全文获取类型
收费全文 | 578篇 |
免费 | 45篇 |
国内免费 | 3篇 |
专业分类
林业 | 47篇 |
农学 | 11篇 |
基础科学 | 3篇 |
78篇 | |
综合类 | 116篇 |
农作物 | 17篇 |
水产渔业 | 57篇 |
畜牧兽医 | 256篇 |
园艺 | 20篇 |
植物保护 | 21篇 |
出版年
2023年 | 12篇 |
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 23篇 |
2019年 | 22篇 |
2018年 | 26篇 |
2017年 | 24篇 |
2016年 | 11篇 |
2015年 | 23篇 |
2014年 | 19篇 |
2013年 | 36篇 |
2012年 | 47篇 |
2011年 | 61篇 |
2010年 | 30篇 |
2009年 | 22篇 |
2008年 | 34篇 |
2007年 | 33篇 |
2006年 | 27篇 |
2005年 | 35篇 |
2004年 | 19篇 |
2003年 | 23篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1892年 | 2篇 |
1891年 | 2篇 |
1890年 | 1篇 |
排序方式: 共有626条查询结果,搜索用时 15 毫秒
31.
Joshua M. Tebbs Melinda H. McCann 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(4):534-551
Insect-vectored plant diseases impact the agricultural community each year by affecting the economic value, the quantity,
and the quality of crops. Controlling the spread of disease is an important area in risk assessment, and understanding the
dynamics of vector populations helps researchers to develop effective treatments. In this article, we consider an experimental
design commonly used by researchers who study plant disease and examine large-sample, likelihood-based hypothesis tests that
can be used to characterize disease-transmission behavior in a stratified population. Small-sample size and power results
along with design considerations are provided. We illustrate our testing procedures using two real data examples and provide
recommendations for plant-disease researchers in the field. 相似文献
32.
Short rotation woody biofuel plantations on reclaimed surface mines in Appalachia can diversify domestic energy supplies and facilitate the reforestation of these disturbed lands. This study examined growth, survival, biomass accumulation and allocation, and nitrogen concentrations following two growing seasons in American sycamore (Platanus occidentalis L.) and black locust (Robinia pseudoacacia L.) seedlings receiving irrigation, granular fertilization, and irrigation + fertilization compared with untreated controls. Fertilization increased basal diameter, height, and stem mass of American sycamore following two growing seasons. Increased stem production was attributed to accelerated development and not shifts in biomass allocation due to treatment. Irrigation and irrigation + fertilization treatments did not enhance growth or biomass accumulation of American sycamore. Similarly, black locust basal diameter, height, and stem mass did not differ among the treatments. Browse surveys showed that more than 76% of black locust seedlings experienced arrested or retrogressed growth due to browse; less than 3% of American sycamores were browsed. This intensive browse by ungulates, likely including reintroduced elk, may have affected growth differences among species and confounded the effects of treatments on black locust. Survival was unaffected by treatment in both species, but mean survival was greatest in American sycamore (80%) compared to black locust (58%). Per tree total nitrogen uptake was highest in fertilized American sycamore (7.9 g) and lowest in irrigated American sycamore (0.9 g). The results of our study suggest that granular fertilizer applications can accelerate seedling growth on reclaimed surface mines in the Appalachian region. 相似文献
33.
Potential role of soil calcium in recovery of paper birch following ice storm injury in Vermont, USA
Joshua M. Halman Paul G. SchabergGary J. Hawley Christopher F. Hansen 《Forest Ecology and Management》2011,261(9):1539-1545
In recent years, an increased number of mature paper birch (Betula papyrifera Marsh.) and heart-leafed paper birch (B. papyrifera var. cordifolia (Regel) Fern.) in northeastern United States forests have exhibited decline symptoms including foliar loss, reduced fine branching, and tree mortality. We assessed crown health, radial growth, and available soil cations in 2006 as a preliminary assessment of factors that may be influencing paper birch decline. Tree rings began to decrease in width in 1998—the year of a severe region-wide ice storm. All trees (regardless of their current decline status) experienced reduced growth starting in 1998 and tree growth continued to decrease for two years following the ice storm. After this generalized growth decrease, trees that now have vigorous crowns showed a marked increase in growth, whereas trees that now have low crown vigor did not rebound in growth, but instead exhibited a significantly higher incidence of locally absent annual rings. Extractable soil-aluminum (Al), a phytotoxic element mobilized by acid deposition, was significantly higher in soils associated with declining trees compared to those adjacent to vigorous trees. Higher soil calcium (Ca) availability was associated with both vigorous crowns and increased radial growth following the 1998 ice storm. Furthermore, increased soil Ca availability was negatively correlated to the percentage of declining trees, and positively related to increased radial growth, whereas elevation was not significantly associated with either parameter. Although previously overlooked as a factor influencing paper birch recovery from injury, we found that available soil Ca was linked to crown vigor and rebounds in growth following an inciting event. 相似文献
34.
