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   50367篇
  免费   2740篇
  国内免费   110篇
林业   1835篇
农学   1877篇
基础科学   301篇
  6150篇
综合类   8440篇
农作物   1634篇
水产渔业   2763篇
畜牧兽医   26641篇
园艺   611篇
植物保护   2965篇
  2019年   438篇
  2018年   794篇
  2017年   853篇
  2016年   773篇
  2015年   642篇
  2014年   773篇
  2013年   1823篇
  2012年   1414篇
  2011年   1761篇
  2010年   1222篇
  2009年   1153篇
  2008年   1750篇
  2007年   1656篇
  2006年   1565篇
  2005年   1448篇
  2004年   1416篇
  2003年   1402篇
  2002年   1216篇
  2001年   1950篇
  2000年   2019篇
  1999年   1537篇
  1998年   595篇
  1997年   530篇
  1996年   477篇
  1995年   627篇
  1994年   537篇
  1993年   472篇
  1992年   1165篇
  1991年   1228篇
  1990年   1197篇
  1989年   1112篇
  1988年   1074篇
  1987年   1095篇
  1986年   1042篇
  1985年   977篇
  1984年   810篇
  1983年   694篇
  1982年   426篇
  1979年   653篇
  1978年   508篇
  1977年   448篇
  1976年   419篇
  1975年   458篇
  1974年   525篇
  1973年   510篇
  1972年   534篇
  1971年   464篇
  1970年   436篇
  1969年   473篇
  1967年   395篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
941.
The influence of induced chronic renal failure on 24-hour urinary excretion and fractional excretion of sodium and potassium was studied in cats. Induction of chronic renal failure significantly increased fractional excretion of potassium (P less than 0.0001) and sodium (P less than 0.05); however, 24-hour urinary excretion of sodium and potassium decreased slightly following induction of chronic renal failure. Fractional excretion and 24-hour urinary excretion of sodium and potassium were compared by linear regression in clinically normal cats, cats with chronic renal failure, and clinically normal and affected cats combined. In clinically normal cats, linear regression revealed only moderate correlation between fractional excretion and 24-hour urinary excretion for sodium and potassium. Linear regression of these same relationships in cats with chronic renal failure, and in clinically normal cats and cats with chronic renal failure combined, indicated low correlation. Fractional excretions of sodium and potassium were not reliable indicators of 24-hour urinary excretion of these electrolytes in cats with chronic renal failure or unknown glomerular filtration rate. Fractional excretion of potassium and sodium correlated only moderately with 24-hour urinary excretion in clinically normal cats.  相似文献   
942.
1. The effect of dietary medium chain triglyceride (MCT) on short‐term food intake was compared with the effect of long chain triglyceride (LCT) in chickens. Maize oil was used as the LCT while glyceryl tricaprylate (C 8) and glyceryl tricaprate (C 10) were used as MCT. Cumulative food intake was determined during the 6 h after the start of feeding.

2. Chicks were given diets containing 200 g C 8/kg diet, 200 g C 10/kg diet or 200 g LCT/kg diet in experiment 1. As early as 30 min after feeding, cumulative food intake in both MCT‐supplemented diets decreased significantly compared with the diet containing LCT.

3. To determine if endogenous cholecystokinin (CCK) was responsible for the decrease in food intake caused by MCT, birds were injected with the CCK‐A receptor antagonist devazepide (DVZ, 1 mg/kg BW) before diet presentation. DVZ had no effect on food intake with either LCT‐ or MCT‐supplemented diets.

4. In experiment 3, chicks were given a choice between either diets containing LCT and C 8, LCT and C 10, or C 8 and C 10 to confirm whether or not the palatability of the diets was influenced by the dietary fat sources. There was no difference in food intake between C 8 and C 10‐supplemented diets. However, chicks preferred the LCT‐supplemented diet compared with either of the diets containing MCT.  相似文献   

