首页 | 官方网站   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   1670篇
  免费   138篇
  国内免费   1篇
工业技术   1809篇
  2024年   2篇
  2023年   18篇
  2022年   36篇
  2021年   94篇
  2020年   48篇
  2019年   44篇
  2018年   55篇
  2017年   51篇
  2016年   66篇
  2015年   55篇
  2014年   78篇
  2013年   94篇
  2012年   98篇
  2011年   141篇
  2010年   107篇
  2009年   102篇
  2008年   90篇
  2007年   102篇
  2006年   58篇
  2005年   59篇
  2004年   55篇
  2003年   35篇
  2002年   36篇
  2001年   20篇
  2000年   23篇
  1999年   18篇
  1998年   22篇
  1997年   29篇
  1996年   23篇
  1995年   19篇
  1994年   17篇
  1993年   13篇
  1992年   9篇
  1991年   8篇
  1990年   6篇
  1989年   6篇
  1988年   9篇
  1987年   9篇
  1986年   6篇
  1985年   8篇
  1984年   4篇
  1983年   8篇
  1982年   3篇
  1981年   5篇
  1979年   3篇
  1975年   5篇
  1973年   2篇
  1961年   1篇
  1960年   1篇
  1958年   1篇
排序方式: 共有1809条查询结果,搜索用时 31 毫秒
81.
82.
Smoking is a major risk factor for several diseases including chronic obstructive pulmonary disease (COPD). To better understand the systemic effects of cigarette smoke exposure and mild to moderate COPD—and to support future biomarker development—we profiled the serum lipidomes of healthy smokers, smokers with mild to moderate COPD (GOLD stages 1 and 2), former smokers, and never-smokers (n = 40 per group) (ClinicalTrials.gov registration: NCT01780298). Serum lipidome profiling was conducted with untargeted and targeted mass spectrometry-based lipidomics. Guided by weighted lipid co-expression network analysis, we identified three main trends comparing smokers, especially those with COPD, with non-smokers: a general increase in glycero(phospho)lipids, including triglycerols; changes in fatty acid desaturation (decrease in ω-3 polyunsaturated fatty acids, and an increase in monounsaturated fatty acids); and an imbalance in eicosanoids (increase in 11,12- and 14,15-DHETs (dihydroxyeicosatrienoic acids), and a decrease in 9- and 13-HODEs (hydroxyoctadecadienoic acids)). The lipidome profiles supported classification of study subjects as smokers or non-smokers, but were not sufficient to distinguish between smokers with and without COPD. Overall, our study yielded further insights into the complex interplay between smoke exposure, lung disease, and systemic alterations in serum lipid profiles.  相似文献   
83.
Drift capacity of reinforced concrete (RC) columns is an important indicator to quantify the seismic vulnerability of RC frame buildings; however, it is challenging to accurately predict this value as the nonlinear behavior can vary greatly by column type. This article proposes a novel, local machine learning (ML) model, called locally weighted least squares support vector machines for regression (LWLS‐SVMR), which integrates LS‐SVMR and locally weighted training criteria to enhance and generalize the prediction of the drift capacity of RC columns, regardless of the type. A database of 160 circular RC columns covering flexure‐, shear‐, and flexure–shear‐critical specimens was developed to train and test the proposed LWLS‐SVMR. The proposed LWLS‐SVMR was validated by comparison with popular existing global and local learning approaches as well as a traditional empirical equation, and the results demonstrated that the proposed LWLS‐SVMR is superior to all other approaches and thus, is a promising artificial intelligence technique for enhancing the prediction of drift capacity, universally across RC flexure‐, shear‐, and flexure–shear‐critical columns. The LWLS‐SVMR exhibits capabilities which may yield it a feasible approach to predict complex, nonlinear behavior in a broad‐spectrum manner.  相似文献   
84.
85.
