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   474篇
  免费   19篇
林业   27篇
农学   21篇
  58篇
综合类   22篇
农作物   15篇
水产渔业   31篇
畜牧兽医   273篇
园艺   6篇
植物保护   40篇
  2024年   1篇
  2023年   2篇
  2022年   20篇
  2021年   10篇
  2020年   4篇
  2019年   12篇
  2018年   6篇
  2017年   16篇
  2016年   8篇
  2015年   14篇
  2014年   15篇
  2013年   30篇
  2012年   25篇
  2011年   36篇
  2010年   19篇
  2009年   16篇
  2008年   16篇
  2007年   30篇
  2006年   27篇
  2005年   31篇
  2004年   21篇
  2003年   19篇
  2002年   15篇
  2001年   21篇
  2000年   12篇
  1999年   9篇
  1998年   6篇
  1997年   1篇
  1996年   2篇
  1994年   1篇
  1993年   1篇
  1992年   10篇
  1991年   5篇
  1990年   2篇
  1989年   5篇
  1988年   3篇
  1987年   6篇
  1986年   2篇
  1985年   2篇
  1984年   1篇
  1982年   1篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1953年   1篇
  1936年   1篇
  1906年   2篇
  1905年   1篇
排序方式: 共有493条查询结果,搜索用时 15 毫秒
101.
Flonicamid (IKI220; N-cyanomethyl-4-trifluoromethylnicotinamide), a pyridinecarboxamide compound, is a novel systemic insecticide with selective activity against hemipterous pests, such as aphids and whiteflies, and thysanopterous pests. The purpose of this study is to clarify the biological properties of flonicamid against aphids. Flonicamid is very active against aphids, regardless of differences in species, stages and morphs. This compound inhibited the feeding behaviour of aphids within 0.5 h of treatment without noticeable poisoning symptoms such as convulsion, and this antifeeding activity was not recoverable until death. The nymphs born from adults exposed to flonicamid for 3 h showed high mortality. The effect of flonicamid on the feeding activity of an individual aphid was studied using electronic monitoring of insect feeding behaviour (EMIF). Although the treated aphid attached the head of its proboscis to the leaf surface, salivation and sap feeding were strongly inhibited. These results suggest that the main insecticidal mechanism of flonicamid is starvation based on the inhibition of stylet penetration to plant tissues.  相似文献   
102.
alpha-Glucosidase inhibitory profile of catechins and theaflavins   总被引:1,自引:0,他引:1  
To clarify the postprandial glucose suppression effect of flavonoids, the inhibitory effects of catechins and theaflavins against alpha-glucosidase (AGH) were examined in this study. It was initially demonstrated that theaflavins and catechins preferentially inhibited maltase rather than sucrase in an immobilized AGH inhibitory assay system. For the maltase inhibitory effects of theaflavins, the effects were observed in descending order of potency of theaflavin (TF)-3-O-gallate (Gal) > TF-3,3'-di-O-Gal > TF-3'-O-Gal > TF. This suggests that the AGH inhibition induced by theaflavins is closely associated with the presence of a free hydroxyl group at the 3'-position of TF as well as the esterification of TF with a mono-Gal group. In addition, the R-configuration at the 3'-position of TF-3-O-Gal showed a higher inhibitory activity than the S-configuration. As a result of a single oral administration of maltose (2 g/kg) in rats, a significant reduction in blood glucose level was observed at a dose of 10 mg/kg of TF-3-O-Gal, demonstrating for the first time that TF-3-O-Gal can suppress glucose production from maltose through inhibition of AGH in the gut.  相似文献   
103.
104.
The indirect fluorescent antibody test (IFAT) revealed seropositivity to Coxiella burnetii in aged non-laying chickens in poultry farms in a prefecture in the central part of Japan. Seropositivity was 7%, and antibody titers ranged from 16 to 64. No DNA fragment specific for C. burnetii was detected in the chickens by nested-PCR. The prevalence of C. burnetii infection in a prefecture of Japan in which poultry farming prospers was 7%.  相似文献   
105.
Blood examinations and genotyping of Factor XI (F11) were performed in growth retardation Japanese Black cattle and their dams. Genotyping of F11 revealed that the recessive homozygous and heterozygous genotype frequencies were 5.2% and 50.0% in the Claudin-16 (CL-16) deficiency group (n=58), 0% and 14.2% in the renal dysplasia group (n=7), 0% and 26.1% in the non-CL-16 deficiency nephritis group (n=23), 8.9% and 46.7% in the hypogenesis syndrome group (n=45), 6.2% and 25.0% in the neonatal weak calf syndrome group (n=32), 9.1% and 38.6% in the respective dams group (n=44), 0% and 23.1% in the normal cattle group (n=13), and 5.9% and 38.2% in total (n=222), respectively. These results showed that the carrier rate of F11 deficiency was high in Japanese Black cattle, and that the CL-16 deficiency, hypogenesis syndrome, neonatal weak calf syndrome, and dams groups had a large amount of recessive homozygous genotype than the other groups. No abnormal bleeding was observed clinically in the present study, and 4 of the recessive homozygous dams showed normal growth and parturition.  相似文献   
106.
