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   435篇
  免费   47篇
  国内免费   1篇
林业   13篇
农学   8篇
基础科学   22篇
  17篇
综合类   126篇
农作物   5篇
水产渔业   15篇
畜牧兽医   261篇
园艺   5篇
植物保护   11篇
  2023年   3篇
  2020年   8篇
  2019年   8篇
  2018年   13篇
  2017年   11篇
  2016年   9篇
  2015年   12篇
  2014年   12篇
  2013年   13篇
  2012年   16篇
  2011年   20篇
  2010年   17篇
  2009年   13篇
  2008年   14篇
  2007年   26篇
  2006年   10篇
  2005年   11篇
  2004年   10篇
  2003年   10篇
  2002年   15篇
  2001年   11篇
  2000年   7篇
  1999年   11篇
  1998年   10篇
  1997年   6篇
  1996年   9篇
  1994年   3篇
  1993年   6篇
  1992年   15篇
  1991年   26篇
  1990年   12篇
  1989年   8篇
  1988年   5篇
  1987年   7篇
  1986年   3篇
  1985年   6篇
  1984年   7篇
  1983年   7篇
  1979年   4篇
  1978年   3篇
  1977年   6篇
  1975年   4篇
  1974年   3篇
  1973年   3篇
  1972年   5篇
  1971年   5篇
  1968年   4篇
  1967年   5篇
  1925年   2篇
  1922年   3篇
排序方式: 共有483条查询结果,搜索用时 31 毫秒
61.
The objective of this retrospective study was to describe signalment, clinical presentation, surgical treatment, outcome, histopathologic, and immunohistochemical characteristics of periocular peripheral nerve sheath tumor in a series of cats. Six cats with a histologic diagnosis of peripheral nerve sheath tumor of the eyelid and/or conjunctiva were identified from 3997 feline ocular histopathologic submissions to the Comparative Ocular Pathology Laboratory of Wisconsin between 1976 and 2002. Medical records were reviewed and data were collected for signalment, eye affected, location, duration, and history of tumor recurrence. Ancillary diagnostic tests, surgical approach, and histopathology were also described. Special stains and immunohistochemistry panels were performed on the tissue. Follow-up information was obtained through telecommunications with the owner and local veterinarian. The mean age of the cats was 8 years (range: 5-15 years). There was an equal distribution of males and females. Breeds represented were two Domestic Long-haired (DLH) cats, three Domestic Short-haired (DSH) cats, and one Manx. The right eye was affected in four cats and the left eye in two cats. The superior eyelid was affected in four cats, the superior conjunctiva in two cats, and the inferior eyelid in one cat. All of the cats that underwent surgical excision, cryoablation, or laser ablation had an average of three recurrences of the tumor. Four of six cats undergoing wide excision with enucleation, exenteration or rhomboid flap had no recurrence of the tumor. Histomorphologically, all of the tumors were of spindle cell type with five of six tumors showing histologic features of Antoni type B tissue. All six tumors stained positive for vimentin. Five of six tumors stained positive for S-100 and laminin. All six tumors were negative for smooth muscle actin. Definitive histologic diagnoses of spindle cell tumors can be difficult. The presence of Antoni A and B histologic patterns as well as immunohistochemical reactivity for vimentin, S-100, and laminin suggest a diagnosis of peripheral nerve sheath tumor. Our findings suggest that local aggressive recurrence is common and that wide surgical excision combined with enucleation or exenteration may be indicated.  相似文献   
62.
63.
An alfalfa experiment was conducted in the Wellton-Mohawk Irrigation and Drainage District of Southwest Arizona to determine the potential for minimizing the salt load in irrigation return flow by decreased leaching. Three leaching treatments of 5, 10, and 20%, replicated five times, were imposed on a 2-ha field. The crop was irrigated with Colorado River water (electrical conductivity of 1.3 dS m?1) through a lateral-move, spray-type irrigation system. Results were compared with those of an adjacent area irrigated with level basin flooding.The average annual evapotranspiration during the 4-year study was 1930 mm. Several indirect measures of the leaching fractions attained gave average values of 6.4, 9.3, and 13.1% for the three leaching treatments. Mean annual yields were 21.5 and 22.9 Mg ha?1 for 1977 and 1978 in the experimental plots, with no significant differences among leaching treatments, and 25.7 and 20.8 Mg ha?1 in the adjacent flooded check. The results suggest that full yields could be attained with as little as 5% leaching.Estimates based on average on-farm irrigation efficiency for alfalfa in the District in 1979, indicate that 5% leaching, if attainable, would reduce the salt load in the irrigation return flow by 39 000 Mg year?1 on 8 000 ha of alfalfa.  相似文献   
64.
