全文获取类型
收费全文 | 6047篇 |
免费 | 276篇 |
国内免费 | 1篇 |
专业分类
林业 | 450篇 |
农学 | 138篇 |
基础科学 | 49篇 |
1010篇 | |
综合类 | 1146篇 |
农作物 | 338篇 |
水产渔业 | 382篇 |
畜牧兽医 | 2138篇 |
园艺 | 231篇 |
植物保护 | 442篇 |
出版年
2023年 | 34篇 |
2022年 | 25篇 |
2021年 | 112篇 |
2020年 | 118篇 |
2019年 | 127篇 |
2018年 | 112篇 |
2017年 | 94篇 |
2016年 | 121篇 |
2015年 | 109篇 |
2014年 | 143篇 |
2013年 | 266篇 |
2012年 | 327篇 |
2011年 | 391篇 |
2010年 | 210篇 |
2009年 | 176篇 |
2008年 | 403篇 |
2007年 | 395篇 |
2006年 | 397篇 |
2005年 | 403篇 |
2004年 | 414篇 |
2003年 | 395篇 |
2002年 | 352篇 |
2001年 | 74篇 |
2000年 | 55篇 |
1999年 | 54篇 |
1998年 | 44篇 |
1997年 | 32篇 |
1996年 | 62篇 |
1995年 | 53篇 |
1994年 | 48篇 |
1993年 | 50篇 |
1992年 | 52篇 |
1991年 | 32篇 |
1990年 | 49篇 |
1989年 | 42篇 |
1988年 | 33篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 42篇 |
1984年 | 43篇 |
1983年 | 39篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1977年 | 29篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 25篇 |
排序方式: 共有6324条查询结果,搜索用时 78 毫秒
91.
Abstract: Stakeholders are an integral part of environmental conflict. Analysing the positions and interests of stakeholders is vital in effective environmental conflict management. This paper reviews the literature related to stakeholders and their dynamics in environmental conflict. It also presents the results of a study relating to a New Zealand transport infrastructure project where the positions and interests of stakeholders have kept on changing during the life of the project. This study plots the changing positions of some of the key stakeholders, towards this project. These stakeholders include a policy manager, a community stakeholder, an environmental stakeholder and a political stakeholder. The paper also analyses the changing positions by identifying and classifying the key drivers for these changes. 相似文献
92.
93.
Hikmet Budak P. Stephen Baenziger Brian S. Beecher Robert A. Graybosch Benjamin T. Campbell Marry J. Shipman Mustafa Erayman Kent M. Eskridge 《Euphytica》2004,137(2):261-270
Hexaploid triticale (X Triticosecale Wittmack) (2n= 6x= 42, AABBRR) and wheat (Triticum aestivum L.) (2n= 6x= 42, AABBDD) differ in their R and D-genomes. This produces differences in both agronomic and end-use quality characteristics. Our objective was to determine how introgressions of individual chromosomes from the D-genome of wheat affect these characteristics of a winter triticale 'Presto'. We studied the effects of 18 D-genome chromosome substitution lines, 15 sib-lines as controls, and five check cultivars at Lincoln, NE in 1996, using a randomized complete block design with two replications. The experiment was repeated at Lincoln and Mead, NE in 1997 and 1998 with 15 substitution lines that survived the first winter in Lincoln, along with their 12 control sibs and five check cultivars. Few D-genome chromosomes had positive effects. Chromosomes 2D, 4D, and 6D significantly reduced plant height when substituted for 2R, 4B, and 6R, respectively. No grain yield increases were associated with any of the D-genome chromosomes tested, but three substitutions decreased the grain yield. Depending on the allele of the hardness gene present, chromosome 5D increased or decreased kernel hardness when substituted for 5R or 5A, respectively. Introgressions of chromosomes 1D and 6D improved end-use quality characteristics of Presto. These results suggest that apart from beneficial effects of individual loci located on the D-genome chromosomes, no major benefit can be expected from D-genome chromosome substitutions. 相似文献
94.
Robert Theiler-Hedtrich 《Euphytica》1994,77(1-2):37-44
Summary Approximately 1000 seedlings from 20 combinations crossed in 1979, 1980 and 1981 (Theiler-Hedtrich 1985a) were tested for
several characters: fruit set (yield), fruit size, fruit colour, formation of abscission layer and bleeding after fruit removal
from fruit stalks, bacterial canker resistance, flowering and harvesting time. From progeny of crosses with Stella as pollinator,
56% (Vittoria × Stella) and 46% (Schüttler × Stella) of the seedlings were self-compatible, of which 14 were high yielding
with good fruit size and quality. From the data recorded it can be concluded:fruit set is a recessive character; only 5 to 20% of very good yielding seedlings were obtained in different progeny, even if the parental
plants were both very good croppers.Fruit juice and skin colour was in most progenies ‘black’ even if they were from combinations with ‘white’ varieties, e.g., Merton Glory or Schüttler.