Shared book reading, and the conversation that accompanies it, can facilitate young children's vocabulary growth. To identify the features of extratextual questions that help 3-year-olds learn unfamiliar words during shared book reading, two experiments explored the impact of cognitive demand level, placement, and an approximation to scaffolding. Asking questions about target words improved children's comprehension and production of word–referent associations, and children with larger vocabularies learned more than children with smaller vocabularies. Neither the demand level nor placement of questions differentially affected word learning. However, an approximation to scaffolding, in which adults asked low demand questions when words first appeared and high demand questions later, did facilitate children's deeper understanding of word meanings as assessed with a definition task. These results are unique in experimentally demonstrating the value for word learning of shifting from less to more challenging input over time. Discussion focuses on why a scaffolding-like procedure improves children's acquisition of elaborated word meanings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
86.
87.
88.
Up to 37% of individuals experience chronic pain during their lifetimes. Approximately one fourth of primary care patients with chronic pain also meet criteria for major depression. Many of these individuals fail to receive psychotherapy or other treatment for their depression; moreover, when they do, physical pain is often not addressed directly. Women, socioeconomically disadvantaged individuals, African Americans, and Latinos all report higher rates of pain and depression compared with other groups. This article describes a version of interpersonal psychotherapy tailored for patients with comorbid depression and chronic pain, interpersonal psychotherapy for depression and pain (IPT-P). IPT-P potentially could be delivered to many patient populations in a range of clinical settings, but this article focuses on its delivery within primary care settings for socioeconomically disadvantaged women. Adaptations include a brief 8-session protocol that incorporates strategies for anticipating barriers to psychotherapy, accepting patients' conceptualization of their difficulties, encouraging patients to consider the impact of their pain on their roles and relationships, emphasizing self-care, incorporating pain management techniques, and flexible scheduling. In addition, IPT-P is designed as an adjunct to usual medical pain treatment, and seeks to engage non–treatment-seeking patients in psychotherapy by focusing on accessibility and relevance of the intervention to concerns common among patients with pain. Identifying patients with comorbid depression and chronic pain and offering IPT-P as a treatment option have the potential to improve clinical outcomes for individuals with depression and chronic pain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
89.
In object substitution masking (OSM) a sparse, temporally trailing 4-dot mask impairs target identification, even though it has different contours from, and does not spatially overlap with the target. Here, we demonstrate a previously unknown characteristic of OSM: Observers show reduced masking at prolonged (e.g., 640 ms) relative to intermediate mask durations (e.g., 240 ms). We propose that with prolonged exposure, the mask's visual representation is consolidated, which allows processing of the lingering target icon to be reinitiated, thereby improving performance. Our findings suggest that when the visual system is confronted with 2 temporally contiguous stimuli, although one may initially gain access to consciousness above the other, the “losing” stimulus is not irreversibly lost to awareness. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
90.
The evaluation of the effects of sugars, metals, acids and other antioxidants on the in vitro antioxidant capacity of purified anthocyanin extract by different techniques was the purpose of this study. Three methods and the ways of expressing their results were evaluated: ABTSTEAC (capacity equivalent to Trolox, by ABTS (2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid))), DPPHTEAC (capacity equivalent to Trolox, by DPPH (2,2‐diphenyl‐1‐picrylhydrazyl)), DPPHEC50 (50% reduction in the radical, by DPPH), DPPH%Sca (reduction in the scavenging capacity, by DPPH), FRAPTEAC (capacity equivalent to Trolox, by FRAP (reduction power of iron)) and FRAPEC50 (50% reduction in the radical, by FRAP). The way of expressing DPPH and FRAP results as EC50 showed the greater interfering extent, mainly when the medium contained tartaric and ascorbic acids. The most coherent method was ABTSTEAC in which only ascorbic acid interfered. Ascorbic acid was shown to interfere in all methods; thus, it must be removed prior to determining the in vitro antioxidant capacity of anthocyanins in food materials.  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-23

京公网安备 11010802026262号