首页 | 本学科首页   官方微博 | 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   4101篇
  免费   112篇
  国内免费   3篇
电工技术   31篇
综合类   3篇
化学工业   728篇
金属工艺   49篇
机械仪表   52篇
建筑科学   143篇
矿业工程   21篇
能源动力   46篇
轻工业   432篇
水利工程   39篇
石油天然气   31篇
无线电   168篇
一般工业技术   541篇
冶金工业   1517篇
原子能技术   12篇
自动化技术   403篇
  2023年   18篇
  2022年   68篇
  2021年   67篇
  2020年   39篇
  2019年   46篇
  2018年   70篇
  2017年   60篇
  2016年   61篇
  2015年   54篇
  2014年   80篇
  2013年   198篇
  2012年   146篇
  2011年   228篇
  2010年   135篇
  2009年   172篇
  2008年   171篇
  2007年   178篇
  2006年   145篇
  2005年   132篇
  2004年   125篇
  2003年   125篇
  2002年   114篇
  2001年   71篇
  2000年   85篇
  1999年   79篇
  1998年   97篇
  1997年   107篇
  1996年   102篇
  1995年   77篇
  1994年   70篇
  1993年   92篇
  1992年   88篇
  1991年   38篇
  1990年   72篇
  1989年   73篇
  1988年   55篇
  1987年   64篇
  1986年   59篇
  1985年   68篇
  1984年   43篇
  1983年   49篇
  1982年   34篇
  1981年   45篇
  1980年   31篇
  1979年   33篇
  1978年   20篇
  1977年   29篇
  1976年   20篇
  1975年   24篇
  1973年   18篇
排序方式: 共有4216条查询结果,搜索用时 15 毫秒
1.
2.
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF.  相似文献   
3.
The present study reports for the first time the performance of silver phosphate (Ag3PO4) microcrystals as photocatalyst (degradation of Rodamine B-RhB) and antifungal agent (against Candida albicansC. albicans) under visible-light irradiation (455 nm). Ag3PO4 microcrystals were synthesized by a simple co-precipitation (CP) method at room temperature. The structural and electronic properties of the as-synthetized Ag3PO4 have been investigated before and after 4 cycles of RhB degradation under visible light using X-ray diffraction (XRD), micro-Raman spectroscopy, UV–Vis spectrophotometer and field emission scanning electron microscopy (FE-SEM) images. The antifungal activity was analyzed in planktonic cells and 48h-biofilm of C. albicans by colony forming units (CFU) counting, confocal laser and FE-SE microscopies. Statistical analysis was carried out using SPSS software. Morphological and structural modifications of Ag3PO4 were observed upon recycling. After 4 recycles, the material maintained its photodegradation property; an eightfold increase in the efficiency of Ag3PO4 was observed in planktonic cells and a two fold increase in biofilm when irradiated under visible light. Thus, higher antifungal effectiveness against C. albicans was obtained when associated with visible-light irradiation.  相似文献   
4.
5.
Cattle access to streams has been linked globally with degradation of stream water quality, driven largely by bank erosion and resultant instream, fine sediment deposition. The majority of evidence on such effects is however based in arid and semiarid regions of the United States and Australia, with few studies relating to cool temperate climates such as Northwest Europe. In this study, “Quorer” resuspendable sediment samples were taken from riffle geomorphic units upstream (control) and at two points downstream (pressure and recovery) of cattle access points in headwater streams in agricultural catchments in Ireland to assess levels of deposited stream sediment. Samples were taken in April/May (2016) prior to the grazing season and in October (2016) at the end of the grazing season. Sites in good‐high ecological status catchments and less than good ecological status catchments were included in the study. Higher levels of sediment were found downstream of cattle access points in both good‐high status and less than good status catchments; however, the impacts of access points were spatially confined to, in most cases, the area immediately downstream of the point of access. There was a strong correlation between deposited sediment mass and organic matter (OM) mass, with levels of OM increasing linearly with deposited sediment mass. Levels of measured sediment were negatively correlated with riparian habitat health (measured using a qualitative habitat assessment). The results of this study highlight the need for measures to prevent cattle access to headwater streams where access points can be many in order to manage local habitat quality and downstream water quality issues.  相似文献   
6.
This study examined the mediating role of health behaviors in the relationship between neuroticism and depressive symptoms among spouse caregivers. Path analysis was used to test a model of the caregiver stress process among 233 caregivers of people with dementia. Results indicate that neuroticism has a significant direct effect on depressive symptoms and also indirectly influences depressive symptoms through health behaviors and perceived stress. When individual health behaviors were examined in the path model, only physical activity served a significant mediating role. These findings suggest that neuroticism may lead to depressive symptoms among caregivers partly through declines in physical activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
7.
A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained ( ) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement.  相似文献   
8.
Updated the report of W. M. Cox and V. Catt (see record 1978-21651-001) by determining the 40 top contributing institutions to the Journal of Applied Psychology, 1976–1982, and assessed the generalizability of productivity rankings based solely on contributions to this journal. A number of industrial and organizational psychologists were asked to indicate all the journals in which psychologists in the field were likely to publish. Five journals suggested by these nominators were used for comparison in the review. A list of the 40 most productive graduate programs based on these 5 journals is included. Results show the inadequacy of Cox and Catt's decision to base productivity ratings solely on contributions to 1 journal. Using 5 journals, 4 programs were catapulted into the top 10 rankings, while 7 programs dropped from top rankings in the Cox study (1970–1975) to below the 65th rank in the present study. Using only the Journal of Applied Psychology contributions, 2 of these programs ranked in the top 10, 1976–1982. (5 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
9.
During large scale wildfires, suppression activities are carried out under the direction of an Incident Management Team (IMT). The aim of the research was to increase understanding of decision processes potentially related to IMT effectiveness. An IMT comprises four major functions: Command, Operations, Planning, and Logistics. Four methodologies were used to study IMT processes: computer simulation experiments; analyses of wildfire reports; interviews with IMT members; and cognitive ethnographic studies of IMTs. Three processes were important determinants of IMT effectiveness: information management and cognitive overload; matching component function goals to overall goals; and team metacognition to detect and counter task‐disruptive developments. These processes appear to be complex multi‐person analogues of individual Incident Command processes identified previously. The findings have implications for issues such as: creating IMTs; training IMTs; managing IMTs; and providing decision support to IMTs.  相似文献   
10.
Reactive zirconia powder was synthesized by the complexation of zirconium metal from zirconium hydroxide using a solution of 8-hydroxiquinoline. The kinetics of zirconia crystallization was followed by X-ray diffraction, scanning electron microscopy and surface area measured by the nitrogen adsorption/desorption technique. The results indicated that zirconia with a surface area as high as 100 m2/g can be obtained by this method after calcination at 500°C. Zirconia presents three polymorphic phases (monoclinic, tetragonal and cubic), which are reversibly interconversible. The cluster model Zr4O8 and Zr4O7 +2 was used for a theoretical study of the stabilization process. The ab initio RHF method was employed with the Gaussian94 program and the total energies and the energy gap of the different phases were calculated and compared with the experimental energy gap. The theoretical results show good reproducibility of the energy gap for zirconia.  相似文献   
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