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   366篇
  免费   36篇
林业   18篇
农学   10篇
  76篇
综合类   34篇
农作物   32篇
水产渔业   17篇
畜牧兽医   186篇
园艺   4篇
植物保护   25篇
  2023年   4篇
  2022年   11篇
  2021年   12篇
  2020年   8篇
  2019年   13篇
  2018年   23篇
  2017年   15篇
  2016年   14篇
  2015年   9篇
  2014年   26篇
  2013年   21篇
  2012年   24篇
  2011年   26篇
  2010年   10篇
  2009年   9篇
  2008年   23篇
  2007年   19篇
  2006年   14篇
  2005年   14篇
  2004年   12篇
  2003年   8篇
  2002年   7篇
  2001年   6篇
  2000年   6篇
  1999年   4篇
  1997年   3篇
  1996年   3篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1984年   6篇
  1983年   3篇
  1981年   2篇
  1979年   3篇
  1976年   1篇
  1975年   4篇
  1974年   3篇
  1973年   3篇
  1972年   2篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1959年   2篇
  1958年   2篇
  1938年   1篇
  1933年   2篇
  1868年   1篇
  1866年   1篇
  1861年   1篇
排序方式: 共有402条查询结果,搜索用时 0 毫秒
21.
Radiotherapy with or without surgery is a common choice for brain tumors in dogs. Although numerous studies have evaluated use of three‐dimensional conformal radiotherapy, reports of definitive‐intent, IMRT for canine intracranial tumors are lacking. Intensity‐modulated radiation therapy has the benefit of decreasing dose to nearby organs at risk and may aid in reducing toxicity. However, increasing dose conformity with IMRT calls for accurate target delineation and daily patient positioning, in order to decrease the risk of a geographic miss. To determine survival outcome and toxicity, we performed a multi‐institutional retrospective observational study evaluating dogs with brain tumors treated with IMRT. Fifty‐two dogs treated with fractionated, definitive‐intent IMRT at four academic radiotherapy facilities were included. All dogs presented with neurologic signs and were diagnosed via MRI. Presumed radiological diagnoses included 37 meningiomas, 12 gliomas, and one peripheral nerve sheath tumor. One dog had two presumed meningiomas and one dog had either a glioma or meningioma. All dogs were treated in the macroscopic disease setting and were prescribed a total dose of 45‐50 Gy (2.25‐2.5 Gy per fraction in 18‐20 daily fractions). Median survival time for all patients, including seven cases treated with a second course of therapy was 18.1 months (95% confidence of interval 12.3‐26.6 months). As previously described for brain tumors, increasing severity of neurologic signs at diagnosis was associated with a worse outcome. Intensity‐modulated radiation therapy was well tolerated with few reported acute, acute delayed, or late side effects.  相似文献   
22.
Mussels close their shell as a protective strategy and the quantification of this behavioral marker may represent an alarm signal when they are exposed to environmental stressors. In the present study, we investigated the ability of the Mediterranean mussel Mytilus galloprovincialis to recover and then the resilience or inertia of valve activity after a pulsing exposition to diverse levels of salinity (5, 10, 20, and 35 PSU as reference value). The trial simulated an event of drastic and sudden reduction of seawater salinity thus mimicking an event of flash flood from intense rain. Valve gaping and movements were measured in continuous cycle for 10 days using a customized magneto-electric device which uses Hall sensors. Results showed that under normal conditions of salinity (35 PSU), the general pattern of valve movements was a continuously open state with sporadic spikes indicating a closing motion. At salinity of 5, PSU mussels reacted by closing their valves, leading to a 77% mortality on the 4th day. At salinity of 10, PSU animals were observed with closed valves for the entire duration of the exposure and no mortality occurred, they showed a significant reduction in the valve activity once the reference value of salinity was re-established. In contrast, salinity of 20 PSU did not trigger a significant behavioral response. Interestingly, there no define rhythms of valve movements were recorded during salinity challenges.  相似文献   
23.
