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   2411篇
  免费   115篇
林业   74篇
农学   91篇
基础科学   4篇
  412篇
综合类   297篇
农作物   324篇
水产渔业   180篇
畜牧兽医   989篇
园艺   26篇
植物保护   129篇
  2022年   31篇
  2021年   48篇
  2020年   29篇
  2019年   42篇
  2018年   64篇
  2017年   57篇
  2016年   58篇
  2015年   62篇
  2014年   71篇
  2013年   112篇
  2012年   129篇
  2011年   164篇
  2010年   87篇
  2009年   80篇
  2008年   127篇
  2007年   129篇
  2006年   90篇
  2005年   91篇
  2004年   91篇
  2003年   93篇
  2002年   69篇
  2001年   63篇
  2000年   52篇
  1999年   49篇
  1998年   13篇
  1997年   18篇
  1996年   13篇
  1994年   14篇
  1992年   24篇
  1991年   33篇
  1990年   31篇
  1989年   28篇
  1988年   20篇
  1987年   28篇
  1986年   27篇
  1985年   27篇
  1984年   20篇
  1983年   19篇
  1979年   20篇
  1978年   11篇
  1977年   19篇
  1976年   11篇
  1974年   17篇
  1973年   23篇
  1972年   18篇
  1971年   15篇
  1970年   18篇
  1969年   19篇
  1968年   12篇
  1966年   11篇
排序方式: 共有2526条查询结果,搜索用时 15 毫秒
981.
A thermograph is used to determine the real-time temperature distribution on the skin temperature wearing clothing treated by different ultra-violet (UV) energy. The thermogram images of body wearing clothing with the 4-channel PET knit fabric irradiated by UV, were compared visually with each other and analyzed quantitatively with image analysis. We analyzed the thermogram in a color image. For image analysis, the Inspector 4.0 (Matrox Electronic System, Ltd.) was used. The surface temperatures, calculated based on the percentage surface area of a given temperature range with an interval of 1 °C, were averaged of five subjects’ surface temperature. From the results of the microclimate temperature, there were not significant differences among the subjects’ surface temperatures wearing different time treated clothes. However, subjective evaluation shows that the clothing treated by UV for 90 min had the lowest thermal sensation and the highest comfort sensation. Based on the image analysis of the thermogram, the calculated thermal sensation of the clothes irradiated by UV for 0 min, 30 min and 90 min, were coincident with the subjective thermal sensation.  相似文献   
982.
In this paper we investigated the human thermoregulatory responses, especially core temperature behavior during exercise and recovery at ambient temperature of 10 °C and 50 % R.H. under the conditions of wearing three kinds of clothing with same weight and different constructions. Six healthy men wore three kinds of clothing: one insulating the upper half of the body thinly and the lower half of the body heavily (clothing A, the weights in the upper and lower halves of the body were 489 g and 1278 g, respectively.), the second one insulating the upper half of the body heavily and the lower half of the body thinly (clothing B, 1212 g and 559 g, respectively.), and the third one insulating the upper and lower halves of the body moderately (clothing C, 899 g and 879 g, respectively.). The level of rectal temperature was the greatest during exercise in clothing C and the lowest during recovery in clothing A. The increasing and decreasing rates of core temperature during exercise and recovery, respectively, were the smallest in clothing B. These findings are discussed in terms of different cooling efficiency from the lower extremities and disfunction of counter current heat exchange system among clothing A, B, and C.  相似文献   
983.
JH Choy  SJ Kwon  GS Park 《Science (New York, N.Y.)》1998,280(5369):1589-1592
The free modulation of interlayer distance in a layered high-transition temperature (high-Tc) superconductor is of crucial importance not only for the study of the superconducting mechanism but also for the practical application of high-Tc superconducting materials. Two-dimensional (2D) superconductors were achieved by intercalating a long-chain organic compound into bismuth-based high-Tc cuprates. Although the intercalation of the organic chain increased the interlayer distance remarkably, to tens of angstroms, the superconducting transition temperature of the intercalate was nearly the same as that of the pristine material, suggesting the 2D nature of the high-Tc superconductivity.  相似文献   
984.
Principles for Sustainable Governance of the Oceans   总被引:1,自引:0,他引:1  
Pressures being exerted on the ocean ecosystems through overfishing, pollution, and environmental and climate change are increasing. Six core principles are proposed to guide governance and use of ocean resources and to promote sustainability. Examples of governance structures that embody these principles are given.  相似文献   
985.
The hydrolytic and photolytic decomposition of diazinon were found to be highly dependent on the solution pH and can be adequately described with a two species distribution model. At light intensities less than 60 W m-2, the photolytic decomposition rate of diazinon increased linearly with the UV light intensity. Both the hydrolytic and photolytic product of diazinon was identified to be 2-isopropyl-4-methyl-6-pyrimidinol (IMP). No further decomposition of IMP was found by hydrolysis, but the S-P bond of the other portion of diazinon molecule after production of IMP (which could be a thiophosphonate) may be ruptured by UV photolylsis to release a sulfate ion.  相似文献   
986.
Potato microtubers were treated with rindite to investigate the effect on dormancy breaking. Postharvest application of rindite by fumigation with 2 ml rindite for 48 hr or 4ml for 24 hr significantly reduced the dormancy period of potato microtubers using a 32 x 15 x 17 cm tightly sealed plastic box. Approximately 2 weeks after the treatments microtubers of all cultivars, Atlantic, Superior, Lemhi Russet, Red Dale and Kennebec started to sprout. The efficiency of the treatments were the greatest for the cv. Lemhi Russet, intermediate for cv. Superior and least for cv. Red Dale. In all cultivars of potato microtubers, more decay was observed the earlier rindite treatment occurred after harvesting, therefore potato microtubers should be treated with rindite at least 2 weeks after harvest when the skin of microtubers is mature. The data indicates that the dormancy of potato microtubers with well-matured skin can be effectively broken with an optimum treatment of rindite.  相似文献   
987.
