全文获取类型
收费全文 | 34419篇 |
免费 | 3433篇 |
国内免费 | 1641篇 |
专业分类
电工技术 | 2488篇 |
技术理论 | 1篇 |
综合类 | 2139篇 |
化学工业 | 5810篇 |
金属工艺 | 2010篇 |
机械仪表 | 2161篇 |
建筑科学 | 2757篇 |
矿业工程 | 1097篇 |
能源动力 | 967篇 |
轻工业 | 2571篇 |
水利工程 | 650篇 |
石油天然气 | 1851篇 |
武器工业 | 293篇 |
无线电 | 4173篇 |
一般工业技术 | 4343篇 |
冶金工业 | 1438篇 |
原子能技术 | 456篇 |
自动化技术 | 4288篇 |
出版年
2024年 | 207篇 |
2023年 | 722篇 |
2022年 | 1466篇 |
2021年 | 1779篇 |
2020年 | 1334篇 |
2019年 | 1067篇 |
2018年 | 1170篇 |
2017年 | 1340篇 |
2016年 | 1091篇 |
2015年 | 1537篇 |
2014年 | 1887篇 |
2013年 | 2070篇 |
2012年 | 2229篇 |
2011年 | 2315篇 |
2010年 | 1954篇 |
2009年 | 1944篇 |
2008年 | 1900篇 |
2007年 | 1686篇 |
2006年 | 1731篇 |
2005年 | 1387篇 |
2004年 | 913篇 |
2003年 | 916篇 |
2002年 | 848篇 |
2001年 | 745篇 |
2000年 | 767篇 |
1999年 | 816篇 |
1998年 | 647篇 |
1997年 | 566篇 |
1996年 | 493篇 |
1995年 | 442篇 |
1994年 | 327篇 |
1993年 | 253篇 |
1992年 | 232篇 |
1991年 | 146篇 |
1990年 | 127篇 |
1989年 | 116篇 |
1988年 | 83篇 |
1987年 | 52篇 |
1986年 | 31篇 |
1985年 | 36篇 |
1984年 | 20篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 3篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
X Jiang M Zhang Y Ding J Yao H Chen D Zhu M Muramatu 《Canadian Metallurgical Quarterly》1998,124(5):980-985
BACKGROUND AND PURPOSE: Mood disorders are common after stroke and may impede physical, functional, and cognitive recovery, making early identification and treatment of potential importance. We aimed to compare the accuracy of the General Health Questionnaire (GHQ-30) and the Hospital Anxiety and Depression (HAD) Scale in detecting psychiatric morbidity after stroke and to determine the most suitable cutoff points for different purposes. METHODS: One hundred five hospital-referred stroke patients completed both the GHQ-30 and HAD Scale 6 months after onset before a blinded psychiatric assessment in which the Schedule for Affective Disorders and Schizophrenia with some supplementary questions was used to determine a DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) diagnosis. Measures were compared in terms of sensitivity, specificity, and receiver operating characteristic curves. RESULTS: No significant differences were found between the GHQ-30 and the HAD Scale in identifying those patients with any DSM-IV diagnosis (P=0.95), grouped depression (P=0.56), or anxiety (P=0.25) disorders. The previously recommended cutoff points for identifying "cases" for the GHQ (4/5) and for the HAD Scale (8/9 and 11/12) were found to be suboptimal in this population. CONCLUSIONS: The GHQ-30 and HAD scale exhibited similar levels of sensitivity and specificity. Data are presented, taking into account the "cost" of false-positives and negatives, to allow a choice of cutoff points suitable for differing situations. 相似文献
52.
以20CrMnTi钢为例,建立了连续冷却渗碳模型;对变温渗碳质量进行了分析计算;对渗碳后的组织情况进行预测,从而对变温渗碳的可行性进行了理论论证. 相似文献
53.
Jian-You Guo Miao Yu Jing Wang Bao-Mei Yao Peng Jiao 《Computer Physics Communications》2010,181(3):550-556
We develop the complex scaling method within the relativistic framework by expanding the Dirac spinors in the complete set of eigensolutions of a harmonic oscillator potential, and present the theoretical formalism of describing the discrete bound and resonant states on the same footing. Based on a well established and frequently used model, we demonstrate the utility and applicability of the extended method and examine the stability of the results with respect to the variations of the parameters of the model. Satisfactory agreements are found for all the calculated results in comparison with some other calculations in references. Especially, the present calculation in the nonrelativistic limit gives a consistent result with that in the nonrelativistic calculation. 相似文献
54.
