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   4156篇
  免费   232篇
  国内免费   328篇
林业   188篇
农学   194篇
基础科学   33篇
  865篇
综合类   1586篇
农作物   194篇
水产渔业   373篇
畜牧兽医   610篇
园艺   61篇
植物保护   612篇
  2024年   17篇
  2023年   77篇
  2022年   94篇
  2021年   141篇
  2020年   154篇
  2019年   167篇
  2018年   127篇
  2017年   196篇
  2016年   210篇
  2015年   189篇
  2014年   231篇
  2013年   377篇
  2012年   330篇
  2011年   319篇
  2010年   287篇
  2009年   252篇
  2008年   191篇
  2007年   223篇
  2006年   205篇
  2005年   146篇
  2004年   118篇
  2003年   104篇
  2002年   78篇
  2001年   65篇
  2000年   69篇
  1999年   54篇
  1998年   69篇
  1997年   40篇
  1996年   32篇
  1995年   42篇
  1994年   21篇
  1993年   18篇
  1992年   11篇
  1991年   16篇
  1990年   10篇
  1989年   9篇
  1988年   10篇
  1987年   2篇
  1986年   3篇
  1985年   6篇
  1983年   1篇
  1982年   1篇
  1978年   1篇
  1977年   1篇
  1973年   1篇
  1955年   1篇
排序方式: 共有4716条查询结果,搜索用时 15 毫秒
961.
为评价速肿消注射液的安全性 ,进行了改良 Karber氏的 LD50 检测、递增剂量的集蓄性检测、骨髓微核检测和精子畸形检测 ,使用小鼠做为实验动物。结果显示此药剂的 LD50 为994.72 mg/ kg,集蓄系数在 5.3以上 ,未出现药物耐受性现象 ;在各自的投药动物及其对照动物之间 ,骨髓微核检测的 PCE微核系数和 PCE/NCE,以及精子畸形检测结果都未出现差异。  相似文献   
962.
In broadly conceived long-term experiments, tobacco was grown in monoculture and with different crop rotations. This paper presents results in terms of the yields achieved and the major yield components for the crops grown, and the proportion of particular tobacco quality classes obtained. In addition to tobacco monoculture (initially only fertilized and later also unfertilized) as the key crop, different types of crop rotations included, besides tobacco, the following crops: winter wheat, maize, soybean, oil-seed rape, and red clover. Experiments involved two 2-year and two 4-year crop rotations, and a 3-year, a 5-year, and a 6-year crop rotation. Experiments were set up on luvic semigley on multilayered Pleistocene sands. Average 10-year results suggest that there is an advantage of crop rotation over monoculture for tobacco leaf yields. The influence of different crop rotation types on yields of other crops was variable, tending towards higher values as the number of crops in rotation was increased. Values obtained for yield components should be considered from two angles: some of the values were primarily influenced by genetic factors, while others were influenced by ecological factors, including crop rotation as an overall biological buffer. With regard to quality classes (IB-III), the growing of flue-cured tobacco in crop rotation represents a great advancement relative to its growth in monoculture, even in a narrower crop rotation.  相似文献   
963.
Citizen science is a popular method for the long-term monitoring of the distribution of wild animals. The application of these methods in different species and environments still poses challenges, especially for aquatic animals. In this study, we investigated the distribution of the Bryde's whale (Balaenoptera edeni) in the Beibu Gulf of China by using scientific boat-based surveys and citizen science approaches using 2 different methods of data collection. First, we built our mobile app (Whale Guard) and installed it on fishermen's phones. Second, we used a popular instant messaging app (WeChat) to create an online fisherman community. We found that the mobile phone app collected far fewer reports (5 reports) than the online community group (42 reports, P < 0.01). By using a variety of incentives, we maintained the fisherman's community's activity without significant user loss (P < 0.01). We also found that the locations collected by social media applications in this study were consistent with observations from scientific boat-based transect surveys. The sightings distribution of Bryde's whales differed from those in previous surveys in that they were present across larger areas. Social media apps reported that 69% of reports was confirmed by more than one person, whereas Whale Guard reports were much lower (0, P <0.001). Community-based citizen science can greatly contribute to the long-term monitoring of Bryde's whales, and it has successfully overcome the challenges of data accessibility, accuracy, and fragmentation. Our study shows how to appropriately use citizen science in different community groups and community-based approaches make them useful for large baleen whale surveys.  相似文献   
964.
ABSTRACT

Case history: Two dogs presented separately to the Small Animal Hospital, University of Florida (Gainsville, FL, USA) for ingestion of ibuprofen. The first dog ingested 561.8?mg/kg ibuprofen in addition to paracetamol and caffeine and vomited prior to admission. This patient also received fluid therapy for 8 hours prior to charcoal haemoperfusion. The second dog ingested 500?mg/kg of ibuprofen and the owners induced vomiting with hydrogen peroxide prior to presentation. Due to the severity of clinical signs, both patients were treated with charcoal haemoperfusion.

