全文获取类型
收费全文 | 1548篇 |
免费 | 44篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 17篇 |
综合类 | 1篇 |
化学工业 | 296篇 |
金属工艺 | 24篇 |
机械仪表 | 34篇 |
建筑科学 | 94篇 |
矿业工程 | 14篇 |
能源动力 | 51篇 |
轻工业 | 105篇 |
水利工程 | 16篇 |
石油天然气 | 107篇 |
无线电 | 59篇 |
一般工业技术 | 166篇 |
冶金工业 | 453篇 |
原子能技术 | 16篇 |
自动化技术 | 140篇 |
出版年
2021年 | 26篇 |
2019年 | 25篇 |
2018年 | 21篇 |
2017年 | 24篇 |
2016年 | 15篇 |
2015年 | 18篇 |
2014年 | 30篇 |
2013年 | 93篇 |
2012年 | 45篇 |
2011年 | 55篇 |
2010年 | 47篇 |
2009年 | 52篇 |
2008年 | 61篇 |
2007年 | 57篇 |
2006年 | 54篇 |
2005年 | 49篇 |
2004年 | 32篇 |
2003年 | 43篇 |
2002年 | 33篇 |
2001年 | 24篇 |
2000年 | 37篇 |
1999年 | 28篇 |
1998年 | 41篇 |
1997年 | 36篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 29篇 |
1993年 | 29篇 |
1992年 | 34篇 |
1991年 | 22篇 |
1990年 | 31篇 |
1989年 | 30篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 28篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 16篇 |
1977年 | 15篇 |
1976年 | 25篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1973年 | 21篇 |
1971年 | 10篇 |
1970年 | 10篇 |
排序方式: 共有1593条查询结果,搜索用时 15 毫秒
101.
Morgenstern Jon; Irwin Thomas W.; Wainberg Milton L.; Parsons Jeffrey T.; Muench Frederick; Bux Donald A. Jr.; Kahler Christopher W.; Marcus Susan; Schulz-Heik Jay 《Canadian Metallurgical Quarterly》2007,75(1):72
This study tested the efficacy of behavioral treatments for alcohol use disorders (AUD) among men who have sex with men (MSM) and who are at risk for HIV transmission. HIV-negative MSM with current AUD (N = 198) were recruited, offered treatment focused on reducing drinking and HIV risk, and followed during treatment and 12 months posttreatment. Participants (n = 89) accepted treatment and were randomized to either 4 sessions of motivational interviewing (MI) or 12 sessions of combined MI and coping skills training (MI + CBT). Other participants (n = 109) declined treatment but were followed, forming a non-help-seeking group (NHS). MI yielded significantly better drinking outcomes during the 12-week treatment period than MI + CBT, but posttreatment outcomes were equivalent. NHS participants significantly reduced their drinking as well. Service delivery and treatment research implications are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
Philippe Marguet Frederick Balagadde Cheemeng Tan Lingchong You 《Journal of the Royal Society Interface》2007,4(15):607-623
Biological research is experiencing an increasing focus on the application of knowledge rather than on its generation. Thanks to the increased understanding of cellular systems and technological advances, biologists are more frequently asking not only ‘how can I understand the structure and behaviour of this biological system?’, but also ‘how can I apply that knowledge to generate novel functions in different biological systems or in other contexts?’ Active pursuit of the latter has nurtured the emergence of synthetic biology. Here, we discuss the motivation behind, and foundational technologies enabling, the development of this nascent field. We examine some early successes and applications while highlighting the challenges involved. Finally, we consider future directions and mention non-scientific considerations that can influence the field''s growth. 相似文献
103.
N. A. Frederick T. A. Sayles S. K. Kim M. B. Maple 《Journal of Low Temperature Physics》2007,147(3-4):321-333
The double superconducting transition in PrOs4Sb12, first observed in specific heat C(T) measurements on single crystal samples, was studied by means of specific heat measurements
on PrOs4Sb12 crystals that had been subjected to applied magnetic fields, substitution of up to 4 Ru for Os, and annealing. The double
superconducting transitions of a batch of single crystals were measured before and after annealing for 5 days at 500°C, to
remove strains and promote homogeniety, with no observed change. Measurements of C(T) near Tc for PrOs4Sb12 in several magnetic fields are also presented, detailing the evolution of the double transition up to 1 T. Samples of Pr(Os1-x Rux)Sb12 with 0.01 ≤ x ≤ 0.04 also appear to display a double superconducting transition in specific heat. In addition, samples
with the smallest Ru concentration measured (x = 0.01) may even display a more isotropic type of superconductivity than pure
PrOs4Sb12 (x = 0). 相似文献
104.
