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   2095篇
  免费   108篇
  国内免费   1篇
林业   109篇
农学   132篇
基础科学   3篇
  373篇
综合类   144篇
农作物   260篇
水产渔业   188篇
畜牧兽医   838篇
园艺   33篇
植物保护   124篇
  2023年   14篇
  2022年   8篇
  2021年   52篇
  2020年   35篇
  2019年   40篇
  2018年   53篇
  2017年   65篇
  2016年   61篇
  2015年   64篇
  2014年   92篇
  2013年   122篇
  2012年   162篇
  2011年   170篇
  2010年   111篇
  2009年   117篇
  2008年   141篇
  2007年   139篇
  2006年   151篇
  2005年   86篇
  2004年   84篇
  2003年   78篇
  2002年   77篇
  2001年   67篇
  2000年   39篇
  1999年   26篇
  1998年   12篇
  1997年   3篇
  1996年   3篇
  1995年   7篇
  1994年   5篇
  1993年   4篇
  1992年   10篇
  1991年   3篇
  1990年   13篇
  1989年   12篇
  1988年   7篇
  1987年   4篇
  1985年   6篇
  1981年   3篇
  1978年   3篇
  1977年   2篇
  1976年   2篇
  1975年   3篇
  1974年   7篇
  1973年   10篇
  1971年   3篇
  1970年   2篇
  1968年   2篇
  1966年   4篇
  1929年   2篇
排序方式: 共有2204条查询结果,搜索用时 15 毫秒
991.
In this study we isolated crude thiosulfinates from Allium tuberosum L. using CH 2Cl 2 and then with silica gel column chromatography purified S-methyl methanthiosulfinate and S-methyl 2-propene-1-thiosulfinate from the crude thiosulfinates. Subsequently, in vitro cytotoxicities against human cancer cells and in vivo antitumor activities of the thiosulfinates were investigated. Their cytotoxicities were strong in human cancer cells, in the order of S-methyl 2-propene-1-thiosulfinate, crude thiosulfinates, and S-methyl methanthiosulfinate. When thiosulfinates were administered consecutively for 7 days at 10, 30, and 50 mg/kg ip, in mice, we found significant increases in the life spans of mice that had been inoculated with Sacorma-180 tumor cells. The crude thiosulfinates also induced apoptosis in MCF-7 cancer cells. These results suggest that thiosulfinates from Allium tuberosum L. inhibit the proliferation of cancer cells via apoptosis and have antitumor activities.  相似文献   
992.
Proton magnetic resonance spectroscopy (1H MRS) provides in vivo biochemical information on tissue metabolites. The purpose of this study was to investigate the serial metabolic changes of 1H MRS in the cerebrum of ischemic dogs. An ischemic stroke was induced in five health laboratory beagle dogs by permanent middle cerebral artery occlusion using a silicone plug. 1H MRS was serially performed three times with a 1.5-T MR system: before, three days after and 10 days after the stroke. Immunohistochemical staining was performed to determine the expression of neuronal nuclei (NeuN) and glial fibrillary acidic protein (GFAP) at both the ipsilateral and contralateral cerebral cortex. Reduced levels of N-acetyl-asparate (p < 0.05), choline (Cho), creatine (Cr) and myo-inositol (mI), and a marked increase in the lactate (Lac) level (p < 0.01) were found at three days after the stroke. At 10 days after the stroke, the levels of Lac significantly increased (p < 0.01); however, the other metabolites were partially elevated. The changes of Cr, Cho and mI were not statistically significant (p > 0.05) when the before and after stroke values were compared. There was a significant loss of NeuN and GFAP immunoreactivity at the ischemic core. 1H MRS may be to a useful diagnostic tool for the evaluation of ischemic stroke in dogs.  相似文献   
993.
