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   20950篇
  免费   480篇
林业   4022篇
农学   1463篇
基础科学   165篇
  3580篇
综合类   916篇
农作物   2346篇
水产渔业   2382篇
畜牧兽医   3046篇
园艺   1217篇
植物保护   2293篇
  2024年   7篇
  2023年   54篇
  2022年   118篇
  2021年   219篇
  2020年   248篇
  2019年   260篇
  2018年   2965篇
  2017年   2905篇
  2016年   1439篇
  2015年   238篇
  2014年   246篇
  2013年   343篇
  2012年   1151篇
  2011年   2450篇
  2010年   2256篇
  2009年   1427篇
  2008年   1566篇
  2007年   1803篇
  2006年   232篇
  2005年   251篇
  2004年   250篇
  2003年   295篇
  2002年   176篇
  2001年   91篇
  2000年   107篇
  1999年   41篇
  1998年   28篇
  1997年   16篇
  1996年   27篇
  1995年   21篇
  1994年   13篇
  1993年   16篇
  1992年   16篇
  1991年   11篇
  1990年   8篇
  1989年   15篇
  1988年   20篇
  1987年   6篇
  1985年   7篇
  1984年   7篇
  1983年   6篇
  1981年   6篇
  1980年   6篇
  1977年   6篇
  1976年   6篇
  1973年   6篇
  1972年   6篇
  1969年   5篇
  1968年   6篇
  1967年   3篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
102.
103.
104.
The aim of this study was to develop regression models for correlation of canine fetal heart development with body size to characterize normal development or suggest cardiac anomalies. Twenty clinically healthy pregnant bitches, either brachycephalic and non-brachycephalic, were examined ultrasonographically. Transabdominal fetal echocardiography was conducted every 4 days from the beginning of cardiac chambers differentiation until parturition. Ten cardiac parameters were measured: length, width and diameter of the heart; heart area; left and right ventricular dimensions; left and right atrial dimensions; and aortic and pulmonary artery diameter. Femoral length, biparietal diameter and abdominal cross-sectional area were also recorded. Regression equations were developed for each parameter of fetal body size, and linear and logarithmic models were compared. The model with the highest correlation coefficient was chosen to produce equations to calculate relative dimensions based on the correlations. Only the left-ventricular chamber differed between the two racial groups. Biparietal diameter was the independent parameter that produced the highest correlation coefficient for the most fetal cardiac dimensions, although good correlations were also observed using femoral length and abdominal cross-sectional area. Heart width and heart diameter were used as surrogates of cardiac development, as these measurements showed the best statistical correlation. Quantitative evaluation of fetal cardiac structures can be used to monitor normal and abnormal cardiac development.  相似文献   
105.
Tendons regenerate poorly due to a dense extracellular matrix and low cellularity. Cellular therapies aim to improve tendon repair using mesenchymal stem cells and tenocytes; however, a current limitation is the low proliferative potential of tenocytes in cases of severe trauma. The purpose of this study was to develop a method useful in veterinary medicine to improve the differentiation of Peripheral Blood equine mesenchymal stem cells (PB-MSCs) into tenocytes. PB-MSCs were used to study the effects of the addition of some growth factors (GFs) as TGFβ3 (transforming growth factor), EGF2 (Epidermal growth factor), bFGF2 (Fibroblast growth factor) and IGF-1 (insulin-like growth factor) in presence or without Low Level Laser Technology (LLLT) on the mRNA expression levels of genes important in the tenogenic induction as Early Growth Response Protein-1 (EGR1), Tenascin (TNC) and Decorin (DCN). The singular addition of GFs did not show any influence on the mRNA expression of tenogenic genes whereas the specific combinations that arrested cell proliferation in favour of differentiation were the following: bFGF2 + TGFβ3 and bFGF2 + TGFβ3 + LLLT. Indeed, the supplement of bFGF2 and TGFβ3 significantly upregulated the expression of Early Growth Response Protein-1 and Decorin, while the use of LLLT induced a significant increase of Tenascin C levels. In conclusion, the present study might furnish significant suggestions for developing an efficient approach for tenocyte induction since the external administration of bFGF2 and TGFβ3, along with LLLT, influences the differentiation of PB-MSCs towards the tenogenic fate.  相似文献   
106.
107.

Background

The pathogenic mechanism of equine recurrent uveitis (ERU) is still poorly defined and many variations between experimental animal models and spontaneous disease exist.

