全文获取类型
收费全文 | 16741篇 |
免费 | 14篇 |
专业分类
林业 | 3634篇 |
农学 | 1299篇 |
基础科学 | 137篇 |
2774篇 | |
综合类 | 724篇 |
农作物 | 2108篇 |
水产渔业 | 1806篇 |
畜牧兽医 | 1286篇 |
园艺 | 1113篇 |
植物保护 | 1874篇 |
出版年
2022年 | 14篇 |
2021年 | 14篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 2747篇 |
2017年 | 2709篇 |
2016年 | 1188篇 |
2015年 | 75篇 |
2014年 | 26篇 |
2013年 | 25篇 |
2012年 | 812篇 |
2011年 | 2156篇 |
2010年 | 2111篇 |
2009年 | 1260篇 |
2008年 | 1320篇 |
2007年 | 1593篇 |
2006年 | 46篇 |
2005年 | 114篇 |
2004年 | 116篇 |
2003年 | 161篇 |
2002年 | 68篇 |
2001年 | 21篇 |
2000年 | 49篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1953年 | 1篇 |
1936年 | 1篇 |
1906年 | 2篇 |
1905年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
Empirical relationships between land use/cover and estuarine condition in the Northeastern United States 总被引:1,自引:0,他引:1
Wilfrid Rodriguez Peter V. August Yeqiao Wang John F. Paul Arthur Gold Norman Rubinstein 《Landscape Ecology》2007,22(3):403-417
Land–water interactions were examined in three regions in the Virginian Biogeographic Province; the southern shore of Cape
Cod, Massachusetts; the Hudson/Raritan region of New York; and the eastern shore of the Delmarva (Delaware/Maryland/Virginia)
Peninsula. Cumulative distribution functions were used to evaluate similarity in environmental condition among estuaries.
Spatial-setting variables (location in a river, coastal lagoon, or in open waters) were associated with variation for some
measures of estuarine condition. Patterns of coastal urban and agriculture gradients were measured and their relationship
with indicators of estuarine condition was modeled statistically. When estuaries were pooled, the highest variation explained
by spatial-setting variables was found for dissolved oxygen (DO, R
2 = 0.44) and salinity (R
2 = 0.58), with DO decreasing in river locations and salinity decreasing with rainfall and sampling locations near rivers.
The explanatory power for the other indicator variables was low and varied from 6% to 27%. Rainfall explained some of the
variation (R
2 = 0.23) in total suspended solids. Moderate (0.4 < | r | < 0.7) to strong (| r | ≥ 0.7) linear associations were found between total urban area and measures of estuarine condition. Within regions, total
urban area was positively associated with Silver (r = 0.59), Cadmium (r = 0.65), and Mercury (r = 0.47) in Cape Cod, and inversely related to DO (r = −0.65) in the Hudson/Raritan region. No associations were found in the Delmarva Peninsula study area. Total area of agriculture
showed a moderate association with Arsenic in Cape Cod, but no other associations were found in the other two regions. Our
analyses show a measurable impact of urban land use on coastal ecosystem condition over large areas of the northeastern United
States. This pattern was most evident when many different landscapes were considered simultaneously. The relationship between
urban development and estuarine condition were weaker within the individual regions studied. The use of land use/cover models
for predicting estuarine condition is a challenging task that warrants enhancements in the type, quantity, and quality of
data to improve our ability to discern relationships between anthropogenic activities on land and the condition of coastal
environments. 相似文献
252.
253.
254.
255.
Takashi Naito Minoru Tanaka Satoshi Taba Tesuya Toyosato Atsushi Oshiro Kazuko Takaesu Kazuo Hokama Tomio Usugi Shinji Kawano 《Journal of General Plant Pathology》2007,73(2):139-141
In 1999, a disease of chrysanthemum [Dendranthema grandiflorum (Ramat.) Kitamura], characterized by virescence of flowers, occurred in Okinawa Prefecture. The causal agent was identified
as “Candidatus Phytoplasma aurantifolia” based on 16S rDNA sequencing.
The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession number AB247462. 相似文献
256.
Julie M. Steed Andreas Baierl Bruce D. L. Fitt 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(4):359-373
In winter oilseed rape experiments at Rothamsted in 2000/01 to 2002/03 growing seasons, the severity of phoma stem canker
epidemics in summer depended on the timing of phoma leaf spot epidemics in the previous autumn, and hence on the timing of
Leptosphaeria maculans ascospore release. The first major release of L. maculans ascospores was earlier in 2000 (26 September) and 2001 (18 September) than in 2002 (21 October). Consequently, the autumn
phoma leaf spot epidemic was also earlier in 2000 and 2001 than in 2002. The resulting stem canker epidemics were severe by
harvest (July) in 2001 and 2002 but not in 2003. No correlation was found between the severity or duration of phoma leaf spotting
(lesion days or lesion °C-days) and the subsequent severity of phoma stem canker epidemics. Rates of leaf production and loss
were similar in the three growing seasons. Out of ca. 25 leaves produced on plants during each season, leaf numbers 10–14 generally remained on plants for the longest. Treatment
with flusilazole + carbendazim in autumn decreased the severity of phoma leaf spotting for several weeks after treatment,
decreased the severity of stem canker the following summer and increased yield significantly in 2001 and 2002 but not in 2003.
