全文获取类型
收费全文 | 136178篇 |
免费 | 7805篇 |
国内免费 | 130篇 |
专业分类
林业 | 5635篇 |
农学 | 4719篇 |
基础科学 | 896篇 |
17589篇 | |
综合类 | 19144篇 |
农作物 | 5106篇 |
水产渔业 | 7102篇 |
畜牧兽医 | 73038篇 |
园艺 | 1820篇 |
植物保护 | 9064篇 |
出版年
2020年 | 1189篇 |
2019年 | 1422篇 |
2018年 | 2241篇 |
2017年 | 2505篇 |
2016年 | 2320篇 |
2015年 | 2022篇 |
2014年 | 2472篇 |
2013年 | 5769篇 |
2012年 | 4379篇 |
2011年 | 5191篇 |
2010年 | 3534篇 |
2009年 | 3572篇 |
2008年 | 5179篇 |
2007年 | 4994篇 |
2006年 | 4662篇 |
2005年 | 4281篇 |
2004年 | 4125篇 |
2003年 | 4188篇 |
2002年 | 3819篇 |
2001年 | 4777篇 |
2000年 | 4650篇 |
1999年 | 3764篇 |
1998年 | 1486篇 |
1997年 | 1468篇 |
1996年 | 1355篇 |
1995年 | 1619篇 |
1994年 | 1335篇 |
1993年 | 1376篇 |
1992年 | 2773篇 |
1991年 | 2913篇 |
1990年 | 2873篇 |
1989年 | 2904篇 |
1988年 | 2613篇 |
1987年 | 2594篇 |
1986年 | 2540篇 |
1985年 | 2400篇 |
1984年 | 1958篇 |
1983年 | 1715篇 |
1982年 | 1154篇 |
1979年 | 1649篇 |
1978年 | 1284篇 |
1977年 | 1135篇 |
1976年 | 1100篇 |
1975年 | 1164篇 |
1974年 | 1357篇 |
1973年 | 1448篇 |
1972年 | 1378篇 |
1971年 | 1195篇 |
1970年 | 1247篇 |
1969年 | 1146篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
C.?Silvar J.?M.?Duncan D.?E.?L.?Cooke N.?A.?Williams J.?Díaz F.?MerinoEmail author 《European journal of plant pathology / European Foundation for Plant Pathology》2005,112(1):43-52
A PCR-based method was developed for the identification and detection of Phytophthora capsici in pepper plants. Three PCR primers (CAPFW, CAPRV1 and CAPRV2) specific for P. capsiciwere designed based on the sequence of its internal transcribed spacer regions. CAPFW/CAPRV1 amplify a 452 bp product from P. capsici DNA whereas CAPFW/CAPRV2 a 595 bp fragment; neither set amplifies DNA from pepper or several fungi pathogenic to pepper. In conventional (single-round) PCR, the limit of detection was 5 pg DNA for both primer sets, whereas in nested PCR the detection limit for both was of 0.5 fg. However, when the dilution series of target DNA were spiked with plant DNA, amplification declined two-fold in both conventional and nested PCR. The CAPFW/CAPRV2 set in conventional PCR was used to detect P. capsici DNA in inoculated plants. Detection occurred as soon as 8h post-inoculation in stem samples from infected but still symptomless plants. The method was also tested to detect fungal DNA in infected soils. 相似文献
992.
993.
Carlos Garrido María Carbú Francisco Javier Fernández-Acero Giles Budge Inmaculada Vallejo Alison Colyer Jesús M. Cantoral 《European journal of plant pathology / European Foundation for Plant Pathology》2008,120(4):409-415
Anthracnose, caused by Colletotrichum spp., is a major disease of cultivated strawberry, Fragaria × ananassa. This study identifies the Colletotrichum spp. which causes strawberry anthracnose in the southwest of Spain. A survey of the region was carried out, and the strains
isolated were identified as C. acutatum by using the polymerase chain reaction (PCR) with genus and species-specific primers, demonstrating that this species is
currently the causal agent of strawberry anthracnose in the studied region. The pathogenicity of C. acutatum and C. gloeosporioides strains was evaluated on two principal strawberry cultivars (cvs Camarosa and Ventana) under field conditions, the latter
being more pathogenic than the former. 相似文献
994.
