全文获取类型
收费全文 | 763篇 |
免费 | 37篇 |
国内免费 | 4篇 |
专业分类
林业 | 37篇 |
农学 | 19篇 |
基础科学 | 20篇 |
99篇 | |
综合类 | 138篇 |
农作物 | 24篇 |
水产渔业 | 46篇 |
畜牧兽医 | 375篇 |
园艺 | 14篇 |
植物保护 | 32篇 |
出版年
2023年 | 6篇 |
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 40篇 |
2012年 | 38篇 |
2011年 | 35篇 |
2010年 | 25篇 |
2009年 | 21篇 |
2008年 | 26篇 |
2007年 | 35篇 |
2006年 | 22篇 |
2005年 | 25篇 |
2004年 | 30篇 |
2003年 | 33篇 |
2002年 | 40篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 17篇 |
1998年 | 8篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 28篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1979年 | 6篇 |
1977年 | 9篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 6篇 |
1969年 | 4篇 |
1968年 | 5篇 |
1967年 | 6篇 |
排序方式: 共有804条查询结果,搜索用时 15 毫秒
131.
132.
M. Igshaan Samuels Nicky Allsopp M. Timm Hoffman 《Strength and Conditioning Journal》2019,72(1):195-203
Pastoral systems are regarded as complex social-ecological systems with components that interact and change over a range of spatial and temporal scales. As such, herd mobility has traditionally been used to respond to the dynamic nature of these systems. However, mobile pastoral systems around the world are becoming more constrained and increasingly fragmented with important implications for herd mobility. This study assessed the spatial distribution of 256 herds and their mobility patterns over a decade in the 10 villages that comprise the spatially constrained Leliefontein pastoral area in South Africa. We developed a hierarchical model of rangeland use, which showed that several stratified and connected socioeconomic, climatic, and environmental factors determined the spatial and temporal use of grazing areas in this 192 000-ha semiarid environment. At the highest level of use, access to the Leliefontein pastoral area is formally regulated. At the next level, the place of residence of herd owners largely defined which village commons was used by their livestock. At the third level of rangeland use, the wealth status of owners determined where in relation to human settlements their herds were located. At the lowest level in the hierarchy, the locations of water and croplands delineated seasonal grazing areas and the movement of stockposts. These stratified factors, together with the overall variability in grazing resource availability and the different decision making processes involved, resulted in high flexibility and diversity of herd mobility patterns at the lowest level of rangeland use. This, in turn, ensured heterogeneity in resource use over a range of spatial and temporal scales. It was concluded that policies should embrace the complexity of the pastoral system and enable the adaptive management of herds. This could reduce the level of vulnerability experienced by pastoralists to climate variability and wider societal change. 相似文献
133.
1引言玉米酒糟副产品已越来越常见,这也促使畜牧生产商不断的投诸于这种饲料。依阿华肉牛研究中心发现:在依阿华州,较饲育场其它生产商相比,牛犊饲养人员较少的利用这一饲料资源。而由Leopold可持续农业发展中心基金赞助的一项维期三年的试验项目正是旨在研究评价不同的饲喂生产雌性肉牛牛犊的方案。(注:此报告为第一年的研究结果。) 相似文献
134.
135.
Mhairi A. Sutherland Keith Erlandson Joe F. Connor Janeen L. Salak-Johnson Paul Matzat Jerry F. Smith John J. McGlone 《Livestock Science》2008,116(1-3):237-245
Loss of pigs during or after transport is a welfare concern, but also an economic concern for producers. Transport losses include animals that are dead on arrival (DOA) at the plant, pigs that are injured, and pigs which are not obviously injured but unwilling or unable to walk (non-ambulatory, non-injured or NANI). The objective of this research was to assess the health of non-ambulatory, non-injured (NANI) pigs relative to control pigs at the processing plant by looking at a range of measures, including complete blood chemistry, anatomy, and pathology to determine potential factors associated with pigs going down. Data were collected from NANI and control pigs at five plants in the midwest USA. Feet and legs and internal organs were inspected and the severity of the pathology scored. Alveolar macrophages were collected and counted. Blood was collected for analysis of hematology, blood chemistry and cortisol concentrations. Titers to common porcine respiratory viruses were measured in pigs from one plant. Hoof and pad problems did not differ overall between control and NANI pigs, however the percentage of severe foot problems was greater (P < 0.05) in NANI compared with control pigs at plants A and E. The percentage of total ulcers, rhinitis, and empty stomachs differed (P < 0.05) between control and NANI pigs at individual plants, but not overall. Blood hematology and chemistry differed (P < 0.05) between NANI and control pigs. Cortisol concentrations did not differ between NANI and control pigs. Titers to swine influenza virus (SIV) H1N1 and H3N2 and porcine circovirus (PCV) were lower (P < 0.01) among NANI compared with control pigs. However, more (P < 0.01) NANI pigs were positive for SIV H1N1 and H3N2 compared with control pigs. Blood hematology, chemistry, and pathology indicate a large difference between NANI and controls pigs. No single health problem was higher among NANI pigs compared to plant-matched control pigs. Rather, several problems appear to contribute to pigs becoming NANI which may differ from one plant too another. 相似文献
136.