It is well known that heart rate or arterial blood pressure may increase in response to surgical stimulation despite the absence of a purposeful movement. However, there is limited information regarding anesthetic requirement for blunting adrenergic response in dogs. This study was designed to compare the minimum alveolar concentrations of sevoflurane required to prevent autonomic response (MAC-BAR) and purposeful movement (MAC) in dogs. Sevoflurane MAC-BAR and MAC were determined in 5 beagle dogs by judging dogs' response to a noxious electrical stimulus applied to the gingiva. The sevoflurane MAC-BAR was significantly higher than MAC (3.33 ± 0.48 vs 2.10 ± 0.28%, P=0.005). These results suggested that autonomic responses occurred at sevoflurane anesthetic concentrations at which purposeful movements were absent.  相似文献   
107.
To investigate the possible transmission of Blastocystis organisms between local rhesus monkeys and children in Kathmandu, Nepal, we compared the subtype (ST) and sequence of Blastocystis isolates from children with gastrointestinal symptoms and local rhesus monkeys. Twenty and 10 Blastocystis isolates were established from 82 and 10 fecal samples obtained from children and monkeys, respectively. Subtype analysis with seven sequence-tagged site (STS) primers indicated that the prevalence of Blastocystis sp. ST1, ST2 and ST3 was 20%, 20% and 60% in the child isolates, respectively. In contrast to human isolates, ST3 was not found in monkey isolates and the prevalence of ST1 and ST2 was 50% and 70%, respectively, including three mixed STs1 and 2 and one isolate not amplified by any STS primers, respectively. Since Blastocystis sp. ST2 has been reported as the most dominant genotype in the survey of Blastocystis infection among the various monkey species, sequence comparison of the 150 bp variable region of the small subunit rRNA (SSU rRNA) gene was conducted among ST2 isolates of humans and monkeys. Sequence alignment of 24 clones developed from ST2 isolates of 4 humans and 4 monkeys showed three distinct subgroups, defined as ST2A, ST2B and ST2C. These three subgroups were shared between the child and monkey isolates. These results suggest that the local rhesus monkeys are a possible source of Blastocystis sp. ST2 infection of humans in Kathmandu.  相似文献   
108.
Summary

Thirteen native pear species have been identified in China, of which P. armeniacaefolia Yu and P. sinkiangensis Yu are specific to Xinjiang. P. armeniacaefolia grows wild and a few cultivars have been assigned to this species. Cultivars of P. sinkiangensis have been suspected to be of hybrid origin involving P. communis L. and P. bretschneideri Rehd. In this study, traditional pear cultivars in Xinjiang were evaluated using RAPD markers and compared with representatives of Occidental pear species, cultivars of P. communis and East Asian pear accessions. The combination of 72 pear accessions and 20 selected primers produced 231 scorable polymorphic RAPD bands, of which some were specific to certain species. Five main groups of pear accessions could be distinguished from UPGMA analysis: 1) P. xerophila Yu, its relatives and one cultivar of P. ussuriensis Max., 2) cultivars of P. sinkiangensis, 3) cultivars of P. pyrifolia Nakai and P. bretschneideri, 4) wild Occidental species, cultivars of P. communis and P. armeniacaefolia, and 5) hybrids between P. communis and Chinese or Japanese pear cultivars. The result of PCA generally agrees with that based on UPGMA. Based on RAPD data, some cultivars traditionally classified as P. bretschneideri should be assigned to P. sinkiangensis. Some heirloom cultivars assigned to P. communis were found to be of hybrid origin involving the Chinese white pear (P. bretschneideri) or sand pear (P. pyrifolia). Our results confirmed that P. sinkiangensis is of hybrid origin and at least P. communis, P. armeniacaefolia and Chinese white pears or sand pears have been involved. A further study is needed to understand how pear species and cultivars in Xinjiang are related to those originated from countries in Central Asia.  相似文献   
109.
With the popularization of green roofing systems, their wind resistant performance is becoming more and more important especially in typhoon areas. A prerequisite study was carried out to determine the aerodynamic characteristics of suitable trees to provide basic scientific data. Shrubby specimens of three tree species appropriate for intensive green roofs with different aerodynamic forms were tested through a boundary layer wind tunnel experiment, including one deciduous tree, one coniferous tree and one broadleaf evergreen tree. Drags and overturning moments under different wind speeds were measured; wind-speed-specific frontal areas and tip displacements were recorded. After initial tests, trees were pruned to investigate the effect of crown porosity, and the effects of view angle and turbulence intensity were also considered. The results showed that even considering frontal area reduction due to increasing wind speeds, drag coefficients decreased with increase in wind speed for deciduous and coniferous trees. Drag coefficient characteristics for different trees agreed well with those obtained from previous researches. The effect of crown porosity varied among tree species, but view angle and turbulence intensity did not significantly affect it.  相似文献   
110.
The objective of the present study was to determine whether selection of fluoroquinolone resistance could be easily induced in Campylobacter jejuni-colonized chickens by treatment with enrofloxacin of representative fluoroquinolones at the inherent dosage licensed in Japan (50 ppm in drinking water for 3 days). In the case of isolates from chickens of study 1, an increase in the population of susceptible isolates appeared after the cessation of treatment and maintained throughout the experiments. On the contrary, our results of study 2 demonstrated that administration of enrofloxacin generated a rapid increase of fluoroquinolone resistance in C. jejuni showing the mutation of Asp-90-Asn in the gyrA gene. Present results indicate that the enrofloxacin treatment for broilers at the inherent dosage is able to select fluoroquinolone resistance in C. jejuni. We conclude that whatever enrofloxacin dosage is used, an emergence of fluoroquinolone resistant of C. jejuni occurs.  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