首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   367篇
  免费   36篇
电工技术   2篇
化学工业   125篇
金属工艺   4篇
机械仪表   6篇
建筑科学   14篇
矿业工程   3篇
能源动力   9篇
轻工业   62篇
水利工程   6篇
无线电   12篇
一般工业技术   60篇
冶金工业   62篇
自动化技术   38篇
  2024年   2篇
  2023年   7篇
  2022年   16篇
  2021年   38篇
  2020年   17篇
  2019年   18篇
  2018年   30篇
  2017年   24篇
  2016年   19篇
  2015年   13篇
  2014年   19篇
  2013年   16篇
  2012年   14篇
  2011年   28篇
  2010年   17篇
  2009年   24篇
  2008年   20篇
  2007年   22篇
  2006年   8篇
  2005年   5篇
  2004年   14篇
  2003年   5篇
  2002年   5篇
  2001年   3篇
  2000年   2篇
  1999年   4篇
  1998年   3篇
  1997年   1篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1982年   1篇
  1976年   1篇
排序方式: 共有403条查询结果,搜索用时 15 毫秒
61.
In the present study, we hypothesized that the rumen bacterial and archaeal communities would change significantly over the transition period of dairy cows, mainly as an adaptation to the classical use of low-grain prepartum and high-grain postpartum diets. Bacterial 16S rRNA gene amplicon sequencing of rumen samples from 10 primiparous Holstein dairy cows revealed no changes over the transition period in relative abundance of genera such as Ruminococcus, Butyrivibrio, Clostridium, Coprococcus, and Pseudobutyrivibrio. However, other dominant genus-level taxa, such as Prevotella, unclassified Ruminococcaceae, and unclassified Succinivibrionaceae, showed distinct changes in relative abundance from the prepartum to the postpartum period. Overall, we observed individual fluctuation patterns over the transition period for a range of bacterial taxa that, in some cases, were correlated with observed changes in the rumen short-chain fatty acids profile. Combined results from clone library and terminal-restriction fragment length polymorphism (T-RFLP) analyses, targeting the methyl-coenzyme M reductase α-subunit (mcrA) gene, revealed a methanogenic archaeal community dominated by the Methanobacteriales and Methanomassiliicoccales orders, particularly the genera Methanobrevibacter, Methanosphaera, and Methanomassiliicoccus. As observed for the bacterial community, the T-RFLP patterns showed significant shifts in methanogenic community composition over the transition period. Together, the composition of the rumen bacterial and archaeal communities exhibited changes in response to particularly the dietary changes of dairy cows over the transition period.  相似文献   
62.
Whilst empirical evidence is available concerning the effect of some aspects of driving behaviour on safety (e.g. speed choice), there is scant knowledge about safety thresholds, i.e. the point at which behaviour can be considered unsafe. Furthermore, it is almost impossible to ascertain the interaction between various aspects of driving behaviour. For example, how might drivers' lateral control of a vehicle be mediated by their speed choice-are the effects additive or do they cancel each other out. Complex experimental or observational studies would need to be undertaken to establish the nature of such effects. As an alternative, a Delphi study was undertaken to use expert judgement as a way of deriving a first approximation of these threshold and combinatory effects. Using a stated preference technique, road safety professionals make judgements about drivers' safe or unsafe behaviour. The aim was to understand the relative weightings that are assigned to a number of driver behaviours and thereby to construct a Safety Index. As expected, experts were able to establish thresholds, above (or below) which changes to the behavioural parameters had minimal impact on safety. This provided us with a Safety Index, based on a model that had face validity and a convincing range of values. However, the experts found the task of combining these driver behaviours more difficult, reflecting the elusive nature of safety estimates. Suggestions for future validation of our Safety Index are provided.  相似文献   
63.
The authors examined correlates of parenting stress among 230 gay adoptive fathers across the United States through an Internet survey. As with previous research on adoptive parents, results showed that fathers with less social support, older children, and children who were adopted at older ages reported more parenting stress. Moreover, gay fathers who had a less positive gay identity also reported more parenting stress. These 4 variables accounted for 33% of the variance in parenting stress; effect sizes were medium to large. Our results suggest the importance of social support and a positive gay identity in facilitating successful parenting outcomes among gay adoptive fathers. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
64.
Wild mushrooms are a vital source of income and nutrition for many poor communities and of value to recreational foragers. Literature relating to the edibility of mushroom species continues to expand, driven by an increasing demand for wild mushrooms, a wider interest in foraging, and the study of traditional foods. Although numerous case reports have been published on edible mushrooms, doubt and confusion persist regarding which species are safe and suitable to consume. Case reports often differ, and the evidence supporting the stated properties of mushrooms can be incomplete or ambiguous. The need for greater clarity on edible species is further underlined by increases in mushroom-related poisonings. We propose a system for categorizing mushroom species and assigning a final edibility status. Using this system, we reviewed 2,786 mushroom species from 99 countries, accessing 9,783 case reports, from over 1,100 sources. We identified 2,189 edible species, of which 2,006 can be consumed safely, and a further 183 species which required some form of pretreatment prior to safe consumption or were associated with allergic reactions by some. We identified 471 species of uncertain edibility because of missing or incomplete evidence of consumption, and 76 unconfirmed species because of unresolved, differing opinions on edibility and toxicity. This is the most comprehensive list of edible mushrooms available to date, demonstrating the huge number of mushrooms species consumed. Our review highlights the need for further information on uncertain and clash species, and the need to present evidence in a clear, unambiguous, and consistent manner.  相似文献   
65.
