全文获取类型
收费全文 | 26058篇 |
免费 | 5228篇 |
国内免费 | 3898篇 |
专业分类
电工技术 | 1450篇 |
技术理论 | 8篇 |
综合类 | 2796篇 |
化学工业 | 2192篇 |
金属工艺 | 688篇 |
机械仪表 | 1880篇 |
建筑科学 | 1612篇 |
矿业工程 | 750篇 |
能源动力 | 907篇 |
轻工业 | 689篇 |
水利工程 | 1013篇 |
石油天然气 | 1038篇 |
武器工业 | 227篇 |
无线电 | 4187篇 |
一般工业技术 | 2846篇 |
冶金工业 | 771篇 |
原子能技术 | 531篇 |
自动化技术 | 11599篇 |
出版年
2024年 | 318篇 |
2023年 | 774篇 |
2022年 | 1482篇 |
2021年 | 1510篇 |
2020年 | 1483篇 |
2019年 | 1201篇 |
2018年 | 1022篇 |
2017年 | 1178篇 |
2016年 | 1268篇 |
2015年 | 1257篇 |
2014年 | 1758篇 |
2013年 | 1864篇 |
2012年 | 2090篇 |
2011年 | 2146篇 |
2010年 | 1728篇 |
2009年 | 1698篇 |
2008年 | 1660篇 |
2007年 | 1746篇 |
2006年 | 1510篇 |
2005年 | 1264篇 |
2004年 | 1073篇 |
2003年 | 898篇 |
2002年 | 788篇 |
2001年 | 635篇 |
2000年 | 537篇 |
1999年 | 407篇 |
1998年 | 333篇 |
1997年 | 306篇 |
1996年 | 234篇 |
1995年 | 184篇 |
1994年 | 162篇 |
1993年 | 110篇 |
1992年 | 97篇 |
1991年 | 67篇 |
1990年 | 61篇 |
1989年 | 81篇 |
1988年 | 42篇 |
1987年 | 22篇 |
1986年 | 32篇 |
1985年 | 33篇 |
1984年 | 21篇 |
1983年 | 24篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1959年 | 4篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Cluster analysis in industrial market segmentation through artificial neural network 总被引:6,自引:0,他引:6
Market segmentation has commonly applied cluster analysis. This study intends to make the comparison of conventional two-stage method with proposed two-stage method through the simulated data. The proposed two-stage method is the combination of self-organizing feature maps and K-means method. The simulation results show that the proposed scheme is better than the conventional two-stage method based on the rate of misclassification. 相似文献
62.
Dan C. DeBorde William W. Woessner Bruce Lauerman Patrick Ball 《Water research》1998,32(12):3781-3785
At the present time, somatic and male-specific coliphage and human enterovirus groups are being considered as indicators of possible pathogenic human enteric virus contamination from fecal contamination. A primary attribute for any indicator of fecal contamination is its prevalence at the source and in associated ground water. It must be consistently found in the source material at concentrations that are measurable with available techniques. Over a period of ten months, male-specific and somatic coliphage ranged from 7000 to 4,000,000 PFU/L in the effluent from a multi-user septic-tank. Unlike the values determined for septic-tank effluent, coliphage concentrations measured in ground water over this same period only varied by five-fold. Coliphage concentration in ground water under the down-gradient edge of the drainfield contained 1000 PFU/L. This concentration decreased at −1 log10/5 m during 17.4 m of ground-water transport. From these data, coliphage concentrations in septic-tank effluent seem sufficient to allow their use as indicators of fecal contamination in ground water. 相似文献
63.
64.
浅谈抽水蓄能电站的特点及其优越性 总被引:2,自引:0,他引:2
本文介绍了国外抽水蓄能电站的发展过程与现状,修建抽水蓄能电站的八大优点。为了改善我省电力系统的运行条件,提出了在我省修建抽水蓄能电站的四点建议。 相似文献
65.
