全文获取类型
收费全文 | 753篇 |
免费 | 51篇 |
国内免费 | 111篇 |
专业分类
林业 | 70篇 |
农学 | 168篇 |
基础科学 | 57篇 |
108篇 | |
综合类 | 317篇 |
农作物 | 47篇 |
水产渔业 | 29篇 |
畜牧兽医 | 57篇 |
园艺 | 26篇 |
植物保护 | 36篇 |
出版年
2024年 | 6篇 |
2023年 | 11篇 |
2022年 | 30篇 |
2021年 | 25篇 |
2020年 | 25篇 |
2019年 | 35篇 |
2018年 | 24篇 |
2017年 | 30篇 |
2016年 | 26篇 |
2015年 | 35篇 |
2014年 | 52篇 |
2013年 | 49篇 |
2012年 | 65篇 |
2011年 | 46篇 |
2010年 | 37篇 |
2009年 | 28篇 |
2008年 | 47篇 |
2007年 | 43篇 |
2006年 | 46篇 |
2005年 | 36篇 |
2004年 | 28篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有915条查询结果,搜索用时 15 毫秒
31.
This paper first analyzes the reason that agricultural geographic information gives rise to semantic heterogeneity and solution thereof.Although OWL (web ontology language) is the standard of ontology ... 相似文献
32.
介绍了大中型轴流潜水泵的基本结构、特点。对该型泵的设计、安装、运行等问题进行了讨论,论述了用该型泵替代目前应用的轴流泵具有的各种优越性。 相似文献
33.
Breed risk of pyometra in insured dogs in Sweden 总被引:1,自引:0,他引:1
Egenvall A Hagman R Bonnett BN Hedhammar A Olson P Lagerstedt AS 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2001,15(6):530-538
An animal insurance database containing data on over 200,000 dogs was used to study the occurrence of pyometra with respect to breed and age during 1995 and 1996 in Swedish bitches <10 years of age. A total of 1,803 females in 1995 and 1,754 females in 1996 had claims submitted because of pyometra. Thirty breeds with at least 800 bitches insured each year were studied using univariate and multivariate methods. The crude 12-month risk of pyometra for females <10 years of age was 2.0% (95% confidence interval = 1.9-2.1%) in 1995 and 1.9% (1.8-2.0%) in 1996. The occurrence of pyometra differed with age, breed, and geographic location. The risk of developing pyometra was increased (identified using multivariate models) in rough Collies, Rottweilers, Cavalier King Charles Spaniels, Golden Retrievers, Bernese Mountain Dogs, and English Cocker Spaniels compared with baseline (all other breeds, including mixed breed dogs). Breeds with a low risk of developing the disease were Drevers, German Shepherd Dogs, Miniature Dachshunds, Dachshunds (normal size), and Swedish Hounds. Survival rates indicate that on average 23-24% of the bitches in the databases will have experienced pyometra by 10 years of age. In the studied breeds, this proportion ranged between 10 and 54%. Pyometra is a clinically relevant problem in intact bitches, and differences related to breed and age should be taken into account in studies of this disease. 相似文献
34.
35.
《The Journal of Applied Poultry Research》2006,15(3):355-361
This experiment was conducted to determine the effects of cage location and tier level with respect to light intensity on egg production and egg quality of hens housed in a semiconfined facility. Hens (ISA Brown, n = 225) at 75 wk of age were placed into 3-tier cages as top (T), middle (M), and bottom (B) tiers located in cages illuminated artificially (EI), by window (FW), or between corridors (C) for 2 mo. Light intensity was measured monthly for each cage at 5 cm from feeders every 6 h. Egg production was recorded daily and egg quality was assessed biweekly. Light intensity was the greatest for cages in the FW group (151.9, 119.8, and 89.8 lx for tiers T, M, and B, respectively), followed by EI (52.6, 54.5, and 51.0 lx for tiers T, M, and B, respectively), and C (44.5, 23.4, and 4.7 lx for tiers T, M, and B, respectively). Hens at location EI had greater egg production than hens at FW and C. Egg production for hens at tier T was also greater than for hens at tiers M and B. Egg production for hens at EI and C decreased quadratically, whereas that for hens at FW decreased linearly from tiers T to B. Cage location, but not tier level, affected egg weight. Hens at EI and FW produced heavier eggs than hens at C. Shape index, yolk color, and yolk index were independent of cage location and tier level. Hens at EI and FW produced eggs with thinner and weaker shells than hens at C. Moreover, eggshell strength increased linearly from tier T to B. Both albumen index and Haugh unit were the greatest for hens at FW, followed by EI and C. Their responses to cage location varied with tier levels. In conclusion, variation in light intensity in multitier cage systems in semiconfined laying hen houses may be a contributing factor for depressed laying performance and egg quality. 相似文献
36.
利用物体运动的连续性,将移动节点的运动规律与距离测量相结合提出了运动预测定位算法,该算法不需要额外的硬件支持,适应能力强,在信标节点密度比较低时提高了性能. 相似文献
37.
Influence of terminal rig configuration on the anatomical hooking location of line-caught yellowfin bream, Acanthopagrus australis 总被引:1,自引:0,他引:1
P. A. BUTCHER & M. K. BROADHURST D. REYNOLDS S. C. CAIRNS 《Fisheries Management and Ecology》2008,15(4):303-313
Abstract Experiments were carried out to test the dependence of anatomical hooking location on terminal rig configuration, and identify strategies by which hook ingestion can be minimised to reduce post-release mortality of angled yellowfin bream, Acanthopagrus australis (Günther). Eighty-five anglers targeted yellowfin bream using different designs and sizes of circle and J hooks and recorded technical, environmental and biological data for each landed fish. Considerably fewer fish (16.6 and 8.5%, respectively) ingested hooks than those hooked in the mouth (82.1 and 88.6%), and a greater percentage of J hooks were ingested than circle hooks or a J hook modified with a 15-mm horizontal bar. Irrespective of hook type, the rate of ingestion also declined with increasing hook weight and decreasing fish size. In cage experiments, significantly more hooks baited with natural soft baits (e.g. intestines and cephalopods) were ingested than those baited with artificial baits, crustaceans or teleosts, while in the field fewer hooks were ingested using artificial bait (e.g. bread and pellets) than terrestrial animals, teleosts, crustaceans, teleost or terrestrial animal intestines, cephalopods or polychaetes. Similarly, rigs with floats, short traces or a sinker only on the hook, along with angling in environments with at least some current reduced ingestion. Based on this study, anglers targeting yellowfin bream should be encouraged to use circle or modified J hooks and, regardless of the hook design, the largest hook size possible attached to short traces or a sinker only and hard baits. 相似文献
38.
39.
对模拟电路提出了一种基于小波与神经网络辅助式结合的故障诊断方法.该方法用小波变换作为模拟电路故障信号的预处理器,大大减少神经网络的输入数目,简化神经网络结构和减少它的训练时间,提高辨识故障能力.在介绍该故障诊断方法的基本原理后。给出了小波函数及故障特征选择的方法. 相似文献
40.