全文获取类型
收费全文 | 155036篇 |
免费 | 6457篇 |
国内免费 | 3160篇 |
专业分类
电工技术 | 4637篇 |
技术理论 | 6篇 |
综合类 | 6599篇 |
化学工业 | 23740篇 |
金属工艺 | 8624篇 |
机械仪表 | 7744篇 |
建筑科学 | 7315篇 |
矿业工程 | 2951篇 |
能源动力 | 3304篇 |
轻工业 | 8229篇 |
水利工程 | 2255篇 |
石油天然气 | 5590篇 |
武器工业 | 460篇 |
无线电 | 16697篇 |
一般工业技术 | 25303篇 |
冶金工业 | 6497篇 |
原子能技术 | 1000篇 |
自动化技术 | 33702篇 |
出版年
2024年 | 301篇 |
2023年 | 1263篇 |
2022年 | 2104篇 |
2021年 | 2888篇 |
2020年 | 2198篇 |
2019年 | 1963篇 |
2018年 | 16314篇 |
2017年 | 15539篇 |
2016年 | 11801篇 |
2015年 | 3277篇 |
2014年 | 3650篇 |
2013年 | 4392篇 |
2012年 | 7420篇 |
2011年 | 14057篇 |
2010年 | 12301篇 |
2009年 | 9361篇 |
2008年 | 10482篇 |
2007年 | 11362篇 |
2006年 | 3898篇 |
2005年 | 4619篇 |
2004年 | 3388篇 |
2003年 | 3239篇 |
2002年 | 2389篇 |
2001年 | 1727篇 |
2000年 | 1967篇 |
1999年 | 2102篇 |
1998年 | 1816篇 |
1997年 | 1451篇 |
1996年 | 1449篇 |
1995年 | 1195篇 |
1994年 | 968篇 |
1993年 | 725篇 |
1992年 | 557篇 |
1991年 | 450篇 |
1990年 | 327篇 |
1989年 | 254篇 |
1988年 | 235篇 |
1987年 | 142篇 |
1986年 | 120篇 |
1985年 | 96篇 |
1984年 | 66篇 |
1983年 | 40篇 |
1982年 | 42篇 |
1968年 | 46篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
Yang Qin Frieder Jäkle 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(1):149-157
The binding of Lewis bases to organoboron polymeric Lewis acids has been studied and the parameters that determine the complexation
equilibrium have been investigated, which include (i) the strength of the individual Lewis acids and Lewis bases, (ii) concentration,
and (iii) temperature. While the strongly Lewis acidic borane polymers poly(4-bis(pentafluorophenyl)borylstyrene) (PS-BPf) and poly(4-(di-2-thienylboryl)styrene) (PS-BTh) form isolable complexes with strong Lewis bases such as 4-t-butylpyridine (tPy), a temperature dependent equilibrium is established with weaker bases such as THF. Similarly, the weakly Lewis acidic
boronate polymer poly(4-diethoxyborylstyrene) (PS-BOEt) undergoes a temperature dependent equilibrium with the strong Lewis base 4-dimethylaminopyridine (DMAP), while poly(4-pinacolatoborylstyrene)
(PS-BPin) does not significantly bind to pyridine bases. Decomplexation of PS-BTh·
t
Py is achieved by treatment with the stronger Lewis acid, B(C6F5)3, thereby confirming the reversible nature of the polymeric Lewis acid–base adducts.
This paper is dedicated to Professor Ian Manners in gratitude of his guidance throughout the years and recognition of his
scientific accomplishments 相似文献
997.
Case-based reasoning (CBR) is one of the main forecasting methods in business forecasting, which performs well in prediction and holds the ability of giving explanations for the results. In business failure prediction (BFP), the number of failed enterprises is relatively small, compared with the number of non-failed ones. However, the loss is huge when an enterprise fails. Therefore, it is necessary to develop methods (trained on imbalanced samples) which forecast well for this small proportion of failed enterprises and performs accurately on total accuracy meanwhile. Commonly used methods constructed on the assumption of balanced samples do not perform well in predicting minority samples on imbalanced samples consisting of the minority/failed enterprises and the majority/non-failed ones. This article develops a new method called clustering-based CBR (CBCBR), which integrates clustering analysis, an unsupervised process, with CBR, a supervised process, to enhance the efficiency of retrieving information from both minority and majority in CBR. In CBCBR, various case classes are firstly generated through hierarchical clustering inside stored experienced cases, and class centres are calculated out by integrating cases information in the same clustered class. When predicting the label of a target case, its nearest clustered case class is firstly retrieved by ranking similarities between the target case and each clustered case class centre. Then, nearest neighbours of the target case in the determined clustered case class are retrieved. Finally, labels of the nearest experienced cases are used in prediction. In the empirical experiment with two imbalanced samples from China, the performance of CBCBR was compared with the classical CBR, a support vector machine, a logistic regression and a multi-variant discriminate analysis. The results show that compared with the other four methods, CBCBR performed significantly better in terms of sensitivity for identifying the minority samples and generated high total accuracy meanwhile. The proposed approach makes CBR useful in imbalanced forecasting. 相似文献
998.
Noises are inevitably introduced in digital image acquisition processes, and thus image denoising is still a hot research problem. Different from local methods operating on local regions of images, the non-local methods utilize non-local information (even the whole image) to accomplish image denoising. Due to their superior performance, the non-local methods have recently drawn more and more attention in the image denoising community. However, these methods generally do not work well in handling complicated noises with different levels and types. Inspired by the fact in machine learning field that multi-kernel methods are more robust and effective in tackling complex problems than single-kernel ones, we establish a general non-local denoising model based on multi-kernel-induced measures (GNLMKIM for short), which provides us a platform to analyze some existing and design new filters. With the help of GNLMKIM, we reinterpret two well-known non-local filters in the united view and extend them to their novel multi-kernel counterparts. The comprehensive experiments indicate that these novel filters achieve encouraging denoising results in both visual effect and PSNR index. 相似文献
999.
Multiset canonical correlation analysis (MCCA) is a powerful technique for analyzing linear correlations among multiple representation data. However, it usually fails to discover the intrinsic geometrical and discriminating structure of multiple data spaces in real-world applications. In this paper, we thus propose a novel algorithm, called graph regularized multiset canonical correlations (GrMCCs), which explicitly considers both discriminative and intrinsic geometrical structure in multiple representation data. GrMCC not only maximizes between-set cumulative correlations, but also minimizes local intraclass scatter and simultaneously maximizes local interclass separability by using the nearest neighbor graphs on within-set data. Thus, it can leverage the power of both MCCA and discriminative graph Laplacian regularization. Extensive experimental results on the AR, CMU PIE, Yale-B, AT&T, and ETH-80 datasets show that GrMCC has more discriminating power and can provide encouraging recognition results in contrast with the state-of-the-art algorithms. 相似文献
1000.