全文获取类型
收费全文 | 301篇 |
免费 | 29篇 |
专业分类
林业 | 109篇 |
农学 | 8篇 |
44篇 | |
综合类 | 12篇 |
农作物 | 13篇 |
水产渔业 | 17篇 |
畜牧兽医 | 93篇 |
园艺 | 4篇 |
植物保护 | 30篇 |
出版年
2023年 | 4篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 3篇 |
2013年 | 8篇 |
2012年 | 12篇 |
2011年 | 9篇 |
2010年 | 13篇 |
2009年 | 6篇 |
2008年 | 5篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1993年 | 5篇 |
1990年 | 6篇 |
1988年 | 2篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1950年 | 3篇 |
1941年 | 2篇 |
1938年 | 4篇 |
1929年 | 5篇 |
1928年 | 2篇 |
1927年 | 9篇 |
1926年 | 3篇 |
1925年 | 3篇 |
1920年 | 6篇 |
1919年 | 2篇 |
1916年 | 3篇 |
1913年 | 5篇 |
1912年 | 2篇 |
1909年 | 2篇 |
1906年 | 3篇 |
1905年 | 6篇 |
1901年 | 3篇 |
1896年 | 3篇 |
1864年 | 3篇 |
排序方式: 共有330条查询结果,搜索用时 15 毫秒
71.
Relation between soil organic matter and yield levels of nonlegume crops in organic and conventional farming systems 总被引:2,自引:0,他引:2
Christopher Brock Andreas Fließbach Hans‐Rudolf Oberholzer Franz Schulz Klaus Wiesinger Frank Reinicke Wernfried Koch Bernhard Pallutt Bärbel Dittman Jörg Zimmer Kurt‐Jürgen Hülsbergen Günter Leithold 《植物养料与土壤学杂志》2011,174(4):568-575
The aim of this study was to evaluate the interaction between yield levels of nonleguminous crops and soil organic matter (SOM) under the specific conditions of organic and conventional farming, respectively, and to identify implications for SOM management in arable farming considering the farming system (organic vs. conventional). For that purpose, correlations between yield levels of nonlegume crops and actual SOM level (Corg, Nt, Chwe, Nhwe) as well as SOM‐level development were examined including primary data from selected treatments of seven long‐term field experiments in Germany and Switzerland. Yield levels of nonlegume crops were positively correlated with SOM levels, but the correlation was significant only under conditions of organic farming, and not with conventional farming treatments. While absolute SOM levels had a positive impact on yield levels of nonlegumes, the yield levels of nonlegumes and SOM‐level development over time correlated negatively. Due to an increased demand of N from SOM mineralization, higher yield levels of nonlegumes obviously indicate an increased demand for OM supply to maintain SOM levels. Since this observation is highly significant for farming without mineral‐N fertilization but not for farming with such fertilization, we conclude that the demand of SOM‐level maintenance or enhancement and thus adequate SOM management is highly relevant for crop production in organic farming both from an agronomical and ecological point of view. Under conventional management, the agronomic relevance of SOM with regard to nutrient supply is much lower than under organic management. However, it has to be considered that we excluded other possible benefits of SOM in our survey that may be highly relevant for conventional farming as well. 相似文献
72.
Repeated monitoring of organic carbon stocks after eight years reveals carbon losses from intensively managed agricultural soils in Western Germany 总被引:1,自引:0,他引:1 下载免费PDF全文
Thomas Steinmann Gerhard Welp Andreas Wolf Britta Holbeck Thomas Große‐Rüschkamp Wulf Amelung 《植物养料与土壤学杂志》2016,179(3):355-366
Past land‐use changes, intensive cropping with large proportions of root crops, and preferred use of mineral fertilizer have been made responsible for proceeding losses of soil organic C (SOC) in the plough layer. We hypothesized that in intensive agriculturally managed regions changes in SOC stocks would be detectable within a decade. To test this hypothesis, we tracked the temporal development of the concentrations and stocks of SOC in 268 arable sites, sampled by horizon down to 60 cm in the Cologne‐Bonn region, W Germany, in 2005 and in 2013. We then related these changes to soil management data and humus balances obtained from farmers' surveys. As we expected that changes in SOC concentrations might at least in part be minor, we fractionated soils from 38 representative sites according to particle size in order to obtain C pools of different stability. We found that SOC concentrations had increased significantly in the topsoil (from 9.4 g kg?1 in 2005 to 9.8 g kg?1 in 2013), but had decreased significantly in the subsoil (from 4.1 g kg?1 in 2005 to 3.5 g kg?1 in 2013). Intriguingly, these changes were due to changes in mineral‐bound SOC rather than to changes in sand‐sized organic matter pools. As bulk density decreased, the overall SOC stocks in the upper 60 cm exhibited a SOC loss of nearly 0.6 t C (ha · y)?1 after correction by the equivalent soil mass method. This loss was most pronounced for sandy soils [?0.73 t SOC (ha · y)?1], and less pronounced for loamy soils [?0.64 t SOC (ha · y)?1]; silty soils revealed the smallest reduction in SOC [?0.3 t SOC (ha · y)?1]. Losses of SOC occurred even with the overall humus balances having increased positively from about 20 kg C (ha · y)?1 (2003–2005) to about 133 kg C (ha · y)?1 (2005–2013) due to an improved organic fertilization and intercropping. We conclude that current management may fail to raise overall SOC stocks. In our study area SOC stocks even continued to decline, despite humus conservation practice, likely because past land use conversions (before 2005) still affect SOC dynamics. 相似文献
73.
