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   31760篇
  免费   3572篇
  国内免费   1514篇
电工技术   2947篇
技术理论   8篇
综合类   3401篇
化学工业   2034篇
金属工艺   586篇
机械仪表   881篇
建筑科学   5300篇
矿业工程   1881篇
能源动力   1496篇
轻工业   2430篇
水利工程   2672篇
石油天然气   1373篇
武器工业   413篇
无线电   1385篇
一般工业技术   2462篇
冶金工业   2832篇
原子能技术   460篇
自动化技术   4285篇
  2024年   81篇
  2023年   479篇
  2022年   968篇
  2021年   1244篇
  2020年   1240篇
  2019年   1026篇
  2018年   1064篇
  2017年   1076篇
  2016年   1495篇
  2015年   1333篇
  2014年   2391篇
  2013年   2589篇
  2012年   2445篇
  2011年   2632篇
  2010年   2003篇
  2009年   2011篇
  2008年   1827篇
  2007年   2005篇
  2006年   1911篇
  2005年   1391篇
  2004年   1116篇
  2003年   987篇
  2002年   756篇
  2001年   582篇
  2000年   432篇
  1999年   332篇
  1998年   261篇
  1997年   190篇
  1996年   169篇
  1995年   123篇
  1994年   113篇
  1993年   73篇
  1992年   62篇
  1991年   59篇
  1990年   50篇
  1989年   46篇
  1988年   47篇
  1987年   29篇
  1986年   27篇
  1985年   15篇
  1984年   21篇
  1983年   18篇
  1982年   15篇
  1981年   12篇
  1980年   9篇
  1979年   8篇
  1975年   7篇
  1965年   16篇
  1961年   6篇
  1959年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The nature of risk needs to be more clearly understood. Risk management could be tightened as a discipline, particularly by adopting an underlying foundation of systems thinking. Risk management, even when well done, has inherent limitations, and these should be well understood, particularly those arising from modelling, completeness, correlation effects, and the often-great uncertainties in estimates of both likelihood and consequence. Modelling is centrally important: both this and risk must be intimately related to decision-making. A clear understanding of this connection is essential to sound work in the discipline.  相似文献   
992.
Evaluation of canning quality of beans is commonly carried out by simple visual inspection that is time-consuming, resource intensive, and biased by the experience of the panelist. Moreover, there is not a standard scale to rate visual quality traits of canned beans. In this research, a machine vision system was implemented and tested for automatic inspection of color (COL) and appearance (APP) in canned black beans. Various color and textural image features (average, standard deviation, contrast, correlation, energy, and homogeneity from red, green, blue, lightness, red/green, yellow/blue, hue, saturation and value color scales) were extracted from beans and brine images, and evaluated to predict the quality rates for COL and APP of a group of bean panelists using multivariate statistics. Sixty-nine commercial canned black bean samples from different brands and markets were used for analysis. In spite of the “fair” agreement among the sensory panelists for COL and APP, as determined by multi-rater Kappa analysis, machine vision data based on partial least squares regression model showed high predictive performance for both COL and APP with correlation coefficients of 0.937 and 0.871, and standard errors of 0.26 and 0.38, respectively. When a classification was performed based on both COL and APP traits, a support vector machine model was able to sort the samples into two sensory quality categories of “acceptable” and “unacceptable” with an accuracy of 89.7%. Using simple color and texture image data, a machine vision system showed potential for the automatic evaluation of canned black beans by COL and/or appearance as a professional visual inspection.  相似文献   
993.
齿坯闭式模锻锻件分精密级和普通级,但国家标准定义的精密级锻件留有单边加工余量,仍需进行粗车和精车。在精密锻造基础上,研究精化齿坯热锻工艺,以进一步提高锻件精度等级,达到减少单边加工余量,进而使精化齿坯直接用于精车。本文对精化齿坯热锻工艺进行了定义,并明确该工艺单边加工余量的范围。因制坯和预锻是决定精化齿坯热锻工艺质量的关键,因此对其工艺流程和工艺重点进行了分析,同时对满足该工艺的设备和模座进行了论述。  相似文献   
994.
The work presented in this paper describes the design for Graduation Project eCoordination System in our department. The proposed eCoordinator provides effective team–team, supervisor–team and coordinator–supervisors–teams collaboration. eCoordinator is an attribute based framework that serves evolving an object oriented software system into agent oriented software system. Nowadays, agent-oriented software development technologies have evolved rapidly; it is emerging as a new paradigm for constructing intelligent more autonomous software systems. Therefore, several methodologies are available and it is difficult to determine the most appropriate methodology for specific project within different domains. This is especially occurs when re-engineering current object oriented software system. The case study is going to be rebuilding a virtual graduation project coordinator in Information Technology Department at King Saud University.  相似文献   
995.
