首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   661篇
  免费   30篇
  国内免费   7篇
工业技术   698篇
  2024年   5篇
  2023年   23篇
  2022年   35篇
  2021年   49篇
  2020年   35篇
  2019年   32篇
  2018年   62篇
  2017年   34篇
  2016年   36篇
  2015年   16篇
  2014年   25篇
  2013年   27篇
  2012年   25篇
  2011年   38篇
  2010年   26篇
  2009年   27篇
  2008年   32篇
  2007年   21篇
  2006年   9篇
  2005年   6篇
  2004年   10篇
  2003年   9篇
  2002年   8篇
  2001年   4篇
  2000年   2篇
  1999年   7篇
  1998年   7篇
  1997年   9篇
  1996年   7篇
  1995年   10篇
  1994年   5篇
  1993年   8篇
  1992年   5篇
  1991年   2篇
  1990年   4篇
  1989年   9篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   3篇
  1984年   6篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1977年   1篇
  1976年   2篇
  1975年   2篇
排序方式: 共有698条查询结果,搜索用时 625 毫秒
11.
Wang  Eric Ke  Wang  Fan  Kumari  Saru  Yeh  Jyh-Haw  Chen  Chien-Ming 《The Journal of supercomputing》2021,77(3):3024-3043
The Journal of Supercomputing - Accidents often occur in the earth—typhoons, floods, earthquakes, traffic accidents and so on. Whether these accidents can be timely and effectively responded...  相似文献   
12.
Formation of spinel phases in ZnO–Sb2O3and ZnO–Sb2O3–Bi2O3systems is studied by the use of X-ray diffraction. The formation of nonstoichiometric Zn2.33Sb0.67O4phase is observed in both the systems at ∼900°C. However, in these systems, at higher temperatures ( T ≥ 1100°C), formation of the inverse spinel phase Zn7Sb2O12is observed. The study has been extended to understand the effect of CrO3doping on the stability of the different spinel phases in the previously mentioned systems. Interestingly, in both the systems, samples doped with CrO3, displayed the presence of Zn2.33Sb0.67O4phase <1200°C, indicating the stabilization of the spinel phase by CrO3.  相似文献   
13.
In distributed systems, user authentication schemes based on password and smart card are widely used to ensure only authorized access to the protected services. Recently, Chang et al. presented an untraceable dynamic-identity-based user authentication scheme with verifiable-password-update. In this research, we illustrate that Chang et al.’s scheme violates the purpose of dynamic-identity contrary to authors’ claim. We show that once the smart card of an arbitrary user is lost, passwords of all registered users are at risk. Using information from an arbitrary smart card, an adversary can impersonate any user of the system. In addition, its password change phase has loopholes and is misguiding. The scheme has no provision for session key agreement and the smart card lacks any verification mechanism. Then we come-up with an improved remote user authentication scheme with the session key agreement, and show its robustness over related schemes.  相似文献   
14.

Estimation of terrestrial water budget at global and regional scales are essential for efficient agricultural water management, flood predictions, and, hydrological modeling. In hydrological modeling, it is a challenging task to quantify the major hydrological components like runoff, evapotranspiration (ET), and total water storage (TWS) due to improper and limited availability of detailed meteorological datasets. Furthermore, there has been no consensus to answer a-decade-long critical question that a less data-intensive models can be an alternate to robust data-intensive models in data scarce conditions. This study aims at multi-model approach over the single models usage for representing the hydrological behaviour in the Kangsabati River Basin (KRB), India. It is done by applying the standard model selection criteria over various hydrological models. Two hydrological models are selected, a semi- distributed model, Variable Infiltration Capacity (VIC-3 L), and a conceptually lumped model, Identification of unit Hydrograph and Component flows from Rainfall, Evapotranspiration and Streamflow (IHACRES). Both models were calibrated against the observed daily discharge at the KRB outlet for the period of 2001–2006 and validated for 2008–2010. The results show that both VIC-3 L and IHACRES produce reasonable runoff estimates at daily and monthly time scale in the KRB. The ET estimates show that VIC-3 L and IHACRES captured the seasonal variations with the percent change of 0.4% and 6.6% respectively. As IHACRES is simpler, parsimonious, fewer parameters, and better performances, it can be useful for hydrological modeling in data-scarce regions.

  相似文献   
15.

Hydrological responses corresponding to the agricultural land use alterations are critical for planning crop management strategies, water resources management, and environmental evaluations. However, accurate estimation and evaluation of these hydrological responses are restricted by the limited availability of detailed crop classification in land use and land cover. An innovative approach using state-of-the-art Variable Infiltration Capacity (VIC) model is utilized by setting up the crop-specific vegetation parameterization and analyse the effect of uniform and heterogeneous agricultural land use over the hydrological responses of the basin, in the Kangsabati River Basin (KRB). Thirteen year simulations (1998–2010) based on two different scenarios i.e., single-crop in agricultural land use (SC-ALU) and multi-crop in agricultural land use (MC-ALU) patterns are incorporated in the model and calibrated (1998–2006) and validated (2007–2010) for the streamflow at Reservoir and Mohanpur in the KRB. The results demonstrated that the VIC model improved the estimates of hydrological components, especially surface runoff and evapotranspiration (ET) at daily and monthly timescales corresponding to MC-ALU than SC-ALU (NSC?>?0.7). Grid-scale ET estimates are improved after incorporating heterogeneous agricultural land use (NSC?>?0.55 and R2?>?0.55) throughout the period of 1998–2010. This study improves our understanding on how the change in agricultural land use in the model settings alters the basin hydrological characteristics, and to provide model-based approaches for best management practices in irrigation scheduling, crop water requirement, and management strategies in the absence of flux towers, eddy covariance, and lysimeters in the basin.

