全文获取类型
收费全文 | 169576篇 |
免费 | 9678篇 |
国内免费 | 325篇 |
专业分类
林业 | 6472篇 |
农学 | 5351篇 |
基础科学 | 1277篇 |
20285篇 | |
综合类 | 29283篇 |
农作物 | 6303篇 |
水产渔业 | 8462篇 |
畜牧兽医 | 88024篇 |
园艺 | 2123篇 |
植物保护 | 11999篇 |
出版年
2018年 | 2352篇 |
2017年 | 2555篇 |
2016年 | 2397篇 |
2015年 | 2052篇 |
2014年 | 2552篇 |
2013年 | 6681篇 |
2012年 | 4641篇 |
2011年 | 5751篇 |
2010年 | 3670篇 |
2009年 | 3741篇 |
2008年 | 5644篇 |
2007年 | 5318篇 |
2006年 | 5128篇 |
2005年 | 4698篇 |
2004年 | 4499篇 |
2003年 | 4507篇 |
2002年 | 4370篇 |
2001年 | 5372篇 |
2000年 | 5152篇 |
1999年 | 4133篇 |
1998年 | 1628篇 |
1997年 | 1652篇 |
1995年 | 1980篇 |
1994年 | 1767篇 |
1993年 | 1670篇 |
1992年 | 3529篇 |
1991年 | 3752篇 |
1990年 | 3716篇 |
1989年 | 3710篇 |
1988年 | 3440篇 |
1987年 | 3502篇 |
1986年 | 3599篇 |
1985年 | 3462篇 |
1984年 | 2898篇 |
1983年 | 2556篇 |
1982年 | 1734篇 |
1981年 | 1685篇 |
1980年 | 1628篇 |
1979年 | 2724篇 |
1978年 | 2214篇 |
1977年 | 1890篇 |
1976年 | 1719篇 |
1975年 | 1832篇 |
1974年 | 2396篇 |
1973年 | 2455篇 |
1972年 | 2353篇 |
1971年 | 2043篇 |
1970年 | 1965篇 |
1969年 | 1882篇 |
1967年 | 1585篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Trevor J. Gilliland Paolo Annicchiarico Bernadette Julier Marc Ghesquière 《Grass and Forage Science》2020,75(3):227-241
Herbage production is regarded as having environment-friendly credentials. However, as the ruminant production it supports is facing major challenges on sustainability, environmental footprint and human health concerns, EU herbage cultivar testing must contribute to the solutions. Before new cultivars can be sold in a member state (MS) and gain EU-wide marketing, they must pass official tests to prove they are both novel (distinct, uniform and stable, DUS) with improved value for cultivation and use (VCU). Herbage species present specific challenges, as their allogamy imposes a wide within-cultivar variation that adds complexity to DUS tests and their “value” is only realized in ruminant produce. Current VCU systems measure production, chemical composition and disease/stress tolerances, often on large numbers of candidate cultivars, but prohibitive labour costs and logistics mean that animal intake, ruminant output or environmental benefits cannot be measured directly. Furthermore, some candidate cultivars with proven superior VCU fail DUS even though the non-distinct comparison is with a significantly lower performing registered cultivar. To resolve these problem cases, a “vmDUS” distinctness tool is proposed, which uses molecular markers but conforms to UPOV-declared principles. A short overview of current grassland research shows smart proxy measures of animal value can easily and quickly be adopted into an integrated pan-European (EU-VCU) test network. The proposed EU-VCU scheme will reallocate test resources to conduct these additional tests by placing MS in data sharing collaborations, while retaining their national listing authority. The benefits to all stakeholders from adopting these new testing procedures are considered. 相似文献
102.
Robert M. Boddey Daniel Rume Casagrande Bruno G. C. Homem Bruno J. R. Alves 《Grass and Forage Science》2020,75(4):357-371
Beef cattle producers seldom use fertilizers for their pastures in tropical regions of Brazil. Slowly, this is changing but because of the need for repeated applications, N fertilizer is rarely applied. The introduction of a forage legume is an appropriate solution for this problem, but until recently adoption has been very low as the legumes generally have not persisted in the sward. We report research on how grazing management can affect the persistence of stoloniferous legumes in pastures of Brachiaria spp. and the problems of establishing and maintaining crown-forming legumes such as Stylosanthes spp. With suitable management, milk or bovine carcass yields can be equal or greater from mixed than from grass-alone pastures fertilized with 120 or 150 kg Nha-1 year−1. In addition to savings in CO2 emissions from fossil fuels for the production and distribution of N fertilizers, nitrous oxide emissions from cattle excreta and legume residues are lower than those from N-fertilized brachiaria grass monocultures. Other studies indicate that enteric methane emissions from cattle may be mitigated when forage legumes are included in their diet. The use of forage legumes in mixed pastures for tropical regions is emerging as a feasible strategy to keep meat and milk production at acceptable levels with reduced greenhouse gas emission rates. 相似文献
103.
Mohammed Faez Guillaume Dom Abdulwali Nada Harhar Hicham Al-Jobory Hala J. 《Plant foods for human nutrition (Dordrecht, Netherlands)》2020,75(2):230-235
Plant Foods for Human Nutrition - Argan oil is prepared by cold pressing argan kernels collected from fully ripe fruit. Argan oil market price is particularly elevated. Consequently, efficient... 相似文献
104.