Transmission of Lawsonia intracellularis from experimentally inoculated pigs to naive swine was demonstrated in this study. The study was conducted using conventional pigs divided into three groups as follows: principles inoculated with L. intracellularis, sentinels, and controls. The pigs were inoculated and paired on 13 and 9 days post-inoculation with a sentinel pig for 7 days. Fecal samples and serum samples were collected throughout the study for polymerase chain reaction (PCR) and antibody testing by indirect fluorescent antibody techniques. After co-mingling, the inoculated group was necropsied; sentinel and control pigs were necropsied 7-14 days later. The intestinal tracts were evaluated grossly and microscopically for lesions. PCR was performed on intestinal mucosal scrapings and feces. Warthin-Starry and fluorescent antibody staining procedures were conducted to confirm colonization with L. intracellularis. Gross and microscopic lesions typical of porcine proliferative enteropathy (PPE) were observed in both the inoculated and sentinel groups. Transmission was demonstrated from inoculated principle pigs to sentinel pigs. PCR results detected cyclical shedding of L. intracellularis in the feces. Seroconversion occurred in pigs that were exposed to L. intracellularis. From this study, it was demonstrated that transmission of L. intracellularis can occur easily in an environment with experimentally infected pigs and that PCR can be a useful tool to monitor fecal shedding of the organism.  相似文献   
65.
OBJECTIVE: To evaluate the use of a modified whole body plethysmograph in awake sheep. ANIMALS: 10 healthy adult sheep. PROCEDURE: Concurrent measurements of specific airway resistance (sR(aw)) and pulmonary resistance (R(L)) were obtained using a novel noninvasive head-out constant-volume plethysmograph and esophageal balloon-pneumotachography, respectively. All data were collected before and after external resistive loading with 1 and 5.6 cm H2O/L/s. Functional residual capacity (FRC) was measured by helium dilution for computation of airway resistance (R(aw)) preloading (R(aw) = sR(aw)/FRC). RESULTS: The sR(aw) and R(L) were closely correlated in 10 adult sheep. Additionally, sR(aw), and R(L) accurately reflected the magnitude of added resistance. The mean FRC was 52 mL/kg and used to calculate R(aw). At baseline, the values for R(aw) were significantly correlated with sR(aw) and R(L). CONCLUSIONS AND CLINICAL RELEVANCE: Precise measurements of sR(aw) and R(aw) at baseline and sR(aw) after external resistive loading were obtained by use of this novel noninvasive plethysmographic technology. This method should have application to veterinary patients or animals used in research in which noninvasive rapid or serial measurements of sR(aw) in the conscious state are required.  相似文献   
66.
67.
68.
69.
70.

Background

Cowpea (Vigna unguiculata L.) is an important grain and forage legume grown throughout sub-Saharan Africa primarily by subsistence farmers on poor, drought prone soils. Genetic improvement of the crop is being actively pursued and numerous functional genomics studies are underway aimed at characterizing gene controlling key agronomic characteristics for disease and pest resistances. Unfortunately, similar to other legumes, efficient plant transformation technology is a rate-limiting step in analysis of gene function in cowpea.

Results

Here we describe an optimized protocol for the rapid generation of transformed hairy roots on ex vitro composite plants of cowpea using Agrobacterium rhizogenes. We further demonstrate the applicability of cowpea composite plants to study gene expression involved in the resistance response of the plant roots to attack by the root parasitic weed, Striga gesnerioides. The utility of the new system and critical parameters of the method are described and discussed herein.

Conclusions

Cowpea composite plants offer a rapid alternative to methods requiring stable transformation and whole plant regeneration for studying gene expression in resistance or susceptibility responses to parasitic weeds. Their use can likely be readily adapted to look at the effects of both ectopic gene overexpression as well as gene knockdown of root associated defense responses and to the study of a broader range of root associated physiological and aphysiological processes including root growth and differentiation as well as interactions with other root pests, parasites, and symbionts.  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