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   2152篇
  免费   10篇
  国内免费   11篇
林业   58篇
农学   15篇
基础科学   1篇
  525篇
综合类   501篇
农作物   38篇
水产渔业   17篇
畜牧兽医   902篇
园艺   27篇
植物保护   89篇
  2023年   9篇
  2022年   15篇
  2021年   7篇
  2020年   3篇
  2019年   8篇
  2018年   8篇
  2017年   7篇
  2016年   6篇
  2015年   8篇
  2014年   12篇
  2013年   10篇
  2012年   209篇
  2011年   263篇
  2010年   44篇
  2009年   27篇
  2008年   173篇
  2007年   187篇
  2006年   164篇
  2005年   162篇
  2004年   158篇
  2003年   126篇
  2002年   133篇
  2001年   67篇
  2000年   98篇
  1999年   30篇
  1998年   8篇
  1997年   7篇
  1996年   10篇
  1995年   11篇
  1994年   17篇
  1993年   12篇
  1992年   17篇
  1991年   17篇
  1990年   14篇
  1989年   17篇
  1988年   7篇
  1987年   8篇
  1986年   3篇
  1985年   4篇
  1984年   6篇
  1983年   3篇
  1980年   7篇
  1978年   4篇
  1976年   4篇
  1966年   3篇
  1963年   3篇
  1909年   2篇
  1908年   4篇
  1902年   2篇
  1897年   4篇
排序方式: 共有2173条查询结果,搜索用时 609 毫秒
81.
Two anti-inflammatory omega-3 polyunsaturated fatty acids (PUFAs) of stearidonic acid (SA) and eicosapentaenoic acid (EPA) and one pro-inflammatory omega-6 PUFA of arachidonic acid (AA) were isolated from the edible brown seaweed Undaria pinnatifida. SA was active against mouse ear inflammation induced by phorbol myristate acetate, with IC50 values of 160, 314, and 235 microg per ear for edema, erythema, and blood flow, respectively. EPA was also active against edema, erythema, and blood flow, with IC50 values of 230, 462, and 236 microg per ear, respectively. Although AA at low concentrations showed anti-inflammatory activities when measured 10 h later, AA doses of more than 243 microg per ear induced inflammatory symptoms 1 h later. Mature thalli generally had larger amounts of PUFAs than young thalli. The algal blade contained more omega-3 PUFAs than were found in other parts, while the holdfast contained extremely high amounts of AA. Late-season thalli showed increased amounts of PUFAs, especially AA.  相似文献   
82.
Monascus-fermented red mold dioscorea (RMD) was proven to produce higher monacolin K levels than red mold rice (RMR) in our previous study. The goal of this study is to investigate whether the novel RMD had more hypolipidemic and antiatherosclerotic effect than traditional red mold rice. The daily dose of RMR for adults was recommended as 1 g, which corresponded to 96 mg/kg/day for hamsters. Therefore, high cholesterol diet-induced hyperlipidemic hamsters were daily administrated with a 0.5-fold (48 mg/kg/day), a 1-fold (96 mg/kg/day), or a 5-fold dose (480 mg/kg/day) of RMD for 8 weeks. Furthermore, a 1-fold dose of RMR (96 mg/kg/day) and unfermented dioscorea (96 mg/kg/day) were also respectively used to evaluate the effect of hypolipidemic and antiarteriosclerosis. The results indicated that only needing a 0.5-fold dose of RMD was able to significantly lower total cholesterol (by 13.78%, p<0.001), triglyceride (by 38.74%, p<0.01), and low-density lipoprotein cholesterol levels (by 43.11%, p<0.05) as well as maintain a high-density lipoprotein cholesterol level, as compared to the hyperlipidemic group. RMD including a higher monacolin K level and a dioscorea substrate was able to exhibit a more significant difference in the hypolipidemic effect than RMR or unfermented dioscorea. Both RMR and dioscorea exhibited potent in vitro antioxidative ability and in vivo protection against hypolipidemia-induced oxidative stress. Therefore, the antioxidative ability of RMD provided by Monascus metabolites (dimerumic acid, tannin, phenol, etc.) as well as dioscorea was able to perform more antiatherosclerotic effects on increasing total antioxidant status, catalase, and superoxide dismutase activity and repressing lipid peroxidation and atherosclerotic plaque than RMR and dioscorea.  相似文献   
83.