This study was performed to determine compensatory growth of juvenile olive flounder fed the extruded pellet (EP) with different feeding regimes. Seven treatments with triplicates of different feeding regimes were prepared; α fish was daily fed for 6 d a week throughout 8 wk (8WF); α fish was starved for 1 wk and then fed for 3 wk twice [(1WS + 3WF) × 2]; β fish was starved for 2 wk and then fed for 6 wk (2WS + 6WF); χ fish was starved for 5 d and then fed for 9 d four times [(5DS + 9DF) × 4]; δ fish was starved for 10 d and then fed for 18 d twice [(10DS + 18DF) × 2]; δ fish was starved for 2 d, fed for 5 d, starved for 3 d, and then fed for 4 d four times [(2DS + 5DF + 3DS + 4DF) × 4]; and φ fish was starved for 4 d, fed for 10 d, starved for 6 d, and then fed for 8 d twice [(4DS + 10DF + 6DS + 8DF) × 2], respectively. Total feeding day was all same, 36 d except for control group (48 d). Weight gain of flounder in the 8WF treatment was higher than that of fish in other treatments. And weight gain of flounder in the 2WS + 6WF treatment was higher than that of fish in the (5DS + 9DF) × 4 and (4DS + 10DF + 6DS + 8DF) × 2 treatments. Feed consumption of flounder in the 8WF treatment was higher than that of fish experienced feed deprivation. Feed efficiency ratio (FER), protein efficiency ratio (PER), and protein retention (PR) were not significantly different among treatments. Chemical composition of the whole body of fish with and without liver, except for moisture content of liver, was not different among treatments. T3 level of fish in the 8WF and 2WS + 6WF treatments was higher than that of fish in the (5DS + 9DF) × 4 treatment. It can be concluded that juvenile olive flounder achieved better compensatory growth at 6‐wk refeeding after 2‐wk feed deprivation compared with that of fish with different feeding regimes. And T3 level of fish seemed to partially play an important role in achieving compensatory growth.  相似文献   
988.
Dryland salinity is a major natural resource management problem imposing large economic and environmental costs in many countries throughout the world. The major cause of dryland salinity is the replacement of perennial native vegetation with annual crops and pastures. This results in greater amounts of water entering a groundwater system, watertable rise and the concentration of naturally occurring salts near the soil surface. Many consider that the best long‐term solution is the re‐establishment of high water use perennial vegetation through production systems such as agroforestry. This paper presents a benefit–cost analysis (BCA) of revegetation to control dryland salinity over a 20‐year period in South Australia. The results of the BCA indicate that market costs are likely to exceed market benefits for broad‐scale revegetation programmes. These results are driven by hydrogeological studies, which indicate that as much as 50 per cent of a ‘problem‐type’ catchment needs to be revegetated to save only 3 per cent of land from being salt affected. The conclusion is that revegetation programmes need to be highly targeted to areas of a catchment with large potential to control salinity, land that has minimal value for other uses and regions with high infrastructure and ecological value. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
989.
A 14‐wk feeding trial was carried out to evaluate the optimum dietary riboflavin (vitamin B2) level in juvenile sea cucumber, Apostichopus japonicus. A total of 360 sea cucumbers averaging 1.49 ± 0.07 g (mean ± SD) were randomly distributed into 18 rectangular plastic tanks, and each tank was then randomly assigned to one of three replicates of six diets containing 0.29 (B20), 4.22 (B24), 8.93 (B29), 17.9 (B218), 56.7 (B257), and 577 (B2577) mg riboflavin/kg diet. At the end of 14 wk of feeding trial, average weight gain (WG) of sea cucumbers fed B29, B218, B257, and B2577 diets were significantly (P < 0.05) higher than that of animals fed B20 diet. WG of sea cucumbers fed B218, B257, and B2577 diets were significantly higher than those of animals fed B20 and B24 diets. Specific growth rate of sea cucumbers fed B29, B218, B257, and B2577 diets were significantly higher than those of animals fed B20 and B24 diets. Feed efficiency of sea cucumbers fed B29, B257, and B2577 diets were significantly higher than those of animals fed B20 and B24 diets. Although significant differences were recorded in proximate composition of sea cucumbers fed the experimental diets, no clear trends were observed. The ANOVA test suggested that the optimum dietary riboflavin level in sea cucumber could be 17.9 mg/kg diet but broken‐line analysis of WG indicated a level of 9.73 mg riboflavin/kg diet. Therefore, these results may indicate that the optimum dietary riboflavin level in sea cucumber could be higher than 9.73 mg/kg diet but lower than 17.9 mg/kg diet.  相似文献   
990.
Poly(lactic acid) (PLA) is known for environmentally friendly material as it is derived from annually renewable crops and biodegradable. Dispersant-free dyeing of PLA fabric with three temporarily solubilized azo disperse dyes which contain β-sulfatoethylsulfonyl group was investigated and their dyeing and fastness properties were compared with those of commercial disperse dyes. The temporarily solubilized azo disperse dyes were successfully applied to PLA fabric without the use of dispersant. The color yield on PLA fabric was dependent on dyebath pH and dyeing temperature as well. The optimum results were obtained at pH 7-8 and 110 °C. The dyes showed markedly higher color yield on PLA fabric when compared to commercial disperse dyes. Wash fastness was very poor to poor but light fastness was good. The COD levels of the dyeing effluent from the temporarily solubilized disperse dyes were considerably lower than those from commercial disperse dyes.  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