Frederick D. Parker 《Cryptologia》2013,37(4):295-313
In 1941, the United States Navy intercepted enough Japanese naval messages to predict the attack on Pearl Harbor if the code which protected them had been solved. The messages would have disclosed that, while the Japanese government cynically conducted diplomatic negotiations with the United States, the Japanese Combined Fleet under Admiral Isoroku Yamamoto, beginning as early as September 1941, systematically prepared ships, crews, weapons, tactics, and a complicated fuel supply system for the most ambitious operation ever undertaken by the Japanese navy. Details of Japan's intentions were hidden from Navy cryptanalysts because of limited manpower resources and because all Japanese navy codes were assigned a lower priority than Japanese diplomatic codes and German submarine threat. 相似文献
105.
Anis Ben Aissa Robert K. Abercrombie Frederick T. Sheldon Ali Mili 《Information Systems and E-Business Management》2012,10(4):433-453
In earlier work, we presented a value based measure of cybersecurity that quantifies the security of a system in concrete terms, specifically, in terms of how much each system stakeholder stands to lose (in dollars per hour of operation) as a result of security threats and system vulnerabilities; our metric varies according to the stakes that each stakeholder has in meeting each security requirement. In this paper, we discuss the specification and design of a system that collects, updates, and maintains all the information that pertains to estimating our cybersecurity measure, and offers stakeholders quantitative means to make security-related decisions. 相似文献
106.
Nanotechnology is an emerging field of science with the potential to generate new and enhance existing products and transform
the production process. US patent data is used to track the emergence of nanotechnologies since 1978. The nanotechnologies
that have undergone the most development are identified using patent citation data and co-citation patterns of patents are
examined to define clusters of related nanotechnologies. The potential for economic impact of the emerging nanotechnologies
is assessed using a generality index. 相似文献
107.
In a sample of 247 college students, the contributions of adult attachment orientations and several other boundary regulation variables to measures of self-splitting (i.e., the tendency to report diffuse and chaotic self-experiences) and other-splitting (i.e., the tendency to acknowledge unstable perceptions of and feelings toward one's friends) were explored. Adult attachment orientations and self-other boundary regulation variables, respectively, explained unique variance in each criterion measure. High levels of attachment anxiety and self-concealment and low levels of self-other differentiation contributed most prominently to self-splitting, whereas high attachment anxiety, low emotional reactivity, and high needs for social approval best predicted other-splitting. Implications of these findings for advancing a more delineated understanding of splitting tendencies are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
108.
Walter A. Wohlmuth Bill Davenport Tyler Bowman Pat Hamilton Robert Hallgren Frederick S. Pool Andy Turudic 《Solid-state electronics》2005,49(12):1978
GaAs MESFETs with novel lowly-doped drain structures have been developed utilizing molecular implants of silicon trifluoride. Short-channel effects in the 1/4 μm enhancement- and depletion-mode transistors have been suppressed with drain-induced barrier height lowering of less than 70 mV/V and pinch-off voltage shifts of less than 220 mV as the gate length was scaled from 1.0 to 1/4 μm. The 3-terminal breakdown, the transconductance to output conductance ratio, and the unity current gain, cut-off frequency were simultaneously optimized. The E-mode device possessed breakdown of >10 V, Gm · Rds > 9.5, Ft > 55 GHz, and nominal on-resistance of 2.1 Ω mm while the D-mode device had breakdown >10 V, Gm · Rds > 6.0, Ft > 45 GHz, and nominal on-resistance of 1.9 Ω mm. These optimized transistors enabled the realization of a variety of low-power digital and high-power mixed signal circuits, using 3-level source-coupled transistor and common-mode logic, such as laser and electro-optic drivers, highly integrated transceivers, multiplexers, demultiplexers, and clock data recover circuits. 相似文献
109.
Robert C. Abt Karen L. Abt Frederick W. Cubbage Jesse D. Henderson 《Biomass & bioenergy》2010,34(12):1679-1686
Key factors driving renewable energy demand are state and federal policies requiring the use of renewable feedstocks to produce energy (renewable portfolio standards) and liquid fuels (renewable fuel standards). However, over the next decade, the infrastructure for renewable energy supplies is unlikely to develop as fast as both policy- and market-motivated renewable energy demands. This will favor the use of existing wood as a feedstock in the first wave of bioenergy production. The ability to supply wood over the next decade is a function of the residual utilization, age class structure, and competition from traditional wood users. Using the North Carolina Renewable Portfolio Standard as a case study, combined with assumptions regarding energy efficiency, logging residual utilization, and traditional wood demands over time, we simulate the impacts of increased woody biomass demand on timber markets. We focus on the dynamics resulting from the interaction of short-run demand changes and long-term supply responses. We conclude that logging residuals alone may be unable to meet bioenergy demands from North Carolina’s Renewable Portfolio Standard. Thus, small roundwood (pulpwood) may be used to meet remaining bioenergy demands, resulting in increased timber prices and removals; displacement of traditional products; higher forest landowner incomes; and changes in the structure of the forest resource. 相似文献
110.
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