全文获取类型
收费全文 | 686篇 |
免费 | 54篇 |
专业分类
林业 | 63篇 |
农学 | 32篇 |
基础科学 | 1篇 |
152篇 | |
综合类 | 19篇 |
农作物 | 52篇 |
水产渔业 | 46篇 |
畜牧兽医 | 323篇 |
园艺 | 6篇 |
植物保护 | 46篇 |
出版年
2023年 | 3篇 |
2022年 | 15篇 |
2021年 | 42篇 |
2020年 | 37篇 |
2019年 | 43篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 38篇 |
2015年 | 26篇 |
2014年 | 27篇 |
2013年 | 45篇 |
2012年 | 58篇 |
2011年 | 65篇 |
2010年 | 31篇 |
2009年 | 36篇 |
2008年 | 38篇 |
2007年 | 31篇 |
2006年 | 23篇 |
2005年 | 35篇 |
2004年 | 16篇 |
2003年 | 29篇 |
2002年 | 11篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有740条查询结果,搜索用时 117 毫秒
731.
A PINOID-dependent binary switch in apical-basal PIN polar targeting directs auxin efflux 总被引:1,自引:0,他引:1
Friml J Yang X Michniewicz M Weijers D Quint A Tietz O Benjamins R Ouwerkerk PB Ljung K Sandberg G Hooykaas PJ Palme K Offringa R 《Science (New York, N.Y.)》2004,306(5697):862-865
Polar transport-dependent local accumulation of auxin provides positional cues for multiple plant patterning processes. This directional auxin flow depends on the polar subcellular localization of the PIN auxin efflux regulators. Overexpression of the PINOID protein kinase induces a basal-to-apical shift in PIN localization, resulting in the loss of auxin gradients and strong defects in embryo and seedling roots. Conversely, pid loss of function induces an apical-to-basal shift in PIN1 polar targeting at the inflorescence apex, accompanied by defective organogenesis. Our results show that a PINOID-dependent binary switch controls PIN polarity and mediates changes in auxin flow to create local gradients for patterning processes. 相似文献
732.
Donald Boulter I. Marta Evans Eric Derbyshire 《Plant foods for human nutrition (Dordrecht, Netherlands)》1973,23(1-3):239-250
Storage globulins contribute 80–90% of the seed protein of many legumes and consist principally of two proteins called vicilin and legumin in peas. The relative proportions of the two proteins has been shown to differ in different legumes by gel-electrophoresis. The essential amino acid composition of vicilin and legumin ofPisum andVicia differ and the possible significance of these findings to screening strategies for improved legume programmes was discussed.Cowpeas were grown in growth cabinets under standard environmental conditions. Seeds were shown to have the same percentage nitrogen and sulphur on a dry-weight basis, irrespective of the position of the pod on the plant, indicating that legume seeds may have a conservative biochemistry.Paper presented at the conference of the International Association for Quality Research on food Plants (CIQ) held in common with the Deutsche Gesellschaft für Qualitätsforschung (Pflanzliche Nahrungsmittel) e.V. (DGQ) in Berlin on 6th October 1972 相似文献
733.
