全文获取类型
收费全文 | 628篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
林业 | 26篇 |
农学 | 10篇 |
基础科学 | 4篇 |
69篇 | |
综合类 | 65篇 |
农作物 | 24篇 |
水产渔业 | 64篇 |
畜牧兽医 | 306篇 |
园艺 | 15篇 |
植物保护 | 69篇 |
出版年
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 17篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 11篇 |
2014年 | 10篇 |
2013年 | 24篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 17篇 |
2008年 | 34篇 |
2007年 | 39篇 |
2006年 | 20篇 |
2005年 | 24篇 |
2004年 | 33篇 |
2003年 | 35篇 |
2002年 | 25篇 |
2001年 | 17篇 |
2000年 | 21篇 |
1999年 | 19篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1950年 | 2篇 |
1947年 | 3篇 |
排序方式: 共有652条查询结果,搜索用时 15 毫秒
101.
Saman Bowatte Russell Tillman Andrew Carran Allan Gillingham David Scotter 《Biology and Fertility of Soils》2008,44(6):805-813
This paper explored the potential of application of in situ ion exchange resin membrane (IEM) technique for assessing soil
nitrogen (N) availability and spatial distribution in New Zealand grazed pastures. Field and incubation experiments conducted
to test the technique proved IEM technique to be a useful approach to monitoring the continuous changes in soil mineral N
in pasture soils. The field testing showed that the IEM technique reflects both differences in pool size and mineral N flux,
while 2-M KCl extraction reflects only pool size at the sampling. Testing the effects of residence time, temperature, soil
inorganic N content, and soil water content through diffusion modeling offers further support for using IEM to explore the
complex dynamics of nitrogen availability in pasture soils. 相似文献
102.
This study focuses on soils in a mountainous catchment area located in the eastern part of the Southern Alps, South Island, New Zealand. The objective was to check the soils for non- or poorly crystalline constituents (metal organic complexes, short-range-order minerals) and if there is a relationship between pedogenesis and aspect and more recent landscape history. The morphology of the soils indicates brown soils (dystric cambisols, dystrudepts) with only few signs of podsolisation. In contrast, selected chemical properties of the soils reveal very strong weathering and leaching. Feo/Fed ratios are high and exceeding 0.6 in almost every soil horizon. Oxalate-extractable aluminium and silicon show prominent peaks in the lower subsoil horizons with 1.76–2.52% Alo and up to 0.68% for Sio on southern aspects. This is considerably higher than the values measured for soils on northern aspects (0.59% to 1.07% Alo, max. 0.26% Sio). This aspect relationship is also applying to phosphate retention reaching values of more than 90% on southern aspects and not more than 70% for northern aspects. Additionally, significant movement of organic matter in soils on southern aspects is evident by measurements of organic carbon and pyrophosphate-extractable Al and Fe. Thus soil formation can be regarded as more advanced on southern aspects. Allophane in association with organic matter can be considered as an important constituent in southern aspect subsoils being responsible for the typical andic properties. Metal-humus complexes and ferrihydrite are of subordinate significance. Considering the actual soil forming conditions under scrub-grassland (esp. soil acidity), it is unlikely that weathering and leaching is still strong enough today to allow significant podsolisation and the formation of short-range-order minerals. Under consideration of existing soil data from other studies it is proposed that these components and the podsolisation features are relicts caused by more acidic conditions under former forest cover which supported a stronger weathering and leaching. 相似文献
103.
Gerard Allan Amber Williams Pablo D. Rabinowicz Agnes P. Chan Jacques Ravel Paul Keim 《Genetic Resources and Crop Evolution》2008,55(3):365-378
Worldwide genetic diversity in 200 individuals comprising 41 castor bean accessions was assessed using amplified fragment
polymorphisms (AFLPs) and simple sequence repeats (SSRs). We found that, despite surveying five continents and 35 countries,
genetic diversity in castor bean germplasm is relatively low (overall H
e = 0.126 for AFLPs and 0.188 for SSRs) compared to estimates of genetic diversity in other plant species. Our data also show
no geographic structuring of genotypes across continents or countries within continents. An assessment of the congruence between
AFLP and SSRs indicates a low correlation (R
2 = 0.19) between the two data sets, but each marker class nonetheless shows similar patterns of low-genetic diversity and
a lack of geographic structure. Our data do suggest that SSRs yield a higher percentage of polymorphic loci, higher heterozyosity
and a greater range of genetic distances, and are therefore more informative than are AFLPs on a locus-by-locus basis. Based
on comparisons with numerous other plant species, we suggest that the lower genetic variation in this worldwide collection
may be due to one or more factors including: sampling strategies that have not captured the full extent of genetic variation
in the species; artifactual variation due to long-term germplasm storage and seed regeneration; or intense selection followed
by domestic cultivation of a limited number of castor bean genotypes, which are widely propagated for their horticultural
and agro-economic value. 相似文献
104.
