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   654篇
  免费   30篇
林业   45篇
农学   33篇
基础科学   1篇
  201篇
综合类   43篇
农作物   41篇
水产渔业   50篇
畜牧兽医   191篇
园艺   14篇
植物保护   65篇
  2024年   1篇
  2023年   7篇
  2022年   13篇
  2021年   19篇
  2020年   19篇
  2019年   21篇
  2018年   28篇
  2017年   15篇
  2016年   15篇
  2015年   21篇
  2014年   27篇
  2013年   44篇
  2012年   35篇
  2011年   56篇
  2010年   23篇
  2009年   36篇
  2008年   51篇
  2007年   43篇
  2006年   30篇
  2005年   39篇
  2004年   26篇
  2003年   29篇
  2002年   25篇
  2001年   8篇
  2000年   7篇
  1999年   1篇
  1998年   5篇
  1997年   5篇
  1996年   2篇
  1995年   3篇
  1993年   2篇
  1992年   7篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1986年   3篇
  1985年   1篇
  1983年   6篇
  1981年   2篇
  1980年   1篇
  1977年   1篇
  1972年   1篇
  1955年   1篇
排序方式: 共有684条查询结果,搜索用时 15 毫秒
641.
White lupin (Lupinus albus) and narrow-leafed lupin (L. angustifolius) have special interest as high-protein feed crops but their cultivation is limited by low grain yields. This study aimed to support breeding programs targeting Italy or other climatically variable south-European regions by investigating within-species adaptation patterns across contrasting Italian environments. An additional aim was comparing species for yielding ability. Eight narrow-leafed and six white lupin cultivars featuring different origin, phenological type (Mediterranean in both species; winter in white lupin; spring in narrow-leafed lupin) and plant architecture (determinate or indeterminate in both species; tall or dwarf in white lupin) were evaluated in a Mediterranean and a subcontinental-climate site under autumn and late-winter sowing. Additive main effects and multiplicative interaction was preferable to joint regression for modeling yield responses. In both species, cross-over GE interaction was observed (P < 0.05), autumn-sown Mediterranean and subcontinental environments were the most-contrasting for GE effects, and widely adapted material included cultivars of Mediterranean phenological type with indeterminate growth. Material with determinate growth was not among the best-yielding entries in any environment, whereas a dwarf winter-type white lupin entry was specifically adapted to autumn-sown subcontinental environments. White lupin displayed larger genetic variation than narrow-leafed lupin for phenology and other traits. Relationships of morphophysiological traits with grain yield were environment-specific and were locally high for some white lupin traits (early flowering, long reproductive phase, high aerial biomass, low proportion of pod wall). White lupin exhibited higher yielding ability than narrow-leafed lupin in all environments but the late-winter sown Mediterranean one, when comparing locally top-yielding cultivars.  相似文献   
642.
Porcine epidemic diarrhoea (PED) is a contagious enteric disease of pigs caused by a coronavirus. A double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) based on the use of monoclonal antibodies was developed for the detection of porcine epidemic diarrhoea virus (PEDV). The DAS-ELISA was compared with RT-PCR in the examination of 506 specimens collected during 2006-2007 from pigs originating from different farms located in the Po valley. Both faecal samples obtained directly from the rectum of live animals showing clinical signs and intestinal samples collected from the caecum of deceased pigs were included in the study. The correlation between the two methods was higher when testing faecal samples (K = 0.97, 95% CI: 0.94-1.00) than testing intestinal samples (K = 0.62, 95% CI: 0.35-0.89). The use of ELISA technology provided an efficient and effective mean of evaluating the presence of coronavirus PED antigen in field samples and indicates that this procedure is a very useful tool in epidemiological studies.  相似文献   
643.
The photoinduced degradation of three anilinopyrimidine fungicides (cyprodinil, pyrimethanil and mepanipyrim) by Fe(III)-polycarboxylate complexes in aqueous solution was investigated. A photochemical redox reaction of Fe(III) complexes of oxalate and citrate occurs during irradiation (simulating sunlight) and is an important source of Fe(II) and a series of oxidants such as H2O2 and O radicals. The mechanism involves the formation of polycarboxylate radicals and/or carbon-centred radicals derived from decarboxylation, whereas the contribution of Fe(OH)2+ to O radical formation is negligible. The attack of O radicals on the fungicide molecules produces numerous photodegradation products, which were identified by means of LC-ES-MS and turned out to be mono- or dihydroxylated derivatives of the active ingredients, except for 2-amino-4,6-dimethylpyrimidine, which is only formed by pyrimethanil. The half-lives of the active ingredients, when submitted to irradiation in the presence of iron(III)-polycarboxylate complexes, were estimated to vary between 28 and 79 min (photodegradation rates in the same conditions: mepanipyrim > cyprodinil > pyrimethanil), and photodegradation is slower in citrate than in oxalate solutions. Photoproducts and their kinetics of formation are very similar for the three fungicides. The OH substitution involves the aromatic and the heterocyclic ring and the nitrogen bridge between the two rings, except for mepanipyrim when the hydroxylation also involves the propynylic side chain.  相似文献   
644.
Preventing tick bites is a fundamental step towards reducing the impact of tick-borne protozoal, bacterial and viral diseases (TBDs) in humans and animals. The aim of this study was to evaluate the efficacy of a combination of imidacloprid 10%/permethrin 50% and of fipronil 10%/S-methoprene 12% against ticks in naturally infected dogs and to assess methodological parameters to calculate drug efficacy on tick immature stages.

