全文获取类型
收费全文 | 13054篇 |
免费 | 563篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 136篇 |
综合类 | 18篇 |
化学工业 | 2439篇 |
金属工艺 | 237篇 |
机械仪表 | 232篇 |
建筑科学 | 864篇 |
矿业工程 | 46篇 |
能源动力 | 351篇 |
轻工业 | 1025篇 |
水利工程 | 161篇 |
石油天然气 | 43篇 |
武器工业 | 1篇 |
无线电 | 895篇 |
一般工业技术 | 2377篇 |
冶金工业 | 2571篇 |
原子能技术 | 58篇 |
自动化技术 | 2211篇 |
出版年
2023年 | 63篇 |
2022年 | 71篇 |
2021年 | 224篇 |
2020年 | 167篇 |
2019年 | 185篇 |
2018年 | 263篇 |
2017年 | 216篇 |
2016年 | 327篇 |
2015年 | 252篇 |
2014年 | 402篇 |
2013年 | 839篇 |
2012年 | 665篇 |
2011年 | 903篇 |
2010年 | 691篇 |
2009年 | 640篇 |
2008年 | 757篇 |
2007年 | 749篇 |
2006年 | 614篇 |
2005年 | 582篇 |
2004年 | 502篇 |
2003年 | 396篇 |
2002年 | 472篇 |
2001年 | 287篇 |
2000年 | 275篇 |
1999年 | 236篇 |
1998年 | 245篇 |
1997年 | 219篇 |
1996年 | 183篇 |
1995年 | 230篇 |
1994年 | 189篇 |
1993年 | 196篇 |
1992年 | 162篇 |
1991年 | 75篇 |
1990年 | 137篇 |
1989年 | 116篇 |
1988年 | 112篇 |
1987年 | 115篇 |
1986年 | 83篇 |
1985年 | 138篇 |
1984年 | 127篇 |
1983年 | 82篇 |
1982年 | 67篇 |
1981年 | 64篇 |
1980年 | 45篇 |
1979年 | 53篇 |
1978年 | 42篇 |
1977年 | 27篇 |
1976年 | 35篇 |
1974年 | 25篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Jamieson David W.; Lydon John E.; Stewart Glenn; Zanna Mark P. 《Canadian Metallurgical Quarterly》1987,79(4):461
We conducted a field experiment to test the idea that students' expectations regarding their teacher's competence would influence their classroom behavior and academic achievement. At the end of a 3-week teaching unit, students in two high school classes who had been given an initial positive expectancy about their teacher's ability and motivation engaged in more appropriate and less inappropriate nonverbal behavior and received significantly higher final grades on the unit than did their peers in two no-expectation control classes. We speculate about both the direct (student-mediated) and indirect (teacher-mediated) processes by which students' expectations came to affect their academic outcomes. We also discuss the importance of group-level expectancies and some ethical issues in student expectancy research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
992.
Mark Prelas Frederick Boody Warren Gallaher Edbertho Leal-Quiros David Mencin Scott Taylor 《Journal of Fusion Energy》1990,9(3):309-313
Experiments are being performed to initiate the cold fusion process in Maxwellian plasmas and sub-atmospheric deuterium gas. Thus far, apparent neutron counts have been observed using a BF3 probe and Ludlum model 2200 digital counter, and a broad 8.1 MeV peak has been observed using a 3-inch sodium iodide crystal and a Nucleus PCA II multichannel analyzer. The results appear to be dependent upon the temperature of the palladium sample, deuterium pressure, and the type of palladium sample used. The results are interesting but not sufficient for any conclusions at this point. 相似文献
993.
D. Niemeier Gregory GouldAlex Karner Mark HixsonBrooke Bachmann Carrie OkmaZiv Lang David Heres Del Valle 《Energy Policy》2008
With the passage of the Global Warming Solutions Act of 2006 (AB32), California has begun an ambitious journey to reduce in-state GHG emissions to 1990 levels by 2020. Under the direction of executive order S-20-06, a mandated Market Advisory Committee (MAC) charged with studying market-based mechanisms to reduce GHG emissions, including cap and trade systems, has recommended taking an “upstream” approach to GHG emissions regulation, arguing that upstream regulation will reduce administrative costs because there are fewer agents. In this paper, we argue that, the total costs to society of a GHG cap and trade scheme can be minimized though downstream regulation, rather than the widely proposed upstream approach. We propose a household carbon trading system with four major components: a state allocation to households, household-to-household trading, households to utility company credit transfers, and utility companies to government credit transfers. The proposed system can also be considered more equitable than carbon taxes and upstream cap and trade systems to control GHG emissions from residential energy use and is consistent with AB32. 相似文献
994.
