全文获取类型
收费全文 | 424篇 |
免费 | 22篇 |
专业分类
林业 | 15篇 |
农学 | 2篇 |
基础科学 | 1篇 |
40篇 | |
综合类 | 79篇 |
农作物 | 10篇 |
水产渔业 | 36篇 |
畜牧兽医 | 245篇 |
园艺 | 1篇 |
植物保护 | 17篇 |
出版年
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 10篇 |
2011年 | 18篇 |
2010年 | 5篇 |
2009年 | 18篇 |
2008年 | 20篇 |
2007年 | 12篇 |
2006年 | 17篇 |
2005年 | 20篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1997年 | 6篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1971年 | 8篇 |
1970年 | 4篇 |
1968年 | 5篇 |
1967年 | 5篇 |
1963年 | 5篇 |
1960年 | 4篇 |
1940年 | 3篇 |
1939年 | 3篇 |
1938年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有446条查询结果,搜索用时 203 毫秒
1.
The activity and inhibition of poly(ADP‐ribose) polymerase‐1 in equine peripheral blood mononuclear cells in vitro 下载免费PDF全文
2.
3.
4.
K. M. Hart St. R. McDow W. Giger D. Steiner H. Burtscher 《Water, air, and soil pollution》1993,68(1-2):75-90
Aerosol photoemission (APE) has been found to be an excellent surrogate measure of particulate PAH concentration in combustion aerosols under a variety of laboratory and field conditions. Samples of oil stove, automobile exhaust, and urban air particulate matter were concurrently analyzed for aerosol photoemission intensity and particulate PAH concentration. In-situ, real-time analysis of the particulate matter was performed by UV-induced electron photoemission. Two photon energies, 4.9 and 6.7 eV, were chosen for irradiation. The latter energy was more sensitive and less selective. Particulate PAH concentrations were determined by collecting the particulate matter on a filter, solvent extracting the filter, and analyses of the extracts by gas chromatography / mass spectroscopy. Linear correlations (0.84≤r2≤1.00) were observed between aerosol photoemission intensities and the sum of particulate PAH concentrations for laboratory and field studies under a wide variety of conditions. The studies performed to date cover a dynamic range of three orders of magnitude (1 to 1000 ng / m3). The time resolution is in the order of a few seconds. 相似文献
5.
Lerat S Gulden RH Hart MM Powell JR England LS Pauls KP Swanton CJ Klironomos JN Trevors JT 《Journal of agricultural and food chemistry》2007,55(25):10226-10231
The presence of the recombinant cp4 epsps gene from Roundup Ready (RR) corn and RR soybean was quantified using real-time PCR in soil samples from a field experiment growing RR and conventional corn and soybean in rotation. RR corn and RR soybean cp4 epsps persisted in soil for up to 1 year after seeding. The concentration of recombinant DNA in soil peaked in July and August in RR corn and RR soybean plots, respectively. A small fraction of soil samples from plots seeded with conventional crops contained recombinant DNA, suggesting transgene dispersal by means of natural process or agricultural practices. This research will aid in the understanding of the persistence of recombinant DNA in agricultural cropping systems. 相似文献
6.
Paul Dijkstra Ayaka Ishizu Stephen C. Hart Egbert Schwartz Bruce A. Hungate 《Soil biology & biochemistry》2006,38(11):3257-3266
Stable isotope analysis is a powerful tool in the study of soil organic matter formation. It is often observed that more decomposed soil organic matter is 13C, and especially 15N-enriched relative to fresh litter and recent organic matter. We investigated whether this shift in isotope composition relates to the isotope composition of the microbial biomass, an important source for soil organic matter. We developed a new approach to determine the natural abundance C and N isotope composition of the microbial biomass across a broad range of soil types, vegetation, and climates. We found consistently that the soil microbial biomass was 15N-enriched relative to the total (3.2 ‰) and extractable N pools (3.7 ‰), and 13C-enriched relative to the extractable C pool (2.5 ‰). The microbial biomass was also 13C-enriched relative to total C for soils that exhibited a C3-plant signature (1.6 ‰), but 13C-depleted for soils with a C4 signature (−1.1 ‰). The latter was probably associated with an increase of annual C3 forbs in C4 grasslands after an extreme drought. These findings are in agreement with the proposed contribution of microbial products to the stabilized soil organic matter and may help explain the shift in isotope composition during soil organic matter formation. 相似文献
7.
