全文获取类型
收费全文 | 343篇 |
免费 | 25篇 |
专业分类
林业 | 27篇 |
农学 | 12篇 |
68篇 | |
综合类 | 14篇 |
农作物 | 28篇 |
水产渔业 | 46篇 |
畜牧兽医 | 139篇 |
园艺 | 8篇 |
植物保护 | 26篇 |
出版年
2023年 | 7篇 |
2022年 | 13篇 |
2021年 | 29篇 |
2020年 | 24篇 |
2019年 | 24篇 |
2018年 | 24篇 |
2017年 | 21篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 11篇 |
2013年 | 23篇 |
2012年 | 20篇 |
2011年 | 23篇 |
2010年 | 11篇 |
2009年 | 8篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有368条查询结果,搜索用时 406 毫秒
111.
Being active in the same environment at different times exposes animals to the effects of very different environmental factors, both biotic and abiotic. In the present study, we used live traps equipped with timing devices to evaluate the potential role of biotic factors (competition and food abundance) on overall overlap in the temporal niche axis of 4 insectivorous small mammals in high‐elevation grassland fields (‘campos de altitude’) of southern Brazil. Based on resources availability (invertebrates), data on animal captures were pooled in 2 seasons: ‘scarcity’ (June 2001–September 2001) and ‘abundance’ (November 2001–May 2002) seasons. We tested for non‐random structure in temporal niche overlap among the species in each season. These species were the rodents Oxymycterus nasutus (Waterhouse, 1837), Deltamys sp., Akodon azarae (Fischer, 1829), and the marsupial Monodelphis brevicaudis Olfers, 1818. The studied community was mainly diurnal with crepuscular peaks. Simulations using the Pianka index of niche overlap indicated that the empirical assemblage‐wide overlap was not significantly different from randomly generated patterns in the abundance season but significantly greater than expected by chance alone in the scarcity season. All the species showed an increase in temporal niche breadth during the abundance season, which appears to be related to longer daylength and high nocturnal temperatures. Patterns on both temporal niche overlap and temporal niche breadth were the opposite to those that we were expecting in the case of diel activity patterns determined by competition for dietary resources. Therefore, we conclude that competition did not seem to be preponderant for determining patterns of temporal niche overlap by the studied community. 相似文献
112.
Gabriela Seiler Dr. Med. Vet. Sigitas Cizinauskas Dr. Med. Vet. Jürg Scheidegger Dr. Med. FMH Johann Lang Dr. Med. Vet. 《Veterinary radiology & ultrasound》2001,42(5):417-422
Magnetic resonance imaging was performed on an eight-year-old, neutered female German Shepherd dog with a history of acute depression, inappetence, and hyperthermia. A lesion in the cerebrum was suspected. Possible differential diagnoses were meningoencephalitis, neoplasia, and vascular lesion (infarction, bleeding). A ring enhancing lesion was found in the basal ganglia on the left side with edema of the surrounding brain tissue. A similar mass lesion was present in the right pterygoid musculature. With inversion recovery sequences an altered composition of the cerebrospinal fluid (CSF) in the left lateral ventricle could be detected. CSF analysis confirmed a pyocephalus, probably due to rupture of a brain abscess into the left lateral ventricle. 相似文献
113.
Gabriela Palomino Fabian Contreras Adolfo Sanchez Carlos Rosas 《Journal of the World Aquaculture Society》2001,32(2):167-176
This present study was designed to investigate the effects of stocking density and water exchange on the growth rate, survival and performance index of L. setiferus postlarvae under controlled laboratory conditions. The experiment was done with postlarvae (PL10 to PL40) at densities of 50, 150, 250 and 350 shrimp/m2 and various different water exchanges rate per day (0, 6, 12 and 18%). The maximum growth rate was obtained for shrimp with 12% water exchange per day at all densities. A reduction of the maximum growth rate was observed in relation to density with the highest values in shrimp stocked in a density of 50 and 150 shrimp/m2 (mean value of 0.53 mg/d) and the lowest in shrimp stocked in a density of 350 shrimp/m2 (0.24 mg/d). The multiple regression equation obtained to relate performance index (growth rate* survival : PI), shrimp density (X1 ) and water exchange (X2 ) was: PI = 0.31 + (0.001) X1 + 0.039 X2 + 2.28 × 10−6 X1 2 + (−0.0017) X2 2 + (0.000026)X1 X2 , R 2 = 0.78; P > 0.03. According to this equation the optimum shrimp density-water exchange comhination was between 5 to 12% of water exchange at stocking density of between 50 and 150 shrimp/m2 . Salinity, ammonia-N and nitrite-N increased according to the time spent in tanks without water exchange. With no (0%) water exchange, water quality parameters measured were outside the optimum for L. setiferus postlarvae. The use of optimum density and water exchange in a nursery system for L. setiferus with optimum variables established is proposed. 相似文献
114.
