全文获取类型
收费全文 | 8382篇 |
免费 | 1169篇 |
国内免费 | 429篇 |
专业分类
电工技术 | 83篇 |
综合类 | 430篇 |
化学工业 | 3671篇 |
金属工艺 | 391篇 |
机械仪表 | 349篇 |
建筑科学 | 158篇 |
矿业工程 | 102篇 |
能源动力 | 201篇 |
轻工业 | 1149篇 |
水利工程 | 10篇 |
石油天然气 | 620篇 |
武器工业 | 90篇 |
无线电 | 552篇 |
一般工业技术 | 1357篇 |
冶金工业 | 190篇 |
原子能技术 | 88篇 |
自动化技术 | 539篇 |
出版年
2024年 | 44篇 |
2023年 | 155篇 |
2022年 | 217篇 |
2021年 | 246篇 |
2020年 | 303篇 |
2019年 | 290篇 |
2018年 | 250篇 |
2017年 | 325篇 |
2016年 | 519篇 |
2015年 | 548篇 |
2014年 | 609篇 |
2013年 | 685篇 |
2012年 | 569篇 |
2011年 | 672篇 |
2010年 | 424篇 |
2009年 | 490篇 |
2008年 | 369篇 |
2007年 | 524篇 |
2006年 | 420篇 |
2005年 | 389篇 |
2004年 | 300篇 |
2003年 | 251篇 |
2002年 | 215篇 |
2001年 | 181篇 |
2000年 | 169篇 |
1999年 | 114篇 |
1998年 | 110篇 |
1997年 | 98篇 |
1996年 | 93篇 |
1995年 | 74篇 |
1994年 | 59篇 |
1993年 | 38篇 |
1992年 | 50篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有9980条查询结果,搜索用时 15 毫秒
101.
In this work, we address the problem of transforming seismic reflection data into an intrinsic rock property model. Specifically, we present an application of a methodology that allows interpreters to obtain effective porosity 3D maps from post-stack 3D seismic amplitude data, using measured density and sonic well log data as constraints. In this methodology, a 3D acoustic impedance model is calculated from seismic reflection amplitudes by applying an L1-norm sparse-spike inversion algorithm in the time domain, followed by a recursive inversion performed in the frequency domain. A 3D low-frequency impedance model is estimated by kriging interpolation of impedance values calculated from well log data. This low-frequency model is added to the inversion result which otherwise provides only a relative numerical scale. To convert acoustic impedance into a single reservoir property, a feed-forward Neural Network (NN) is trained, validated and tested using gamma-ray and acoustic impedance values observed at the well log positions as input and effective porosity values as target. The trained NN is then applied for the whole reservoir volume in order to obtain a 3D effective porosity model. While the particular conclusions drawn from the results obtained in this work cannot be generalized, such results suggest that this workflow can be applied successfully as an aid in reservoir characterization, especially when there is a strong non-linear relationship between effective porosity and acoustic impedance. 相似文献
102.
We present an entropic component analysis for identifying key parameters or variables and the joint effects of various parameters that characterize complex systems. This approach identifies key parameters through solving the variable selection problem. It consists of two steps. First, a Bayesian approach is utilized to convert the variable selection problem into the model selection problem. Second, the model selection is achieved uniquely by evaluating the information difference of models by relative entropies of these models and a reference model. We study a geological sample classification problem, where a brine sample from Texas and Oklahoma oil field is considered, to illustrate and examine the proposed approach. The results are consistent with qualitative analysis of the lithology and quantitative discriminant function analysis. Furthermore, the proposed approach reveals the joint effects of the parameters, while it is unclear from the discriminant function analysis. The proposed approach could be thus promising to various geological data analysis. 相似文献
103.
