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   2003篇
  免费   122篇
  国内免费   9篇
林业   151篇
农学   118篇
基础科学   38篇
  460篇
综合类   145篇
农作物   272篇
水产渔业   183篇
畜牧兽医   440篇
园艺   76篇
植物保护   251篇
  2024年   3篇
  2023年   19篇
  2022年   61篇
  2021年   79篇
  2020年   93篇
  2019年   127篇
  2018年   142篇
  2017年   129篇
  2016年   133篇
  2015年   71篇
  2014年   84篇
  2013年   212篇
  2012年   111篇
  2011年   131篇
  2010年   104篇
  2009年   67篇
  2008年   120篇
  2007年   57篇
  2006年   45篇
  2005年   38篇
  2004年   33篇
  2003年   32篇
  2002年   24篇
  2001年   17篇
  2000年   27篇
  1999年   16篇
  1998年   15篇
  1997年   12篇
  1996年   16篇
  1995年   13篇
  1994年   7篇
  1993年   4篇
  1992年   8篇
  1991年   6篇
  1990年   8篇
  1989年   6篇
  1988年   3篇
  1987年   7篇
  1986年   4篇
  1985年   5篇
  1984年   9篇
  1983年   4篇
  1982年   2篇
  1981年   4篇
  1979年   5篇
  1975年   3篇
  1973年   3篇
  1972年   2篇
  1971年   3篇
  1967年   3篇
排序方式: 共有2134条查询结果,搜索用时 796 毫秒
991.
992.
Adrenergic receptor (AR) expression has been demonstrated at several sites of primary and metastatic tumour growth and may influence proliferation, survival, metastasis and angiogenesis. AR antagonists like propranolol and carvedilol inhibit proliferation, induce apoptosis and synergize with chemotherapy agents in some cancers. Radiation resistance is mediated in many cells by upregulation of pro‐survival pathways, which may be influenced by ARs. Studies evaluating AR antagonists combined with radiation are limited. The purpose of this study was to determine the effect of propranolol and carvedilol on viability and radiosensitivity in sarcoma cell lines. The hypothesis was that propranolol and carvedilol would increase radiosensitivity in four primary bone sarcoma cell lines. Single agent propranolol or carvedilol inhibited cell viability in all cell lines in a concentration‐dependent manner. The mean inhibitory concentrations (IC50) for carvedilol were approximately 4‐fold lower than propranolol and may be clinically relevant in vivo. Immunoblot analysis confirmed AR expression in both human and canine sarcoma cell lines; however, there was no correlation between baseline AR protein expression and radiosensitivity. Short duration treatment with carvedilol and propranolol did not significantly affect clonogenic survival. Prolonged exposure to propranolol and carvedilol significantly decreased the surviving fraction of canine osteosarcoma cells after 3Gy radiation. Based on our results and possible in vivo activity in dogs, further studies investigating the effects of carvedilol on sarcoma are warranted.  相似文献   
993.

The study was carried out to determine phenolic compounds, antioxidant activity, total lipids, saturated fatty acids, unsaturated fatty acids, and volatile organic compounds (VOCs) of 18 different walnut (Juglans regia L.) cultivars and genotypes grown in Usak province, Turkey. The biochemical compounds were identified for each cultivar and genotype and a comparative evaluation was carried out. The results showed that most of the biochemical compounds are significantly varying among each other (p?<?0.05). The existence and abundance of the biochemical compounds in the cultivars and genotypes have not only found to be a cause of differentiation, but they have been important parameters for the similarities among the cultivars and genotypes. Total phenolic content and antioxidant activity ranged from 750.67 to 1245.64?mg GAE ml?1 and from 42.46 to 56.50% in kernels, respectively. The highest contents of the phenolic compounds were noted from gallic acid (11991?mg kg?1), ellagic acid (1057.16?mg kg?1), catechin (425.4?mg kg?1), and rutin (216.6?mg kg?1), as an average of all cultivars and genotypes. The highest lipid contents were noted from ‘Franquette’ and ‘Fernette’ as 64.28% and 63.26%, respectively, while the lowest content was noted from ‘Oguzlar 77’ (52.52%). A total of 42 VOCs were described from the 18 different walnut cultivars and genotypes. Overall, results showed that the phenolic profiles, fatty acids composition, and VOCs play an important role in similarities and diversities among the cultivars. According to the results, 7 different clusters were developed from the 18 cultivars and genotypes. Herein, ‘Fernor’, ‘Maras 18’, ‘Arslan Local Type’ and ‘Cisco’ cultivars were found to have the lowest biochemical compositions. The superior cultivars or genotypes, in terms of the abundance of the biochemical composition, were found to be ‘Gulizar Hanim Type’, ‘Lara’, ‘Pedro’, ‘Tulane’, ‘Fernette’, ‘Balkan’ and ‘Franquetta’, where they were found to develop 3 clusters by 1:3:3, respectively.