Using dioscorea root as substrate of Monascus species was found to stimulate monacolin K (cholesterol-lowering agent) formation in our previous study, but the mycotoxin-citrinin has never been studied. This study used dioscorea root as the liquid medium to culture Monascus purpureus NTU 568 using a 6.6 L jar fermentor. Culture pH value, dioscorea concentration, and ethanol concentration were used as the factors of response surface methodology (RSM) to investigate the optimal culture condition for high monacolin K production and low citrinin formation. Monacolin K and citrinin formation of M. purpureus NTU 568 under submerged dioscorea medium were respectively found to be significantly formed by 148% and 147%, as compared to that under submerged rice medium. The reason is due to the pH value (3.5) of dioscorea medium involved in the formation of Monascus cell amount and secondary metabolite. RSM results further indicated that lowering the pH value to 2.5 would result in high monacolin K and citrinin concentrations as well as high biomass in fixed dioscorea amount, implying that pH value may stimulate the formation of monacolin K and citrinin through increasing Monascus cell amount. Lowering dioscorea and ethanol concentration was able to increase the ratio of monacolin K level to citrinin level. The optimal culture condition (pH 5.7, 1% dioscorea concentration, and 0.5% ethanol concentration) would increase monacolin K levels to 27.9 mg/g (by 47%) and decrease citrinin level to 2.15 microg/g (by 54%), as compared to control conditions (pH 3.5, 5% dioscorea, and ethanol free).  相似文献   
84.
AIMS: To document infant feeding methods in the first six months of life in Xinjiang Uygur Autonomous Region, People's Republic of China, 2003-2004. Some problems with breast-feeding in the area are explained. METHODS: A longitudinal study of infant feeding practices was undertaken. A total of 1219 mothers who delivered babies during 2003 and 2004 were interviewed in five hospitals or institutes, and after discharge were contacted in person or by telephone at approximately monthly intervals to obtain details of infant feeding practices. Multivariate logistic regression analysis was used to explore factors associated with breast-feeding initiation. RESULTS: 'Any breast-feeding' rates at discharge and at 0.5, 1.5, 2.5, 3.5, 4.5 and 6 months were 92.2, 91.3, 89.9, 88.8, 87.7, 86.0 and 73.0%, respectively. 'Exclusive breast-feeding' rates at discharge and at 0.5, 1.5, 2.5, 3.5, 4.5 and 6 months were 66.2, 47.6, 30.1, 25.8, 22.1, 13.0 and 6.2%, respectively. The main problem of breast-feeding in Xinjiang was the early introduction of formula or water. The average duration of 'exclusive breast-feeding' was 1.8 months (95% confidence interval (CI) 1.7-2.0), of 'full breast-feeding' 2.8 months (95% CI 2.7-2.9) and of 'any breast-feeding' 5.3 months (95% CI 5.2-5.4). CONCLUSIONS: Infant feeding methods in Xinjiang were documented in this study and the main problems with infant feeding in Xinjiang are discussed. Further studies are needed to identify factors associated with 'exclusive breast-feeding' and duration.  相似文献   
85.
Incorporation of stearic acid into canola oil to produce trans-free structured lipid (SL) as a healthy alternative to partially hydrogenated fats for margarine formulation was investigated. Response surface methodology was used to study the effects of lipozyme RM IM from Rhizomucor miehei and Candida rugosa lipase isoform 1 (LIP1) and two acyl donors, stearic acid and ethyl stearate, on the incorporation. Lipozyme RM IM and ethyl stearate gave the best result. Gram quantities of SLs were synthesized using lipozyme RM IM, and the products were compared to SL made by chemical catalysis and fat from commercial margarines. After short-path distillation, the products were characterized by GC and RPHPLC-MS to obtain fatty acid and triacylglycerol profiles, 13C NMR spectrometry for regiospecific analysis, X-ray diffraction for crystal forms, and DSC for melting profile. Stearic acid was incorporated into canola oil, mainly at the sn-1,3 positions, for the lipase reaction, and no new trans fatty acids formed. Most SL products did not have adequate solid fat content or beta' crystal forms for tub margarine, although these may be suitable for light margarine formulation.  相似文献   
86.
