全文获取类型
收费全文 | 32321篇 |
免费 | 2982篇 |
国内免费 | 1490篇 |
专业分类
电工技术 | 3109篇 |
技术理论 | 1篇 |
综合类 | 3625篇 |
化学工业 | 4664篇 |
金属工艺 | 735篇 |
机械仪表 | 1618篇 |
建筑科学 | 2379篇 |
矿业工程 | 690篇 |
能源动力 | 694篇 |
轻工业 | 2363篇 |
水利工程 | 549篇 |
石油天然气 | 845篇 |
武器工业 | 221篇 |
无线电 | 2500篇 |
一般工业技术 | 3788篇 |
冶金工业 | 1363篇 |
原子能技术 | 234篇 |
自动化技术 | 7415篇 |
出版年
2024年 | 103篇 |
2023年 | 358篇 |
2022年 | 590篇 |
2021年 | 804篇 |
2020年 | 846篇 |
2019年 | 837篇 |
2018年 | 808篇 |
2017年 | 981篇 |
2016年 | 1118篇 |
2015年 | 1180篇 |
2014年 | 1897篇 |
2013年 | 1974篇 |
2012年 | 2424篇 |
2011年 | 2659篇 |
2010年 | 2003篇 |
2009年 | 2020篇 |
2008年 | 1761篇 |
2007年 | 2081篇 |
2006年 | 1872篇 |
2005年 | 1532篇 |
2004年 | 1322篇 |
2003年 | 1224篇 |
2002年 | 998篇 |
2001年 | 769篇 |
2000年 | 662篇 |
1999年 | 568篇 |
1998年 | 500篇 |
1997年 | 399篇 |
1996年 | 329篇 |
1995年 | 306篇 |
1994年 | 234篇 |
1993年 | 196篇 |
1992年 | 165篇 |
1991年 | 129篇 |
1990年 | 120篇 |
1989年 | 129篇 |
1988年 | 112篇 |
1987年 | 72篇 |
1986年 | 59篇 |
1985年 | 83篇 |
1984年 | 89篇 |
1983年 | 105篇 |
1982年 | 115篇 |
1981年 | 41篇 |
1980年 | 31篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1964年 | 11篇 |
1955年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Numerical dissipation acts as artificial viscosity to make smoke viscous. Reducing numerical dissipation is able to recover visual details smeared out by the numerical dissipation. Great efforts have been devoted to suppress the numerical dissipation in smoke simulation in the past few years. In this paper we investigate methods of combating the numerical dissipation. We describe visual consequences of the numerical dissipation and explore sources that introduce the numerical dissipation into course of smoke simulation. Methods are investigated from various aspects including grid variation, high-order advection, sub-grid compensation, invariant conservation, and particle-based improvement, followed by discussion and comparison in terms of visual quality, computational overhead, ease of implementation, adaptivity, and scalability, which leads to their different applicability to various application scenarios. 相似文献
32.
In the present research, nanostructured Pd–Cd alloy electrocatalysts with different compositions were produced using the electrodeposition process. The morphology of the samples was studied by scanning electron microscopy analysis. Also, the elemental composition of the samples was determined by energy-dispersive X-ray spectroscopy and elemental mapping tests. Tafel polarization and electrochemical impedance spectroscopy methods were employed to determine the electrochemical corrosion properties of the synthesized samples in a solution containing 0.5 M sulfuric acid and 0.1 M formic acid. The linear sweep voltammetry, cyclic voltammetry, and chronoamperometry techniques were also employed to evaluate the electrocatalytic activity of prepared samples toward the oxidation of formic acid. In this respect, the influence of some factors such as formic acid and sulfuric acid concentrations and also potential scan rate was investigated. Compared to the pure Pd sample, the Pd–Cd samples were more reactive for the oxidation of formic acid. Besides, the sample with a lower amount of Pd (Pd1·3Cd) demonstrated much higher electrocatalytic activity than the Pd7·1Cd and Pd2·1Cd samples. The observed high mass activity of 15.06 A mg?1Pd for the Pd1·3Cd sample which is 21.1 times higher than Pd/C is an interesting result of this study. 相似文献
33.
This study addresses the problem of choosing the most suitable probabilistic model selection criterion for unsupervised learning
of visual context of a dynamic scene using mixture models. A rectified Bayesian Information Criterion (BICr) and a Completed
Likelihood Akaike’s Information Criterion (CL-AIC) are formulated to estimate the optimal model order (complexity) for a given
visual scene. Both criteria are designed to overcome poor model selection by existing popular criteria when the data sample
size varies from small to large and the true mixture distribution kernel functions differ from the assumed ones. Extensive
experiments on learning visual context for dynamic scene modelling are carried out to demonstrate the effectiveness of BICr
and CL-AIC, compared to that of existing popular model selection criteria including BIC, AIC and Integrated Completed Likelihood
(ICL). Our study suggests that for learning visual context using a mixture model, BICr is the most appropriate criterion given
sparse data, while CL-AIC should be chosen given moderate or large data sample sizes. 相似文献
34.
