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   24759篇
  免费   920篇
  国内免费   33篇
电工技术   329篇
综合类   38篇
化学工业   5666篇
金属工艺   380篇
机械仪表   477篇
建筑科学   1308篇
矿业工程   100篇
能源动力   621篇
轻工业   1895篇
水利工程   233篇
石油天然气   71篇
无线电   1818篇
一般工业技术   4510篇
冶金工业   4531篇
原子能技术   196篇
自动化技术   3539篇
  2023年   215篇
  2022年   359篇
  2021年   568篇
  2020年   338篇
  2019年   431篇
  2018年   537篇
  2017年   463篇
  2016年   633篇
  2015年   558篇
  2014年   749篇
  2013年   1419篇
  2012年   1163篇
  2011年   1510篇
  2010年   1075篇
  2009年   1014篇
  2008年   1150篇
  2007年   1089篇
  2006年   946篇
  2005年   761篇
  2004年   746篇
  2003年   660篇
  2002年   564篇
  2001年   428篇
  2000年   362篇
  1999年   403篇
  1998年   752篇
  1997年   553篇
  1996年   442篇
  1995年   411篇
  1994年   377篇
  1993年   363篇
  1992年   270篇
  1991年   195篇
  1990年   270篇
  1989年   260篇
  1988年   215篇
  1987年   224篇
  1986年   226篇
  1985年   266篇
  1984年   224篇
  1983年   223篇
  1982年   207篇
  1981年   194篇
  1980年   168篇
  1979年   193篇
  1978年   165篇
  1977年   185篇
  1976年   231篇
  1975年   160篇
  1974年   123篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In advancement of Pyrosil®‐technology a new kind of precursor delivery was developed, build and tested on real substrates. A Lab‐demonstrator was build to demonstrate the resources of the technology.  相似文献   
2.
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps.  相似文献   
3.
4.
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.  相似文献   
5.
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies.  相似文献   
6.
描述汽车显示器架构中的外部和内部接口及整合选型方案.  相似文献   
7.
This paper presents data relating to the performance of sprinklers and detectors in real office fire situations. For sprinklers, these data are additional to that associated with the standardized testing used to determine the design delivery density and pressure requirements for various occupancy situations, and provide a useful insight into the effect of sprinklers on developing fires with various office situations. The data given in this paper include the times for activation of various types of sprinkler heads (normal and fast response), the efficacy of the systems as far as extinguishment is concerned, estimates of the maximum size of the fires prior to commencement of extinguishment and associated air temperatures at various locations within the office enclosures. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
8.
The cellulose solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) was successfully applied as reaction medium for the synthesis of allyl cellulose by conversion of the polymer with allyl chloride in the presence of solid NaOH. Samples with degree of substitution from 0.50 to 2.98 were accessible by varying the molar ratio anhydroglucose unit:allyl chloride:NaOH and reaction time. DMSO/TBAF was found to be an efficient reaction medium for the preparation of highly functionalized samples from spruce sulfite pulp with degree of polymerization of about 500 even in a scale of 50 g. The allyl cellulose samples were characterized by means of FTIR- and NMR spectroscopy. Size exclusion chromatography revealed negligible polymer degradation during synthesis and purification of the samples.  相似文献   
9.
10.
For decades, it is believed that astringency is due to the polyphenol-induced complexation of proline-rich salivary proteins in the oral cavity. In order to compare for the first time the human sensory threshold concentrations and the salivary protein binding activity of a series of astringent stimuli, human saliva protein was incubated for 5 min at 37 °C in the presence of astringent food-derived compounds and, after micro-centrifugation, the amount of the target molecules in the supernatant was quantitatively determined by HPLC-UV/Vis. Significant protein binding was observed for (−)-epigallocatechin-3-gallate, (−)-gallocatechin-3-gallate, (+)-gallocatechin, and (−)-catechin-3-gallate, all of which containing at least one galloyl moiety in the molecule and exhibiting rather high sensory thresholds of more than 200 μmol/L. In comparison, (+)-catechin and procyanidin B2, both lacking in any galloyl function, showed only comparatively low binding activity and, most interestingly, quercetin-3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside and 3-carboxymethyl-indole-1-N-β-d-glucopyranoside did not show any protein binding at all, although the later N- and O-glycosides exhibited extraordinarily low sensory threshold concentrations of less than 0.001 and 0.0003 μmol/L, respectively. The data give some first evidence that the quantity of the non-bound, “free” astringent stimulus in the saliva liquid might be more closely related to the sensory perception of astringency than the amount complexed or precipitated by proteins. It is therefore questionable as to whether oral perception of astringency is related to the complexation and/or precipitation of salivary proteins.  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