首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   167篇
  免费   5篇
  国内免费   1篇
林业   4篇
农学   2篇
基础科学   7篇
  25篇
综合类   33篇
农作物   2篇
水产渔业   11篇
畜牧兽医   72篇
园艺   3篇
植物保护   14篇
  2023年   3篇
  2020年   3篇
  2019年   6篇
  2018年   5篇
  2017年   1篇
  2016年   1篇
  2015年   2篇
  2014年   3篇
  2013年   6篇
  2012年   6篇
  2011年   11篇
  2010年   4篇
  2009年   2篇
  2008年   9篇
  2007年   9篇
  2006年   13篇
  2005年   5篇
  2004年   4篇
  2003年   11篇
  2002年   3篇
  2001年   2篇
  2000年   1篇
  1999年   6篇
  1998年   2篇
  1997年   3篇
  1996年   1篇
  1995年   5篇
  1994年   1篇
  1993年   4篇
  1992年   3篇
  1991年   4篇
  1990年   1篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   4篇
  1985年   3篇
  1983年   3篇
  1982年   1篇
  1981年   3篇
  1978年   1篇
  1977年   2篇
  1975年   1篇
  1974年   2篇
  1973年   1篇
  1972年   1篇
  1971年   2篇
  1970年   1篇
  1969年   1篇
  1967年   1篇
排序方式: 共有173条查询结果,搜索用时 0 毫秒
31.
A 6-year-old female Alaska Malamute dog was presented for evaluation of abdominal enlargement referred by a local veterinarian. On the history, the owner complained of chronic abdominal enlargement initiated more than 4 months ago, reduced appetite, occasional vomiting and general dullness. He also complained of greenish mucous intermittent vaginal discharge starting 10 days ago. The bitch was chronically treated with medroxiprogesterone acetate. A laparatomy was performed and fluid in the abdomen was found and aspirated during the surgery. Also a very fluid-filled distended uterus and a mass in the distal part of the left uterine horn were found. The mass was encapsulated by the omentum, but areas of necrosis and calcification were identified. Histopathological diagnosis was endometrial adenocarcinoma.  相似文献   
32.
Estuarine habitats provide rearing opportunities for the juvenile life stage of anadromous fishes. Because survival is positively correlated with juvenile performance, these estuarine habitats play an important role in population abundance and productivity. To provide information for the recovery of several depressed stocks of Chinook salmon in the Columbia River Basin, we sought to identify the factors that explain variability in performance. Using otolith‐derived estimates of juvenile somatic growth rate as an index of recent performance, we observed a negative nonlinear relationship between growth rate and day of year, and a decreasing and increasing trend of growth rate over the 8 years of this study and distance from the river mouth respectively. Using a generalised linear modelling approach, we found that variability in juvenile somatic growth rate was best explained by where and when individuals were collected, their body size, contaminant loads, stock of origin, and whether a fish was hatchery produced or unmarked. Lastly, we argue that a considerable improvement to the growth rate of juveniles in estuarine habitats is physiologically possible. The results of this 8‐year study provide a baseline of the performance of juvenile Chinook salmon to evaluate habitat restoration programs and to compare against future anthropogenic conditions.  相似文献   
33.
While much is known about the metabolism of exogenous nutrients such as glucose, lactate, pyruvate, amino acids by oocytes and pre-implantation mammalian embryos, the role of endogenous stores, particularly lipid, has been largely overlooked. The presence of lipid within oocytes and early embryos has been long known, and comparisons between species indicate that the amounts and types of lipid present vary considerably. Large amounts of intracellular lipid can compromise the success of cryopreservation and the removal of such lipid has been the subject of considerable effort. In this review, we present evidence that strongly suggests a metabolic role for lipid, specifically with regard to energy provision, in the late-stage oocyte and the pre-implantation embryo. We focus initially on oxygen consumption as a global indicator of metabolic activity, before reviewing different approaches that either have been designed to investigate directly, or have revealed indirectly the role of endogenous lipid in energy generation. These fall under five headings: (i) fatty acid oxidation; (ii) inhibition of triglyceride oxidation; (iii) culture in the absence of exogenous substrates; (iv) cytoplasmic organization; and (v) delipidation. On the basis of the data derived from these studies, we conclude that there is strong evidence for the utilization of endogenous lipid as an energy substrate by oocytes and early embryos.  相似文献   
34.
Amprolium, a coccidiostat added to poultry feed, occurs in excreta at concentrations of 204 μ g?1 and investigations were made of the effect of this quantity of amprolium on the biochemistry of soil to which manure had been applied.Greenhouse experiments showed that 0.8 μg g?1 amprolium was found in soil pots 80 days after treatment with manure at the equivalent of 56.1 t ha?1 and was detectable 20 days following treatment at the equivalent of 11.2 t ha?1.Laboratory experiments indicated that amprolium was differentially adsorbed to two complexing media, soil and manure. Since amprolium was a constituent of treated manure, it was expected that the amprolium manure-soil system would offer various sites for adsorption of amprolium. Mixing amprolium with soil and with soil plus untreated manure yielded approximately the same effect on amprolium adsorption based on recoveries in water solution, and as methanol extractable. However, total recovery of amprolium from treated manure added to soil was only a fraction of the above, indicating the high complexing capacity of the manure.No effect on soil respiration was observed by either pure amprolium or amprolium as a constituent of treated manure. The higher rate of manure application caused greater respiration due to the presence of more readily oxidizable organic matter, but the respiration pattern attributed to the manure component was not unlike the respiration pattern of the Guelph loam soil.  相似文献   
35.
