全文获取类型
收费全文 | 538篇 |
免费 | 47篇 |
国内免费 | 3篇 |
专业分类
林业 | 57篇 |
农学 | 17篇 |
基础科学 | 4篇 |
101篇 | |
综合类 | 69篇 |
农作物 | 29篇 |
水产渔业 | 36篇 |
畜牧兽医 | 201篇 |
园艺 | 15篇 |
植物保护 | 59篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 16篇 |
2021年 | 24篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 25篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 15篇 |
2013年 | 20篇 |
2012年 | 46篇 |
2011年 | 42篇 |
2010年 | 29篇 |
2009年 | 20篇 |
2008年 | 37篇 |
2007年 | 26篇 |
2006年 | 31篇 |
2005年 | 32篇 |
2004年 | 16篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有588条查询结果,搜索用时 0 毫秒
41.
In the context of attested global changes, accurate estimation of whether climatic fluctuations impact on population demographic parameters is needed for adequate management, especially for migratory species. We present a capture-recapture analysis linking survival rates of the vulnerable Lesser Kestrel (Falco naumanni) to annual rainfalls in the Sahel region, considered as a proxy of climatic conditions on wintering grounds. Recapture data were obtained from field observations of individuals ringed and sexed as juveniles over a 14-year monitoring period (1994-2007). We addressed a common but problematic situation in birds where: (i) sex is known with certainty for first-summer or older birds but only suspected for juveniles, and (ii) a large proportion of individuals never return to the study population (e.g. transient behavior). Transient behavior and unknown sexes were explicitly integrated considering a two age class in a multistate capture-recapture model. Survival was time-varying for juveniles (geometric mean: 0.499 ± 0.021) but constant - and higher - for adults (0.718 ± 0.013). Yearling survival probabilities were strongly correlated with rainfalls in the Sahel, suggesting a high dependence of juvenile upon the wintering conditions. While taking sex uncertainty into account, we detected no sex-dependence in survival. Incorporating the sensitivity of survival of wintering migratory birds to climatic variables such as precipitations in arid Sahelian ecosystem may allow to model conservation scenarios with a greater realism. Finally, we encourage the development of international management strategies for migratory species on wintering areas in addition to the existing conservation actions on summering Mediterranean grounds. 相似文献
42.
Amanda D. Bambrick Joann K. Whalen Robert L. Bradley Alain Cogliastro Andrew M. Gordon Alain Olivier Naresh V. Thevathasan 《Agroforestry Systems》2010,79(3):343-353
Land use affects the carbon sequestration potential of soils across landscapes. Tree-based intercropping (TBI) systems where
annual crops are grown between established tree rows are expected to exhibit spatial heterogeneity in the soil organic carbon
(SOC) content due to differences in carbon input and decomposition rates of litter from trees and herbaceous plants. This
study aimed to quantify variability in the SOC of TBI systems, compare the SOC content of TBI and nearby conventional agroecosystems,
and determine if SOC was related to soil fertility. The TBI research sites were established 4 years (St. Paulin and St. Edouard,
Quebec, Canada), 8 years (St. Remi, Quebec, Canada) and 21 years (Guelph, Ontario, Canada) before soil samples were collected
for this study. The SOC content was greater within 0.75 m of the tree row than in the intercropped space at the St. Edouard
and St. Remi sites. At the Guelph site, the SOC was spatially heterogeneous in plots with Norway spruce (Picea abies L.) but not hybrid poplar (Populus deltoides × P. nigra clone DN-177), probably due to litterfall distribution. Formerly a tree plantation, the TBI system at St. Remi contained
77% more SOC than a nearby conventional agroecosystem, while there was 12% more SOC in the TBI system than the conventional
agroecosystem at Guelph. There was no difference in the SOC content of 4-year old TBI sites and nearby conventional agroecosystems.
However, an increase in SOC at all TBI sites was positively related to the plant-available N concentrations, indicating the
benefit of temperate TBI systems for soil fertility. 相似文献
43.