为了探讨长江上游流域水土流失及泥沙输移规律,选取嘉陵江中游的支流李子溪为典型流域进行分析研究,在实地调查,野外测验及应用1960年-1991年实测降雨、径流、输沙资料的基础上,利用单因子相关分析和多因子回归分析,分别建立了输水利沙量、最大输沙率计算方程。在此基础上,参照径流瞬时单位线原理,以线性时不变系统为基础,建立输沙瞬时单位线模型。通过输沙单位线与时段净侵蚀量的卷积得到流域出口断面的输沙率过程 相似文献
66.
New measurements of the vapor-phase viscosity of phenol were performed from 437 up to 624 K and for densities between 0.006 and 0.023 mol · L–1 in an all-quartz oscillating-disk viscometer with small gaps. Thus, including our own measurements reported earlier, experimental data are available in the temperature range between 376 and 639 K and in the density range from 0.001 up to 0.023 mol · L–1. The data were evaluated with a density series for the viscosity in which only a linear density contribution is included. The values of the second viscosity virial coefficient obtained for phenol as well as for benzene, toluene, and p-xylene were compared with results of the Rainwater-Friend theory and of the modified Enskog theory on the basis of the Lennard-Jones 12-6 potential. The agreement is reasonable, when the potential parameter ratios determined by Bich and Vogel are used. The influence of bound dimers seems to be already taken into account in the three-monomer contribution according to Hoffman and Curtiss.Paper dedicated to Professor Joseph Kestin. 相似文献
67.
The reduction of CO2 emissions and fuel consumption from road transportation constitutes an important pillar of the European Union strategy for implementing the Kyoto Protocol. The commitment to reduce passenger car average CO2 emissions at 140 g/km in 2008 signed by European car manufacturers and the European Commission is up to now the most important initiative towards limiting CO2 emissions from road transportation and particularly from passenger cars. Until today, annual reports show the manufacturers’ efforts in limiting CO2 emissions is within the intermediate target set by the commitment and these results are incorporated in emissions estimations and scientific studies. This paper analyses the origin of the progress achieved so far in CO2 emissions and attempts an assessment of the commitment using independent experimental emission data. Additionally, the applicability of the commitment-monitoring data into policy and decision-making tools is being examined. The results indicate that a significant part of the reductions achieved so far is due to a market shift towards diesel vehicle sales and that no reduction factors should be applied yet in CO2 emissions estimation models. 相似文献
68.
A novel successive learning algorithm based on a Test Feature Classifier is proposed for efficient handling of sequentially provided training data. The fundamental characteristics of the successive learning are considered. In the learning, after recognition of a set of unknown data by a classifier, they are fed into the classifier in order to obtain a modified performance. An efficient algorithm is proposed for the incremental definition of prime tests which are irreducible combinations of features and capable of classifying training patterns into correct classes. Four strategies for addition of training patterns are investigated with respect to their precision and performance using real pattern data. A real-world problem of classification of defects on wafer images has been dealt with by the proposed classifier, obtaining excellent performance even through efficient addition strategies. 相似文献
69.
薄层反射波非零炮检距的属性特征 总被引:1,自引:0,他引:1
本文从薄层顶、底界面反射波的走时入手,研究了薄层反射波在非零炮检距集上出现的干涉现象,导出了薄层反射波在出现干涉时的炮检距计算公式,说明薄层干涉出现的炮检距是多变量函数,即随着埋藏深度h、地层速度v、薄层厚度Δh以及地震波的主频f*的变化而改变。本文重点分析了地层厚度Δh和地震子波主频f*对反射波振幅特性和频率特性的影响。在充分分析薄层反射的振幅、频谱随炮检距变化关系的基础上,指出在应用叠前信息(如AVO分析)进行储层预测等方面的研究时,应充分考虑薄层反射波的干涉和调谐现象带来的振幅和频率特征的变化。 相似文献
70.