全文获取类型
收费全文 | 1072篇 |
免费 | 32篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 227篇 |
金属工艺 | 9篇 |
机械仪表 | 10篇 |
建筑科学 | 56篇 |
矿业工程 | 1篇 |
能源动力 | 23篇 |
轻工业 | 142篇 |
水利工程 | 37篇 |
石油天然气 | 8篇 |
无线电 | 63篇 |
一般工业技术 | 189篇 |
冶金工业 | 227篇 |
原子能技术 | 3篇 |
自动化技术 | 106篇 |
出版年
2024年 | 24篇 |
2023年 | 27篇 |
2022年 | 39篇 |
2021年 | 54篇 |
2020年 | 43篇 |
2019年 | 46篇 |
2018年 | 63篇 |
2017年 | 42篇 |
2016年 | 49篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 40篇 |
2012年 | 54篇 |
2011年 | 85篇 |
2010年 | 72篇 |
2009年 | 42篇 |
2008年 | 63篇 |
2007年 | 50篇 |
2006年 | 46篇 |
2005年 | 34篇 |
2004年 | 25篇 |
2003年 | 27篇 |
2002年 | 14篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 8篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1970年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1955年 | 1篇 |
1929年 | 1篇 |
1926年 | 4篇 |
1925年 | 11篇 |
排序方式: 共有1104条查询结果,搜索用时 15 毫秒
1.
Emily Jackson Levitt David L. Pelletier Charlotte Dufour Alice N. Pell 《Food Security》2011,3(3):363-381
Coordination across sectors to address undernutrition with its varied underlying causes remains a challenge in developing countries. In Afghanistan, harmonization of health and agriculture policies and actions to reduce endemic undernutrition occurred during 2002-2007. This qualitative case study explores the forms of harmonization, enabling features and constraints in the policy process. We interviewed 57 stakeholders (39 central level, 18 provincial) involved in public nutrition or food security issues. Forms of harmonization included written policies, reseach, training and advocacy. Important features of the policy process included: policy entrepreneurs with operational and strategic capacity, consensus-building using a shared causal framework, working groups and strategic alliances. This case presents an interesting alternative to a national nutrition coordinating body, an approach that has met with mixed results, often due to the lack of authority, budget, and operational capacity of such a body to oversee ministries and enforce national nutrition objectives. Mid-level professionals mobilized into task forces achieved much with the support of national and international partners. This study highlights the importance of building capacity for sustaining change through local institutions. 相似文献
2.
Past, present and future precipitation in the Middle East: insights from models and observations 总被引:1,自引:0,他引:1
Black E Brayshaw DJ Rambeau CM 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2010,368(1931):5173-5184
Anthropogenic changes in precipitation pose a serious threat to society-particularly in regions such as the Middle East that already face serious water shortages. However, climate model projections of regional precipitation remain highly uncertain. Moreover, standard resolution climate models have particular difficulty representing precipitation in the Middle East, which is modulated by complex topography, inland water bodies and proximity to the Mediterranean Sea. Here we compare precipitation changes over the twenty-first century against both millennial variability during the Holocene and interannual variability in the present day. In order to assess the climate model and to make consistent comparisons, this study uses new regional climate model simulations of the past, present and future in conjunction with proxy and historical observations. We show that the pattern of precipitation change within Europe and the Middle East projected by the end of the twenty-first century has some similarities to that which occurred during the Holocene. In both cases, a poleward shift of the North Atlantic storm track and a weakening of the Mediterranean storm track appear to cause decreased winter rainfall in southern Europe and the Middle East and increased rainfall further north. In contrast, on an interannual time scale, anomalously dry seasons in the Middle East are associated with a strengthening and focusing of the storm track in the north Mediterranean and hence wet conditions throughout southern Europe. 相似文献
3.
4.
