全文获取类型
收费全文 | 6302篇 |
免费 | 1133篇 |
国内免费 | 782篇 |
专业分类
电工技术 | 456篇 |
综合类 | 1105篇 |
化学工业 | 246篇 |
金属工艺 | 60篇 |
机械仪表 | 290篇 |
建筑科学 | 134篇 |
矿业工程 | 76篇 |
能源动力 | 84篇 |
轻工业 | 502篇 |
水利工程 | 134篇 |
石油天然气 | 130篇 |
武器工业 | 70篇 |
无线电 | 934篇 |
一般工业技术 | 414篇 |
冶金工业 | 49篇 |
原子能技术 | 72篇 |
自动化技术 | 3461篇 |
出版年
2024年 | 13篇 |
2023年 | 71篇 |
2022年 | 146篇 |
2021年 | 224篇 |
2020年 | 215篇 |
2019年 | 243篇 |
2018年 | 247篇 |
2017年 | 221篇 |
2016年 | 280篇 |
2015年 | 328篇 |
2014年 | 433篇 |
2013年 | 441篇 |
2012年 | 565篇 |
2011年 | 562篇 |
2010年 | 457篇 |
2009年 | 448篇 |
2008年 | 494篇 |
2007年 | 549篇 |
2006年 | 391篇 |
2005年 | 330篇 |
2004年 | 265篇 |
2003年 | 262篇 |
2002年 | 171篇 |
2001年 | 127篇 |
2000年 | 119篇 |
1999年 | 91篇 |
1998年 | 88篇 |
1997年 | 53篇 |
1996年 | 55篇 |
1995年 | 57篇 |
1994年 | 48篇 |
1993年 | 46篇 |
1992年 | 38篇 |
1991年 | 32篇 |
1990年 | 27篇 |
1989年 | 15篇 |
1988年 | 17篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有8217条查询结果,搜索用时 234 毫秒
101.
The Naive Bayes (NB) learning algorithm is simple and effective in many domains including text classification. However, its performance depends on the accuracy of the estimated conditional probability terms. Sometimes these terms are hard to be accurately estimated especially when the training data is scarce. This work transforms the probability estimation problem into an optimization problem, and exploits three metaheuristic approaches to solve it. These approaches are Genetic Algorithms (GA), Simulated Annealing (SA), and Differential Evolution (DE). We also propose a novel DE algorithm that uses multi-parent mutation and crossover operations (MPDE) and three different methods to select the final solution. We create an initial population by manipulating the solution generated by a method used for fine tuning the NB. We evaluate the proposed methods by using their resulted solutions to build NB classifiers and compare their results with the results of obtained from classical NB and Fine-Tuning Naïve Bayesian (FTNB) algorithm, using 53 UCI benchmark data sets. We name these obtained classifiers NBGA, NBSA, NBDE, and NB-MPDE respectively. We also evaluate the performance NB-MPDE for text-classification using 18 text-classification data sets, and compare its results with the results of obtained from FTNB, BNB, and MNB. The experimental results show that using DE in general and the proposed MPDE algorithm in particular are more convenient for fine-tuning NB than all other methods, including the other two metaheuristic methods (GA, and SA). They also indicate that NB-MPDE achieves superiority over classical NB, FTNB, NBDE, NBGA, NBSA, MNB, and BNB. 相似文献
102.
The performance of search operators varies across the different stages of the search/optimization process of evolutionary algorithms (EAs). In general, a single search operator may not do well in all these stages when dealing with different optimization and search problems. To mitigate this, adaptive search operator schemes have been introduced. The idea is that when a search operator hits a difficult patch (under-performs) in the search space, the EA scheme “reacts” to that by potentially calling upon a different search operator. Hence, several multiple-search operator schemes have been proposed and employed within EA. In this paper, a hybrid adaptive evolutionary algorithm based on decomposition (HAEA/D) that employs four different crossover operators is suggested. Its performance has been evaluated on the well-known IEEE CEC’09 test instances. HAEA/D has generated promising results which compare well against several well-known algorithms including MOEA/D, on a number of metrics such as the inverted generational distance (IGD), the hyper-volume, the Gamma and Delta functions. These results are included and discussed in this paper. 相似文献
103.
In order to quantitatively describe the difference of optimum active and inert ratio of various metamorphic grade coking coals,the rule of coke micro-strength index (MSI),determinated by adding different proportions of inert content to ten kinds of single coal,changing with active and inert ratio has been investigated.Three kinds of change rule of the MSI of ten kinds of single coal changing with active and inert ratio have been obtained in the research.It has been demonstrated that Gauss curve model is the optimal model to describe the optimum active and inert ratio of different metamorphic grade coals.On this basis,the optimum active and inert ratio of different metamorphic grade coals can be given. 相似文献
104.
