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   28917篇
  免费   1532篇
  国内免费   11篇
林业   1199篇
农学   918篇
基础科学   195篇
  4650篇
综合类   3681篇
农作物   1101篇
水产渔业   1868篇
畜牧兽医   14596篇
园艺   376篇
植物保护   1876篇
  2021年   286篇
  2020年   277篇
  2019年   384篇
  2018年   624篇
  2017年   663篇
  2016年   646篇
  2015年   463篇
  2014年   618篇
  2013年   1238篇
  2012年   1045篇
  2011年   1228篇
  2010年   845篇
  2009年   854篇
  2008年   1209篇
  2007年   1137篇
  2006年   994篇
  2005年   905篇
  2004年   822篇
  2003年   840篇
  2002年   731篇
  2001年   884篇
  2000年   891篇
  1999年   686篇
  1998年   301篇
  1997年   305篇
  1995年   297篇
  1992年   444篇
  1991年   537篇
  1990年   457篇
  1989年   430篇
  1988年   411篇
  1987年   421篇
  1986年   371篇
  1985年   396篇
  1984年   348篇
  1983年   300篇
  1982年   249篇
  1979年   389篇
  1978年   295篇
  1977年   296篇
  1976年   304篇
  1975年   318篇
  1974年   336篇
  1973年   304篇
  1972年   295篇
  1971年   250篇
  1969年   301篇
  1968年   272篇
  1967年   332篇
  1966年   306篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
192.
Reasons for performing study: Type 2 diabetes mellitus (T2DM) is diagnosed rarely in equine practice although it may be under‐recognised. A greater awareness of the condition and therapeutic considerations would be to the benefit of such cases presenting in practice. More investigation into the pharmacological management of these cases is needed. Objectives: Three cases of diabetes mellitus were investigated using a specific test for insulin sensitivity and pancreatic β cell function in order to define accurately and characterise the existence of T2DM in all 3 subjects. Methods: The insulin‐modified frequently sampled i.v. glucose tolerance test was performed in each case and the data so obtained were subject to minimal model analysis of insulin‐glucose dynamics. Cases were then monitored following treatment using a combination of dietary modification, metformin, glibenclamide and pergolide. Results: Marked insulin resistance was identified in each case and, furthermore, severe pancreatic β cell dysfunction was present therefore classifying each case as end stage T2DM. Treatment was nevertheless associated with restoration of normoglycaemia in all cases. Conclusions: T2DM in horses may be more common than generally considered. In some cases individuals may respond to therapy aimed at restoring insulin sensitivity and pancreatic function. Drugs used in other species for the treatment of T2DM have not yet been adequately tested in horses. Potential relevance: T2DM should be considered as an important differential diagnosis in mature to elderly horses and ponies suffering from weight loss, polydipsia and polyuria. Clinicians should be encouraged to offer treatment and management advice when such cases are encountered.  相似文献   
193.
1. This study aimed to evaluate the effects of juniper oil on growth performance and meat quality in quails to determine its use as a safe and natural method to reduce overdependence on the use of antibiotic.

2. A total of 1000 1-d-old Pharaoh (Coturnix coturnix Pharaoh) quails, including both males and females, were divided into 4 groups containing 250 quails and treated as follows: (1) a control group with 0 mg volatile oil/kg diet; (2) 100 mg/kg juniper oil; (3) 150 mg/kg juniper oil and (4) 200 mg/kg juniper oil. The diets were prepared fresh for each treatment. The experiment was carried out for 42 d.

3. The results of the study showed that supplementation with juniper oil (100 and 150 mg/kg) caused a significant increase in live weight, live weight gain and carcass yields during the growing and finishing periods. Feed intake and feed conversion ratio were not significantly influenced by treatments.

4. The quails given rations containing juniper oil had reduced thiobarbituric acid levels in raw thigh meat samples at different storage times. Juniper oil was found to have significant antioxidant activity and prevented lipid oxidation in stored meat.

5. In conclusion, natural antioxidants such as a juniper oil can be used instead of synthetic antioxidants to retard lipid oxidation in animal diets to improve meat product quality and animal performance.  相似文献   

