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   163855篇
  免费   8479篇
  国内免费   143篇
林业   6943篇
农学   4636篇
基础科学   1088篇
  18281篇
综合类   32569篇
农作物   6495篇
水产渔业   7249篇
畜牧兽医   83869篇
园艺   1889篇
植物保护   9458篇
  2018年   1993篇
  2017年   2233篇
  2016年   2056篇
  2015年   1761篇
  2014年   2181篇
  2013年   5873篇
  2012年   4136篇
  2011年   5090篇
  2010年   3303篇
  2009年   3358篇
  2008年   5113篇
  2007年   4726篇
  2006年   4525篇
  2005年   4246篇
  2004年   4277篇
  2003年   4283篇
  2002年   4050篇
  2001年   4970篇
  2000年   4968篇
  1999年   3752篇
  1998年   1591篇
  1997年   1595篇
  1995年   1853篇
  1994年   1664篇
  1993年   1681篇
  1992年   3383篇
  1991年   3727篇
  1990年   3624篇
  1989年   3614篇
  1988年   3274篇
  1987年   3395篇
  1986年   3563篇
  1985年   3474篇
  1984年   2745篇
  1983年   2509篇
  1982年   1673篇
  1981年   1629篇
  1979年   2583篇
  1978年   2045篇
  1977年   1709篇
  1976年   1618篇
  1975年   1730篇
  1974年   2277篇
  1973年   2325篇
  1972年   2303篇
  1971年   2210篇
  1970年   2103篇
  1969年   1929篇
  1968年   1605篇
  1967年   1720篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
The aim of this study was to evaluate dietary supplementation of different levels of dehydrated bocaiuva pulp (DBP) on the productive performance of laying quails, and on lipid oxidation, and quality in their eggs. A total of 120 quails were distributed in a completely randomized design with six treatments (0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% of DBP), five replicates and four birds per experimental unit. To evaluate lipid oxidation, the eggs were collected on five consecutive days at the end of the trial and distributed in a completely randomized experimental design in a 6 × 5 factorial scheme (eggs from quails fed different levels of DBP × evaluated fresh and after 7, 14, 21 and 28 days). The antioxidant potential of diets was improved (p < 0.05) when the DBP was added estimated as 2,2'‐azinobis‐3‐ethylbenzothiazolin‐6‐sulfonic acid (ABTS) free radical scavenging capacity. No effect (p > 0.05) was observed on feed intake, hen‐day egg production and feed conversion (kg/kg and kg/dz). There were no changes (p > 0.05) in the egg weight, Haugh unit, yolk index or eggshell percentage. Although no difference was observed (p > 0.05), when comparing each level with the control, a negative linear effect (p < 0.05) on specific gravity was observed. In addition, only the treatment with 0.5% pulp exhibited lower (p < 0.05) eggshell thickness compared with the control (0%). Thiobarbituric acid reactive substances (TBARS) analysis showed that as the dietary pulp level was increased, malondialdehyde content decreased linearly (p < 0.05) in the egg yolks, regardless of the storage period. Inclusion of DBP in the diets had no effect (p > 0.05) on the concentration of conjugated dienes in the eggs. The diets containing DBP showed a potential antioxidant effect, reducing the degree of lipid oxidation in egg yolk. However, no beneficial effects were observed on performance and egg quality.  相似文献   
982.
983.

Background

Immune‐mediated polyarthopathy (IMPA) is common in dogs, and is monitored by serial arthrocenteses.

Hypothesis/Objectives

Plasma C‐reactive protein (CRP), interleukin‐6 (IL‐6), and CXCL8 (interleukin‐8) would serve as noninvasive markers of joint inflammation in IMPA.

Animals

Nine client‐owned dogs with idiopathic IMPA; 6 healthy controls.

Methods

Prospective study. Plasma CRP, IL‐6, and CXCL8 were measured by ELISA at baseline, 2, and 4 weeks during treatment with prednisone at 50 mg/m2/day. Arthrocenteses, the canine brief pain inventory (CBPI), and accelerometry collars were used to assess joint inflammation, lameness, and mobility at all 3 time points.

Results

C‐reactive protein concentrations were higher in IMPA dogs (median 91.1 μg/mL, range 76.7–195.0) compared with controls (median <6.3 μg/mL, <6.3–13.7; P = .0035), and were significantly lower at week 2 (10.6 μg/mL, <6.3–48.8) and week 4 (<6.3 μg/mL, <6.3–24.4; P < .001).C‐reactive protein was correlated with median CBPI scores (r = 0.68; P = .0004), joint cellularity (r = 0.49, P = .011), and mobility by accelerometry (r = −0.42, P = .048). Plasma IL‐6 concentrations were also higher in IMPA dogs (median 45.9 pg/mL), compared with controls (median <15.7 pg/mL; P = .0008). IL‐6 was lower in IMPA dogs by week 4 (<15.7 pg/mL; P = .0099), and was modestly correlated with CBPI scores (r = 0.47, P = .023). CXCL8 did not differ significantly between IMPA and healthy dogs.