995.
Mitchell D Stamm Tiffany M Heng‐Moss Frederick P Baxendale Blair D Siegfried Roch E Gaussoin Daniel D Snow David A Cassada 《Pest management science》2013,69(2):285-291
BACKGROUND: Neonicotinoid insecticides are generally efficacious against many turfgrass pests, including several important phloem‐feeding insects. However, inconsistencies in control of western chinch bugs, Blissus occiduus, have been documented in field efficacy studies. This research investigated the efficacy of three neonicotinoid insecticides (clothianidin, imidacloprid and thiamethoxam) against B. occiduus in buffalograss under field conditions and detected statistically significant differences in B. occiduus numbers among treatments. A subsequent study documented the relative quantity and degradation rate of these insecticides in buffalograss systemic leaf tissues, using HPLC. RESULTS: Neonicotinoid insecticides initially provided significant reductions in B. occiduus numbers, but mortality diminished over the course of the field studies. Furthermore, while all three neonicotinoids were present in the assayed buffalograss leaf tissues, imidacloprid concentrations were significantly higher than those of clothianidin and thiamethoxam. Over the course of the 28 day study, thiamethoxam concentrations declined 700‐fold, whereas imidacloprid and clothianidin declined only 70‐fold and 60‐fold respectively. CONCLUSIONS: Field studies continued to verify inconsistencies in B. occiduus control with neonicotinoid insecticides. This is the first study to document the relative concentrations of topically applied neonicotinoid insecticides in buffalograss systemic leaf tissues. Copyright © 2012 Society of Chemical Industry 相似文献
996.
C. P. Musoli F. Pinard A. Charrier A. Kangire G. M. ten Hoopen C. Kabole J. Ogwang D. Bieysse C. Cilas 《European journal of plant pathology / European Foundation for Plant Pathology》2008,122(4):451-460
Coffee wilt disease (CWD) caused by Fusarium xylarioides, considered to be a soil-inhabiting fungus, is endemic in several African countries, affecting commercially important coffee
species and causing serious economic losses. Coffee wilt disease development in naturally infected Coffea canephora fields at the Coffee Research Institute in Uganda was assessed from April 2001 to March 2006 to generate information about
temporal and spatial spread of the disease. Maps of diseased trees were also generated from the data. Semi-variance analysis
was performed on the data to show the spatio-temporal structure of disease. Host influence on the spatio-temporal structure
was deduced from the distribution pattern of diseased and healthy trees and analysis of variance. Results show that the temporal
disease epidemic progress was slow. The disease was found to spread from initial infections to healthy neighbouring trees,
resulting in an aggregated pattern. An infected tree could infect up to three healthy trees away, in any direction. Disease
foci formed and expanded with time, coalescing but punctuated in spots planted with resistant hosts. There were varying levels
of susceptibility among host genotypes, affecting the rates and levels of epidemic development. The implications of the findings
to the control of CWD are discussed. 相似文献
997.
998.
