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   3187篇
  免费   56篇
  国内免费   2篇
电工技术   33篇
综合类   1篇
化学工业   382篇
金属工艺   32篇
机械仪表   54篇
建筑科学   177篇
矿业工程   10篇
能源动力   77篇
轻工业   262篇
水利工程   47篇
石油天然气   21篇
无线电   204篇
一般工业技术   420篇
冶金工业   1085篇
原子能技术   31篇
自动化技术   409篇
  2021年   22篇
  2020年   13篇
  2019年   32篇
  2018年   42篇
  2017年   41篇
  2016年   37篇
  2015年   27篇
  2014年   54篇
  2013年   140篇
  2012年   90篇
  2011年   116篇
  2010年   90篇
  2009年   120篇
  2008年   120篇
  2007年   110篇
  2006年   106篇
  2005年   82篇
  2004年   89篇
  2003年   87篇
  2002年   76篇
  2001年   71篇
  2000年   50篇
  1999年   55篇
  1998年   258篇
  1997年   161篇
  1996年   126篇
  1995年   100篇
  1994年   73篇
  1993年   86篇
  1992年   49篇
  1991年   38篇
  1990年   55篇
  1989年   35篇
  1988年   31篇
  1987年   33篇
  1986年   31篇
  1985年   41篇
  1984年   38篇
  1983年   33篇
  1982年   36篇
  1981年   29篇
  1980年   20篇
  1979年   17篇
  1978年   17篇
  1977年   35篇
  1976年   64篇
  1975年   20篇
  1974年   24篇
  1973年   23篇
  1972年   15篇
排序方式: 共有3245条查询结果,搜索用时 218 毫秒
1.
2.
Project portfolio management (PPM) bridges strategy and project management. Traditional research in PPM has primarily investigated the rational, top-down and structural aspects of strategizing. By doing so, it has failed to focus on the underlying practices that are triggered by the strategy and how these practices frame strategy implementation. Practice-based research provides a methodological lens to explore the reality of strategic enactment through the project portfolio. Practice-based perspectives are under-represented in PPM research; therefore the aim of this paper is to provide an agenda for further practice-based research in PPM. Central to this agenda is a concern with various aspects of practice, including its discursivity, representation, dynamic capabilities, leadership and materiality.  相似文献   
3.
Abnormal activation of Toll-like receptor (TLRs) signaling can result in colon cancer development. The aim of this study was to investigate the expression of important TLRs in different histological types of colorectal polyps and evaluate their relationship with intestinal microbiota. The expression levels of TLR2, 3, 4, and 5 were analyzed in intestinal biopsy specimens of 21 hyperplastic polyp (HP), 16 sessile serrated adenoma (SSA), 29 tubular adenoma (TA), 21 villous/tubulovillous (VP/TVP) cases, and 31 normal controls. In addition, selected gut bacteria including Streptococcus bovis, Enterococcus faecalis, Enterotoxigenic Bacteroides fragilis (ETBF), Fusobacterium nucleatum, Porphyromonas spp., Lactobacillus spp., Roseburia spp., and Bifidobacterium spp. were quantified in fecal samples using absolute qRT PCR, and, finally, the association between TLRs and these gut microbiota- was evaluated by Spearman’s correlation coefficient. Higher expression of TLR2 and TLR4 in VP/TVP and TA, and lower expression levels of TLR3 and TLR5 in all type of polyps were observed. The differences in TLR expression patterns was not only dependent on the histology, location, size, and dysplasia grade of polyps but also related to the intestinal microbiota patterns. TLR2 and TLR4 expression was directly associated with the F. nucleatum, E. faecalis, S. bovis, Porphyromonas, and inversely to Bifidobacterium, Lactobacillus, and Roseburia quantity. Furthermore, TLR3 and TLR5 expression was directly associated with Bifidobacterium, Roseburia, and Lactobacillus quantity. Our results suggest a possible critical role of TLRs during colorectal polyp progression. An abnormal regulation of TLRs in relation to gut microbial quantity may contribute to carcinogenesis.  相似文献   
4.
5.
Among the rights in the Bill of Rights contained in the South African Constitution is the right to access adequate housing. This right is bound up with other rights in the Constitution, including the right to have human dignity respected, and the right to, inter alia water and health care. The right to adequate housing is also included in several international human rights declarations including the Universal Declaration of Human Rights by the United Nations. However, the right to access adequate housing is more than just shelter but includes a number of other elements such as security of tenure, and access to basic services and facilities. Housing must be affordable and accessible. It must be safe and habitable and be culturally acceptable. Moreover, adequate housing is well located with respect to economic and other opportunities. The provision of housing and basic services has been the focus of the ANC-led government since 1994, and a major portion of municipal resources has been dedicated to providing water and sanitation to particularly the poorest households, while over 4.3 million state-subsidized housing opportunities have been delivered. whereas the scale of delivery has been impressive, has it really impacted on the lives of people in remote communities? Research conducted in the Joe Morolong Municipality in the Northern Cape Province regarding the realization of the right to access adequate housing reveals that the right to adequate housing has at best, only been partially realized. In addition to interviews with office bearers and municipal officials, 120 households were interviewed (of which half were from self-built houses and half were residing in “RDP” houses) regarding their interpretation and experience of the right to access adequate housing in the municipality. The study reveals that the structures do not meet the criteria for adequate housing and the provision of water and sanitation remains a challenge. Access to health and education facilities is poor, due to the low densities and vast distances between settlements.  相似文献   
6.
Near-infrared (NIR) activatable upconversion nanoparticles (UCNPs) enable wireless-based phototherapies by converting deep-tissue-penetrating NIR to visible light. UCNPs are therefore ideal as wireless transducers for photodynamic therapy (PDT) of deep-sited tumors. However, the retention of unsequestered UCNPs in tissue with minimal options for removal limits their clinical translation. To address this shortcoming, biocompatible UCNPs implants are developed to deliver upconversion photonic properties in a flexible, optical guide design. To enhance its translatability, the UCNPs implant is constructed with an FDA-approved poly(ethylene glycol) diacrylate (PEGDA) core clad with fluorinated ethylene propylene (FEP). The emission spectrum of the UCNPs implant can be tuned to overlap with the absorption spectra of the clinically relevant photosensitizer, 5-aminolevulinic acid (5-ALA). The UCNPs implant can wirelessly transmit upconverted visible light till 8 cm in length and in a bendable manner even when implanted underneath the skin or scalp. With this system, it is demonstrated that NIR-based chronic PDT is achievable in an untethered and noninvasive manner in a mouse xenograft glioblastoma multiforme (GBM) model. It is postulated that such encapsulated UCNPs implants represent a translational shift for wireless deep-tissue phototherapy by enabling sequestration of UCNPs without compromising wireless deep-tissue light delivery.  相似文献   
7.
Neural Computing and Applications - Milling by mechanical means is vital unit operation in pharmaceutical processing which can be used for controlling particle size reduction. This approach can be...  相似文献   
8.
In an era of population ageing, the primary home is increasingly viewed as a personal resource that can perform a pension role in retirement. This article assesses the extent to which Australians aged 45 years and over withdraw housing equity through in situ mortgage equity withdrawal (MEW), downsizing and selling up. We find that the incidence of housing equity withdrawal has increased over the last decade despite a global financial crisis. MEW is the dominant form of equity release among those under pension age, while downsizing or selling up is more frequent among those above pension age. Downsizing and selling up are more likely to be prompted by adverse life events than MEW. Selling up is typically an option of last resort. Our findings offer insights into important debates around homeownership societies and the welfare role performed by owner-occupied housing in mid-to-late life.  相似文献   
9.
10.
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