Sunday Olusanya OlatunjiAuthor Vitae Abdulazeez AbdulraheemAuthor Vitae 《Computers in Industry》2011,62(2):147-163
In this work, the use of type-2 fuzzy logic systems as a novel approach for predicting permeability from well logs has been investigated and implemented. Type-2 fuzzy logic system is good in handling uncertainties, including uncertainties in measurements and data used to calibrate the parameters. In the formulation used, the value of a membership function corresponding to a particular permeability value is no longer a crisp value; rather, it is associated with a range of values that can be characterized by a function that reflects the level of uncertainty. In this way, the model will be able to adequately account for all forms of uncertainties associated with predicting permeability from well log data, where uncertainties are very high and the need for stable results are highly desirable. Comparative studies have been carried out to compare the performance of the proposed type-2 fuzzy logic system framework with those earlier used methods, using five different industrial reservoir data. Empirical results from simulation show that type-2 fuzzy logic approach outperformed others in general and particularly in the area of stability and ability to handle data in uncertain situations, which are common characteristics of well logs data. Another unique advantage of the newly proposed model is its ability to generate, in addition to the normal target forecast, prediction intervals as its by-products without extra computational cost. 相似文献
104.
105.
基于自动调焦的微机控制显微硬度计 总被引:1,自引:0,他引:1
传统显微硬度计自动化程序不高,难以满足现代信息处理与分析要求,本文提出的基于自动调焦的微机控制技术应用传统显微硬度计中,能对各种金相试样进行自动测试,实践中取得了很好的效果。 相似文献
106.
MA Jie-ming 《数字社区&智能家居》2008,(5)
结合开发与应用实践,介绍了在ASP平台下调用Crystal Reports报表设计软件实现数据打印的原理和方法。 相似文献
108.
G. J. Gruber 《Journal of Nondestructive Evaluation》1980,1(4):263-276
Shape and size are the most important defect characteristics that need to be determined for the reliable prediction of the remaining service lifetime of a defective structure or part. The analytical and supporting experimental results presented in this paper concern a general, pattern recognition-based, ultrasonic defect identification and sizing method. The satellite-pulse technique (SPT) is based on the interpretation, in terms of defect types (shapes) and dimensions, of the separation in time of arrival between the readily detected specularly reflected pulse and its generally ignored tip-diffracted or tangentially scattered satellite contained in the received waveform. Calibration procedures were also developed that enable the ultrasonic examiner to read the time scale of the oscilloscope for equivalent crack depth or void diameter as appropriate. 相似文献
109.
丙烯-乙烯共聚物Vistamaxx的结构性能表征 总被引:1,自引:0,他引:1
Vistamaxx(VM)是一种新型的茂金属催化的丙烯-乙烯共聚物,其丙烯质量分数在70%以上,组成与结晶性介于无定型的乙丙橡胶与结晶性的聚丙烯之间,是一种柔软且有弹性的聚烯烃材料。对VM进行了红外光谱(FTIR)、广角X射线衍射(WAXD)、示差扫描量热(DSC)以及力学性能的测试分析,结果表明:VM中的乙烯质量分数在20%以下;VM的Tg在-24℃以下;VM的结晶度较低,其结晶具有聚丙烯α-型晶体结构特点,分子链中较短的链段可在室温以下结晶表现出二次结晶现象;VM是一种透明性高、力学性能优异的热塑性弹性体材料。 相似文献
110.
由于杂环化合物具有广泛的生物活性,且具低毒、高效、对环境友好、结构多样化等多种优点,已成为当今药物开发的热点.以烟碱乙酰胆碱受体拮抗剂5-氯-2-苯并噁唑酮(商品名氯唑杀宗,chlorzoxazone)为先导,依据电子等排原理,将5-氯-2-苯并噁唑酮变换为以5-氯-2-苯并噻唑酮,设计了一系列5-氯-2-苯并噻唑酮衍生物,以期开发具有新型结构的烟碱乙酰胆碱受体拮抗剂.在合成方面,以4-氯-2-氨基苯硫醇为起始原料与脲素在酸性条件下闭环反应生成中间体5-氯-2-苯并噻唑酮,该中间体经重结晶纯化后,在碱性条件下,与一系列带有良好生物活性基团的卤代烃发生亲核取代,合成了六个未见文献报道的苯并噻唑衍生物,所有化合物均经过MS、[1 H]NMR进行了结构表征,其生物活性有待研究. 相似文献