全文获取类型
收费全文 | 4062篇 |
免费 | 183篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 42篇 |
化学工业 | 791篇 |
金属工艺 | 92篇 |
机械仪表 | 98篇 |
建筑科学 | 258篇 |
矿业工程 | 13篇 |
能源动力 | 211篇 |
轻工业 | 438篇 |
水利工程 | 28篇 |
石油天然气 | 6篇 |
无线电 | 300篇 |
一般工业技术 | 842篇 |
冶金工业 | 240篇 |
原子能技术 | 33篇 |
自动化技术 | 858篇 |
出版年
2023年 | 24篇 |
2022年 | 48篇 |
2021年 | 96篇 |
2020年 | 64篇 |
2019年 | 77篇 |
2018年 | 80篇 |
2017年 | 107篇 |
2016年 | 123篇 |
2015年 | 100篇 |
2014年 | 145篇 |
2013年 | 297篇 |
2012年 | 252篇 |
2011年 | 338篇 |
2010年 | 218篇 |
2009年 | 226篇 |
2008年 | 259篇 |
2007年 | 231篇 |
2006年 | 178篇 |
2005年 | 159篇 |
2004年 | 145篇 |
2003年 | 121篇 |
2002年 | 118篇 |
2001年 | 79篇 |
2000年 | 56篇 |
1999年 | 46篇 |
1998年 | 63篇 |
1997年 | 57篇 |
1996年 | 39篇 |
1995年 | 45篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 27篇 |
1989年 | 20篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 24篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 10篇 |
排序方式: 共有4250条查询结果,搜索用时 140 毫秒
71.
We obtain subquadratic algorithms for 3SUM on integers and rationals in several models. On a standard word RAM with w-bit words, we obtain a running time of
. In the circuit RAM with one nonstandard AC
0 operation, we obtain
. In external memory, we achieve O(n
2/(MB)), even under the standard assumption of data indivisibility. Cache-obliviously, we obtain a running time of
. In all cases, our speedup is almost quadratic in the “parallelism” the model can afford, which may be the best possible.
Our algorithms are Las Vegas randomized; time bounds hold in expectation, and in most cases, with high probability. 相似文献
72.
Jolita Ralyt Manfred A. Jeusfeld Per Backlund Harald Kühn Nicolas Arni-Bloch 《Information Systems》2008,33(7-8):754
Interoperability is a key property of enterprise applications, which is hard to achieve due to the large number of interoperating components and semantic heterogeneity. The inherent complexity of interoperability problems implies that there exists no silver bullet to solve them. Rather, the knowledge about how to solve wicked interoperability problems is hidden in the application cases that expose those problems. The paper addresses the question of how to organise and use method knowledge to resolve interoperability problems. We propose the structure of a knowledge-based system that can deliver situation-specific solutions, called method chunks. Situational Method Engineering promotes modularisation and formalisation of method knowledge in the form of reusable method chunks, which can be combined to compose a situation-specific method. The method chunks are stored in a method chunk repository. In order to cater for management and retrieval, we introduce an Interoperability Classification Framework, which is used to classify and tag method chunks and to assess the project situation in which they are to be used. The classification framework incorporates technical as well as business and organisational aspects of interoperability. This is an important feature as interoperability problems typically are multifaceted spanning multiple aspects. We have applied the approach to analyse an industry case from the insurance sector to identify and classify a set of method chunks. 相似文献
73.
Andras Ferencz Erik G. Learned-Miller Jitendra Malik 《International Journal of Computer Vision》2008,77(1-3):3-24
Object identification is a specialized type of recognition in which the category (e.g. cars) is known and the goal is to recognize
an object’s exact identity (e.g. Bob’s BMW). Two special challenges characterize object identification. First, inter-object
variation is often small (many cars look alike) and may be dwarfed by illumination or pose changes. Second, there may be many
different instances of the category but few or just one positive “training” examples per object instance. Because variation
among object instances may be small, a solution must locate possibly subtle object-specific salient features, like a door
handle, while avoiding distracting ones such as specular highlights. With just one training example per object instance, however,
standard modeling and feature selection techniques cannot be used. We describe an on-line algorithm that takes one image from
a known category and builds an efficient “same” versus “different” classification cascade by predicting the most discriminative
features for that object instance. Our method not only estimates the saliency and scoring function for each candidate feature,
but also models the dependency between features, building an ordered sequence of discriminative features specific to the given
image. Learned stopping thresholds make the identifier very efficient. To make this possible, category-specific characteristics
are learned automatically in an off-line training procedure from labeled image pairs of the category. Our method, using the
same algorithm for both cars and faces, outperforms a wide variety of other methods. 相似文献
74.
