全文获取类型
收费全文 | 1671篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 283篇 |
金属工艺 | 20篇 |
机械仪表 | 20篇 |
建筑科学 | 104篇 |
矿业工程 | 11篇 |
能源动力 | 22篇 |
轻工业 | 225篇 |
水利工程 | 23篇 |
石油天然气 | 6篇 |
无线电 | 44篇 |
一般工业技术 | 159篇 |
冶金工业 | 626篇 |
原子能技术 | 3篇 |
自动化技术 | 161篇 |
出版年
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 24篇 |
2020年 | 19篇 |
2019年 | 20篇 |
2018年 | 25篇 |
2017年 | 28篇 |
2016年 | 36篇 |
2015年 | 18篇 |
2014年 | 27篇 |
2013年 | 100篇 |
2012年 | 52篇 |
2011年 | 83篇 |
2010年 | 65篇 |
2009年 | 42篇 |
2008年 | 64篇 |
2007年 | 70篇 |
2006年 | 76篇 |
2005年 | 62篇 |
2004年 | 60篇 |
2003年 | 58篇 |
2002年 | 49篇 |
2001年 | 35篇 |
2000年 | 38篇 |
1999年 | 36篇 |
1998年 | 22篇 |
1997年 | 34篇 |
1996年 | 33篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 12篇 |
1990年 | 32篇 |
1989年 | 23篇 |
1988年 | 19篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1978年 | 10篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有1710条查询结果,搜索用时 0 毫秒
71.
The relationship between government actions and innovation in environmental control technology is important for the design of cost-effective policies to achieve environmental goals. This paper examines such relationships for the case of sulfur dioxide control technology for U.S. coal-fired power plants. The study employs several complementary research methods, including analyses of key government actions, technology patenting activity, technology performance and cost trends, knowledge transfer activities, and expert elicitations. Our results indicate that government regulation appears to be a greater stimulus to inventive activity than government-sponsored research support alone, and that the anticipation of regulation also spurs inventive activity. Regulatory stringency focuses this activity along particular technical pathways and is a key factor in creating markets for environmental technologies. We also find that with greater technology adoption, both new and existing systems experience notable efficiency improvements and capital cost reductions. The important role of government in fostering knowledge transfer via technical conferences and other measures is also seen as an important factor in promoting environmental technology innovation. 相似文献
72.
Bekaert B Cooper ML Green FR McNulty H Pentieva K Scott JM Molloy AM Rayman MP 《Molecular nutrition & food research》2008,52(11):1324-1333
The level of plasma total homocysteine (tHcy), long known to be B vitamin dependent, has recently been shown to be inversely associated with plasma selenium (Se) concentration in human subjects. We therefore, chose to investigate the interaction between Se, tHcy and B vitamins in a double-blind, placebo-controlled trial where 501 healthy UK elderly volunteers were randomly allocated to receive 100, 200, or 300 microg Se/day as high-Se-yeast, or placebo-yeast for 6 months. Plasma Se, tHcy, folate, vitamin B-12, pyridoxal-5'-phosphate (PLP) and its catabolite, 4-pyridoxic acid, were measured in all participants at baseline and in samples from the placebo, 100 and 300 microg Se/day groups, at follow-up. At baseline, Se was inversely correlated with tHcy but only in males (p < 0.001). Before supplementation, tHcy concentration was significantly lower in the highest compared to the lowest Se tertile in males (p < 0.05), and in females when folate concentrations were also in the top tertile (p < 0.05). The effect of folate, PLP and vitamin B-12 concentrations on plasma tHcy correlated with Se concentration at baseline. After 6 months of Se supplementation, only Se concentration had changed significantly. Supplementation with Se does not affect tHcy concentration in the UK elderly population. 相似文献
73.
