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   110篇
  免费   21篇
林业   1篇
农学   1篇
  8篇
综合类   23篇
水产渔业   1篇
畜牧兽医   91篇
园艺   1篇
植物保护   5篇
  2022年   1篇
  2021年   2篇
  2020年   3篇
  2018年   11篇
  2017年   5篇
  2016年   7篇
  2015年   2篇
  2014年   6篇
  2013年   14篇
  2012年   1篇
  2011年   5篇
  2010年   4篇
  2009年   4篇
  2008年   3篇
  2007年   4篇
  2006年   3篇
  2005年   4篇
  2004年   4篇
  2003年   3篇
  2002年   3篇
  2001年   3篇
  2000年   1篇
  1998年   6篇
  1997年   4篇
  1996年   2篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1990年   3篇
  1989年   1篇
  1987年   1篇
  1986年   1篇
  1985年   3篇
  1984年   1篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1973年   1篇
  1972年   1篇
  1968年   1篇
  1967年   1篇
  1924年   1篇
  1909年   1篇
排序方式: 共有131条查询结果,搜索用时 15 毫秒
91.
Fluorine and B concentrations in foliage and foliar injury symptoms produced by these contaminants closely followed the changing pattern of atmospheric emissions from a fiberglass plant. Typical F injury symptoms on foliage were replaced by B injury symptoms as F emissions were reduced. Foliar concentrations of B in excess of 300 ppm accumulated by plants exposed to atmospheric B emissions produced injury symptoms on sensitive species similar to those produced by toxic concentrations of B absorbed through roots. Water-soluble F and B concentrations in soil decreased with increasing distance from the fiberglass plant. Soluble B concentrations in soil within 150 m of the plant were above levels known to be injurious to many plant species. Water-soluble F in soil in the same area increased the F content of some native plants above 50 ppm by the end of the growing season. Silver maples (Acer saccharinum) growing near the fiberglass plant had delayed growth of new shoots in the spring and had increasingly higher contents of F and B in trunk sap with proximity to the fiberglass plant. Control of F and then B emissions by the company resulted in reduced concentrations of these elements in foliage and a reduction in the degree and extent of vegetation injury around the plant.  相似文献   
92.
BACKGROUND: In the mid‐southern region of the United States, sugarcane borer, Diatraea saccharalis (F.), is a major target pest of transgenic maize expressing Bacillus thuringiensis (Bt) proteins. Novel transgenic maize technologies containing two or more pyramided Bt genes for controlling lepidopteran pests have recently become commercially available. Insect resistance management (IRM) is an important issue in the sustainable use of Bt crop technologies. The objective of this study was to determine the frequency of resistance alleles in field populations of D. saccharalis to the new pyramided Bt maize technologies. RESULTS: A total of 382 F2 family lines derived from 735 feral larvae/pupae of D. saccharalis collected from six locations in Louisiana and Mississippi during 2008 and 2009 were screened for resistance to three new Bt maize technologies: MON 89034, Genuity? VT Triple Pro? and SmartStax?. None of the 382 F2 isoline families survived on the Bt maize leaf tissue for ≥ 12 days in the F2 screen. The joint frequency for two‐ or three‐gene resistance models with 95% probability in these populations was estimated to be < 0.0063 to MON 89034 and < 0.003 to VT Triple Pro? and SmartStax?. CONCLUSION: These results suggest that the resistance allele frequency in D. saccharalis to the three pyramided Bt maize technologies is low in the mid‐southern region of the United States, which should meet the rare resistance assumption of the currently used IRM strategy for Bt maize. Copyright © 2011 Society of Chemical Industry  相似文献   
93.
The relative response of poppy (Papaver somniferum L.) and eight crop and vegetable species to excess manganese was investigated in a glasshouse, solution culture experiment. Plant yields and manganese concentrations were measured after two and six weeks growth at five levels of manganese (10–800 μM).

Poppies were highly sensitive to manganese toxicity in solution culture and reductions in shoot yield occurred at lower manganese levels in solution and at lower shoot manganese concentrations than that for the following sensitive species, ranked in order of increasing tolerance : brussels sprout, barley, green beans, lucerne and grean pea. In contrast lupins, oats and sugar beet were relatively tolerant producing about 80% or more of maximum shoot yield at the highest solution manganese level (800 μM Mn).

In this study the sensitivity of poppy, and brussels sprout, to manganese excess was attributed to their low shoot manganese “toxicity threshold values”; and their capacity to partition a high proportion of total plant manganese and dry matter to the shoot at solution manganese levels ≥ 100 μM.

