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   327篇
  免费   22篇
  国内免费   3篇
林业   20篇
农学   11篇
基础科学   4篇
  63篇
综合类   16篇
农作物   13篇
水产渔业   29篇
畜牧兽医   164篇
园艺   11篇
植物保护   21篇
  2023年   4篇
  2022年   10篇
  2021年   14篇
  2020年   11篇
  2019年   8篇
  2018年   12篇
  2017年   11篇
  2016年   12篇
  2015年   11篇
  2014年   17篇
  2013年   18篇
  2012年   32篇
  2011年   24篇
  2010年   13篇
  2009年   16篇
  2008年   26篇
  2007年   22篇
  2006年   14篇
  2005年   15篇
  2004年   9篇
  2003年   14篇
  2002年   21篇
  2001年   3篇
  2000年   4篇
  1999年   3篇
  1998年   1篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1990年   1篇
  1985年   1篇
  1984年   1篇
排序方式: 共有352条查询结果,搜索用时 390 毫秒
101.
Strains of Mucor piriformis were isolated from orchard soils and from packinghouse dump-tank waters. Pathogen propagules were not found in fruit sample washings. M. piriformis was the most prevalent of the Mucor isolates, only one of 67 isolates was a different Mucor sp., possibly M. racemosus. The population of the pathogen propagules fluctuated in an annual cyclic pattern, declining in warm months and increasing after harvest. The viability of sporangiospores was markedly affected by rain. There was a good correlation (r=0.88) between the number of recovered propagules in the soil and the amount of rainfall. M. piriformis isolates caused decay on pear at 0°C after 14 days.  相似文献   
102.
H5 highly pathogenic avian influenza (HPAI) viruses have spread worldwide, and antigenic variants of different clades have been selected. In this study, the national stockpiled vaccine prepared from A/duck/Hokkaido/Vac-1/2004 (H5N1) strain was evaluated for the protective efficacy against H5N8 HPAI virus isolated in Kumamoto prefecture, Japan, in April 2014. In the challenge test, all of the vaccinated chickens survived without showing any clinical signs and reduced virus shedding. It was concluded that the present stockpiled vaccine was effective against the H5N8 HPAI virus.  相似文献   
103.
104.
ObjectiveTo compare the cardiopulmonary effects of intravenous (IV) and intramuscular (IM) medetomidine and butorphanol with or without MK-467.Study designProspective, randomized experimental cross-over.AnimalsEight purpose–bred beagles (two females, six males), 3–4 years old and weighing 14.5 ±1.6 kg (mean ± SD).MethodsAll dogs received four different treatments as follows: medetomidine 20 μg kg?1 and butorphanol tartrate 0.1 mg kg?1 IV and IM (MB), and MB combined with MK-467,500 μg kg?1 (MBMK) IV and IM. Heart rate (HR), arterial blood pressures (SAP, MAP, DAP), central venous pressure (CVP), cardiac output, respiratory rate (fR), rectal temperature (RT) were measured and arterial blood samples were obtained for gas analysis at baseline and at 3, 10, 20, 30, 45 and 60 minutes after drug administration. The cardiac index (CI), systemic vascular resistance index (SVRI) and oxygen delivery index (DO2I) were calculated. After the follow-up period atipamezole 50 μg kg?1 IM was given to reverse sedation.ResultsHR, CI and DO2I were significantly higher with MBMK after both IV and IM administration. Similarly, SAP, MAP, DAP, CVP, SVRI and RT were significantly lower after MBMK than with MB. There were no differences in fR between treatments, but arterial partial pressure of oxygen decreased transiently after all treatments. Recoveries were uneventful following atipamezole administration after all treatments.Conclusions and clinical relevanceMK-467 attenuated the cardiovascular effects of a medetomidine-butorphanol combination after IV and IM administration.  相似文献   
105.
Mutations in DKC1 cause dyskeratosis congenita (DC), a disease characterized by premature aging and increased tumor susceptibility. The DKC1 protein binds to the box H + ACA small nucleolar RNAs and the RNA component of telomerase. Here we show that hypomorphic Dkc1 mutant (Dkc1m) mice recapitulate in the first and second generations (G1 and G2) the clinical features of DC. Dkc1m cells from G1 and G2 mice were impaired in ribosomal RNA pseudouridylation before the onset of disease. Reductions of telomere length in Dkc1m mice became evident only in later generations. These results suggest that deregulated ribosome function is important in the initiation of DC, whereas telomere shortening may modify and/or exacerbate DC.  相似文献   
106.
Suppression of microRNA-silencing pathway by HIV-1 during virus replication   总被引:1,自引:0,他引:1  
MicroRNAs (miRNAs) are single-stranded noncoding RNAs of 19 to 25 nucleotides that function as gene regulators and as a host cell defense against both RNA and DNA viruses. We provide evidence for a physiological role of the miRNA-silencing machinery in controlling HIV-1 replication. Type III RNAses Dicer and Drosha, responsible for miRNA processing, inhibited virus replication both in peripheral blood mononuclear cells from HIV-1-infected donors and in latently infected cells. In turn, HIV-1 actively suppressed the expression of the polycistronic miRNA cluster miR-17/92. This suppression was found to be required for efficient viral replication and was dependent on the histone acetyltransferase Tat cofactor PCAF. Our results highlight the involvement of the miRNA-silencing pathway in HIV-1 replication and latency.  相似文献   
107.