A miniarray system was developed for the simultaneous detection of porcine circovirus type 1 (PCV1) and type 2 (PCV2) in pigs. The system consists of a polymerase chain reaction (PCR) step to amplify target viral DNA, followed by detection of the amplified DNA using a membrane-anchored probe array and an avidin-alkaline phosphatase (Av-AP) indicator system. The lower limit of detection of PCV using the miniarray was 101.9 tissue culture infectious dose 50 (TCID50)/ml and 102.08TCID50/ml for PCV1 and PCV2, respectively, and 100 viral copies/μl for both PCV1 and PCV2. We validated the miniarray system using 141 lymph node specimens from pigs with suspected postweaning multisystemic wasting syndrome or porcine dermatitis and nephropathy syndrome. Of the 141 samples evaluated, 55 were identified as positive for PCV by the miniarray. Relative to in situ hybridization, the sensitivity and specificity of the miniarray was 100% and 98.9%, respectively. In contrast to other microarray systems, the miniarray does not require a DNA chip reader, since the results can be determined by visual inspection of colorized spots on a nylon membrane. This system represents an effective alternative method for the differential detection of PCV1 and PCV2 in pigs, as well as the maintenance of PCV-free cell lines and pre-screening of commercial vaccines for possible contamination.  相似文献   
994.
Sacral osteochondrosis in two German Shepherd Dogs   总被引:1,自引:1,他引:0  
Two young adult male castrated German Shepherd Dogs were referred for evaluation of intermittent episodes of hindlimb pain. Physical examination suggested lumbosacral stenosis, and plain radiographs and computed tomography revealed lesions consistent with sacral osteochondrosis. One dog had osteochondral fragments removed surgically; the other was managed conservatively. The surgically treated dog had complete resolution of clinical signs whereas the dog managed conservatively had repeated episodes of mild pain and received one short course of non-steroidal anti-inflammatory medication in 18 months. Sacral osteochondrosis has not been previously reported in Australia.  相似文献   
995.
Human umbilical cord blood-derived mesenchymal stem cells (MSCs) are known to possess the potential for multiple differentiations abilities in vitro and in vivo. In canine system, studying stem cell therapy is important, but so far, stem cells from canine were not identified and characterized. In this study, we successfully isolated and characterized MSCs from the canine umbilical cord and its fetal blood. Canine MSCs (cMSCs) were grown in medium containing low glucose DMEM with 20% FBS. The cMSCs have stem cells expression patterns which are concerned with MSCs surface markers by fluorescence-activated cell sorter analysis. The cMSCs had multipotent abilities. In the neuronal differentiation study, the cMSCs expressed the neuronal markers glial fibrillary acidic protein (GFAP), neuronal class III β tubulin (Tuj-1), neurofilament M (NF160) in the basal culture media. After neuronal differentiation, the cMSCs expressed the neuronal markers Nestin, GFAP, Tuj-1, microtubule-associated protein 2, NF160. In the osteogenic & chondrogenic differentiation studies, cMSCs were stained with alizarin red and toluidine blue staining, respectively. With osteogenic differentiation, the cMSCs presented osteoblastic differentiation genes by RT-PCR. This finding also suggests that cMSCs might have the ability to differentiate multipotentially. It was concluded that isolated MSCs from canine cord blood have multipotential differentiation abilities. Therefore, it is suggested that cMSCs may represent a be a good model system for stem cell biology and could be useful as a therapeutic modality for canine incurable or intractable diseases, including spinal cord injuries in future regenerative medicine studies.  相似文献   
996.
997.
Objective  To determine the incidence, etiology, and concurrent ophthalmic findings in small breed dogs that presented with cataracts.
Animal studied  Five hundred and sixty-one small breed dogs (942 eyes) were presented to the Veterinary Medical Teaching Hospital of Seoul National University between July 2002 and December 2007 with cataract.
Procedure  The medical records of small breed dogs with cataract were reviewed. The reason for presentation, cataract duration, bilaterality, breed, gender, age, vision, etiology, stage of cataract development, concurrent ophthalmic findings, IOP, ocular ultrasonography findings, and scotopic electroretinography (ERG) findings were investigated.