Olivier Brandenberger Dr Med Vet Fabrice Rossignol DVM Diplomate ECVS Antoine Lechartier DVM Diplomate ECVS Céline Mespoulhès‐Rivière DVM Diplomate ECVS Amelie Vitte DVM Anthony Rossignol Norm Ducharme DVM PhD Diplomate ACVS Karl Joseph Boening Dr Med Vet Diplomate ECVS 《Veterinary surgery : VS》2017,46(5):705-713
44.
Bergerot Benjamin Lemasle Pierre-Gilles Boussard Hugues Betbeder Julie Jambon Olivier Georges Romain Croci Solène Burel Françoise Baudry Jacques 《Landscape Ecology》2022,37(1):159-174
Landscape Ecology - To analyze the scales at which landscape structure influences ecological processes, two approaches with different underlying ecological assumptions exist; the usual threshold... 相似文献
45.
H. J. M. de Vries J. G. J. Olivier R. A. van den Wijngaart G. J. J. Kreileman A. M. C. Toet 《Water, air, and soil pollution》1994,76(1-2):79-131
In the integrated IMAGE 2.0 model the “Energy-Industry System” is implemented as a set of models to develop global scenarios for energy use and industrial processes and for the related emissions of greenhouse gases on a region specific basis. The Energy-Economy model computes total energy use, with a focus on final energy consumption in end-use sectors, based on economic activity levels and the energy conservation potential (“end-use approach”). The Industrial Production and Consumption model computes the future levels of activities other than energy use, which lead to greenhouse gas emissions, based on relations with activities defined in the Energy-Economy model. These two models are complemented by two emissions models, to compute the associated emissions by using emission factors per compound and per activity defined. For investigating energy conservation and emissions control strategy scenarios various techno-economic coefficients in the model can be modified. In this paper the methodology and implementation of the “Energy-Industry System” models is described as well as results from their testing against data for the period 1970–1990. In addition, the application of the models is presented for a specific scenario calculation. Future extensions of the models are in preparation. 相似文献
46.
Auffray C Fogg D Garfa M Elain G Join-Lambert O Kayal S Sarnacki S Cumano A Lauvau G Geissmann F 《Science (New York, N.Y.)》2007,317(5838):666-670
The cellular immune response to tissue damage and infection requires the recruitment of blood leukocytes. This process is mediated through a classical multistep mechanism, which involves transient rolling on the endothelium and recognition of inflammation followed by extravasation. We have shown, by direct examination of blood monocyte functions in vivo, that a subset of monocytes patrols healthy tissues through long-range crawling on the resting endothelium. This patrolling behavior depended on the integrin LFA-1 and the chemokine receptor CX(3)CR1 and was required for rapid tissue invasion at the site of an infection by this "resident" monocyte population, which initiated an early immune response and differentiated into macrophages. 相似文献
47.
Hans Jacquemyn Carmen Van Mechelen Rein Brys Olivier Honnay 《Biological conservation》2011,(1):416-422
Calcareous grasslands, most of which are man made and therefore depend on some kind of human interference for their maintenance, are among the most species-rich communities on Earth at a small scale. For many centuries, most of these grasslands have been used as extensive pasture. However, after 1900, and particularly from 1940 onwards, livestock grazing has declined throughout Europe leading to the abandonment of low intensity grasslands over large areas. To conserve the remaining grasslands or to restore recently abandoned grasslands, better insights about the effects of grassland management on above and belowground species diversity are needed. Here, we describe the results of an 11-year experiment to investigate the role of grassland management (grazing, mowing and abandonment) in determining species composition and diversity both in the aboveground vegetation and the seed bank of a calcareous grassland in Belgium. Species diversity declined by about 60% 11 years after abandonment, from 29 species m−2 to as few as 12 species m−2. Plots that were grazed remained constant in species richness, whereas mown sites lost about 20% of their original species. Abandoned plots were largely dominated by a few grass species, in particular Festuca rubra. Concomitant with changes in the aboveground vegetation, both the number of species found in the seed bank and seed density (number of seeds m−2) had changed significantly 11 years after abandonment. Species diversity and seed density were significantly lower in abandoned plots than in grazed or mown plots. We conclude that abandonment of calcareous grasslands may lead to rapid decline of plant species diversity both in the aboveground vegetation and in the seed bank. As a result, seed banks probably have a limited role to play in the restoration of recently abandoned grasslands. 相似文献
48.
