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   2423篇
  免费   111篇
  国内免费   2篇
电工技术   15篇
综合类   4篇
化学工业   515篇
金属工艺   18篇
机械仪表   21篇
建筑科学   107篇
矿业工程   3篇
能源动力   35篇
轻工业   348篇
水利工程   34篇
石油天然气   1篇
无线电   83篇
一般工业技术   323篇
冶金工业   844篇
原子能技术   4篇
自动化技术   181篇
  2024年   4篇
  2023年   35篇
  2022年   87篇
  2021年   90篇
  2020年   57篇
  2019年   47篇
  2018年   63篇
  2017年   50篇
  2016年   57篇
  2015年   45篇
  2014年   63篇
  2013年   117篇
  2012年   111篇
  2011年   162篇
  2010年   128篇
  2009年   129篇
  2008年   154篇
  2007年   126篇
  2006年   107篇
  2005年   95篇
  2004年   85篇
  2003年   69篇
  2002年   76篇
  2001年   42篇
  2000年   52篇
  1999年   44篇
  1998年   39篇
  1997年   48篇
  1996年   42篇
  1995年   45篇
  1994年   55篇
  1993年   36篇
  1992年   32篇
  1991年   9篇
  1990年   25篇
  1989年   16篇
  1988年   25篇
  1987年   13篇
  1986年   7篇
  1985年   11篇
  1984年   6篇
  1983年   7篇
  1982年   5篇
  1981年   6篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1974年   2篇
  1970年   1篇
  1968年   2篇
排序方式: 共有2536条查询结果,搜索用时 743 毫秒
991.
Beneficial reuse as an alternative to disposal is increasingly being considered in management of contaminated sediments dredged from harbors. The risk of metal leaching into groundwater in reuse of phosphate and thermal treated sediments was assessed with sequential extraction, synthetic precipitation leaching procedure (SPLP), and leaching as a function of pH and liquid to solid ratio (L/S). Sequential extraction revealed that phosphate addition at 5% by dry weight, followed by calcination at 700°C reduced metal association with exchangeable/carbonate and organic phases and increased that with sparingly soluble residuals. Over the pH range 4 to 9, metal leachability varied by two to four orders of magnitude while varying L/S over 5 to 100 showed little difference. The SPLP revealed that risk to groundwater criteria based on applying a dilution attenuation factor (DAF) of 13 (New Jersey) to groundwater quality levels were achieved. Risk criteria based on a DAF of 1 (Florida and Wisconsin) were exceeded for Pb, Cd, and Mn; thermodynamic analysis demonstrates that the criteria cannot be satisfied should dissolution control pore water concentrations.  相似文献   
992.
993.
This study examined whether parents of adolescents experiencing depressive symptoms or disorder make more negative and fewer positive attributions for their adolescents’ behavior than do parents of nondepressed adolescents, and whether parental attributions for adolescents’ behavior contribute to parenting behavior, above and beyond the adolescents’ behavior. Parents and adolescents (76 girls and 48 boys) participated in videotaped problem-solving interactions (PSIs). Each parent subsequently watched the videotape and offered attributions for their adolescent’s behavior. In addition, parent and adolescent behavior during the PSIs was coded. Mothers and fathers in families of nondepressed adolescents made significantly fewer negative attributions for their children’s behavior than did parents in families of adolescents with diagnostic or subdiagnostic levels of depressive symptoms. Moreover, mothers’ and fathers’ negative attributions were related to greater levels of observed aggressive behavior and lower levels of observed facilitative behavior during the PSIs controlling for both demographic characteristics and the relative level of adolescent aggressive and facilitative behavior during the PSI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
994.
The Treatment Integrity Planning Protocol (TIPP) provides a structured process for collaboratively creating a treatment integrity assessment within a consultation framework. The authors evaluated the effect of the TIPP on the implementation of an intervention designed to improve the consistency of students' mathematics performance. Treatment integrity was assessed via permanent products and teacher self-report assessments resulting from TIPP completion. Results showed that (a) 3 teachers' treatment integrity declined within the first week of implementation and increased subsequent to completion of the TIPP, (b) teachers accurately reported their level of treatment integrity, and (c) the relationship between treatment integrity and student outcomes was unclear. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
995.