This assessment is focussed on wrought magnesium alloys for lightweight applications, particularly in the transport sector. The challenges to their wider use are summarised, including poor low temperature formability, corrosion issues, dissimilar metal joining, and limited precipitation strengthening. The fundamental origins of these challenges, and current research to address them, are highlighted. Key developments such as the use of dilute rare earth additions to manipulate texture for improved formability are discussed. Opportunities to exploit the unique properties of wrought magnesium alloys where further research is required are identified.  相似文献   
996.
Because lately the low bioindicative value of tolerant species from different taxonomic groups is often questioned, in this study, we hypothesized that tolerant diatoms may be used for effective temporal assessments of human pressure. We tested this on the lowland Bzura River in central Poland, on 156 diatom samples (DSs) from two study periods of 1972 with extremely severe point‐source water pollution and of 2002–2004, where the complex wastewater management in the river catchment improved water quality considerably. Out of the total 295 diatom species recorded in the samples, only 133 tolerant ones were included in the study. Patterns in their abundance were recognized with a Kohonen artificial neural network (self‐organizing map, SOM), whereas the species significantly associated with each SOM cluster of diatom samples were identified with the indicator value (IndVal) index and the Monte Carlo test. If the hypothesis tested was not supported, the assignation of DSs to the SOM clusters would be random. However, the separation of DSs from 1972 and 2002–2004 was almost perfect because the number of exceptions was as low as 4.5%. In addition, the relatively high number (64 out of 133) of tolerant species significantly associated with any SOM cluster (and respective environmental conditions at sites from which samples assigned to it come) supports the hypothesis tested. This means that almost half of the studied species are not evenly distributed in particular clusters as might be expected for highly tolerant species. The study proves that the abundances of many diatom species, currently classified as tolerant, carry quite precise information on the differences in the quality of the environment, and indicates those tolerant diatom species whose bioindicative potential may be highest. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
997.
Qualitative and quantitative effects on the contents of minor components of cold‐pressed high‐oleic rapeseed oil (HORO) were evaluated in a function of different roasting temperatures (80, 100, 120 and 140 °C). Along with roasting temperature elevation, a significant increase in the content of total tocopherols up to 32% (mainly γ‐T homologue) and a slight increase of total sterols concentration (up to 5%) were observed, whereas no significant changes in the fatty acid composition occurred during seeds thermal pretreatment. Additionally, an increased degree of hydrolysis and lipid oxidation was reported; however, obtained results were within codex limits. The peroxide value of the oil ranged from 1.30 to 2.34 mEq O2 kg?1, while the acid value did not exceed 0.46 mg/KOH g. Principal component analysis was capable of differentiating between rapeseed oils acquired from seeds pretreated with different roasting temperatures.  相似文献   
998.
This study proposes an analytical and flexible terrain risk assessment method for military surveillance applications for mobile assets. Considering the risk as the degree of possibility of insurgent presence, the assessment method offers an efficient evaluation of risk in the surrounding terrain for military combat operating posts or observation posts. The method is designed for unmanned aerial vehicles as the surveillance assets of choice to improve the effectiveness of their use. Starting with the area map and geographical data, the target terrain is first digitized for space representation. Then the data of nine geographical parameters are used to formulate five contributing risk factors. These factors are incorporated in an analytical framework to generate a composite map with risk scores that reveal the potential high-risk spots in the terrain. The proposed method is also applied to a real-life case study of COP Kahler in Afghanistan, which was a target for insurgent attacks in 2008. The results confirm that when evaluated with the developed method, the region that the insurgents used to approach COP Kahler has high concentration of high-risk cells.  相似文献   
999.
Probabilistic estimation of dietary exposure to DON, including its acetylated derivatives, and type B trichothecenes from cereals and cereal-based products in Chinese populations was investigated in the current work. Different cut-offs as proposed Maximum levels (MLs) for DON in various raw cereals and/or cereal-based foods were assessed based on the risk assessment results. Occurrence data was documented from 31 provinces of China over the year 2010–2013. Food consumption data was obtained from the National Diet and Nutrition Survey conducted in 2002. Dietary exposure was implemented by Monte Carlo (MC) simulations and Bootstrap resampling. The exposure distributions were specified as percentiles with confidence intervals (95% CIs) and compared with the group provisional maximum tolerable daily intake (PMTDI) of 1 μg/kg bw/day and the group acute reference dose (ARfD) of 8 μg/kg bw/day for DON and its acetylated derivatives. Results indicate that 75% of children and 90% of the general population and the adults are under the group PMTDI value, while 99% of the three populations are under ARfD value. However, under the assumptions of the proposed cut-offs, the P99.9 percentiles would decrease significantly. The probabilistic assessment in this study indicated that high-end exposure to DON and its derivatives should be concerned, especially for children. Rigorous formulation of maximum limits for DON and its derivatives in the relevant foodstuffs combined with increased monitoring should be considered as an effective way to reduce risk.  相似文献   
1000.
通过建立电压等级与投资、运行成本的函数关系,以成本最小为原则对电压等级进行优化。提出了考虑经济性因素的"几何均值"原则,并从经济性角度对电压等级序列优化提出数学模型。  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