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   636篇
  免费   41篇
林业   37篇
农学   16篇
  134篇
综合类   44篇
农作物   45篇
水产渔业   63篇
畜牧兽医   271篇
园艺   24篇
植物保护   43篇
  2024年   2篇
  2023年   11篇
  2022年   20篇
  2021年   44篇
  2020年   31篇
  2019年   41篇
  2018年   29篇
  2017年   23篇
  2016年   30篇
  2015年   21篇
  2014年   30篇
  2013年   34篇
  2012年   51篇
  2011年   59篇
  2010年   30篇
  2009年   28篇
  2008年   41篇
  2007年   37篇
  2006年   40篇
  2005年   24篇
  2004年   23篇
  2003年   9篇
  2002年   10篇
  2000年   4篇
  1998年   1篇
  1996年   1篇
  1994年   1篇
  1989年   1篇
  1988年   1篇
排序方式: 共有677条查询结果,搜索用时 15 毫秒
671.
The effects of land use on soil organic and inorganic phosphorus (P) stocks were assessed in the Pampas, Argentina. Three hundred and eighty-six paired sites widely distributed over an area of ca. 50 Mha were sampled. Land use types included soils under trees, uncropped soils, cropped soils at the pasture phase of a mixed rotation, cropped soils at the crop phase of a mixed rotation, and flooded soils. Slight differences in organic P stocks were found among land uses. Organic P was 21–35% lower in flooded soil than in the other treatments in the 0–100 cm depth. Inorganic P was significantly lower (ca. 27%) in pasture and cropped soils than in the uncropped controls at 0–25 cm depth. The ratios of organic P/inorganic P and organic C/organic P decreased with depth and did not significantly differ among the sites. The influence of cultivation on inorganic P to a depth of 100 cm depended on the initial phosphorus content of the soil. Soils rich in phosphorus lost substantial amounts of their phosphorus stocks, in some cases losses were as high as 70%, whereas phosphorus-poor soils presented only small changes in their inorganic P levels.  相似文献   
672.
In the present work, we established and characterized a 3D functional polarized primary bovine oviduct epithelial cells (BOECs) culture on free-floating type I collagen hydrogels (rafts) at an air-liquid interface (ALI). Intercellular junctions, ultrastructural cellular morphology and the expression of the OVGP1 closely recapitulated those of the in vivo epithelium lining. These morphological and physiological epithelial cell features were maintained under standard DMEM/F12 with 10% foetal bovine serum culture medium for at least 28 days of ALI culture. The versatility of the BOECs raft cultures should allow testing of toxicity compounds, in vitro evaluation of physiological or pathological oviductal states, and the study of epithelial-mesenchymal interactions that are critical for the maintenance of oviductal homeostasis.  相似文献   
673.
In the present paper we report on the effects of the insertion of the Agrobacterium rhizogenes rolC gene in the tomato (Solanum lycopersicum L., formerly Lycopersicon esculentum Mill.) cultivar Tondino. Several transgenic lines were successfully obtained, between which two clones, rolC1 and rolC3, were chosen for the analysis of morpho-productive traits as well as of the endogenous levels of auxin and abscisic acid. Consistent with the known phenotypic effect of this gene, the transformed tomato plants were significantly shorter than the corresponding controls. On the other hand, even if yield was not affected by the transformation in terms of average number of fruits produced, fruit weight was significantly lower in the transgenics with respect to the controls. Therefore, insertion of the rolC gene does not lead to an improvement in plant productivity.  相似文献   
674.
A case of aural carcinoma with chondroid metaplasia at metastatic foci in an 8-year-old male pug is described. Multiple metastases in both lungs and the right submandibular, parotid, retropharyngeal, cervical and prescapular lymph nodes were detected. Histologically, the skin of the right ear canal appeared to be diffusely infiltrated by cords and nests of neoplastic epithelial cells, showing multifocal contiguity with the overlying hyperplastic squamous epithelium. Most of the carcinomatous cells were arranged in a glandular-like pattern, with formation of lumens containing epithelial cells attached to the peripheral cell layer by elongated intercellular bridges. Scattered foci of keratinization with central accumulations of compact, laminated keratin were also observed, and histochemical stains failed to detect mucinous secretory material. Even though histological and histochemical findings were compatible with a diagnosis of acantholytic squamous cell carcinoma, CAM5.2 immunostaining was detectable in the majority, although not all, neoplastic cells, confirming a diagnosis of poorly differentiated ceruminous gland carcinoma. Pulmonary metastatic nodules revealed multifocal areas of cartilaginous metaplasia with apparent transition of carcinomatous cells to chondroid cells, showing nuclear atypia and focal cytokeratin immunostaining. Carcinomatous cells surrounding chondroid areas also revealed focal vimentin and S100 immunoreactivity. Histological evidence of transition between the two components, as well as the presence of intermediate cells displaying both epithelial and mesenchymal immunohistochemical features, strongly indicated a final diagnosis of carcinosarcoma, in which chondrosarcomatous elements were derived from carcinoma cells.  相似文献   
675.
Objective– Failure of passive transfer in neonatal alpacas is often corrected by IV administration of commercial camelid plasma. The goal of this study was to characterize changes in pulmonary function, gas exchange, and cardiovascular parameters associated with IV plasma transfusion. Design– Prospective clinical study. Setting– A university‐based referral hospital. Animals– Eleven clinically healthy alpaca crias (age: 1–18 days) with failure of passive transfer (IgG<8 g/L [800 mg/dL]). Interventions– Thirty milliliters per kilogram of commercial camelid plasma was administered IV over 90 minutes. Before and after the transfusion, the following cardiopulmonary measurements were obtained: arterial blood gas analysis, pulmonary functional residual capacity (FRC), PCV, total plasma protein and echocardiographic M‐mode measures. Additionally, central venous pressure and indirect arterial blood pressure were monitored throughout the plasma transfusion. Measurements and Main Results– The IV plasma transfusion resulted in significantly reduced PCV (−5.4±5.1%), increased total plasma protein (+4±4 g/L [0.4±0.4 g/dL]), elevated central venous pressure and changes in left and right ventricular M‐mode indices, consistent with plasma volume expansion. Transfusion was further associated with a significant increase in arterial oxygen pressure (PaO2) (+11.2±15 mm Hg) and decrease in FRC (−5.6±8.3 mL/kg). Conclusions– IV administration of 30 mL/kg camelid plasma to neonatal crias resulted in measurable plasma volume expansion and a concurrent reduction in FRC. Administration of this quantity of plasma appeared to be safe in healthy neonatal crias. However, changes in lung volume associated with plasma administration may create risks for crias with underlying cardiopulmonary or systemic disease.  相似文献   
676.
677.
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