全文获取类型
收费全文 | 20439篇 |
免费 | 1125篇 |
国内免费 | 1205篇 |
专业分类
林业 | 2732篇 |
农学 | 1846篇 |
基础科学 | 536篇 |
2933篇 | |
综合类 | 8355篇 |
农作物 | 1410篇 |
水产渔业 | 610篇 |
畜牧兽医 | 1489篇 |
园艺 | 836篇 |
植物保护 | 2022篇 |
出版年
2024年 | 98篇 |
2023年 | 316篇 |
2022年 | 552篇 |
2021年 | 624篇 |
2020年 | 706篇 |
2019年 | 779篇 |
2018年 | 572篇 |
2017年 | 835篇 |
2016年 | 1004篇 |
2015年 | 768篇 |
2014年 | 957篇 |
2013年 | 1373篇 |
2012年 | 1699篇 |
2011年 | 1438篇 |
2010年 | 1171篇 |
2009年 | 1253篇 |
2008年 | 1137篇 |
2007年 | 1234篇 |
2006年 | 1015篇 |
2005年 | 814篇 |
2004年 | 698篇 |
2003年 | 540篇 |
2002年 | 431篇 |
2001年 | 387篇 |
2000年 | 325篇 |
1999年 | 289篇 |
1998年 | 232篇 |
1997年 | 193篇 |
1996年 | 166篇 |
1995年 | 194篇 |
1994年 | 140篇 |
1993年 | 142篇 |
1992年 | 133篇 |
1991年 | 128篇 |
1990年 | 113篇 |
1989年 | 90篇 |
1988年 | 68篇 |
1987年 | 61篇 |
1986年 | 25篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
伴随着中国经济的迅速发展,民用及工业建筑类的照明水平逐年提高。在照明设计中,应遵循在满足现代化工业厂房使用要求的同时,采用合理的技术措施达到节能、节约的设计理念,使热电厂的照明设计总体达到"安全可靠、经济适用、符合国情"的要求。 相似文献
972.
充分了解和掌握病虫害发生规律及传染途径,做到防重于治,科学、合理、安全使用农药,才能在病虫害防治方面取得明显效果。 相似文献
973.
漯河市沙澧河公园植物配置模式应用技术探讨 总被引:1,自引:0,他引:1
在漯河市沙澧河公园植物营造过程中,科学筛选适宜品种,充分利用乡土树种,进行合理配置,营造连续性滨河公园园林景观,构建地带性植物群落,既美化了环境,也保证了生态平衡。 相似文献
974.
T. Aftab M. M. A. Khan M. Idrees M. Naeem M. Ram 《Journal of Agronomy and Crop Science》2010,196(6):423-430
Boron is an essential plant micronutrient and the range between deficient and toxic levels of boron is narrow for most of the plants. Like other elements, boron becomes toxic to growth at high concentrations. High boron concentrations in soil reduce crop productivity in many areas of the world. The effect of increasing levels of boron (0, 0.50, 1.00, 1.50, 2.00 mm ) on oxidative stress, antioxidant defence response and changes in artemisinin content in Artemisia annua were investigated in the present study. Boron toxicity reduced the growth parameters viz. stem height, fresh weight and dry weight. Treatments induced oxidative stress resulting in lower net photosynthetic rate, stomatal conductance, internal CO2 and total chlorophyll content. The increased activities of antioxidant enzymes like CAT, POX and SOD were also noted in response to increasing levels of boron stress. However, H2O2 and artemisinin content were found to be high up to 1.00 mm concentration of boron compared to control, and on applying higher doses, further reduced contents were obtained. Thus, the results suggest that a mild stress of boron can be utilized for enhanced artemisinin production. 相似文献
975.
《Communications in Soil Science and Plant Analysis》2012,43(12):1299-1310
Abstract A simple and rapid procedure for the determination of nitrate in fresh leaf tissue, suitable for use by relatively untrained operators is presented. The method requires only 4 reagents and can be carried out in less than 20 min from start to finish. A 400 mg sample of fresh leaf tissue is macerated briefly with 5 drops of 10 N sulphuric acid, diluted with 10.0 ml of water and filtered. Nitrate‐N is estimated on an aliquot of the filtered extract by reducing the nitrate to nitrite by shaking with powdered zinc in ammonium hydroxide solution for 3 min. The reduced mixture is allowed to settle (5 min) and an aliquot is withdrawn through a cotton‐wool plug thus removing any particles of the zinc. The filtered aliquot is then reacted with a single colour reagent to yield a pink azo‐dye, the intensity of which is directly proportional to the amount of nitrate. The method was found to have a coefficient of variation of about 4%. When compared with the phenoldisulphonic acid method for nitrate, on aliquots of the some plant extract, it yielded values which were on average 94.6% of those obtained with the former method. The coefficient of variation between the methods was 7%. 相似文献
976.
小盆径盆花因其价格低、体量小,越来越受到消费者的欢迎。通过对潍坊市居民消费小盆径盆花的情况进行调查,结果表明,小盆径盆花比大盆径盆花受欢迎,栽植盆器精美的小盆径盆花比用一般盆器栽植的盆花受欢迎。因此,发展小盆径盆花的生产与销售,是盆花生产的方向。 相似文献
977.
研究了玉米象Sitophilus zeamais(Motschulsky)不同虫态(2~3龄幼虫、1~2龄蛹和羽化1天成虫)体内三种保护酶过氧化氢酶(CAT)、过氧化物酶(POD)和超氧歧化酶(SOD)活力在电子束5个辐照剂量下酶活性的变化。试验结果表明,不同虫态玉米象CAT活力为:羽化1d成虫1~2龄蛹2~3龄幼虫;POD活力为:1~2龄蛹羽化1d成虫2~3龄幼虫;SOD活力为:1~2龄蛹2~3龄幼虫羽化1d成虫。辐照处理后,保护酶活力随辐照剂量的增加呈现先上升后下降的趋势,本实验结果有助于阐明电子束辐照加强对储粮害虫生理生化效应研究。 相似文献
978.
抚顺西排土场矸石山阴坡随着排矸年限的增加,物种多样性发生变化,物种数由初期的4科5种增至后期14科29种。植被由最初的鹅绒藤+豚草+刺蒺藜群落,逐步演变到榆树群落。在阴坡,不同排矸年限的样地,植物群落多样性指数随着排矸时间的延长而增加;物种综合多样性指数、丰富度指数与排矸年限呈显著正相关关系。 相似文献
979.
980.
《Communications in Soil Science and Plant Analysis》2012,43(9):937-951
Abstract An inexpensive hand held reflectometer was used to estimate NO3 concentration with Merckoquant NO3 indicator strips. For KNO3 solutions a fourfold improvement in precision was obtained over the visual method of colour comparison. The instrument calibration was stable over several days and not affected by temperature in the range 8–34o C. The reflectometer showed quantitatively that increasing temperature (8–34oC) reduced the optimal time for reading the strips from 120s to 40s. With standard NO3 solutions a simple hyperbolic transformation of the reflectometer readings produced a linear calibration of good fit (r2=0.99). NO3 could be estimated in different soil types within half an hour. The results agreed well with values from ion chromatography (r2 =0.97, slope=1.07). Plant sap analysis was moderately precise (r2 =0.92) but inaccurate and underestimated by more than 60% values obtained by ion chromatography. This discrepancy was not caused by the reflectometer but seemed to be due to factors within the plant sap that interfered with the NO3 colour reaction in the Merckoquant strips. 相似文献