全文获取类型
收费全文 | 5178篇 |
免费 | 221篇 |
国内免费 | 8篇 |
专业分类
林业 | 309篇 |
农学 | 159篇 |
基础科学 | 44篇 |
782篇 | |
综合类 | 830篇 |
农作物 | 238篇 |
水产渔业 | 436篇 |
畜牧兽医 | 2040篇 |
园艺 | 152篇 |
植物保护 | 417篇 |
出版年
2023年 | 31篇 |
2022年 | 38篇 |
2021年 | 100篇 |
2020年 | 117篇 |
2019年 | 126篇 |
2018年 | 87篇 |
2017年 | 101篇 |
2016年 | 97篇 |
2015年 | 105篇 |
2014年 | 117篇 |
2013年 | 244篇 |
2012年 | 283篇 |
2011年 | 348篇 |
2010年 | 192篇 |
2009年 | 153篇 |
2008年 | 342篇 |
2007年 | 291篇 |
2006年 | 296篇 |
2005年 | 300篇 |
2004年 | 267篇 |
2003年 | 272篇 |
2002年 | 263篇 |
2001年 | 57篇 |
2000年 | 65篇 |
1999年 | 69篇 |
1998年 | 52篇 |
1997年 | 44篇 |
1996年 | 42篇 |
1995年 | 38篇 |
1994年 | 46篇 |
1993年 | 54篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 41篇 |
1989年 | 35篇 |
1988年 | 32篇 |
1987年 | 37篇 |
1986年 | 28篇 |
1985年 | 35篇 |
1984年 | 40篇 |
1983年 | 36篇 |
1982年 | 20篇 |
1981年 | 33篇 |
1980年 | 23篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1975年 | 18篇 |
1974年 | 23篇 |
1973年 | 24篇 |
排序方式: 共有5407条查询结果,搜索用时 588 毫秒
981.
James A. Entry 《Water, air, and soil pollution》2012,223(9):6109-6121
The Loxahatchee National Wildlife Refuge (Refuge) developed as a system with waters low in nutrients. Today, the Refuge wetlands are impacted by inflows containing elevated nutrient concentrations originating from agricultural sources. We analyzed water quality sampled at 54 sites in the Refuge. The Refuge was divided into northern, central, and southern latitudinal areas and then perimeter, transition, and the interior zones based on distance from the canal towards the Refuge interior. In the perimeter zone, total dissolved solids (TDS), silicon (Si), and total phosphorus (TP) concentrations in water were higher in the northern than the central area and TDS, Si, SO4, and TP concentrations in water were higher in the central than the southern area. In general TDS, Ca, Cl, Si, SO4, and TP loads in the northern perimeter, transition, and interior zones decreased from 2005 to 2009. The decrease is less pronounced in the central and southern areas than the northern area. As water flowed southward for over 30?km from the northern to the southern area in the perimeter zone, most water quality parameters analyzed were reduced in the water column. However, large amounts of Ca and Cl were added to the water column indicating that canal water is continually diffusing and intruding into the Refuge in all zones. In the perimeter zone, and to a lesser degree in the transition zone, the Refuge has accumulated substantial amounts of Ca, Si, SO4, and TP in vegetation and soils during the sampling period. 相似文献
982.
983.
A field study was conducted at North Platte, Nebraska in 2007–2009, imposing eight irrigation treatments, ranging from dryland to fully irrigated. Four of the eight treatments allowed for various degrees of water stress only after tasseling and silking. In 2007, corn yield ranged from 8.9 Mg ha?1 with a season total of 41 mm of irrigation water to 11.5 Mg ha?1 for the fully irrigated treatment (264 mm of irrigation water). The treatment with the greatest reduction in irrigation water after tasseling and silking (158 mm) had a mean yield of 10.9 Mg ha?1, only 0.6 Mg ha?1 less than the fully irrigated treatment. In 2009, yields ranged from 12.6 to 13.5 Mg ha?1. There were no significant yield differences between the irrigation treatments for several possible reasons: more in-season precipitation and cooler weather required less irrigation water; much of the irrigation water was applied after the most water-stress sensitive stages of tasseling and silking; and lower atmospheric demand allowed for soil water contents well below 50 % management allowed depletion (MAD) not to cause any yield losses. 相似文献
984.