The application of these results to field grown poppy is discussed in relation to interactions between manganese and other elements which modify plant tolerance to manganese excess.  相似文献   

94.
A 5‐month‐old intact male Basset Hound presented for evaluation of pain and crepitation during manipulation of the temporomandibular joint, worse on the right side. A computed tomography (CT) scan of the head was performed. The CT images demonstrated the osseous features of temporomandibular joint dysplasia and facilitated a 3D reconstruction, which allowed better visualization of the dysplastic features. The patient responded to conservative management with a tape muzzle with no recurrence reported by the owner 6 months after presentation.  相似文献   
95.
CASE HISTORY: A 6-year-old, spayed, female, domestic short-haired cat presented with severe erythroderma and scaling skin. She showed disturbed gait and mild behavioural changes.

CLINICAL FINDINGS: The cat had a generalised, erythematous, scurfy dermatitis with marked, multifocal crusting and skin thickening. The skin was painful and contracted, which appeared to prevent normal freedom of movement.

DIAGNOSIS: The cat was suspected to have a paraneoplastic syndrome. A mediastinal mass was located and histologically confirmed as thymoma. The cat was diagnosed with a thymoma-associated cutaneous paraneoplastic syndrome.

CLINICAL RELEVANCE: This is a rare condition with few reports in the literature. The skin changes, both grossly and histologically, were considered to be different from those described in cases of paraneoplastic dermatosis associated with pancreatic neoplasia. The clinical presentation was characteristic and more cases may occur in practice than are recognised. In this case, as in previous reports, the tumour was grossly resectable, which could lead to cure of the clinical condition.  相似文献   
96.
97.
Butorphanol has been used clinically to provide analgesia in alpacas, but cardiovascular effects have not been reported. Using a randomized cross‐over design, eight healthy, young adult female alpacas (3 ± 1 SD years) weighing 64 ± 9 SD kg were anesthetized with isoflurane by mask followed by tracheal intubation and maintenance of anesthesia with 1.75% et (isoflurane) in oxygen. Two treatments, butorphanol (0.1 mg kg–1 IV) and control (saline, IV) were assigned to the animals in a randomized manner allowing a minimum of two weeks between treatments. While anesthetized, animals were instrumented for measurement of cardiovascular variables including systolic, diastolic, and mean arterial blood pressure, pulmonary arterial pressure, pulmonary capillary wedge pressure, central venous pressure, cardiac output (CO) and pulmonary temperature (TEMP). CO was measured via thermodilution using 5 mL of iced 5% dextrose and recording the average of three replicate measurements. Cardiac index, systemic vascular resistance (SVR) and pulmonary vascular resistance were also calculated. Arterial and mixed venous blood samples were collected for blood gas analysis [pH, pO2, pCO2, (HCO3?), BE, Hbsat]. Variables were collected at baseline (time 0) and at 5, 10, 15, 30, 45, and 60 minutes following injection. Variables were analyzed by anova for repeated measures with post‐hoc differences between means identified using the Bonferroni comparison (p < 0.05). SVR decreased five minutes after administration of butorphanol (Huynh Feldt corrected p = 0.045) and remained decreased for 60 minutes. TEMP decreased with time in both groups (Huynh Feldt corrected p = 0.000027), but groups were not different between each other. Other cardiovascular and blood gas variables were not different between groups. We conclude that butorphanol (0.1 mg kg–1 IV) had minimal effects on the cardiovascular system of these alpacas, causing a mild decrease in SVR.  相似文献   
98.
Prostaglandin F2α (PGF2α) is a main luteolytic factor in vivo; however, its direct luteolytic influence on steroidogenic cells of bovine corpus luteum (CL) is controversial and not fully understood. The aim of the study was to clarify PGF2α action on bovine CL in different in vivo and in vitro conditions and to examine whether the contact among all main types of CL cells is necessary for luteolytic PGF2α action. In experiment 1, the bovine CL (day 15 of the oestrous cycle) was perfused using in vivo microdialysis system with dinoprost (an analogue of PGF2α) for 0.5 h. Dinoprost caused a short‐time increase in progesterone (P4), whose concentration decreased thereafter (at 6‐, 10‐, 12‐ and 24‐h after treatment). In experiment 2, the direct effect of PGF2α on P4 accumulation in CL steroidogenic cells cultured in monolayer (day 15 of the cycle) was determined. PGF2α after 24 h of incubation increased P4 accumulation in steroidogenic CL cells. In experiment 3 steroidogenic, endothelial