Clinical findings: The concentrations of ibuprofen in the blood of the dogs prior to treatment were 478 and 301?mg/L. During the treatment ibuprofen concentrations were reduced by 95.8% and 45.5%, respectively, with no treatment side effects and minimal clinical signs after treatment.

Diagnosis: Toxicity due to ingestion of ibuprofen toxicity that was successfully treated with charcoal haemoperfusion.

Clinical relevance: In the cases described here minimal benefit was seen after 3 hours of treatment using one haemoperfusion cartridge. This is in contrast to a previously published report in which dogs were treated for 6 hours with two charcoal haemoperfusion cartridges. This suggests that one cartridge may be sufficient. The amount of ibuprofen ingested was not a reliable predictor of the concentration in blood at the initiation of treatment. Charcoal haemoperfusion is an effective means of reducing plasma concentrations of ibuprofen, however, its use may be limited by its cost and availability.  相似文献   
965.
Phthorimaea operculella (Zeller) is a worldwide pest of potato. Plant-borne chemicals would be potential alternatives of synthetic chemical fumigants against P. operculella in the storage. Asari Radix et Rhizoma is derived from the dry roots and rhizomes of Asarum heterotropoides Fr. Schmidt var. mandshuricum, A. sieboldii Miq. var. seoulense, or A. sieboldii. In this study, fumigant toxicity and oviposition deterrent of volatile constituents from ARR, δ-3-carene, γ-terpinene, terpinolene, eucarvone, 3,5-dimethoxytoluene, and methyleugenol were tested against P. operculella. The preliminary verification of preventive and control effects of eucarvone, 3,5-dimethoxytoluene and methyleugenol on P. operculella was carried out by simulating warehouse experiments. The results indicated that the six compounds above had fumigation toxic effects on the adults and eggs of P. operculella. Among them, δ-3-carene, γ-terpinene, and terpinolene had weaker fumigation effects than those of eucarvone, 3,5-dimethoxytoluene, and methyleugenol. The LC50 values of eucarvone, 3,5-dimethoxytoluene, and methyleugenol against adult P. operculella were 1.01, 1.78, 1.51 mg/liter air, respectively. The LC50 values against egg P. operculella were 1.09, 0.55, 0.30 mg/liter air, respectively. The oviposition deterrent experiment showed that only methyleugenol (at 5 and 1 mg/ml) and eucarvone (5 mg/ml) had a substantial oviposition deterrent effect. The simulated warehouse experiment verified that methyleugenol, eucarvone, and 3,5-dimethoxytoluene protected potatoes from P. operculella and demonstrated that methyleugenol had the best preventive and control effects. It was concluded that methyleugenol was the active ingredient with the most potential in the volatiles from ARR on P. operculella control and merit further study as botanic fumigant.  相似文献   
966.
通过对海南农垦国有开割胶园职工家庭长期承包实践与成效的研究,分析存在的问题,并提出进一步完善的建议和对策。  相似文献   
967.
Abstract

The purpose of this study was to determine the level of Ba in plants necessary to cause yield depressions. Barium levels of about 2% in bush bean leaves and 1% in barley leaves decreased yields considerably. The levels were obtained after application of 2000 μg Ba per g of soil as Ba(NO3)2 with equivalent nitrate added in controls.  相似文献   
968.
废水生物处理中的毒物影响及其工程对策   总被引:6,自引:0,他引:6  
本文简要评述了各种废水生物处理过程中所遇到的毒物影响以及应采取的相应工程对策 ,并提出了今后的发展方向。  相似文献   
969.
魏钧 《北京农业》2012,(30):161
加强农村河道管理是行政主管部门的一项法定职责,结合江苏省江阴市青阳镇的实践就建立农村河道长效管理运行机制做些探索和思考。  相似文献   
970.
Caulogenic calli with a high differentiation potency were induced from mature embryos ofPicea jezoensis seeds stored over a long time, for 29 years, resulting in the active formation of adventitious buds. Embryos began to induce calli within 3 weeks of cultivating on LP medium containing 3 μM BAP and 1 μM 2,4-D. Then, the calli proliferated and transformed into caulogenic calli with bud primordia in 8 weeks. The caulogenic calli increased actively with the addition of 500 mg/l ofl-glutamine in the medium. Furthermore, caulogenic calli, induced on LP medium containingl-glutamine, resulted in the formation of adventitious buds, which elongated after transferring the calli into LP medium with 0.1 μM BAP, but withoutl-glutamine. It appears that the number of adventitious buds and the process of shoot elongation are influenced by the kind of nitrogen contained in the medium for callus induction. A part of this study was presented at the 107th Annual Meeting of the Japanese Forestry Society (1996).  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