全文获取类型
收费全文 | 1309篇 |
免费 | 59篇 |
国内免费 | 45篇 |
专业分类
林业 | 199篇 |
农学 | 52篇 |
基础科学 | 54篇 |
97篇 | |
综合类 | 511篇 |
农作物 | 47篇 |
水产渔业 | 17篇 |
畜牧兽医 | 223篇 |
园艺 | 89篇 |
植物保护 | 124篇 |
出版年
2024年 | 2篇 |
2023年 | 23篇 |
2022年 | 21篇 |
2021年 | 42篇 |
2020年 | 27篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 32篇 |
2016年 | 53篇 |
2015年 | 38篇 |
2014年 | 67篇 |
2013年 | 57篇 |
2012年 | 91篇 |
2011年 | 103篇 |
2010年 | 85篇 |
2009年 | 123篇 |
2008年 | 103篇 |
2007年 | 96篇 |
2006年 | 74篇 |
2005年 | 54篇 |
2004年 | 47篇 |
2003年 | 26篇 |
2002年 | 29篇 |
2001年 | 31篇 |
2000年 | 19篇 |
1999年 | 22篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1976年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1413条查询结果,搜索用时 15 毫秒
991.
992.
The functional attributes of specific point mutations, R30K, S291G, and I392T, associated with full-length acetylcholinesterase (AChE) cDNAs of organophosphate (OP)- and carbamate-resistant Colorado potato beetles (CPB), were determined using site-directed mutagenesis and baculovirus expression. Enzymatic and inhibitory properties of altered recombinant acetylcholinesterases (rAChEs) were examined. S291G increased the hydrolysis of substrates with larger substituted alkyl groups (e.g., BTC vs ATC) and increased the inhibitory action of inhibitors with larger alkyl groups (e.g., paraoxon, DFP, and N-propyl carbofuran vs. azinphosmethyl-oxon and N-methyl carbofuran). R30K in conjunction with S291G enhanced the hydrolysis activity of larger substrates and the inhibitory action of larger inhibitors. I392T attenuated the effects of S291G in that the altered rAChE with both S291G and I392T elicited substrate specificity and inhibitory properties more similar to the susceptible form of AChE without mutations. 相似文献
993.
小尾寒羊高繁殖力候选基因RBP4的研究 总被引:6,自引:0,他引:6
以视黄醇结合蛋白4(retinol binding protein 4,RBP4)基因为候选基因,采用PCR-SSCP技术分析了RBP4基因在高繁殖力绵羊品种(小尾寒羊、湖羊)以及低繁殖力绵羊品种(多赛特羊、萨福克羊)中的单核苷酸多态性,同时研究这个基因对小尾寒羊高繁殖力的影响。结果表明:RBP4基因扩增片段在4个绵羊品种中存在PCR-SSCP多态性。BB基因型只出现在高繁殖力绵羊品种中,而低繁殖力绵羊品种则没有BB基因型;AB基因型频率随着绵羊繁殖力的降低而升高;AA基因型只出现在小尾寒羊、多赛特羊中。BB基因型小尾寒羊产羔数分别比AA和AB基因型多0.52只(Pd0.05)和0.67只(Pd0.05),AA和AB基因型小尾寒羊产羔数没有显著差异(P〉0.05)。本研究检测的绵羊RBP4基因座位与小尾寒羊高繁殖力相关。 相似文献
994.
995.
996.
Stephen Clarke 《Integrated Pest Management Reviews》2001,6(3-4):293-301
The operational Integrated Pest Management program for the southern pine beetle (SPB), Dendroctonus frontalis, currently consists of five components: prevention, prediction, detection, evaluation, and direct control. Full implementation of the program is hampered by economic, regulatory, and management constraints, and devastating SPB outbreaks still occur periodically. Recommendations for improving implementation include gaining public acceptance of the program, devising new management strategies, developing area-wide suppression techniques, coordinating efforts among landowners and government agencies, and revising the environmental analysis process. Severe outbreaks will continue without the creation of less susceptible forest conditions and more stable timber markets, plus the development of improved prediction, detection, communication, and suppression practices. 相似文献
997.
几种杀虫剂对烟草甲幼虫的触杀毒力 总被引:1,自引:0,他引:1
利用烟虫幼虫作试虫,测定了不同浓度的灭多威,乙酰甲胺磷,敌敌畏和敌百虫等4种药剂在48h和72h后的触杀毒力,发现灭多威对烟草甲幼虫触杀活性最高,药效发挥最快,乙酰甲胺磷次之,敌百虫活性最小,药效发挥最慢。 相似文献
998.