35.
We extend the definition of the classical Jacobi polynomials withindexes α, β>−1 to allow α and/or β to be negative integers. We show that the generalized Jacobi polynomials, with indexes corresponding to the number of boundary conditions in a given partial differential equation, are the natural basis functions for the spectral approximation of this partial differential equation. Moreover, the use of generalized Jacobi polynomials leads to much simplified analysis, more precise error estimates and well conditioned algorithms.Mathematics subject classification 1991. 65N35, 65N22, 65F05, 35J05 相似文献
36.
Feng Juanni Guo Xuefeng Xu Chunjie Zhang Zhongming 《中国稀土学报(英文版)》2006,24(1):120-120
As-east mierostruetures and their distribution of Mg-Zn-Y ternary alloy with high magnesium, low zinc and yttrium were examined using Nikon Epiphot optical microscopy (OM), RigakuD/max-3C X- ray diffraetion (XRD), and JEOL JSM-6700F scanning electron microscopy (SEM) equipped with an energydispersive X-ray spectroscopy (EDS). In the as-east mierostructures, Yttrium and zinc tend to segregate at grain boundaries, 相似文献
37.
38.
A Lattice Approach to Image Segmentation 总被引:1,自引:0,他引:1
Jean Serra 《Journal of Mathematical Imaging and Vision》2006,24(1):83-130
After a formal definition of segmentation as the largest partition of the space according to a criterion σ and a function
f, the notion of a morphological connection is reminded. It is used as an input to a central theorem of the paper (Theorem
8), that identifies segmentation with the connections that are based on connective criteria. Just as connections, the segmentations can then
be regrouped by suprema and infima. The generality of the theorem makes it valid for functions from any space to any other
one. Two propositions make precise the AND and OR combinations of connective criteria.
The soundness of the approach is demonstrated by listing a series of segmentation techniques. One considers first the cases
when the segmentation under study does not involve initial seeds. Various modes of regularity are discussed, which all derive
from Lipschitz functions. A second category of examples involves the presence of seeds around which the partition of the space
is organized. An overall proposition shows that these examples are a matter for the central theorem. Watershed and jump connection
based segmentations illustrate this type of situation. The third and last category of examples deals with cases when the segmentation
occurs in an indirect space, such as an histogram, and is then projected back on the actual space under study.
The relationships between filtering and segmentation are then investigated. A theoretical chapter introduces and studies the
two notions of a pulse opening and of a connected operator. The conditions under which a family of pulse openings can yield a connected filter are clarified. The ability of segmentations
to generate pyramids, or hierarchies, is analyzed. A distinction is made between weak hierarchies where the partitions increase
when going up in the pyramid, and the strong hierarchies where the various levels are structured as semi-groups, and particularly
as granulometric semi-groups.
The last section is based on one example, and goes back over the controversy about “lattice” versus “functional” optimization.
The problem is now tackled via a case of colour segmentation, where the saturation serves as a cursor between luminance and
hue. The emphasis is put on the difficulty of grouping the various necessary optimizations into a single one. 相似文献
39.
文章介绍了一种新型的短波跳频通信技术——差分跳频,分析了差分跳频技术区别于常规跳频技术的主要特点。针对按序列检测的信号接收方法,对差分跳频通信系统在AWGN信道下的性能进行了理论分析,同时做出相应的计算机仿真,证实了差分跳频通信技术和按序列检测方法的结合,使通信系统在AWGN信道下的性能得到了比较显著的提升。 相似文献
40.
几种酚类抗氧剂在润滑油中的应用 总被引:2,自引:0,他引:2
采用旋转氧弹法、高压差示扫描量热法等方法研究了5种酚类抗氧剂对6种润滑油基础油氧化安定性的改善效果。结果表明:向加氢基础油中加入0.25%(质量分数)抗氧剂2246-S和RHY510(含硫酚类抗氧剂),可使HVIWH125,HVIWH150,HVIWH500,KN4006,KN40105种润滑油基础油的诱导期由27~88min提高到226~397min;使HVIWH125,HVIWH150,HVIWH300,HVIWH500,KN4006,KN40106种润滑油基础油的起始氧化温度由193.34~198.90℃提高到205.48~230.27℃。 相似文献