Evaluation of reticulocyte hemoglobin content (RET‐He) in the diagnosis of iron‐deficient erythropoiesis in dogs 下载免费PDF全文
Jannika Fuchs Andreas Moritz Esther Grußendorf Jörg Lechner Felix Neuerer Rafael Nickel Thomas Rieker Claudia Schwedes Dennis B. DeNicola James Russell Natali Bauer 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2017,46(4):558-568
Background
Reticulocyte hemoglobin content provided by the Siemens ADVIA (CHr) is an established marker of iron deficiency. The IDEXX ProCyte Dx hematology analyzer now provides a similar variable, reticulocyte hemoglobin equivalent (RET‐He).Objectives
The objective was to evaluate RET‐He and its diagnostic utility in dogs, and to calculate a cutoff value for diagnosing iron‐deficient erythropoiesis (IDE). Furthermore, the prevalence of RET‐He values below this cutoff value was established.Methods
One hundred and seventy‐one CBCs of healthy dogs were used to establish a RI. Stability of RET‐He was evaluated by repeated measurements over 48 hours (n = 10). The 25‐run coefficient of variation (CV) was calculated, and correlation and bias between measurements of RET‐He and CHr were assessed (n = 190). A cutoff value for diagnosing IDE was calculated. The utility of RET‐He in the detection of IDE was evaluated in 123 dogs. The prevalence of low RET‐He values was assessed retrospectively in a multicenter study (2012–2014) under participation of 7 veterinary clinics.Results
Reticulocyte hemoglobin equivalent with an RI of 22.2 to 28.6 pg was statistically stable over 48 hours (P = .10). The CV was 1.8%. A fair correlation (ρ = 0.74) between RET‐He and CHr with a small bias of ?0.6 pg was found. The cutoff value for diagnosing IDE was 20.9 pg (sensitivity: 85%; specificity: 99%). The prevalence of RET‐He values below 20.9 pg was 10.3% (1084/10,553 dogs).Conclusions
RET‐He on the ProCyte Dx is a precise screening tool in dogs to detect iron‐deficient erythropoiesis. 相似文献74.
AT Le Souëf M Barry DH Brunton R Jakob-Hoff B Jackson 《New Zealand veterinary journal》2013,61(6):340-344
CASE HISTORY: An adult female Duvaucel's gecko (Hoplodactylus duvaucelii) from a threatened species breeding programme presented due to a prolonged gestation period and distended abdomen.CLINICAL AND PATHOLOGICAL FINDINGS: The gecko was in lean body condition with an irregularly shaped, firm mass in the coelomic cavity. Radiographically there was a diffuse radio-opacity within the coelomic cavity with cranial displacement of the right lung field. Ultrasonography revealed a round homogenous abdominal mass of medium echogenicity with an echogenic capsule. Haematology showed a leucocytosis with a moderate left shift in heterophils and toxic changes. Bilateral ovariectomy was performed to remove two ovarian granulomas and Salmonella enterica subspecies houtenae (IV) was cultured from the ovarian tissue. The gecko recovered well from the surgery, regained weight and remained in good health 3 years following the surgery.DIAGNOSIS: Pre-ovulatory stasis and ovarian granulomas associated with infection with Salmonella enterica subsp. houtenae.CLINICAL RELEVANCE: The surgery described in this case resulted in recovery of the gecko, which despite its loss of reproductive capability is of value as an education animal. This is the first report of pre-ovulatory stasis and ovarian granulomas associated with infection with Salmonella enterica in a Duvaucel's gecko and is also the first reported case of pre-ovulatory stasis in a viviparous lizard species. The case adds to knowledge regarding potential reproductive pathology in lizards, which is particularly important information for managers of captive lizard breeding programmes. 相似文献
75.