137.
Elizabeth A. Hoffman Turi K. Aarnes Carolina H. Ricco Pereira Phillip Lerche Richard M. Bednarski Mary A. McLoughlin 《Veterinary anaesthesia and analgesia》2018,45(6):754-759
Objective
To determine the effect of oral trazodone on the minimum alveolar concentration (MAC) of isoflurane in dogs.Study design
Prospective blinded, single-observer, randomized crossover experimental study.Animals
Six adult (age 6.8 ± 1.6 months) healthy dogs (three males and three females), weighing 24.8 ± 3.4 kg (mean ± standard deviation).Methods
Each dog was anesthetized twice with a minimum of 7 days between anesthetic episodes. Dogs were randomly assigned to be administered two treatments in a crossover design: premedication with trazodone (8 mg kg?1; TRAZ–ISO) orally 2 hours prior to an anesthetic episode or no (ISO). Dogs were anesthetized with intravenous propofol (6 mg kg?1) and isoflurane in >95% oxygen. Isoflurane MAC was determined using an iterative bracketing technique with electrodes placed in the buccal mucosa. Hemodynamic variables were compared at the lowest end-tidal isoflurane concentration at which each dog did not respond. A paired t test was used to assess the effect of treatment on outcome variables with significance set to a value of p < 0.05.Results
The MAC concentration (mean ± standard deviation) in dogs administered TRAZ–ISO was 0.85 ± 0.17% compared with 1.02 ± 0.11% in those administered ISO (p = 0.01, 95% confidence interval ?0.25 to ?0.05), resulting in a mean MAC reduction of 17 ± 12%. There were no differences in hemodynamic variables between treatments.Conclusions and clinical relevance
Premedication of dogs with oral trazodone (8 mg kg?1) 2 hours prior to anesthetic induction has a significant isoflurane MAC sparing effect with no significant observed hemodynamic benefit. 相似文献138.
Soluble solids comprise most of onion bulb dry mass, and dehydrator onion cultivars are developed from breeding populations
that have high dry mass content. Realized and narrow-sense heritability estimates were obtained for the soluble solids content
(SSC) trait in two open-pollinated dehydrator onion breeding populations (BP) using response to selection and half-sib family
analysis. Parental populations, designated as BP9335-U and BP9243-U, were derived from two-way crosses of lines advanced as
open- pollinated (OP) populations to the F7 or F_6 generation, respectively. BP9335-U had one previous selection cycle for
increased SSC and BP9243-U had three SSC selection cycles. In these experiments, parental populations were screened again
for high SSC, and selected bulbs were intermated to form half-sib progeny groups, designated as BP9335-S and BP9243-S. Mean
SSC was increased by 6.6% and a realized heritability estimate of 0.64 was obtained for BP9335-S. Mean SSC was increased by
6.3% and a realized heritability estimate of 0.36 was obtained for BP9243-S. Narrow-sense heritability estimates of 0.58 ±0.05
and 0.30 ±0.03 were obtained for parental populations BP9335-U and BP9243-U, respectively. Narrow-sense heritability estimates
of 0.40 ± 0.03 and 0.63 ± 0.23 were obtained for progeny populations derived from selected high-SSC bulbs of these lines (BP9335-S
and BP9243-S), respectively, indicating that there is significant additive genetic control of the SSC trait in these populations.
Significant differences in half-sib family performance in the advanced groups BP9335-S and BP9243-S demonstrate that progeny
testing was effective for evaluating phenotypic selections.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
139.
140.