The effect of 50% shading and NO3:NH4 ratio (0:100, 75:25, 50:50, and 25:75) in the nutrient solution on growth, yield, quality and N metabolism in hydroponically grown strawberry (Fragaria × ananassa var Camarosa) was evaluated. Both fresh and dry weights of leaves were significantly lower when a high concentration of either NO3 (100%) or NH4 (75%) was the sole N source in the nutrient solution. In unshaded plants, increasing of both NH4 and NO3 ratio in the nutrient solution reduced photosynthetic (Pn) rate, however in shaded plants the reduction of Pn became more pronounced at a higher ratio of NH4 in the nutrient solution. The yield in terms of fresh and dry weight of fruit per plant was significantly increased at the 75:25 and 50:50 (NO3:NH4) treatments. Fruit size was significantly affected by the treatments, so that the biggest fruits in both shaded and unshaded plants were obtained under the 75:25 and 50:50 (NO3:NH4) treatments. Total soluble solid (TSS) in unshaded plants was increased with increasing NH4 ratio in the nutrient solution, however in shaded plants it was reduced at high NH4 ratio in the nutrient solution. In both shaded and unshaded plants, higher concentration of NH4 significantly reduced the post-harvest life of the fruits. The increase of tissue N concentration was nearly proportional to the NH4 concentration in the nutrient solution. The activity of nitrate reductase (NR) was increased by increasing NH4 from 0 to 50% and then reduced at a higher ratio of NH4 in the solution. Shading increased NH4 concentration so that the shaded plant had nearly twice as high NH4 concentration in the leaves. The increase of NH4 concentration induced by shading could be partially the reduction of NH4 assimilate because of the shortage of carbohydrate. 相似文献
999.
Peter M. Groffman James M. Tiedje Delbert L. Mokma Stephen Simkins 《Landscape Ecology》1992,7(1):45-53
Large scale analyses of biogeochemical processes are necessary for understanding anthropogenic effects on global climate and
environmental quality. Regional scale estimates of denitrification from forest soils in southern lower Michigan USA were produced
by stratifying the region into landscape experimental units using soil texture and natural drainage classes, and extrapolating
data to larger areas using a geographic information system (GIS). Previous landscape-scale research established relationships
between soil texture and drainage and denitrification and quantified annual denitrification N loss in nine soil texture/drainage
groups. All forest soils within the region (64 series) were assigned to one of these nine groups based on their texture and
drainage characteristics and were assigned an annual denitrification N loss value. A regional estimate of denitrification
was produced by multiplying the areal extent of each of the nine soil groups by their annual denitrification N loss value.
Loam-textured soils underlie 47% of the regional forest and accounted for 73% of the forest denitrification. Sandy soils were
found under 44% of the regional forest but produced only 5% of the regional denitrification. Clay loam soils underlie 9% of
the regional forest and produced 22% of the denitrification. Annual denitrification N loss for the region was estimated as
1.4×107 kg N/yr. We used denitrification enzyme activity (DEA) as a proxy for annual denitrification N loss to determine if the relationship
between denitrification and soil texture and natural drainage that we observed at the landscape scale held up at the regional
scale. DEA was measured in 22 soils across the region and was strongly related to soil texture and natural drainage (r2=0.61), suggesting that extrapolation of data from the landscape to the regional scale was justified. 相似文献
1000.
S. Goldental-Cohen I. Biton Y. Many K. Tavrizov A.M. Dourou H. Zemach 《The Journal of Horticultural Science and Biotechnology》2019,94(4):488-498
A typical olive (Olea europaea L.) inflorescence consists of about 20 flowers. However, in many cultivars, only one fruit develops. This is due to massive abscission of flowers and fruitlets, which occurs during the first month after anthesis. In this study, we used the olive cultivar 'Barnea' to characterize the abscission mechanism and to try to increase fruit set by increasing the number of developed fruit per inflorescence. Removing the lateral flowers 3 weeks before anthesis increased fruit set by more than 50%. Removing all inflorescences but one from a branch increased the number of developed fruits from 0.93 to 2.8 during 2017 and from 0.91 to 3.34 fruits per inflorescence in 2018. Sugar quantification in the pistil revealed that starch level is high on the day of anthesis and low 25 days later in abscised as well as in developed fruit. Soluble carbohydrates are low on the day of anthesis, low in abscised flowers/fruitlets 25 days after anthesis and high in developed fruit. Screening the natural variation found in the Israeli germplasm collection revealed that in most cultivars less than one fruit per inflorescence has developed. However, there are unique cultivars with a higher fruit set. 相似文献