全文获取类型
收费全文 | 1203篇 |
免费 | 303篇 |
国内免费 | 291篇 |
专业分类
电工技术 | 65篇 |
综合类 | 164篇 |
化学工业 | 24篇 |
金属工艺 | 8篇 |
机械仪表 | 50篇 |
建筑科学 | 15篇 |
矿业工程 | 12篇 |
能源动力 | 12篇 |
轻工业 | 8篇 |
水利工程 | 19篇 |
石油天然气 | 7篇 |
武器工业 | 9篇 |
无线电 | 211篇 |
一般工业技术 | 43篇 |
冶金工业 | 5篇 |
原子能技术 | 2篇 |
自动化技术 | 1143篇 |
出版年
2024年 | 8篇 |
2023年 | 30篇 |
2022年 | 43篇 |
2021年 | 61篇 |
2020年 | 68篇 |
2019年 | 67篇 |
2018年 | 54篇 |
2017年 | 76篇 |
2016年 | 95篇 |
2015年 | 105篇 |
2014年 | 130篇 |
2013年 | 90篇 |
2012年 | 129篇 |
2011年 | 134篇 |
2010年 | 109篇 |
2009年 | 101篇 |
2008年 | 104篇 |
2007年 | 107篇 |
2006年 | 71篇 |
2005年 | 53篇 |
2004年 | 45篇 |
2003年 | 18篇 |
2002年 | 27篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有1797条查询结果,搜索用时 328 毫秒
1.
Somnath Karmakar 《Polycyclic Aromatic Compounds》2019,39(2):159-171
Eigensolutions of {X( = C,B,N),Y( = C,B,N)}-cyclacene graphs with next nearest neighbor (nnn) interactions have been obtained in analytical forms by adapting n-fold rotational symmetry followed by two-fold rotational symmetry (or a plane of symmetry). Expressions of eigensolution indicate the subspectral relationship among such cyclacenes with an even number of hexagonal rings e.g., eigenvalues of {X,Y}-di-cyclacene are found in the eigenspectra of all such even cyclacenes. Total π-electron energies and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps are calculated using the analytical expressions obtained and are found to vary negligibly with the variation of nnn interactions in such cyclacenes. Total π-electron energy is found to increase due to increase in restriction intensity of nnn interactions, whereas the HOMO–LUMO gap of polyacenecs having the even number of hexagonal rings and with one electron at each site (atom) decreases with increase in the restriction intensity since such systems contain degenerate half-filled HOMO (bonding or nonbonding) that are much more vulnerable for perturbations imposed through nnn interactions. 相似文献
2.
3.
毛家河水电站库区岩溶发育特征及邻谷渗漏分析 总被引:1,自引:0,他引:1
毛家河水电站位于碳酸盐岩地区,库首距左岸邻谷可渡河14—23km、距右岸邻谷北盘江干流14.8km,水库两岸大型落水洞、溶洞及地下岩溶管道相对较为发育。为初步判断水库存在邻谷渗漏的可能性,对水库两岸可溶岩地层岩溶发育形态、特征及规律进行了勘察,并根据现场地质调查资料对3条可疑渗漏带进行了分析论证。 相似文献
4.
We study the application of the geographic nearest neighbor approach to two problems. The first problem is the construction of an approximately minimum length rectilinear Steiner tree for a set ofn points in the plane. For this problem, we introduce a variation of a subgraph of sizeO(n) used by YaO [31] for constructing minimum spanning trees. Using this subgraph, we improve the running times of the heuristics discussed by Bern [6] fromO(n
2
log
n) toO(n log2
n). The second problem is the construction of a rectilinear minimum spanning tree for a set ofn noncrossing line segments in the plane. We present an optimalO(n logn) algorithm for this problem. The rectilinear minimum spanning tree for a set of points can thus be computed optimally without using the Voronoi diagram. This algorithm can also be extended to obtain a rectilinear minimum spanning tree for a set of nonintersecting simple polygons.The results in this paper are a part of Y. C. Yee's Ph.D. thesis done at SUNY at Albany. He was supported in part by NSF Grants IRI-8703430 and CCR-8805782. S. S. Ravi was supported in part by NSF Grants DCI-86-03318 and CCR-89-05296. 相似文献
5.
