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   62740篇
  免费   2850篇
  国内免费   42篇
林业   2532篇
农学   1653篇
基础科学   429篇
  6183篇
综合类   14783篇
农作物   2475篇
水产渔业   2367篇
畜牧兽医   31136篇
园艺   644篇
植物保护   3430篇
  2017年   559篇
  2016年   542篇
  2014年   546篇
  2013年   1872篇
  2012年   1217篇
  2011年   1449篇
  2010年   919篇
  2009年   881篇
  2008年   1434篇
  2007年   1406篇
  2006年   1384篇
  2005年   1389篇
  2004年   1328篇
  2003年   1396篇
  2002年   1359篇
  2001年   1496篇
  2000年   1477篇
  1999年   1211篇
  1998年   532篇
  1997年   542篇
  1995年   597篇
  1994年   575篇
  1993年   564篇
  1992年   1310篇
  1991年   1396篇
  1990年   1452篇
  1989年   1490篇
  1988年   1404篇
  1987年   1365篇
  1986年   1403篇
  1985年   1378篇
  1984年   1152篇
  1983年   1008篇
  1982年   721篇
  1981年   689篇
  1980年   645篇
  1979年   1128篇
  1978年   917篇
  1977年   819篇
  1976年   770篇
  1975年   861篇
  1974年   1126篇
  1973年   1063篇
  1972年   1129篇
  1971年   1080篇
  1970年   1023篇
  1969年   874篇
  1968年   711篇
  1967年   846篇
  1966年   694篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Morbidity (greater than or equal to 1 disease condition) for pups sold from 3 pet stores from January 1987 through December 1988 ranged from 54 to 68%. In 1 store, morbidity was higher for store pups, compared with pups originating from private parties, for such disease conditions as "kennel cough," diarrhea, and several species of gastrointestinal parasites. In-store mortality ranged from 5 to 9.5% of pups arriving for sale.  相似文献   
992.
Genetic parameters of piglet survival traits and birth weight were estimated on the first generation data of a selection experiment aimed at improving piglet survival using a multiple trait linear and threshold model. Data on 5293 piglets for survival at birth, at day one after birth and during the entire nursing period, as well as individual birth weight and litter size, were recorded in an outdoor production system. Genetic effects of piglet survival traits and birth weight were estimated based on threshold and Gaussian models, respectively, using a Bayesian approach. The statistical model included as fixed effects selection group, parity, gender, fostering, gestation length and month of farrowing and, alternatively, an adjustment for litter size. Direct genetic effects (i.e. the piglet's genetic potential) for piglet survival and birth weight were estimated separately, whereas maternal genetic and environmental effects could only be estimated for the given data structure in a combined litter effect. Posterior means of heritabilities for direct genetic effects of survival at birth, at first day after birth and the entire nursing period, as well as birth weight, were 0.08, 0.07, 0.08 and 0.20, respectively. Genetic correlations among survival traits were in the range of 0.29 to 0.40 and indicate that these traits were mainly attributable to different genetic effects. Genetic correlations between direct effects of survival traits and birth weight ranged between 0.18 and 0.23 and were reduced when weights of stillborn piglets were omitted in the analysis or the traits were adjusted for litter size. The magnitudes of direct genetic effects of survival traits are substantially higher than estimates in the literature, which may indicate that these traits have a higher genetic influence under outdoor conditions. The use of birth weight in the multiple trait estimation provided important information for the estimation of survival traits due to its favourable genetic correlations with survival, its high heritability and its high information content as a continuously measured trait.  相似文献   
993.
Background: Marked eosinophilic meningitis or meningoencephalomyelitis (EME) is rarely reported in dogs and the cause is usually undetermined. Long-term prognosis for dogs with cerebrospinal fluid (CSF) eosinophilia is variable.
Animals: Twenty-three client-owned dogs.
Methods: Retrospective case series. Dogs with eosinophilic CSF, defined as total nucleated cell count (TNCC) >3 cells/μL with >20% eosinophils, were identified by a computerized search of all dogs having cisternal and/or lumbar CSF analyzed as part of the diagnostic workup between 1992 and 2007.
Results: TNCC in CSF ranged from 4 to 4,740 cells/μL (median 84 cells/μL, reference range ≤3 cells/μL), with 22 to 95% (median 78%) eosinophils in the differential count. An infectious agent was identified on necropsy in 4 of 23 (17%) dogs ( Cryptococcus neoformans [n = 2], Neospora caninum [n = 1], and Baylisascaris procyonis [n = 1]). Each of these dogs had progressive neurologic deterioration. Sixteen dogs had idiopathic EME. Magnetic resonance imaging (MRI) findings were abnormal in 7 of 13 dogs with EME; 2 dogs had focal lesions and 5 dogs had multifocal lesions. Clinical signs in 12 of 16 (75%) dogs with idiopathic EME resolved with prednisone treatment. Three dogs with acute intervertebral disc herniations recovered after decompressive surgery alone.
Conclusions: Idiopathic EME is a common cause of eosinophilic pleocytosis in dogs. MRI findings are variable. Infectious causes of EME were less common and had a poor prognosis.  相似文献   
994.
Regarding the estimation of the energy concentration or digestibility of herb-dominated forage and plant samples from winter pastures, it could be expected that the estimation is only reliable when in vitro methods with rumen fluid as inoculum (= gas production techniques) are used. For the verification of this thesis based on logical reflections, an in vitro-method with rumen fluid added as inoculum, as well as chemical, and enzymatic methods were applied under consideration of existing estimating functions. As a possible reason for the observed divergence of the methods, effects of fungal infections or, respectively, secondary compounds in herbs are discussed. At the present state of knowledge, it is adequate to estimate the energy concentration in vitro by gas tests, as far as fattening types like suckler cows and beef cattle are concerned, maybe in contrast to the forage evaluation for dairy cows.  相似文献   
995.