985.
Background
The human body exhibits a variety of biological rhythms. There are patterns that correspond, among others, to the daily wake/sleep cycle, a yearly seasonal cycle and, in women, the menstrual cycle. Sine/cosine functions are often used to model biological patterns for continuous data, but this model is not appropriate for analysis of biological rhythms in failure time data. 相似文献986.
Missing plants in potato crops can be caused by diseases and other factors, and can result from non-emergence or from plants incapacitated at any time during the growing season. Field experiments were conducted to simulate missing plants and to estimate the resulting yield losses by removing different percentages of plants at random from plots at emergence and/or later stages. The recorded yield losses were not proportional to the percentage of missing plants. Two surveys of fields of table stock and seed stock of the cultivar Netted Gem in New Brunswick in 1972 showed that approximately 25% of the plants were missing at emergence, probably causing around8% loss in total tuber yield. Assuming all cultivars have similar levels of misses, the yield loss clue to missing plants at emergence in New Brunswick in 1972 was equivalent to a financial loss of approximately $1 1/2 million. 相似文献
987.
988.
989.
D. T. Westermann T. A. Tindall D. W. James R. L. Hurst 《American Journal of Potato Research》1994,71(7):417-431
Potassium and N fertilization is often required for maximum potato (Solanum tuberosum L.) production. Nitrogen, K, and K-sources (KCl, K2SO4 are known to affect yield and quality of potatoes but N and K interactions as affected by K-source have not been defined. This study evaluated the N*K and K-source interactions on Russet Burbank tuber yields and specific gravity (SG) in two irrigated field experiments. Nitrogen rates of 0, 112, 224 or 336 kg ha-1 were combined with selected K rates of 0,112, 224 or 448 kg ha-1 as either KC1 or K2SO4 in an incomplete factorial. A multiple linear regression model was fit to the data and used to predict yield and SG for a complete factorial for each K-source. Both N and K applications increased yields independent of K-source. Nitrogen decreased yields at the 336 kg ha-1 rate. Potassium increased yields up to 448 kg K ha-1. Both K-sources decreased SG a similar amount with N application; without N, KC1 decreased SG but K2SO4 did not. Nitrogen also decreased SG. Petiole NO3-N and K concentrations were positively related to yields and negatively to specific gravities. The petiole K concentration 100 days after planting should be above 4.5 for highest tuber yields. The N*K*K-source interaction was important for yields at low available N and for SG at adequate N availabilities. This study showed that N or K fertilizers can be applied according to their respective soil test concentration and the crop’s requirement, generally without consideration of K-source. 相似文献
990.
R. G. Novy D. L. Corsini S. L. Love J. J. Pavek A. R. Mosley S. R. James D. C. Hane C. C. Shock K. A. Rykbost C. R. Brown R. E. Thornton 《American Journal of Potato Research》2003,80(5):295-301
‘Alturas’, a late-maturing, high-yielding, russet potato cultivar with high tuber specific gravity, was released in 2002 by the USDA-ARS and the Agricultural Experiment Stations of Idaho, Oregon, and Washington. Originally selected for dehydration processing, its cold-sweetening resistance also makes it suitable for processing out of storage into french fries and other frozen potato products. Culinary quality is high, with larger tubers suitable for fresh market if heavily russeted skin is not essential. Alturas consistently produced greater total and U.S. No. 1 yields than ‘Russet Burbank’ and ‘Ranger Russet’ in southern Idaho trials. Across other western trial sites, total yields of Alturas have on average been 29% and 14% greater than Russet Burbank and Ranger Russet, respectively. Alturas is resistant to Verticillium wilt (Verticillium dahliae) and early blight (Alternaria solani). Compared with Russet Burbank and Ranger Russet, Alturas is less susceptible to corky ringspot and foliar and tuber infection by late blight (Phytophthora infestans). It also is less susceptible to tuber net necrosis and Fusarium dry rot than Russet Burbank, and is more resistant to common scab (Streptomyces scabies) than Ranger Russet. However, Alturas is more susceptible to infection by PVY and PVX than Ranger Russet. Total nitrogen application recommendations for Alturas are approximately 40% less than those for Russet Burbank. Alturas requires 15% to 20% more water during the growing season than does Russet Bur-bank. 相似文献