Several lupines (Lupinus spp.) present on western U.S. rangelands contain alkaloids that are teratogenic to livestock and cause congenital birth defects in calves (crooked calf disease). Periodically, large losses of calves due to lupine-induced "crooked calf disease" occur in northern Oregon and eastern Washington state. Five lupine populations from this area representing three species (L. leucophyllus, L. sulfureus, and L. sericeus) were evaluated taxonomically and by gas chromatography/mass spectrometry, and the major alkaloids in each lupine species were identified. The teratogenic alkaloid anagyrine was present in both of the lupine species responsible for the high outbreaks in east-central Washington and northeastern Oregon. However, the alkaloid profiles of the two lupines identified as L. leucophyllus were dissimilar, as were the alkaloid profiles of the two lupines identified as L. sulfureus. Botanical classification is not sufficient to determine potential teratogenicity, and it must be followed by chemical characterization to determine risk to livestock.  相似文献   
87.
Lee YA  Chan CW 《Phytopathology》2007,97(2):195-201
ABSTRACT Burkholderia cenocepacia (genomovar III of B. cepacia complex), the causal agent of banana finger-tip rot, is a common plant-associated bacterium but also an important opportunistic pathogen of humans. To better understand the nature of B. cenocepacia from banana, the genetic variation among B. cenocepacia isolates from various banana-growing regions in southern Taiwan was examined. Forty-four serial isolates recovered from diseased banana stigmata from three banana-growing regions during the periods ranging from 2002 to 2004 were investigated. All B. cenocepacia isolates picked from quinate-yeast extract tetracycline-polymyxin semiselective medium could cause onion maceration and were polymerase chain reaction (PCR) positive for bcscV, which is a type III secretion gene present in all members of the B. cepacia complex except B. cepacia (formerly genomovar I). Genetic diversity was assessed using recA PCR restriction fragment length polymorphism, recA nucleotide sequence analysis, and pulsed-field gel electrophoresis assays. The assays revealed the genetic variability among the isolates and also allowed us to trace the relationship among isolates. The isolates all were assigned to genomovar III and consisted of two groups, A and B, which corresponded to recA lineage IIIA and IIIB. The group B strains were separated into B1 and B2 subgroups and the B1 strains were further divided into distinct lineages. The B1 strains were the most frequently detected and occurred in all regions tested. There was no significant difference between strains from each subgroup in the virulence on banana fingers of cv. Cavendish. PCR assays were further used to determine whether B. cenocepacia from banana contained the cable pilus subunit gene (cblA), IS1356, and B. cepacia epidemic strain marker (BCESM), which are DNA markers associated with epidemic B. cepacia clinic strains. The results indicated that cblA and IS1356 were absent but the BCESM was found in all isolates. The present study revealed that banana is a natural reservoir of genetically diversified B. cenocepacia strains.  相似文献   
88.
Lee S  Hamelin RC  Six DL  Breuil C 《Phytopathology》2007,97(9):1177-1185
ABSTRACT The sapstaining fungal pathogen Ophiostoma clavigerum is associated with the mountain pine beetle (Dendroctonus ponderosae), which is currently the most destructive forest pest in North America. The genetic diversity of O. clavigerum populations collected from five sites in Canada and two sites in the United States was estimated with amplified fragment length polymorphism (AFLP) analysis. Genomic DNA from 170 O. clavigerum isolates was digested with EcoRI and PstI and amplified with six primer sets. A total of 469 AFLP markers consisting of 243 monomorphic and 226 polymorphic loci were scored. The overall genetic diversity of the O. clavigerum population was low (Hs = 0.0531) and the differentiation of the seven O. clavigerum populations was moderate (Phi = 0.143). Genetic distances among the populations were not significantly correlated with geographic distance (r = 0.3235, P = 0.074). Two genetically distinct groups in the O. clavigerum populations were shown by unique AFLP profiles and the unweighted pair group method with arithmetic averages. Further work to characterize biological differences between the two groups will be needed to confirm whether cryptic species are present in the O. clavigerum population.  相似文献   
89.
