全文获取类型
收费全文 | 17793篇 |
免费 | 110篇 |
国内免费 | 2篇 |
专业分类
林业 | 3712篇 |
农学 | 1327篇 |
基础科学 | 142篇 |
3023篇 | |
综合类 | 872篇 |
农作物 | 2139篇 |
水产渔业 | 2000篇 |
畜牧兽医 | 1551篇 |
园艺 | 1156篇 |
植物保护 | 1983篇 |
出版年
2024年 | 6篇 |
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 29篇 |
2020年 | 37篇 |
2019年 | 53篇 |
2018年 | 2773篇 |
2017年 | 2734篇 |
2016年 | 1234篇 |
2015年 | 121篇 |
2014年 | 58篇 |
2013年 | 88篇 |
2012年 | 884篇 |
2011年 | 2222篇 |
2010年 | 2171篇 |
2009年 | 1318篇 |
2008年 | 1397篇 |
2007年 | 1653篇 |
2006年 | 117篇 |
2005年 | 173篇 |
2004年 | 171篇 |
2003年 | 229篇 |
2002年 | 112篇 |
2001年 | 26篇 |
2000年 | 56篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1979年 | 4篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
Characterization of Doayo and Kapsiki taurine cattle breeds of Cameroon in their natural environment
Data were collected on live weight (LW), heart girth (HG), height-at-withers (HW), trunk length (TL), age, sex, and coat color
of 207 taurines cattle—122 of the Doayo (Namchi) breed and 85 of the Kapsiki (Kirdi) breed. The animals, aged 1 to 20 years,
were selected from 60 herds randomly selected from villages of Poli of Faro and Mokolo of Tsanga, divisions of the North and
Far North Regions of Cameroon. The data were analyzed using the SAS program with a linear model, applying standard tests.
Results indicated no breed effect (P > 0.05) in the growth trends of LW, HG, HW, and TL. HG and TL were highly significantly (P < 0.0001) related to LW. The growth pattern for the two breeds was the same since the linear contrast of least square means
for the traits at various age groups did not differ (P > 0.05) significantly. The breeds attained maturity as from 4 years. In the absence of breed effect (P > 0.05), a single regression equation was established for the estimation of live weight as thus LW = - 244.42 ( ±22.57 ) kg + 2.49 ( ±0.23 ) HG + 1.04 ( ±0.25 ) TL {\hbox{LW}} = - {244}.{42 }\left( {\pm {22}.{57}} \right){\hbox{ kg}} + {2}.{49 }\left( {\pm 0.{23}} \right){\hbox{ HG}} + {1}.0{4 }\left( {\pm 0.{25}} \right){\hbox{ TL}} , with HG contributing up to 70% of total variation and TL, 2%. This equation could be used to develop a measuring band useful
in the rural environment for commercial and clinical veterinary purposes. 相似文献
132.
The consumption of solid feed is essential for successful transition from a pre-ruminant to a functional digestive tract. Lambs fed starter rations containing highly fermentable carbohydrates often experience dramatic changes in concentrations of rumen and blood metabolites. The optimal amount of roughage required in the diet of pre-ruminant animals is still unclear. The objective of this study was to determine the effect of feeding alfalfa hay on performance and rumen development in young Balouchi lambs. In a completely randomized design, 30 lambs were fed one of three experimental diets consisting of a control, without alfalfa hay (C), a diet containing 7.5% alfalfa hay (A1), and a diet containing 15% alfalfa hay (A2). Lambs fed A1 and A2 diets had lower dry matter intake during the pre-weaning period (P?0.01) and overall (P?=?0.02), but feed conversion ratio and average daily gain were not affected by feeding alfalfa hay. Concentration of beta-hydroxybutyric acid was higher in C compared with the A1 and A2 groups (P?0.01). Concentrations of glucose and non-esterified fatty acids did not differ among the groups of animals. Feeding alfalfa hay reduced thickness of the rumen epithelial keratinized layer (P?=?0.04) and increased thickness of muscular layer (P?=?0.05). We concluded that including 15% alfalfa hay in the starter diet could reduce thickness of the keratinization layer and increase muscularity of rumen wall without adverse effects on growth and performance of newborn lambs. 相似文献
133.
