全文获取类型
收费全文 | 538篇 |
免费 | 54篇 |
国内免费 | 2篇 |
专业分类
林业 | 43篇 |
农学 | 25篇 |
基础科学 | 2篇 |
88篇 | |
综合类 | 59篇 |
农作物 | 34篇 |
水产渔业 | 35篇 |
畜牧兽医 | 227篇 |
园艺 | 19篇 |
植物保护 | 62篇 |
出版年
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 42篇 |
2012年 | 25篇 |
2011年 | 30篇 |
2010年 | 19篇 |
2009年 | 19篇 |
2008年 | 24篇 |
2007年 | 27篇 |
2006年 | 30篇 |
2005年 | 29篇 |
2004年 | 25篇 |
2003年 | 27篇 |
2002年 | 26篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1977年 | 4篇 |
1974年 | 3篇 |
1973年 | 9篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1967年 | 3篇 |
1964年 | 4篇 |
1963年 | 4篇 |
1962年 | 3篇 |
1955年 | 5篇 |
排序方式: 共有594条查询结果,搜索用时 15 毫秒
111.
Marina L. Leis M. Elyse Salpeter Bianca S. Bauer Dale L. Godson Bruce H. Grahn 《Veterinary ophthalmology》2017,20(4):365-371
A 15‐year‐old, neutered male, Shih Tzu cross developed progressive corneal stromal thickening and vascularization of the right eye, and 5 months later, of the left eye. Both eyes became blind due to extensive corneal opacification and were enucleated. Light microscopic examination revealed a diffuse corneal infiltrate of neoplastic mesenchymal cells, and immunohistochemistry revealed diffuse cytoplasmic vimentin immunoreactivity and variable cytoplasmic and nuclear immunoreactivity for S100 in the neoplastic cells. Transmission electron microscopy revealed desmosomes between contiguous cells, thread‐like cytoplasmic processes coated with basement membrane, extracellular bundles of collagen, and axonal degeneration consistent with features of a nerve sheath neoplasm. This is the first report of primary, bilateral corneal nerve sheath sarcoma in a canine. 相似文献
112.
Clayton S. MILLER Mark HEBBLEWHITE John M. GOODRICH Dale G. MIQUELLE 《Integrative zoology》2010,5(4):378-389
Over the past half century, wildlife research has relied on technological advances to gain additional insight into the secretive lives of animals. This revolution started in the 1960s with the development of radio telemetry and continues today with the use of Global Positioning System (GPS)-based research techniques. In the present paper we review the history of radio telemetry from its origins with grizzly bears in Yellowstone to its early applications in tiger research and conservation in Asia. We address the different types of data that are available using radio telemetry as opposed to using other research techniques, such as behavioral observations, camera trapping, DNA analysis and scat analysis. In the late 1990s, the rapid development of GPS collar technology revolutionized wildlife research. This new technology has enabled researchers to dramatically improve their ability to gather data on animal movements and ecology. Despite the ecological and conservation benefits of radio telemetry, there have been few telemetry studies of tigers in the wild, and most have been on the Bengal or Amur subspecies. We close with an assessment of the current tiger conservation efforts using GPS technology and discuss how this new information can help to preserve tigers for future generations. 相似文献
113.
114.
Benjamin M. Rau Robin Tausch Alicia Reiner Dale W. Johnson Jeanne C. Chambers Robert R. Blank Annmarrie Lucchesi 《Strength and Conditioning Journal》2010,63(2):197-202
Increases in pinyon and juniper woodland cover associated with land-use history are suggested to provide offsets for carbon emissions in arid regions. However, the largest pools of carbon in arid landscapes are typically found in soils, and aboveground biomass cannot be considered long-term storage in fire-prone ecosystems. Also, the objectives of carbon storage may conflict with management for other ecosystem services and fuels reduction. Before appropriate decisions can be made it is necessary to understand the interactions between woodland expansion, management treatments, and carbon retention. We quantified effects of prescribed fire as a fuels reduction and ecosystem maintenance treatment on fuel loads, ecosystem carbon, and nitrogen in a pinyon–juniper woodland in the central Great Basin. We found that plots containing 30% tree cover averaged nearly 40 000 kg · ha?1 in total aboveground biomass, 80 000 kg · ha?1 in ecosystem carbon (C), and 5 000 kg · ha?1 in ecosystem nitrogen (N). Only 25% of ecosystem C and 5% of ecosystem N resided in aboveground biomass pools. Prescribed burning resulted in a 65% reduction in aboveground biomass, a 68% reduction in aboveground C, and a 78% reduction in aboveground N. No statistically significant change in soil or total ecosystem C or N occurred. Prescribed fire was effective at reducing fuels on the landscape and resulted in losses of C and N from aboveground biomass. However, the immediate and long-term effects of burning on soil and total ecosystem C and N is still unclear. 相似文献
115.