36.
1. A steady state model of heat production and loss in crated broiler chickens is presented. 2. The model is based on physiological factors and uses experimental data from various sources. 3. Although many of the required parameters are not well defined at present, the model allows a better understanding of the processes which lead to hyperthermic stress in crated broiler chickens, and is relevant to the design of ventilation systems for poultry transporters.  相似文献   
37.
Contrary to the prediction of the Z-scheme model of photosynthesis, experiments demonstrated that mutants of Chlamydomonas containing photosystem II (PSII) but lacking photosystem I (PSI) can grow photoautotrophically with O2 evolution, using atmospheric CO2 as the sole carbon source. Autotrophic photosynthesis by PSI-deficient mutants was stable both under anaerobic conditions and in air (21 percent O2) at an actinic intensity of 200 microeinsteins per square meter per second. This PSII photosynthesis, which was sufficient to support cell development and mobility, may also occur in wild-type green algae and higher plants. The mutants can survive under 2000 microeinsteins per square meter per second with air, although they have less resistance to photoinhibition.  相似文献   
38.
Objective To assess the innate resistance of naive Bos taurus, Bos taurus cross Bos indicus and Bos indicus cattle to virulent Babesia bovis, B bigemina and Anaplasma marginale parasites. Design Groups of 10, pure B indicus, fi B indicus cross,/B indicus cross and pure B taurus steers were infected with virulent B bovis, B bigemina and A marginale parasites. Procedure Sequential infections were carried out by intravenous inoculation of infected blood containing 1 times 108 parasites of B bovis, followed by B bigemina and then A marginale. To assess resistance, measurements were made of parasitaemia, rectal temperature, packed cell volume and the number within a group requiring chemotherapy to control infection. There was a recovery period between each infection. Results Infection with B bovis showed that pure B indicus steers were significantly more resistant to B bovis infection than the other groups, with none of this group requiring treatment. There was no significant difference between fi B indicus cross and/B indicus cross with 30% and 20%, respectively, of steers in these groups requiring treatment. The pure B taurus steers were significantly more affected then those in the other three groups with 80% requiring treatment. Infections of B bigemina produced a mild response in comparison to that of B bovis and none of the steers required treatment. However, the pure B taurus group was significantly more affected than the other three groups for all other measurements. After the A marginale infection, B indicus steers were moderately affected with 50% requiring treatment, whereas 70% of the fi B indicus group, 80% of the /B indicus cross group and 100% of the pure B taurus group required treatment. Conclusions All breeds of cattle, ranging from pure B indicus to pure B taurus may be at risk of severe disease if exposed to virulent A marginale. The results confirm that pure B indicus cattle are relatively resistant to B bovis, but there could be a significant risk of severe mortalities if cross-bred herds are exposed to virulent infection.  相似文献   
39.
SUMMARY: A survey by mail was used to determine the views of beef producers in the Boophilus microplus endemic area of Queensland on the control of and vaccination against tick fever. Data from 448 questionnaires were analysed, representing 2.7% of beef producers in the survey area. Producers considered buffalo fly ( Haematobia irritans exigua ) infestation as the most important problem whereas tick fever ranked sixth overall. Private veterinarians were regarded as the most important source of information on vaccines for cattle followed by a weekly rural newspaper. From the survey we estimate that about 33% of producers used the tick fever vaccine produced by the Tick Fever Research Centre of Queensland Department of Primary Industries but there were significant (P < 0.05) variations between regions and herds. Large herds (≥ 400 head) in south-east Queensland were the most likely to be vaccinated against tick fever. Of the producers who did not use the vaccine, over 70% replied that there was no need to vaccinate because of the low risk of the disease in their herds. In 52% of unvaccinated herds the treatment of animals with acaricide was considered the most important means of tick fever control and 61% of these herds comprised Bos indicus x Bos taurus or Bos indicus cattle.  相似文献   
40.
ABS制动工况台架测试模拟   总被引:4,自引:1,他引:3  
汽车制动防抱死系统(ABS)台架测试需要模拟ABS工作所需的运行工况,研究了ABS制动工况台架测试模拟方法,设计了工况模拟及设定的人机界面,根据不同路况和不同车速下的实际制动工况轮速曲线,构造出ABS台架测试所需的轮速模拟工况.通过轮速信号再现装置驱动伺服电动机带动齿圈旋转以生成设定的轮速信号,为ABS在各种工况下的台架模拟测试提供了必要的运行环境.ABS台架测试系统的运行表明,再现的轮速信号适用于ABS台架测试,所生成的模拟工况满足ABS台架性能测试和强化试验的要求.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号