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   242213篇
  免费   2686篇
  国内免费   430篇
电工技术   4307篇
综合类   257篇
化学工业   39620篇
金属工艺   9417篇
机械仪表   7417篇
建筑科学   5463篇
矿业工程   1394篇
能源动力   5175篇
轻工业   24824篇
水利工程   2478篇
石油天然气   5103篇
武器工业   32篇
无线电   25141篇
一般工业技术   45068篇
冶金工业   45448篇
原子能技术   5967篇
自动化技术   18218篇
  2021年   2149篇
  2019年   2055篇
  2018年   3526篇
  2017年   3458篇
  2016年   3733篇
  2015年   2267篇
  2014年   3932篇
  2013年   10236篇
  2012年   6209篇
  2011年   8366篇
  2010年   6589篇
  2009年   7288篇
  2008年   7636篇
  2007年   7758篇
  2006年   6939篇
  2005年   6080篇
  2004年   5844篇
  2003年   5627篇
  2002年   5699篇
  2001年   5570篇
  2000年   5394篇
  1999年   5311篇
  1998年   12576篇
  1997年   8905篇
  1996年   6863篇
  1995年   5336篇
  1994年   4743篇
  1993年   4627篇
  1992年   3671篇
  1991年   3393篇
  1990年   3595篇
  1989年   3474篇
  1988年   3305篇
  1987年   2900篇
  1986年   2938篇
  1985年   3376篇
  1984年   3222篇
  1983年   2895篇
  1982年   2744篇
  1981年   2821篇
  1980年   2724篇
  1979年   2627篇
  1978年   2687篇
  1977年   2952篇
  1976年   3805篇
  1975年   2368篇
  1974年   2244篇
  1973年   2379篇
  1972年   1971篇
  1971年   1862篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Immunoglobulin absorption by the calf has been the subject of considerable research. Despite these efforts little is known about the cytological events that occur at the level of the intestinal epithelial cell. These events have been studied extensively and characterized in the laboratory rodent; however, there have been few attempts to make corollaries between the two species. All neonatal animals display certain similarities in their intestinal morphology that may be correlated, with immunoglobulin absorption. Selectivity in absorption appears to be variable among neonatal animal species; however, all demonstrate some selectivity. Selectivity in absorption implies that receptors are a necessary component in the transport of immunoglobulins. Selectivity further requires binding of immunoglobulins to an endocytic vesicle membrane to ensure transport through the cell, circumvention of intracellular digestion, and release at the basolateral cell membrane. A decrease of immunoglobulin absorption may be accomplished in a variety of ways such as competition between intestinal microbes and immunoglobulins for a common receptor on the intestinal epithelial cell. An additional consideration is aberrant synthesis or recycling of the cell membrane receptor, as induced by metabolic decelerators such as cortisol. Failure to recycle immunoglobulin receptors also would decrease efficiency of absorption.  相似文献   
972.
973.
The transformation of an oxide lattice into a metal lattice is analyzed using the reported data and the results of our studies of the reduction of disseminated lump ores. The crystallochemical transformations are shown to occur due to oxide saturation with charged anion vacancies followed by the decomposition of their supersaturated solid solution. The appearance of charged anion vacancies as a result of oxygen removal from an oxide becomes possible after the “loosening” of its oxide lattice by thermal vacancies. The interaction of reducing and thermal vacancies near the free oxide surface induces the detachment of some microregions of the oxide lattice that have the structures of intermediate reduction products.  相似文献   
974.
The effect of small chromium and yttrium additions (0.14–1.0 wt%) on the recrystallization of Al-Sc alloys having 0.1–0.4% Sc is studied with polarized light. The microstructure of cold-rolled samples annealed at 100–630°C for 1 h is examined. The chromium and yttrium additions are found to slightly affect the recrystallization temperature of the Al-Sc alloys: they increase or decrease it slightly depending on the scandium content.  相似文献   
975.
In this study, the effects of low energy ultrasound irradiation on landfill leachate treatment by means of sequencing bath reactor were investigated. The aim of this work was to estimate the influence of leachate irradiation time on aerobic treatment efficiency. The sonification of the leachate was carried out in static conditions using the disintegrator UD-20. The field frequency of 22 kHz (the power output equals to 180 W) and amplitude of 12 microm was applied. The sonification time was changed in the range of 30-140 s. It was found that ultrasonic pretreatment enhances the subsequent aerobic digestion resulting in a better degradation of landfill leachate. The sonification of raw leachate leads to enhancement of COD and ammonia removal as compare to experiment without ultrasound.  相似文献   
976.