Baptista-Fernandes T Marques C Roos Rodrigues O Santos-Gomes GM 《Comparative immunology, microbiology and infectious diseases》2007,30(1):41-53
This study aims to characterize the intra-specific variability of virulence in Leishmania infantum zymodeme MON-1 strains isolated from dogs and immunocompetent and immunosuppressed patients through the evaluation of growth pattern, infective ability and immunopathogenicity. Two of the strains, classified as the most virulent, presented higher levels of macrophage infection, increased promastigote replication in culture medium and as well as amastigote multiplication within macrophages. These strains caused the most pathogenic infection inducing splenomegalia and maximum parasite loads in spleen and liver of BALB/c mice. The other strains exhibited either low virulence, with reduced infective capability and low replication levels, or an intermediate virulent phenotype showing mixed features similar to low and high virulent phenotypes. A correlation between the infectivity, growth dynamics and pathogenicity of each strain and the humoral and cellular immune response was demonstrated. Strains with accentuated virulent phenotype induced higher levels of anti-Leishmania IgG1 antibodies and TGF-beta but reduced production of IFN-gamma. Virulence phenotype seems to be a characteristic of each strain regardless of the host (dog or human) from which it was firstly isolated. 相似文献
115.
Lactoferrin (LF), a glycogen of the transferrin family with anti-bacterial and immunomodulatory properties, is expressed in various secretions and tissues. Cutaneous LF serves as a mast cell stabilising compound, modulates T cell activity and is found during IgE-mediated late phase reactions at allergen challenged sites. Culicoides hypersensitivity (CHS) in horses is a common IgE-mediated allergic dermatitis, characterised by an early and late phase cutaneous reaction upon allergen challenge. The aim of the study presented here was to examine whether LF mRNA expression in skin biopsies from horses affected by CHS prior to and 4h following intradermal challenge with a commercial C. nubeculosus extract is modified in comparison to skin biopsies from non-affected horses. In order to obtain reliable data, real time PCR was performed and genes of interest were normalized using three different housekeeping genes, beta-actin, GAPDH, beta-2-microglobulin. In comparison to non-affected horses, higher variation in LF mRNA levels both prior to and post-intradermal challenge with C. nubeculosus extract was seen in horses affected by CHS. However, the statistical analysis demonstrated that LF mRNA expression was not significantly different between CHS affected and non-affected horses prior to intradermal challenge with C. nubeculosus extract. Intradermal injection of C. nubeculosus extract did not result in local upregulation of LF mRNA at 4h post-injection. LF mRNA expression was therefore not significantly different pre- or post-intradermal challenge with C. nubeculosus extract in either group. Our data indicate that clinically normal skin of horses affected by CHS is not characterized by modified maintenance levels of LF mRNA. In contrast to human skin allergen challenged sites, LF mRNA levels in horses affected by CHS are not significantly different to that of control sites at 4h post-injection of C. nubeculosus extract. 相似文献
116.
117.
ELASTOGRAPHIC EVALUATION OF NATURALLY OCCURING TENDON AND LIGAMENT INJURIES OF THE EQUINE DISTAL LIMB 下载免费PDF全文
Meghann Lustgarten W. Rich Redding Raphael Labens Weston Davis Thomas M. Daniel Emily Griffith Gabriela S. Seiler 《Veterinary radiology & ultrasound》2015,56(6):670-679
Compression elastography is an ultrasonographic technique that estimates tissue strain and may have utility in diagnosing and monitoring soft tissue injuries in the equine athlete. Recently, elastography has been proven to be a feasible and repeatable imaging modality for evaluating normal tendons and ligaments of the equine distal forelimb. The purposes of this prospective study were to investigate the ability of elastography to detect spontaneously occurring lesions of equine tendons and ligaments diagnosed with magnetic resonance imaging (MRI) and gray‐scale ultrasound (US) and to characterize the differences in the elastographic appearance of acute vs. chronic injuries. Fifty seven horses with a total of 65 lesions were evaluated. Images were assessed quantitatively and qualitatively. Acute lesions were found to be significantly softer (P < 0.0001) than chronic lesions (P < 0.0001) and the stiffness of lesions increased with progression of healing (P = 0.0138). A negative correlation between lesion hypoechogenicity and softness was appreciated with more hypoechoic lesions appearing softer (P = 0.0087) and more hyperechoic regions harder (P = 0.0002). A similar finding occurred with increased signal intensity on short tau inversion recovery (STIR) and proton density (PD) MRI sequences correlating with increased softness on elastography (P = 0.0164). Using US and MRI as references, commonly encountered soft tissue injuries of the equine distal limb could be detected with elastography. However, elastography was limited for detecting small, proximal injuries of the hindlimb proximal suspensory ligament. Elastographic evaluation of equine tendons and ligaments may allow better characterization of lesion chronicity and severity, and sequential examinations may optimize lesion management, rehabilitation, and return to training. 相似文献
118.