Olawale Mashood Aliyu Oluwayemisi Oluwatosin Adeigbe Joshua Adedokun Awopetu 《Journal of Crop Science and Biotechnology》2011,14(2):143-150
The problem of declining tree yield has led to an investigation into the effectiveness of foliar application of exogenous
hormones to improve flowering, fruit set, and fruit retention in cashew. Five exogenous hormones, one Gibberellic Acid (GA3) and four Auxins (IAA, IBA, NAA, and 2,4-D) at seven different rates of application (0 mg L−1, 10 mg L−1, 25 mg L−1, 50 mg L−1, 100 mg L−1, 250 mg L−1, and 500 mg L−1) were tested on six yield-related components of the two Brazilian cashew genotypes. This trial was a factorial split-split-plot
design with each treatment replicated five times within a tree and three replications (three trees) per genotype. Responses
varied significantly between exogenous hormones, concentrations and genotypes. The cashew plants used showed hormone-specific
and optimum concentration response patterns. Of the five exogenous hormones tested, GA3 was most effective as its application at 50–100 mg L−1 gave five-fold improvements in flowering (precocity and number of hermaphrodite flowers) and fruiting, and about 69% increase
in fruit retention ability and 25% in nut size. Panicles treated with GA3 also produced relatively bigger nuts compared to the untreated. Days to flowering was found to be hormone sensitive, while
production of hermaphrodite flowers, fruit set, and nut development tended to be concentration specific. The GA3 exhibited a broad concentration tolerance among the five exogenous hormones investigated. Our data showed that using GA3 at 50 mg L−1 will enhance flowering precocity, shorten flowering duration, increase production of hermaphrodite flowers and fruit set
significantly, and resultant nuts develop optimally with high percentage retention. Thus, it suggests cashew yield could be
increased by exogenous foliar application of GA3 at 50–100 mg L−1 at pre-blooming stage. 相似文献
35.
36.
Hanson RE Crowley JL Bowring SA Ramezani J Gose WA Dalziel IW Pancake JA Seidel EK Blenkinsop TG Mukwakwami J 《Science (New York, N.Y.)》2004,304(5674):1126-1129
We show that intraplate magmatism occurred 1106 to 1112 million years ago over an area of two million square kilometers within the Kalahari craton of southern Africa, during the same magnetic polarity chron as voluminous magmatism within the cratonic core of North America. These contemporaneous magmatic events occurred while the Rodinia supercontinent was being assembled and are inferred to be parts of a single large igneous province emplaced across the two cratons. Widespread intraplate magmatism during Rodinia assembly shows that mantle upwellings required to generate such provinces may occur independently of the supercontinent cycle. 相似文献
37.
Troy DS 《Science (New York, N.Y.)》1891,18(456):247-249
38.
A fundamental aspect of visuomotor behavior is deciding where to look or move next. Under certain conditions, the brain constructs an internal representation of stimulus location on the basis of previous knowledge and uses it to move the eyes or to make other movements. Neuronal responses in primary visual cortex were modulated when such an internal representation was acquired: Responses to a stimulus were affected progressively by sequential presentation of the stimulus at one location but not when the location was varied randomly. Responses of individual neurons were spatially tuned for gaze direction and tracked the Bayesian probability of stimulus appearance. We propose that the representation arises in a distributed cortical network and is associated with systematic changes in response selectivity and dynamics at the earliest stages of cortical visual processing. 相似文献
39.
The extent to which synaptic activity can signal a sensory stimulus limits the information available to a neuron. We determined the contribution of individual synapses to sensory representation by recording excitatory postsynaptic currents (EPSCs) in cerebellar granule cells during a time-varying, quantifiable vestibular stimulus. Vestibular-sensitive synapses faithfully reported direction and velocity, rather than position or acceleration of whole-body motion, via bidirectional modulation of EPSC frequency. The lack of short-term synaptic dynamics ensured a highly linear relationship between velocity and charge transfer, and as few as 100 synapses provided resolution approaching psychophysical limits. This indicates that highly accurate stimulus representation can be achieved by small networks and even within single neurons. 相似文献
40.