceived justice and weaker for individuals high in justice. The findings of factors predicting effort withdrawal contribute to the open source literature, which tends to focus on contribution and motivations, but not on what impacts changes in individual contribution levels. 相似文献
148.
Jianyong Wang Yuzhou Zhang Lizhu Zhou George Karypis Charu C. Aggarwal 《Data mining and knowledge discovery》2009,18(1):1-29
In recent years we have witnessed several applications of frequent sequence mining, such as feature selection for protein
sequence classification and mining block correlations in storage systems. In typical applications such as clustering, it is
not the complete set but only a subset of discriminating frequent subsequences which is of interest. One approach to discovering
the subset of useful frequent subsequences is to apply any existing frequent sequence mining algorithm to find the complete
set of frequent subsequences. Then, a subset of interesting subsequences can be further identified. Unfortunately, it is very
time consuming to mine the complete set of frequent subsequences for large sequence databases. In this paper, we propose a
new algorithm, CONTOUR, which efficiently mines a subset of high-quality subsequences directly in order to cluster the input
sequences. We mainly focus on how to design some effective search space pruning methods to accelerate the mining process and
discuss how to construct an accurate clustering algorithm based on the result of CONTOUR. We conducted an extensive performance
study to evaluate the efficiency and scalability of CONTOUR, and the accuracy of the frequent subsequence-based clustering
algorithm. 相似文献
149.
Graph matching is a fundamental problem that arises frequently in the areas of distributed control, computer vision, and facility allocation. In this paper, we consider the optimal graph matching problem for weighted graphs, which is computationally challenging due the combinatorial nature of the set of permutations. Contrary to optimization-based relaxations to this problem, in this paper we develop a novel relaxation by constructing dynamical systems on the manifold of orthogonal matrices. In particular, since permutation matrices are orthogonal matrices with nonnegative elements, we define two gradient flows in the space of orthogonal matrices. The first minimizes the cost of weighted graph matching over orthogonal matrices, whereas the second minimizes the distance of an orthogonal matrix from the finite set of all permutations. The combination of the two dynamical systems converges to a permutation matrix, which provides a suboptimal solution to the weighted graph matching problem. Finally, our approach is shown to be promising by illustrating it on nontrivial problems. 相似文献
150.
Chung-In Um In-Han Kim Yeon-Mu Choi Thomas F. George 《Journal of Low Temperature Physics》1994,95(3-4):547-578
The temperature variations of the diffusion coefficientD(T), thermal diffusion ratio k
T
(T) and thermal conductivity (T) in a dilute solution of3He atom in two-dimensional liquid helium are evaluated explicitly by solving the kinetic equations via phonon-phonon, phonon-roton, roton-roton, impurityelementary excitation and impurity-impurity scatterings. In the low-temperature region, the main contributions toD(T) and (T) come from the interactions between phonons and impurities, while in the high-temperature region the interactions between impurities and whole elementary excitations contribute more strongly toD(T) and (T) than those of only elementary excitations. For a dilute solution, the thermal diffusion ratio k
T
(T), neglecting the internal mass counterflow, is much smaller than the effective thermal diffusion ratio k
T
*
(T), which is a function of thermostatic properties. The effective thermal conductivity eff is much larger than the thermal conductivity and has different temperature dependence from the thermal conductivity. The behaviors of the two-dimensional diffusion coefficient and thermal conductivity are much like the bulk case, where they exhibit exponential decay with increasing temperature, although they are much smaller than those of the bulk case. 相似文献