DS Grum D Cook DR Gardner JM Roper JA Pfister MH Ralphs 《Journal of agricultural and food chemistry》2012,60(33):8083-8089
Locoism is a toxic syndrome of livestock caused by the ingestion of a subset of legumes known as locoweeds endemic to arid and semiarid regions of the western United States. Locoweeds contain the toxic alkaloid swainsonine, which is produced by the endophytic fungi Undifilum species. Two chemotypes of plants can coexist within toxic populations of locoweeds: chemotype 1 plants are defined as individuals containing swainsonine concentrations greater than 0.01% and quantitatively greater amounts of Undifilum, while chemotype 2 plants are defined as individuals containing less than 0.01% swainsonine and quantitatively smaller amounts of Undifilum. To elucidate the mechanisms that govern chemotypes, the amount of Undifilum in seeds/embryos was manipulated, thus altering subsequent swainsonine concentrations in three locoweed species: Astragalus mollissimus, Astragalus lentiginosus, and Oxytropis sericea. Chemotype 1 seeds that were fungicide-treated or had the seed coat removed resulted in plants with swainsonine concentrations comparable to those in chemotype 2 plants. Conversely, embryos from seeds of chemotypes 1 and 2 that were inoculated with the endophyte resulted in plants with swainsonine concentrations comparable to those of chemotype 1 plants. This reproducible interconversion between the two swainsonine chemotypes suggests that the quantity of endophyte present in the seed at the time of germination is a key determinant of the eventual chemotype. Additionally, this is the first report of the inoculation of locoweeds with the endophyte Undifilum species. 相似文献
116.
117.
Surveillance and control activities for bovine tuberculosis (bTB) in free-ranging Michigan white-tailed deer (Odocoileus virginianus) have now been underway for over a decade. Significant progress has been made, lowering apparent prevalence in deer in the core area by >60%, primarily via reduction of deer densities through hunting, and restrictions on public feeding and baiting of deer. These broad strategies of the Michigan Department of Natural Resources (MDNR), implemented with the cooperation of Michigan deer hunters, halved the deer population in the bTB endemic area. However, as hunters see fewer deer, their willingness to sustain aggressive harvests has waned, and public resentment of control measures has grown. During the past four years, apparent prevalence in core area deer has held approximately steady just below 2%. After bottoming out in 2004 at an estimated 10-12 deer/km(2), deer numbers have since rebounded by ~ 30%. Public compliance with baiting and feeding restrictions has been variable. In general, hunters in the core area do not perceive bTB as a problem, in spite of 13 years of MDNR outreach. To date, MDNR has expended more than US$23 million on TB-related activities. Of late, a substantial portion of that funding has been diverted to support other programs which have suffered from budget shortfalls. Livestock herd breakdowns continue to occur sporadically, averaging 3-4 per year 2005 to present. In total, 46 cattle and 4 captive deer herds have been diagnosed bTB positive statewide, the majority yielding only 1 positive animal. Five cattle herds were twice infected, one thrice. Michigan Department of Agriculture (MDA) policy emphasis has shifted towards obtaining producer support for wildlife risk mitigation and farm biosecurity. Funding has proven a limiting factor, with the majority of the US$63 million spent to date devoted to whole herd testing. Nevertheless, some initiatives justify cautious optimism. Promising research to support eventual vaccination of wild deer continues. Some hunters and landowners have begun to recognize the costs of high deer densities and supplemental feeding. A peninsula-wide ban on baiting and feeding was enacted. Some cattle producers, recognizing their precarious circumstances, have begun work to change long-held prevailing opinions among their peers about farm biosecurity. Yet formidable challenges remain, and evidence suggests that eradication of bTB, if it can be achieved, will take decades, and will require greater public and political resolve than has been demonstrated thus far. 相似文献
118.