Mark Linton Aideen B. Mackle Vivek K. Upadhyay Alan L. Kelly Margaret F. Patterson 《Innovative Food Science and Emerging Technologies》2008,9(4):423-428
Camembert-type cheese was produced from: raw bovine milk; raw milk inoculated with 2 or 4 log CFU/ml Listeria monocytogenes; raw milk inoculated with L. monocytogenes and subsequently pressure-treated at 500 MPa for 10 min at 20 °C; or uninoculated raw milk pressure-treated under these conditions. Cheeses produced from both pressure-treated milk and untreated milk had the typical composition, appearance and aroma of Camembert. Curd and cheese made from inoculated, untreated milk contained large numbers of L. monocytogenes throughout production. An initial inoculum of 1.95 log CFU/ml in milk increased to 4.52 log CFU/g in the curd and remained at a high level during ripening, with 3.85 log CFU/g in the final cheese. Pressure treatment inactivated L. monocytogenes in the raw milk at both inoculum levels and the pathogen was not detected in any of the final cheeses produced from pressure-treated milk. Therefore high pressure may be useful to inactivate L. monocytogenes in raw milk that is to be used for the production of soft, mould-ripened cheese.
Industrial relevance
This paper demonstrates the potential of high pressure (HP) for treatment of raw milk to be used in the manufacture of soft cheeses. HP treatment significantly reduced the level of Listeria monocytogenes in the raw milk and so allowed the production of safer non-thermally processed camembert-like soft cheese. 相似文献74.
As the fish community changed in the Beaver Archipelago (northern Lake Michigan), so has the diet of breeding Double-crested Cormorants (Phalacrocorax auritus). In 2000, the energetically dense alewife (Alosa pseudoharengus) dominated the diet, but more recently, the relatively low quality round goby (Neogobius melanostomus) has become the most common prey item. Additionally, cormorant control measures have been underway in the archipelago. This study investigated decreases in cormorant chick numbers and changes in chick bioenergetics in response to this change in diet, as well as the influence of control efforts, and compared these results to an earlier study. Two colonies, one actively controlled the other only controlled following completion of this study, were investigated to determine changes in colony size throughout the breeding season, document chick diet, measure chick growth, and determine chick survivorship to fledging. The bioenergetics model estimated that in 2010, chicks consumed a greater biomass of prey to reach fledging due to the change in diet, but lower biomass overall due to fewer chicks in the system. Control efforts in combination with the change in diet reduced chick numbers. Overall, the impact of cormorant chicks on available fish biomass has declined in recent years due to control efforts. However, the birds have the potential to consume a greater biomass of round goby in the absence of control. The impact of cormorants on fisheries resources is complicated by the abundance and effects of non-native species. 相似文献
75.
The stretch of the St. Lawrence River near Cornwall, Ontario, Canada, between the Moses–Saunders power dam to the eastern outlet of Lake St. Francis in Québec, is currently listed as an Area of Concern (AOC), and has restrictive fish consumption advisories in place, largely due to high mercury levels. This study examined long-term temporal trends of mercury concentrations in northern pike, smallmouth bass, walleye and yellow perch from the St. Lawrence River, including the Cornwall AOC. In addition, differences in fish mercury concentrations among river sections were compared for each species using historical (1975–1979) and recent (2000–2011) data. Statistically significant declines in mercury concentrations were observed in all river sections for yellow perch (~ 40%), as well as in northern pike and walleye in at least one river section. For the river section encompassing the AOC, recent mercury concentrations are 33–59% lower than historical mercury concentrations for all four species. Further, a comparison of recent mercury concentrations between the AOC river section and other Ontario lakes/rivers suggests that AOC mercury values are within the 75th percentile of values for other Ontario water bodies in three of the four species considered. However, current fish mercury values for the AOC river section remain higher than one or more upstream river sections. These results indicate that recovery is still ongoing in this AOC. 相似文献
76.
