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   5205篇
  免费   157篇
  国内免费   87篇
电工技术   93篇
综合类   7篇
化学工业   1001篇
金属工艺   127篇
机械仪表   210篇
建筑科学   97篇
矿业工程   2篇
能源动力   195篇
轻工业   259篇
水利工程   28篇
石油天然气   8篇
无线电   911篇
一般工业技术   930篇
冶金工业   565篇
原子能技术   25篇
自动化技术   991篇
  2024年   8篇
  2023年   35篇
  2022年   126篇
  2021年   127篇
  2020年   48篇
  2019年   68篇
  2018年   79篇
  2017年   84篇
  2016年   111篇
  2015年   109篇
  2014年   185篇
  2013年   380篇
  2012年   277篇
  2011年   328篇
  2010年   235篇
  2009年   271篇
  2008年   275篇
  2007年   242篇
  2006年   231篇
  2005年   198篇
  2004年   167篇
  2003年   158篇
  2002年   127篇
  2001年   118篇
  2000年   86篇
  1999年   99篇
  1998年   250篇
  1997年   150篇
  1996年   114篇
  1995年   72篇
  1994年   96篇
  1993年   61篇
  1992年   45篇
  1991年   54篇
  1990年   36篇
  1989年   45篇
  1988年   53篇
  1987年   39篇
  1986年   32篇
  1985年   24篇
  1984年   28篇
  1983年   24篇
  1982年   11篇
  1981年   16篇
  1980年   15篇
  1979年   9篇
  1978年   12篇
  1977年   18篇
  1976年   34篇
  1974年   7篇
排序方式: 共有5449条查询结果,搜索用时 15 毫秒
1.
Multimedia Tools and Applications - With the advancement of technology and the spread of the COVID19 epidemic, learning can no longer only be done through face-to-face teaching. Numerous digital...  相似文献   
2.
Wang  Chen  Bao  Chun-Hui  Wu  Wan-Yu  Hsu  Chia-Hsun  Zhao  Ming-Jie  Zhang  Xiao-Ying  Lien  Shui-Yang  Zhu  Wen-Zhang 《Journal of Materials Science》2022,57(26):12341-12355
Journal of Materials Science - Molybdenum oxide (MoOx) films had been grown by using plasma-enhanced atomic layer deposition (PEALD) with Mo(CO)6 precursor and O2 plasma reactant in a substrate...  相似文献   
3.
Di(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in the manufacture of polyvinylchloride plastics and has been associated with concerns regarding male reproductive toxicity. In this study, we hypothesized that maternal exposure to DEHP induces transgenerational inheritance of adult-onset adverse reproductive outcomes through the male germline in the F1, F2, and F3 generations of male offspring. Pregnant rats were treated with 5 or 500 mg of DEHP/kg/day through gavage from gestation day 0 to birth. The offspring body weight, anogenital distance (AGD), anogenital index (AGI), sperm count, motility, and DNA fragmentation index (DFI) were measured for all generations. Methyl-CpG binding domain sequencing was performed to analyze sperm DNA methylation status in the F3. DEHP exposure at 500 mg/kg affected AGD, AGI, sperm count, mean DFI, and %DFI in the F1; AGD, sperm count, and mean DFI in the F2; and AGD, AGI, mean DFI, and %DFI in the F3. DEHP exposure at 5 mg/kg affected AGD, AGI, sperm count, and %DFI in the F1; sperm count in the F2; and AGD and AGI in F3. Compared with the control group, 15 and 45 differentially hypermethylated genes were identified in the groups administered 5 mg/kg and 500 mg/kg DEHP, respectively. Moreover, 130 and 6 differentially hypomethylated genes were observed in the groups administered 5 mg/kg and 500 mg/kg DEHP. Overall, these results demonstrated that prenatal exposure to DEHP caused transgenerational epigenetic effects, which may explain the observed phenotypic changes in the male reproductive system.  相似文献   
4.
Wireless Personal Communications - In recent years, many wireless communication services have become indispensable for our daily life, such as voice telephoning and the internet surfing. However,...  相似文献   
5.
摘 要:目的 了解六六六(hexachlorocyclohexanes,HCHs)与滴滴涕(dichloro diphenyl trichloroethanes,DDTs)在杭州湾南岸滩涂沉积物中的污染现状。方法 于2018年4月,采集杭州湾南岸地区4个采样点不同深度(0~80 cm)滩涂沉积物,利用气相色谱-串联质谱法(gas chromatography tandem mass spectrometry, GC-MS/MS)测定了该区域中HCHs与DDTs的含量,对其分布规律进行分析,使用共识沉积物质量基准法对其生态学风险进行了评估。结果 所有样品中均检出,HCHs与DDTs含量分别为4.20~6.24 μg/kg与3.37~4.73 μg/kg,主要以β-HCH、δ-HCH以及DDE为主,其污染主要来源于历史性工业品,整体污染处于较低水平;20.3%的沉积物样品中DDEs含量以及28.1%的样品DDTs总量介于阈值效应浓度(threshold concentration, TECs) 和可能效应浓度(probable effect concentration, PECs)之间。结论 杭州湾南岸沉积物中HCHs与DDTs的污染处于较低水平,具有较小的生态学风险。  相似文献   
6.
7.
8.
The turn-on mechanism of silicon-controlled rectifier (SCR) devices is essentially a current triggering event. While a current is applied to the base or substrate of an SCR device, it can be quickly triggered on into its latching state. In this paper, latchup-free electrostatic discharge (ESD) protection circuits, which are combined with the substrate-triggered technique and an SCR device, are proposed. A complementary circuit style with the substrate-triggered SCR device is designed to discharge both the pad-to-V/sub SS/ and pad-to-V/sub DD/ ESD stresses. The novel complementary substrate-triggered SCR devices have the advantages of controllable switching voltage, adjustable holding voltage, faster turn-on speed, and compatible to general CMOS process without extra process modification such as the silicide-blocking mask and ESD implantation. The total holding voltage of the substrate-triggered SCR device can be linearly increased by adding the stacked diode string to avoid the transient-induced latchup issue in the ESD protection circuits. The on-chip ESD protection circuits designed with the proposed complementary substrate-triggered SCR devices and stacked diode string for the input/output pad and power pad have been successfully verified in a 0.25-/spl mu/m salicided CMOS process with the human body model (machine model) ESD level of /spl sim/7.25 kV (500 V) in a small layout area.  相似文献   
9.
The intent of a binomial effect size display (BESD) is to show "the [real-world] importance of [an] effect indexed by a correlation [r]" (R. Rosenthal, 1994, p. 242) by reexpressing this correlation as a success rate difference (SRD) (e.g., treatment group success rate - control group success rate). However, SRDs displayed in BESDs generally overestimate real-world SRDs implied by correlations of (a) dichotomous X and Y variables (φ coefficients), (b) dichotomous X and continuous Y variables (point-biserial coefficients [rphs]). and (c) continuous X and Y variables (rxys). Furthermore, overestimation biases are larger for rxys than for rphs. Differences in the sizes of biases linked to different correlations suggest that BESD SRDs reported for different correlations are not comparable. The stochastic difference index (N. Cliff, 1993: A. Vargha & H. D. Delaney, 2000) is recommended as an alternative to the BESD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
10.
A method is presented for the construction of fixed-order compensators to provide H norm constraint for linear control systems with exogenous disturbances. The method is based on the celebrated bounded-real lemma that predicates the H norm constraint via a Riccati inequality. The synthesis of fixed-order controllers whose dimensions are less than the order of a given plant, is demonstrated by a set of sufficient conditions along with a numerical algorithm.  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