We used Monte Carlo simulations to evaluate the sensitivity of tag-recovery mortality estimates to inaccuracies in tag shedding, handling mortality, and tag reporting. The data-generating model used in the simulations assumed that tagging was conducted annually for 4 years with tag recoveries occurring over a 4-year period. Several different combinations of instantaneous fishing (F) and natural (M) mortality were evaluated in the simulations. The data-generating model additionally assumed that immediate-shedding and handling-mortality rates equaled 2.5% and 0%, respectively, and that chronic shedding was a sigmoidal function of months since tagging. Two spatial patterns of reporting rates were considered—one where reporting was a function of distance from the tagging site and one where reporting was a random generation across the study area. Maximum likelihood estimates of F and M were calculated from the recovery of tags from the data-generating model under different assumed rates of tag shedding, handling mortality, and tag reporting. We found that assumptions about reporting rates resulted in the most variability in mortality estimates regardless of which combination of F and M was evaluated, with assumptions about chronic shedding also contributing substantially to overall variability in mortality estimates for most mortality combinations. Assumptions about immediate tag shedding and handling mortality had relatively minor effects on mortality estimates compared to reporting rate. When planning a tag-recovery study, care should be taken to ensure that chronic shedding and tag-reporting rates are accurately measured, as inaccurate measurements in these factors can result in significant errors in mortality estimates. 相似文献
995.
This paper investigates the flexure of prestressed concrete beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) sheets, focusing on ductility and cracking behavior. Structural ductility of a beam strengthened with CFRP sheets is critical, considering the abrupt and brittle failure of CFRP sheets themselves. Cracking may also affect serviceability of a strengthened beam, and may be especially important for durability. Midscale prestressed concrete beams (L = 3.6?m) are constructed and a significant loss of prestress is simulated by reducing the reinforcement ratio to observe the strengthening effects. A nonlinear iterative analytical model, including tension of concrete, is developed and a nonlinear finite-element analysis is conducted to predict the flexural behavior of tested beams. The prestressed CFRP sheets result in less localized damage in the strengthened beam and the level of the prestress in the sheets significantly contributes to the ductility and cracking behavior of the strengthened beams. Consequently, the recommended level of prestress to the CFRP sheets is 20% of the ultimate design strain with adequate anchorages. 相似文献
996.
Mark Bhatti 《Housing Studies》2001,16(1):39-52
Housing studies have much to contribute to the debate about sustainable futures and yet there has been a lack of critical engagement with environmentalism. This paper sets out to show how the environmental debate can be enhanced by three traditional perspectives found within housing studies; these are: neo-classical economics, Weberian sociology and Marxism. It is suggested that housing researchers have begun to incorporate environmental issues into housing analysis, but we need to go further and engage in the environmental debate through the development of an eco-sensitive housing concept. The paper is a contribution towards an environmental understanding of the housing process. 相似文献
997.
998.
Liu David; Wellman Henry M.; Tardif Twila; Sabbagh Mark A. 《Canadian Metallurgical Quarterly》2008,44(2):523
Theory of mind is claimed to develop universally among humans across cultures with vastly different folk psychologies. However, in the attempt to test and confirm a claim of universality, individual studies have been limited by small sample sizes, sample specificities, and an overwhelming focus on Anglo- European children. The current meta-analysis of children's false-belief performance provides the most comprehensive examination to date of theory-of-mind development in a population of non-Western children speaking non-Indo-European languages (i.e., Mandarin and Cantonese). The meta-analysis consisted of 196 Chinese conditions (127 from mainland China and 69 from Hong Kong), representing responses from more than 3,000 children, compared with 155 similar North American conditions (83 conditions from the United States and 72 conditions from Canada). The findings show parallel developmental trajectories of false-belief understanding for children in China and North America coupled with significant differences in the timing of development across communities-children's false-belief performance varied across different locales by as much as 2 or more years. These data support the importance of both universal trajectories and specific experiential factors in the development of theory of mind. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
Central naloxone injections were used to show that endogenous opioids in the ventral tegmental area (VTA) regulate consumption of palatable foods. Peripheral injections of naloxone were more effective in reducing the consumption of a sweet solution in normally fed rats than in animals maintained at 85% of their free-feeding body weight. A dose of 10 μg/side naloxone injected into the VTA reduced consumption in normally fed rats, whereas a dose of 25 μg/side did the same in food-restricted animals. The inactive isomer, (+) naloxone, did not reduce consumption; the effect has anatomical specificity. Naloxone effectively decreases the eating of palatable foods, but not eating for survival. This has important implications for the use of opioid antagonists in weight-loss programs. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
1000.
Mark A. Norris Leonard Meirovitch 《International journal for numerical methods in engineering》1989,28(10):2451-2463
Structures are often characterized by parameters, such as mass and stiffness, that are spatially distributed. Parameter identification of distributed structures is subject to many of the difficulties involved in the modelling problem, and the choice of the model can greatly affect the results of the parameter identification process. Analogously to control spillover in the control of distributed-parameter systems, identification spillover is shown to exist as well and its effect is to degrade the parameter estimates. Moreover, as in modelling by the Rayleigh–Ritz method, it is shown that, for a Rayleigh–Ritz type identification algorithm, an inclusion principle exists in the identification of distributed-parameter systems as well, so that the identified natural frequencies approach the actual natural frequencies monotonically from above. 相似文献