Salmonella hold considerable promise as vaccine delivery vectors for heterologous antigens in chickens. Such vaccines have the potential additional benefit of also controlling Salmonella infection in immunized birds. As a way of selecting attenuated strains with optimal immunogenic potential as antigen delivery vectors, this study screened 20 novel Salmonella Typhimurium vaccine strains, differing in mutations associated with delayed antigen synthesis and delayed attenuation, for their efficacy in controlling colonization by virulent Salmonella Typhimurium, as well as for their persistence in the intestine and the spleen. Marked differences were observed between strains in these characteristics, which provide the basis for selection for further study as vaccine vectors.  相似文献   
24.
25.
An obscure sesquiterpene, rotundone, has been identified as a hitherto unrecognized important aroma impact compound with a strong spicy, peppercorn aroma. Excellent correlations were observed between the concentration of rotundone and the mean 'black pepper' aroma intensity rated by sensory panels for both grape and wine samples, indicating that rotundone is a major contributor to peppery characters in Shiraz grapes and wine (and to a lesser extent in wine of other varieties). Approximately 80% of a sensory panel were very sensitive to the aroma of rotundone (aroma detection threshold levels of 16 ng/L in red wine and 8 ng/L in water). Above these concentrations, these panelists described the spiked samples as more 'peppery' and 'spicy'. However, approximately 20% of panelists could not detect this compound at the highest concentration tested (4000 ng/L), even in water. Thus, the sensory experiences of two consumers enjoying the same glass of Shiraz wine might be very different. Rotundone was found in much higher amounts in other common herbs and spices, especially black and white peppercorns, where it was present at approximately 10000 times the level found in very 'peppery' wine. Rotundone is the first compound found in black or white peppercorns that has a distinctive peppery aroma. Rotundone has an odor activity value in pepper on the order of 50000-250000 and is, on this criterion, by far the most powerful aroma compound yet found in that most important spice.  相似文献   
26.
Summary Somatic embryos of genotype R11 of the alfalfa variety Pampeana were produced from embryogenic calli derived from leaf sections. They were induced by an auxin shock and its development was attempted on six different media. The best condition for somatic embryo production was inducing callus on MS medium plus 10 M 2,4-D and 4,6 M KIN and transferring them, after the auxin shock, to MS with 10–20 mM NH4 + and 30 mM proline. More than 500 somatic embryos per plate were produced. Embryos were grown to plants on MS or half strength MS media and all regenerated plants resembled the original R11 genotype. This technique could be useful in alfalfa Pampeana improvement using genetic modification.  相似文献   
27.
S. berthaulltii Hawkes, a wild potato species, possesses two types of glandular trichomes on its leaf surface: types A and B wich confer resistance to insects. Preliminary results indicated that the presence of glandular trichomes also confers resistance to Phytophthora infestans, the causal agent of late blight. In this paper we report the evaluation of trichome characteristics (density and exudate activities) performed on 8 lines of potato, including the control varieties Desirée and Tropicana, 5 hybrid lines derived from intercrosses and backcrosses between S. tuberosum and S. berthaultii and one accession of S. berthaultii. Whole plants of the 8 genotypes were inoculated with a spore suspension of Phytophthora infestans in order to evaluate their resistance to late blight. The resultant disease incidence correlated negatively with type A trichome density and with polyphenol-oxidase (PPO) activity of type A trichome glands. The removal of type B trichomes exudate by leaf dipping in ethanol did not influence the disease development after artificial inoculation of detached leaves. Type B trichome exudate was extracted and the fraction corresponding to Fatty Acids Sucrose Esters (FASE) was recovered after Thin Layer Chromatography and tested on the fungal mycelium in vitro. The FASE exhibited a slight inhibitory effect on mycelium growth. The results of the experiments are discussed, and several hypotheses regarding the possible role of types A and B trichomes are formulated. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
28.