《国际计算机数学杂志》2012,89(4):709-713
Let S be a semigroup. We consider the relation γ and its transitive closure γ*. The relation γ is the smallest equivalence relation on S so that S/γ* is a commutative semigroup. Based on the relation γ, we define a neighbourhood system for each element of S, and we present a general framework of the study of approximations in semigroups. The connections between semigroups and operators are examined. 相似文献
105.
Yu Malitsky 《Optimization methods & software》2018,33(1):140-164
The paper concerns with novel first-order methods for monotone variational inequalities. They use a very simple linesearch procedure that takes into account a local information of the operator. Also, the methods do not require Lipschitz continuity of the operator and the linesearch procedure uses only values of the operator. Moreover, when the operator is affine our linesearch becomes very simple, namely, it needs only simple vector–vector operations. For all our methods, we establish the ergodic convergence rate. In addition, we modify one of the proposed methods for the case of a composite minimization. Preliminary results from numerical experiments are quite promising. 相似文献
106.
Hugo Cruz-Hipolito Pablo Fernandez Ricardo Alcantara Javid Gherekhloo Maria Dolores Osuna Rafael De Prado 《International journal of molecular sciences》2015,16(9):21363-21377
Herbicides that inhibit acetyl coenzyme A carboxylase (ACCase) are commonly used in Mexico to control weedy grasses such as little seed canarygrass (Phalaris minor). These herbicides are classified into three major families (ariloxyphenoxypropionates (APP), cyclohexanodiones (CHD), and, recently, phenylpyrazolines (PPZ)). In this work, the resistance to ACCase (APP, CHD, and PPZ) inhibiting herbicides was studied in a biotype of Phalaris minor (P. minor) from Mexico, by carrying out bioassays at the whole-plant level and investigating the mechanism behind this resistance. Dose-response and ACCase in vitro activity assays showed cross-resistance to all ACCase herbicides used. There was no difference in the absorption, translocation, and metabolism of the 14C-diclofop-methyl between the R and S biotypes. The PCR generated CT domain fragments of ACCase from the R biotype and an S reference were sequenced and compared. The Ile-1781-Leu and Asp-2078-Gly point mutations were identified. These mutations could explain the loss of affinity for ACCase by the ACCase-inhibing herbicides. This is the first report showing that this substitution confers resistance to APP, CHD, and PPZ herbicides in P. minor from Mexico. The mutations have been described previously only in a few cases; however, this is the first study reporting on a pattern of cross-resistance with these mutations in P. minor. The findings could be useful for better management of resistant biotypes carrying similar mutations. 相似文献
107.
地震照明分析技术在深海地震数据采集设计中的应用 总被引:3,自引:0,他引:3
中国南海北部陆缘深水海域是形成大型油气区的有利区域。但由于该区水深急剧变化,峡谷纵横,构成了海底崎岖的地形地貌带,给该区的油气勘探带来了困难。本文利用高斯射线束地震波正演模拟方法,研究了南海白云凹陷深水崎岖海底区地震波对地下目的层的激发照明以及检波器接收照明能量的分布特征。针对不同接收缆数、不同排列长度及不同激发方向对海底崎岖界面和深部目的层的激发与接收照明能量的模拟分析,初步认识崎岖海底和下伏目的层地震波能量的分布特征,以及不同观测系统参数对地震采集能量的影响程度,为南海崎岖深海区地震采集参数设计提供了依据。 相似文献
108.
109.
鉴于低渗透油藏水平井压裂设计中参数多且交叉影响,采用常规方法进行正交优化存在较多局限性,结合油田生产实际,选择油井的累积产油量、累积注水量和累积产水量作为分析对象,提出一种以生产净现值最大化为目标,基于自适应遗传算法的水平井压裂参数优化方法.该方法根据个体适应值大小自动选择合适的交叉与变异概率,有效避免了传统遗传算法的“早熟”和盲目搜索等问题;通过编程实现了对水平段长度、裂缝半长、裂缝条数以及裂缝导流能力的自动优化求解.以长庆油区某油田的实际资料为基础,分析了五点井网下水平井压裂参数优化过程,分析结果表明,该方法参数覆盖范围更广,与枚举法需计算4 096次才能确定最优解相比,新方法只需迭代200次,大大提高了求解速度,增强了算法的实用性. 相似文献
110.