Korbinian Pieper Tibor Schuster Olivier Levionnois Ulrike Matis Alessandra Bergadano 《Veterinary journal (London, England : 1997)》2011,187(3):335-341
To assess the antinociceptive efficacy of transdermal (TD) buprenorphine (B) in dogs, a prospective, positive-controlled experimental study was performed in 10 healthy Beagles. In an open label crossover design, the dogs initially received intravenous B (IVB, 0.02 mg kg?1) as a positive control, followed by TDB (52.5 μg h?1) 4 months later. Blood was collected at regular intervals for determination of the plasma concentrations of B ([B]) and its metabolite norbuprenorphine. The antinociceptive efficacy was assessed using thermal and mechanical models of nociception. The peak concentration [B] was 1.54 ng mL?1 (±1.98) 60 h after TDB application, although three dogs had no measurable [B] after TDB. Maximum thermal threshold (TT) was 52.6 °C (±0.48) at 1 h after IVB administration and 51.63 °C (±1.01) 72 h after TDB application. The significant increase in TT indicated that effective antinociception was achieved beyond 36 h after the application of TDB, lasting until patch removal. There was hysteresis between [B] and the antinociceptive effect. 相似文献
49.
Christophe Tourenq Olivier Combreau Serguei B Pole Gao Xinji Frédéric Launay 《Biological conservation》2005,121(1):1-8
Relative abundance and density estimates of Asian houbara were assessed during the breeding season in two breeding grounds of migrant populations (China and south Kazakhstan) and in one breeding ground of a resident population (Oman), between 1998 and 2002. For the study period, the relative abundance was from 0.004 to 0.06 individual per km driven and density estimates varied from 0.01 to 0.2 houbara per km2. Relative abundance and density of houbara declined by 63% and 69%, respectively in China, by 60% and 49%, respectively in Kazakhstan and by 50% and 75%, respectively in Oman. Overall, an average of 27-30% annual decline in both relative abundance and density was observed for the three regions. Despite being legally a strictly protected species in China, Kazakhstan and Oman, houbara are heavily hunted and poached on all their migration routes and wintering grounds. The current levels of hunting and poaching are not sustainable and without the immediate agreement and implementation of international conservation measures, the Asian houbara may face extinction in the wild in the foreseeable future. 相似文献
50.
Velasco J Marmesat S Berdeaux O Márquez-Ruiz G Dobarganes C 《Journal of agricultural and food chemistry》2005,53(10):4006-4011
Major short-chain glycerol-bound compounds were investigated in olive oil (OO) and conventional sunflower oil (SO) during thermoxidation at 180 degrees C for 5, 10, and 15 h. These compounds included methyl heptanoate (C7:0), methyl octanoate (C8:0), methyl 8-oxo-octanoate (8-oxo-C8:0), methyl 9-oxononanoate (9-oxo-C9:0), dimethyl octanodiate (C8:0 diester), and dimethyl nonanodiate (C9:0 diester), which were analyzed by GC after derivatization of triacylglycerols to fatty acid methyl esters. An acceptable linear correlation (r = 0.967) was found between the total content of these compounds and the total content of polar compounds, suggesting that quantitation of the major short-chain glycerol-bound compounds provides a good indication of the total alteration level of oils heated at frying temperature. Samples with levels of polar compounds around 25% on oil showed total contents within 2-3 mg/g of oil. To determine the content of these compounds in used frying oils, 10 samples from restaurants and fried-food outlets in Spain were analyzed. Results showed total levels between 2.13 and 7.56 mg/g of oil in samples with contents of polar compounds ranging from 18.8 to 55.5% on oil. Samples with levels of polar compounds of approximately 25% showed total contents of the short-chain compounds similar to those found in the thermoxidized oils, that is, within 2-3 mg/g of oil. 相似文献