Katharine M. Marko Edward S. Rutherford Brian J. Eadie Thomas H. Johengen Margaret B. Lansing 《Journal of Great Lakes research》2013
Drowned river mouth lakes are major features of coastal Great Lakes habitats and may influence nutrient and organic matter contributions from watersheds to near shore coastal zones. In May through October 2003, we measured loads of nutrients, surficial sediment, and seston to track the delivery of riverine-derived materials from the lower Muskegon River Watershed (MRW) into the near shore area of southeast Lake Michigan. Nutrient flux data indicated that seasonal loads of 1800 metric tons (MT) of particulate organic carbon, 3400 MT of dissolved organic carbon, and 24 MT of total phosphorus were discharged from the lower Muskegon River, with approximately 33% of TP load and 53% of the POC load intercepted within the drowned river mouth terminus, Muskegon Lake. Carbon: phosphorus molar ratios of seston in Muskegon River (C:P = 187) and Muskegon Lake (C:P = 176) were lower than in Lake Michigan (C:P = 334), indicating phosphorus limitation of phytoplankton in near shore Lake Michigan. Isotopic signatures of seston collected in Muskegon Lake were depleted in δ13C (− 30.8 ± 1.6‰) relative to the isotope signatures of seston from Lake Michigan (− 26.2 ± 1.3‰) or the mouth of the Muskegon River (− 28.1 ± 0.5‰), likely due to the presence of biogenic methane in Muskegon Lake. Seston δ15N increased on a strong east-to-west gradient within Muskegon Lake, indicating significant microbial processing of nutrients. The extent of nutrient uptake in Muskegon Lake altered the chemical and isotopic characterization of seston flowing into Lake Michigan from Muskegon River. 相似文献
77.
78.
Brady Sonya S.; Dolcini M. Margaret; Harper Gary W.; Pollack Lance M. 《Canadian Metallurgical Quarterly》2009,28(2):238
Objective: This study examined whether uncontrollable stressful life events were associated with sexual risk taking among adolescents across a 1-year period, and whether supportive friendships modified associations. Design: Participants were 159 sexually active African American adolescents (57% male; mean age [SD] = 17.0 [1.5] years at baseline). Participants were recruited for in-person interviews through random digit dialing in one inner-city neighborhood characterized by high rates of poverty and crime relative to the surrounding city. Main Outcome Measures: Dependent variables included substance use before sexual activity and inconsistent condom use. Results: Among adolescents who reported low levels of supportive friendships, uncontrollable stressors were associated with greater levels of sexual risk taking over time. In contrast, uncontrollable stressors were not associated with sexual risk taking among adolescents who reported high social support from friends; risk taking was typically moderate to high among these adolescents. Conclusion: Different processes may explain sexual risk taking among adolescents with varying levels of social support from friends. Adolescents with low support may be prone to engagement in health risk behavior as a stress response, while adolescents with high support may engage in risk behavior primarily due to peer socialization of risk. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
This study examined the effectiveness of the opposing expert safeguard against unreliable expert testimony and whether beliefs about experts as hired guns and general acceptance mediate the effect of opposing expert testimony on juror decisions. We found strong evidence that the presence, but not the content, of opposing expert testimony affected jurors’ trial judgments and that these effects were mediated by mock jurors’ beliefs about general acceptance. The presence of an opposing expert affected jurors’ ratings of the general acceptance of research investigating sexual harassment in the workplace. Jurors’ beliefs about general acceptance then affected jurors’ ratings of plaintiff expert competence and research, which affected juror ratings of the probability that the plaintiff experienced a hostile work environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
80.
In collaboration with the Armed Forces Institute of Pathology's Department of Defense DNA Registry, the National Institute of Standards and Technology recently evaluated the performance of a short tandem repeat multiplex with dried whole blood stains on four different commercially available identification card matrixes. DNA from 70 stains that had been stored for 19 months at ambient temperature was extracted or directly amplified and then processed using routine methods. All four storage media provided fully typeable (qualitatively identical) samples. After standardization, the average among-locus fluorescence intensity (electropherographic peak height or area) provided a suitable metric for quantitative analysis of the relative amounts of amplifiable DNA in an archived sample. The amounts of DNA in Chelex extracts from stains on two untreated high-purity cotton linter pulp papers and a paper treated with a DNA-binding coating were essentially identical. Average intensities for the aqueous extracts from a paper treated with a DNA-releasing coating were somewhat lower but also somewhat less variable than for the Chelex extracts. Average intensities of directly amplified punches of the DNA-binding paper were much larger but somewhat more variable than the Chelex extracts. Approximately 25% of the observed variation among the intensity measurements is shared among the four media and thus can be attributed to intrinsic variation in white blood count among the donors. All of the evaluated media adequately "bank" forensically useful DNA in well-dried whole blood stains for at least 19 months at ambient temperature. 相似文献