Results  The most frequently presented breeds were the Miniature/Toy Poodle ( n  = 112, 20.0%), Yorkshire Terrier ( n  = 110, 19.6%), and Shih Tzu ( n  = 95, 16.9%). The Miniature/Toy Poodle showed a significantly higher odds ratio for cataract formation (2.6). The proportion of female cataract patients was significantly higher than that of male cataract patients in the overall population ( P  < 0.05). The Miniature/Toy Poodles had significantly higher numbers of females affected with cataract ( P  < 0.01). The mean age for cataract formation was 8.3 ± 3.9 years. The mean age at onset in the Miniature/Toy Poodle and Yorkshire Terrier was significantly higher, whereas that in the Miniature Schnauzer group was significantly lower ( P  < 0.0001). Clinical signs related to lens induced uveitis had a tendency to increase with cataract progression ( P  < 0.05). There were no significant differences in the b-wave amplitude for mixed rod cone response by stage ( P  = 0.137).
Conclusions  Small breed dogs with cataracts had characteristics with regard to age of onset and gender distribution, depending on the breed.  相似文献   
998.
Journal of Crop Science and Biotechnology - Worldwide, grain consumption is increased and grain prices are rising. This has led to a steady increase in the production of highly productive and more...  相似文献   
999.
Cold tolerance at the seedling stage of rice is an important phenotypic trait that causes normal plant growth and stable rice production in temperate regions as well as tropical high-lands in Asia and Africa. In order to find quantitative trait loci (QTLs)/genes associated with cold tolerance, we constructed a linkage map using 153 recombinant inbred lines (RILs) derived from a cross between a cold-tolerant temperate japonica cultivar, Geumobyeo, and a cold-sensitive tropical japonica breeding line, IR66160-121-4-4-2. The RILs were phenotyped for cold tolerance or sensitivity based on the degrees of cold tolerance as cold tolerance indices at the seedling stage. The seedlings for cold-tolerance/-sensitive traits were scored on the 7th day of the recovery period at 25°C after cold treatment at 10°C. Two QTLs (qCTS4a and qCTS4b) associated with cold tolerance at the seedling stage were identified on the long and short arms of chromosome 4 with an LOD score of 2.89 and 2.75, respectively, using composite interval mapping. The QTLs were flanked by simple sequence repeat (SSR) markers RM3648-RM2799 and RM3375a-RM558 that explained 8.3 and 7.8% of the total phenotypic variation, respectively. Seven of the selected RILs expressed cold tolerance at both the seedling and reproductive stages. The SSR markers associated with the QTLs will be useful for tracking favorable QTLs/genes into cold-sensitive elite cultivars and may have potential for pyramiding different QTLs for the improvement of cold tolerance in rice.  相似文献   
1000.
BACKGROUND: In the natural environment, photodegradation is one of the most common degradative processes of pesticides. In order to reduce the photodegradation of pesticides, and so increase their killing activity against target pests, chitosan‐coated beeswax solid lipid nanoparticles (CH‐BSLNs) were prepared by a combination of hot homogenization and sonication, with deltamethrin as an active ingredient. RESULTS: Under optimal conditions, the highest encapsulation efficiency (95%) and a high payload of deltamethrin (approximately 12.5%) were achieved. In direct photolysis, in the case of CH‐BSLNs after UV irradiation for 24 h, 37.3% of deltamethrin remained, as opposed to only 14.6% of the free‐form deltamethrin. In addition, in indirect photolysis, in the case of CH‐BSLNs after UV irradiation for 2 h in 2% acetone solution, approximately 74.5% of deltamethrin remained, as opposed to only 37.6% of the free‐form deltamethrin. CONCLUSION: CH‐BSLNs showed good protection for deltamethrin against photodegradation. This novel nanocarrier may be useful in crop protection as an economical strategy to enhance the effect of pesticides in the field and protect the environment as well. Copyright © 2012 Society of Chemical Industry  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