Conclusions

Plasma CRP and IL‐6 might be useful surrogate markers of synovial inflammation and disease activity in dogs with IMPA.  相似文献   
984.
A 14-y-old spayed female Labrador Retriever was presented with an 8-mo history of chronic vomiting. Abdominal ultrasound and gastrointestinal endoscopy revealed a mass protruding into the gastric lumen, with cytologic features suggestive of sarcoma. A partial gastrectomy was performed; the gastric body and antrum were thickened, with a cerebriform appearance of the mucosal surface. Histologic examination revealed a submucosal neoplastic proliferation of fusiform cells variably arranged in irregular bundles and scattered whorls. Fusiform cells strongly reacted to antibodies against vimentin, S100, and neuron-specific enolase; glial fibrillary acidic protein was moderately and multifocally expressed. Pancytokeratin, KIT, α–smooth muscle actin, and desmin were nonreactive. Histologic and immunohistochemical findings suggested a diagnosis of gastric sarcoma with features referable to a non-GIST (gastrointestinal stromal tumor), non–smooth muscle NIMT (non-angiogenic, non-lymphogenic intestinal mesenchymal tumor). The overlying gastric mucosa was thickened by elongated and dilated gastric glands, predominantly lined by intensely periodic acid-Schiff–stained mucous cells. This altered mucosal architecture was suggestive of Ménétrier-like disease. Although this disease has been hypothesized to predispose to gastric adenocarcinoma in dogs, an association with gastric sarcoma has not been documented previously in the veterinary literature, to our knowledge.  相似文献   
985.
Calves were vaccinated orally, subcutaneously or intraperitoneally with a smooth, plasmid-cured strain of Salmonella enterica serovar typhimurium, strain 81. Oral vaccination was not effective, as only 1/5 calves survived challenge with virulent S. typhimurium. Strain 81 was attenuated for calves, as only a slight rise in rectal temperatures was detected after vaccination. The organism was excreted by some calves in the faeces, but no signs of diarrhoea were observed after vaccination. After parenteral vaccination, strain 81 was able to reach the intestines, gastric associated lymphoid tissues and other internal lymphoid tissues and remained viable for up to 14 days in the bovine host. After oral challenge with a virulent strain, 9/10 vaccinated calves survived challenge as opposed to 4/10 control calves (p<0.5). Diarrhoea was present in all calves of the control groups, but in only 4/10 of the vaccinated calves. The clinical reactions of the vaccinated calves were milder than in the control calves, as the rises in rectal temperatures were lower, diarrhoea was less severe, and the challenge strain was present in fewer organs from vaccinated calves than control calves. This study showed that parenterally administered Salmonella vaccines can induce both mucosal and systemic immunity, and it is postulated that this capability of strain 81 is related to its colonisation of lymphoid tissues and other systemic and intestinal tissues. This study confirmed that plasmid-cured strains were attenuated in the bovine host and conferred significant protection after parenteral vaccination, but not oral vaccination.  相似文献   
986.
In the last years the number of isolations of Salmonella enterica subspecies enterica serovar paratyphi B (S. paratyphi B) sent to the national salmonella reference laboratory of Germany has increased steadily. Most of the isolates originated from fowl or poultry products. The bacteriological, serological and biochemical properties of the isolates were investigated. Special emphasis was given to the utilization of d-tartrate which subgroups the serovar. All of them belonged to the d-tartrate positive variant, which is generally considered less virulent for humans and was formerly called S. java. The performance of various tests is compared and in addition the possibility of the spread within the production line is discussed.  相似文献   
987.
988.
Tuberculosis caused by Mycobacterium bovis was diagnosed in 36 of 68 (53%) brushtail possums (Trichosurus vulpecula) trapped in August 1992 from a population of exceptionally low density (trap catch <3%) on a forest-scrub margin in Westland, New Zealand. The prevalence of tuberculosis in possums, based solely on gross lesions, was at least twice that previously recorded in New Zealand, and was about seven times that recorded from the same population in 1980. More male (66%) than female (33%) possums had grossly visible tuberculous lesions. The distribution of infection appeared continuous along the forest-scrub margin. Both stoats (Mustela erminea) and one of six hares (Lepus europaeus occidentalis) trapped were also infected with M. bovis.  相似文献   
989.
990.
OBJECTIVE: To evaluate quality of duodenal tissue specimens obtained endoscopically from dogs and cats and submitted to 1 of 2 diagnostic laboratories for evaluation. DESIGN: Case series. SAMPLE POPULATION: Slides from 50 consecutive canine and 50 consecutive feline endoscopically obtained duodenal tissue specimens submitted to laboratory 1 and 49 consecutive canine and 46 consecutive feline specimens submitted to laboratory 2. PROCEDURE: Slides were examined independently by 3 investigators, and each tissue piece on each slide was classified as clearly inadequate, questionable, or clearly adequate on the basis of 4 criteria. An overall score was then assigned to the slide. RESULTS: Slides from laboratory 1 were more likely to be scored as clearly adequate and less likely to be scored as clearly inadequate than slides from laboratory 2. Clearly adequate slides from laboratory 1 had a higher number of clearly adequate pieces of tissue than did clearly adequate slides from laboratory 2. Slides scored as clearly adequate had a higher number of individual tissue pieces than did slides scored as clearly inadequate. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the quality of endoscopically obtained duodenal tissue specimens submitted to laboratories can vary, possibly because of differences in experience of individuals collecting biopsy specimens. Results suggest that at least 8 individual tissue pieces should be submitted when performing endoscopic biopsy of the duodenum in dogs and cats.  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