Jeff R. Powell Rachel G. Campbell Kari E. Dunfield Robert H. Gulden Miranda M. Hart David J. Levy-Booth John N. Klironomos K. Peter Pauls Clarence J. Swanton Jack T. Trevors Pedro M. Antunes 《Applied soil ecology》2009,41(1):128-136
Most soybeans grown in North America are genetically modified (GM) to tolerate applications of the broad-spectrum herbicide glyphosate; as a result, glyphosate is now extensively used in soybean cropping systems. Soybean roots form both arbuscular mycorrhizal (AM) and rhizobial symbioses. In addition to individually improving host plant fitness, these symbioses also interact to influence the functioning of each symbiosis, thereby establishing a tripartite symbiosis. The objectives of this study were to (1) estimate the effects of glyphosate on the establishment and functioning of AM and rhizobial symbioses with GM soybean, and (2) to estimate the interdependence of the symbioses in determining the response of each symbiosis to glyphosate. These objectives were addressed in two experiments; the first investigated the importance of the timing of glyphosate application in determining the responses of the symbionts and the second varied the rate of glyphosate application. Glyphosate applied at recommended field rates had no effect on Glomus intraradices or Bradyrhizobium japonicum colonization of soybean roots, or on soybean foliar tissue [P]. N2-fixation was greater for glyphosate-treated soybean plants than for untreated-plants in both experiments, but only when glyphosate was applied at the first trifoliate soybean growth stage. These data deviate from previous studies estimating the effect of glyphosate on the rhizobial symbiosis, some of which observed negative effects on rhizobial colonization and/or N2-fixation. We did observe evidence of the response of one symbiont (stimulation of N2-fixation following glyphosate) being dependent on co-inoculation with the other; however, this interactive response appeared to be contextually dependent as it was not consistent between experiments. Future research needs to consider the role of environmental factors and other biota when evaluating rhizobial responses to herbicide applications. 相似文献
8.
9.
Tim G. B. Hart 《Agriculture and Human Values》2011,28(3):321-333
Technologies and services provided to resource-poor farmers need to be relevant and compatible with the context in which they
operate. This paper examines the contribution of extension services to the food security of resource-poor farmers in a rural
village in South Africa. It considers these in terms of the local context and the production of African vegetables in household
food plots. A mixture of participatory, qualitative and quantitative research tools, including a household survey, is used
to argue that local production practices contribute more to food security requirements than the extension services. This is
because of the ability of African vegetables to grow relatively well in semi-arid areas where other exotic plants do not,
their ability to provide at least two foodstuffs during their life cycle, and the ability of either the fruit or the leaves,
or both, to be dried and stored for consumption in the winter months. These crops can make a significant contribution in terms
of household food security, but a number of social and agroecological factors are constraining their production and placing
their availability under threat. Despite this, the extension services remain focused on certain activities within vegetable
garden projects, even when these are not meeting their proposed purpose—food security by means of cash-crop production. The
paper concludes that social and agroecological constraints could be improved if the extension services were changed. This
could include the use of context specific and low-cost technologies to ensure that these crops are able to increase their
contribution to household food security for resource-poor farmers in semi-arid areas. 相似文献
10.
Concerns about the long-term sustainability of overstocked dry conifer forests in western North America have provided impetus for treatments designed to enhance their productivity and native biodiversity. Dense forests are increasingly prone to large stand-replacing fires; yet, thinning and burning treatments, especially combined with other disturbances such as drought and grazing, may enhance populations of colonizing species, including a number of non-native species. Our study quantifies plant standing crop of major herbaceous species across contrasting stand structural types representing a range in disturbance severity in northern Arizona. The least disturbed unmanaged ponderosa pine stands had no non-native species, while non-native grasses constituted 7–11% of the understory plant standing crop in thinned and burned stands. Severely disturbed wildfire stands had a higher proportion of colonizing native species as well as non-native species than other structural types, and areas protected from grazing produced greater standing crop of native forbs compared to grazed unmanaged stands. Standing crop of understory plants in low basal area thinned and burned plots was similar to levels on wildfire plots, but was comprised of fewer non-native graminoids and native colonizing plants. Our results also indicate that size of canopy openings had a stronger influence on standing crop in low basal area plots, whereas tree density more strongly constrained understory plant standing crop in dense stands. These results imply that treatments resulting in clumped tree distribution and basal areas <10 m2 ha−1 will be more successful in restoring native understory plant biomass in dense stands. Multiple types and severity of disturbances, such as thinning, burning, grazing, and drought over short periods of time can create greater abundance of colonizing species. Spreading thinning and burning treatments over time may reduce the potential for non-native species colonization compared to immediately burning thinned stands. 相似文献