Kay MK Cartwright EJ Maceachern D McCullough J Barzilay E Mintz E Duchin JS Macdonald K Turnsek M Tarr C Talkington D Newton A Marfin AA 《Journal of food protection》2012,75(4):762-764
We report a cluster of severe diarrheal disease caused by Vibrio mimicus infection among four persons who had consumed leftover crayfish the day after a private crayfish boil. Gastrointestinal illness caused by Vibrio mimicus has not been reported previously in Washington State. Three cases were laboratory confirmed by stool culture; using PCR, isolates were found to have ctx genes that encode cholera toxin (CT). Two of the cases were hospitalized under intensive care with a cholera-like illness. The illnesses were most likely caused by cross-contamination of cooked crayfish with uncooked crayfish; however, V. mimicus was not isolated nor were CT genes detected by PCR in leftover samples of frozen crayfish. Clinicians should be aware that V. mimicus can produce CT and that V. mimicus infection can cause severe illness. 相似文献
5.
How many mountains can we mine? Assessing the regional degradation of central appalachian rivers by surface coal mining 总被引:2,自引:0,他引:2
ES Bernhardt BD Lutz RS King JP Fay CE Carter AM Helton D Campagna J Amos 《Environmental science & technology》2012,46(15):8115-8122
Surface coal mining is the dominant form of land cover change in Central Appalachia, yet the extent to which surface coal mine runoff is polluting regional rivers is currently unknown. We mapped surface mining from 1976 to 2005 for a 19,581 km(2) area of southern West Virginia and linked these maps with water quality and biological data for 223 streams. The extent of surface mining within catchments is highly correlated with the ionic strength and sulfate concentrations of receiving streams. Generalized additive models were used to estimate the amount of watershed mining, stream ionic strength, or sulfate concentrations beyond which biological impairment (based on state biocriteria) is likely. We find this threshold is reached once surface coal mines occupy >5.4% of their contributing watershed area, ionic strength exceeds 308 μS cm(-1), or sulfate concentrations exceed 50 mg L(-1). Significant losses of many intolerant macroinvertebrate taxa occur when as little as 2.2% of contributing catchments are mined. As of 2005, 5% of the land area of southern WV was converted to surface mines, 6% of regional streams were buried in valley fills, and 22% of the regional stream network length drained watersheds with >5.4% of their surface area converted to mines. 相似文献
6.
Nuclei from meristem tissue cells of onion bulbs γ-irradiated (60–90 Gy) for sprout inhibition and non-irrádiated control bulbs were isolated periodically during ambient (27–32°C) storage, stained with the fluorochrome 4′,6-diamidino-2-phenylindole and their DNA distribution histograms measured by flow cytometry (FCM). Nuclei from irradiated onions showed a broader DNA distribution profile appearing as a wide (high) coefficient of variation (CV, 4–78%) of the G0/G1 peak as compared with non-irradiated samples (CV, 2.39%). The DNA index (DI) of the diploid cells in control onions was 1 as against 0.74 in irradiated samples which indicated the presence of G0/G1 cells with abnormal DNA content in the meristem tissue cells of irradiated onions. The results indicate the potential application of quantitating changes in DNA content using FCM by determining CV of the G0/G1 peak as well as DI for differentiating irradiated from non-irradiated onion bulbs. 相似文献
7.
Previous research has established that exposure to novel male mice can disrupt intrauterine implantation of fertilised ova in inseminated females and that much of this effect is mediated by factors in the male urine. The present studies were designed to examine whether the steroid content of male urine is sufficient to account for this effect. Pregnancy was terminated by exogenous 17beta-oestradiol administered intranasally on days 2-4 after insemination in doses as low as 0.14 microg/day. Enzyme immunoassay indicated that male mouse urine reliably contains unconjugated 17beta-oestradiol and testosterone. A small but significant increase in the amount of urinary oestradiol was observed in males housed nearby previously inseminated females as opposed to those housed in isolation. This influence was absent in the sire and absent in novel males when the sire was also present. The quantity of active steroids in novel male urine approaches the level sufficient to account for the disruption of implantation in nearby inseminated females. 相似文献
8.