943.
944.
Two experiments were conducted to determine (i) the effects of protein-rich trees (PRTs) and (ii) the effects of leucaena treated with NaOH solution and leucaena plus polyethylene glycol (PEG) on nutrient digestibility, nitrogen (N) balance, urinary purine derivatives excretion and blood metabolites in Thai swamp buffaloes. In Experiment 1, animals were fed with rice straw as a basal diet and one of the four PRT supplements: (i) oven-dried rain tree pods (RTPP, control); (ii) sun-dried leucaena leaves; (iii) sun-dried cassia leaves and (iv) sun-dried mulberry leaves. Fibre digestibility and N balance were lower (P < 0.05), but microbial N in the rumen was higher (P < 0.05) in animals supplemented with RTPP than in those fed with the other supplements. In Experiment 2, animals were fed with rice straw as a basal diet and leucaena were treated in one of three ways: (i) untreated (control), (ii) leucaena treated with NaOH solution and (iii) leucaena + PEG. Fibre digestibility and N balance in the rumen improved (P < 0.05) in animals supplemented with leucaena + PEG, but microbial N was not increased. The study demonstrated a way of using local PRTs for a suitable and worthwhile method to improve the quality of buffalo feeding systems in the tropics.  相似文献   
945.
Bullous pemphigoid (BP) is an autoimmune subepithelial blistering dermatosis of humans, dogs, cats and pigs. It is characterized by skin-fixed and circulating IgG autoantibodies that target one or both BP antigens. An immunological homologue of BP in humans was diagnosed in two horses with cutaneous and mucosal ulcerations as well as microscopic subepithelial vesiculation. Immunological investigations revealed similar findings for both the horses. Direct immunofluorescence demonstrated the presence of IgG deposited linearly at the dermoepidermal junction in mucosal and skin biopsy specimens. Indirect immunofluorescence testing confirmed the existence of circulating basement membrane-specific IgG autoantibodies. Using intact and salt-split epithelial substrates, serum IgG were shown to target antigens situated not only at the basal, but also at the lateral and apical aspects of stratum basale keratinocytes. Immunoblotting and ELISA corroborated that the IgG from affected horses, but not those from normal controls, exhibited high immunoreactivity against the NC16A extracellular domain of type XVII collagen (BPAG2, BP180). Equine BP could be proposed, therefore, as another spontaneous model of this most common basement membrane autoimmune dermatosis of humans.  相似文献   
946.
A young, female Maltese dog was presented with intermittent vomiting of bile. Biochemical evidence of persistent mild hepatopathy had been present for 11 months. Exploratory celiotomy was performed. Absence of the gallbladder with malformation of the quadrate lobe of the liver was identified. There was histological evidence of bile duct proliferation and portal fibrosis.  相似文献   
947.
Three juvenile sable antelope (Hippotragus niger) were diagnosed with bilateral aural hyalohyphomycosis based on histopathology. All three animals were suspected to be immunodeficient based on low IgG levels determined using the zinc sulfate turbidity test. The serum and hepatic copper levels of one animal were below the bovine reference range. Clinical signs in the three animals included bilateral ventral deviation of the pinnae with multifocal subcutaneous aural tumefaction and poor body condition. Numerous septate, nonpigmented fungal hyphae were found within the auricular cartilage, dermis, and subcutaneous granulomas. No significant fungal agents were isolated by culture, and no signs of systemic fungal dissemination were identified except for a concurrent fungal rhinitis in one animal.  相似文献   
948.
This study was undertaken to determine the hydrophobicity of the luminal surface of the equine stomach and to elucidate the ultrastructure of the lining imparting that property. Gastric and duodenal mucosal samples from 5 horses were collected immediately after euthanasia and subjected to surface contact angle measurement using a goniometer. Gastric mucosal samples from 4 horses and a foal were examined by electron microscopy following a fixation procedure known to preserve phospholipids and oligolamellar structures. Contact angles for the equine gastric glandular mucosal surface (mean +/- s.e. 78.0 +/- 11.0 degrees) were greater than for the duodenum (33.4 +/- 8.7 degrees), (P = 0.003). The contact angles for gastric squamous tissue (50.4 +/- 4.5 degrees) tended to be greater than for duodenum (P = 0.15). Electron microscopy revealed the existence of surfactant as abundant osmiophilic phospholipid material within both squamous and glandular gastric mucosae. These results indicate the hydrophobic nature of the equine gastric mucosae. We propose that the water-repellent nature of the stomach contributes to the 'gastric mucosal barrier' and is imparted by surface-active phospholipid adsorbed to the surface. Phospholipids may also be utilised as a physical barrier to back-diffusion of acid by lining intracellular canaliculi and oxyntic ducts where other defence mechanisms are absent.  相似文献   
949.
Objectives : To describe the use of absorbable gelatin sponges as haemostatic implants in clinical veterinary surgical cases and to document any related postoperative complications. Methods : Practice databases were searched for the product names “Gelfoam” and “Spongostan”. Patient records were retrieved and data regarding patient signalment, surgical procedure, National Resource Council (NRC) wound classification, source of haemorrhage, pre‐ and postoperative body temperature, postoperative complications, time to discharge and details of any postoperative imaging were recorded and reviewed. Follow‐up information was obtained by repeat clinical examination or telephone interview with either the owner or referring veterinary surgeon. Cases with incomplete surgical records or those which were not recovered from anaesthesia were excluded from the analysis. Results : Fifty cases (44 dogs and 6 cats) satisfied the inclusion criteria. Satisfactory haemostasis was achieved in 49 cases with one case requiring reoperation during which a second gelatin sponge was used. There were no detected hypersensitivity responses or confirmed postoperative complications relating to the use of gelatin sponges during the follow‐up period (median 13 months). Clinical Significance : This is the first review of the use of gelatin sponges in clinical veterinary surgery and suggests that gelatin sponges are safe to use in cats and dogs.  相似文献   
950.
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