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   14341篇
  免费   393篇
  国内免费   59篇
电工技术   260篇
综合类   16篇
化学工业   2284篇
金属工艺   367篇
机械仪表   362篇
建筑科学   219篇
矿业工程   73篇
能源动力   703篇
轻工业   1173篇
水利工程   190篇
石油天然气   84篇
无线电   1627篇
一般工业技术   2775篇
冶金工业   3044篇
原子能技术   198篇
自动化技术   1418篇
  2024年   39篇
  2023年   177篇
  2022年   505篇
  2021年   505篇
  2020年   409篇
  2019年   407篇
  2018年   554篇
  2017年   512篇
  2016年   483篇
  2015年   280篇
  2014年   446篇
  2013年   892篇
  2012年   518篇
  2011年   678篇
  2010年   541篇
  2009年   531篇
  2008年   476篇
  2007年   389篇
  2006年   332篇
  2005年   263篇
  2004年   247篇
  2003年   222篇
  2002年   180篇
  2001年   143篇
  2000年   147篇
  1999年   196篇
  1998年   831篇
  1997年   490篇
  1996年   435篇
  1995年   322篇
  1994年   250篇
  1993年   287篇
  1992年   149篇
  1991年   163篇
  1990年   123篇
  1989年   126篇
  1988年   144篇
  1987年   124篇
  1986年   103篇
  1985年   123篇
  1984年   97篇
  1983年   109篇
  1982年   107篇
  1981年   98篇
  1980年   100篇
  1979年   54篇
  1978年   48篇
  1977年   89篇
  1976年   164篇
  1975年   35篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The relative risk of death by calendar date of diagnosis was investigated in a population-based incident cohort of 845 (463 males:382 females) IDDM diagnosed in Leicestershire before the age of 17 years between 1940 and 1989. The mortality status of 844 (99.9%) patients was determined as of the 31 December 1991, representing 14,346 person-years of risk. Trends in relative risk of death were investigated using Cox proportional hazards modelling for within cohort comparisons and age/sex and calendar time adjusted standardized mortality ratios (SMR) using generalized linear modelling for external comparisons. Median age at diagnosis was 10 years (range 3 months to 16 years); median duration of diabetes 15 years (range 1-51 years). Forty-four patients had died (5.2%; median age at death 31 years, range 11-51 years). A further four patients died at presentation (within 24 h) from ketoacidosis and are excluded from all analyses. Calendar date of diagnosis was found to be an important predictor of mortality. Adjusting for attained age there was evidence of a decline in relative risk of death with calendar date of diagnosis of 3.4% (95% CI, 0.005-6.9%) per annum, equivalent to a 32% fall per decade (95% CI, 5-51%), or 84% (95% CI, 21-97) from 1940 to 1989. The data are consistent with a large fall in mortality between the 1940s and 1950s representing over 50% of the total reduction in mortality between 1940 and 1991. Neither sex nor age at diagnosis were significant predictors of mortality. Over the study period 1940-89 the SMR (male and female combined) fell from 981 (541-1556) to 238 (60-953) relative to the general population. This population-based study shows that the prognosis for Type 1 (insulin-dependent) diabetes mellitus has improved markedly over the period 1940-1991.  相似文献   
102.
1. Calcium disodium ethylenediaminetetraacetate (CaNa2 EDTA) and meso-2,3-dimercaptosuccinic acid (DMSA) individually and in permutation-combination in various doses (0.1, 0.2 and 0.4 mmol/kg bodyweight) were investigated for their efficacy to mobilize lead from vital tissues into urine and faeces and to restore the lead-sensitive biochemical parameters in lead pre-exposed rats with a view to develop the most acceptable treatment regimen for lead poisoning with a minimal loss of endogenous essential elements. 2. The combined therapy was more effective than a single chelator treatment. 3. The combination of 0.2 mmol/kg CaNa2EDTA + 0.4 mmol/kg DMSA caused a lower depletion of zinc, calcium and iron but possessed almost equal capability to that of 0.4 mmol/kg CaNa2EDTA + 0.4 mmol/kg DMSA to produce urinary as well as faecal excretion of lead, to reduce the tissue burden of lead, including that of the brain, and to reverse lead-induced biochemical alterations. 4. The combination of 0.2 mmol/kg CaNa2EDTA + 0.4 mmol/kg DMSA has shown a definite improvement over previously reported combinations in terms of removal of lead from tissues, particularly the brain, restoration of urinary delta-aminolevulinic acid levels and a decrease in the loss of body zinc and is, therefore, recommended for the treatment of lead intoxication.  相似文献   
103.
2014 aluminium alloy was subjected to various thermomechanical ageing (TMA) treatments which included partial peak ageing (25% and 50%), warm rolling (10% and 20%) and further ageing to peak hardness level at 160 ° C. The tensile tests reveal that TMA treatments cause a substantial improvement in tensile properties and thermal stability. The electron microscopic studies reveal that the TMA treatments affect substantially the ageing characteristics. The TMA Ib treatment yields the finest needles having longitudinal dimensions of 40nm. The TMA treatments also lead to precipitate-dislocation networks of different densities. It is observed that TMA IIb treatment results in the densest precipitate-dislocation tangles of all the TMA treatments. As a result, a significant improvement in the tensile properties of 2014 aluminium alloy has been observed.  相似文献   
104.