Patrick J. Starks Brad C. Venuto John A. Eckroat Tom. Lucas 《Strength and Conditioning Journal》2011,64(2):178-186
Eastern redcedar (Juniperus virginiana L.) is an aggressively spreading native species in Oklahoma grasslands. It decreases rangeland forage production, and has been implicated in reducing stream flow and groundwater recharge. Industrial-scale plans to use redcedar as a biofuel source are being considered. Optimal placement of redcedar-based industries requires determination of redcedar availability. Such large-area inventories of redcedar mass can be practically addressed via aircraft or satellite remote sensing. Therefore, we conducted a study in central and western Oklahoma to develop and test a remote-sensing–based allometric equation relating redcedar canopy area to aboveground dry mass (AGM). We used automated methods to measure tree canopy area from georectified, pan-sharpened, multispectral QuickBird images having a spatial resolution of 0. 45 m2 per pixel ground sample area. We also measured the canopy area and fresh and dry mass of these trees with the use of destructive sampling techniques. Regression analysis showed that satellite-derived measurements of canopy coverage explained about 85% of field-measured redcedar dry AGM in the study plots. The resulting allometric equation was applied to an independent data set, yielding dry AGM of 38.2 metric tons ? ha?1, which was well within the field-measured range of 36–43 metric tons ? ha?1. The allometric equation was then applied to Natural Resources Conservation Service measurements of redcedar canopy coverage for 17 counties in Oklahoma, to determine that the area of interest contains a median value of about 11.5 million metric tons of redcedar AGM. These results indicate that 0.45-m2 spatial resolution multispectral imagery can be a useful tool for rapid and reliable measurement of redcedar dry AGM. 相似文献
134.
Jeremy Midgley Huyam Altayeb Patrick Mbosso 《African Journal of Range and Forage Science》2016,33(2):127-129
Pseudo-galls of three East African acacia (Vachellia) species were compared to determine the correlates of gall colour and their potential defensive functions. Although all three species produce white thorns, the pseudo-galls of V. gerrardii and V. drepanolobium are dark coloured. In contrast, pseudo-galls of V. seyal var. fistula are white. Associated with this, they are thin-walled and poorly used by aggressive mutualistic ants. We suggest that this weak functionality is compensated for by the highly visible white colour. This aposematism may also involve mimicry as only the fistula variety of V. seyal has galls and only this variety co-occurs with other Vachellia species that have functional galls. Vachellia seyal seyal does not have pseudo-galls and this variety does not occur with other Vachellia species that have pseudo-galls. 相似文献
135.
Rice CC Kruger JM Venta PJ Vilnis A Maas KA Dulin JA Maes RK 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2002,16(3):293-302
Feline caliciviruses (FCVs) are potential etiologic agents in feline idiopathic lower urinary tract disease (I-LUTD). By means of a modified virus isolation method, we examined urine obtained from 28 male and female cats with nonobstructive I-LUTD, 12 male cats with obstructive I-LUTD, and 18 clinically healthy male and female cats. All cats had been routinely vaccinated for FCV. Two FCVs were isolated; I (FCV-U1) from a female cat with nonobstructive I-LUTD, and another (FCV-U2) from a male cat with obstructive I-LUTD. To determine the genetic relationship of FCV-U1 and FCV-U2 to other FCVs. capsid protein gene RNA was reverse transcribed into cDNA, amplified, and sequenced. Multiple amino acid sequence alignments and phylogenetic trees were constructed for the entire capsid protein, hypervariable region E, and the more conserved (nonhypervariable) regions A, B, D, and F. When compared to 23 other FCV isolates with known biotypes, the overall amino acid sequence identity of the capsid protein of FCV-U1 and FCV-U2 ranged from 83 to 96%; identity of hypervariable regions C and E ranged from 58 to 85%. Phylogenetically, FCV-U1 clearly separated from other FCV strains in phenograms based on nonhypervariable regions. In contrast, FCV-U2 consistently segregated with the Urbana strain in all phenograms. Clustering of isolates by geographic origin was most apparent in phenograms based on nonhypervariable regions. No clustering of isolates by biotype was apparent in any phenograms. Our results indicate that FCV-UI and FCV-U2 are genetically distinct from other known vaccine and field strains of FCV. 相似文献
136.
