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   20篇
  国内免费   1篇
林业   49篇
农学   10篇
基础科学   1篇
  166篇
综合类   18篇
农作物   24篇
水产渔业   45篇
畜牧兽医   148篇
园艺   14篇
植物保护   20篇
  2023年   3篇
  2022年   7篇
  2021年   12篇
  2020年   13篇
  2019年   7篇
  2018年   12篇
  2017年   20篇
  2016年   15篇
  2015年   15篇
  2014年   17篇
  2013年   30篇
  2012年   44篇
  2011年   37篇
  2010年   23篇
  2009年   19篇
  2008年   47篇
  2007年   32篇
  2006年   20篇
  2005年   36篇
  2004年   28篇
  2003年   18篇
  2002年   24篇
  2001年   3篇
  2000年   2篇
  1998年   2篇
  1997年   2篇
  1996年   3篇
  1995年   1篇
  1992年   1篇
  1989年   1篇
  1976年   1篇
排序方式: 共有495条查询结果,搜索用时 31 毫秒
101.
In this study, the hypothesis that food-derived opioid peptides besides β-casomorphin 7 might modulate the production of mucin via a direct action on epithelial goblet cells was investigated in HT29-MTX cells used as a model of human colonic epithelium. Seven milk whey or casein peptides, a human milk peptide, and a wheat gluten-derived peptide with proved or probable ability to bind μ- or δ-opioid receptors were tested on the cell culture. Significantly increased secretion of mucins was found after exposure to six of the assayed peptides, besides the previously described β-casomorphin 7, as measured by an enzyme-linked lectin assay (ELLA). Human β-casomorphin 5 and α-lactorphin were selected to study the expression of mucin 5AC gene (MUC5AC), the HT29-MTX major secreted mucin gene. α-Lactorphin showed increased expression of MUC5AC from 4 to 24 h (up to 1.6-fold over basal level expression), although differences were statistically different only after 24 h of exposure. However, this increased expression of MUC5AC did not reach significance after cell treatment with human β-casomorphin 5. In conclusion, six food-derived peptides have been identifed with described or probable opioid activity that induce mucin secretion in HT29-MTX cells. Concretely, α-lactorphin is able to up-regulate the expression of the major secreted mucin gene encoded by these cells.  相似文献   
102.
103.
This paper reports a study on the thermal stability and flame-retardant properties of microencapsulated phase change materials (PCMs) with clay nano-particles (Clay-NPs) doped gelatin/sodium alginate shell. The novel microcapsules were fabricated by the technique of complex coacervation using gelatin and sodium alginate as the shell and PCM n-eicosane as the core. Their flame retardant property as well as their practicable thermal performances when incorporated into woven cotton fabrics by pad-dry-cure were investigated. Thermal storage/release properties of the prepared microcapsules were analyzed using DSC instrument. Thermal gravimetry (TG) analysis was performed to measure the thermal stability and surface morphology of the microcapsules was observed by means of optical microscopy and SEM. The DSC results indicated that the latent heat storage capacity of prepared microcapsules changed in range of 97-114 J/g. The microcapsules had spherical shape with particle sizes between 1.37 μm and 1.6 μm. The PCM microcapsules (PCMMs) and nano-composite PCM microcapsules (NCPCMMs) with clay-NPs doped gelatin/sodium alginate shell were found to have good potential for developing thermal comfort in textiles. Comparing with conventional PCMMs, NCPCMMs have significantly better thermal stability. Nano-composite structure of the NCPCMMs, in which clay-NPs doped in the polymeric shell structure, attributed to increase the shell thermal stability. Improved flame retardant properties of the cotton fabrics treated with NCPCMs were declared as a result of flame retardant tests. Thermo-regulating properties of the fabrics were proved by thermal history (THistory) measurement results from releasing heat from microcapsules.  相似文献   
104.