针对燃气行业人工抄表费时费力等问题,提出一种基于GPRS和无线多跳网络技术的燃气无线抄表系统,在分析传统抄表系统的结构以及传输方式优缺点的基础上介绍了系统的总体结构、工作原理以及各部分组成和功能。采用计算机网络和数据库等技术,使得该系统具有功能强大、使用方便、可扩展性好等特点,可实现对整个燃气输配系统的监控,有效提高燃气公司的管理水平和服务效率。 相似文献
55.
Segmenting center of interests (COIs) from pictures is an important but highly challenging problem for researchers in computer vision and image processing. The capability of understanding the meanings of pictures by computers can lead to breakthroughs in a wide range of applications including Web image search and online picture-sharing communities. In this paper, a two-level strategy is presented, which consists of a rough segmentation stage and a fine segmentation stage. In the first level, a picture is partitioned into four regions by using a block clustering method based on color and texture features, and the COI within the picture is distinguished from the background according to the principles of photographic composition. This stage aims to determine the approximate region of the target. In the second level, a novel active contour model is established based on shape information and vector method, where the image energy is defined by a hue gradient and the external energy is generated from either a triangular inner force or a supplementary force. This stage tries to extract the boundary of the target accurately. Experimental results on photos downloaded from the Internet show the feasibility and effectiveness of the proposed method. 相似文献
56.
一种基于组策略的过滤式特征选择算法 总被引:1,自引:0,他引:1
MRMR算法具有快速、高效等优势,在处理高维数据方面较为流行。基于此,提出一种基于组策略的MRMR改进算法(MRMRE),该算法不仅考虑单个特征属性的相关性与冗余性,同时针对特征组间的相互关系进行研究。算法以MRMR算法为框架,以CCA作为度量基准,选择SVMs作为基分类器,使其特征选择效果提升。在UCI机器学习数据库中图像与基因序列数据集上的大量实验表明:与MRMR算法相比,所提出的算法其特征选择结果具有更高的结果稳定性与分类精度。 相似文献
57.
Wireless channels comprise various signal characteristics that correspond to different features. This research applies digital signal processing to first excavate and categorize various features found in the channel data. Then, borrowing from graph theory, fast clustering analysis and decision tree modeling are introduced to identify unique “fingerprint” characteristics. Finally, two scenarios were tested using artificial neural networks to identify and verify their applicability in different geographical locations. 相似文献
58.
International Journal of Control, Automation and Systems - Vibration disturbances with variable instantaneous frequencies can be found in many industrial applications. Therefore, rejecting... 相似文献
59.
This paper proposes a method for solving the stochastic multiple criteria decision making (SMCDM) problem, where consequences of alternatives with respect to criteria are represented by random variables with probability distributions. Firstly, definitions and related analysis of dominance degree of one probability distribution over another are given. Then, by calculating the dominance degrees, the dominance degree matrix of alternative pairwise comparisons with respect to each criterion is built. Further, using PROMETHEE II method, an overall dominance degree matrix of alternative pairwise comparisons is constructed, and a net flow of each alternative is calculated. Based on the obtained net flows, a ranking of alternatives is determined. Finally, numerical examples for the three cases are given to illustrate the use of the proposed method. 相似文献
60.
Three-dimensional quantitative structure-activity relationship (3D-QSAR) models were developed using comparative molecular field analysis (CoMFA) and comparative molecular similarity analysis (CoMSIA) on a series of agonists of thyroid hormone receptor beta (TRbeta), which may lead to safe therapies for non-thyroid disorders while avoiding the cardiac side effects. The reasonable q(2) (cross-validated) values 0.600 and 0.616 and non-cross-validated r(2) values of 0.974 and 0.974 were obtained for CoMFA and CoMSIA models for the training set compounds, respectively. The predictive ability of two models was validated using a test set of 12 molecules which gave predictive correlation coefficients (r(pred)(2)) of 0.688 and 0.674, respectively. The Lamarckian Genetic Algorithm (LGA) of AutoDock 4.0 was employed to explore the binding mode of the compound at the active site of TRbeta. The results not only lead to a better understanding of interactions between these agonists and the thyroid hormone receptor beta but also can provide us some useful information about the influence of structures on the activity which will be very useful for designing some new agonist with desired activity. 相似文献