Prolonged computer work with an extended neck is commonly believed to be associated with an increased risk of neck-shoulder disorders. The aim of this study was to compare neck postures during computer work between female cases with neck-shoulder disorders, and healthy referents. Based on physical examinations, 13 cases and 11 referents were selected among 70 female air traffic controllers with the same computer-based work tasks and identical workstations. Postures and movements were measured by inclinometers, placed on the forehead and upper back (C7/Th1) during authentic air traffic control. A recently developed method was applied to assess flexion/extension in the neck, calculated as the difference between head and upper back flexion/extension. Results: cases and referents did not differ significantly in neck posture (median neck flexion/extension: -10 degrees vs. -9 degrees ; p=0.9). Hence, the belief that neck extension posture is associated with neck-shoulder disorders in computer work is not supported by the present data. 相似文献
75.
76.
Skrökki A 《Meat science》1995,39(2):311-315
Additives such as sodium nitrate, potassium nitrate, sodium nitrite, phosphates and sodium chloride in sausages and various meat products were examined. Nitrate, nitrite and phosphate concentrations were below the maximum permitted levels, but most of the samples examined contained large amounts of sodium chloride and were thus "extra salted". Sausage factories should lower the salt concentrations in their products. 相似文献
77.
Erik Valentine Bachtiar Markus Rüggeberg Stefan Hering Michael Kaliske Peter Niemz 《Materials and Structures》2017,50(6):248
In this study, several theoretical models to numerically estimate shear properties of orthotropic materials are introduced. These approaches are based on the combination of Hankinson’s empirically derived formula with other empirical and analytical calculations. Next to shear moduli, which are estimated from the elastic moduli and Poisson’s ratios, shear strengths are also estimated from the in-axis strengths. The models are validated by mechanical tests on walnut wood (Juglans regia L.), for which a sufficient data set can be found in literature. The Arcan test is used to estimate the shear moduli, while the shear block test is used to estimate the shear strengths. The results show that the model, which is based on a combined use of Hankinson’s formula and tensor rotation, gives the best estimation of shear moduli as evaluated by the minimum differences to the experimentally obtained results. For the shear strengths, a combination of Hankinson’s formula and Norris’ failure criterion shows the best agreement in comparison to the experimental data. The theoretical calculations may be used for a time efficient estimation of shear modulus and strength in comparison to the very time-consuming experimental estimation. 相似文献
78.
Erik Svenning Martin Fagerström Fredrik Larsson 《International journal for numerical methods in engineering》2016,108(1):76-90
The effective response of microstructures undergoing crack propagation is studied by homogenizing the response of statistical volume elements (SVEs). Because conventional boundary conditions (Dirichlet, Neumann and strong periodic) all are inaccurate when cracks intersect the SVE boundary, we herein use first order homogenization to compare the performance of these boundary conditions during the initial stage of crack propagation in the microstructure, prior to macroscopic localization. Using weakly periodic boundary conditions that lead to a mixed formulation with displacements and boundary tractions as unknowns, we can adapt the traction approximation to the problem at hand to obtain better convergence with increasing SVE size. In particular, we show that a piecewise constant traction approximation, which has previously been shown to be efficient for stationary cracks, is more efficient than the conventional boundary conditions in terms of convergence also when crack propagation occurs on the microscale. The performance of the method is demonstrated by examples involving grain boundary crack propagation modelled by conventional cohesive interface elements as well as crack propagation modelled by means of the extended finite element method in combination with the concept of material forces. © 2016 The Authors. International Journal for Numerical Methods in Engineering Published by John Wiley & Sons Ltd. 相似文献
79.
80.
This paper presents a Danish study of mitigation directed at nature protection in environmental impact assessment (EIA) of infrastructure projects. The study is based on a document analysis of EIA reports, a workshop held with EIA professionals, and a study of two cases. The paper takes a point of departure in the mitigation hierarchy as a central conceptual framework, identifies which mitigation measures have been suggested in the EIA reports, and compares this to the mitigation hierarchy. Further, the paper explores the dynamics behind which mitigation measures are chosen and later implemented. The findings point to a discrepancy between the prevention principle embedded in the mitigation hierarchy and the actual EIA practice with increased use of nature compensation. Further, the research reveals significant variation in the design of mitigation measures, e.g. in the level of detail used in describing them and the level of clarity as to aims and actions. 相似文献