Exogenous application of thiamine (vitamin B1) during imbibition improved germination and seedling development of bean (Phaseolus vulgaris L. cv. Lasso) seeds, which were exposed to soaking injury by submergence. Leaching of the vitamin into the incubation medium was not increased in submerged seeds. However, translocation of the thiamine reserves from the cotyledons to the seedling axis was reduced in response to soaking injury. After exogenous application of free thiamine to the seeds, thiaminedi-phosphate (TDP), which is the physiologically active coenzyme form of thiamine, accumulated in the seedling axis of submerged seeds, suggesting an increased demand for thiamine-dependent metabolic reactions in these tissues. Limited oxygen supply of the seeds during the soaking period induces a shift from respiration to fermentation of carbohydrates. Neither thiamine-dependent ethanolic fermentation, nor ATP production or adenylate energy charge (AEC) of the seedling axis were affected by exogenous thiamine application, suggesting that there is no limitation of thiamine-dependent reactions in the energy metabolism of the seedlings. Thus the physiological mechanisms improving germination and seedling development of submerged seeds in response to thiamine seed treatment are still not clear. 相似文献
76.
Emilia T Quinitio Joana Joy dela Cruz‐Huervana Fe D Parado‐Estepa 《Aquaculture Research》2018,49(1):75-80
Starvation and exposure to formalin were investigated as possible stress tests for evaluating the quality of mud crab, Scylla serrata, larvae. For the starvation stress test, newly hatched zoeae stocked in 150‐ml containers were either starved or fed rotifers. Similarly, newly hatched zoeae were stocked in containers with seawater of 0 (control), 20, 30 and 40 mg/L formalin for the formalin stress test. The zoeae from the same batches were used for seed production to monitor their performance and validate the results of stress tests. Starvation was found to be unsuitable for larval quality evaluation. However, the impact of initial food deprivation on the newly hatched larvae indicates that feeding immediately after hatching is necessary for mud crab larvae. Exposure of larvae to 40 mg/L formalin for 3 hr appeared to be a reliable and practical method for larval quality assessment as the survival of larvae in the mass production tanks validated the classification of good and poor quality batches in the stress tests. On this basis, a hatchery operator can decide which batch should be cultured further. Finally, there appears to be a link between the quality of larvae and the performance at the megalopa and early juvenile crabs. 相似文献
77.
Recent studies suggest that ovarian follicular atresia is associated with DNA fragmentation and degeneration of granulosa cells, the hallmark of programmed cell death or apoptosis. Apoptosis of granulosa cells play a major role in follicular atresia. These studies have also demonstrated the involvement of tumour suppressors, apoptotic proteins and survival factors. These factors contribute to the developmental decision as to whether the ovarian follicles mature or undergo atresia. However, the precise temporal and molecular events involved in the apoptotic pathways in this process need to be elucidated. The present report summarizes the role of Jun N‐terminal kinase (JNK), p38 mitogen activated protein kinase (p38 MAPK), and extracellular‐signal regulated kinase (ERK)‐signalling module in the regulation of pro‐ and anti‐apoptotic factors of the granulosa cells in regulating follicular atresia. The findings presented here suggest that the loss of tropic hormone support is translated into the attenuation of Raf‐1‐MAPK/ERK kinase (MEK)‐ERK‐signalling pathway of the granulosa cells and this results in the decreased phosphorylation of the pro‐apoptotic BAD. 相似文献
78.
79.
B.C. Brüler F.S. Jojima G. Dittrich A.T. Giannico M.G. Sousa 《Journal of Veterinary Cardiology》2018,20(4):254-266
Objectives
To investigate QT instability in dogs with myxomatous mitral valve disease (MMVD) and to determine if this is associated with arrhythmogenesis.Animals
One hundred sixty-seven MMVD dogs that met the study criteria were included.Methods
Echocardiographic and electrocardiographic data were gathered. Fifty consecutive QT intervals were recorded for each dog. Both heart rate–corrected and uncorrected QT intervals were used to calculate average QT (QTa), QT variance (QTv), total instability (TI), short-term instability (STI), and long-term instability (LTI). Sensitivity and specificity of QTa, QTv, TI, STI, and LTI in identifying arrhythmias and cardiac remodeling were calculated. Patient follow-ups were obtained for analyses of disease progression and survival.Results
An increase related to progression was documented for all the studied indices. QTa and STI best identified dilated hearts and arrhythmias, respectively. Dogs with QTa >272 ms and STI >8 ms were 15% more likely to develop ventricular arrhythmias (likelihood ratios of 2.31 [P = 0.0008] and 2.09 [P = 0.0049], respectively). A QTa >258 ms discriminated American College of Veterinary Internal Medicine stage B1 from stages B2/C disease with a sensitivity of 63% and specificity of 61%. Dogs in American College of Veterinary Internal Medicine stage C of MMVD have higher STI and 3.34 times increased risk of developing arrhythmias when values more than 8 ms are reached. All indices except LTI and QTv showed prognostic value, with increases relating to all-cause mortality.Conclusion
Analyses of QT intervals demonstrated changes in STI, LTI, and TI. Increased QT prolongation and instability are significantly related to mortality and may be useful in determining prognosis of MMVD patients. 相似文献80.
Marcela Wolf Stephany B. Lucina Bruna C. Brüler Giovana L.R. Tuleski Vinícius B.C. Silva Marlos G. Sousa 《Journal of Veterinary Cardiology》2018,20(3):175-185