DKNNS:面向延迟敏感型应用的可扩展精确分布式K近邻搜索算法研究 总被引:1,自引:0,他引:1
为了降低用户访问延迟,延迟敏感型网络应用需要选择合适的邻近服务节点响应用户访问请求.分布式K近邻搜索通过可扩展的选择距任意用户节点邻近的K个服务节点,可以有效满足网络应用延迟优化的目的.已有工作在精确度以及可扩展性等方面存在不足.针对可扩展精确的K近邻搜索问题,文中提出了分布式K近邻搜索方法DKNNS(distributed K nearest neighbor search).DKNNS将大量的服务节点组织为邻近性感知的多级环,通过最远节点搜索机制选择优化的K近邻搜索初始化节点,然后基于回退方式快速的在目标节点邻近区域发现K个近邻.基于理论分析,模拟测试以及真实环境下的部署实验发现,在不同规模的节点集合下,DKNNS算法能够确定近似最优的K个服务节点.且DKNNS的查询延迟,查询开销均显著低于Meridian算法.最后,DKNNS的返回结果相对于Meridian具有较高的稳定性. 相似文献
6.
7.
链路预测是研究复杂网络结构和演化机制的重要工具,提高链路预测的精度具有重要价值。针对传统的基于网络拓扑结构相似性算法预测精度偏低的问题,从网络优化去噪的角度进行分析,提出了一种基于K-shell分解与邻居节点度(KSDNN)去噪的链路预测方法。该方法首先从全局的角度通过K-shell分解对复杂网络中所有节点进行重要性排序,然后从局部的角度结合节点邻居节点的度对节点重要性进行综合评判,最后对网络数据进行优化后进行链路预测。通过在四个不同的真实网络进行验证,实验结果表明,所提方法预测精度优于K-shell去噪的方法,且相较于传统算法预测精度平均提升了2%左右。 相似文献
8.
《Computer methods and programs in biomedicine》2014,116(3):226-235
Breast cancer continues to be a significant public health problem in the world. Early detection is the key for improving breast cancer prognosis. Mammogram breast X-ray is considered the most reliable method in early detection of breast cancer. However, it is difficult for radiologists to provide both accurate and uniform evaluation for the enormous mammograms generated in widespread screening. Micro calcification clusters (MCCs) and masses are the two most important signs for the breast cancer, and their automated detection is very valuable for early breast cancer diagnosis. The main objective is to discuss the computer-aided detection system that has been proposed to assist the radiologists in detecting the specific abnormalities and improving the diagnostic accuracy in making the diagnostic decisions by applying techniques splits into three-steps procedure beginning with enhancement by using Histogram equalization (HE) and Morphological Enhancement, followed by segmentation based on Otsu's threshold the region of interest for the identification of micro calcifications and mass lesions, and at last classification stage, which classify between normal and micro calcifications ‘patterns and then classify between benign and malignant micro calcifications. In classification stage; three methods were used, the voting K-Nearest Neighbor classifier (K-NN) with prediction accuracy of 73%, Support Vector Machine classifier (SVM) with prediction accuracy of 83%, and Artificial Neural Network classifier (ANN) with prediction accuracy of 77%. 相似文献
9.
Abdul Majid Safdar Ali Mubashar Iqbal Nabeela Kausar 《Computer methods and programs in biomedicine》2014
This study proposes a novel prediction approach for human breast and colon cancers using different feature spaces. The proposed scheme consists of two stages: the preprocessor and the predictor. In the preprocessor stage, the mega-trend diffusion (MTD) technique is employed to increase the samples of the minority class, thereby balancing the dataset. In the predictor stage, machine-learning approaches of K-nearest neighbor (KNN) and support vector machines (SVM) are used to develop hybrid MTD-SVM and MTD-KNN prediction models. MTD-SVM model has provided the best values of accuracy, G-mean and Matthew's correlation coefficient of 96.71%, 96.70% and 71.98% for cancer/non-cancer dataset, breast/non-breast cancer dataset and colon/non-colon cancer dataset, respectively. We found that hybrid MTD-SVM is the best with respect to prediction performance and computational cost. MTD-KNN model has achieved moderately better prediction as compared to hybrid MTD-NB (Naïve Bayes) but at the expense of higher computing cost. MTD-KNN model is faster than MTD-RF (random forest) but its prediction is not better than MTD-RF. To the best of our knowledge, the reported results are the best results, so far, for these datasets. The proposed scheme indicates that the developed models can be used as a tool for the prediction of cancer. This scheme may be useful for study of any sequential information such as protein sequence or any nucleic acid sequence. 相似文献
10.