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   294篇
  免费   23篇
林业   16篇
农学   6篇
  34篇
综合类   25篇
农作物   8篇
水产渔业   32篇
畜牧兽医   178篇
园艺   9篇
植物保护   9篇
  2024年   1篇
  2023年   2篇
  2022年   4篇
  2021年   10篇
  2020年   12篇
  2019年   13篇
  2018年   17篇
  2017年   10篇
  2016年   6篇
  2015年   7篇
  2014年   8篇
  2013年   14篇
  2012年   26篇
  2011年   28篇
  2010年   8篇
  2009年   15篇
  2008年   15篇
  2007年   19篇
  2006年   30篇
  2005年   9篇
  2004年   15篇
  2003年   16篇
  2002年   12篇
  2001年   4篇
  2000年   1篇
  1999年   3篇
  1998年   1篇
  1996年   2篇
  1994年   3篇
  1993年   1篇
  1989年   2篇
  1979年   1篇
  1978年   1篇
  1975年   1篇
排序方式: 共有317条查询结果,搜索用时 15 毫秒
311.
Thiafentanil oxalate, previously known as A-3080, is a synthetic opioid used for chemical immobilization of a variety of nondomestic hoofstock species. This study compared the combination of thiafentanil oxalate, medetomidine, and ketamine (TMK; 0.09 +/- 0.02 mg/kg, 0.01 +/- 0.003 mg/kg, and 1.36 +/- 0.33 mg/kg, respectively) with the combination of medetomidine and ketamine (MK; 0.09 +/- 0.02 mg/kg and 3.48 +/- 0.55 mg/kg, respectively) for anesthetization of 17 captive male axis deer (Axis axis) for vasectomy. Nine deer received TMK and eight deer received MK via projectile syringe during the months of January and February, 2005. Mean induction and arousal times, vital signs, and arterial blood gas values were monitored and compared. All animals received supplemental oxygen during the surgical procedure. Animals receiving TMK were reversed with naltrexone (100 mg/mg thiafentanil) and atipamazole (5 mg/mg medetomidine). Animals receiving MK were reversed with atipamazole (5 mg/mg medetomidine). Two MK animals and three TMK animals required supplementation with ketamine i.v. immediately upon handling. Six of the nine animals immobilized with TMK required intubation for positive-pressure ventilation. Two of these six animals also required isoflurane to maintain anesthesia. Mean induction time was 3.5 +/- 2.0 min in the TMK group, and 9.8 +/- 6.7 min in the MK group. Despite shorter mean induction times, animals anesthetized with TMK experienced unpredictable inductions, apnea, muscle rigidity, limb movement, and significant respiratory and metabolic lactic acidosis. MK resulted in smoother inductions, better respiratory function, and less adverse metabolic disturbances, and thus was considered superior to TMK for anesthesia in captive axis deer at the dosages tested.  相似文献   
312.
Hydrocarbons emissions were measured from an aerationtank of a municipal wastewater treatment pilot plant. The collected off-gas samples werecharacterised for C2–C7 hydrocarbons usingGC-FID analytical technique while the total volatileorganic compounds (TVOC) were measured using acontinuous hydrocarbon gas analyser. Approximately,the estimated emission rates for 1 m3 of wastewaterfrom this aeration tank were 5 mgC of C2–C7hydrocarbons, and an average of 7 gC of TVOC. Withexception to toluene, all other measured hydrocarbonsare emitted less than 1 mgC day-1. The results supportthe view that a significant reduction in annualemissions of hydrocarbons from wastewater treatmentplants in Vienna has taken place.  相似文献   
313.
For the routine determination of metals in environmental samples, we require microwave-assisted digestion methods that yield ‘total’ or ‘near-total’ recoveries while avoiding the use of HF acid. As inductively coupled plasma mass spectrometry (ICP-MS) is the method of detection, it is desirable to minimize the use of HCl to avoid spectral interferences caused by high Cl concentrations. Using certified reference materials, we performed a series of modifications to the US EPA method 3051 which included: increasing the temperature and durations of microwave digestion, varying the ratio of sample mass to acid volume, and alterations to the compositions of the acid digestion mixture. The experiments were conducted using urban particulate matter (NIST-1648), coal fly ash (NBS-1633) and six CANMET certified reference materials (Till-2, Till-3, Till-4, LKSD-1, LKSD-2 and LKSD-4), in two laboratories (Health Canada and Environment Canada) using different microwave digestion systems and different ICP-MS instruments. Our modified microwave-assisted nitric acid digestion method improved recoveries for Pb, Zn, V, Fe and Cu approaching ‘total’ recoveries in the same matrices determined using X-ray fluorescence (XRF) and instrumental neutron activation analysis (INAA) as reported in the certificates of analysis. Recoveries for other elements such as Cr and Ni compared well with ‘near-total’ recoveries yielded by traditional (non-assisted) acid digestion methods.  相似文献   
314.
The effect of the proximity of a motorway on the pH of leaf surfaces and cell sap in clonal birch trees and privet was investigated. With advancing foliar age or time of exposure, the pH-values rose slightly on the surfaces of the leaves. However, emissions from the motorway lowered the pH on the leaf surfaces, which can be explained by the acidity of exhaust gases. In contrast, emissions tended to increase pH of leaf homogenates; however, this effect was not consistent.  相似文献   
315.
For vision, insect and vertebrate eyes use rhabdomeric and ciliary photoreceptor cells, respectively. These cells show distinct architecture and transduce the light signal by different phototransductory cascades. In the marine rag-worm Platynereis, we find both cell types: rhabdomeric photoreceptor cells in the eyes and ciliary photoreceptor cells in the brain. The latter use a photopigment closely related to vertebrate rod and cone opsins. Comparative analysis indicates that both types of photoreceptors, with distinct opsins, coexisted in Urbilateria, the last common ancestor of insects and vertebrates, and sheds new light on vertebrate eye evolution.  相似文献   
316.
317.
  1. Free-flowing rivers (FFRs) are important surrogates for freshwater biodiversity as there are increasingly fewer rivers that reflect intact habitat and species diversity from source to sea. The status and changes in the ecological condition or protection of FFRs is not explicitly reported on in global biodiversity targets. Indices are proposed for reporting such changes to the Sustainable Development Goals (SDGs) 6 and 15, Aichi Target 11, and the post-2020 global biodiversity framework.
  2. FFRs were identified at a countrywide scale in South Africa for protection, planning, monitoring, and assessing changes in their ecological condition and protection status. They were selected and prioritized using criteria co-produced with national, provincial, and local river managers and policy makers. Given the high competition for water resources and the unlikely possibility for strictly protecting all FFRs, a subset of FFRs, termed ‘flagship FFRs’, was identified.
  3. Methods for reporting changes in the protection levels of prioritized FFRs at a countrywide scale were developed, which included indices of FFRs related to global targets: the loss of the extent of FFRs in a natural and largely natural ecological condition for SDG 6; changes in the connectivity of FFRs included in the post-2020 global biodiversity framework targets; and changes in protection levels of FFRs for Aichi Target 11 and SDG 15.1.2.
  4. Flagship FFRs attracted targeted management initiatives and thus maintained their connectivity and ecological condition. This was not true when all FFRs were considered; in the broader set of FFRs, longitudinal fragmentation increased and ecological condition declined from 2011 to 2018.
  5. Considering the increasing pressures rivers are likely to experience from human and climate change impacts, particularly in semi-arid to temperate environments, urgent prioritization and monitoring of FFRs is called for so that a targeted set of protection and management strategies can be applied.
  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