ABSTRACT: At birth, the immune system is still in development making neonates more susceptible to infections. The recognition of microbial ligands is a key step in the initiation of immune responses. It can be mimicked to stimulate the immune system by the use of synthetic ligands recognising pattern recognition receptors. In human and mouse, it has been found that neonatal cytokine responses to toll-like receptor (TLR) ligands differ in many ways from those of adults but the relevant studies have been limited to cord blood and spleen cells. In this study, we compared the responses in neonate and adult sheep to CpG oligodeoxynucleotides (ODN), a TLR9 ligand, in both a mucosal and a systemic organ. We observed that in response to CpG-ODN more IL-12 was produced by neonatal than adult sheep cells from mesenteric lymph nodes (MLN) and spleen. This higher IL-12 response was limited to the first 20 days after birth for MLN cells but persisted for a longer period for spleen cells. The major IL-12-producing cells were identified as CD14+CD11b+. These cells were poor producers of IL-12 in response to direct stimulation with CpG-ODN and required the cooperation of other MLN cells. The difference in response to CpG-ODN between neonates and adults can be attributed to both a higher proportion of CD14+CD11b+ cells in neonate lambs and their higher capacity to produce IL-15. The IL-15 increases IL-12 production by an amplifying feedback loop involving CD40.  相似文献   
105.
The US3 protein is a unique protein kinase only present in the Alphaherpesvirinae subfamily of the herpesviruses. Studies performed with several alphaherpesviruses demonstrated that the US3 protein is involved in cytoskeleton modifications during viral infection and displays anti-apoptotic activity. However, the US3 protein of BoHV-5 has not been studied up to now. As reported for other alphaherpesviruses, our results showed that BoHV-5 US3 confers resistance against apoptosis and induces cytoskeletal reorganization leading to cell rounding, actin stress fiber breakdown and cell projections that interconnect cells. The expression of a kinase-dead version of BoHV-5 US3 showed that the anti-apoptotic activity and the induction of cell projections are kinase-dependent whereas kinase activity is not absolutely required for actin stress fiber breakdown. Besides, the kinase-dead version of US3, but not the wild type protein, was found excluded from the nucleus. These results constitute the first report on the BoHV-5 US3 functions, and highlight that there are functional differences and similarities among US3 proteins of different alphaherpesviruses.  相似文献   
106.
Fluid catalytic cracking of heavy ends to high-value liquid fuels is a common unit operation in oil refineries. In this process, the heavy feedstock that contains sulfur is cracked to light products. Sulphur content is hence redistributed in the liquid and gaseous products and coke of the catalyst used in this process. The coke is later burnt in the regenerator releasing sulfur into the discharged flue gas as SO2. In the present work, comprehensive emission inventories for a fluid catalytic cracking unit in a typical oil refinery are prepared. These inventories are based on calculations that assume complete combustion of catalyst coke in the regenerator. Yearly, material balances for both SO2 and particulate matters emissions are carried out taking into account seasonal variations in the operation of the process unit. The results presented in this article reflect the variation of sulfur in feedstock originating from various units in the refinery. The refinery operations are not dependant on seasons but controlled by market-driven conditions to maximize the profit. The seasonal impact on refinery emissions is minimal due to its operation at optimum capacity fulfilling the international market demand. The data presented and analyzed here can be used to assess the hazardous impact of SO2 and particulate matter emissions on surrounding areas of the refinery.  相似文献   
107.
Infectious diseases and aetiological agents related to female reproductive systems were extensively covered compared to its male counterpart. There needs a proper study to bridge this gap, where microflora and infectious agents of both male and female reproductive are mutually intelligible. With this study, we aimed to evaluate the microbial contamination of the preputial cavity and also screened for abortion-causing agents which are zoonotic as well. In goats, such types of abortions are caused by Brucella melitensis, Chlamydophila, Campylobacter and Coxiella etc. One of the major sources of contamination of semen is the preputial cavity, which is exposed to the external environment leading to spread of infection into the female via semen straws or by natural service. In the current study, good quality bucks (n = 32, Barbari = 12, Jamunapari = 10, Jakhrana = 10) which were routinely used for semen collection were screened for their preputial swabs, for the presence of the above pathogens. For detection of Brucella melitensis, OMP31 based TaqMan® probe real-time PCR assay was used, and for Chlamydia, 16srRNA gene based SYBR® green real-time PCR assay was employed for detection of Chlamydophila abortus. While for Campylobacter spp. and Coxiella burnetii, 16srRNA gene based conventional PCR and Trans-PCR were used, respectively. In the current study, of the screened preputial swabs, none of them showed positive for Brucella and Coxiella, but of the screened 32 samples 17 showed positive for Chlamydia (53.13%) and two (6.25%) showed positive for Campylobacter spp. The current study emphasizes on the farms and laboratories which were regularly involved in screening of brucellosis also often overlook the other potential non-brucella pathogens, causing abortions eventually incurring severe economic losses to the goat keepers.  相似文献   
108.
