全文获取类型
收费全文 | 999篇 |
免费 | 89篇 |
国内免费 | 1篇 |
专业分类
林业 | 58篇 |
农学 | 26篇 |
基础科学 | 5篇 |
109篇 | |
综合类 | 187篇 |
农作物 | 51篇 |
水产渔业 | 54篇 |
畜牧兽医 | 542篇 |
园艺 | 11篇 |
植物保护 | 46篇 |
出版年
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 22篇 |
2013年 | 42篇 |
2012年 | 32篇 |
2011年 | 46篇 |
2010年 | 30篇 |
2009年 | 26篇 |
2008年 | 36篇 |
2007年 | 39篇 |
2006年 | 32篇 |
2005年 | 28篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 26篇 |
2001年 | 14篇 |
2000年 | 25篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 19篇 |
1990年 | 26篇 |
1989年 | 26篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 19篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 14篇 |
1972年 | 15篇 |
1969年 | 7篇 |
1967年 | 7篇 |
排序方式: 共有1089条查询结果,搜索用时 31 毫秒
41.
42.
There is an urgent need to standardize the methods used to assess the growth of multipurpose trees. Most of the standard methods so far described have been developed specifically for use in multilocational trial networks. This paper was prepared for the F/FRED/ICRAF Workshop on MPTS Assessment Methods, held in Thailand in May 1991 to develop internationally-recognised standards for assessment methodology. It critically reviews the methods prescribed by different networks for height and diameter measurement, and for biomass estimation, giving researchers a range of methodological options to consider and re-emphasizing the need, all too often neglected, to define assessment methods clearly and unambiguously. 相似文献
43.
P. J. Baldwin H. T. L. Stewart P. R. Bird W. I. Hamer D. W. Flinn K. N. Cumming D. J. Connor 《Agroforestry Systems》1988,6(1):213-233
From 1983 to 1985, a network of agroforestry research trials was established at six localities throughout Victoria. This paper describes experimental designs and establishment procedures used at the trial sites. The overall aim of the research program is to provide definitive information on the costs and benefits of a wide range of agroforestry combinations. Accordingly, trials were established at the following locations to test a total of 93 tree species grown in combination with specific types of agriculture:
- Carngham (near Ballarat) — sheep grazing andPinus radiata D. Don (radiata pine);
- Hamilton (several sites) — sheep grazing and mixed tree species;
- Kyabram — irrigated pastures andEucalyptus grandis W. Hill ex Maiden (flooded gum);
- Rutherglen — cereal cropping and shelterbelts;
- Myrtleford — irrigatedMentha spp. (mint) and two clones ofPopulus spp. (poplar); and
- Neerim South (near Warragul) — cattle grazing and mixed tree species.
44.
It is predicted that dryland salinity will affect up to 17 Mha of the Australian landscape by 2050, and therefore, monitoring the health of tree plantings and remnant native vegetation in saline areas is increasingly important. Casuarina glauca Sieber ex Spreng. has considerable salinity tolerance and is commonly planted in areas with a shallow, saline water table. To evaluate the potential of using the nitrogenous composition of xylem sap to assess salinity stress in C. glauca, the responses of trees grown with various soil salinities in a greenhouse were compared with those of trees growing in field plots with different water table depths and groundwater salinities. In the greenhouse, increasing soil salinity led to increased allocation of nitrogen (N) to proline and arginine in both stem and root xylem sap, with coincident decreases in citrulline and asparagine. Although the field plots were ranked as increasingly saline-based on ground water salinity and depth-only the allocation of N to citrulline differed significantly between the field plots. Within each plot, temporal variation in the composition of the xylem sap was related to rainfall, rainfall infiltration and soil salinity. Periods of low rainfall and infiltration and higher soil salinity corresponded with increased allocation of N to proline and arginine in the xylem sap. The allocation of N to citrulline and asparagine increased following rainfall events where rain was calculated to have infiltrated sufficiently to decrease soil salinity. The relationship between nitrogenous composition of the xylem sap of C. glauca and soil salinity indicates that the analysis of xylem sap is an effective method for assessing changes in salinity stress in trees at a particular site over time. However, the composition of the xylem sap proved less useful as a comparative index of salinity stress in trees growing at different sites. 相似文献
45.
46.
47.