Brassica oleracea L. is an important species that originated in the eastern Mediterranean area. From there, B. oleracea L. subsp. capitata (L.) DC. convar. botrytis (L.) Alef. var. italica Plenck (broccoli) was introduced into Italy where considerable diversification took place. Several landraces of broccoli, which are highly appreciated by local people for their organoleptic traits, are presently cultivated in both large fields and home gardens. In this study, 10 landraces, 4 synthetics derived from landraces and 4 of the most used F1 hybrids were characterised for morpho-physiological and molecular traits with the principal aim of feeding information into the landrace protection schemes being developed in Italy and into breeding programs. The landraces and derived synthetics are well differentiated from each other and from the F1 hybrids for important agronomic and genetic traits. The principal component analysis based on analysis of morpho-physiological traits showed that overall the 2 main components accounted for 67.74 % of the total variation. The neighbour joining tree, based on 23 microsatellite markers, grouped accessions into 2 main clusters. One includes one synthetic variety and 2 F1 hybrids, while the other cluster includes all the other accessions. There were also several sub clusters. Most of the materials examined showed within-accession diversity. The information gathered in this study can be used to protect landraces through the schemes presently being developed in Italy and to register them in the European common catalogue of “conservation varieties”. In situ (on-farm) conservation of landrace diversity is discussed with reference to landrace use.  相似文献   
29.
Phaseolus vulgaris L. is an important species that originated in Mesoamerica. A Mesoamerican and an Andean gene pool are usually distinguished in the domesticated forms. Many bean landraces are still cultivated in Italy and the Department of Applied Biology maintains an ex situ collection of 146 landraces. Although protection schemes are being developed in Italy, most landraces are extinct or at risk of extinction. To facilitate their conservation and use, geographical, morphological, biochemical and molecular (SSR) data were collected and analysed to estimate the diversity and the genetic structure of the collection. Data confirmed that both the Mesoamerican and the Andean gene pools were introduced in Italy and, although a distinction between the two gene pools exists, the Italian landrace diversity is clearly structured in three clusters that are not simply ascribable to the original gene pools. The observed structure appears also to be due to adaptation to the different environmental conditions determined by altitude. This was confirmed by assessing the presence of selective effects for some of the SSR used in this study. Finally, a certain extent of admixture in Italian landrace diversity suggests past (or recurring) hybridisation events among gene pools. The combined use of morphological, biochemical and molecular data clearly distinguished almost all the landraces. The data gathered here can assist landrace in situ protection schemes that are being developed in Italy, be used to register landraces in the European common catalogue of ‘conservation varieties’ for seed commercialisation and contribute to a better use of Italian common bean diversity in breeding for organic and conventional production systems.  相似文献   
30.
Herbage feeding with only little input of concentrates plays an important role in milk production in grassland dominated countries like Switzerland. The objective was to investigate the effects of a solely herbage‐based diet and level of milk production on performance, and variables related to the metabolic, endocrine and inflammatory status to estimate the stress imposed on dairy cows. Twenty‐five multiparous Holstein cows were divided into a control (C+, = 13) and a treatment group (C?, = 12), according to their previous lactation yield (4679–10 808 kg) from week 3 ante partum until week 8 post‐partum (p.p.). While C+ received fresh herbage plus additional concentrate, no concentrate was fed to C? throughout the experiment. Within C+ and C?, the median of the preceding lactation yields (7752 kg) was used to split cows into a high (HYC+, HYC?)‐ and low‐yielding (LYC+, LYC?) groups. Throughout the study, HYC+ had a higher milk yield (35.9 kg/d) compared to the other subgroups (27.2–31.7 kg/d, p < 0.05). Plasma glucose (3.51 vs. 3.72 mmol/l) and IGF‐1 (66.0 vs. 78.9ng/mL) concentrations were lower in HYC?/LYC? compared to HYC+/LYC+ cows (p < 0.05). Plasma FFA and BHBA concentrations were dramatically elevated in HYC? (1.1 and 1.6 mmol/l) compared to all other subgroups (mean values: 0.5 and 0.6 mmol/l, p < 0.05). Saliva cortisol, plasma concentrations of serum amyloid A (SAA), haptoglobin (Hp), beta‐endorphin (BE) and activity of alkaline phosphatase (AP) were not different between C+ and C?. In conclusion, herbage‐fed high‐yielding cows without supplementary concentrate experienced a high metabolic load resulting in a reduced performance compared to cows of similar potential fed accordingly. Low‐yielding cows performed well without concentrate supplementation. Interestingly, the selected markers for inflammation and stress such as cortisol, Hp, SAA, BE and AP gave no indication for the metabolic load being translated into compromised well‐being.  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