全文获取类型
收费全文 | 61216篇 |
免费 | 8372篇 |
国内免费 | 6479篇 |
专业分类
电工技术 | 4831篇 |
技术理论 | 2篇 |
综合类 | 6425篇 |
化学工业 | 2448篇 |
金属工艺 | 3665篇 |
机械仪表 | 7650篇 |
建筑科学 | 1795篇 |
矿业工程 | 2055篇 |
能源动力 | 911篇 |
轻工业 | 3199篇 |
水利工程 | 717篇 |
石油天然气 | 823篇 |
武器工业 | 405篇 |
无线电 | 5187篇 |
一般工业技术 | 3921篇 |
冶金工业 | 3441篇 |
原子能技术 | 113篇 |
自动化技术 | 28479篇 |
出版年
2024年 | 550篇 |
2023年 | 2402篇 |
2022年 | 3893篇 |
2021年 | 4022篇 |
2020年 | 3512篇 |
2019年 | 2509篇 |
2018年 | 1975篇 |
2017年 | 2081篇 |
2016年 | 2349篇 |
2015年 | 2556篇 |
2014年 | 3927篇 |
2013年 | 3257篇 |
2012年 | 4276篇 |
2011年 | 4585篇 |
2010年 | 3465篇 |
2009年 | 3434篇 |
2008年 | 3258篇 |
2007年 | 3742篇 |
2006年 | 3456篇 |
2005年 | 2998篇 |
2004年 | 2315篇 |
2003年 | 1975篇 |
2002年 | 1741篇 |
2001年 | 1444篇 |
2000年 | 1161篇 |
1999年 | 928篇 |
1998年 | 737篇 |
1997年 | 629篇 |
1996年 | 497篇 |
1995年 | 428篇 |
1994年 | 353篇 |
1993年 | 294篇 |
1992年 | 214篇 |
1991年 | 140篇 |
1990年 | 143篇 |
1989年 | 139篇 |
1988年 | 107篇 |
1987年 | 53篇 |
1986年 | 67篇 |
1985年 | 21篇 |
1983年 | 23篇 |
1982年 | 19篇 |
1965年 | 24篇 |
1964年 | 27篇 |
1963年 | 25篇 |
1961年 | 21篇 |
1959年 | 20篇 |
1958年 | 19篇 |
1957年 | 27篇 |
1955年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
介绍一种基于变频调速控制的全自动定量包装机,结构简单,组态灵活,性价比高,可广泛应用于食品饲料等行业,现场运行实践证明其通用性好,准确度和可靠性高、速度快、稳定性好。并论述变频器控制系统的设计及使用中的注意问题。 相似文献
93.
94.
The standardization data for the California Verbal Learning Test-Second Edition (CVLT-II; D. C. Delis, J. H. Kramer, E. Kaplan, & B. A. Ober, 2000) were used to evaluate the base rate of 6 specific discrepancies between various key variables. The results indicated that CVLT-II performance discrepancies should equal or exceed 1 or 1.5 z score points (depending on the individual comparison) in the hypothesized direction to be considered potentially unusual. However, because about 1 in 3 persons in the standardization sample displayed at least 1 such large discrepancy, it is concluded that these base rates should be viewed only as a starting point for interpretation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
95.
