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   17064篇
  免费   898篇
  国内免费   17篇
林业   828篇
农学   561篇
基础科学   122篇
  2509篇
综合类   2677篇
农作物   911篇
水产渔业   951篇
畜牧兽医   8313篇
园艺   199篇
植物保护   908篇
  2020年   161篇
  2019年   182篇
  2018年   310篇
  2017年   365篇
  2016年   261篇
  2015年   198篇
  2014年   316篇
  2013年   666篇
  2012年   497篇
  2011年   620篇
  2010年   428篇
  2009年   410篇
  2008年   632篇
  2007年   552篇
  2006年   513篇
  2005年   455篇
  2004年   420篇
  2003年   430篇
  2002年   373篇
  2001年   487篇
  2000年   475篇
  1999年   373篇
  1998年   180篇
  1997年   202篇
  1996年   157篇
  1995年   193篇
  1993年   165篇
  1992年   280篇
  1991年   315篇
  1990年   308篇
  1989年   312篇
  1988年   291篇
  1987年   246篇
  1986年   295篇
  1985年   254篇
  1984年   209篇
  1983年   207篇
  1979年   250篇
  1978年   166篇
  1977年   155篇
  1975年   171篇
  1974年   235篇
  1973年   215篇
  1972年   251篇
  1971年   230篇
  1970年   203篇
  1969年   192篇
  1968年   158篇
  1967年   160篇
  1966年   161篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
1. This study was conducted to determine the effects of heat stress on fearfulness, leucocyte components, oxidative stress and lipid peroxidation in two commercial broiler strains, Cobb (C) and Ross (R). 2. At 36 and 37 d of age birds were exposed to 38 +/- 1 degree C for 3 h. Rectal temperatures, duration of tonic immobility (TI), haematocrit values, proportions of leucocyte components (heterophil, lymphocyte, basophil, eosinophil, monocyte), malondialdehyde (MDA) concentrations and antioxidant enzyme activities (CAT, SOD, GPx) of all the birds were determined, before and after heat treatment. 3. Rectal temperatures increased and haematocrit values decreased in birds exposed to heat stress. Heat stress caused a significant increase in heterophil/lymphocyte and in basophil ratios. 4. Exposing birds to heat stress increased duration of TI, suggesting heat-stressed birds tended to be more fearful. 5. Heat stress resulted in a significant Genotype x Treatment interaction for MDA concentration. CAT, SOD and GPx activities; MDA concentrations in heat-stressed R strain birds were greater than in heat-stressed C strain birds.  相似文献   
62.
A captive 16-year-old male camel (Camelus ferus bactrianus) was euthanized after a prolonged period of inappetence leading to cachexia. At necropsy, there was a 7 cm large, tan, firm, well-demarcated nodule in the tunica muscularis and serosa of the distal region of C3. Histologically, a gastric adenocarcinoma was diagnosed. Numerous metastases were found in the liver and the hepatic lymph nodes, in the wall of the portal vein and the aorta, in the lung, heart, and pleura parietalis. Osseous metaplasia was found within the pleural and aortic metastases. In the mucosa of the glandular region of the C3 compartment a diffuse marked hypertrophy of rugae resembling cerebral convolutions was observed. The lesion was characterized by glandular hyperplasia and stromal inflammation and oedema. These changes closely resembled Menétrier's disease described in humans. To our knowledge, this is the first report of concomitant metastatic gastric adenocarcinoma and gastric hyperplasia in a camel.  相似文献   
63.
An 8-year-old ovariohysterectomized Chow Chow was referred because of dermatologic lesions diagnosed as pemphigus foliaceus. Intolerance to orally administered corticosteroids necessitated the use of methylprednisolone pulse therapy. One week after treatment, diabetes mellitus was diagnosed on the basis of blood and urine test results. For 3 years after treatment, the dog has remained a well-regulated diabetic. Complete remission of pemphigus foliaceus is maintained by alternate-day, orally administered prednisone (0.5 mg/kg of body weight).  相似文献   
64.
The department of National Parks and Protection of Wild Nature sent five (two males, three females) adult long-legged buzzards for investigation of their deaths to Ankara University Veterinary Faculty. Facial bones of buzzards were evaluated. Distinguishing facial features such as strong os premaxillare, cavum nasale filled with spider webbing-like structures, prominent os prefrontalis and processes, H-shaped paraglossum were determined. In this study, we investigated the anatomic properties of facial bones in long-legged buzzard. We also aimed to identify the data using these bones in order to separate different bird species.  相似文献   
65.
