全文获取类型
收费全文 | 97729篇 |
免费 | 19806篇 |
国内免费 | 30468篇 |
专业分类
林业 | 9902篇 |
农学 | 8138篇 |
基础科学 | 9220篇 |
36321篇 | |
综合类 | 44461篇 |
农作物 | 8253篇 |
水产渔业 | 7202篇 |
畜牧兽医 | 12328篇 |
园艺 | 4978篇 |
植物保护 | 7200篇 |
出版年
2024年 | 1003篇 |
2023年 | 1567篇 |
2022年 | 2641篇 |
2021年 | 2513篇 |
2020年 | 3919篇 |
2019年 | 7243篇 |
2018年 | 6622篇 |
2017年 | 8028篇 |
2016年 | 8302篇 |
2015年 | 9002篇 |
2014年 | 8207篇 |
2013年 | 8820篇 |
2012年 | 9462篇 |
2011年 | 8389篇 |
2010年 | 7360篇 |
2009年 | 6498篇 |
2008年 | 5505篇 |
2007年 | 5364篇 |
2006年 | 4620篇 |
2005年 | 4063篇 |
2004年 | 3454篇 |
2003年 | 2840篇 |
2002年 | 2521篇 |
2001年 | 2188篇 |
2000年 | 1855篇 |
1999年 | 1480篇 |
1998年 | 1269篇 |
1997年 | 1256篇 |
1996年 | 1114篇 |
1995年 | 1160篇 |
1994年 | 1159篇 |
1993年 | 921篇 |
1992年 | 934篇 |
1991年 | 787篇 |
1990年 | 603篇 |
1989年 | 598篇 |
1988年 | 530篇 |
1987年 | 397篇 |
1986年 | 402篇 |
1985年 | 211篇 |
1984年 | 197篇 |
1983年 | 190篇 |
1982年 | 190篇 |
1981年 | 234篇 |
1980年 | 192篇 |
1979年 | 151篇 |
1978年 | 130篇 |
1975年 | 109篇 |
1965年 | 137篇 |
1964年 | 140篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
91.
92.
The effect of exploratory laparotomy on the serum and peritoneal haptoglobin concentrations of the pony. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Serum haptoglobin concentration was used as an indicator of the acute phase response in ponies undergoing exploratory laparotomy. Preoperative, 1 h intraoperative, 3 h, 6 h, 12 h and 24 h postoperative blood samples and 48 h postoperative peritoneal fluid samples were obtained for haptoglobin analysis. A spectrophotometric assay based on cyanmethemoglobin binding capacity (CyanBC) was used to determine haptoglobin concentrations. The preoperative reference range for serum haptoglobin concentrations in these ponies was 25-60 mg CyanBC/dL. Intraoperative and 3 h postoperative blood samples had decreased haptoglobin concentrations when compared to preoperative values. Serum haptoglobin concentrations began to rise by the 6 h postoperative sample and were generally elevated above preoperative values by the 24 h postoperative sample. Two of the ten ponies had mild signs of postoperative colic which were associated with twofold elevations in serum haptoglobin concentrations and fivefold elevations in peritoneal fluid haptoglobin concentrations. 相似文献
93.
Feline leukemia virus detection by immunohistochemistry and polymerase chain reaction in formalin-fixed, paraffin-embedded tumor tissue from cats with lymphosarcoma.
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M L Jackson D M Haines S M Meric V Misra 《Canadian journal of veterinary research》1993,57(4):269-276
The prevalence of feline leukemia virus (FeLV) antigen and DNA was assessed in formalin-fixed, paraffin-embedded tumor tissues from 70 cats with lymphosarcoma (LSA). Tissue sections were tested for FeLV gp70 antigen using avidinbiotin complex (ABC) immunohistochemistry (IHC); DNA was extracted and purified from the same tissue blocks for polymerase chain reaction (PCR) amplification of a 166 base pair region of the FeLV long terminal repeat (LTR). Results were related to antemortem FeLV enzyme-linked immunosorbent assay (ELISA) for serum p27 antigen, anatomic site of LSA, and patient age. Viral DNA was detected by PCR in 80% of cases and viral antigen by IHC in 57% of cases. Seventeen cases were PCR-positive and IHC-negative; one case was PCR-negative and IHC-positive. Clinical records included FeLV ELISA results for 30 of 70 cats. All 19 ELISA-positive cats were positive by PCR and IHC; of the 11 ELISA-negative cats that were negative by IHC, seven were positive by PCR. When evaluated according to anatomic site, FeLV DNA and antigen were detected less frequently in intestinal LSAs than in multicentric and mediastinal tumors. Lymphosarcoma tissues from cats < 7 yr were several fold more likely to be positive for FeLV antigen by IHC than were tumors from cats > or = 7 yr. However, there was no significant difference in PCR detection of FeLV provirus between LSAs from cats < 7 yr and those > or = 7 yr.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
94.