  相似文献   
994.
 采用单因素试验和响应面分析等方法优化解淀粉芽胞杆菌ZF57的发酵工艺。得到解淀粉芽胞杆菌ZF57发酵的最优条件为山梨醇10 g·L-1、棉籽饼粉17 g·L-1、NaH2PO4 0.5 g·L-1、Na2HPO4 0.4 g·L-1,初始pH 7.0、装液量80 mL/250mL三角瓶、接种量2.1%、培养温度30℃、转速180 r·min-1、发酵时间32 h,此时含菌量达到3.8×108 CFU·mL-1,较优化前提高了80%。明确了解淀粉芽胞杆菌微粉剂的最佳配方为解淀粉芽胞杆菌母粉50%,白炭黑10%,分散剂木质素磺酸钠1%,表面活性剂十二烷基硫酸钠4%,保护剂羧甲基纤维素钠1%,硅藻土补足至100%。该制剂含菌量为3.26×109 CFU·mL-1,平均粒径8.31 μm,分散指数98.16%,浮游性指数85.37,含水率1.42%,坡度角68°,各项检测结果均符合标准。解淀粉芽胞杆菌ZF57微粉剂对黄瓜棒孢叶斑病的田间防治效果高达97.12%。  相似文献   
995.
<正>果胶杆菌(Pectobacterium)可引起马铃薯、黄瓜等多种作物的软腐病,具有十分广泛的寄主范围。近年来,随着甜瓜种植规模的不断扩大,山东、河北、辽宁等多个甜瓜种植区出现茎秆严重腐烂的现象,发病初期甜瓜茎秆出现褐色病斑,然后逐渐腐烂,导致植株整株死亡,造成了严重的经济损失。本研究对山东寿光、昌乐和莱西疑似甜瓜茎软腐病的病株进行调查采样(图1-A、B),通过病原菌分离鉴定和致病性测定,为该地区细菌病害的病原分析提供实验参考。  相似文献   
996.
Fig (Ficus carica) is an exotic deciduous plant that is grown worldwide. Fungal diseases pose a major threat to fig plants, affecting their fruit quality and production. This study was conducted to characterize the fungal isolates associated with leaf blight, stem rot and fruit rot of F. carica in Malaysia through morphological analysis, DNA sequencing, multigene phylogenetic analysis and pathogenicity tests. From September 2018 to March 2019, 30 blighted leaves and 30 rotted stems and fruits of F. carica were collected from several nurseries in Malaysia. Thirty fungal isolates that belonged to Lasiodiplodia theobromae (27 isolates) and L. brasiliensis (three isolates) were identified based on morphological characteristics, comparison of DNA sequences and phylogenetic analysis of the internal transcribed spacer (ITS), elongation translation factor 1-α (tef1-α), β-tubulin (tub2) and DNA-directed RNA polymerase II subunit (rpb2). Among the 27 isolates of L. theobromae, nine isolates were obtained from leaves, eight isolates from stems and 10 isolates from fruits, whereas the three isolates of L. brasiliensis were obtained from stems (two isolates) and a leaf (one isolate). The results of pathogenicity tests revealed that L. theobromae and L. brasiliensis isolates were responsible for leaf blight and stem rot of F. carica, whereas fruit rot was caused by L. theobromae isolates. The present study highlighted two different species, L. theobromae and L. brasiliensis, as the causal agents of leaf blight and stem rot of F. carica. Additionally, L. theobromae caused fruit rot of F. carica in Malaysia.  相似文献   
997.
 建立了土壤中芸薹根肿菌荧光定量PCR(qPCR)快速检测及风险预警体系。确定了芸薹根肿菌qPCR检测的特异性引物PbF/PbR,对根肿菌质粒DNA的检测灵敏度为1.612×10-6 ng·μL-1,比普通PCR高出1 000倍;对土壤和基质中芸薹根肿菌孢子的最低检测下限均为10 个·g-1,而土壤和基质带菌的发病阈值分别为100和1 000 个·g-1,高于该浓度时根肿病发生风险大。本研究建立的芸薹根肿菌qPCR技术体系检测下限远低于发病阈值,可以快速、准确、定量地检测出采自四川绵阳、湖北恩施、江苏无锡、山东青岛、辽宁沈阳、山西运城、内蒙古巴彦淖尔和宁夏固原等8个地区的27份田间土壤中芸薹根肿菌的数量,实现对十字花科根肿病的监测预警,为制定产前病害防控方案提供依据。  相似文献   
998.