The high cost of fish meal in tilapia diets warrants the potential use of cottonseed meal (CSM) as an alternative source of high quality protein. The effects of varying levels of CSM (0, 25, 50, 75 and 100%) as fish meal protein replacement on growth, blood parameters, spleen characteristics, free and bound gossypol in blood plasma, haemoglobin and haematocrit were determined in tilapia. Gossypol (C(30)H(30)O(8)) is a polyphenolic substance found in cottonseed that has known toxic effects in fish. Tilapias (n = 219, average weight = 11.3 +/- 3.9 g) were randomly distributed into 15, 32-L glass aquaria, representing five dietary treatments and three replicates per treatment. Each aquarium containing 13-16 fish was supplied with thermoregulated, recirculating water (27 +/- 1 degrees C) at 1 L min(-1) flow rate and photoperiod was constant (12 h L/12 h D). Fish fed 25-50% CSM protein replacement showed similar body weights and total lengths as the controls at the completion of the 16-week trial. Fish fed 75 and 100% CSM protein replacement showed a significant decline in body weight and total length. Fish fed 25-100% CSM protein replacement had significantly lower haematocrit and haemoglobin (ANOVA/LSD, P < 0.05) compared with levels in controls. The decline was most prominent in groups fed diets with 50-100% CSM protein replacement. Total and free gossypol concentrations of blood plasma significantly increased with increasing levels of CSM replacement (P < 0.05). No gossypol was found in blood plasma of fish from the control group. The occurrence of immature and abnormal erythrocytes was significantly greater among fish fed 75 and 100% CSM diets compared with fish fed 0-50% CSM diets. Spleen-somatic index (spleen weight/body weight x 100) did not differ between control fish and fish fed 50-100% CSM diets. Spleen abnormalities, such as large depositions of haemosiderin and melanin pigments and proliferation of melano-macrophage centres, lymphocytic depletion of the white pulp areas (hypocellularity), and presence of vacuoles and necrotic areas were observed among fish fed 50-100% CSM protein diets. In general, the pathological effects of gossypol in tilapia (low haemoglobin and haematocrit levels, abundance of immature red blood cells or polychromatocytes, abnormal spleen morphology) were similar to the effects of vitamin E and/or vitamin C deficiencies observed in other studies.  相似文献   
90.
Ursolic acid (UA), a triterpenoid compound found in plants, is used in the human diet and in medicinal herbs and possesses a wide range of biological benefits including antioxidative, anti-inflammatory, and anticarcinogenic effects. Endothelial expression of allograft inflammatory factor-1 (AIF-1) mediates vasculogenesis, and nitric oxide (NO) produced by endothelial NO (eNOS) represents a mechanism of vascular protection. It is unclear whether UA affects the neovascularization mediated by AIF-1 and eNOS expression. This study investigated the effects and mechanisms of UA on angiogenesis in vivo in hind limb ischemic animal models and in vitro in human coronary artery endothelial cells (HCECs). This study explored the impact of UA on endothelial cell (EC) activities in vitro in HCECs, vascular neovasculogenesis in vivo in a mouse hind limb ischemia model, and the possible role of AIF-1 in vasculogenesis. The results demonstrate that UA enhances collateral blood flow recovery through induction of neovascularization in a hind limb ischemia mouse model. In vitro data showed that UA increases tube formation and migration capacities in human endothelial cells, and exposing HCECs to UA increased AIF-1 expression through a NO-related mechanism. Moreover, UA administration increased capillary density and eNOS and AIF-1 expression in ischemic muscle. These findings suggest that UA may be a potential therapeutic agent in the induction of neovascularization and provide a novel mechanistic insight into the potential effects of UA on ischemic vascular diseases.  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