全文获取类型
收费全文 | 2874篇 |
免费 | 289篇 |
国内免费 | 1篇 |
专业分类
林业 | 236篇 |
农学 | 121篇 |
基础科学 | 27篇 |
620篇 | |
综合类 | 102篇 |
农作物 | 166篇 |
水产渔业 | 428篇 |
畜牧兽医 | 1164篇 |
园艺 | 65篇 |
植物保护 | 235篇 |
出版年
2024年 | 7篇 |
2023年 | 42篇 |
2022年 | 52篇 |
2021年 | 123篇 |
2020年 | 132篇 |
2019年 | 159篇 |
2018年 | 158篇 |
2017年 | 171篇 |
2016年 | 170篇 |
2015年 | 122篇 |
2014年 | 155篇 |
2013年 | 174篇 |
2012年 | 222篇 |
2011年 | 236篇 |
2010年 | 120篇 |
2009年 | 111篇 |
2008年 | 154篇 |
2007年 | 131篇 |
2006年 | 122篇 |
2005年 | 82篇 |
2004年 | 76篇 |
2003年 | 64篇 |
2002年 | 71篇 |
2001年 | 50篇 |
2000年 | 35篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 29篇 |
1996年 | 18篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 7篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1934年 | 2篇 |
1930年 | 1篇 |
1926年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有3164条查询结果,搜索用时 125 毫秒
941.
Pre-release techniques aim to increase the searching by the predators for their prey. Keeping bug predators for periods without
food before their release can increase the search ability of these insects. However, this practice can increase the cannibalism
during mass rearing. Brontocoris tabidus (Signoret) and Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) were kept for 12, 24, 36 and 48 h without food or with only Eucalyptus cloeziana plants in order to verify the occurrence of cannibalism on adults and eggs. Insects kept for periods longer than 24 h showed
higher cannibalism on adults and eggs and the presence of a E. cloeziana plant decreased the cannibalism during all the treatment periods. These predators preferred to attack first the eggs rather
than the adults, probably because of the inability of the former to avoid predation. The pre-release period should not exceed
24 h and plants must be provided to the predators in order to reduce the occurrence of cannibalism and increase the predatory
capacity of these natural enemies. 相似文献
942.
Corella-Madueño MA Harris MK Fu-Castillo AA Martínez-Téllez MA Valenzuela-Soto EM Gálvez-Ruiz JC Vargas-Arispuro I 《Pest management science》2011,67(12):1522-1527
BACKGROUND: Plant volatiles have complex intra‐ and interspecific effects in the environment that include plant/herbivore interactions. Identifying the quantity and quality of volatiles produced by a plant is needed to aid the process of determining which chemicals are exerting what effects and then examining whether these effects can be manipulated to benefit society. The qualitative characterization of volatile compounds emitted by pecan, Carya illinoinensis (Wang.) K. Koch, was begun in order to establish a database for investigating how these volatiles affect Acrobasis nuxvorella Nuenzig, a monophagous pest of pecan. Headspace solid‐phase microextraction combined with gas chromatography–mass spectrometry was used for the analysis of the volatile constituents of pecan during three phenological stages (dormant buds, intact new shoot growth and intact nutlets) of the Western Schley and Wichita cultivars. RESULTS: About 111 distinct compounds were identified from the two cultivars, accounting for ~99% of the headspace volatiles. The chromatographic profiles of both varieties revealed variations in the volatile composition and proportion between cultivars, with a predominance of terpene hydrocarbons, of the sesquiterpenes class, as well as monoterpenes. CONCLUSION: The significantly higher responsiveness recorded for the larvae of A. nuxvorella to C. illinoinensis shoots indicates that the larvae may be activated by terpenes emanating from the new shoot growth. This is the first study that has examined volatiles of pecan in Mexico. Copyright © 2011 Society of Chemical Industry 相似文献
943.
