全文获取类型
收费全文 | 257篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
林业 | 8篇 |
农学 | 11篇 |
基础科学 | 2篇 |
37篇 | |
综合类 | 37篇 |
农作物 | 7篇 |
水产渔业 | 24篇 |
畜牧兽医 | 90篇 |
园艺 | 19篇 |
植物保护 | 30篇 |
出版年
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 15篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 18篇 |
2007年 | 14篇 |
2006年 | 6篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1960年 | 1篇 |
1899年 | 1篇 |
排序方式: 共有265条查询结果,搜索用时 31 毫秒
21.
KR Arrigo DL Worthen MP Lizotte P Dixon G Dieckmann 《Science (New York, N.Y.)》1997,276(5311):394-397
A numerical model shows that in Antarctic sea ice, increased flooding in regions with thick snow cover enhances primary production in the infiltration (surface) layer. Productivity in the freeboard (sea level) layer is also determined by sea ice porosity, which varies with temperature. Spatial and temporal variation in snow thickness and the proportion of first-year ice thus determine regional differences in sea ice primary production. Model results show that of the 40 teragrams of carbon produced annually in the Antarctic ice pack, 75 percent was associated with first-year ice and nearly 50 percent was produced in the Weddell Sea. 相似文献
22.
Middle Paleolithic assemblages from the Indian subcontinent before and after the Toba super-eruption
Petraglia M Korisettar R Boivin N Clarkson C Ditchfield P Jones S Koshy J Lahr MM Oppenheimer C Pyle D Roberts R Schwenninger JL Arnold L White K 《Science (New York, N.Y.)》2007,317(5834):114-116
The Youngest Toba Tuff (YTT) eruption, which occurred in Indonesia 74,000 years ago, is one of Earth's largest known volcanic events. The effect of the YTT eruption on existing populations of humans, and accordingly on the course of human evolution, is debated. Here we associate the YTT with archaeological assemblages at Jwalapuram, in the Jurreru River valley of southern India. Broad continuity of Middle Paleolithic technology across the YTT event suggests that hominins persisted regionally across this major eruptive event. 相似文献
23.
Wynne PH 《Science (New York, N.Y.)》1899,10(250):535-536
24.
25.
The Thirteen Towers of Chankillo run north to south along a low ridge within a fourth-century B.C.E. ceremonial complex in north coastal Peru. From evident observing points within the adjacent buildings to the west and east, they formed an artificial toothed horizon that spanned-almost exactly-the annual rising and setting arcs of the Sun. The Chankillo towers thus provide evidence of early solar horizon observations and of the existence of sophisticated Sun cults, preceding the Sun pillars of Incaic Cusco by almost two millennia. 相似文献
26.
Effects of genotype,environment, and postharvest storage on the total ascorbate content of potato (Solanum tuberosum) tubers 总被引:1,自引:0,他引:1
The total ascorbate content of potato tubers from 33 Solanum tuberosum genotypes grown at three geographically diverse sites in Europe in each of two years was determined immediately postharvest and after approximately 4 months of storage at 4 degrees C. Statistically significant differences in total ascorbate concentration were observed between genotypes both at harvest and after storage. In all genotypes, the levels of ascorbate decreased during storage. These results are discussed in terms of their implications for diet and health as well as in terms of breeding for improved vitamin C content in potatoes. 相似文献
27.
Clive A. Henrick Barbara A. Garcia Gerardus B. Staal David C. Cerf Richard J. Anderson Karen Gill Henry R. Chinn Jeffrey N. Labovitz Michael M. Leippe Sam L. Woo Robert L. Carney Douglas C. Gordon Gustave K. Kohn 《Pest management science》1980,11(2):224-241
A new series of substituted 2-anilino-3-methylbutyrates has been prepared; bioassay data for these compounds on Heliothis virescens, Musca domestica, Aphis fabae and Tetranychus urticae are presented and discussed. Some unexpected relationships were observed between the nature of the substituents and the biological activity. Increases in foliar stability were noted with certain substitution patterns. Both α-cyano-3-phenoxybenzyl 3-methyl-2-(α, α, α,2-tetrafluoro-p-toluidino)butyrate and the corresponding 2-(2-chloro-α, α, α-trifluoro-p-toluidino)-3-methylbutyrate showed good stability in air and light, and exhibited biological activities of a similar nature and potency to those of previously known synthetic pyrethroids. Esters of the (R)-2- anilino-3-methylbutyric acids are far more active than those prepared from the (S)-enantiomers. The (R)-configuration at C-2 in these acids is sterically equivalent to the active absolute configuration at the chiral carbon α to the carboxylate group in both the permethrin and the fenvalerate types of pyrethroids. A new class of insecticidal 2-(isoindolin-2-yl)alkanoates is also reported. In this series the most biologically active analogue was α-cyano-3-phenoxybenzyl 3-methyl-2-(4,5,6,7-tetrafluoroisoindolin-2-yl)butyrate. These esters were considerably less stable than the anilino analogues on exposure to air and light. 相似文献
28.
Summary Various cardiorespiratory and metabolic indices were assessed during treadmill exercise in Thoroughbred and Standardbred racehorses with T wave changes in 4 or more leads on the electrocardiogram or second-degree atrio-ventricular (AV) block, and in horses that had no abnormalities on clinical examination, resting electrocardiography or upper respiratory tract endoscopy. No significant differences in heart rate, plasma lactate concentration, arterial blood gases, oxygen uptake, run time, peak velocity, or blood and red cell volumes were found between normal horses and horses with T wave changes or second-degree AV block. These results indicate that some electrocardiographic findings that are considered by some clinicians to indicate cardiac dysfunction, may have little effect on exercise capacity. 相似文献
29.
Bendiocarb is recommended for the control of a wide range of arthropod pests associated with buildings. They include ants, bed bugs, carpet beetles, cockroaches, fleas and silverfish. The compound is currently being developed for the control of adult Musca domestica L. Preliminary tests in the laboratory gave promising results and subsequently a series of field experiments were conducted in the Middle East. These involved treatment of farm buildings, a slaughterhouse and parts of an urban area in which domestic refuse was the source of the fly problem. The trials demonstrated that bendiocarb spray (2.4 g a.i. + 10 g sucrose/litre) will effectively control adult flies for a period of 7–14 days in hot, arid climatic conditions. 相似文献
30.