全文获取类型
收费全文 | 522篇 |
免费 | 15篇 |
专业分类
林业 | 25篇 |
农学 | 48篇 |
基础科学 | 2篇 |
65篇 | |
综合类 | 33篇 |
农作物 | 108篇 |
水产渔业 | 24篇 |
畜牧兽医 | 195篇 |
园艺 | 8篇 |
植物保护 | 29篇 |
出版年
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 17篇 |
2016年 | 13篇 |
2015年 | 12篇 |
2014年 | 20篇 |
2013年 | 33篇 |
2012年 | 21篇 |
2011年 | 32篇 |
2010年 | 19篇 |
2009年 | 14篇 |
2008年 | 34篇 |
2007年 | 22篇 |
2006年 | 22篇 |
2005年 | 26篇 |
2004年 | 25篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 11篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1961年 | 2篇 |
1958年 | 3篇 |
1933年 | 1篇 |
1926年 | 1篇 |
1925年 | 1篇 |
1923年 | 2篇 |
排序方式: 共有537条查询结果,搜索用时 15 毫秒
441.
The properties of polarizing films prepared using iodine vapor and using I2/KI solution are compared to investigate the possibility of using vapor phase iodine adsorption in preparing polarizing film. The structure of PVA films drawn to different draw ratios and the amount of iodine adsorbed in drawn PVA films using iodine vapor were investigated. Increases in the degree of crystallinity, crystalline orientation index and birefringence with increase in draw ratio of PVA film, were observed by WAXD and polarizing microscope analysis. The amounts of iodine adsorbed by PVA film were 2–4 wt% for 20 min. UV-visible analysis suggests that I3 ? and I5 ? structures of iodine exist in the polarizing film after drawing in boric acid solution. Single transmittance and degree of polarization of polarizing films prepared using iodine vapor were about 30–50 % and over 99 %, respectively, at total draw ratios of over 3. The possibility of employing vapor phase adsorption of iodine instead of solution adsorption to prepare commercial polarizing film is suggested. 相似文献
442.
Sung Hwoan Cho Young Soo Lim Jong Ha Lee Jong Kwan Lee Sangun Park Sang Min Lee 《Journal of the World Aquaculture Society》2003,34(1):85-91
The effects of feeding rate and feeding frequency on survival, growth and body composition of ayu post‐larvae (0.15 g in body weight and 3.5 cm in total length) were investigated in this study. A factorial experimental design of two feeding rates (3 and 6% of body weight of fish per meal) five feeding frequencies (one meal in 2 d, one meal a day, two meals a day, four meals a day, and six meals a day) with three replicates was used. Survival of ayu post‐larvae was significantly (P 0.05) affected by feeding frequency but not by feeding rate. Survival of ayu improved linearly with feeding frequency at both feeding rates. Weight and length gains and specific growth rate (SGR) of ayu was significantly (P 0.05) affected by feeding frequency but not by feeding rate, with weight and length gains and SGR linearly elevated with increasing feeding frequency at both feeding rates. The greatest weight and length gains were observed in fish receiving six meals daily at both feeding rates; however, no significant difference in weight gain was observed among two, four, and six meals a day, or in length gain between four and six meals a day. Feed efficiency ratio (FER) was significantly (P 0.05) affected by both feeding rate and feeding frequency. FER linearly decreased with feeding frequency at both feeding rates or feeding rate in the same feeding frequency. When the total daily amount of feed supply was constant with various feeding frequencies at different feeding rates (one meal a day at 3% feeding rate and one meal in 2 d at 6% feeding rate, two meals a day at 3% feeding rate and one meal a day at 6% feeding rate, or four meals a day at 3% feeding rate and two meals a day at 6% feeding rate), improvement in survival, weight and length gains, and SGR was observed in fish with higher feeding frequency at lower feeding rate. Moisture, protein, and lipid content of fish were not significantly (P > 0.05) affected by either feeding rate or feeding frequency. However, lipid content of ayu linearly increased with feeding frequency at 6% feeding rate. The highest body lipid content was observed in fish receiving six meals daily at both feeding rates. Ash content of fish was significantly (P 0.05) affected by feeding frequency but not by feeding rate. Based on performance of ayu, it can be concluded that optimum feeding rate and feeding frequency for ayu post‐larvae (an initial weight of 0.15 g) were 3% per meal and four meals a day, respectively, under these experimental conditions. 相似文献
443.