Regulation of lysine metabolism and endosperm protein synthesis by the opaque-5 and opaque-7 maize mutations 总被引:3,自引:0,他引:3
Azevedo RA Lea PJ Damerval C Landry J Bellato CM Meinhardt LW Le Guilloux M Delhaye S Varisi VA Gaziola SA Gratão PL Toro AA 《Journal of agricultural and food chemistry》2004,52(15):4865-4871
Two high lysine maize endosperm mutations, opaque-5 (o5) and opaque-7 (o7), were biochemically characterized for endosperm protein synthesis and lysine metabolism in immature seeds. Albumins, globulins, and glutelins, which have a high content of lysine, were shown to be increased in the mutants, whereas zeins, which contain trace concentrations of lysine, were reduced in relation to the wild-type lines B77xB79+ and B37+. These alterations in the storage protein fraction distribution possibly explain the increased concentration of lysine in the two mutants. Using two-dimensional polyacrylamide gel electrophoresis of proteins of mature grains, variable amounts of zein polypeptides were detected and considerable differences were noted between the four lines studied. The analysis of the enzymes involved in lysine metabolism indicated that both mutants have reduced lysine catabolism when compared to their respective wild types, thus allowing more lysine to be available for storage protein synthesis. 相似文献
944.
Yagüe C Bayarri S Conchello P Lázaro R Pérez-Arquillué C Herrera A Ariño A 《Journal of agricultural and food chemistry》2005,53(13):5105-5109
A multicolumn solid-phase extraction cleanup for the determination of organophosphorus (OP) and organochlorine (OC) pesticides plus PCB congeners in virgin olive oil is presented. The method involves dissolution of the olive oil in hexane, followed by a cleanup system using a diatomaceous earth column (Extrelut-QE) with reversed (C(18)) and normal (alumina) phase SPE columns. Determination of OPs was by GC-NPD, while the OCs and PCBs were analyzed using GC-ECD. Recovery assays for OPs varied from 81.7% to 105.3%, for OCs ranged between 74.3% and 99.4%, while for PCBs were from 60.1% to 119.2%. Quantitation limits ranged from 10 to 25 microg/kg olive oil for OPs, and from 1 to 6 microg/kg olive oil for OCs and PCBs. In the case of positive samples, the confirmation of pesticide identity was performed by ion-trap GC-MS/MS. The applicability of the method was assayed with 19 virgin olive oil samples collected from different olive mills of Aragón (Spain). Only one OP pesticide (acephate) was detected in one sample at a concentration of 10 microg/kg. Organochlorine pesticides were found in 5-47% of samples at very low levels ranging from 1.5 to 5.2 microg/kg. PCBs were found in 20-90% of samples, showing concentrations between 2.3 and 17.3 microg/kg. 相似文献
945.
The purpose of this study is to identify species, hybrids, and cultivars of edible Citrus species with high contents of diosmin as a functional compound and also to identify the developmental progress of the fruit in which it reaches maximum levels; these findings would be useful for extraction purposes and for the modulating effect of plant growth regulators on diosmin content to increase the level of this flavone. The results obtained reveal that the highest contents of diosmin are present in immature fruits of certain varieties of citron (Buda's finger) and lemon (Meyer), whereas the contents in the edible parts of the fruits are irrelevant from a pharmacological point of view. Similarly, it is shown that it is possible to increase the content of this flavone using hormonal treatments (6-benzylaminopurine and 2,4-dichlorophenoxyacetic acid) during the early stages of fruit growth. 相似文献
946.
Use of cholinesterase activity in monitoring organophosphate pesticide exposure of cattle produced in tropical areas. 总被引:3,自引:0,他引:3
V T Pardío N Ibarra M A Rodríguez K N Waliszewski 《Journal of agricultural and food chemistry》2001,49(12):6057-6062
The use of cholinesterase activity as a biochemical method for monitoring organophosphate pesticide exposure in cattle is described herein. Determination of cholinesterase activity of whole blood, erythrocyte, and plasma was carried out according to the Ellman modified kinetic method. The mean baseline acetylcholinesterase activities of 9.549 +/- 3.619 IU/mL in whole blood, 9.444 +/- 3.006 IU/mL in erythrocytes, and 0.149 +/- 0.063 IU/mL in plasma were estimated for steers from the control group. Results of multivariate analysis showed that the general responses between the control and experimental groups (in vivo, monitoring and case studies) treated with Coumaphos and Fenthion were statistically different, and the general responses of these experimental groups were statistically different over time as well. Among the fractions that were analyzed, the erythrocyte acetylcholinesterase activity could be adequate for the diagnosis of exposure or acute poisoning in cattle as it showed a good within-run and between-run precision with CVs <10% better than those in plasma. 相似文献
947.
