全文获取类型
收费全文 | 28161篇 |
免费 | 711篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 346篇 |
综合类 | 14篇 |
化学工业 | 6120篇 |
金属工艺 | 586篇 |
机械仪表 | 482篇 |
建筑科学 | 1220篇 |
矿业工程 | 332篇 |
能源动力 | 690篇 |
轻工业 | 1846篇 |
水利工程 | 229篇 |
石油天然气 | 249篇 |
无线电 | 1858篇 |
一般工业技术 | 4302篇 |
冶金工业 | 6494篇 |
原子能技术 | 270篇 |
自动化技术 | 3868篇 |
出版年
2022年 | 255篇 |
2021年 | 431篇 |
2020年 | 277篇 |
2019年 | 356篇 |
2018年 | 437篇 |
2017年 | 390篇 |
2016年 | 505篇 |
2015年 | 423篇 |
2014年 | 642篇 |
2013年 | 1704篇 |
2012年 | 978篇 |
2011年 | 1266篇 |
2010年 | 971篇 |
2009年 | 1023篇 |
2008年 | 1201篇 |
2007年 | 1119篇 |
2006年 | 1013篇 |
2005年 | 927篇 |
2004年 | 784篇 |
2003年 | 753篇 |
2002年 | 748篇 |
2001年 | 510篇 |
2000年 | 416篇 |
1999年 | 492篇 |
1998年 | 547篇 |
1997年 | 489篇 |
1996年 | 532篇 |
1995年 | 494篇 |
1994年 | 510篇 |
1993年 | 471篇 |
1992年 | 446篇 |
1991年 | 284篇 |
1990年 | 433篇 |
1989年 | 402篇 |
1988年 | 347篇 |
1987年 | 414篇 |
1986年 | 354篇 |
1985年 | 452篇 |
1984年 | 473篇 |
1983年 | 401篇 |
1982年 | 381篇 |
1981年 | 305篇 |
1980年 | 303篇 |
1979年 | 364篇 |
1978年 | 304篇 |
1977年 | 244篇 |
1976年 | 235篇 |
1975年 | 248篇 |
1974年 | 220篇 |
1973年 | 229篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
Terrorism: A Reference Handbook, Stephen Atkins, Santa Barbara, ABC-CLIO (1992), 199 pp. Terrorism: Roots, Impact, Responses, Lawrence Howard (Ed.), Prager, New York (1992), 193 pp. Hostage-Taking Terrorism: Incident Response Strategy, Alastair MacWillson, St Martins, New York (1992), 263 pp. 相似文献
14.
15.
We will analyze the economic sensitivity of new energy-saving technologies to weather, future energy price, and system lifetime uncertainties. Graphical rate of return analysis is employed. A representative residential solar water heating investment is analyzed to illustrate the impact of uncertainties. The wide range of reasonable rates of return found suggests some considerations for policy makers and some areas of future research. 相似文献
16.
Previous papers have demonstrated that low-cost off-peak electricity can be used to provide auxiliary heating for a passive-solar-heated residence. This paper describes the development of optimal control strategies for the operation of this auxiliary heating system. The temperature in the residence throughout the day as determined by computer simulation is presented for several optimal and conventional control strategies. The optimal control strategies improved the temperature control in the building compared to the conventional strategies. All strategies were shown to depend heavily on weather prediction. Computer simulations showed that errors in weather prediction had a small effect on heating cost and a large effect on being able to maintain the desired indoor temperature. 相似文献
17.
Mass transport in wood during drying can have different mechanisms at different periods of drying. Depending on the current moisture content (MC) and the structure of the wood, the driving forces for the mass transport are essentially different. Above the fiber saturation point (FSP), the lumens are partially saturated and the transport of liquid (free) water occurs as a consequence of capillary action. On the other hand, below the FSP, bound water within the cell walls is conveyed by diffusion, and water vapor in the lumens moves under influence of pressures gradient. Based on these considerations, a unified model is presented that takes into account the transport of the different moisture phases. Simulation of the drying of a Norway spruce sample at 50°C from about 135 to 7% MC is carried out using the finite element method (FEM). Comparison between the simulated average MC and the experimental observations obtained from X-ray computed tomography (CT) shows reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation. Finally, the influence of absolute permeability on the average MC is studied. 相似文献
18.
Prentky Robert A.; Knight Raymond A.; Lee Austin F. S. 《Canadian Metallurgical Quarterly》1997,65(1):141
This study examined the predictive efficacy of 10 rationally derived, archivally coded variables for assessing reoffense risk among extrafamilial child molesters. Follow-up data on 111 child molesters who were discharged from the Massachusetts Treatment Center between 1960 and 1984 were used. Degree of sexual preoccupation with children, paraphilias, and number of prior sexual offenses predicted sexual recidivism. Juvenile and adult antisocial behavior, paraphilias, and low amount of contact with children predicted nonsexual victim-involved and violent recidivism. Area under the receiver-operating characteristic curves in all three analyses indicated discrimination that was substantially better than chance, ranging from .73 to .79. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
Reports an error in "Does reward increase or decrease creativity" by Robert Eisenberger and Michael Selbst (Journal of Personality and Social Psychology, 1994[Jun], Vol 66[6], 1116-1127). In the aforementioned article, Figures 1 and 2 were interchanged. The figures appear with their correct captions in the erratum. (The following abstract of the original article appeared in record 1994-40652-001.) Two studies involving 504 school children investigated why behaviorists and cognitively oriented investigators have come to opposite conclusions about reward's effects on creativity. A monetary reward for a high degree of divergent thought in 1 task (word construction) increased children's subsequent originality in a different task (picture drawing). The same reward, made contingent on a low degree of divergent thought, reduced this generalized originality. These effects were eliminated by using a large reward and were restored by keeping the large reward out of the children's sight. The results suggest that reward training increases generalized creativity when (1) a high degree of divergent thought is required and (2) the reward is presented in not too salient a fashion. The findings are consistent with a 2-factor interpretation of rewarded creativity effects that incorporates learned industriousness and selective attention. [A correction concerning this article appears in Journal of Personality & Social Psychology, 1994(Jul), Vol 67(1), 125. Figures 1 and 2 were interchanged.] (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
20.
The question of "What makes things seem similar?" is important both for the pivotal role of similarity in theories of cognition and for an intrinsic interest in how people make comparisons. Similarity frequently involves more than listing the features of the things to be compared and comparing the lists for overlap. Often, the parts of one thing must be aligned or placed in correspondence with the parts of the other. The quantitative model with the best overall fit to human data assumes an interactive activation process whereby correspondences between the parts of compared things mutually and concurrently influence each other. An essential aspect of this model is that matching and mismatching features influence similarity more if they belong to parts that are placed in correspondence. In turn, parts are placed in correspondence if they have many features in common and if they are consistent with other developing correspondences. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献