  相似文献   
16.
In Fifth Generation (5G) Heterogeneous Mobile Networks (HetNets), deploying dense small cell networks makes user association more challenging. The process of collecting cell load information from the User Equipments (UEs) and broadcasting the feedback message involves significant overhead and time complexity. Moreover, the UEs may not know the optimum cell to reselect, satisfying its data rate requirements. In order to overcome these drawbacks, in this paper, we propose to design an Hierarchical and Hybrid Cell Load Balancing (HHCLB) technique using Selective Handoff. In this technique, the UEs of each cell are grouped into clusters depending on their proximity distance. Each cluster contains a cluster controller (CC) which is in charge of determining the intra-cell load and redirecting the cell-reselection request of a UE. If the data rate of any UE in a cluster becomes less than its required rate, then the cell reselection process is performed. By simulation results, it is shown that load balancing can be done proactively (implicitly) by the CCs when the load is unbalanced or can be done on demand (explicitly) when a UE send a request for cell reselection. In the case of Macro cells, HHCLB attains 71% higher throughput for low load scenario and 59% higher throughput for high load scenario. Similarly, in the case of Femto cells, HHCLB attains 19% higher throughput for low load scenario and 27% higher throughput for high load scenario.  相似文献   
17.
In this digital era, where Internet of Things (IoT) is increasing day by day, use of resource constrained devices is also increasing. Indeed, the features such as low cost, less maintenance, more adaptive to hostile environment, etc. make the wireless multimedia devices to be the best choice as the resource constrained devices. For the security, the end user device requires to establish the session key with the server before transferring the data. Mobile is one of the device having more and more usage as wireless multimedia device in recent years. In 2013, Li et al. proposed an efficient scheme for the wireless mobile communications and claimed it to be secure against various attacks. Recently, Shen et al. claimed that the scheme of Li et al. is still vulnerable to the privileged insider attack, the stolen verifier attack and finally proposed a scheme to withstand the mentioned and other attacks. However, in this paper we claim that the scheme of Shen et al. is still susceptible to the user anonymity, the session specific temporary information attack and the replay attack. In addition, Shen et al.’s scheme requires more time due to many operations. Further, we propose an efficient scheme that is secure against various known attacks and due to reduced time complexity our scheme is a preferred choice for the wireless mobile networks and hence for wireless multimedia systems.  相似文献   
18.
Surface ultrastructures of gill filaments and secondary lamellae of Rita rita and Cirrhinus mrigala, inhabiting different ecological habitat, were investigated to unravel adaptive modifications. R. rita is a sluggish, bottom dwelling carnivorous catfish, which inhabits regions of river with accumulations of dirty water. It retains its viability for long time if taken out of water. C. mrigala is an active bottom dwelling Indian major carp, which lives in relatively clean water and dies shortly after taken out of water. In R. rita, gill septa between gill filaments are reduced. Microridges on epithelial cells covering gill filaments are often continuous and arranged concentrically. Secondary lamellae are extensive. The epithelium appears corrugated, show irregular elevations and shallow depressions, and microridges on epithelial cells appear fragmented. In C. mrigala, in contrast, the gill septa are extensive. Microridges on epithelial cells covering gill filaments are fragmented. Secondary lamellae are less extensive. The epithelium appears smooth and microridges on epithelial cells are relatively inconspicuous. These differences have been considered adaptive modification in relation to habit and ecological niches inhabited by two fish species. Presence of mucous goblet cells on gill filaments is discussed in relation to their functions including precipitation of the sediments and preventing clogging of gill filaments. Infrequent mucous goblet cells in the epithelium of secondary lamellae in two fish species are considered an adaptation, minimizing thickness of the epithelium to reduce barrier between blood and water for favoring gasses exchange with increased efficiency.  相似文献   
19.
Sexually dimorphic cognitive performance in men (n=42) and women (n=42) was related to testosterone, estradiol, progesterone, luteinizing hormone, follicle-stimulating hormone, and sex hormone binding globulin, measured in 10-ml blood samples collected between 0900 and 1030 and, among women, during the follicular phase of the menstrual cycle. Significant sex differences favored men on spatial tasks (Mental Rotation and Judgment of Line Orientation) and on an inhibition task and favored women on a verbal task (category fluency). However, there were no significant relationships between any of the hormones and cognitive performance, suggesting that there are few, if any, consistent, substantial relationships between endogenous, nonfluctuating levels of gonadal hormones or gonadotropins and these cognitive abilities in men or women. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号