为有效防控十字花科蔬菜生产中的毁灭性病害——根肿病,以尖孢镰孢菌Fusarium oxysporum和辣椒疫霉Phytophthora capsici为指示菌,利用平板对峙法对分离自土壤的1 198株细菌进行筛选,进通过盆栽试验筛选对十字花科根肿病具有良好防效的生防菌株,并基于形态学特征、生理生化特性及16S rDNA、gyrB和atpD多基因系统发育分析对生防菌株进行鉴定,同时测定其抑菌谱和田间防效。结果表明,通过对峙培养筛选获得115株有抑菌效果的生防菌株,采用盆栽试验获得1株对根肿病菌具有拮抗效果的菌株,命名为ZF480。结合形态学特征和系统发育分析结果将该菌株鉴定为副地衣芽胞杆菌Bacillus paralicheniformis。菌株ZF480对野油菜黄单胞野油菜变种Xanthomonas campestris pv. campestris等10种病原菌具有拮抗效果,抑菌谱较宽,对白菜根肿病的盆栽防效和田间防效分别达到72.82%和64.08%。表明副地衣芽胞杆菌菌株ZF480对十字花科根肿病具有显著的防效,可作为生防菌进一步开发利用。  相似文献   
999.
Although the intramedullary nailing is thought to be the method of choice for treatment of closed tibial shaft, there is ongoing debate on the optimal surgical approach in patients with open types of these fractures. In addition, choosing between the reamed and unreamed intramedullary nailing is still an issue for the orthopedic surgeons. In present study, we aimed to compare the outcome and consequences of OA tubular external fixation vs. unreamed intramedullary nailing in open grade IIIA-IIIB tibial shaft fractures. In a randomized clinical trial, 50 patients with open tibial shaft fractures (grades IIIA-IIIB) were recruited in Tabriz Shohada teaching centre in a 2-year period of time. They randomized in two equal groups underwent either AO tubular external fixation or unreamed intramedullary nailing. These 2 groups were matched for sex, age and fracture-grade. The follow-up time was one year. Union time, surgical outcome, postoperative complications and the ambulation time were compared between the two groups. Twenty five patients, 20 males and 5 females with a mean age of 30.80 +/- 5.24 years were allocated in unreamed intramedullary group and 25 other patients, 22 males and 3 females with a mean age of 28.92 +/- 8.88 years were studied in the external fixation group (p = 0.70 and 0.37, respectively). The two groups were matched for sex (p = 0.70) and age (p = 0.37). The time of union was 3, 4, 5 and 6 < or = weeks after operation in 28, 12, 32 and 28% of the cases in unreamed intramedullary group vs. 4, 12, 48 and 36% of the cases in external fixation group, respectively (p = 0.14). Post-operative infection, soft tissue injury, malunion and nonunion were documented in 16, 8, 0 and 4% of the cases in unreamed intramedullary group vs. 32, 12, 24 and 8% of the cases in external fixation group, respectively (p = 0.19, 0.50, 0.02 and 0.50, respectively). The mean ambulation time after operation was 2.92 +/- 2.43 weeks in the unreamed intramedullary nailing group vs. 2.68 +/- 2.14 weeks in the external fixation group (p = 0.71). Our results are in favor of unreamed intramedullary nailing against external fixation in treatment of open tibial shaft fractures.  相似文献   
1000.
A sero-epidemiological survey of human and equine H3 influenza A virus infections in dogs and cats using the hemagglutination inhibition (HI) and neuraminidase inhibition (NI) tests was conducted. Serum samples were collected from 582 dogs and 237 cats in Japan during the periods 2002-2008 and 1997-2008, respectively. Although no HI antibodies against equine H3 virus were detected, 9 (3.8%) from cats and 12 (2.1%) from dogs were HI-positive against human H3 virus. Only one serum each from dogs and cats was NI-positive against N2 virus. These findings suggest that although equine H3 influenza virus infections have not been prevalent in companion animals, human H3N2 influenza A virus infections have occurred in dogs and cats in recent years in Japan.  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