全文获取类型
收费全文 | 13516篇 |
免费 | 1076篇 |
国内免费 | 218篇 |
专业分类
电工技术 | 456篇 |
技术理论 | 1篇 |
综合类 | 493篇 |
化学工业 | 2683篇 |
金属工艺 | 399篇 |
机械仪表 | 515篇 |
建筑科学 | 730篇 |
矿业工程 | 226篇 |
能源动力 | 392篇 |
轻工业 | 2352篇 |
水利工程 | 194篇 |
石油天然气 | 488篇 |
武器工业 | 52篇 |
无线电 | 964篇 |
一般工业技术 | 2140篇 |
冶金工业 | 758篇 |
原子能技术 | 70篇 |
自动化技术 | 1897篇 |
出版年
2024年 | 45篇 |
2023年 | 185篇 |
2022年 | 284篇 |
2021年 | 479篇 |
2020年 | 374篇 |
2019年 | 370篇 |
2018年 | 498篇 |
2017年 | 552篇 |
2016年 | 496篇 |
2015年 | 466篇 |
2014年 | 651篇 |
2013年 | 1091篇 |
2012年 | 874篇 |
2011年 | 953篇 |
2010年 | 783篇 |
2009年 | 722篇 |
2008年 | 752篇 |
2007年 | 697篇 |
2006年 | 677篇 |
2005年 | 456篇 |
2004年 | 370篇 |
2003年 | 362篇 |
2002年 | 322篇 |
2001年 | 318篇 |
2000年 | 268篇 |
1999年 | 254篇 |
1998年 | 318篇 |
1997年 | 234篇 |
1996年 | 174篇 |
1995年 | 161篇 |
1994年 | 126篇 |
1993年 | 85篇 |
1992年 | 58篇 |
1991年 | 43篇 |
1990年 | 35篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 17篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 28篇 |
1982年 | 20篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1975年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
油井管几种连接结构及密封型式 总被引:1,自引:0,他引:1
油井管的连接结构大多采用螺纹连接,不仅要求螺纹有较高的强度,而且还要有良好的密封性。介绍了油井管的几种连接结构及其密封型式。 相似文献
212.
介绍了自硬呋喃树脂在高铬铸铁生产中的实际应用 ,从原材料的选取 ,树脂砂的制备工艺 ,到采用该砂进行造型制芯的操作要点均作了较为详细的阐述。实践证明 ,采用自硬呋喃树脂砂生产高铬铸铁泵类过流件 ,可较好地满足其尺寸精度、表面光洁度要求 ,能有效地克服裂纹等铸造缺陷的产生 相似文献
213.
本文采用声发射能量技术研究低强度、高塑性材料α-Ti的形变、断裂特征。发现声发射总能量ΣE与长程应力场σ-σs间存在lgΣE-lg(σ-σs)的线性关系,曲线的拐点即为开裂点。因而有可能利用这种方法较精确地测定出低强度、高塑性材料的开裂点,为这类材料的断裂力学测试解决了一个难题。 α-Ti的形变、断裂过程中存在两种声发射源:位错运动引起的滑移和裂纹的徽开裂和长大。 相似文献
214.
利用微合金化法设计了引线框架用Cu-Fe-P合金的成分(Cu-2.5Fe-0.12Zn-0.03P-0.05Mg-0.05Cr-0.05RE),采用金相显微镜(OM)和高分辨电子显微镜(HRTEM)研究了合金的微观组织,测定了合金的抗拉强度、伸长率及电导率等性能.试验结果表明,在其他试验条件相同的情况下,冷轧后的合金板材经550 ℃×4 h时效后处于过时效状态,球形的析出相γ-Fe粗化,尺寸在50~100 nm的范围,合金的强度为482 MPa,显微硬度HV为161,电导率为39.7 MS/m;经450 ℃×4 h时效后处于欠时效状态,呈球形的γ-Fe相尺寸在20 nm以下,抗拉强度为417 MPa,显微硬度HV为139,电导率是30.4 MS/m;经550 ℃×2 h 450 ℃×2 h时效后处于峰值时效状态,球形的γ-Fe相尺寸在20~50 nm的范围,此时合金的抗拉强度为510 MPa,显微硬度HV为168,导电率为40.6 MS/m. 相似文献
215.
216.