The sulfated peptide phytosulfokine (PSK) is an intercellular signal that plays a key role in cellular dedifferentiation and proliferation in plants. Using ligand-based affinity chromatography, we purified a 120-kilodalton membrane protein, specifically interacting with PSK, from carrot microsomal fractions. The corresponding complementary DNA encodes a 1021-amino acid receptor kinase that contains extracellular leucine-rich repeats, a single transmembrane domain, and a cytoplasmic kinase domain. Overexpression of this receptor kinase in carrot cells caused enhanced callus growth in response to PSK and a substantial increase in the number of tritium-labeled PSK binding sites, suggesting that PSK and this receptor kinase act as a ligand-receptor pair.  相似文献   
108.
In semen cryopreservation, egg yolk is still widely used as a non-penetrating cryoprotectant. Much has been developed in the search for alternatives for this biological product. This work aimed to evaluate the processed egg yolk through ultracentrifugation and/or sonication in the cryopreservation of swine semen. Twenty-seven semen doses were purchased from a commercial boar stud and processed for cryopreservation using egg yolk lactose 11% (control) extender, processed using two different methods: high-speed centrifugation and sonication. Then, they were submitted to freeze-thawing protocol and were assessed for kinematic and cell structural parameters. Samples in which extenders underwent centrifugation had better results in velocity parameters, meanwhile those that only sonication was performed had poorest results in this parameter. The preservation of the membrane and mitochondria structure had better results when the diluent was only centrifuged in comparison with the other treatments. Therefore, centrifugation of extender containing egg yolk is important for better cryopreservation of swine semen.  相似文献   
109.
The effects of tea polyphenols on the invasion of highly metastatic human fibrosarcoma HT1080 cells through a monolayer of human umbilical vein endothelial cells (HUVECs) and the accompanying basal membrane were investigated. Among the tea polyphenols tested, epicatechin gallate (ECg), epigallocatechin gallate (EGCg), and theaflavin strongly suppressed the invasion of HT1080 cells into the monolayer of HUVECs/gelatin membrane, whereas epicatechin, epigallocatechin, tea flavonols, tea flavones, and gallate derivatives had no effect. Both theaflavin-digallate and theasinensin D showed a weak invasion inhibitory effect. ECg significantly inhibited the invasion without cytotoxicity against cancer cells and HUVECs. Ester-type catechins (ECg and EGCg) and theaflavin strongly suppressed the gelatin degradation mediated by matrix metalloproteinase (MMP) 2 and MMP-9, which were secreted into the conditioned medium of HT1080 cells. In conclusion, among the tea polyphenols tested, ECg was considered to be the agent with the most potential antimetastasis activity because it inhibited invasion in the absence of cytotoxicity.  相似文献   
110.
OBJECTIVE: To describe how urbanisation influences the nutrition and health transition in South Africa by using data from the THUSA (Transition and Health during Urbanisation of South Africans) study. DESIGN: The THUSA study was a cross-sectional, comparative, population-based survey. SETTING: The North West Province of South Africa. SUBJECTS: In total, 1854 apparently healthy volunteers, men and women aged 15 years and older, from 37 randomly selected sites. Pregnant and lactating women, those with diagnosed chronic diseases and taking medication, with acute infections or inebriated were excluded but screened for hypertension and diabetes mellitus. Subjects were stratified into five groups representing different levels of urbanisation in rural and urban areas: namely, deep rural, farms, squatter camps, townships and towns/cities. OUTCOME MEASURES AND METHODS: Socio-economic and education profiles, dietary patterns, nutrient intakes, anthropometric and biochemical nutrition status, physical and mental health indicators, and risk factors for non-communicable diseases (NCDs) were measured using questionnaires developed or adapted and validated for this population, as well as appropriate, standardised methods for the biochemical analyses of biological samples. RESULTS: Subjects from the rural groups had lower household incomes, less formal education, were shorter and had lower body mass indices than those in the urban groups. Urban subjects consumed less maize porridge but more fruits, vegetables, animal-derived foods and fats and oils than rural subjects. Comparing women from rural group 1 with the urban group 5, the following shifts in nutrient intakes were observed: % energy from carbohydrates, 67.4 to 57.3; from fats, 23.6 to 31.8; from protein, 11.4 to 13.4 (with an increase in animal protein from 22.2 to 42.6 g day(-1)); dietary fibre, 15.8 to 17.7 g day(-1); calcium, 348 to 512 mg day(-1); iron from 8.4 to 10.4 mg day(-1); vitamin A from 573 to 1246 mug retinol equivalents day(-1); and ascorbic acid from 30 to 83 mg day(-1). Serum total cholesterol, low-density lipoprotein cholesterol and plasma fibrinogen increased significantly across groups; systolic blood pressure >140 mmHg was observed in 10.4-34.8% of subjects in different groups and diabetes mellitus in 0.8-6.0% of subjects. Women in groups 1 to 5 had overweight plus obesity rates of 48, 53, 47, 61 and 61%, showing an increase with urbanisation. Subjects from group 2 (farm dwellers) showed the highest scores of psychopathology and the lowest scores of psychological well-being. The same subjects consistently showed the lowest nutrition status. CONCLUSIONS: Urbanisation of Africans in the North West Province is accompanied by an improvement in micronutrient intakes and status, but also by increases in overweight, obesity and several risk factors for NCDs. It is recommended that intervention programmes to promote nutritional health should aim to improve micronutrient status further without leading to obesity. The role of psychological strengths in preventing the adverse effects of urbanisation on health needs to be examined in more detail.  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