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   29309篇
  免费   1102篇
  国内免费   111篇
电工技术   381篇
综合类   229篇
化学工业   5306篇
金属工艺   641篇
机械仪表   608篇
建筑科学   998篇
矿业工程   100篇
能源动力   976篇
轻工业   3970篇
水利工程   254篇
石油天然气   160篇
武器工业   6篇
无线电   2277篇
一般工业技术   4215篇
冶金工业   6278篇
原子能技术   239篇
自动化技术   3884篇
  2024年   57篇
  2023年   167篇
  2022年   548篇
  2021年   837篇
  2020年   555篇
  2019年   632篇
  2018年   722篇
  2017年   814篇
  2016年   763篇
  2015年   573篇
  2014年   876篇
  2013年   1473篇
  2012年   1314篇
  2011年   1653篇
  2010年   1196篇
  2009年   1249篇
  2008年   1131篇
  2007年   1000篇
  2006年   787篇
  2005年   851篇
  2004年   916篇
  2003年   819篇
  2002年   805篇
  2001年   700篇
  2000年   544篇
  1999年   529篇
  1998年   2037篇
  1997年   1329篇
  1996年   923篇
  1995年   603篇
  1994年   475篇
  1993年   532篇
  1992年   220篇
  1991年   284篇
  1990年   225篇
  1989年   192篇
  1988年   206篇
  1987年   158篇
  1986年   166篇
  1985年   180篇
  1984年   129篇
  1983年   90篇
  1982年   116篇
  1981年   121篇
  1980年   116篇
  1979年   90篇
  1978年   75篇
  1977年   138篇
  1976年   224篇
  1975年   83篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
In order to analyze the interrelationships between free erythrocyte protoporphyrins and the usual iron intake in adult students, biochemical, and hematological values, and dietary daily intake, obtained using the recall method during seven days, were studied. Hematocrit (Hto.), hemoglobin (Hb) and free erythrocyte protoporphyrins (FEP) were determined in a group of 145 female university students, healthy according to the standard parameters of the Buenos Aires University Health Department. Mean iron intake was 23.0 +/- 1.5 mg per day, about 44% being provided by animal sources; 74.5% of the population was within the recommended daily intake according to FAO/WHO; only 0.7% of the population did not cover protein requirements while 35% did not cover energy needs. Hto. and Hb were below normal levels in 7.8% of the population when compared with standards according to ICNND. To obtain information about normal values to FEP, expressed as microgram/100 ml red cells (FEP% r.c.) and FEP/Hb ratio, the group of students with adequate intake of energy and proteins who had normal values for Hb and Hto. was selected. This group, including 94 women, had a mean FEP% r.c. of 15.71 +/- 7.26 and a mean FEP/Hb ratio of 0.44 +/- 0.21. There was observed an inverse correlation between FEP% r.c. and FEP/Hb with total iron intake (r = 0.80 and r = 0.78, respectively) and between FEP% r.c. and Hb concentration (r = 0.81). These results confirm the usefulness of the free erythrocyte protoporphyrins determination as a good index of iron stores and usual intake of this population.  相似文献   
92.
The effect of oral administration, for 24 or 48 hr, of different octadeca fatty acids containing a 9,12-dienoic structure on the fatty acid composition and Δ9 desaturation activity of liver microsomes of rat fed a fat-free diet was studied. The ethyl esters of linoelaidic and γ-linolenic acids, the methyl ester of linoleic acid and free columbinic acid were administered to rats maintained on a fat-free diet. The supplementation of the fat-free diet with linoelaidate produced no relevant changes in the fatty acid composition pattern of liver microsomes and did not modify the percentage of conversion of palmitic to palmitoleic acid. The addition of linoleate or γ-linolenate to the fat-free diet returned liver microsome Δ9 desaturation activity toward the control and partially restored the liver microsome fatty acid spectrum found in the fat-free diet. Columbinic acid (5-trans-9-cis,12-cis-18∶3), which cannot be transformed into arachidonic acid, also decreased the Δ9 desaturation activity enhanced by the fat-free diet and evoked changes in the microsomal fatty acid composition similar to those produced by the ω6 fatty acids. These results suggest that the modulation of Δ9 desaturase activity evoked by dietary administration of unsaturated acids of ω6 series would depend on thecis double bond configuration of these acids.  相似文献   
93.
A method for determining the distribution of cationic shrink-resist resins on wool has been developed. The method is based on a staining technique, using an anionic fluorescent brightening agent (FBA) under specific conditions in which the FBA stains the cationic resin in preference to the wool. When the stained samples are observed under ultraviolet radiation by means of the optical microscope, the areas on the wool fibres where resin is located fluoresce, whereas areas free from resin appear dark. The technique is simple and rapid, and enables the regularity of deposition of cationic resins on wool to be followed when the various parameters which play a role in the pretreatment of the fibre and the application of resins are changed. Regularity of resin deposition is important in the achievement of high levels of shrink-resistance in treated fabrics.  相似文献   
94.
95.
96.
97.
98.
Fractal dimension applied to plant identification   总被引:2,自引:0,他引:2  
This article discusses methods to identify plants by analysing leaf complexity based on estimating their fractal dimension. Leaves were analyzed according to the complexity of their internal and external shapes. A computational program was developed to process, analyze and extract the features of leaf images, thereby allowing for automatic plant identification. Results are presented from two experiments, the first to identify plant species from the Brazilian Atlantic forest and Brazilian Cerrado scrublands, using fifty leaf samples from ten different species, and the second to identify four different species from genus Passiflora, using twenty leaf samples for each class. A comparison is made of two methods to estimate fractal dimension (box-counting and multiscale Minkowski). The results are discussed to determine the best approach to analyze shape complexity based on the performance of the technique, when estimating fractal dimension and identifying plants.  相似文献   
99.
This paper reports results of research into the definition of requirements for new consumer products––specifically, electro-mechanical products. The research dealt with the derivation of design requirements that are demonstrably aligned with stakeholder needs. The paper describes a comprehensive process that can enable product development teams to deal with statements of product requirements, as originally collected through market research activities, in a systematic and traceable manner from the early, fuzzy front end, stages of the design process. The process described has been based on principles of systems engineering. A case study from its application and evaluation drawn from the power sector is described in this paper. The case study demonstrates how the process can significantly improve product quality planning practices through revision of captured product requirements, analysis of stakeholder requirements and derivation of design requirements. The paper discusses benefits and issues from the use of the process by product development teams, and identifies areas for further research. Finally, the conclusions drawn from the reported research are presented.
Vassilis AgouridasEmail:
  相似文献   
100.
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