Only from the combination Schiittler (‘white’) × Stella (‘black’), 50% of the seedlings were ‘white’; Stella therefore is
heterozygous for the character of fruit juice and skin colour.Fruit size is evenly distributed in progeny with respect to the fruit size of their parent plants.Abscission layer formation and non-bleeding is a genetically complex character. In combinations where both parent plants formed fruits with complete abscission layers
and which were not bleeding after fruit removal from the stalk, this character was inherited only to 50% (Vittoria × Schüttler)
or 85% (Vittoria × Frühe von der Weid) in the progeny. For the genetical control of this character further studies are necessary.Bacterial canker susceptibility was evenly distributed in seedlings from all combinations even if the highly resistant cv. Vittoria was used as one parent
plant, thereby not confirming the expected results of a higher proportion of resistant seedlings from combinations with Vittoria.Flowering and harvest time of the seedlings from different combinations was within the range of the parent plants. Only in the combination of Vittoria
× Stella (mid-to late-ripening season) one seedling out of 99 was found to form ripe fruits two weeks earlier than the parental
plants. From the seedlings tested 40 have been chosen for further evaluation or genetical studies. 相似文献
95.
Robert Koebner 《Euphytica》2003,129(3):399-402
Volume Contents
Contents Volume 129 2003 相似文献96.
Evaluation of seedling and adult plant resistance to stem rust in European wheat cultivars 总被引:2,自引:0,他引:2
A total of 105 European wheat cultivars were assessed for seedling and adult plant resistance (APR) to stem rust using an
array of Australian isolates of Puccinia graminis f. sp. tritici. Twenty-seven cultivars were susceptible at both seedling and adult plant growth stages. Twelve catalogued seedling stem
rust resistance genes (Sr7b, Sr8a, Sr8b, Sr9b, Sr9g, Sr11, Sr15, Sr17, Sr29, Sr31, Sr36 and Sr38) were detected in the remaining cultivars, and 13 cultivars carried additional seedling resistance genes that could not be
postulated with the isolates used. Low levels of APR to stem rust were found in the cultivars Artaban, Forno, Mec, Mercia,
Pandas and Vlada. Although the genetic identity of this APR was not determined, it was clear that the only designated stem
rust APR gene Sr2 was not present in any of the cultivars tested based on the absence of the linked traits seedling chlorosis and pseudo black
chaff. One of these cultivars, Forno, is believed to carry the leaf rust APR gene Lr34, previously reported to be associated with improved resistance to stem rust. A detailed genetic characterisation of the APRs
in these cultivars will be needed to understand their modes of inheritance and relationships with catalogued stem rust resistance
genes. Such knowledge may help in developing cultivars with effective gene combinations that confer higher levels of protection. 相似文献
97.
Sweetpotato virus disease (SPVD) is due to the dual infection and synergistic interaction of Sweetpotato feathery mottle potyvirus (SPFMV) and Sweetpotato chlorotic stunt crinivirus(SPCSV), and causes up to 98% yield loss in sweetpotato in East Africa. This study was conducted to determine the inheritance
of resistance to SPVD in sweetpotato and to estimate the nature of genetic variance. Ten parental clones varying in reaction
to SPVD were crossed in a half diallel mating design to generate 45 full-sib families. The families were graft-inoculated
with SPCSV and SPFMV to induce SPVD and evaluated for resistance in a randomized complete block design at two sites in Namulonge,
Uganda during 1998–2000. In serological assays for SPFMV and SPCSV,resistance to symptom development and recovery from initial
systemic SPVD symptoms, characterised resistant genotypes. Genetic component analysis showed significant effects for both
general combining ability (GCA) and specific combining ability (SCA) for resistance to SPVD. GCA to SCA variance component
ratios were large (0.51–0.87), hence GCA effects were more important than SCA effects. Resistant parents exhibited high GCA
indicating that additive gene effects were predominant in the inheritance of resistance to SPVD and recovery. Narrow-sense
heritability (31–41%) and broad-sense heritability (73–98%) were moderate to high, indicating that rapid genetic gains for
SPVD resistance could be accomplished by mass selection breeding techniques. Two genotypes, New Kawogo and Sowola, had high
negative GCA effects and had several families in specific crosses,which exhibited rapid recovery from SPVD,and are promising
parents for enhancement of SPVD resistance and recovery.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
98.
