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   1326篇
  免费   26篇
电工技术   14篇
综合类   2篇
化学工业   145篇
金属工艺   14篇
机械仪表   41篇
建筑科学   84篇
能源动力   27篇
轻工业   94篇
水利工程   18篇
石油天然气   1篇
无线电   99篇
一般工业技术   162篇
冶金工业   495篇
原子能技术   12篇
自动化技术   144篇
  2022年   7篇
  2021年   14篇
  2020年   10篇
  2019年   9篇
  2018年   14篇
  2017年   10篇
  2016年   14篇
  2014年   17篇
  2013年   70篇
  2012年   41篇
  2011年   36篇
  2010年   41篇
  2009年   36篇
  2008年   38篇
  2007年   35篇
  2006年   31篇
  2005年   35篇
  2004年   23篇
  2003年   25篇
  2002年   25篇
  2001年   27篇
  2000年   27篇
  1999年   27篇
  1998年   115篇
  1997年   64篇
  1996年   49篇
  1995年   41篇
  1994年   29篇
  1993年   35篇
  1992年   15篇
  1991年   16篇
  1990年   24篇
  1989年   23篇
  1988年   34篇
  1987年   15篇
  1986年   12篇
  1985年   15篇
  1984年   16篇
  1983年   28篇
  1982年   15篇
  1981年   13篇
  1980年   13篇
  1979年   24篇
  1978年   11篇
  1977年   23篇
  1976年   32篇
  1975年   11篇
  1974年   11篇
  1973年   8篇
  1972年   9篇
排序方式: 共有1352条查询结果,搜索用时 15 毫秒
21.
The fine structure and cellular associations of the large pigment cells (LPC's) of the compound eye of the house fly were studied with high voltage and conventional electron microscopy. Depending on the sector of the compound eye, the facets are either rectangular or hexagonal. The underside of each facet has indentations exactly aligned with those on top into which inserts an angulated sleeve of LPC's. Under the rectangular lens facet 6 or 8 small compact (in cross section) LPC's join four elongate LPC's. Clusters of compact cells alternate in this ring with elongate ones. Compact cells compress together and become quadrangular (in cross section) several microns below their insertion into the lens and form "building block" corners while elongate cells form "side rails" for the rectangular type of distal pseudocone enclosure. Beneath hexagonal facets all LPC's are rather elongate with out corner cells. In both facet types LPC's enclose the pseudocone for a longitudinal distance of 4 mum and then are displaced as bordering cells by a sleeve of two corneal pigment cells (CPC's), each of which encloses half of the proximal pseudocone. For the following 6 mum of longitudinal distance these concentric sleeves of CPC's and LPC's form a double layer around the pseudocone. At about 10 mum below lens base the two sleeves separate; LPC's become attenuated and extend cable-like to the basement membrane and CPC's enclose the proximal pseudocone, Semper cells and distal retinula. The junction between lens and LPC's has critical structural value in that (1) this is the sole anchorage to the lens by the lengthy remainder of the ommatidium, and (2) LPC's enclose the semiliquid pseudocone in the most distal portion of the pseudocone. In addition to vertical support, the LPC's send out numerous lateral processes that make structural contact among themselves, with the corneal pigment cells and the photoreceptor cells. The structural features of this array are discussed relative to possible physiological roles.  相似文献   
22.
We give a distributed approximation algorithm for job scheduling in a ring architecture. In contrast to many other parallel scheduling models, the model we consider captures the influence of the underlying communications network by specifying that task migration from one processor to another takes time proportional to the distance between those two processors in the network. As a result, our algorithm must balance computational load and communication time. The algorithm is simple, requires no global control, and yields schedules of length at most 4.22 times optimal. We also give a lower bound on the performance of any distributed algorithm and the results of simulation experiments which suggest better performance than does our worst-case analysis.  相似文献   
23.