From July to August 2004, 45 privately owned dogs of various sexes, ages, breeds, coat length and habits were enrolled in a trial carried out in an area (radius approximately 50 km) in Southern Italy. Three homogeneous groups (both for dog population and tick population) were formed: 15 dogs treated with imidacloprid 10% and permethrin 50% spot-on (group A), 15 dogs treated with fipronil 10% and methoprene 12% spot-on (group B) and 15 untreated dogs (group C). The dogs in each group were then sub-grouped according to their age and weight. Two different treatments were administered (time 0 and +28 days) to groups A and B, and the dogs were checked weekly for tick infestation until day +56 post-treatment (p.t.). Twenty-four areas distributed on the whole body surface were examined for ticks at each follow-up, while only at time 0 and at day +56 p.t., ticks were collected from the dogs and identified.

For the immature stages a semi-quantitative method was adopted and the load of immature stages was evaluated and grouped into four classes up to day +56 p.t. when the mean number of immature ticks (MIT) for each infection class was evaluated.

All the adult ticks collected were identified as brown dog ticks (Rhipicephalus sanguineus). Immature stages were first compared at day +28 p.t.. The efficacy of both products used in groups A and B on adult ticks was high and generally very similar. Conversely, the efficacy of imidacloprid 10% and permethrin 50% against immatures was higher than that of fipronil 10% and methoprene 12% throughout the observation period with statistically significant differences (p < 0.05) at day +28 p.t. (i.e. group A = 98.52%, group B = 72.40%).

On the whole, in analysing the efficacy of both products against adult plus immature ticks, it was found that the combination of imidacloprid 10% and permethrin 50% was more effective than fipronil 10% and methoprene 12%, with the differences being statistically significant at day +28 p.t. (group A = 98.43%, group B = 77.56%).  相似文献   