Marta Planellas Anna Bassols Carlo Siracusa Yolanda Saco Mercè Giménez Raquel Pato Josep Pastor 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2009,38(3):348-352
Background: In veterinary medicine, there is increasing interest in measuring acute phase proteins as a tool in the diagnosis and monitoring of neoplastic diseases. Although mammary neoplasms are the most common type of cancer in dogs, acute phase proteins have not been extensively evaluated in dogs with mammary tumors. Objectives: The aim of this study was to evaluate serum haptoglobin (Hp) and C‐reactive protein (CRP) concentrations in the dogs with mammary tumors and assess their potential association with malignancy. Methods: A retrospective study of dogs with mammary tumors was performed. Serum concentrations of CRP and Hp were determined in healthy control dogs (n=20) and dogs with mammary tumors before surgery (n=41). Mammary tumors were grouped as carcinomas (n=24), fibrosarcoma (n=1), malignant mixed tumors (n=7), benign mixed tumors (n=6), and adenomas (n=3). CRP and Hp concentrations were compared in dogs with different tumor types and were also compared based on tumor size, lymph node infiltration, skin ulceration, fixation to underlying tissue, and time between tumor identification and removal. Results: Hp concentration was significantly (P<.043) higher in dogs with mammary tumors (median 2.03 g/L, range 0.09–2.94 g/L) compared with controls (1.38 g/L, range 0.08–3.00 g/L), but the range of values overlapped considerably. CRP concentration was higher in dogs with carcinomas (4.70 mg/L, range 0.63–128.96 mg/L) vs controls (2.11 mg/L, range 0.25–6.57 mg/L) (P=.0008) and in dogs with ulcerated skin (14.8 mg/L, range 5.7–128.9 mg/L, n=3) compared with those without ulceration (2.4 mg/L, range 0.11–30.3 mg/L, n=38) (P=.048). Conclusions: Serum Hp and CRP do not appear to have value in diagnosing or predicting malignancy of mammary tumors in dogs. Higher CRP concentrations in dogs with mammary carcinoma suggest a role for inflammation in this tumor type. 相似文献
734.
ASTRID BÖHNE Christina SCHULTHEIS Delphine GALIANA‐ARNOUX Alexander FROSCHAUER Qingchun ZHOU Cornelia SCHMIDT Yvonne SELZ Catherine OZOUF‐COSTAZ Agnès DETTAI Béatrice SEGURENS Arnaud COULOUX Sylvie BERNARD‐SAMAIN Valérie BARBE Stefan CHILMONCZYK Frédéric BRUNET Amandine DARRAS Marta TOMASZKIEWICZ Marie SEMON Manfred SCHARTL Jean‐Nicolas VOLFF 《Integrative zoology》2009,4(3):277-284
In contrast to mammals and birds, fish display an amazing diversity of genetic sex determination systems, with frequent changes during evolution possibly associated with the emergence of new sex chromosomes and sex‐determining genes. To better understand the molecular and evolutionary mechanisms driving this diversity, several fish models are studied in parallel. Besides the medaka (Oryzias latipes Temminck and Schlegel, 1846) for which the master sex‐determination gene has been identified, one of the most advanced models for studying sex determination is the Southern platyfish (Xiphophorus maculatus, Günther 1966). Xiphophorus maculatus belongs to the Poeciliids, a family of live‐bearing freshwater fish, including platyfish, swordtails and guppies that perfectly illustrates the diversity of genetic sex‐determination mechanisms observed in teleosts. For X. maculatus, bacterial artificial chromosome contigs covering the sex‐determination region of the X and Y sex chromosomes have been constructed. Initial molecular analysis demonstrated that the sex‐determination region is very unstable and frequently undergoes duplications, deletions, inversions and other rearrangements. Eleven gene candidates linked to the master sex‐determining gene have been identified, some of them corresponding to pseudogenes. All putative genes are present on both the X and the Y chromosomes, suggesting a poor degree of differentiation and a young evolutionary age for platyfish sex chromosomes. When compared with other fish and tetrapod genomes, syntenies were detected only with autosomes. This observation supports an independent origin of sex chromosomes, not only in different vertebrate lineages but also between different fish species. 相似文献
735.
Gratacós-Cubarsí M Fernandez-García A Picouet P Valero-Pamplona A García-Regueiro JA Castellari M 《Journal of agricultural and food chemistry》2007,55(11):4610-4616
Tetracycline (TC) and 4-epitetracycline (4eTC) degradation, as well as anhydrotetracycline (ATC) and 4-epianhydrotetracycline (4eATC) formation, has been evaluated in thermally treated chicken breast, pig loin, and pig loin with added back-fat. Samples containing TC and 4eTC residues were submitted to microwave or boiling heating, extracted with a mixture of McIlvaine buffer/methanol (75:25), and analyzed by high-performance liquid chromatography-diode array detection on a phenyl-hexyl reverse phase chromatographic column. The formation of ATC and 4eATC, as well as of two unidentified compounds, was described for the first time in edible meat samples submitted to mild thermal treatments, similar to those applied at home to cook foods. Degradation of TC and 4eTC and formation of ATC and 4eATC versus time of treatment fitted satisfactorily a first-order kinetic. Even if the potential toxic effects of these breakdown compounds should be further investigated, their formation in cooked meat should be taken into account when maximum residue limits are established. 相似文献
736.
