全文获取类型
收费全文 | 22415篇 |
免费 | 1375篇 |
国内免费 | 2625篇 |
专业分类
林业 | 2275篇 |
农学 | 1891篇 |
基础科学 | 2987篇 |
4722篇 | |
综合类 | 9866篇 |
农作物 | 786篇 |
水产渔业 | 914篇 |
畜牧兽医 | 1508篇 |
园艺 | 326篇 |
植物保护 | 1140篇 |
出版年
2024年 | 294篇 |
2023年 | 643篇 |
2022年 | 921篇 |
2021年 | 851篇 |
2020年 | 918篇 |
2019年 | 1011篇 |
2018年 | 686篇 |
2017年 | 1025篇 |
2016年 | 1230篇 |
2015年 | 1100篇 |
2014年 | 1169篇 |
2013年 | 1276篇 |
2012年 | 1631篇 |
2011年 | 1678篇 |
2010年 | 1387篇 |
2009年 | 1303篇 |
2008年 | 1227篇 |
2007年 | 1293篇 |
2006年 | 1098篇 |
2005年 | 919篇 |
2004年 | 720篇 |
2003年 | 585篇 |
2002年 | 462篇 |
2001年 | 354篇 |
2000年 | 335篇 |
1999年 | 308篇 |
1998年 | 276篇 |
1997年 | 272篇 |
1996年 | 234篇 |
1995年 | 231篇 |
1994年 | 187篇 |
1993年 | 164篇 |
1992年 | 157篇 |
1991年 | 146篇 |
1990年 | 122篇 |
1989年 | 91篇 |
1988年 | 63篇 |
1987年 | 22篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1963年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
桃品种需冷量评价模式的探讨 总被引:34,自引:2,他引:34
通过1986~2001年对450余份桃品种需冷量的7.2℃模式、0~7.2℃模式(不包括0℃)和犹它模式比较分析,归纳出桃品种需冷量的评价模式为:以秋季日平均温度稳定低于7.2~C的日期为需冷量测定的起点,以0~7.2℃累积低温值作为需冷量的评价标准比较适宜;犹它模式在中需冷量和长需冷量范围内能有效预测休眠的结束,而不适宜低需冷量品种的测定;7.2℃模式不适宜作为需冷量的评价模式。品种的需冷量与叶芽开放和始花期的相关系数分别为0.52和0.58,均达到极显著水平。提出了桃品种需冷量评价的系列标准参照品种。 相似文献
52.
新疆冬小麦农田蒸散估算模型的研究 总被引:1,自引:0,他引:1
本文在田间试验资料的基础上,综合考虑了影响冬小麦农田蒸散的气象、生物学特性和土壤水分等因素,选用蒸发力、冬小麦的叶面积指数和相对有效土壤湿度建立了新疆冬小麦农田蒸散估算模型,并且检验了该模型的计算效果。 相似文献
53.
荒漠化发生发展的过程实际上是指在自然和人为因素的作用下,生态系统结构遭受破坏、功能过程受阻和演变发生异化的过程,其防治的根本措施是恢复和重建健康的生态系统。所以,景观生态学理念在荒漠化的研究和防治中有着重要的意义。本文从荒漠化与生态系统结构、功能变化、荒漠化与生物多样性、荒漠化生态系统的物质循环和能量流动以及荒漠化生态系统的稳定性等方面论述了景观生态学理念在荒漠化研究中应用的可行性,并重点分析了景观生态学关于景观格局变化的评价指标与荒漠化土地动态变化之间的关系。 相似文献
54.
Norman Owen-Smith 《Landscape Ecology》2004,19(7):761-771
Large mammalian herbivores are notorious for their propensity towards population irruptions and crashes, yet many herbivore populations remain relatively stable. I explore how resource heterogeneity within landscapes dampens population instability, using a metaphysiological modelling approach considering patch state distributions. Resource heterogeneity is functionally stabilizing through spreading consumption away from preferred resources before these become critically depleted. Lower-quality resources act as a buffer against starvation during critical periods of the seasonal cycle. Enriching resource quality is destabilizing, even if patch diversity is maintained, because food quantity then becomes the limitation. The potential consequences of landscape fragmentation are explored using the Serengeti ecosystem, characterised by broadscale resource gradients, as a hypothetical example. Further insights provided by the model are illustrated with specific examples concerning the effects of patch scales and waterpoint distribution. A metaphysiological modelling approach enables the basic consequences of landscape heterogeneity to be distinguished from further effects that may arise from specific patch scales and configurations, without the distracting detail of spatially explicit models. 相似文献
55.
Traffic has a considerable effect on population and community dynamics through the disruption and fragmentation of habitat
and traffic mortality. This paper deals with a systematic way to acquire knowledge about the probabilities of successful road
crossing by mammals and what characteristics affect this traversability. We derive a model from traffic flow theory to estimate
traffic mortality in mammals related to relevant road, traffic and species characteristics. The probability of successful
road crossing is determined by the pavement width of the road, traffic volume, traversing speed of the mammals and their body
length. We include the traversability model in a simple two-patch population model to explore the effects of these road, traffic
and species characteristics on population dynamics. Analysis of the models show that, for our parameter ranges, traffic volume
and traversing speed have the largest effect on traffic mortality. The population size is especially negatively affected when
roads have to be crossed during the daily movements. These predictions could be useful to determine the expected effectiveness
of mitigating measures relative to the current situation. Mitigating measures might alter the road and traffic characteristics.