Robert J. Johnston James J. Opaluch Thomas A. Grigalunas Marisa J. Mazzotta 《Growth and change》2001,32(3):305-325
This paper investigates differences in non‐market farmland amenity values estimated using distinct methodologies, with a focus on the potential causes and policy implications. The paper compares farmland amenity values generated by a hedonic property value model and a contingent choice model, both estimated from data collected in the Peconic Estuary System of Suffolk County, NY. The analysis demonstrates that a combination of non‐market valuation methodologies can provide policy insights not otherwise available to those relying on any single approach, and illustrates types of information that may be obscured by methodologies used in isolation. 相似文献
99.
Jinhe Bai Eugene A. Mielke Paul M. Chen Robert A. Spotts Maryna Serdani James D. Hansen Lisa G. Neven 《Postharvest Biology and Technology》2006,40(3):207-215
A manually operated high-pressure hot-water washing system consisting of a boiler, hot-water mixing tank, contact loop, heat exchanger, spray mixing tank, high-pressure hot-water washing manifold, low-pressure fresh water rinse manifold, and pressure pump was constructed and installed in a packingline. The system developed 20–50 °C washing water at pressures up to 980 kPa. ‘d’Anjou’ pears (Pyrus communis L.), shortly after harvest, and after storage for 3 and 4 months in regular air (RA) or for 4, 7 and 8 months in controlled atmosphere (CA) at −1 °C were washed through the packingline with different wetting agents (0.1% Silwet, 0.01 and 0.1% Defoamer, and water), water pressures (regular and high-pressure (210–980 kPa)), water temperatures (control (tap water, 4–22 °C), 40 °C, and 50 °C), and brushes (soft and firm), respectively. The effect of the washing conditions on fruit quality was investigated after 1 month of storage at −1 °C to simulate shipping condition, and then again after 1 week at 20 °C to simulate marketing condition. Hot-water caused severe heat scald. When nozzle temperature was 50 °C, the incidence of heat scald increased to over 50% for the fruit stored in RA for 3 months. Combined with hot-water, 540 kPa high-pressure washing increased the incidence of friction discoloration. There were lower incidences of friction discoloration and heat scald for fruit stored in CA for 7 months, in comparison to that in RA for 3 months. However, those fruit did not ripen properly as indicated by a high extractable juice content. Fruit washed at harvest had minor incidences of friction discoloration regardless of different brushes, water pressures, and wetting agents. Fruit washed after storages in either 4 months RA or 4 or 8 months CA suffered a high incidence of friction discoloration including scuffing symptoms and pressure marking. The firm brushes caused a higher incidence of friction discoloration mainly because of scuffing symptoms. However, no differences were found between different water pressures and wetting agents with respect to friction discoloration. Fruit stored for 4 months RA suffered 26–28% friction discoloration in comparison to 16–18% in CA stored fruit with firm brush washing. Extended CA storage increased friction discoloration even with soft brush washing. The results suggest that a washing system with high-pressure spray, <30 °C warm water, wetting agent Defoamer and rotating soft brushes were significantly effective in removing surface pests and decay control without causing internal or external damage of fruit. 相似文献
100.
Chronic cardiovascular and neurodegenerative complications induced by hyperglycemia have been considered to be associated most relevantly with endothelial cell damages (ECD). The protective effects of the aqueous extract of Psidium guajava L. budding leaves (PE) on the ECD in human umbilical vein endothelial cell (HUVEC) model were investigated. Results revealed that glyoxal (GO) and methylglyoxal (MGO) resulting from the glycative and autoxidative reactions of the high blood sugar glucose (G) evoked a huge production of ROS and NO, which in turn increased the production of peroxynitrite, combined with the activation of the nuclear factor kappaB (NFkappaB), leading to cell apoptosis. High plasma glucose activated p38-MAPK, and high GO increased the expressions of p38-MAPK and JNK-MAPK, whereas high MGO levels induced the activity of ERK-MAPK. Glucose and dicarbonyl compounds were all found to be good inducers of intracellular PKCs, which together with MAPK acted as the upstream triggering factor to activate NFkappaB. Conclusively, high plasma glucose together with dicarbonyl compounds can trigger the signaling pathways of MAPK and PKC and induce cell apoptosis through ROS and peroxynitrite stimulation and finally by NFkappaB activation. Such effects of PE were ascribed to its high plant polyphenolic (PPP) contents, the latter being potent ROS inhibitors capable of blocking the glycation of proteins, which otherwise could have brought forth severe detrimental effects to the cells. 相似文献