本试验所用动物为53—57日龄雄性大白鼠(sprague——Dawley品系),初始体重为121.73±3.95g,试验期为大白鼠生长发育旺期的21天。试验拟研究不同粗蛋白水平(10%、15%、20%、25%和30%)及两个能量水平(消化能:3.6和3.9kcal/g)的饲粮对大白鼠生长发育及各种体成分的影响。结果表明,当饲粮蛋白质供应充分时,大白鼠生长随饲粮能量浓度的提高而改善;而当饲粮蛋白质供应感觉不足时,提高能量浓度对生长无益。机体各项成分指杯中,以蛋白质、脂肪、水分沉积受饲粮蛋白质,能量浓度影响显著;而蛋白质、脂肪沉积在很大程度上受饲粮能朊比的影响,饲粮中添加脂肪可使大白鼠机体肥胖。 相似文献
95.
SUMMARY An aqueous suspension of air-dried, hammer-milled leaf of Terminalla oblongata (yellow-wood) was administered to sheep by gavage, as a single dose of 5 to 20 g (dry weight)/kg body weight. Doses of 15 g/kg, or more, caused depression, Inappetence, abdominal pain and reduced ruminal movements within 24 to 48 h and some sheep also showed dyspnoea, oplsthotonus and champing of the Jaws. Haematology and blood gas and acid-base measurements were unaffected. In sheep given a dose of 12.5 g/kg, or more, plasma osmolality, aspartate aminotransferase activity and potassium and bilirubin concentrations Increased while plasma total protein markedly decreased and plasma sodium concentration and alkaline phosphatase activity remained normal. Most sheep were necropsled 48 h after dosing. The liver showed zonal hepatocellular necrosis, the pattern of which varied with the dose given. No renal lesions were observed, although one sheep given a very high dose became azotaemic and hyperkalaemic. Hydrothorax, hydroperlcardlum and ascltes developed In sheep given doses of 15 or 20 g/kg. 相似文献
96.
97.
J Tetens S A Barker M Waguespack G Hosgood 《Canadian journal of veterinary research》2001,65(2):133-135
The objectives were to use high performance liquid chromatography (HPLC) to validate an established method for adenine nucleotide separation in equine colonic mucosal tissue, to determine the inherent variability in the tissue and extraction method, and to determine the stability of ATP, ADP, and AMP in the tissue with time. Equine colonic mucosal tissue obtained from a single horse was immediately submersed in liquid nitrogen, and stored at -70 degrees C. Samples were lyophilized, extracted, and separated by HPLC. The limit of quantitation was 0.05 microg/mL. The coefficient of variation for the instrument was less than 10% for all nucleotides measured. When the tissue was not homogenized prior to sampling, there were significant differences in adenine nucleotide content between samples. However, when the tissue was homogenized prior to analysis, these differences were no longer significant. There was no significant decrease in ATP, ADP, or AMP content over a 54-day analysis period. 相似文献
98.
Transmission of porcine reproductive and respiratory syndrome virus from persistently infected sows to contact controls. 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M D Bierk S A Dee K D Rossow S Otake J E Collins T W Molitor 《Canadian journal of veterinary research》2001,65(4):261-266
The objective of this study was to determine if porcine reproductive and respiratory syndrome virus (PRRSV) could persist in non-pregnant sows and if persistently infected sows could transmit virus to naive contact controls. Twelve PRRSV-naive, non-pregnant sows (index sows) were infected with a field isolate of PRRSV and housed in individual isolation rooms for 42 to 56 days postinfection. Following this period, 1 naive contact sow was placed in each room divided by a gate allowing nose-to-nose contact with a single index sow. Index sows were not viremic at the time of contact sow entry. Virus nucleic acid was detected by polymerase chain reaction, and infectious virus was detected by virus isolation in sera from 3 of the 12 contact sows at 49, 56, and 86 days postinfection. All 3 infected contacts developed PRRSV antibodies. Virus nucleic acid was detected in tissues of all of the 12 index sows at 72 or 86 days postinfection. Nucleic acid sequencing indicated that representative samples from index and infected contacts were homologous (> 99%) to the PRRSV used to infect index sows at the onset of the study. This study demonstrates that PRRSV can persist in sows and that persistently infected sows can transmit virus to naive contact animals. 相似文献
99.
可持续发展类型与测度的理论探讨 总被引:2,自引:0,他引:2
可持续发展的类型划分与可持续发展的测度是可持续发展理论研究的重要内容。科学反应可持续发展的特征 ,有利于可持续发展类型划分 ,是可持续发展测度的依据和目标。本文运用人地关系协调分析法与经济分析法 ,特别是与替代弹性不变生产函数分析法 (C.E.S生产函数 )相结合 ,提出了可持续的人均国内生产总值 ,探讨了可持续发展中人文资本、自然资本相互协调、相互依存的关系特征 ,建立可持续发展测度的指标系统和可持续发展的类型体系 相似文献
100.