The effects of these changes on traffic mortality and population dynamics could be analysed by calculating the number of traffic
victims before and after the mitigating measures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
56.
The invasive ability of Cynodon dactylon is dependent on self dispersal and on cultivation practices. Tillage can seriously change patch biomass and spatial structure, spreading vegetative propagules of the weed. The objectives of this study were: (i) to quantify the effect on non‐inversion tillage on dispersal, establishment and colonization of C. dactylon and (ii) to propose a simple model considering soil cultivation effects and light availability on spatial growth of weed patches. Two experiments were carried out, exploring different soils and environmental conditions. Spatial distribution of vegetative units differed when tillage was conducted with different non‐inversion implements and could be described by simple functions. A minimum patch biomass seems necessary before vegetative structures are vulnerable to movement by cultivation. Only a small proportion of the biomass dispersed from original patches was able to establish. However, simulation showed that the area colonized by C. dactylon mostly increased by means of tillage dispersal, both with and without crop competition, in one growing cycle. It appears sensible to consider changing cultivation practices to reduce weed dispersal and to use crop competition for light to create unsuitable habitats limiting weed colonization. 相似文献
57.
Summary:This study was conducted to develop a suitable model for describing the growth pattern of the yak. The data used consisted of body weight records of 76 growing yak aged between 5 to 37 months. Three mathematical models were applied to describe the growth curves during this development period:①Y1=20.105 + 11. 250x-0. 526x2 ;used for describing the growth curve of yak aged 5 to 13 months;②Y2 = -359.687 + 49. 977x - 1. 249x2 ;used for animals aged 13 to 25 months;and ③Y3 = -833. 339 + 63. 772x - 1. 019x2 ;used for animals aged 25 to 37 months. 相似文献
58.
59.
Effect of dasatinib in a xenograft mouse model of canine histiocytic sarcoma and in vitro expression status of its potential target EPHA2
下载免费PDF全文
![点击此处可从《Journal of veterinary pharmacology and therapeutics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
K. Ito R. Miyamoto H. Tani S. Kurita M. Kobayashi K. Tamura M. Bonkobara 《Journal of veterinary pharmacology and therapeutics》2018,41(1):e45-e48
Canine histiocytic sarcoma (HS) is an aggressive and highly metastatic tumor. Previously, the kinase inhibitor dasatinib was shown to have potent growth inhibitory activity against HS cells in vitro, possibly via targeting the EPHA2 receptor. Here, the in vivo effect of dasatinib in HS cells was investigated using a xenograft mouse model. Moreover, the expression status of EPHA2 was examined in six HS cell lines, ranging from insensitive to highly sensitive to dasatinib. In the HS xenograft mouse model, dasatinib significantly suppressed tumor growth, as illustrated by a decrease in mitotic and Ki67 indices and an increase in apoptotic index in tumor tissues. On Western blot analysis, EPHA2 was only weakly detected in all HS cell lines, regardless of sensitivity to dasatinib. Dasatinib likely results in the inhibition of xenograft tumor growth via a mechanism other than targeting EPHA2. The findings of this study suggest that dasatinib is a targeted therapy drug worthy of further exploration for the treatment of canine HS. 相似文献
60.
The construction and application of a population physiologically based pharmacokinetic model for methadone in Beagles and Greyhounds
下载免费PDF全文
![点击此处可从《Journal of veterinary pharmacology and therapeutics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Trevor Elwell‐Cuddy Miao Li Butch KuKanich Zhoumeng Lin 《Journal of veterinary pharmacology and therapeutics》2018,41(5):670-683
Methadone is an opioid analgesic in veterinary and human medicine. To help develop appropriate pain management practices and to develop a quantitative model for predicting methadone dosimetry, a flow‐limited multiroute physiologically based pharmacokinetic (PBPK) model for methadone in dogs constructed with Berkeley Madonna? was developed. The model accounts for intravenous (IV), subcutaneous (SC), and oral administrations, and compartmentalizes the body into different components. This model was calibrated from plasma pharmacokinetic data after IV administration of methadone in Beagles and Greyhounds. The calibrated model was evaluated with independent data in both breeds of dogs. One advantage of this model is that most physiological parameter values for Greyhounds were taken directly from the original literature. The developed model simulates available pharmacokinetic data for plasma concentrations well for both breeds. After conducting regression analysis, all simulated datasets produced an R 2 > 0.80 when compared to the measured plasma concentrations. Comparative analysis of the dosimetry of methadone between the breeds suggested that Greyhounds had ~50% lower 24‐hr area under the curve (AUC) of plasma or brain concentrations than in Beagles. Furthermore, population analysis was conducted with this study. This model can be used to predict methadone concentrations in multiple dog breeds using breed‐specific parameters. 相似文献