The present study investigates whether interepisode mood regulation impairment contributes to disturbances in sleep onset latency (SOL) and rapid eye movement (REM) sleep. Individuals with interepisode bipolar disorder (n = 28) and healthy controls (n = 28) slept in the laboratory for 2 baseline nights, a happy mood induction night, and a sad mood induction night. There was a significant interaction whereby on the happy mood induction night the bipolar group exhibited significantly longer SOL than did the control group, while there was no difference on the baseline nights. In addition, control participants exhibited shorter SOL on the happy mood induction night compared to the baseline nights, a finding that was not observed in the bipolar group. On the sad mood induction night, participants in both groups had shorter SOL and increased REM density when compared to the baseline nights. Bipolar participants exhibited heightened REM density compared to control participants on both nights. These results raise the possibility that regulation of positive stimuli may be a contributor to difficulties with SOL, while hyperactivity may be characteristic of REM sleep. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
996.
Stress and anxiety have been shown to increase smoking motivation. There is limited experimental data on depressed or sad mood and smoking. This study investigated the effects of two induced moods on smoking behavior. Depression scores were examined as a potential moderator and mood changes were tested as a potential mediator. Smokers (N = 121) were randomly assigned to receive either a sad induction or a neutral induction via standardized film clips. Among participants with higher depression scores, smoking duration and the number of cigarette puffs were greater in response to the sad condition. There was also a marginal interactive effect on the change in expired air carbon monoxide among this subsample; however, no differences in smoking latency or craving were observed. Changes in positive mood partially mediated the effect of condition on smoking behavior among participants with high depression scores. There was no modifying effect of gender or mediating effect of negative mood changes. The results provide preliminary support that decreases in positive mood may have a greater influence on smoking behavior among depression-prone smokers than less psychiatrically vulnerable smokers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
997.
998.
The current study was conducted to characterize discriminated avoidance learning in mice by using a Y-maze task. In Experiment 1, the task parameters were manipulated, including the amount of time spent in the start arm, the amount of time to make the avoidance response, and the intertrial interval (ITI) using C57?×?SJL F1 hybrid mice. Avoidance performance was significantly improved with longer times to avoid the shock and longer ITIs. In Experiment 2, mice from 4 inbred strains (BALB/cByJ, DBA/2J, C57BL/6J, and SJL/J), an F1 hybrid (C57?×?SJL), and 1 outbred strain (CD1) were tested with various ITIs. Strain differences were observed in avoidance learning, with BALB, DBA, C57?×?SJL and CD1 mice showing significantly better avoidance learning than C57 mice, which were better than SJL mice. These data demonstrate that Y-maze performance is significantly influenced by the genetic background of the mouse and the parameters of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
999.
This study examined levels of intrusion and avoidance symptoms and their relationships to past life stress, current emotional support, disease-related variables, and age in 125 women with metastatic breast cancer. The results indicate that a sizable proportion of these women experienced clinically significant levels of intrusion and avoidance symptoms related to their cancer, particularly those with both more stressful past life events and higher current levels of aversive emotional support. Additionally, both types of symptoms were associated with shorter time since recurrence, and avoidance symptoms were associated with smaller emotional support networks. These results indicate that metastatic breast cancer is an emotionally traumatic event for a significant proportion of women, particularly those with past life stressors and unsupportive social environments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
1000.
This analysis uses data from a survey of Toronto commuter cyclists that collected information regarding accident history as well as regular commute route to work or school. By relating the route information of the 1196 respondents to facility attributes in a Geographic Information System (GIS), defensible estimates of travel exposure on roads, off-road paths and sidewalks were developed. The rate of collision on off-road paths and sidewalks was lower than for roads. The relative rates for falls and injuries suggest these events are least common on-road followed by off-road paths, and finally most common on sidewalks. The rate of major injuries, an injury that required medical attention, was greatest on sidewalks and the difference between paths and sidewalks was negligible. These rates suggest a need for detailed analysis of sidewalk and off-road path bicycle safety. The absolute event rates per bicycle kilometer were found to be between 26 and 68 times higher than similar rates for automobile travel, re-confirming the urgent bicycle safety crisis. Examination of rates for sub-groups of cyclists suggest that experience is an important factor in bicycle safety. The same survey conducted in Ottawa, Canada found event rates much lower than Toronto. This result may confirm urban form, traffic levels and attitude do affect bicycle safety. The analysis also demonstrates a successful method to quantify bicycle travel exposure information and should be considered for further use as complement to other existing techniques.  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