Audrey G. Quentin Anthony P. O’Grady Christopher L. Beadle Dale WorledgeElizabeth A. Pinkard 《Agricultural and Forest Meteorology》2011,151(3):356-364
Partial defoliation has been shown to affect the water relations and transpiration (gas exchange) of plants. Over one growing season, the water relations in response to partial (∼45%) defoliation were examined in four-year-old Eucalyptus globulus trees in southern Australia. Daily maximum transpiration rates (Emax), maximum canopy conductance (GCmax), and diurnal patterns of tree water-use were measured over a period of 215 days using the heat-pulse technique in adjacent control (non-defoliated) and defoliated trees. Sap-flux measurements were used to estimate canopy conductance and soil-to-leaf hydraulic conductance (KP); leaf water potential (Ψ) and climate data were also collected. Following the removal of the upper canopy layer, defoliated trees exhibited compensatory responses in transpiration rate and canopy conductance of the remaining foliage. Defoliated E. globulus had similar predawn but higher midday Ψl, transpiration rates (E), canopy conductance (GC) and KP compared to the non-defoliated controls, possibly in response to increased water supply per unit leaf area demonstrated by higher midday Ψl. Higher E in defoliated E. globulus trees was the result of higher GC in the morning and early afternoon. This paper also incorporates the cumulative effect of defoliation, in a phenomenological model of maximum canopy conductance of E. globulus. These results contribute to a mechanistic understanding of plant responses to defoliation, in particular the often observed up-regulation of photosynthesis that also occurs in response to defoliation. 相似文献
119.
The soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is a major pest of soybeans (Glycine max L. Merrill) in the central and southern United States. Soybean cyst nematode causes stunted top growth, root pruning and symptoms of mineral element deficiency in soybeans. The objective of this study was to determine the effect of two selections of SCN (I selected on PI209332 and IV selected on PI 89772) on macronutrient uptake, translocation, and tissue concentrations of soybean and to determine the elemental composition of cysts isolated from roots. Soybeans were grown in plastic tubes in the greenhouse where the middle one‐third of the Hodge fine sand (Typic Udipsamment) contained 0, 25,000, or 50,000 SCN eggs. After 35 days, plants were harvested and tissue nutrient element concentrations were determined. Plants infested with both SCN selections were smaller and had much less root volume than controls. Dry weight of each plant tissue decreased as SCN population was increased. Root concentration of potassium (K) and magnesium (Mg) was decreased, whereas root calcium (Ca) and phosphorus (P) concentrations were increased with SCN treatments. Leaf Mg and Ca concentrations increased with SCN treatment. Magnesium uptake per unit root volume was decreased, but Mg translocation (% of total plant content in aerial portion) was increased with SCN treatment. Calcium uptake per unit of root volume was increased, but translocation was unchanged by SCN treatment. The Ca and P concentration of cysts isolated from the soybean roots was high. This high concentration of Ca in cysts is interesting based on the greater root Ca concentration and uptake per unit of root volume in SCN infested plants. Since total uptake and root concentrations of both K and Mg were decreased by SCN treatment, infested soybeans might require very high levels of K and Mg fertilization. These results indicate that K and Mg fertility should be followed closely in SCM‐infested soybean fields. 相似文献
120.
Dale R. Mutch Donald Penner Frank Roggenbuck Richard W. Chase 《American Journal of Potato Research》1984,61(9):577-586
Chemical vine desiccation is an important management practice for late season potatoes (Solanum tuberosum L.) in Michigan. A number of desiccants are registered; however, most Michigan growers apply dinoseb (2-sec- butyl-4,6-dinitrophenol). Greenhouse experiments were initiated to evaluate the potential of ammonium salts and ethephon (2-chloroethyl)phosphonic acid) to increase the efficacy of the chemical harvest aids dinoseb and endothall (7-oxabicyclo[2,2,1]heptane-2,3-dicarboxylic acid) on potato vines. Temperature and potato vine position were evaluated to determine their influence on vine desiccation. All treatments with endothall applied at 0.6 kg/ha resulted in unsatisfactory potato vine desiccation. Ethephon and ammonium sulfate increased efficacy of dinoseb. High temperature both before and after treatment contributed to greater dinoseb efficacy. The horizontal placing of potato vines resulted in the desired desiccation rating of 9.0 or greater using the combination of dinoseb at 2.8 kg/ha, plus ammonium sulfate at 9 kg/ha plus 2.4 L/ha X-77 surfactant.3 相似文献