Sung Min Nam Jong Whi Kim Dae Young Yoo Hyo Young Jung Jung Hoon Choi In Koo Hwang Je Kyung Seong Yeo Sung Yoon 《Journal of veterinary science (Suw?n-si, Korea)》2016,17(1):13-20
In this study, we investigated the effects of chronic aluminum (Al) exposure for 10 weeks on cell proliferation and neuroblast differentiation in the hippocampus of type 2 diabetic rats. Six-week-old Zucker diabetic fatty (ZDF) and Zucker lean control (ZLC) rats were selected and randomly divided into Al- and non-Al-groups. Al was administered via drinking water for 10 weeks, after which the animals were sacrificed at 16 weeks of age. ZDF rats in both Al- and non-Al-groups showed increases in body weight and blood glucose levels compared to ZLC rats. Al exposure did not significantly affect body weight, blood glucose levels or pancreatic β-cells and morphology of the pancreas in either ZLC or ZDF rats. However, exposure to Al reduced cell proliferation and neuroblast differentiation in both ZLC and ZDF rats. Exposure to Al resulted in poor development of the dendritic processes of neuroblasts in both ZLC and ZDF rats. Furthermore, onset and continuation of diabetes reduced cell proliferation and neuroblast differentiation, and Al exposure amplified reduction of these parameters. These results suggest that Al exposure via drinking water aggravates the impairment in hippocampal neurogenesis that is typically observed in type 2 diabetic animals. 相似文献
444.
W De Jong 《Agroforestry Systems》1996,34(3):277-290
Swidden-fallow agroforestry among ribereño farmers in the Peruvian Amazon has been reported to show important regional variation. In this paper diversity in terra firme swidden-fallow agroforestry is described for a single village, Santa Rosa, located at the lower Ucayali river, Peru. Local forest gardens differ in managed species composition, wedding patterns, and yield levels. Most of the produce from Santa Rosa forest gardens is locally consumed; only little is traded. Many forest species are actively tended for planted in forest gardens. These systems have the function of suppliers of a range of products. Variation inforest garden management is a result of farmer' individual perception of the need for such products.
Resumen Informas sobre agroforesteria de chacra y barbecho en la Amazonia Peruana mentionan la variabilidad de tales sistemas, segun la localidad de donde se encuentran. En el presente articulo se describe diversidad de agroforesteria de chacra y barbecho en un solo pueblo, Santa Rosa, ubicado en el bajo rio Ucayali, Peru. Los jardines forestales alli se distinguen por la composicion de especies, frecuencia e intensidad de deshierbo, y cantidades de productos obtenidos de ellos. La mayoria de los productos de los jardines forestales de Santa Rosa son consumidos localmente; solamente unos pocos son comercializados. Muchas especies forestales son cuidados o sembrados en los jardines forestale.. Estos sistemas tienen la funcion de prover una seria de productos. Variacion en el manejo de jardines forestales son el resultado de la percepcion individual de agricultores para la necesidad de estos productos.相似文献
445.
446.
Antioxidant activity of Litsea cubeba 总被引:5,自引:0,他引:5
The antioxidant activity of Litsea cubeba was studied in terms of three different assay systems: DPPH assay, peroxidase/guaiacol assay, and TBA test. The L. cubeba methanol extract and its fractions showed remarkable antioxidant activity in comparison with alpha-tocopherol and ascorbic acid. 相似文献
447.
A Yoon H Aleyas AG George JA Park SO Han YW Hyun BH Lee JH Song HJ Cho JG Eo SK 《Research in veterinary science》2007,83(1):73-81
To assess the correlation between the nature of immunity induced by different types of immunogens and the establishment of latent infection by wild-type pseudorabies virus (PrV), we used a murine model immunized with different immunogens, the PrV modified live vaccine (MLV), inactivated vaccine (IAV), and commercial oil-adjuvant subunit vaccine (OSV), via either intranasal (i.n.) or intramuscular (i.m.) route. Both MLV and IAV induced a different nature of immunity biased to Th1- and Th2-type, respectively, as judged by the ratio of PrV-specific IgG isotypes (IgG2a/IgG1) and the profile of cytokine IL-2, IL-4, and IFN-gamma production. In contrast, the OSV induced a lower isotype IgG2a to IgG1 ratio and higher level of IL-2 production. The MLV (inducing Th1-type) provided more effective protection against a virulent wild-type PrV challenge than IAV and OSV (inducing Th2- and mixed type, respectively). In addition, the MLV impeded the establishment of a latent infection with wild-type PrV, and the decrease in the PrV latency load by immunization with the MLV appeared to be mediated by the immune T-cells. These results demonstrate the substantial role of the immune responses driven by preceding vaccination in modulating the establishment of PrV latency caused by the post-infection of a field virus. 相似文献
448.