Sources of mercury wet deposition in Eastern Ohio, USA 总被引:3,自引:0,他引:3
Keeler GJ Landis MS Norris GA Christianson EM Dvonch JT 《Environmental science & technology》2006,40(19):5874-5881
In the fall of 2002, an enhanced air monitoring site was established in Steubenville, Ohio as part of a multi-year comprehensive mercury monitoring and source apportionment study to investigate the impact of local and regional coal combustion sources on atmospheric mercury deposition in the Ohio River Valley. This study deployed advanced monitoring instrumentation, utilized innovative analytical techniques, and applied state-of-the-art statistical receptor models. This paper presents wet deposition data and source apportionment modeling results from daily event precipitation samples collected during the calendar years 2003-2004. The volume-weighted mean mercury concentrations for 2003 and 2004 were 14.0 and 13.5 ng L(-1), respectively, and total annual mercury wet deposition was 13.5 and 19.7 microg m(-2), respectively. Two new EPA-implemented multivariate statistical models, positive matrix factorization (PMF) and Unmix, were applied to the data set and six sources were identified. The dominant contributor to the mercury wet deposition was found by both models to be coal combustion (approximately 70%). Meteorological analysis also indicated that a majority of the mercury deposition found at the Steubenville site was due to local and regional sources. 相似文献
9.
The performance of the technique of diffusive gradients in thin films (DGT) was characterized in well-defined systems containing cadmium with chloride and nitrate ions, simple organic ligands (nitrilotriacetic acid and diglycolic acid), and Suwannee river fulvic acid for the pH range 5-8. Cd was fully labile in all Cd, Cl-, and NO3- solutions tested (I= 0.1 and 0.01 M), even atvery low Cd concentrations (10 nM), consistent with there being no binding of Cd to the diffusive gel. Diffusion coefficients of Cd-nitritotriacetic acid (NTA) and Cd-diglycolic acid (DGA) species were measured and found to be ca. 25-30% lower than the equivalent coefficient for free metal ions. These values were used to calculate concentrations of labile Cd from DGT measurements in solutions of Cd with NTA or DGA. Cd-NTA and Cd-DGA species were found to be fully DGT-labile. DGT devices that used a diffusive gel with a reduced pore size, which retarded the passage of fulvic acid species through the gel, were used to estimate the proportion of Cd complexed by fulvic acid. These results were compared with predictions of the solution speciation from models with default parameter values. ECOSAT, incorporating the NICA-Donnan model, correctly predicted the magnitude of the binding and its pH dependence, while predictions from WHAM V (with humic ion binding model V) and WHAM 6 (with humic ion binding model VI) were less satisfactory at predicting the pH dependence. Reasonable fits to the data could be obtained from WHAM 6 when the effective binding constant log K(MA) was changed from 1.6 to 1.5, the value of deltaLK1 from 2.8 to 1.0 to minimize the dependence on pH, and the value of deltaLK2 from 1.48 to 1.0 to decrease the strength of the strong bidentate and tridentate binding sites. 相似文献
10.
C Barr Taylor Nancy Houston Miller Rebecca P Cameron Emily Wien Fagans Smita Das 《Nicotine & tobacco research》2005,7(1):129-137
The present study aimed to determine whether tobacco use cessation rates observed in controlled trials of a hospital-based tobacco use cessation program could be replicated when the program was disseminated to a wide range of hospitals in a two-stage process including implementation and institutionalization phases. Using a nonrandomized, observational design, we recruited six hospitals to participate in the study. The research team helped implement the program during the first year of participation (implementation) and then withdrew from active involvement during the second year (institutionalization). The mean 6-month self-reported cessation rates were 26.3% (range = 17.6%-52.8%) for the implementation phase and 22.7% (range = 12.9%-48.2%) for the institutionalization phase. Hospitals with paid professionals providing the program had the best outcomes. Inpatient tobacco use cessation programs are feasible to implement and should target a 6-month self-reported cessation rate of at least 25%. 相似文献