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   99篇
  免费   4篇
林业   7篇
农学   3篇
  20篇
综合类   8篇
农作物   1篇
水产渔业   24篇
畜牧兽医   18篇
园艺   3篇
植物保护   19篇
  2023年   2篇
  2022年   1篇
  2021年   2篇
  2020年   1篇
  2019年   2篇
  2018年   5篇
  2017年   1篇
  2015年   4篇
  2014年   1篇
  2013年   14篇
  2012年   6篇
  2011年   5篇
  2010年   6篇
  2009年   2篇
  2008年   6篇
  2007年   6篇
  2006年   9篇
  2005年   6篇
  2004年   5篇
  2003年   5篇
  2002年   5篇
  2001年   1篇
  2000年   1篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1993年   1篇
  1988年   1篇
  1987年   1篇
  1973年   1篇
排序方式: 共有103条查询结果,搜索用时 31 毫秒
91.
92.
A single nucleotide polymorphism (snp) in the cytochrome b gene confers resistance to strobilurin fungicides in Erysiphe graminis DC fsp tritici Marchal. On the basis of this point mutation three different types of molecular markers have been developed. Cleaved amplified polymorphic sequences and allele-specific PCR were used to score resistant and sensitive isolates from specifically selected regional populations across Europe. The results of molecular tests were in total agreement with the resistance phenotypes revealed by in vivo tests. Serial dilutions of mixed samples (resistant/sensitive) delimited the detection for strobilurin-resistant alleles to a range of 10-50% for both marker classes. Due to these detection limits no mixture of mitochondria within individual isolates was found. Denaturing high performance chromatography was used to increase the detection sensitivity for the mutant allele. Although the detection limit was lowered to 5-10%, there was no evidence for the existence of mixed mitochondrial genotypes.  相似文献   
93.
Scrotal (n = 66), inguinal (n = 7) and abdominal (n = 36) testes from pigs differing in age (from 1 day to 4 years) were collected after slaughtering or by castration, fixed in 4% formalin and examined by light microscopy. The expression of vimentin, desmin, alpha-actin and PCNA was detected by immunohistochemical technique. Histologically no differences between scrotal and cryptorchid testes are obvious during the prepubertal period, until the age of 10-12 weeks, but with the onset of puberty degenerative alterations (Sertoli-cell-only morphology, giant cells) in dystopic testes occur. Additionally the differentiation of the interstitial cells is disturbed in abdominal testes resulting in a deviating expression pattern of alpha-actin. The Sertoli cells show different distribution patterns (basal, perinuclear, apical) of vimentin depending on the position of the testis and the age of the animal.  相似文献   
94.
Experimental forest plantations to study biodiversity–ecosystem functioning (BEF) relationships have recently been established in different regions of the world, but subtropical biomes have not been covered so far. Here, we report about the initial survivorship of 26 tree species in the first such experiment in subtropical China. In the context of the joint Sino–German–Swiss Research Unit “BEF-China,” 271 experimental forest plots were established using 24 naturally occurring tree species and two native commercial conifers. Based on the survival inventories carried out in November 2009 and June 2010, the overall survival rate was 87 % after the first 14 months. Generalized mixed-effects models showed that survival rates of seedlings were significantly affected by species richness, the species’ leaf habit (deciduous or evergreen), species identity, planting date, and altitude. In the first survey, seedling establishment success decreased with increasing richness levels, a tendency that disappeared in the second survey after replanting. Though evergreen species performed less well than deciduous species with establishment rates of 84 versus 93 % in the second survey, their planting success exceeded the general expectation for subtropical broad-leaved evergreen species. These results have important implications for establishing mixed-species plantations for diversity conservation and improvement of ecosystem functioning in the Chinese subtropics and elsewhere. Additional costs associated with mixed-species plantations as compared to conventional plantations also demonstrate the potential of upscaling BEF experiments to large-scale afforestation projects.  相似文献   
95.
Tropical regions have been reported to play a key role in climate dynamics. To date, however, there are uncertainties in the timing and the amplitude of the response of tropical ecosystems to millennial-scale climate change. We present evidence of an asynchrony between terrestrial and marine signals of climate change during Heinrich events preserved in marine sediment cores from the Brazilian continental margin. The inferred time lag of about 1000 to 2000 years is much larger than the ecological response to recent climate change and appears to be related to the nature of hydrological changes.  相似文献   
96.