The aim of the study was to investigate the influence of growth hormone (GH) on Vitamin D3 metabolism and the subsequent effects on calcium (Ca) homeostasis and skeletal growth in growing dogs. A group of Miniature Poodles received supraphysiological doses of GH (GH group; n = 6; 0.5 IU GH per kg body per day) from 12 to 21 weeks of age and was compared with a control placebo-treated group (n = 8). Biologic activity of GH in the GH compared to the control group was indicated by (a) the 2.5- to 3.5-fold increase in the plasma concentrations of insulin-like growth factor I (IGF-I), (b) the increased production of 1,25-dihydroxycholecalciferol as indicated by the significantly increased plasma 1,25-dihydroxycholecalciferol concentrations and the 12.9-fold increase in renal 1alpha-hydroxylase gene expression, and (c) the inhibited production of 24,25-dihydroxycholecalciferol as indicated by the significantly lower plasma 24,25-dihydroxycholecalciferol concentrations and the similar levels of renal 24-hydroxylase gene expression. Despite the distinct effects on Vitamin D(3) metabolism in the GH group, there were only moderate effects on the intestine, i.e. at 20 weeks of age there was a significant increase of 14.4 and 5.6% in fractional absorption of Ca and phosphate (Pi), respectively, compared to the control group. GH administration resulted in significantly elevated glomerular filtration rate, with no differences in Pi urine excretion as a result of a concomitant increase in the tubular reabsorption of Pi. GH had only limited disturbing effects on endochondral ossification as indicated by the maintenance of the regularity of the growth plates. However, GH had specific anabolic effects on bone formation without concomitant effect on bone resorption that may result in disorders of skeletal remodeling and manifestation of enostosis.  相似文献   
996.
997.
Seven goats were given a single dose of an aqueous extract derived from 30 g (wet weight) of Narthecium ossifragum per kg liveweight. Their serum creatinine and urea concentrations increased to day 5 but then fell to normal by day 10. Serum magnesium increased to day 4 and decreased to normal by day 9. Their serum calcium concentration was lower than normal on days 4, 5 and 6. Histopathological examination of the kidneys of goats killed or found dead 2, 4, 6, 8, 11 or 16 days after dosing revealed tubular epithelial cell degeneration and necrosis. Regeneration of the tubular epithelium and signs of interstitial fibroplast proliferation and fibrosis could be seen in animals killed on days 8, 11, 16 and 42. No signs of liver damage were observed in 3 goats dosed with the insoluble plant material from 40 g (wet weight) Narthecium ossifragum per kg liveweight. The total dose was divided into three doses, which were given intraruminally within 7 h. The activities of aspartate aminotransferase, -glutamyl-transferase and glutamate dehydrogenase remained within the normal range in all 10 goats after dosing.  相似文献   
998.
A high-calorie oral rehydration solution (ORS) with glutamine (n=11) was more effective in correcting plasma, extracellular fluid and blood volume than solutions without (one WHO-type solution, n=6, and two high-glucose but glutamine-free solutions, n=7, n=12). It was the only solution to improve plasma volume significantly within 48 h and sustain the improvement throughout treatment; similarly, it was the only solution to correct packed-cell volume within 48 h and sustain the benefit to the end of treatment. At the end of treatment, the glutamine-treated calves were the only ones to avoid a significant weight loss compared with their pre-diarrhoeic values. The crucial difference between this solution and those used with glutamine previously is that it gave significant nutritional support whereas WHO type solutions did not. It also had more favourable effects on hyponatraemia and metabolic acidosis than a standard ORS. Use of a high-calorie ORS for 4 days (rather than 2 days of 50:50 admixture with milk replacer) brought additional beneficial effects on blood glucose and body weight.  相似文献   
999.
A 10-year-old male cat was presented with sudden onset of respiratory difficulties. Clinical examinatlon revealed an acute dyspnoea with cyanosis associated with a left systolic heart murmur. Standard thoracic radiographs excluded pulmonary oedema and showed very few pulmonary changes given the intensity of the respiratory compromlse. Echocardiographic examination revealed hypertrophic cardiomyopathy and a thrombus In the right pulmonary artery. Pulmonary sclntlgraphy confirmed a pulmonary thromboembolism with hypovascularisatlon of the left cranial lobe and of the ventral segment of the right lobe. Conservative treatment was instituted using an antibiotic (doxycycllne), anticoagulants (heparin, coumadine) and a calcium lnhlbitor (diltiazem). The cat was given absolute rest. The general condition of the animal improved.  相似文献   
1000.
Fourteen dogs with histologically-confirmed transitional cell carcinoma (TCC) of the urinary bladder were treated with 300 mg/m2 carboplatin every 3 weeks. Response to therapy was assessed with abdominal radiography, double contrast cystography, urinary bladder ultrasonography and thoracic radiography before therapy and at 6–week intervals during therapy. Dogs were monitored for hematologic toxicity with a CBC and platelet count performed immediately before and 10 to 14 days after carboplatin treatment. Tumor responses included progressive disease in 11 dogs and stable disease in 1 dog. Two dogs were euthanized due to carboplatin toxicity before assessment of tumor response. Toxicity included thrombocytopenia with or without neutropenia in 7 dogs and gastrointestinal toxicity in 6 dogs. Carboplatin therapy was not beneficial in the treatment of TCC in the 14 dogs in this study.  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