Vocalizations During Electroejaculation in Anaesthetized Adult and Young Pampas Deer (Ozotoceros bezoarticus) Males
下载免费PDF全文
![点击此处可从《Reproduction in domestic animals》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The aim of this study was to characterize the vocalizations produced during electroejaculation under general anaesthesia in pampas deer males and to determine whether the characteristics of those vocalizations differ in adult and young pampas deer males. Electroejaculation was applied to 13 adults (AM) and 13 young (YM) males under general anaesthesia. Vocalizations were digitally recorded, and the number and duration of vocalizations, the latency in relation to each voltage, the total time vocalizing, and the structure of the fundamental frequency (F0) [initial frequency (Fstart), maximal frequency (Fmax), minimal frequency (Fmin) and final frequency (Fend)] were analysed. No male vocalized with 0 V; the number of animals that vocalized increased at 2 and 3 V and increased again at 4, 5 and 6 V (p < 0.05). The latency time from the beginning of each series (each voltage) decreased until 4 V (p < 0.01). The number of vocalizations/voltage increased from 4 V (p < 0.05). The length of each vocalization and the total time during which animals vocalized were greater in YM than AM (p = 0.02 and p = 0.01, respectively). Similarly, the fundamental frequencies were higher in YM than AM (p ≤ 0.05). Overall, we concluded that the vocalizations emitted during electroejaculation in pampas deer under general anaesthesia are related to the voltage applied during the process. Young males vocalize more time, probably due to a greater sensibility to the electric stimulation. The differences in the characteristics of the vocalizations between adult and young males may be related to the anatomic differences in the neck of adult or young males. 相似文献
48.
C. J. Bodaan L. Panizzi A. J. Stewart E. Cypher L. Whitfield C. B. Riley 《Equine Veterinary Education》2014,26(7):341-344
A 5‐month‐old Warmblood cross colt was presented with focal swelling of the ventral abdomen extending from the umbilicus to the scrotum in the absence of colic signs. Palpation and ultrasound examination revealed the presence of incarcerated large intestine within the subcutaneous space adjacent to the caudal ventral abdomen and prepuce. Surgery was performed and revealed that the umbilical hernia sac had ruptured, and confirmed that the left dorsal and ventral colon were present in the subcutaneous space. The mild degree of vascular compromise of the large colon did not necessitate resection and so it was replaced within the abdomen. The abdominal wall defect was closed and the subcutaneous dead space was reduced by using a walking suture pattern. Herniation of the large colon through the umbilicus with dissection through the subcutaneous tissues of the ventral abdominal wall and prepuce has not been previously reported in foals. Ultrasonography permits differentiation of herniated small intestine from large intestine. 相似文献
49.
While stocking floodplain depressions or beels with fingerlings is a common form of fisheries management in Bangladesh, bio‐economic guidance for improving the outcome of stocking strategies is sparse. The Community‐Based Fisheries Management (CBFM) Project, funded by the Ford Foundation and the UK Government's Department for International Development (DfID) promoted stocking practices in beels throughout the country as a means to improve fisher livelihoods. This paper describes an empirical bio‐economic model developed using data generated under the CBFM project. The model offers guidance on selecting stocking densities depending upon the available size (length) of fingerlings to maximize profit and return on investment while minimizing risk. Because large fingerlings are relatively inexpensive and have lower rates of natural mortality, the model predicts that it is more profitable to stock large fingerlings at low densities than small fingerlings at high densities. These general recommendations were found to be largely insensitive to the market price for harvested fish. To minimize credit burden and financial risk, minimum stocking densities should be selected according to the length of fish available that maximizes profit. Because of its empirical nature, the model recommendations may not be applicable beyond the project sites. Furthermore, it is recommended that attempts be made to field test the model predictions before widespread adoption or promotion. 相似文献
50.
The Effects of a Land Drainage Scheme on the Salmonid Populations of the River Camowen, Co. Tyrone 总被引:1,自引:0,他引:1
Annual electro fishing surveys were carried out over an 11-year period at five sites on an upland river, which was subject to dredging operations in connection with a land drainage scheme. Four of the sites were dredged 3 years after the start of the survey and one control site remained undredged throughout. The results indicated that dredging operations initially reduced Salmonid densities and that there was subsequently a progressive downstream recovery, with fry densities taking up to 6 years to improve at the most downstream site. Yearling and older fish recovered to pre-drainage scheme levels more rapidly than fry. Changes in population structure were also observed at three of the dredged sites. Two sites were considerably deepened and finally contained larger numbers of older fish than prior to the drainage scheme. The opposite effect was found to have taken place at a site, which became shallower as a result of drainage works, and contained larger numbers of fry at the end of the survey. Increased fish growth rates were also observed at all sites over the experimental period, and this may have been correlated with enrichment of the river system by leaching from increased fertilizer usage within the catchments. 相似文献