Guillaume Gory Delphine N. Rault Laure Gatel Claire Dally Patrick Belli Laurent Couturier Eddy Cauvin 《Veterinary radiology & ultrasound》2014,55(5):552-560
Differential diagnoses for regurgitation and vomiting in dogs include diseases of the gastroesophageal junction. The purpose of this cross‐sectional study was to describe ultrasonographic characteristics of the abdominal esophagus and gastric cardia in normal dogs and dogs with clinical disease involving this region. A total of 126 dogs with no clinical signs of gastrointestinal disease and six dogs with clinical diseases involving the gastroesophageal junction were included. For seven euthanized dogs, ultrasonographic features were also compared with gross pathology and histopathology. Cardial and abdominal esophageal wall thicknesses were measured ultrasonographically for all normal dogs and effects of weight, sex, age, and stomach filling were tested. Five layers could be identified in normal esophageal and cardial walls. The inner esophageal layer was echogenic, corresponding to the cornified mucosa and glandular portion of the submucosa. The cardia was characterized by a thick muscularis, and a transitional zone between echogenic esophageal and hypoechoic gastric mucosal layers. Mean (±SD) cardial wall thicknesses for normal dogs were 7.6 mm (±1.6), 9.7 mm (±1.8), 10.8 mm (±1.6), 13.3 mm (±2.5) for dogs in the <10 kg, 10–19.9 kg, 20–29.9 kg and ≥30 kg weight groups, respectively. Mean (±SD) esophageal wall thicknesses were: 4.1 mm (±0.6), 5.1 mm (±1.3), 5.6 mm (±1), and 6.4 mm (±1.1) for the same weight groups, respectively. Measurements of wall thickness were significantly correlated with dog weight group. Ultrasonography assisted diagnosis in all six clinically affected dogs. Findings supported the use of transabdominal ultrasonography as a diagnostic test for dogs with suspected gastroesophageal disease. 相似文献
137.
Susan L. Kraft DVM Patrick R. Gavin DVM PHD Lyle R. Wendling MD Venkat K. Reddy BVSC PHD 《Veterinary radiology & ultrasound》1989,30(4):147-158
Magnetic resonance (MR) images of the canine brain were acquired during investigation of dogs with neurologic disease. A paramagnetic contrast medium was used for enhancement. MR provided images with excellent contrast between grey and white matter, as well as brain tissue and cerebrospinal fluid. Good resolution and anatomic detail of the canine brain were obtained. A series of images was compiled and labelled as a reference for MR anatomy of the canine brain. 相似文献
138.
G. Elizabeth Pluhar DVM MS Russell L. Tucker DVM Patrick R. Gavin DVM PhD Rodney S. Bagley DVM Mitsuhiko Takeuchi DVM 《Veterinary radiology & ultrasound》1997,38(2):112-115
A new of performing cerebral sinus venography was developed that opacivies both the ventral and most of the dorsal venous sinus systems. A pediatric angiographic catheter was introduced into the external jugular vein and advanced to the level of the temporal sinus. Iodinated contrast medium was injected manually and radiographs were made. Subtraction radiography was used to visualize vessels field wit contast medium. Venography was simple and relatively non-invasive and was considered safe. The technique was used to confirm occlusion of the transverse venous sinus in healthy dogs that had undergone radical craniectomies. 相似文献
139.
140.
Leonard Omadang Martin Chamai Emmanuel Othieno Andrew Okwi Francis Olaki Inangolet Francis Ejobi Peter Oba Michael Ocaido 《Tropical animal health and production》2018,50(1):11-17
A cross-sectional study was done from March 2013 to May 2014 to assess knowledge, attitudes, and practices towards cystic echinococcosis (CE) or hydatidosis among selected pastoral and agro-pastoral communities in Uganda. A structured questionnaire was administered to 381 respondents. Multivariate logistic regression analysis was done to find the relationship between knowledge about CE and factors such as age, sex, and level of education across all regions. The odds ratio and confidence interval were used to determine the difference in responses across regions. It was shown that age above 36 years was significantly (p < 0.001) associated with awareness about CE in livestock. Likewise, uneducated (p < 0.0001) and agro-pastoralists (p = 0.01) were significantly less knowledgeable than the educated and pastoralists across all regions. The overall knowledge towards CE in livestock was low 17.8% (95% CI = 14.0–21.6). Dog ownership was high and they never dewormed their freely roaming dogs. Dogs shared water with livestock. In conclusion, knowledge about CE in livestock was low across all regions. Therefore, public health education and formulation of policies towards its control by the relevant stakeholders should be done. Also, the true prevalence of CE in livestock needs to be done so that the magnitude and its public health significance are elucidated. 相似文献