The Cornell Net Carbohydrate and Protein System (CNCPS), a mechanistic model that predicts nutrient requirements and biological values of feeds for cattle, was modified for use with sheep. Published equations were added for predicting the energy and protein requirements of sheep, with a special emphasis on dairy sheep, whose specific needs are not considered by most sheep-feeding systems. The CNCPS for cattle equations that are used to predict the supply of nutrients from each feed were modified to include new solid and liquid ruminal passage rates for sheep, and revised equations were inserted to predict metabolic fecal N. Equations were added to predict fluxes in body energy and protein reserves from BW and condition score. When evaluated with data from seven published studies (19 treatments), for which the CNCPS for sheep predicted positive ruminal N balance, the CNCPS for sheep predicted OM digestibility, which is used to predict feed ME values, with no mean bias (1.1 g/100 g of OM; P > 0.10) and a low root mean squared prediction error (RMSPE; 3.6 g/100 g of OM). Crude protein digestibility, which is used to predict N excretion, was evaluated with eight published studies (23 treatments). The model predicted CP digestibility with no mean bias (-1.9 g/100 g of CP; P > 0.10) but with a large RMSPE (7.2 g/100 g of CP). Evaluation with a data set of published studies in which the CNCPS for sheep predicted negative ruminal N balance indicated that the model tended to underpredict OM digestibility (mean bias of -3.3 g/100 g of OM, P > 0.10; RMSPE = 6.5 g/100 g of OM; n = 12) and to overpredict CP digestibility (mean bias of 2.7 g/100 g of CP, P > 0.10; RMSPE = 12.8 g/100 g of CP; n = 7). The ability of the CNCPS for sheep to predict gains and losses in shrunk BW was evaluated using data from six studies with adult sheep (13 treatments with lactating ewes and 16 with dry ewes). It accurately predicted variations in shrunk BW when diets had positive N balance (mean bias of 5.8 g/d; P > 0.10; RMSPE of 30.0 g/d; n = 15), whereas it markedly overpredicted the variations in shrunk BW when ruminal balance was negative (mean bias of 53.4 g/d, P < 0.05; RMSPE = 84.1 g/d; n = 14). These evaluations indicated that the Cornell Net Carbohydrate and Protein System for Sheep can be used to predict energy and protein requirements, feed biological values, and BW gains and losses in adult sheep.  相似文献   
66.
67.
Approximately 88% of Norwegian dairy cattle are housed in tie stalls. Free stall housing for all dairy cattle will be implemented within 20 years. This means that the majority of existing stalls will be rebuilt in the near future. Fifty-seven free stall herds of the Norwegian Red breed were randomly selected and 1547 cows and 403 heifers were trimmed by 13 claw trimmers during the late winter and spring of 2002. The claw trimmers had been taught diagnosing and recording of claw lesions. Environment, management- and feeding routines were also recorded. Fifty-three herds had concrete slatted alleys while 4 had solid concrete. Thirty-five herds had concrete as a stall base, while 17 had rubber mats, 2 had wood and 3 had deep litter straw beds. The prevalence of lameness was 1.6% in hind claws. Models for lameness and claw lesions were designed to estimate the influence of different risk factors and to account for the cluster effects within herd and claw trimmer. Detected risk factors for lameness were: parity three and above and narrow cubicles; for heel horn erosions: lactation stage around 5-7 months after calving and solid concrete alleys; for haemorrhages of the white line: lactation stage around 3-5 months after calving and solid concrete alleys; for haemorrhages of the sole: parity one, lactation stage around 5-7 months after calving and short cubicles, for white line fissures: slatted concrete alleys; for asymmetrical claws: parities two and above and for corkscrewed claws: solid concrete alleys. The prevalence of lameness in heifers was low, however 29% had one or more claw lesions. Heifers that were housed in pens or free stalls had more heel-horn erosions, haemorrhages of the sole and white-line fissures than heifers in tie stalls. As new free stalls are being built, it is important to optimise the conditions for claw health.  相似文献   
68.
The glycosoaminoglycans in the digestive apparatus of immature fish have important biological functions and are involved in morphofunctional differentiation. The aim of this study was to investigate the glycoconjugate histochemistry in the different parts of the digestive apparatus (oesophagus, stomach, intestine) of Umbrina cirrosa (L.) fry using classical histochemical reactions (periodic acid-Schiff, Alcian blue pH 2.5, Alcian blue/periodic acid-Schiff, high iron diamine, low iron diamine) in conjunction with glycolytic digestions that degrade different classes of glycosoaminoglycans. No differences were observed in the reactivity to conventional histochemical staining of the oesophagus, stomach or intestine among 27-, 34- or 44-day-old fry. In the oesophagus, the mucopolysaccharides contained chondroitin sulphates B and A and/or C, heparan sulphate and chondroitin. In the stomach, only neutral glycoconjugates were revealed, whereas in the intestine there were only chondroitin sulphates. Some differences in the type and content of glycoconjugates were found in Umbrina cirrosa (L.) fry compared to those of adult subjects, probably related to different dietary habits and to changes in the environmental conditions.  相似文献   
69.
70.
Craniofacial malformation in 64 sheep was phenotypically described as mandibular distoclusion. Digital radiographs were examined in order to determine the degree of morphological changes in certain bones of the skull. Therefore, laterolateral standardised digital radiographs were used to determine anatomic reference points. Subsequently, five reference lines were defined and 16 linear and seven angular measurements were determined to describe malformations in the bones of the skull. Statistical analysis revealed a significant shortening of the rostral part of the corpus mandibulae and of the ramus mandibulae. However, the molar part of the mandible remained unchanged. These morphological changes caused premolar and molar malocclusion. No further craniofacial abnormalities, such as an elongation of the maxilla or of the incisive bone, were identified. In conclusion, the phenotypically observed mandibular distoclusion is caused by a shortening of specific parts of the mandible. This form of ovine craniofacial malformation is therefore best described as brachygnathia inferior.  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