The changes in egg lipids and fatty acid compositions that occur during embryonic development of spotted wolf‐fish, Anarhichas minor, were examined by monitoring individual egg batches from the time of spawning (egg stripping) until hatching. The lipids, present as 3.7±0.1% of the wet mass of the freshly stripped eggs, contained high percentages of monoenes (monounsaturated fatty acids (MUFAs), ca. 33%) and polyenes (ca. 43%) and approximately 20% saturated fatty acids (SFAs). The fatty acid profiles were dominated by a small number of fatty acids. The major SFA was 16:0 (ca. 14%), the dominant MUFA was 18:1 n‐9 (ca. 21%), and among the polyenes, the n‐3 highly unsaturated fatty acids (HUFAs) 22:6 n‐3 docosahexaenoic acid (DHA) and 20:5 n‐3 eicosapentaenoic acid (EPA) were present in the highest concentrations (EPA, ca. 16%; DHA, ca. 19%). The n‐6 HUFA 20:4 n‐6 arachidonic acid (AA) was present as ca. 1% of the total fatty acids in the freshly stripped eggs. This resulted in an AA:EPA of ca. 0.07, which is lower than reported for eggs of many other fish species. As embryonic development progressed, the percentage contribution of AA to the total fatty acids almost doubled. There were also increases in the relative proportions of SFAs (due mainly to an increase in the percentage of 16:0 to ca. 16% at hatch) and DHA (to ca. 23%), and there was a corresponding decrease in the percentage of MUFAs (mostly brought about by a decrease in the percentage of 18:1 n‐9 to ca. 18% at hatch). The most marked changes occurred towards the end of incubation. The percentage of EPA changed little during incubation. This implies that there was selective retention of DHA, 16:0 and AA, and these fatty acids were probably incorporated into cell membranes. MUFAs, particularly 18:1 n‐9, seem to have been catabolized to provide energy for the developing embryo, and some EPA also seems to have been utilized as an energy source. Survival of eggs to the eyed stage (range ca. 10–80%) and to hatch (ca. 5–75%) was negatively correlated with the %AA, %EPA and AA:DHA of the freshly stripped eggs. There was also a negative correlation between AA:EPA and egg survival, which implies that there is not a universal requirement for a high AA:EPA to ensure high rates of survival of fish eggs.  相似文献   
97.
Atlantic salmon (Salmo salar L.) smolts were exposed to ammonia at 4 °C in an open flow system. The concentrations of un-ionized ammonia nitrogen (NH3-N) and total ammonia nitrogen (TAN) were increased abruptly twice during a period of 28 days. For concentrations in the range 1–15 µgl–1 un-ionized ammonia nitrogen (4.3–21.1 mgl–1 TAN), no effects were observed on the smolts. However, plasma glucose was not measured in this range. The observed results for higher concentrations may be divided into two categories of sublethal effects. (1) In smolts exposed to the concentration range 19–37 µgl–1 NH3-N (average 26 µgl–1 NH3-N; 34.9–50.5 mgl–1 TAN), the mean plasma glucose concentration was 1.3 times the mean of the control group. No other measured parameters were significantly altered. (2) For smolts exposed to 37–65 µgl–1 NH3-N (average 47 µgl–1 NH3-N; 57.7–84.5 mgl–1 TAN), the mean plasma glucose concentration was increased to 2.3 times, the mean plasma chloride level was reduced to 0.9 times, and mean haematocrit was increased to 1.1 times the control values. Histological examination of the gill tissue revealed extensive lamellar hypertrophy. Weight, length, condition factor and ventilation frequency were not significantly affected and no mortality took place during the exposure period (1–65 µgl–1 NH3-N; 4.3–84.5 mgl–1 TAN). Plasma glucose seemed to be the most sensitive parameter in detecting the sublethal stress response, and this investigation may thus demonstrate the importance of measuring plasma glucose in experiments concerning safe levels for ammonia.  相似文献   
98.
99.
Resveratrol, piceatannol, ε-viniferin, r-viniferin, r2-viniferin, and hopeaphenol are naturally occurring polyphenols, associated with potentially beneficial health effects. We developed a rapid liquid chromatography-ultraviolet detection (LC-UV) method, allowing for the simultaneous determination of these six compounds in biological samples in less than 2.5 min with standard LC equipment. Using this method for the assessment of the stability of the six analytes, we demonstrated that all stilbene polyphenols disappear rapidly in Dulbecco's modified Eagle's medium (e.g., half-life of resveratrol of 1 h). In contrast, the tetramer hopeaphenol was stable over the maximum incubation time of 72 h. In incubations with liver microsomes, ε-viniferin was rapidly glucuronidated, although to a lower extent than resveratrol. Hopeaphenol was not glucuronidated at all. Given that glucuronidation is the major metabolic pathway for polyphenols, hopeaphenol might exhibit significantly different pharmacokinetic properties than other polyphenols. When chemical and metabolic stability as well as biological activity of hopeaphenol are taken together, these findings warrant further investigation of this polyphenol.  相似文献   
100.
Marine sediments from the Chilean continental margin are used to infer millennial-scale changes in southeast Pacific surface ocean water properties and Patagonian ice sheet extent since the last glacial period. Our data show a clear "Antarctic" timing of sea surface temperature changes, which appear systematically linked to meridional displacements in sea ice, westerly winds, and the circumpolar current system. Proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore, but reveal a variable glacier-response time of up to approximately 1000 years, which may explain some of the current discrepancies among terrestrial records in southern South America.  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