CCL2 induces neural stem cell proliferation and neuronal differentiation in
Niemann-Pick type C mice
Yu Ri HONG Hyun LEE Min Hee PARK Jong Kil LEE Ju Youn LEE Hwa Deok SUH Min Seock JEONG Jae-Sung BAE Hee Kyung JIN 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(6):693-699
Niemann-Pick type C disease (NP-C) is a rare and ultimately fatal lysosomal storage
disorder with variable neurologic symptoms. Loss of neuronal function and neuronal cell
death occur in the NP-C brain, similar to the findings for other neurodegenerative
diseases. Targeting of neuronal cells in the brain therefore represents a potential
clinical intervention strategy to reduce the rate of disease progression and improve the
quality of life. We previously reported that bone marrow stem cells show a neurogenic
effect through CCL2 (also known as monocyte chemoattractant protein-1, MCP-1) secretion in
the brains of NP-C mice. However, the direct effect of CCL2 on neurogenesis has not been
ascertained. Here, to define neurogenic effects of CCL2 in NP-C, we applied human
recombinant CCL2 to neural stem cells (NSCs) derived from NP-C mice. CCL2-treated NSCs
showed significantly increased capacity for self-renewal, proliferation and neuronal
differentiation. Similar results were observed in the subventricular zone of NP-C mice
after CCL2 treatment. Furthermore, infusion of CCL2 into the NP-C mouse brain resulted in
reduction of neuroinflammation. Taken together, our results demonstrate that CCL2 is a
potential new therapeutic agent for NP-C. 相似文献
449.
Conjugated fatty acids and methane production by rumen microbes when incubated with linseed oil alone or mixed with fish oil and/or malate 下载免费PDF全文
We hypothesized that manipulating metabolism with fish oil and malate as a hydrogen acceptor would affect the biohydrogenation process of α‐linolenic acid by rumen microbes. This study was to examine the effect of fish oil and/or malate on the production of conjugated fatty acids and methane (CH4) by rumen microbes when incubated with linseed oil. Linseed oil (LO), LO with fish oil (LO‐FO), LO with malate (LO‐MA), or LO with fish oil and malate (LO‐FO‐MA) was added to diluted rumen fluid, respectively. The LO‐MA and LO‐FO‐MA increased pH and propionate concentration compared to the other treatments. LO‐MA and LO‐FO‐MA reduced CH4 production compared to LO. LO‐MA and LO‐FO‐MA increased the contents of c9,t11‐conjugated linoleic acid (CLA) and c9,t11,c15‐conjugated linolenic acid (CLnA) compared to LO. The content of malate was rapidly reduced while that of lactate was reduced in LO‐MA and LO‐FO‐MA from 3 h incubation time. The fold change of the quantity of methanogen related to total bacteria was decreased at both 3 h and 6 h incubation times in all treatments compared to the control. Overall data indicate that supplementation of combined malate and/or fish oil when incubated with linseed oil, could depress methane generation and increase production of propionate, CLA and CLnA under the conditions of the current in vitro study. 相似文献
450.
Park MS Lee HY Li SP Koh PO Bahk JY Chung BC Kim MO 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2007,69(1):25-30
Neural transplantation is one of the most promising treatments for neurodegenerative disorders. Survival rates of embryonic dopamine (DA) neurons following transplantation are low, between 2% and 20% in a number of animal models. To further establish survival changes of the transplanted gestational day 13.5 ventral mesencephalic (VM) cells into left intact adult rat striata so that design strategies of increasing survival of DA neurons, the tyrosine hydroxylase (TH) expression of VM-derived progenitor cells has been examined using immunohistochemistry and Western blot analysis. TH immunostaining revealed that the grafted VM cells developed to mature TH-positive neurons strongly at 3 weeks, peaked at 4 weeks, thereafter, gradually dropped following the degenerative expression of the grafted cells at both 5 and 6 weeks after transplantation. Western blot analysis also showed that the TH proteins were maximally expressed at 4 weeks post-grafting. Our finding suggested that the peak of surviving VM-derived TH positive cells occurred approximately 4 weeks after transplantation. 相似文献