Objectives

The aim of our study was to investigate if Th17 cell-mediated response plays role in the pathogenesis of the used experimental model in horses and to reveal its pathological findings.

Methods

Experimental uveitis was induced in 6 healthy horses. The concentrations of retinal autoantigen CRALBP and IL-17 were measured using ELISA in aqueous humor and vitreous body of the 12 inflamed eyes as well as in 12 control non-inflamed eyes taken from 6 horses in slaughter house. After centrifugation of the two eye media, smears were prepared and cytological investigation was performed. Tissue specimens were taken from all eye globes and were submitted to histopathological investigation.

Results

CRALBP and IL-17 concentrations were significantly elevated in eye media of horses with experimental uveitis in comparison with controls. Cytological and histopathological findings corresponded to the changes characteristic of chronic immune-mediated inflammation with mononuclear cell infiltration of uvea, choroid, retina, and eye media as well as severe retinal destruction.

Conclusions

Our study demonstrated the involvement of the retinal autoantigen CRALBP as well as IL-17 in the pathogenesis of experimental uveitis in horses. These findings suggests that this experimental uveitis in horses may serve as a suitable animal model for investigation of IL-17- mediated immune response during spontaneous autoimmune uveitis in horses as well as in humans.
  相似文献   
108.
The aim of this study was to compare the accuracy of two methods used to estimate testicular volume in the collared peccary. Calliper and ultrasonographic measurements of testicular dimensions (length, width and height) of both testes were taken on five adult collared peccaries. The testicular volume was calculated by Lambert's empiric formula: length (L) × width (W) × height (H) × 0.71, the formula of an ellipsoid L × W × H × 0.52, and Hansen's formula: L × W2 × 0.52. The calculated volumes were then compared with the actual ones, which were estimated by water displacement. The mean of true testicular volume was 22.65 ± 1.52 ml. Lambert's formula estimated testicular volume more accurately when ultrasound measurements were taken. However, when the calliper was the methodology used, the results were closest to the true volume, especially when Ellipsoid formula and Hansen's formula were applied, and underestimated the true volumes by 1.53 ± 1.75 ml and 1.53 ± 1.65 ml, respectively. This specific application of technologies in wild animals has the potential to revolutionize the selection process for the collared peccary entering artificial insemination or natural breeding programmes.  相似文献   
109.
This study was performed in a sample of 20 dogs (n = 20) and aimed to: (1) characterize the mandible height (Mh), mandibular canal height (MCh) and distance between the inter‐dental alveolar margin and the mandibular canal (dIAM‐MC) dimensions, and (2) to develop mathematical models that express the insight's mandible anatomy of those important mandible structural elements allowing the prediction of their dimensions using physical parameters such as patient body weight (Wg) and the canine tooth width at the free gingival margin level‐(wCGM). Lateral‐view X‐rays of both sides of the skull were taken for all the individuals. Three mathematical prediction models were developed to calculate Mh, MCh and dIAM‐MC. Achieved proportions of the mandible considered parameters regarding its height were of 36.45% for MCh, 50.90% for dMAI‐MC and 12.65% for vMC. Statistically significant differences were registered between the Wg and wCGM (P = 0.00), Mh (P = 0.00), MCh (P = 0.00) and dIAM‐MC (P = 0.00). Only the Wg presented a strong correlation with the wCGM (R = 0.58), Mh (R = 0.70), dIAM‐MC (R = 0.60) and MCh (R = 0.68). These models will allow a clinician to estimate the size of the mandible structures by only using data obtained during the physiological examination, with a sufficiently high prediction capacity and a very low standard error. The study points out the relationships of physiological parameters such as Wg and wCGM with mandible anatomical structural elements considered as important in oral surgery. The results of this study give the surgeon a new additional tool providing more information on the mandible anatomical structures and its relationships. This reduces the risk of iatrogenic lesions during the oral surgical procedures and improves patient safety.  相似文献   
110.
The main goal of this study was to obtain new isolates of Leptospira spp. from sheep. A total of 10 kidney samples and 44 blood samples were collected from sheep slaughtered in Pelotas, Southern Brazil. One isolate was obtained which was identified by 16S rRNA gene sequencing and serogrouping to be Leptospira noguchii serogroup Autumnalis. Microscopic agglutination test (MAT) evaluation revealed that 4.5% of the sheep sera reacted against the Autumnalis serogroup. This is the first report of isolation of L. noguchii from sheep. Together these findings indicate that L. noguchii infections may be a potentially important veterinary problem in this domestic animal species.  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