全文获取类型
收费全文 | 997篇 |
免费 | 39篇 |
专业分类
电工技术 | 5篇 |
综合类 | 6篇 |
化学工业 | 182篇 |
金属工艺 | 8篇 |
机械仪表 | 6篇 |
建筑科学 | 89篇 |
矿业工程 | 1篇 |
能源动力 | 10篇 |
轻工业 | 157篇 |
水利工程 | 20篇 |
石油天然气 | 4篇 |
无线电 | 34篇 |
一般工业技术 | 126篇 |
冶金工业 | 293篇 |
原子能技术 | 1篇 |
自动化技术 | 94篇 |
出版年
2024年 | 5篇 |
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 32篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 31篇 |
2017年 | 22篇 |
2016年 | 26篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 52篇 |
2012年 | 41篇 |
2011年 | 89篇 |
2010年 | 59篇 |
2009年 | 54篇 |
2008年 | 69篇 |
2007年 | 63篇 |
2006年 | 56篇 |
2005年 | 56篇 |
2004年 | 47篇 |
2003年 | 43篇 |
2002年 | 43篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有1036条查询结果,搜索用时 15 毫秒
181.
Forest bioenergy or forest carbon? Assessing trade-offs in greenhouse gas mitigation with wood-based fuels 总被引:1,自引:0,他引:1
McKechnie J Colombo S Chen J Mabee W MacLean HL 《Environmental science & technology》2011,45(2):789-795
The potential of forest-based bioenergy to reduce greenhouse gas (GHG) emissions when displacing fossil-based energy must be balanced with forest carbon implications related to biomass harvest. We integrate life cycle assessment (LCA) and forest carbon analysis to assess total GHG emissions of forest bioenergy over time. Application of the method to case studies of wood pellet and ethanol production from forest biomass reveals a substantial reduction in forest carbon due to bioenergy production. For all cases, harvest-related forest carbon reductions and associated GHG emissions initially exceed avoided fossil fuel-related emissions, temporarily increasing overall emissions. In the long term, electricity generation from pellets reduces overall emissions relative to coal, although forest carbon losses delay net GHG mitigation by 16-38 years, depending on biomass source (harvest residues/standing trees). Ethanol produced from standing trees increases overall emissions throughout 100 years of continuous production: ethanol from residues achieves reductions after a 74 year delay. Forest carbon more significantly affects bioenergy emissions when biomass is sourced from standing trees compared to residues and when less GHG-intensive fuels are displaced. In all cases, forest carbon dynamics are significant. Although study results are not generalizable to all forests, we suggest the integrated LCA/forest carbon approach be undertaken for bioenergy studies. 相似文献
182.
David Warshawsky Heather Dowty Weiling Xue Kent Mitchell Joanne Schneider Kathy Ladow 《Polycyclic Aromatic Compounds》2013,33(1-4):25-29
N-Heterocyclic aromatics, such as carbazole and acridine derivatives, are environmental carcinogenic pollutants. Examples of these compounds are 7H-dibenzo[c,g]carbazole (DBC) and dibenz[a,j]acridine (DBA). The ionization potential (IP) for DBC is lower than for DBA. DBC is metabolized in lung and liver by way of phenols or directly through radical cations. DBC-induced liver and lung tumors have mutations in the 61st codon of ras. DBA is metabolized in skin by way of a diol-epoxide of DBA. DBA-induced skin tumors have mutations in 12th, 13th and 61st codons of ras. In summary, the metabolic activation of DBC proceeds through different adduction pattern pathways than does DBA and leads to different ras mutational spectra. 相似文献
183.
184.
LaChance Heather; Feldstein Ewing Sarah W.; Bryan Angela D.; Hutchison Kent E. 《Canadian Metallurgical Quarterly》2009,23(4):598
Nationally, college drinkers exhibit the highest rates of alcohol consumption and represent the largest percentage of problem drinkers. Group motivational enhancement therapy (GMET) has been found to catalyze problem drinking reductions among college student samples. Although research supporting the use of single-session GMET in college samples (general and mandated) is emergent, no studies have evaluated a comprehensive model of the potential active ingredients of this group intervention. College students (N = 206; 88% White; 63% men; M age = 18.6) mandated to a university alcohol diversion program were randomly assigned to 1 of 3 conditions: the standard-of-care 2-session “Focus on Alcohol Concerns” education group (FAC), a single GMET, or a single alcohol information-only control group (AI) to evaluate the role of 5 putative mediators: readiness to change, self-efficacy, perceived risk, norm estimates, and positive drinking expectancies. At 3- and 6-month follow-ups, GMET students demonstrated greater reductions in problem drinking outcomes (drinks per drinking day, hazardous drinking symptoms, and alcohol-related problems). Of the 5 mediators proposed, only self-efficacy emerged as a significant mediator. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
185.
Kaslow Nadine J.; Thompson Martie P.; Brooks Amy E.; Twomey Heather B. 《Canadian Metallurgical Quarterly》2000,14(4):585
This study compared ratings of family functioning between female African American suicide attempters (n?=?126) and nonattempters (n &≠?112) (aged 18-64 yrs). Attempters reported poorer family-of-creation (physical and nonphysical partner abuse, family strengths, and marital adjustment) and family-of-origin (physical, sexual, and emotional abuse and emotional neglect) functioning than did controls. In a multivariate logistic regression, only marital discord and childhood sexual abuse were risk factors for suicide attempts. A cumulative risk model was also tested and indicated that the presence of 4 or more of the risk factors increased a woman's likelihood of making a nonfatal suicide attempt more than threefold. This study offers one of the first investigations of the families of suicidal African American women and highlights the importance of focusing on family concerns when working with this population. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
186.