A study was conducted on the effect of supplemental nitrogen (N) (20 hg/ha) applied as a foliar spray or to the soil on seed production, protein percentage, and protein fractions of rice. Plants were grown in a greenhouse over two different periods of time, i.e., August 1988 to January 1989 (Period I), and December 1988 to April 1989 (Period II). Nitrogen was applied to the leaves 10 and 20 days after anthesis (DAA), and to the soil at anthesis and at 15 DAA. Average temperature was 28.7°C during Period I and 32°C during Period II, corresponding to 18.7 and 22.0 growing degree‐day/day (GDD/day), respectively. The difference in GDD/day reduced the plant cycle from 130 days during Period I to 109 days during Period II. Plants grown during Period II had larger numbers of spikelets, a higher percentage of “full grown grains”;, and higher grain weight. Although percentage crude protein was about the same for the two periods, prolamin content was increased and the albumin+globulin fraction was decreased during Period II, but with no difference in glutelin content. The increase in number of spikelets, percent full grains, and grain weight appeared to result in a greater energy demand for plants grown during Period II. This may explain the increase in prolamins, since prolamin synthesis requires less energy than globulin or albumin synthesis. There was a simultaneous decrease in albumin and globulin synthesis during Period II. The content of glutelins, which represent the major reserve proteins in rice grains, was constant during both periods.  相似文献   
109.
Investment in small and large-scale revegetation in Australia is growing in response to concerns regarding the sustainability and productivity of agricultural landscapes. Site preparation and management––such as soil cultivation, weed control, fertilising, mulching, use of treeguards and watering––are major costs associated with small-scale revegetation. The aim of this study has been to investigate local revegetation knowledge and practices to determine the usefulness of each management practice for achieving success and to determine whether some practices are more suited to particular climatic zones. A national online revegetation survey was conducted to ascertain current small-scale revegetation practices and the factors that drive these choices. Management practices were found to be strongly associated with climate. Mulch, fertiliser, weed control and watering were applied more frequently in higher rainfall and higher temperature zones. Soil cultivation and treeguards were used more frequently in lower rainfall and lower temperature zones. These findings suggest that there may be some benefit in modifying existing revegetation guidelines to reflect climatic zones and management flexibility.
Sonia GrahamEmail:
  相似文献   
110.
Turbulent fluxes of carbon, water and energy were measured at the Wind River Canopy Crane, Washington, USA from 1999 to 2004 with eddy-covariance instrumentation above (67 m) and below (2.5 m) the forest canopy. Here we present the decomposition of net ecosystem exchange of carbon (NEE) into gross primary productivity (GPP), ecosystem respiration (R(eco)) and tree canopy net CO(2) exchange (DeltaC) for an old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)-western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest. Significant amounts of carbon were recycled within the canopy because carbon flux measured at the below-canopy level was always upward. Maximum fluxes reached 4-6 micromol m(-2) s(-1) of CO(2) into the canopy air space during the summer months, often equaling the net downward fluxes measured at the above-canopy level. Ecosystem respiration rates deviated from the expected exponential relationship with temperature during the summer months. An empirical ecosystem stress term was derived from soil water content and understory flux data and was added to the R(eco) model to account for attenuated respiration during the summer drought. This attenuation term was not needed in 1999, a wet La Ni?a year. Years in which climate approximated the historical mean, were within the normal range in both NEE and R(eco), but enhanced or suppressed R(eco) had a significant influence on the carbon balance of the entire stand. In years with low respiration the forest acts as a strong carbon sink (-217 g C m(-2) year(-1)), whereas years in which respiration is high can turn the ecosystem into a weak to moderate carbon source (+100 g C m(-2) year(-1)).  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