Marcela Pacola Tiara Moraes Guimarães João Paulo Gonsiorkiewicz Rigon Lucas Moraes Jacomassi João William Bossolani Josiane Viveiros Gabriela Ferraz de Siqueira Patrícia Pereira Dias Juliano Carlos Calonego Carlos Alexandre Costa Crusciol 《Soil Use and Management》2023,39(4):1388-1402
Combining deep tillage (DT) with lime application at greater depths may improve sugarcane yield. The objective of this study was to evaluate the impact of conventional tillage (CT) and DT systems and liming on sugarcane productivity and soil physical attributes. The experiment was conducted in a clayey-textured Rhodic Hapludox soil cultivated with sugarcane for two growing seasons (first and third ratoons) using a randomized block design with four treatments and four repetitions. The treatments consisted of DT without liming (DT0), DT with liming (DT2), CT without liming (CT0) and CT with liming (CT2). In addition to sugarcane stalk and sugar yields, macroporosity (MA), microporosity (MI), total soil porosity (TP), weighted average diameter (WAD), aggregate stability index (ASI), soil penetration resistance (SPR), pH, potential acidity (H + Al), total soil organic carbon (SOC), particulate organic carbon (POC), mineral-associated organic carbon (MOC), calcium (Ca) and magnesium (Mg) were analysed. DT2 promoted the best soil conservation effect on sugarcane. In general, DT, regardless of lime application, reduced SOC and POC in soil surface layer. Nevertheless, in the long term, localized lime addition resulted in significant reductions in compaction, reaching values below 2 MPa. The soil fertility improvement provided by DT2 promoted increased sucrose concentrations and stalks yield. Considering that there was an improvement in the physical quality and fertility of soil for better plant development, the deep tillage with localized lime addition can be considered an effective alternative for sugarcane cultivation. 相似文献
119.
Khadim DAWAR Kamil SARDAR Mohammad ZAMAN Christoph MLLER Alberto SANZ-COBENA Aamir KHAN Azam BORZOUEI Ana Gabriela PREZ-CASTILLO 《土壤圈》2021,31(2):323-331
Nitrification inhibitors are widely used in agriculture to mitigate nitrous oxide(N2O)emission and increase crop yield.However,no concrete information on their mitigation of N2O emission is available under soil and environmental conditions as in Pakistan.A field experiment was established using a silt clay loam soil from Peshawar,Pakistan,to study the effect of urea applied in combination with a nitrification inhibitor,nitrapyrin(2-chloro-6-tri-chloromethyl pyridine),and/or a plant growth regulator,gibberellic acid(GA_3),on N2O emission and the nitrogen(N)uptake efficiency of maize.The experimental design was a randomized complete block with five treatments in four replicates:control with no N(CK),urea(200 kg N ha-1)alone,urea in combination with nitrapyrin(700 g ha-1),urea in combination with GA_3(60 g ha-1),and urea in combination with nitrapyrin and GA_3.The N2O emission,yield,N response efficiency,and total N uptake were measured during the experimental period.The treatment with urea and nitrapyrin reduced total N2O emission by 39%–43%and decreased yield-scaled N2O emission by 47%–52%,relative to the treatment with urea alone.The maize plant biomass,grain yield,and total N uptake increased significantly by 23%,17%,and 15%,respectively,in the treatment with urea and nitrapyrin,relative to the treatment with urea alone,which was possibly due to N saving,lower N loss,and increased N uptake in the form of ammonium;they were further enhanced in the treatment with urea,nitrapyrin,and GA_3 by 27%,36%,and 25%,respectively,probably because of the stimulating effect of GA_3 on plant growth and development and the reduction in biotic and abiotic stresses.These results suggest that applying urea in combination with nitrapyrin and GA_3 has the potential to mitigate N2O emission,improve N response efficiency,and increase maize yield. 相似文献
120.
Ana Gabriela PREZ-CASTILLO CristinaCHINCHILLA-SOTO Jorge Alberto ELIZONDO-SALAZAR RonnyBARBOZA Dong-Gill KIM Christoph MLLER AlbertoSANZ-COBENA Azam BORZOUEI Khadim DAWAR MohammadZAMAN 《土壤圈》2021,31(2):265-278
Urea is the most common nitrogen(N)fertilizer used in the tropics but it has the risk of high gaseous nitrogen(N)losses.Use of nitrification inhibitor has been suggested as a potential mitigation measure for gaseous N losses in N fertilizer-applied fields.In a field trial on a tropical Andosol pastureland in Costa Rica,gaseous emissions of ammonia(NH3)and nitrous oxide(N2O)and grass yield were quantified from plots treated with urea(U;41.7 kg N ha-1application-1)and urea plus the nitrification inhibitor nitrapyrin(U+NI;41.7 kg N ha-1application-1and 350 g of nitrapyrin for each 100 kg of N applied)and control plots(without U and NI)over a six-month period(rainy season).Volatilization of NH3(August to November)in U(7.4%±1.3%of N applied)and U+NI(8.1%±0.9%of N applied)were not significantly different(P>0.05).Emissions of N2O in U and U+NI from June to November were significantly different(P<0.05)only in October,when N2O emission in U+NI was higher than that in U.Yield and crude protein production of grass were significantly higher(P<0.05)in U and U+NI than in the control plots,but they were not significantly different between U and U+NI.There was no significant difference in yield-scaled N2O emission between U(0.31±0.10 g N kg-1dry matter)and U+NI(0.47±0.10 g N kg-1dry matter).The results suggest that nitrapyrin is not a viable mitigation option for gaseous N losses under typical N fertilizer application practices of pasturelands at the study site. 相似文献