Post vaccination and colostral peste des petits ruminants antibody dynamics in research flocks of Kirdi goats and Foulbe sheep of north Cameroon 总被引:2,自引:0,他引:2
We studied Kirdi goats and Foulbe sheep kept on-station at the Institute of Agricultural Research for Development (IRAD), Garoua to look at their immunological response following vaccination with a specific peste des petits ruminant (PPR) virus vaccine. Pre-vaccination PPR antibody seroprevalences were 44 and 29% in goats and sheep, respectively. Seroprevalences following vaccination were 100% in both species. Titres remained above the protection threshold level (1:10) in both species at 12 months. Maternal antibodies in young animals were detectable to up to 6 months of age but fell below the protection threshold level at 3.5 and 4.5 months in lambs and kids, respectively. Kids and lambs from immunised or exposed dams should be vaccinated at 4 and 5 months of age, respectively. 相似文献
999.
Six Sarcocystis species from reindeer (S. grueneri, S. rangi, S. tarandivulpes, S. hardangeri, S. rangiferi and S. tarandi) have previously been genetically characterised. The aim of this study was to identify possible definitive hosts for S. hardangeri, S. rangiferi and S. tarandi by including the six species in phylogenetic analyses of the Sarcocystidae, and also to investigate the phylogenetic relationships between the species from reindeer and those from other hosts. The study also aimed at revealing whether the inclusion of six Sarcocystis species from the same intermediate host would have any effect on previously inferred phylogenetic relationships within the Sarcocystidae. The complete small subunit (ssu) rRNA gene sequences of all six Sarcocystis species from reindeer were used in the phylogenetic analyses along with ssu rRNA gene sequences of 85 other members of the Coccidea. Trees were constructed using Bayesian analysis and maximum likelihood estimations. All six Sarcocystis species from reindeer were placed together with other Sarcocystis species using an even-toed ungulate as their intermediate host. The three canine transmitted species, S. grueneri, S. rangi, S. tarandivulpes, formed a sister group to other Sarcocystis species with a canine definitive host. The position of S. hardangeri on the tree suggested that it uses another type of definitive host than the other Sarcocystis species in this clade. Considering the geographical distribution and infection intensity of S. hardangeri, corvid birds are perhaps its most likely definitive hosts. The phylogenetic position, geographical distribution, prevalence and morphological similarity to feline transmitted Sarcocystis species in closely related Cervidae suggest that the most likely definitive hosts of S. rangiferi and S. tarandi are felines, and in Norway notably the lynx. The overall phylogeny of the Sarcocystidae did not change by the inclusion of the six Sarcocystis species from reindeer. This study suggests that phylogentic analysis can be a useful tool in the search for possible definitive hosts for those Sarcocystis species for which they are unknown and difficult to find solely by other methods. 相似文献
1000.
Romański KW 《Research in veterinary science》2008,85(2):324-332
As feeding is not a factor disrupting the migrating motor (myoelectric) complex (MMC) in sheep, it is presumed that the fed pattern is absent in this animal species. In turn, feeding may stimulate ovine gastrointestinal motility. To verify this discrepancy the myoelectric activities of the antrum and duodeno-jejunum were recorded in seven adult sheep. Additionally, the relationship between electrical and mechanical activity was tested in four of these animals by means of strain gauge force transducers mounted near the duodenal electrodes. Chronic experiments were conducted in fasted and non-fasted sheep before, during, and after standard feeding. Fodder was offered during the duodenal phases 1, 2a, or 2b of the MMC. Two types of responses to feeding (an unspecific and a specific fed pattern) were denoted. A simple increase in spike burst intensity, i.e. without their special deployment and assessed as the myoelectric activity index (unspecific fed pattern), was observed in the abomasal antrum and small bowel during and after feeding in the course of phase 2b of the MMC in non-fasted and fasted sheep. In the abomasal antrum its duration was longer than in the small intestine. In non-fasted animals the unspecific fed pattern was more pronounced in the abomasal antrum than in the small bowel, while its duration was longer in fasted animals. The specific fed pattern was evoked in the duodeno-jejunum during feeding initiated in the course of phase 2b of the MMC exclusively in non-fasted animals. During this pattern, the spike burst series were significantly reduced compared with those which appeared during phase 2b of the MMC and dispersed single spike bursts predominated. The average duration of the specific fed pattern was 3-4 min and it arrived 2-7 min after feeding onset. In the remaining periods during feeding, the spike burst pattern resembled that often observed during phase 2b of the MMC. Thus the confined fed pattern is present in sheep and its character depends upon the gastrointestinal region and feeding habits. 相似文献