In real world, the automatic detection of liver disease is a challenging problem among medical practitioners. The intent of this work is to propose an intelligent hybrid approach for the diagnosis of hepatitis disease. The diagnosis is performed with the combination of k‐means clustering and improved ensemble‐driven learning. To avoid clinical experience and to reduce the evaluation time, ensemble learning is deployed, which constructs a set of hypotheses by using multiple learners to solve a liver disease problem. The performance analysis of the proposed integrated hybrid system is compared in terms of accuracy, true positive rate, precision, f‐measure, kappa statistic, mean absolute error, and root mean squared error. Simulation results showed that the enhanced k‐means clustering and improved ensemble learning with enhanced adaptive boosting, bagged decision tree, and J48 decision tree‐based intelligent hybrid approach achieved better prediction outcomes than other existing individual and integrated methods.  相似文献   
105.
Singh  Dilbag  Kumar  Vijay  Kaur  Manjit 《Applied Intelligence》2021,51(5):3044-3051

The extensively utilized tool to detect novel coronavirus (COVID-19) is a real-time polymerase chain reaction (RT-PCR). However, RT-PCR kits are costly and consume critical time, around 6 to 9 hours to classify the subjects as COVID-19(+) or COVID-19(-). Due to the less sensitivity of RT-PCR, it suffers from high false-negative results. To overcome these issues, many deep learning models have been implemented in the literature for the early-stage classification of suspected subjects. To handle the sensitivity issue associated with RT-PCR, chest CT scans are utilized to classify the suspected subjects as COVID-19 (+), tuberculosis, pneumonia, or healthy subjects. The extensive study on chest CT scans of COVID-19 (+) subjects reveals that there are some bilateral changes and unique patterns. But the manual analysis from chest CT scans is a tedious task. Therefore, an automated COVID-19 screening model is implemented by ensembling the deep transfer learning models such as Densely connected convolutional networks (DCCNs), ResNet152V2, and VGG16. Experimental results reveal that the proposed ensemble model outperforms the competitive models in terms of accuracy, f-measure, area under curve, sensitivity, and specificity.

  相似文献   
106.
The Journal of Supercomputing - Cluster-based routing protocols have been proven efficient in prolonging the life cycle of wireless sensor networks (WSNs). Periodic and multi-hop clustering are the...  相似文献   
107.
Neural Computing and Applications - Grouping the sensor nodes into clusters is an effective way to organize wireless sensor networks and to prolong the networks’ lifetime. This paper presents...  相似文献   
108.
Microsystem Technologies - In this article, a rectangular solid-core photonic crystal fiber (PCF) is proposed as temperature sensor. The air-holes of the PCF have been filled with Ethyl alcohol...  相似文献   
109.
Estimation of elastic constant of rocks using an ANFIS approach   总被引:4,自引:0,他引:4  
The engineering properties of the rocks have the most vital role in planning of rock excavation and construction for optimum utilization of earth resources with greater safety and least damage to surroundings. The design and construction of structure is influenced by physico-mechanical properties of rock mass. Young's modulus provides insight about the magnitude and characteristic of the rock mass deformation due to change in stress field. The determination of the Young's modulus in laboratory is very time consuming and costly. Therefore, basic rock properties like point load, density and water absorption have been used to predict the Young's modulus. Point load, density and water absorption can be easily determined in field as well as laboratory and are pertinent properties to characterize a rock mass. The artificial neural network (ANN), fuzzy inference system (FIS) and neuro fuzzy are promising techniques which have proven to be very reliable in recent years. In, present study, neuro fuzzy system is applied to predict the rock Young's modulus to overcome the limitation of ANN and fuzzy logic. Total 85 dataset were used for training the network and 10 dataset for testing and validation of network rules. The network performance indices correlation coefficient, mean absolute percentage error (MAPE), root mean square error (RMSE), and variance account for (VAF) are found to be 0.6643, 7.583, 6.799, and 91.95 respectively, which endow with high performance of predictive neuro-fuzzy system to make use for prediction of complex rock parameter.  相似文献   
110.
Phase transformation studies have been made of the Mn-Al alloys with compositions near the equiatomic range with or without small amounts of carbon, copper and nickel, using differential thermal analysis, X-ray diffraction and optical and electron microscopy. The high temperature hexagonal phase obtained by quenching, transforms to the ferromagnetic phase between 500 and 550° C and on further heating transforms back to the hexagonal phase between 750 and 950° C. Also, on controlled cooling of the phase from about 900° C, the ferromagnetic phase is formed between 800 and 670° C. TEM studies have shown the presence of the B19 ordered phase, ferromagnetic phase and Mn5Al8 precipitates even in quenched alloys.  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