全文获取类型
收费全文 | 2502篇 |
免费 | 68篇 |
国内免费 | 1篇 |
专业分类
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 |
出版年
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