Helms-Erikson Heather; Tanner Jennifer L.; Crouter Ann C.; McHale Susan M. 《Canadian Metallurgical Quarterly》2000,14(4):658
The authors examined the links between mothers' work qualities and their individual well-being and marital quality, as well as adolescent daughters' and sons' gender-role attitudes, as a function of mothers' provider-role attitudes, in 134 dual-earner families. In home interviews, mothers described their work, provider-role attitudes, family relationships, and mental health; their offspring reported gender-role attitudes. Women's attitudes about breadwinning were coded into main-secondary, coprovider, and ambivalent coprovider groups. Mothers' provider-role attitudes moderated the links between status indicators and mothers' depression, marital conflict, and daughters' gender-role attitudes. For example, depression and marital conflict were negatively related to coprovider mothers' earnings and occupational prestige. The same was not true for main-secondary and ambivalent coprovider mothers. These findings underscore the importance of considering employed women's interpretation of their work roles when exploring work-family links. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
187.
Using coal to produce transportation fuels could improve the energy security of the United States by replacing some of the demand for imported petroleum. Because of concerns regarding climate change and the high greenhouse gas (GHG) emissions associated with conventional coal use, policies to encourage pathways that utilize coal for transportation should seek to reduce GHGs compared to petroleum fuels. This paper compares the GHG emissions of coal-to-liquid (CTL) fuels to the emissions of plug-in hybrid electric vehicles (PHEV) powered with coal-based electricity, and to the emissions of a fuel cell vehicle (FCV) that uses coal-based hydrogen. A life cycle approach is used to account for fuel cycle and use-phase emissions, as well as vehicle cycle and battery manufacturing emissions. This analysis allows policymakers to better identify benefits or disadvantages of an energy future that includes coal as a transportation fuel. We find that PHEVs could reduce vehicle life cycle GHG emissions by up to about one-half when coal with carbon capture and sequestration is used to generate the electricity used by the vehicles. On the other hand, CTL fuels and coal-based hydrogen would likely lead to significantly increased emissions compared to PHEVs and conventional vehicles using petroleum-based fuels. 相似文献
188.
Clelia Nistic Francesca Pagliari Emanuela Chiarella Joana Fernandes Guerreiro Maria Grazia Marafioti Ilenia Aversa Geraldine Genard Rachel Hanley Daniel Garcia-Caldern Heather Mandy Bond Maria Mesuraca Luca Tirinato Maria Francesca Spadea Joao Carlos Seco 《International journal of molecular sciences》2021,22(18)
Breast cancer is the most frequent cancer in women worldwide and late diagnosis often adversely affects the prognosis of the disease. Radiotherapy is commonly used to treat breast cancer, reducing the risk of recurrence after surgery. However, the eradication of radioresistant cancer cells, including cancer stem cells, remains the main challenge of radiotherapy. Recently, lipid droplets (LDs) have been proposed as functional markers of cancer stem cells, also being involved in increased cell tumorigenicity. LD biogenesis is a multistep process requiring various enzymes, including Diacylglycerol acyltransferase 2 (DGAT2). In this context, we evaluated the effect of PF-06424439, a selective DGAT2 inhibitor, on MCF7 breast cancer cells exposed to X-rays. Our results demonstrated that 72 h of PF-06424439 treatment reduced LD content and inhibited cell migration, without affecting cell proliferation. Interestingly, PF-06424439 pre-treatment followed by radiation was able to enhance radiosensitivity of MCF7 cells. In addition, the combined treatment negatively interfered with lipid metabolism-related genes, as well as with EMT gene expression, and modulated the expression of typical markers associated with the CSC-like phenotype. These findings suggest that PF-06424439 pre-treatment coupled to X-ray exposure might potentiate breast cancer cell radiosensitivity and potentially improve the radiotherapy effectiveness. 相似文献
189.
Stice Eric; Shaw Heather; Bohon Cara; Marti C. Nathan; Rohde Paul 《Canadian Metallurgical Quarterly》2009,77(3):486
In this meta-analytic review, the authors summarized the effects of depression prevention programs for youth as well as investigated participant, intervention, provider, and research design features associated with larger effects. They identified 47 trials that evaluated 32 prevention programs, producing 60 intervention effect sizes. The average effect for depressive symptoms from pre-to-posttreatment (r = .15) and pretreatment to-follow-up (r = .11) were small, but 13 (41%) prevention programs produced significant reductions in depressive symptoms and 4 (13%) produced significant reductions in risk for future depressive disorder onset relative to control groups. Larger effects emerged for programs targeting high-risk individuals, samples with more females, samples with older adolescents, programs with a shorter duration and with homework assignments, and programs delivered by professional interventionists. Intervention content (e.g., a focus on problem-solving training or reducing negative cognitions) and design features (e.g., use of random assignment and structured interviews) were unrelated to effect sizes. Results suggest that depression prevention efforts produce a higher yield if they incorporate factors associated with larger intervention effects (e.g., selective programs with a shorter duration that include homework). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
190.
Correspondence between judgments of learning (JOLs) and actual recall tends to be poor when the same items are studied and recalled multiple times (e.g., A. Koriat, L. Sheffer, & H. Ma’ayan, 2002). The authors investigated whether making relevant metamemory knowledge more salient would improve the association between actual and predicted recall as a function of repeated exposure to the same study list. In 2 experiments, participants completed 4 study–recall phases involving the same list of items. In addition to having participants make item-by-item JOLs during each study phase, after the 1st study–recall phase participants also generated change-in-recall estimates as to how many more or fewer words they would recall given another exposure to the same study list. This estimation procedure was designed to highlight repeated study as a factor that can contribute to recall performance. Activating metamemory knowledge about the benefits of repeated study for recall in this way allowed participants to accurately express this knowledge in a free-recall context (Experiment 2), but less so when the memory test was cued recall (Experiment 1). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献