Silva BM Andrade PB Mendes GC Valentão P Seabra RM Ferreira MA 《Journal of agricultural and food chemistry》2000,48(7):2853-2857
The phenolic compounds present in 17 samples of Portuguese commercial and three homemade quince jams were analyzed by reversed-phase HPLC/DAD, to determine their authenticity. Two different extraction methods were needed for the complete definition of quince jams profiles, one of them including an Amberlite XAD-2 cleaning step. These analyses showed that all the samples presented a similar profile composed of at least eight identified phenolic compounds, several unidentified characteristic procyanidin polymers, and sodium benzoate as preservative of quince jams. Several samples also contained arbutin, suggesting that these quince jam samples were fraudulently adulterated with pear puree. 相似文献
948.
Rosana Tidon Denise Ferreira Leite Bárbara Ferreira Dobbin Leão 《Biological conservation》2003,112(3):299-305
The drosophilid Zaprionus indianus was not collected in Brazil, despite on-going drosophilid collecting, until 1999. Since 1999 this species has become common in Brazil. We present data on collections of Z. indianus in central Brazil, since its first occurrence in this region, with the goal of discussing its route of introduction in South America and aspects of its adaptation to the environment. Collections made during a 2-year period show different seasonal distribution patterns of this insect. In contrast with the low population sizes registered in 1999, during the summer of 2000 a large proliferation of this insect was detected. We show that Z. indianus is more common in the savanna sites and that its population peaks during the wet season. These preferences are discussed, and the hypothesis that the introduction in South America should have occurred in the southeast region of this continent is defended. 相似文献
949.
To enhance efficiency of breeding programmes for Sclerotinia sclerotiorum resistance in sunflower capitula, two separate resistance tests have been recommended. However, the time necessary to develop
genotypes with two types of resistance makes this impractical. A strategy to combine the two tests was consequently proposed
to reduce the number of seasons per selection cycle, but genetic studies were necessary to determine if it could be applied
in breeding programmes. This was the objective of this work. Data from two genetically different sunflower inbred lines and
their F1, F2 and backcross generations were analysed in two years to determine the genetics of resistance to S. sclerotiorum in capitula measured by application on the same plants of a mycelium test combined with an ascospore test. Effects of maternal
origin were detected when the reciprocal generations were evaluated for the mycelium test. This suggests the importance of
choice of the inbred line used as female in population formation by hybridisation. Progeny subjected to the mycelium test
did not show any change in relative reactions to two S. sclerotiorum isolates suggesting that ranking genotypes according to the results of combined S. sclerotiorum tests is repeatable across Sclerotinia isolates and experimental seasons. Moderate narrow sense heritability indicated that selection of the best F2 plants should
be effective. Genetic gain from selection is possible because a reduction of lesion areas produced by the mycelium test can
be expected. Additive gene effects contribute significantly to reduction in lesion area. Consequences of results in population
improvement for S. sclerotiorum resistance in capitula are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
950.
The primary gene pool (GP-1) of a crop is composed of gene reservoirs that cross easily with the domesticated, while the crosses
regularly produce fertile offspring. The GP-1 is further subdivided into cultivated and wild gene pools. The cultivated gene
pool encompasses commercial stocks of the crop, as well as landraces. The wild GP-1 of the crop comprises putative ancestors
and closely related species that show a fair degree of fertile relationships with the domesticate. Two South American wild
subspecies of cassava (M. flabellifolia and M. peruviana) were proposed as natural members of the wild GP-1 of the crop. Another Brazilian species(M. pruinosa) is morphologically so close to both wild subspecies that it may turn out as another member of the wild GP-1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献