Wheat allergies are potentially life-threatening because of the high risk of anaphylaxis. Wheats belong to four genotypes represented in thousands of lines and varieties. Monitoring changes to wheat allergens is critical to prevent inadvertent ntroduction of hyper-allergenic varieties via breeding. However, validated methods for this purpose are unavailable at present. As a proof-of-concept study, we tested the hypothesis that salt-soluble wheat allergens in our mouse model will be identical to those reported for humans. Groups of Balb/cJ mice were rendered allergic to durum wheat salt-soluble protein extract (SSPE). Using blood from allergic mice, a mini hyper-IgE plasma bank was created and used in optimizing an IgE Western blotting (IEWB) to identify IgE binding allergens. The LC-MS/MS was used to sequence the allergenic bands. An ancient Aegilops tauschii wheat was grown in our greenhouse and extracted SSPE. Using the optimized IEWB method followed by sequencing, the cross-reacting allergens in A. tauschii wheat were identified. Database analysis showed all but 2 of the durum wheat allergens and all A. tauschii wheat allergens identified in this model had been reported as human allergens. Thus, this model may be used to identify and monitor potential changes to salt-soluble wheat allergens caused by breeding.  相似文献   
24.
A sharp interface model has been developed to model intermediate-phase growth under the influence of electromigration in a binary system. Simulation results show that the phase growth rate depends on both the magnitude and the direction of the applied current. With the current density fixed, at early times, there is a parabolic growth behavior for the intermediate phase, while at longer times, there is a linear phase growth behavior when the electron flow aids diffusion of atoms; however, a limiting thickness is found when the electron flow hinders diffusion. Qualitative analysis shows that the longer time behavior also holds in a binary system with multiple intermediate phases present.  相似文献   
25.
Measuring construction productivity in an accurate, repeatable and reliable way represents a significant problem at a building project level of enquiry. The research develops a measurement framework that balances simplified data gathering against explanatory ability. It aims to assist analytically driven process improvement. Debate and discourse are used to draw upon the extant literature in creating a logic-based flow of ideas to develop the framework. Targeted use of empirical cost and site process data from case studies are presented to punctuate the discourse. The derived approach advocates multifactor measurement inclusive of labour and temporary production infrastructure inputs, set against Gross Floor Area outputs. Emphasis is placed on separately measuring homogenous and heterogeneous parts of work processes. A reductionist approach is used to operationalize measurement where projects are categorized according to fitness-for-purpose criteria and links made between systems, activities and tasks. Emphasizing measurement of homogenous parts of the work is new to the literature. It enables delineated measurement between work involving mass economies of scale (homogenous work), versus customized work (heterogeneous work). The approach enables improved benchmarking, diagnostic and predicative options. A course of ongoing research is provided to assist ongoing development and implementation.  相似文献   
26.
In 2010, the Australian residential construction sector contributed about 28% of the value of all construction and was responsible for 8% of the total energy consumption. Residential construction will continue to increase to cope with the demand due to population growth. Owing to land scarcity, construction on sloping sites has become a common construction method for residential development in Australia. This method has economic benefits but poses environmental issues as it damages topsoil, disturbs natural drainage and groundwater pathways and imposes additional stress on soil under fill. The life cycle energy consumption of the construction process is examined in relation to residential projects on sloping sites on a range of slopes and soil types in New South Wales, Australia. Forty-one detached dwellings were selected and a service life of 60 years assumed for the study. The research findings reveal that the slope for each type of soil has a positive correlation with life cycle energy consumption. As part of the onsite construction process, the results also show that the energy consumption of construction on sloping sites plays a significant factor in the life cycle energy analysis of a building.  相似文献   
27.
28.
正Ground control is the science of studying and controlling the behavior of rock strata in response to mining operations.Ground-control-related research has seen significant advancements over the last 40 years, and these accomplishments are well documented in the proceedings of the annual International Conference on Ground Control in Mining (ICGCM)[1].  相似文献   
29.
30.
Urban environments are not considered areas with conservation importance. However greenspaces in cities have been previously identified as areas with significant avian biodiversity. We investigated the distribution and diversity of birds in what are increasingly considered as Metropolitan Manila's last greenspaces; the University of the Philippines campus, military cemeteries and two government operated parks. Using species–area analysis, abundance and diversity indices, TWINSPAN ordination and logistic regression to determine important landscape features for species presence, we describe the distribution of bird communities and diversity in Metropolitan Manila. Two major bird community groupings were observed. These are the urban exploiters and the urban adaptable with the former occurring in high abundances and the latter in low abundances in greenspaces. The number of built and natural spatial entities determines abundances. Species area analysis suggests that the greenspaces are distinct habitats that preserve faunal uniqueness whereas urbanization tends to decrease diversity. These observations suggest that greenspaces harbor significant avian biodiversity as well as the presence of endemic and threatened species. As the greenspaces possess remnant wetland and wooded habitat we recommend that they be preserved and maintained by ensuring that these habitats are incorporated in any urban development plan.  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