CL and immune cells (day 15 of the cycle) were incubated with PGF2α in cocultures for 24 h in glass tubes and the levels of P4, stable metabolites of nitric oxide (NO) and leukotriene (LT) C4 were determined. Although PGF2α treatment increased P4 secretion in homogeneous steroidogenic CL cell culture, the decrease in P4 secretion in cocultures of all types of CL cells was observed. The secretion of NO and LTC4 increased after the treatment of PGF2α both in pure cultures of CL cells and in cocultures. The interactions between endothelial and immune cells with steroidogenic CL cells are needed for luteolytic PGF2α action within the bovine CL. Our results indicate that the cell coculture model, including the main types of CL cells, is the most approximate to study PGF2α role in vitro.  相似文献   
99.
Objective To determine the infectivity and transmissibility of Hendra virus (HeV). Design A disease transmission study using fruit bats, horses and cats. Procedure Eight grey-headed fruit bats (Pteropus poliocephalus) were inoculated and housed in contact with three uninfected bats and two uninfected horses. In a second exper iment, four horses were inoculated by subcutaneous injection and intranasal inoculation and housed in contact with three uninfected horses and six uninfected cats. In a third experi ment, 12 cats were inoculated and housed in contact with three uninfected horses. Two surviving horses were inoculated at the conclusion of the third experiment: the first orally and the second by nasal swabbing. All animals were necropsied and examined by gross and microscopic pathological methods, immunoperoxidase to detect viral antigen in formalin-fixed tissues, virus isolation was attempted on tissues and SNT and ELISA methods were used to detect HeV-specific antibody. Results Clinical disease was not observed in the fruit bats, although six of eight inoculated bats developed antibody against HeV, and two of six developed vascular lesions which contained viral antigen. The in-contact bats and horses did not seroconvert. Three of four horses that were inoculated devel oped acute disease, but in-contact horses and cats were not infected. In the third experiment, one of three in-contact horses contracted disease. At the time of necropsy, high titres of HeV were detected in the kidneys of six acutely infected horses, in the urine of four horses and the mouth of two, but not in the nasal cavities or tracheas. Conclusions Grey-headed fruit bats seroconvert and develop subclinical disease when inoculated with HeV. Horses can be infected by oronasal routes and can excrete HeV in urine and saliva. It is possible to transmit HeV from cats to horses. Transmission from P poliocephalus t o horses could not be proven and neither could transmission from horses to horses or horses to cats. Under the experimental conditions of the study the virus is not highly contagious.  相似文献   
100.
Oocyte has been considered the major contributor for embryo thermo‐tolerance. However, it was shown that sperm factors can be transferred to the oocyte during fertilization, raising the question of whether the absence of such factors could interfere on embryo thermo‐tolerance. In this study, we used parthenogenesis to generate bovine embryos without spermatozoa in order to test whether the absence of sperm factors could influence their thermo‐sensitiveness at early stages. In vitro fertilized (IVF) and parthenogenetic (PA) embryos at 44 h post‐insemination/chemical activation were exposed to 38.5°C (control) or 41°C (heat shock) for 12 h and then developed for 48 h and up to blastocyst stage. Apoptosis index and expression of PRDX1, GLUT1, GLUT5 and IGF1r genes in blastocysts derived from heat‐shocked embryos were also evaluated. The heat shock decreased the blastocyst rate at day seven (p < 0.05) for IVF embryos and at day eight (p < 0.01) for both IVF and PA embryos. Total cell number was not affected by heat shock in IVF and PA blastocysts, but there was an increased proportion (p < 0.05) of apoptotic cells in heat‐shocked embryos when compared to controls. There was no interaction (p > 0.05) between method of activation (IVF and PA) and temperature (38.5°C or 41.5°C) for all developmental parameters evaluated. Expression of GLUT1 gene was downregulated (p < 0.05) by heat shock in both IVF and PA blastocyst whereas expression of GLUT5 and IGF1r genes was downregulated (p < 0.05) by heat shock in PA blastocysts. Those data show that the heat shock affects negatively the embryo development towards blastocysts stage, increases the apoptotic index and disturbed the expression of some genes in both IVF and PA embryos, indicating that the presence or absence of sperm factors does not influence the sensitivity of the bovine embryo to heat shock.  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