645.
Alpha1-acid glycoprotein (AGP) is an immunomodulatory protein expressed by hepatocytes in response to the systemic reaction that follows tissue damage caused by inflammation, infection or trauma. This paper presents the detection of bovine AGP (boAGP) in mammary secretions (colostrum and milk) and mammary gland tissue. Bovine AGP was detected by Western blotting in all the samples analysed, and could be quantified in colostrum at 162 (+/- 63.7) microg/mL and 114.5 (+/- 67.8) microg/mL during the first 12 h and 24 h respectively. In mature milk, the boAGP concentration clearly decreased and was no longer detectable using the Radial Immunodiffusion (RID) technique. The concentration of mature milk boAGP was therefore semi-quantified using an anion-exchange chromatographic procedure that allowed the concentration of the protein to be determined. The presence of AGP in bovine milk was confirmed by the internal sequence analysis performed following purification to homogeneity of the protein from milk. The concentration of AGP in bovine milk with low SCC (< 250,000) was very similar to that from bovine milk with high SCC (> 250,000). In order to investigate the origin of AGP in bovine milk, a search for mRNA was carried out in somatic cells and mammary gland tissue: mRNA expression of the boAGP gene was detected in mammary gland tissue, but not in somatic cells. Finally, the cDNA sequence of the boAGP was determined, and is hereby presented.  相似文献   
646.
The association of pancreatic disorders with fat necrosis in domestic animals is rare. This report concerns a case of cutaneous/subcutaneous necrotizing panniculitis and steatitis associated with a pancreatic adenocarcinoma in an 11-year-old male Siamese cat. Clinical investigation revealed variably sized nodules on the trunk, limbs and abdomen. Some of them were ulcerated; others showed a shiny yellow necrotic background featuring irregular sinus tracts. The cat was euthanized at the owner's request before a diagnosis could be made. At necropsy, abundant oily material resembling mustard replaced the subcutaneous tissue and small yellow nodules were disseminated in the omentum, mesentery and serosa of the abdomen. A multilobulated mass arising from the anterior pancreatic head was found along with liver and lymph node metastasis. Histopathology showed wide fistulous tracts draining necrotic fat from the subcutis toward the surface and multifocal areas of necrotic adipocytes replacing the panniculus. Duct-like structures and tubules lined by neoplastic epithelial cells were observed in the primary pancreatic tumour and in the metastatic sites. The aetiology of the fat necrosis was possibly the result of systemic release of lipolytic pancreatic enzymes.  相似文献   
647.
Sixty-nine cats were treated for injection-site sarcomas at the Veterinary Teaching Hospital of Grugliasco, Turin (Italy). The animals were divided into two subgroups: those subjected to four doxorubicin cycles combined with radical surgical excision 10 days after the second chemotherapy cycle (group A, 49 cats) or those treated with surgery alone (group B, 20 cats). Each cat was monitored for lung metastasis and local recurrence. In group A, 28 cats were alive at the end of the follow-up period. In this group, the recurrence rate was 40.8% while lung metastasis occurred in 12% of cats. In group B, eight animals were alive at the end of the follow-up period, while the rates of recurrence and metastasis were 35% and 10%. Neither the median disease-free interval nor the median overall survival was reached in either group. Moreover, there were no statistically significant differences between the two groups.  相似文献   
648.
Protox inhibitors are applied as foliar sprays, thus causing very rapid cellular collapse and desiccation of many troublesome weeds in the presence of light. In many respects, they appear to be ideal herbicides, because they act rapidly and do not harm mammals under normal conditions. The main limitation to their widespread adoption is that few crops are naturally resistant to them. Crop tolerance has mainly been pursued with the synthesis of the cyclic imide classes containing 5- and 6-membered heterocycles, including pyrazole, pyridazine, 1,2,4-triazine, triazolinone and trifluoromethyluracil derivatives. Because of their structural novelties and biological performance, active investigations on heterocyclic protox inhibitors have been carried out in our laboratories and we have found 3-arylpyrroles to be a new class of light-activated, membrane-disrupting herbicides. They are active on both grass and broadleaf weeds at low rates. The synthesis and structure-activity relationships are presented.  相似文献   
649.
To evaluate the effects of a dietary supplementation with biotin on heavy pigs' productive performances (including meat and cured hams quality), 45 Landrace×Large White barrows with an initial average body weight (BW) of 35 kg were allocated to three experimental groups: a control group (A) fed with a maize/soybean diet and two treatment groups (B and C) receiving the same diet as group A but with the addition of crystalline biotin at 150 and 300 ppb, respectively. Pigs were fed at the rate of 9% of their metabolic BW (BW0.75) up to a maximum of 3.2 kg/pig per day. Pigs were slaughtered at about 160 kg BW. Animals on biotin diets showed a higher (P<0.05) average daily weight gain (ADG) during the finishing phase. The addition of biotin to the diet resulted in lower L* and hue values of loin (P<0.05). The dietary treatment significantly affected the fatty acid composition of the subcutaneous fat of the fresh thigh, resulting in an increase of saturated acids and in a lowering of the sum of unsaturated acids and the iodine number in biotin-treated animals (P<0.05).Our results indicate that biotin may play a positive role on heavy pigs' growth, meat quality and the sensory and technological properties of cured hams.  相似文献   
650.
Platelet derived growth factor receptor (PDGFR)α and PDGFRβ are tyrosine kinase receptors that are overexpressed in 70–80% of human osteosarcomas (OSAs) and may be suitable therapeutic targets for specific kinase inhibitors (TKIs). Canine OSA shows histopathological and clinical features similar to human OSA, and is considered an excellent model in comparative oncology. This study investigated PDGF-A, PDGF-B, PDGFRα and PDGFRβ expression in 33 canine OSA samples by immunohistochemistry and in seven primary canine OSA cell lines by Western blot and quantitative PCR analysis.Immunohistochemical data showed that PDGF-A and PDGF-B are expressed in 42% and 60% of the OSAs analysed, respectively, while PDGFRα and PDGFRβ were expressed in 78% and 81% of cases, respectively. Quantitative PCR data showed that all canine OSA cell lines overexpressed PDGFRα, while 6/7 overexpressed PDGFRβ and PDGF-A relative to a normal osteoblastic cell line. Moreover, in vitro treatment with a specific PDGFR inhibitor, AG1296, caused a dose- and time-dependent decrease in AKT phosphorylation. Collectively, these data show that PDGFRs/PDGFs are co-expressed in canine osteosarcomas, which suggests that an autocrine and/or paracrine loop is involved and that they play an important role in the aetiology of OSA. PDGFRs may be suitable targets for the treatment of canine OSA with a specific TKI.  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