全文获取类型
收费全文 | 3925篇 |
免费 | 256篇 |
国内免费 | 6篇 |
专业分类
林业 | 682篇 |
农学 | 79篇 |
基础科学 | 7篇 |
788篇 | |
综合类 | 279篇 |
农作物 | 140篇 |
水产渔业 | 234篇 |
畜牧兽医 | 1688篇 |
园艺 | 84篇 |
植物保护 | 206篇 |
出版年
2023年 | 26篇 |
2022年 | 29篇 |
2021年 | 45篇 |
2020年 | 73篇 |
2019年 | 52篇 |
2018年 | 146篇 |
2017年 | 139篇 |
2016年 | 165篇 |
2015年 | 97篇 |
2014年 | 135篇 |
2013年 | 263篇 |
2012年 | 265篇 |
2011年 | 254篇 |
2010年 | 134篇 |
2009年 | 126篇 |
2008年 | 208篇 |
2007年 | 229篇 |
2006年 | 210篇 |
2005年 | 188篇 |
2004年 | 183篇 |
2003年 | 174篇 |
2002年 | 161篇 |
2001年 | 110篇 |
2000年 | 98篇 |
1999年 | 59篇 |
1998年 | 27篇 |
1997年 | 35篇 |
1996年 | 22篇 |
1995年 | 63篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 12篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 25篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1980年 | 21篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1973年 | 8篇 |
1970年 | 10篇 |
排序方式: 共有4187条查询结果,搜索用时 0 毫秒
11.
Dr. Heinrich Härdtl 《Journal of pest science》1941,17(4):43-47
Ohne Zusammenfassung 相似文献
12.
13.
Rough vaccines in animal brucellosis: structural and genetic basis and present status 总被引:14,自引:0,他引:14
Moriyón I Grilló MJ Monreal D González D Marín C López-Goñi I Mainar-Jaime RC Moreno E Blasco JM 《Veterinary research》2004,35(1):1-38
Brucellosis control and eradication requires serological tests and vaccines. Effective classical vaccines (S19 in cattle and Rev 1 in small ruminants), however, induce antibodies to the O-polysaccharide of the lipopolysaccharide which may be difficult to distinguish from those resulting from infection and may thus complicate diagnosis. Rough attenuated mutants lack the O-polysaccharide and would solve this problem if eliciting protective immunity; the empirically obtained rough mutants 45/20 and RB51 have been used as vaccines. Strain 45/20 is reportedly unstable and it is not presently used. RB51 is increasingly used instead of S19 in some countries but it is rifampicin resistant and its effectiveness is controversial. Some controlled experiments have found good or absolute protection in adult cattle vaccinated orally (full dose) or subcutaneously (reduced dose) and in one field experiment, RB51 was reported to afford absolute protection to calves and to perform better than S19. Controlled experiments in calves, however, have shown reduced doses of RB51 to be ineffective, full doses only partially effective, and RB51 less effective than S19 against severe challenges. Moreover, other observations suggest that RB51 is ineffective when prevalence is high. RB51 is not useful in sheep and evidence in goats is preliminary and contradictory. Rough mutants obtained by molecular biology methods on the knowledge of the genetics and structure of Brucella lipopolysaccharide may offer alternatives. The B. abortus manBcore (rfbK) mutant seems promising in cattle, and analyses in mice suggest that mutations affecting only the O-polysaccharide result in better vaccines than those affecting both core and O-polysaccharide. Possible uses of rough vaccines also include boosting immunity by revaccination but solid evidence on its effectiveness, safety and practicality is not available. 相似文献
14.
15.
16.
Uses of game resources are under constant debate. One such debate focuses on hunting tourism and its contributions to rural economics. To prioritize future investment and inform policy decisions, it is necessary to identify the full economic consequences of the operation of hunting tourism companies in rural areas. However, the true economic significance of these typically small-scale companies is not apparent when examined on an industrial scale. These companies may nevertheless serve as a sustainable solution to local-scale rural challenges. In this article, the regional economic significance of hunting tourism is estimated for the East Lapland sub-region of northern Finland through the use of Computable General Equilibrium simulation models. Although these models are known to effectively evaluate short- and long-term regional economic effects of industries such as tourism, they have not previously been applied to evaluate hunting tourism. 相似文献
17.
18.
19.
20.
Time-frequency and complexity analyses for differentiation of physiologic murmurs from heart murmurs caused by aortic stenosis in Boxers 总被引:1,自引:0,他引:1
Höglund K Ahlstrom CH Häggström J Ask PN Hult PH Kvart C 《American journal of veterinary research》2007,68(9):962-969
OBJECTIVE: To investigate whether time-frequency and complexity analyses of heart murmurs can be used to differentiate physiologic murmurs from murmurs caused by aortic stenosis (AS) in Boxers. ANIMALS: 27 Boxers with murmurs. PROCEDURES: Dogs were evaluated via auscultation and echocardiography. Analyses of time-frequency properties (TFPs; ie, maximal murmur frequency and duration of murmur frequency > 200 Hz) and correlation dimension (T(2)) of murmurs were performed on phonocardiographic sound data. Time-frequency property and T(2) analyses of low-intensity murmurs in 16 dogs without AS were performed at 7 weeks and 12 months of age. Additionally, TFP and T(2) analyses were performed on data obtained from 11 adult AS-affected dogs with murmurs. RESULTS: In dogs with low-intensity murmurs, TFP or T(2) values at 7 weeks and 12 months did not differ significantly. For differentiation of physiologic murmurs from murmurs caused by mild AS, duration of murmur frequency > 200 Hz was useful and the combination assessment of duration of frequency > 200 Hz and T(2) of the murmur had a sensitivity of 94% and a specificity of 82%. Maximal murmur frequency did not differentiate dogs with AS from those without AS. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that assessment of the duration of murmur frequency > 200 Hz can be used to distinguish physiologic heart murmurs from murmurs caused by mild AS in Boxers. Combination of this analysis with T(2) analysis may be a useful complementary method for diagnostic assessment of cardiovascular function in dogs. 相似文献