Nowakowski A. Justin Peaden J. Mark Tuberville Tracey D. Buhlmann Kurt A. Todd Brian D. 《Landscape Ecology》2020,35(4):893-906
Landscape Ecology - Thermal traits likely mediate organismal responses to changing thermal environments. As temperatures increase, predicting species responses will depend on understanding how... 相似文献
105.
Aartsma Yavanna Hao Yueyi Dicke Marcel van der Werf Wopke Poelman Erik H. Bianchi Felix J. J. A. 《Landscape Ecology》2020,35(4):907-919
Landscape Ecology - Tritrophic interactions may be affected by local factors and the broader landscape context. At small spatial scales, carnivorous enemies of herbivorous insects use... 相似文献
106.
Howe Alexander A. Landhäusser Simon M. Burney Owen T. Long James N. Mock Karen E. 《New Forests》2020,51(2):367-378
New Forests - In seedling-based reforestation operations, seed source is known to be an influential variable affecting outplanting success. Adaptive variation among seed sources may also be an... 相似文献
107.
Sepsis of the calcaneal bursae (CB) presents significant treatment challenges with limited clinical data available in the literature. The objective of this retrospective cohort study was to assess the clinical outcomes associated with CB lavage using either a through-and-through needle or bursoscopic technique. Clinical records of 29 horses treated for septic calcaneal bursitis using either technique between 2005 and 2019 were reviewed. Fisher’s exact test was used to assess statistical significance between first surgical technique and success at first surgery (i.e. not requiring >1 lavage), survival to discharge and return to work (RTW). Bursoscopy was performed in 13/29 (44.8%) cases, and needle lavage in 16/29 (55.2%). In the needle group, 12 (75%) horses were discharged following the first surgery. Four had repeat interventions; two (12.5%) had needle lavage and two (12.5%) had bursoscopy. Of the two horses to have repeat needle lavage, one was subjected to euthanasia and one discharged, and of the two that underwent bursoscopy, one was discharged and one received a third bursoscopy prior to discharge. In the bursoscopy group, seven (53.8%) were discharged and three (23.1%) were subjected to euthanasia following the first surgery. Three (23.1%) received a second bursoscopic lavage with one discharged, one subjected to euthanasia and one having a third bursoscopic lavage prior to discharge. Overall, 18/24 (75%) followed up cases RTW, 10 (55.5%) from the needle group, eight (44.4%) the bursoscopy group. No statistically significant differences between first surgical technique used and success at first surgery (no subsequent lavage(s) required), survival to discharge or return to work were detected. The main limitations of this study are that it is a retrospective study, has a small population with limited statistical power and potential selection bias. No statistically significant differences existed between the outcomes of the two techniques, contrary to the belief that bursoscopic lavage is superior. Larger, multicentred studies, with greater statistical power are required to further assess this relationship. 相似文献
108.
Journal of Soils and Sediments - 相似文献
109.
Natural resistance in cottonseed to Aspergillus flavus infection has not been explored to date. A green fluorescent protein (GFP) expressing A. flavus strain was used to assess the resistance of seed from 35 cotton varieties from Gossypium arboreum, G. barbadense, and G. hirsutum. Mature cotyledons devoid of seed coat were wounded, inoculated, and assessed for innate resistance to A. flavus infection. Of the initial 35 varieties tested, we observed a range of resistance to infection in representatives of all three species. A subset of 15 representatives was further analyzed. Within this group, G. arboreum cultivar A2 186 and G. hirsutum cultivar SA 1582 were most resistant to fungal infection. The most susceptible cultivar in this group was G. hirsutum SA 1595. The remaining 12 representatives tested in the secondary screen (3 G. arboreum, 3 G. barbadense, and 6 G. hirsutum lines) exhibited intermediate resistance. We did not observe any relationship between species and resistance. Within each species, there was a range of responses to fungal infection. Future studies using this methodology to screen additional diploid and tetraploid cotton lines may enable us to identify naturally resistant germplasm that can be used to develop cotton with enhanced resistance to fungal infection. 相似文献
110.
Assessing vulnerability of New Zealand lakes to loss of conservation value from invasive fish impacts 下载免费PDF全文
- Predictions of invasion risk for seven non‐indigenous fish species, ecological impact scores for individual species, and lake conservation rankings were linked to develop Invasion Risk Impact (IRI) and Lake Vulnerability (LV) indices that help identify New Zealand lakes most at risk of loss of conservation value from potential multi‐species invasions.
- Species‐specific IRI scores (the product of predicted invasion risk and species impact) highlighted Eurasian perch (Perca fluviatilis) and the brown bullhead (Ameiurus nebulosus), as the species most likely to spread and cause ecological harm in lakes. For 3431 lakes >1 ha throughout New Zealand, total IRI tended to be highest for lowland riverine and dune lakes most of which are already colonized by multiple invasive fish species.
- The LV index indicated that lakes most at risk of loss of conservation value from invasive fish impacts were predominantly (i) in the northern half of the North Island where several uncommon lake types occur, and (ii) along the west coast of the South Island where conservation value is often greater, largely because of low catchment modification.
- The IRI and LV indices can be used to assist with setting priorities for surveillance monitoring, advocacy, and response planning targeted at preventing the establishment of invasive fish in moderate‐to‐high value lakes most susceptible to ecological impacts. Both indices can be adapted to accommodate alternative impact and conservation scoring systems, providing a flexible tool for local‐ and national‐scale assessments of lake vulnerability to fish invasion impacts.