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   2502篇
  免费   68篇
  国内免费   1篇
电工技术   14篇
综合类   2篇
化学工业   371篇
金属工艺   26篇
机械仪表   32篇
建筑科学   99篇
矿业工程   5篇
能源动力   31篇
轻工业   342篇
水利工程   13篇
石油天然气   11篇
武器工业   1篇
无线电   75篇
一般工业技术   344篇
冶金工业   910篇
原子能技术   3篇
自动化技术   292篇
  2023年   10篇
  2022年   34篇
  2021年   45篇
  2020年   35篇
  2019年   30篇
  2018年   42篇
  2017年   25篇
  2016年   46篇
  2015年   43篇
  2014年   34篇
  2013年   140篇
  2012年   72篇
  2011年   109篇
  2010年   95篇
  2009年   84篇
  2008年   130篇
  2007年   137篇
  2006年   131篇
  2005年   109篇
  2004年   107篇
  2003年   72篇
  2002年   86篇
  2001年   37篇
  2000年   40篇
  1999年   47篇
  1998年   49篇
  1997年   45篇
  1996年   55篇
  1995年   53篇
  1994年   49篇
  1993年   35篇
  1992年   53篇
  1991年   12篇
  1990年   44篇
  1989年   46篇
  1988年   33篇
  1987年   23篇
  1986年   35篇
  1985年   41篇
  1984年   30篇
  1983年   23篇
  1982年   30篇
  1981年   27篇
  1980年   14篇
  1979年   32篇
  1978年   15篇
  1977年   16篇
  1976年   13篇
  1975年   16篇
  1974年   13篇
排序方式: 共有2571条查询结果,搜索用时 15 毫秒
141.
Attitude formation has been thought to require the characteristics of acquiring and accepting new information. However, some evidence exists to suggest that even though comprehension may be reduced by distracting stimuli, this distraction can actually aid persuasion. In order to test such a hypothesis, two experimental groups were tested under different conditions. Group A listened to an emotional message about segregation, and was tested for comprehension and attitude change. Group B was also exposed to the same persuasive message, but during the message presentation, subjects were shown 35mm color slides containing visual stimuli irrelevant to the message. Results indicated that the distracting stimuli produced a significant reduction in recall of information, while also producing a significant opinion shift.  相似文献   
142.
Investigated the effect on the learning of science subject content of having students respond to questions of different degrees of complexity following segments of instruction. The study involved 193 7th-grade students in 5 groups. Questions of differing degrees of complexity were interspersed every 20th frame of the programmed instruction material for 3 treatment groups. The 4th treatment group read a paragraph related to the questions. The 5th group acted as a control. The groups that completed the instructional materials and responded to the interspersed questions scored significantly higher than the group that completed the instructional materials and did not respond to questions. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
143.
Sampled 719 White females, ages 60–75 yrs; half of the Ss were widows and half were currently married, living with a spouse. For each marital-status group, half were childless and half had living children. Results reveal that contact with relatives, friends, and associates was more important for Ss' well-being than contact with children and that well-being was enhanced by quality of interaction. Perceived quality of child contact appeared to be influenced by Ss' perceptions of other social relationships. Weak support for equity theory explanations of relationship satisfaction was found. For Ss with children the amount of interaction appeared unimportant whereas for childless Ss the amount and quality of contact with others was positively related to well-being. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
144.
145.
This paper describes the application of a survival analysis model and a Classification and Regression Trees (CART) model to a data set comprising times to growth of a yeast cocktail inoculated into media simulating a fruit-based or alcoholic food or drink, and covering over 900 combinations of five environmental factors (alcohol, pH, sucrose, sorbate and temperature). Growth was determined as either the time to growth within a 150-day time period or as no-growth after 150 days. Models were developed which could either predict the likelihood of growth occurring within the 150 day period, or the time to grow, either in days or in one of three categories chosen to represent a rapid (1-14 days), medium (15-30 days) or slow (31-150 days) growth response. Growth was observed in 29% of the experimental conditions and demonstrated that the yeasts used were able to grow under extreme environmental conditions, for example at a pH value of 2.1, a temperature of 2 degrees C, a sucrose concentration of 55% (w/w) or an alcohol concentration of 12% (w/v). Generally, both models provided a reasonable fit to the data, and successfully predicted the growth class in 84% of cases. Direct comparisons of the models were made to determine the more suitable for predicting the growth of yeasts in food systems. The survival analysis model was preferred for this data set because it was more fail-safe than the CART model. In food validation studies, the survival model generally gave reliable predictions of time to growth in a range of 23 different food and drink products and is considered to be a reliable model to predict the likelihood and speed of yeast spoilage for a range of fruit-based or alcoholic food or drinks.  相似文献   
146.
147.
148.
149.
An essential assumption for the usefulness of basing accident prevention measures on minor incidents is the common cause hypothesis: that causal pathways of near misses are similar to those of actual accidents (such as injuries and damages). The idea of a common cause hypothesis was originally proposed by Heinrich in his seminal book "Industrial Accident Prevention" [McGraw-Hill, New York]. In this paper, it is argued that the hypothesis of similarity of causes for major and minor accidents has become confounded with the interdependence of the ratio relationship between severity and frequency. This confounded view of the hypothesis has led to invalid tests of the hypothesis and erroneous conclusions. The evidence from various studies is examined and it is concluded that the hypothesis has not been properly understood or tested. Consequently, such a proper test was carried out using data from the UK railways which were analysed using the confidential incident reporting and analysis system (CIRAS) 21 cause taxonomy. The results provide qualified support for the common cause hypothesis with only three out of the 21 types of causes having significantly different proportions for the three consequence levels investigated: 'injury & fatality', 'damage' and 'near miss'.  相似文献   
150.
Elucidation of molecular-level interactions controlling the sorption of organic compounds in soils is of major theoretical and practical interest. Sorption of pi-electron donor compounds, pentamethylbenzene (PMB), naphthalene (NAPH), and phenanthrene (PHEN), in a number of soils was found to increase with decreasing pH in the range of approximately pH 2.5-7. This behavior could not be attributed to pH-dependent alteration of the hydrophobic character of humic substances, pi-H-bonding, interaction with mineral surfaces, interaction with black carbons, solute coplanarity, or pH effects on solute activity coefficient. No significant effect of pH was observed for non-pi-donor hydrophobic compounds, whether planar or not: trans-1,2-dichlorocyclohexane (DCCH), hexachloro-1,3-butadiene (HCBD), 1,2,4-trichlorobenzene (TCB), 2,2',5,5'-tetrachlorobiphenyl, and 3,3',4,4'-tetrachlorobiphenyl. The opposite pH effect was observed for 2-nonanol and 2-nonanone, which are non-pi-donors, but capable of H-bonding. Also, no pH-dependent sorption was observed between the pi-donor PHEN and alumina, a model inorganic surface. We propose that the pi-donor solutes interact with pi-acceptor sites in soil organic matter (SOM), including aromatic rings with multiple carboxyl groups, aromatic amines, or heteroaromatic amines. The pi-acceptor ability of such aromatic moieties would increase with protonation. pi-pi Interactions between PMB, NAPH, and PHEN, and model SOM acceptors, 1,3,5-benzenetricarboxylic acid (BTA), 1,4,5,8-naphthalenetetracarboxylic acid (NTA), and pyridine (PY) in methanol and methanol-water, were verified by the appearance of pH-dependent upfield 1H NMR chemical shifts induced by ring current effects. UV/vis spectra showed pH-dependent charge-transfer bands for various donors with NTA. No NMR shifts or charge-transfer bands were found for nondonor compounds paired with the model acceptors.  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