L. Ponsatí V. Acuña I. Aristi M. Arroita E. García‐Berthou D. von Schiller A. Elosegi S. Sabater 《河流研究与利用》2015,31(8):1003-1016
Dams regulate downstream hydrology and modify water quality, which in turn can impinge on the biota, especially in rivers naturally subject to large hydrological variability, such as those under Mediterranean climate. The effect of dams on biofilms was analysed in three tributaries (Cinca, Siurana and Montsant) of the Ebro River (NE Spain). We hypothesized that flow regulation would lead to lower spatial variability of biofilms on the streambed and to a decrease in their metabolic rate per unit biomass, especially during low flow periods. Biofilm characteristics were studied in five transects evenly spaced along river reaches upstream (control) and downstream (impact) of dams in each river, along with riverbed granulometry, hydraulics and water chemistry. Chlorophyll‐a, respiratory activity, photosynthetic capacity and efficiency, and extracellular enzymatic activities (β‐d ‐glucosidase, alkaline phosphatase and leucine‐amino‐peptidase) of epilithic biofilms were measured in different seasons. Spatial variability of chemical and biological variables was reduced downstream of the dams. Chlorophyll‐a concentration, photosynthetic efficiency and respiration capacity were higher in impact than in control reaches, but generally, low inorganic phosphorus concentrations resulted in comparable phosphatase activities downstream and upstream of dams. On the other hand, β‐d ‐glucosidase and leucine‐amino‐peptidase activities were higher at impact reaches. Biofilms were thicker and metabolically more active at the impact reaches, with higher ability to transform dissolved organic matter. Overall, results from this study provide evidence that dams can largely affect the structure and activity of river biofilms, with foreseeable important consequences for river ecosystem functioning. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
217.
A model for atmospheric pollutant transport is proposed considering an advection–diffusion–reaction equation. A splitting method is used to decouple the advection, diffusion and reaction parts. A scheme based on finite volume, finite difference and backward differentiation formula is used for solving an atmospheric transport-chemistry problem. 相似文献
218.
C. Mattar J. C. Jiménez-Muñoz A. Santamaría-Artigas L. Olivera-Guerra J. A. Sobrino 《International journal of remote sensing》2015,36(19-20):5045-5060
This paper presents the Global Atmospheric Profiles derived from Reanalysis Information (GAPRI) database, which was designed for earth surface temperature retrieval. GAPRI is a comprehensive compilation of selected atmospheric vertical profiles at global scale which can be used for radiative transfer simulation in order to obtain generalized algorithms to estimate land surface temperature (LST). GAPRI includes information on geopotential height, atmospheric pressure, air temperature, and relative humidity derived from the European Centre for Medium-Range Weather Forecasts Re-Analysis data from year 2011. The atmospheric profiles are structured for 29 vertical levels and extracted from a global spatial grid of about 0.75° × 0.75° latitude–longitude with a temporal resolution of 6 hours. The selection method is based in the extraction of clear sky profiles over different atmospheric weather conditions such as tropical, mid-latitude summer, subarctic, and arctic, while also considering sea and land areas and day- and night-time conditions. The GAPRI database was validated by comparing land and sea surface temperature values derived from it to those obtained using other existing atmospheric profile databases and in situ measurements. Moreover, GAPRI was also compared to previous radiosonde atmospheric profiles using simulated split-window algorithms. Results show good agreement between GAPRI and previous atmospheric databases, thus demonstrating the potential of GAPRI for studies related to forward simulations in the thermal infrared range. GAPRI is a freely available database that can be modified according to the user’s needs and local atmospheric conditions. 相似文献
219.
Decision recommendations are a set of alternative options for clinical decisions (e.g., diagnosis, prognosis, treatment selection, follow-up, and prevention) that are provided to decision makers by knowledge-based Clinical Decision Support Systems (k-CDSS) as aids. We propose to follow a “reasoning over domain” approach for the generation of decision recommendations by gathering and inferring conclusions from production rules. In order to rationalize our approach, we present a specification that will sustain the logic models supported in the knowledge bases we use for persistence. We introduce first the underlying knowledge model and then the necessary extensions that will convey toward the solution of the reported needs. The starting point of our approach is the proposition of Reflexive Ontologies (RO). Here, we go a step further, proposing an extension of RO that includes the handling and reasoning that production rules provide. Our approach speeds up the recommendation generation process. 相似文献
220.