Three-dimensional models, or pharmacophores, describing Euclidean constraints on the location on small molecules of functional
groups (like hydrophobic groups, hydrogen acceptors and donors, etc.), are often used in drug design to describe the medicinal
activity of potential drugs (or ‘ligands’). This medicinal activity is produced by interaction of the functional groups on
the ligand with a binding site on a target protein. In identifying structure-activity relations of this kind there are three
principal issues: (1) It is often difficult to “align” the ligands in order to identify common structural properties that
may be responsible for activity; (2) Ligands in solution can adopt different shapes (or `conformations’) arising from torsional
rotations about bonds. The 3-D molecular substructure is typically sought on one or more low-energy conformers; and (3) Pharmacophore
models must, ideally, predict medicinal activity on some quantitative scale. It has been shown that the logical representation
adopted by Inductive Logic Programming (ILP) naturally resolves many of the difficulties associated with the alignment and
multi-conformation issues. However, the predictions of models constructed by ILP have hitherto only been nominal, predicting
medicinal activity to be present or absent. In this paper, we investigate the construction of two kinds of quantitative pharmacophoric
models with ILP: (a) Models that predict the probability that a ligand is “active”; and (b) Models that predict the actual
medicinal activity of a ligand. Quantitative predictions are obtained by the utilising the following statistical procedures
as background knowledge: logistic regression and naive Bayes, for probability prediction; linear and kernel regression, for
activity prediction. The multi-conformation issue and, more generally, the relational representation used by ILP results in
some special difficulties in the use of any statistical procedure. We present the principal issues and some solutions. Specifically,
using data on the inhibition of the protease Thermolysin, we demonstrate that it is possible for an ILP program to construct
good quantitative structure-activity models. We also comment on the relationship of this work to other recent developments
in statistical relational learning.
Editors: Tamás Horváth and Akihiro Yamamoto 相似文献
96.
Masters Rich S. W.; MacMahon Ken M. A.; Pall Hardev S. 《Canadian Metallurgical Quarterly》2004,49(1):79
Objective: This study examined whether disruption of performance is moderated in Parkinson's disease (PD) patients who acquire their motor behaviors in an implicit manner. Method: Twenty-seven patients with PD learned a hammering task in errorless (implicit) or errorful (explicit) conditions and were tested for robustness of motor performance under a secondary task load, which required them to continuously count backward as they performed the hammering task. Results: Patients in the errorless (implicit) motor learning condition exhibited robustness to secondary task loading, whereas patients in the errorful (explicit) motor learning condition did not. Conclusions: Implicit motor learning techniques should be considered by PD rehabilitation specialists in cases in which existing disruption to movements is exacerbated by conscious control. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
97.
讨论了不同分布两两NQD列的Jamison型加权乘积和的强稳定性。推广了不同分布独立列部分和和同分布NQD列部分和情形相类似的结论,得到了一些新的结果。 相似文献
98.
Rats exposed to a footshock show conditional fear when reexposed to the shock context. Immediate presentation of shock after placement in the context significantly reduces this fear. Preexposure to the context in the absence of shock, coupled with a minimum preshock interval during training, overcomes this immediate shock deficit. Because rats learn about the context during preexposure and express that learning after being reinforced, the context preexposure effect is an aversive analogue of latent learning. The authors examined the effect of the N-methyl-D-aspartate (NMDA) receptor antagonist D,L-2-amino-5-phosphovalerate (APV) on the facilitatory effect of context preexposure. Rats were preexposed to a chamber after APV administration. The next day they were placed in the same chamber without drug and received shock 35 s later. APV blocked the facilitatory effect of preexposure. Therefore NMDA receptors are important for contextual latent learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
基于支持向量机的多类分类研究 总被引:1,自引:0,他引:1
现今流行的分类方法的重要基础是传统的统计学,前提是要有足够的样本,当样本数目有限时容易出现过学习的问题,导致分类效果不理想。引入支持向量机方法,它基于统计学习理论,采用了结构风险最小化原则代替经验风险最小化原则,较好的解决了小样本学习的问题;又由于采用了核函数思想,把非线性空间的问题转换到线性空间,降低了算法的复杂度。对其相关内容包括优化算法及多类分类问题的解决进行了研究,最后用一个实例说明了该方法的可行性和有效性。 相似文献
100.
在文献[1]的基础上,提出几个改进的模糊加权平均滤波器。本文的方案不仅同时考虑了相邻像素对中心像素的兼容性以及中心像素对相邻像素的兼容性,而且还考虑到了权系数对局部环境的适应性。实验结果表明,该方法相比文献[1]中的模糊加权平均滤波器以及标准的均值滤波器、中值滤波器在噪声消除与边缘保留方面具有更好的性能。 相似文献