Gómez-Rico A Salvador MD La Greca M Fregapane G 《Journal of agricultural and food chemistry》2006,54(19):7130-7136
This study investigated the effect of both the degree of ripening of the olive fruit and irrigation management-rain-fed, two different regulated deficit irrigations (RDI), the method proposed by the Food and Agriculture Organization of the United Nations (known as FAO), and 125 FAO (125% FAO)-on the phenolic and volatile composition of Cornicabra virgin olive oils obtained during two crop seasons. Secoiridoid phenolic derivatives greatly decreased upon increase of both irrigation and ripening, for example, the 3,4-DHPEA-EDA content decreased from 770 to 450 mg/kg through fruit ripening under rain-fed conditions and from 676 to 388 mg/kg from rain-fed conditions to FAO irrigation treatment (at a ripeness index of approximately 4). Moreover, secoiridoid derivatives of hydroxytyrosol decreased more than those of tyrosol. The levels of major volatile components decreased in the course of ripening but were higher in irrigated olive oils: for example, the E-2-hexenal content ranged between 4.2 and 2.6 mg/kg (expressed as 4-methyl-2-pentanol) over fruit maturation under rain-fed conditions and between 8.0 and 3.5 mg/kg under FAO scheduling. It is important to note that where water was applied only from the beginning of August (RDI-2), when oil begins to accumulate in the fruit, the resulting virgin olive oil presented a phenol and volatile profile similar to those of the FAO and 125 FAO methods, but with a considerable reduction in the amount of water supplied to the olive orchard. 相似文献
737.
Ignacio A. Ciampitti Esteban A. Ciarlo Marta E. Conti 《Biology and Fertility of Soils》2008,44(4):581-588
The purpose of this study was to evaluate, during the phenological stages of inoculated soybean crop [Glycine max (L.) Merrill], the effect of different N fertilization levels and inoculation with Bradyrhizobium japonicum on N2O emissions from the soil. Gas emissions were evaluated at field conditions by the static-chamber method. Nitrogen fertilization
increased N2O emissions significantly (P < 0.05). The variable that best explained cumulative N2O emissions during the whole soybean growing season was the soil nitrate level (r
2 = 0.1899; P = 0.0231). Soil moisture presented a greater control on N2O emissions between the grain-filling period and the crop commercial maturity (r
2 = 0.5361; P < 0.0001), which coincided with a positive balance of the available soil N, as a consequence of the decrease in crop requirements
and root and nodular decomposition. Only soil soluble carbon (r
2 = 0.29; P = 0.019) and moisture (r
2 = 0.24; P = 0.039) were correlated with N2O emissions during the residue decomposition period. The relationship between soil variables and N2O emissions depended on crop phenological or stubbles decomposition stages. 相似文献
738.
Marta Leirós Jon A. Sánchez Eva Alonso Mostafa E. Rateb Wael E. Houssen Rainer Ebel Marcel Jaspars Amparo Alfonso Luis M. Botana 《Marine drugs》2014,12(2):700-718
The marine habitat provides a large number of structurally-diverse bioactive compounds for drug development. Marine sponges have been studied over many years and are found to be a rich source of these bioactive chemicals. This study is focused on the evaluation of the activity of six diterpene derivatives isolated from Spongionella sp. on mitochondrial function using an oxidative in vitro stress model. The test compounds include the Gracilins (A, H, K, J and L) and tetrahydroaplysulphurin-1. Compounds were co-incubated with hydrogen peroxide for 12 hours to determine their protective capacities and their effect on markers of apoptosis and Nrf2/ARE pathways was evaluated. Results conclude that Gracilins preserve neurons against oxidative damage, and that in particular, tetrahydroaplysulphurin-1 shows a complete neuroprotective activity. Oxidative stress is linked to mitochondrial dysfunction and consequently to neurodegenerative disorders like Parkinson and Alzheimer diseases, Friedreich ataxia or Amyotrophic lateral sclerosis. This neuroprotection against oxidation conditions suggest that these metabolites could be interesting lead candidates in drug development for neurodegenerative diseases. 相似文献
739.