194.
195.
196.
The aim of this study was to determine the developmental anatomy of intrinsic cardiac ganglia with respect to epicardiac ganglionated nerve plexus in the human fetuses at different gestation stages. Twenty fetal hearts were investigated applying a technique of histochemistry for acetylcholinesterase to visualize the epicardiac neural ganglionated plexus with its subsequent examinations on total (non-sectioned) hearts. Most epicardiac ganglia embodied multilayered neurons and were oval in shape, but some ganglia involved neurons lying in one layer or had the irregular appearance because of their extensions along inter-ganglionic nerves. The mean ganglion area of fetuses at gestation stages of 15–40 weeks was 0.03 ± 0.008 mm2. The largest epicardiac ganglia, reaching in area 0.4 mm2, were concentrated on the dorsal surface of both atria. The particular fused or "dual" ganglia were identified at the gestation stages of 23–40 weeks, but they composed only 2.3 ± 0.7% of all found epicardiac ganglia. A direct positive correlation was determined between the fetal age and the ganglion area (mm2) as well as between the fetal age and the number of inter-ganglionic nerves. The revealed appearance of epicardiac ganglia in the human fetuses at 15–40 weeks of gestation confirms their prenatal development and presumable intrinsic remodelling.  相似文献   
197.
198.
To evaluate the effect of Spanish summer commercial journeys on the stress response of young bulls born and reared under extensive conditions, 2 replicates of a transport from an assembly centre to a growing-finishing farm were studied. Journeys lasted 27 h, involving a total of 62 young bulls. Variables under study included haematocrit, red blood cell count (RBC), total white blood cell count (WBC), differential WBC counts, serum haptoglobin (Hp), cortisol, glucose, creatine phosphokinase (CPK), lactate dehydrogenase (LDH), total protein, and albumin at loading, at the end of an intermediate market stop, and at the unloading. Before the beginning of the journey elevated WBC and neutrophil counts, and high Hp values were detected, reflecting high stress levels probably as a consequence of previous procedures associated with the grouping at the assembly centre. Some stress was also detected at the end of the market stop, with cortisol increasing from 6.5 to 12.6 ± 2.0 ng/mL (< 0.001), although a change in Hp concentration was not observed. Neither CPK and LDH activities, related to muscular tissue damage, nor haematocrit and RBC count, related to dehydration revealed a significant effect of this first stage of the journey on the physical stress of the young bulls. Subsequent 13 h transport to the growing-finishing farm induced an increase in Hp levels from 0.48 to 0.78 ± 0.16 mg/mL (< 0.001), reflecting an onset of the acute stress response, although cortisol levels immediately after the unloading were similar to those found before loading at the market, suggesting that calves got accustomed to transport. At the end of the journey some dehydration and physical stress were also detected. Overall, our study provides new information to the discussion of the effect of temperatures during cattle transport. Although an improvement in pre-transport conditions is essential if the welfare of assembled and transported cattle is to be improved, the stress-related alteration of cattle physiology under Spanish summer commercial transport conditions is similar to that observed under colder conditions.  相似文献   
199.
Examination of 41 extracted, apically infected mandibular cheek teeth (CT) without obvious causes of infection included radiography, computerised axial tomography and decalcified and undecalcified histology. In CT with recent infections, some pulps remained viable, with proliferative soft and calcified tissue changes confined to the apex. With more advanced CT infections, occlusal pulpar exposure was sometimes present (in 34% of the 41 CT), some infected pulp chambers were filled with necrotic pulp or food, and extensive destructive or proliferative changes were present in the calcified apical tissues.No physical route of infection to the apex was found in 24 CT (59%) that consequently were believed to have anachoretic infections. Fractures involving pulps, including fissure fractures between the clinical crown and infected pulps, were found in eight (20%) CT. Some CT had vertical, full length periodontal destruction between the infected apex and the gingival margin that were believed to be the route of infection in four (19%) CT and dysplastic changes were believed to have caused one (2%) infections.  相似文献   
200.
BACKGROUND: Urea and creatinine are the most frequently used indirect markers in plasma and serum of glomerular filtration rate in dogs. Both have been shown to lack sensitivity but their diagnostic efficiency for the diagnosis of kidney disease has been minimally investigated. OBJECTIVE: The purpose of this retrospective study was to investigate the influence of possible factors of variation on both analytes and to determine whether specific decision rules should be drawn up for subpopulations of dogs. METHODS: The results of urea and creatinine measurements, breed, sex, age, and health status (healthy, renal disease, or nonrenal disease) of 3822 dogs were collected from the archives of 5 veterinary clinics. Data were analyzed with univariate and multivariate decision rules with and without adjustment. RESULTS: There were significant effects and interactions of almost all of the sources of variation. Slight improvements in diagnostic efficiency were obtained by adjusting the decision rules to these sources of variations. Univariate decision rules gave approximately the same diagnostic efficiency for urea and creatinine concentrations, with sensitivity and specificity in the range of 70% and 90%, respectively, using the upper limit of the reference interval as the threshold value. Multivariate decision rules provided only minor improvements in diagnostic efficiency. CONCLUSION: Simultaneous measurement of both urea and creatinine is of limited diagnostic value over the analysis of a single variable. Creatinine is the preferred analyte as it is affected by fewer extrarenal factors of variation.  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