Nikki Baggaley Allan Lilly Kirsty Blackstock Karen Dobbie Adam Carson Fraser Leith 《Soil Use and Management》2020,36(1):19-26
Surface runoff, erosion, compaction and the leaching of potential pollutants from land can degrade the soil resource and damage the water environment, reducing crop yields, causing loss of valuable nutrients and organic matter, together with increasing flood risk. Increasingly, it is recognized that scientific information must be translated into practical tools to change practices and protect the soil and water resource. Working alongside agencies in Scotland, we applied a suite of simple, transparent, rule-based models to identify areas most at risk of exporting sediment and pollutants that may degrade water quality based on field-scale (1:25,000) soil maps. The maps have been used by Scottish Environment Protection Agency, Scottish Water and Scottish Government to assess soil risks to waters from field to regional scale. The work brought scientists together with policy makers, agencies and the water industry to pool their knowledge to apply these practical tools for decision-making. It highlights the need to apply existing knowledge to answer salient questions. All three examples described show that providing the right type of information, which is based on fundamental soils data, can directly influence the implementation of policies, investment and monitoring decisions and provide evidence in support of government. However, this requires both researchers and agency scientists to develop skills as knowledge brokers and to normalize the use of soil data in everyday agency settings. 相似文献
105.
Forecasting the Genetic Impacts of Net Pen Failures on Gulf of Mexico Cobia Populations Using Individual‐based Model Simulations 下载免费PDF全文
Tanya L. Darden John D. Robinson Allan E. Strand Michael R. Denson 《Journal of the World Aquaculture Society》2017,48(1):20-34
Offshore net pen fish farming provides a cost‐efficient means for production of marine finfish, and there is great interest in development of net pen operations in domestic waters. However, there are concerns over the possible genetic and ecological impacts that escaped fish may have on wild populations. We used individual‐based simulations, with parameter values informed by life history and genetic data, to investigate the short‐term (50 yr) impacts of net pen failures on the genetic composition of cobia, Rachycentron canadum, stocks in the Gulf of Mexico. Higher net pen failure rates resulted in greater genetic impacts on the wild population. Additionally, the use of more genetically differentiated source populations led to larger influxes of non‐native alleles and greater temporal genetic change in the population as a result of net pen failure. Our results highlight the importance of considering the appropriate source population for broodstock collection in net pen aquaculture systems and help to provide a general set of best management practices for broodstock selection and maintenance in net pen aquaculture operations. A thorough understanding of the genetic diversity, stock structure, and population demography of target species is important to determine the impact escapees can have on wild populations. 相似文献
106.
The change in soil carbon (C) concentration, soil pH and major nutrients for approximately 1,000 topsoil sampled from on-farm experimental sites over a thirty-year period from 1950 to 1980 in north-east Scotland are summarized. This period coincided with increased agricultural intensification, which included regular liming and fertilizer additions. During 2017, 37 of these sites were resampled and reanlaysed. While pH and extractable phosphorus (P) and potassium (K) increased over this period, there was no detectable change in the percentage loss on ignition. Composite soil samples were taken by auger from a depth of 0–15 cm and compared with the corresponding archived samples collected at the initiation of each experiment. Analysis of these resampled soils indicated no significant change in soil carbon (C), although soil pH, extractable magnesium (Mg) and K and Nitrogen (N) concentrations were significantly greater (p < .001) but extractable soil P concentration was significantly less (p = .015) compared with the original samples. Even though measuring C concentration alone is a poor indicator of overall changes in soil C stocks, it does provide a relative quick “early warning” of C losses that would justify a more comprehensive measure of stocks. 相似文献
107.