The most effective timings for flusilazole + carbendazim application were when leaves 7–11 were present on most plants and
at least 10% of plants were affected by phoma leaf spot. Two half-dose applications of fungicide reduced phoma stem canker
and increased yield more than a single full dose application when phoma leaf spot epidemics were early (<800 °C-days after
sowing). 相似文献
257.
Andreas Kofoet Mathias Fink 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(4):369-381
Epidemics of Peronospora parasitica are strongly affected by temperature and air moisture, and the interaction of these factors. Because a significant percentage
of radish plants are grown in greenhouses, it may be possible to influence epidemics by altering the greenhouse climate. The
objective of this study was to test the hypothesis that epidemics of P. parasitica can be modelled by the effects of air temperature and moisture in the greenhouse. Such a model could then be used to analyse
greenhouse climate control strategies with regard to managing downy mildew. Five radish crops were grown under greenhouse
conditions with set-points for heating and ventilation intended to obtain favourable conditions for disease development during
the first part of the growing cycle. Subsequent to this first phase, unfavourable conditions were set until harvest. Disease
incidence was measured once a week until the radishes reached marketable size. In addition, experiments were carried out in
growth chambers in which inoculated plants were subjected to air temperatures between 8 and 27°C, and disease incidence and
sporulation intensity were measured. Data from these two experiments were then used to estimate model parameters. In this
model, the interactions of air temperature (T) and water vapour saturation deficit (SD) were adequately described by a multiplicative
relationship. The simulated epidemics by the fitted model were highly correlated with the observed epidemics (r = 0.91, R
2 = 0.83, n = 29). Parameter estimates indicated that T of ca. 20°C and SD < 0.03 hPa resulted in the highest rates of disease development
and that the rate was zero when SD > 2.0 hPa. Both experimental data and simulations showed that epidemics of P. parasitica can be effectively controlled by managing the greenhouse climate. 相似文献
258.
Kana Naito Yasuhiro Ishiga Kazuhiro Toyoda Tomonori Shiraishi Yuki Ichinose 《Journal of General Plant Pathology》2007,73(4):281-285
Flagellin in Pseudomonas syringae is a potent elicitor of defense responses including hypersensitive cell death in dicot plants. The oligopeptides flg22 consisting
of 22 conserved amino acids near the N-terminus of flagellins is reported to induce plant defense responses. Because glycosylation
of the central domain of flagellin affects its elicitor activity, we investigated whether any peptide sequence in addition
to flg22 is required for flagellin-induced hypersensitive reaction. A study of recombinant flagellin polypeptides indicated
that the N-terminal domain including the conserved flg22 is required for flagellin-induced hypersensitive cell death in Arabidopsis thaliana. 相似文献
259.
Alessandro Zanzotto Federica Autiero Diego Bellotto Gianluca Dal Cortivo Gianluca Lucchetta Michele Borgo 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(2):183-192
During a 6-year study, grapevine propagation materials and young grapevines were analysed to evaluate the presence of internal
wood discolouration and the occurrence of fungal species involved in Petri disease. The intensity of wood discolouration increased
with the ageing of the plants. The maximum incidence of dark streaks was observed in the rootstock while necrosis originating
from buds or nodes were notably present in the trunk and cordon of older vines. In contrast, the highest levels of brown-red
halo symptoms, defined as discoloured areas around the pith, were recorded in the early growth stages. Phaeoacremonium spp. and Phaeomoniella chlamydospora were usually isolated from the rooted-grafts and the 3-year old plants, respectively. The number of infected grapevines increased
with age. Most of the P. chlamydospora strains were isolated from dark streaks or dots, while Phaeoacremonium spp. were detected in brown-red halo symptoms and other symptomatic or asymptomatic wood. The greatest incidence of the two
fungal taxa was recorded in the lower parts of the grapevine, including the roots and rootstock. 相似文献
260.
Anne Moussart Caroline Onfroy Angelique Lesne Magali Esquibet Eric Grenier Bernard Tivoli 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(1):57-69
Ditylenchus dipsaci, the stem nematode of alfalfa (Medicago sativa), Mycosphaerella pinodes, cause of Ascochyta blight in pea (Pisum sativum) and Aphanomyces euteiches, cause of pea root rot, result in major yield losses in French alfalfa and pea crops. These diseases are difficult to control
and the partial resistances currently available are not effective enough. Medicago truncatula, the barrel medic, is the legume model for genetic studies, which should lead to the identification and characterization
of new resistance genes for pathogens. We evaluated a collection of 34 accessions of M. truncatula and nine accessions from three other species (two from M. italica, six from M. littoralis and one from M. polymorpha) for resistance to these three major diseases. We developed screening tests, including standard host references, for each
pathogen. Most of the accessions tested were resistant to D. dipsaci, with only three accessions classified as susceptible. A very high level of resistance to M. pinodes was observed among the accessions, none of which was susceptible to this pathogen. Conversely, a high level of variation,
from resistant to susceptible accessions, was identified in response to infection by A. euteiches. 相似文献