Jacek Bełdowski Marta Szubska Magdalena Bełdowska Katarzyna Jankowska Ewa Kotlarska Bożena Graca 《Journal of Soils and Sediments》2018,18(12):3424-3436
Purpose
Mercury speciation in sediments is linked to environmental conditions and processes. Domination of particular mercury species depends on its source, displays considerable seasonal behavior, and may be further modified due to oxygen levels, icing conditions, or the input of fresh organic matter. The purpose of this study was to examine the coastal area of the Gulf of Gdańsk in terms of mercury contamination and the influence of seasonal environmental changes on its speciation.Materials and methods
In three highly dynamic coastal sites, mercury speciation in sediments was studied in relation to other environmental parameters (redox conditions, organic matter concentration, bacteria abundance, etc.). Sediment and water samples were collected monthly during a 3-year study. Sequential extraction of sediments was used for identification of four inorganic mercury species: dissolved, bound with fulvic and humic acids, mercury sulfide, and residual fraction. Cold vapor atomic fluorescence spectrometry (CV-AFS) was used for extracts and liquid sample analysis. Total mercury in sediments was measured with atomic absorption spectrometry (AAS). Changes in salinity were analyzed by measurements of chloride and sulfate ion concentrations using ion chromatography. Bacteria number and biomass were measured by direct counting using epifluorescence microscopy.Results and discussion
Seasonal changes in mercury speciation were observed at all sites and attributed to different processes. Labile mercury fraction contribution varied from 0 to 80%. The speciation patterns varied locally as the stations selected for the study are diversified in terms of anthropogenic impact, water dynamics, and output from land. Mercury concentrations at all stations fluctuated during phytoplankton blooms, icing of marine waters, precipitation, or increased surface runoff from the land. In this local scale, the global climate changes are visible already as environmental conditions in studied area changed in comparison to elder research.Conclusions
Obtained results suggest that although mercury emissions to the environment have decreased in recent years, local weather conditions, which may be intensified by climate change, seriously affect the bioavailability of past mercury deposits in coastal sediments.740.
Margherita Santoni Leonardo Verdi Shamina Imran Pathan Marco Napoli Anna Dalla Marta Francesca Romana Dani Gaio Cesare Pacini Maria Teresa Ceccherini 《Soil Use and Management》2023,39(1):588-605
The implementation of environmentally friendly agricultural policies has increased the need to compare agricultural aspects of conventional (CON) and organic farming (ORG) systems. The objective of the present work was to compare the effects of an organic and conventional long-term experiment on bacterial and fungal biomass and activity, as well as soil CO2 emission and readily available nitrogen forms in a soil cultivated with Helianthus annuus L. The microbial biomass was more active and abundant in ORG as well as soil CO2 emission. Despite being less abundant, fungi were more active than bacteria in both ORG and CON experiments. 16S rRNA gene sequencing showed that the ORG treatment had a significantly greater bacterial richness than CON. Cyanobacteria, Actinobacteria and Proteobacteria were the most abundant phyla contributing more than others to the differences between the two systems. Moreover, the soil and content was not significantly different between ORG and CON, while was less in ORG. ORG sunflower yield was significantly less compared with CON. While much remains to be discovered about the effects of these agricultural practices on soil chemical properties and microbial diversity, our findings may contribute to this type of investigation. 相似文献