A hit optimization protocol applied to the first nonnucleoside inhibitor of the ATPase activity of human DEAD-box RNA helicase DDX3 led to the design and synthesis of second-generation rhodanine derivatives with better inhibitory activity toward cellular DDX3 and HIV-1 replication. Additional DDX3 inhibitors were identified among triazine compounds. Biological data were rationalized in terms of structure-activity relationships and docking simulations. Antiviral activity and cytotoxicity of selected DDX3 inhibitors are reported and discussed. A thorough analysis confirmed human DDX3 as a valid anti-HIV target. The compounds described herein represent a significant advance in the pursuit of novel drugs that target HIV-1 host cofactors.  相似文献   
66.
Dermatophilus congolensis is a bacterial pathogen mostly of ruminant livestock in the tropics/subtropics and certain temperate climate areas. It causes dermatophilosis, a skin disease that threatens food security by lowering animal productivity and compromising animal health and welfare. Since it is a prevalent infection in ruminants, dermatophilosis warrants more research. There is limited understanding of its pathogenicity, and as such, there is no registered vaccine against D. congolensis. To better understanding the genomics of D. congolensis, the primary aim of this work was to investigate this bacterium using whole-genome sequencing and bioinformatic analysis. D. congolensis is a high GC member of the Actinobacteria and encodes approximately 2527 genes. It has an open pan-genome, contains many potential virulence factors, secondary metabolites and encodes at least 23 housekeeping genes associated with antimicrobial susceptibility mechanisms and some isolates have an acquired antimicrobial resistance gene. Our isolates contain a single CRISPR array Cas type IE with classical 8 Cas genes. Although the isolates originate from the same geographical location there is some genomic diversity among them. In conclusion, we present the first detailed genomic study on D. congolensis, including the first observation of tet(Z), a tetracycline resistance-conferring gene.  相似文献   
67.
The frequency of responses cotton top tamarins (Saguinus oedipus) emitted indicative of self-recognition to a mirror was compared with the frequencies of responses emitted to digitized photographs of tamarins (Experiment 1) and to videotapes of real-time or prior tamarin action (Experiment 2). Results indicated more attentional responses toward the mirror in both studies, but behavioral indices of self-recognition were not consistently generated by the mirror. The 2 experiments confirmed that real-time self-reflection is a condition that generates heightened attention and ram examples of particular mirror-specific behaviors in tamarins. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
68.
Low-cost, chemically activated carbon materials, Pellet-600 and PVA-300, were prepared at relatively low temperatures and show more effective removal efficiency of Cr(VI) from water than commercially available activated carbons tested. The Pellet-600 is a pelletized carbon material with high mesoporous volumes and surface area, and the PVA-300 is composed of a high surface area carbon coating on a fiberglass mat substrate. A much faster adsorption kinetics and a much higher adsorption capacity for Cr(VI) are achieved by the Pellet-600. At very low concentrations of Cr(VI), the PVA-300 displays a strong adsorption ability for Cr(VI). XPS data show an increase in the atomic ratio of Cr/C and oxidation of carbon materials after adsorption of Cr(VI). These results suggest that a high content of mesopores with a high surface area and surface functional groups greatly improve the Cr(VI) removal efficiency from water.  相似文献   
69.
Promises are positioned centrally in the study of psychological contract breach and are argued to distinguish psychological contracts from related constructs, such as employee expectations. However, because the effects of promises and delivered inducements are confounded in most research, the role of promises in perceptions of, and reactions to, breach remains unclear. If promises are not an important determinant of employee perceptions, emotions, and behavioral intentions, this would suggest that the psychological contract breach construct might lack utility. To assess the unique role of promises, the authors manipulated promises and delivered inducements separately in hypothetical scenarios in Studies 1 (558 undergraduates) and 2 (441 employees), and they measured them separately (longitudinally) in Study 3 (383 employees). The authors’ results indicate that breach perceptions do not represent a discrepancy between what employees believe they were promised and were given. In fact, breach perceptions can exist in the absence of promises. Further, promises play a negligible role in predicting feelings of violation and behavioral intentions. Contrary to the extant literature, the authors’ findings suggest that promises may matter little; employees are concerned primarily with what the organization delivers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
70.
Triple negative breast cancer (TNBC) is one of the breast cancers with poorer prognosis and survival rates. TNBC has a disproportionally high incidence and mortality in women of African descent. We report on the evaluation of Ru-IM ( 1 ), a water-soluble organometallic ruthenium compound, in TNBC cell lines derived from patients of European (MDA-MB-231) and African (HCC-1806) ancestry (including IC50 values, cellular and organelle uptake, cell death pathways, cell cycle, effects on migration, invasion, and angiogenesis, a preliminary proteomic analysis, and an NCI 60 cell-line panel screen). 1 was previously found highly efficacious in MDA-MB-231 cells and xenografts, with little systemic toxicity and preferential accumulation in the tumor. We observe a similar profile for this compound in the two cell lines studied, which includes high cytotoxicity, apoptotic behavior and potential antimetastatic and antiangiogenic properties. Cytokine M-CSF, involved in the PI3/AKT pathway, shows protein expression inhibition with exposure to 1 . We also demonstrate a p53 independent mechanism of action.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号