Woods AM McIlmoil CJ Rankin EN Packer AA Stevens JC Macievic JA Brown AB Porter JP Judd AM 《Domestic animal endocrinology》2008,35(2):217-230
The release of adrenal steroids during acute stress is primarily regulated by adrenocorticotropic hormone (ACTH). In contrast, during chronic inflammatory stress additional factors are involved in regulating adrenal function. Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that increases ACTH release from the pituitary. In addition, LIF and LIF receptors (LIFR) are expressed in the human adrenal cortex and the human adrenocortical tumor cell line H295R. Furthermore, LIF increases basal and ACTH-stimulated cortisol release from H295R cells. However, the expression of LIF and LIFR in non-human adrenal glands and the effects of LIF on the release of cortisol from adrenal cells of non-human species have not been determined. Furthermore, the effects of LIF on adrenal androgen release from all species are unknown. In this study, immunohistochemistry, Western blots, RT-PCR, and nucleotide sequencing was utilized to demonstrate that LIF and its receptor are expressed throughout the bovine adrenal cortex. Although LIF did not modify basal cortisol release from dispersed cells isolated from the bovine adrenal zona fasciculate, this cytokine increased ACTH-stimulated release of cortisol from these cells in a manner dependent on the LIF concentration and exposure interval. In contrast, LIF in a concentration-dependent and time-dependent manner decreased basal and ACTH-stimulated adrenal androgen release from dispersed cells isolated from the bovine adrenal zona reticularis. Because LIF release increases during inflammatory stress and this cytokine stimulates adrenal cortisol release and inhibits adrenal androgen release, this cytokine may play an important role in regulating the release of adrenal steroids during inflammatory stress. 相似文献
108.
Developing a methodology for the measurement of governance in the context of water management requires a clear understanding of what is meant by (good) governance, and what is meant by IWRM—terms which are often, but incorrectly, used almost interchangeably. This paper sets out the foundations developed for the STRIVER project upon which an assessment of governance could be made. It identifies the key principles of good governance as being accountability, participation and transparency, and seeks to elucidate the relationship between good governance and IWRM, especially in relation to the specific role of law. The paper concludes that while the two are not mutually exclusive, the access points between them appear to concentrate around issues relating to equity, the protection of “silent” interests and the importance of governance in facilitating feedback mechanisms. 相似文献
109.
This study describes the digestible protein (DP) and digestible energy (DE) utilization in juvenile mulloway, and determined
the requirements for maintenance. This was achieved by feeding triplicate groups of fish weighing 40 or 129 g held at two
temperatures (20 or 26°C), on a commercial diet (21.4 g DP mJ DE−1) at four different ration levels ranging from 0.25% of its initial body weight to apparent satiation over 8 weeks. Weight
gain and protein and energy retention increased linearly with increasing feed intake. However, energy retention efficiency
(ERE) and protein retention efficiency (PRE) responses were curvilinear with optimal values, depending on fish size, approaching
or occurring at satiated feeding levels. Maximum predicted PRE was affected by body size, but not temperature; PRE values
were 0.50 and 0.50 for small mulloway, and 0.41 and 0.43 for large mulloway, at 20 and 26°C respectively. ERE demonstrated
a similar response, with values of 0.42 and 0.43 for small, and 0.32 and 0.34 for large mulloway at 20 and 26°C respectively.
Utilization efficiencies for growth based on linear regression for DP (0.58) and DE (0.60) were independent of fish size and
temperature. The partial utilization efficiencies of DE for protein (k
p) and lipid (k
l) deposition estimated using a factorial multiple regression approach were 0.49 and 0.75 respectively. Maintenance requirements
estimated using linear regression were independent of temperature for DP (0.47 g DP kg−0.7 day−1) while maintenance requirements for DE increased with increasing temperature (44.2–49.6 kJ DE kg−0.8 day−1). Relative feed intake was greatest for small mulloway fed to satiation at 26°C and this corresponded to a greater increase
in growth. Large mulloway fed to satiation ate significantly more at 26°C, but did not perform better than the corresponding
satiated group held at 20°C. Mulloway should be fed to satiation to maximize growth potential if diets contain 21.4 g DP mJ DE−1. 相似文献
110.
Dimitrios G Karpouzas Ioannis O Giannakou Allan Walker Simon R Gowen 《Pest management science》1999,55(11):1089-1094
Soils were collected from a potato-growing area in Serres, Northern Greece, where the nematicide ethoprophos was reported to have lost its effectiveness against cyst nematodes following 30 years of regular use. Incubation studies with ethoprophos and two bioassays using root-knot nematodes demonstrated that, in this heavily treated soil, the nematicide was degraded rapidly and nematicidal activity persisted only up to 14 days. In soil from an adjacent field with no known history of nematicide use during the preceding 14 years, ethoprophos was degraded more slowly and retained its nematicidal activity for more than 35 days. Ethoprophos efficacy was extended when the soil that had been treated in the field was autoclaved, although the effect was only transitory. The addition of ‘pre-conditioned’ soil from the previously treated field to samples of soil from the previously untreated field resulted in a significant acceleration of ethoprophos degradation compared with that observed in unamended soil from the previously untreated field. © 1999 Society of Chemical Industry 相似文献