Components of dietary fiber (soluble nonstarch polysaccharide, pectin, hemicellulose, cellulose and lignin), water, energy, protein, lipid and starch were measured in banana, breadfruit, cassava, coconut, mango, pawpaw, plantain, sweet potato, taro and Pacific yam, all from the Pacific Island Kingdom of Tonga. The Tongan foods were generally higher in dietary fiber than New Zealand foods, consistent with the hypothesis that dietary fiber is an important factor contributing to a lower incidence of certain gastrointestinal disorders in Tonga, than in New Zealand.  相似文献   
977.
Owing to the rough warehouse handling of storage sacks in tropical areas in Africa, a suitable storage sack should not support de novo growth of fungal spores because this would reduce the tensile strength of the packaging material and act as a springboard for infecting grain contents. This paper reports the effect of activity of saprophytic fungi on the tensile strength of jute and woven polypropylene sacks. New woven polypropylene sacks carried lower levels of fungal spores (1.3×101 cfu/72 cm2) than jute sacks (3.0×103 cfu/72 cm2). The natural mould penetration and growth was examined on sections (4×5 cm) of both jute and woven polypropylene after previous incubation at relative humidities of 55, 60, 65, 70, 75, 80, 90 and 95% for 10 weeks by placing them on Sabouraud's Agar. There was a significant difference (P = 0.05 level of significance) between the higher penetration of mould growth on jute sacks and that obtained on woven polypropylene sacks. Saprophytic fungi (Aspergillus candidus, A. flavus, A. fumigatus, A. niger, A. japonicus, A. parasiticus, A. ustus, Fusarium oxysporium, F. moniliforme, Penicillium verucosum var. cyclopium, Rhizopus oryzae and Trichoderma viride) isolated from jute sacks reduced tensile strength, measured by an Instron Model 1026, by 50–75% after 10 weeks at 90% R.H. Same fungal species on woven polypropylene sacks did not alter the tensile strength. Woven polypropylene sacks did not absorb moisture whilst the moisture content of jute sacks increased by 5.3–6.0% in 10 weeks at 90% R.H. with concomitant increase in mould and yeast counts by 1–2 log cycles. Evidence is presented to show that there was a positive correlation between the final mycoflora on jute sacks and loss in tensile strength. No correlation, however, was found between the total aerobic bacteria on jute sacks and the concomitant reduction in tensile strength. Fungi therefore play a major role in the reduction of tensile strength of jute sacks. Sterilization by gamma irradiation (8.0 kGy) of jute and woven polypropylene sacks did not affect their intrinsic tensile strength. Woven polypropylene sacks therefore have many microbiological and physical advantages over the traditional jute sacks to merit their use for grain storage in tropical areas like Ghana.  相似文献   
978.
The secondary effluent from municipal plants in Korea generally represents higher BOD with lower SS. Therefore, more soluble forms of organics and NH4-N need to be removed to improve its effluent for reuse. In this study reuse possibility of secondary effluent and CSO (combined sewer overflow) using BAF (biological aerated filter) was evaluated. The tertiary application with 1.2 h EBCT, SS, BOD and COD showed stable concentrations less than 1.3, 1.3 and 6.2 mg/L, respectively. Nitrogen could be nitrified even at 7 degrees suggesting BAF can be used for a water reuse method as well as an effective add-on facility in cold regions. However, BAF was not stable with CSO application at increased flow rates suggesting CSO must be equalised prior to application. Disinfection was necessary even during normal weather conditions.  相似文献   
979.
980.
Participants' usage of informational variables in learning visual relative-mass discrimination in collisions was tracked by means of PROBIT correlations. Four groups received feedback that was true or accorded with either of three nonspecificational cue variables. A majority in each group adopted the feedback, but several participants defied the false feedback. Unlike in previous research, the fit to data of the relative-mass invariant could not be bettered by post hoc linear combinations of the cues. Discriminability was lower in the use of the invariant. Analytic complexity was rejected as an explanation for discriminability differences. A "smart mechanism" for pickup of the relative-mass invariant was developed as an extension of G. Johansson's (1950/1994) vector model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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