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   1041篇
  免费   31篇
  国内免费   6篇
林业   138篇
农学   32篇
基础科学   10篇
  244篇
综合类   15篇
农作物   64篇
水产渔业   58篇
畜牧兽医   380篇
园艺   37篇
植物保护   100篇
  2023年   9篇
  2022年   18篇
  2021年   27篇
  2020年   19篇
  2019年   9篇
  2018年   26篇
  2017年   39篇
  2016年   25篇
  2015年   42篇
  2014年   56篇
  2013年   132篇
  2012年   37篇
  2011年   49篇
  2010年   33篇
  2009年   45篇
  2008年   49篇
  2007年   79篇
  2006年   62篇
  2005年   52篇
  2004年   35篇
  2003年   30篇
  2002年   36篇
  2001年   43篇
  2000年   30篇
  1999年   26篇
  1998年   7篇
  1997年   7篇
  1996年   6篇
  1995年   4篇
  1993年   3篇
  1992年   7篇
  1991年   8篇
  1990年   13篇
  1989年   3篇
  1988年   1篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1981年   1篇
  1979年   3篇
  1978年   1篇
排序方式: 共有1078条查询结果,搜索用时 31 毫秒
1.
Plant Foods for Human Nutrition - Adipose tissue is an endocrine organ and its endocrine function is closely associated with type 2 diabetes mellitus. Valeriana officinalis (Valerian) exerts some...  相似文献   
2.
A cross-sectional serological survey was carried out to screen the equine population of the nonendemic state of Alabama for the presence of detectable antibody titers against Corynebacterium pseudotuberculosis. A second objective was to determine the association of detectable titers with risk factors such as exposure to ruminants or previous travel to endemic states. A total of 342 equine serum samples from 40 Alabama counties were analyzed using the synergistic hemolysis inhibition test (SHI). The prevalence of detectable antibody titers (≥1:8) was 52.5% (95% confidence interval [CI], 47%–57.9%). Titers ≥1:128 were detected in 2.63% (95% CI, 1.2%–4.9%), and titers ≥1:512 were detected in 0.3% (95% CI, 0%–1.6%) of the sampled population. In the final generalized linear model, age (P < .001), breed (P = .023), and contact with cattle (P = .05) were associated with increasing SHI titers. Contact with goats was associated in the initial but not in the final analysis (P = .19). Previous travel was not associated with increasing SHI titer (P = .97). The results demonstrated a high prevalence of low detectable titers and low prevalence of titers ≥ 1:128 in a nonendemic population. Further evaluation of SHI cutoff titers and accuracy is warranted to reduce the risk of a false positive diagnosis.  相似文献   
3.
In an effort to extract additional data from farinograph experiments a model was developed to simulate the measurements and correlate the parameters of the model with results from baking tests. This additional information can be used in bakeries to predict the baking properties of the flours and adjust the recipes to maintain a constant product quality. For this eight different flours were characterized with a farinograph and 13 different results from baking experiments. An approach with five nonlinear differential equations was able to model the farinograph measurements very well (average R2 = 0.995 ± 0.005). While a stepwise multilinear regression only showed weak correlations in cross validation between a single parameter of the model and the baking volume (R2 = 0.745) and the volume yield (R2 = 0.796) respectively, the artificial neuronal network was more successful. For the baking weight (R2 = 0.926), the dough yield gross (R2 = 0.909) and net (R2 = 0.913) strong correlations were found. A good correlation for the baking volume (R2 = 0.853) was also determined, while the volume yield showed comparable results to the linear regression (R2 = 0.792).  相似文献   
4.
A 9-year-old multiparous Thoroughbred broodmare presented for evaluation of acute signs of colic. The patient had a 4-month history of poor appetite, weight loss, and decreased body condition after parturition, despite appropriate feeding by the farm to minimize weight loss associated with increased nutrient requirements. The patient was diagnosed with a diaphragmatic hernia through transabdominal and thoracic ultrasonography. The diaphragmatic hernia was repaired surgically under general anesthesia.  相似文献   
5.
Solanum glaucophyllum (SG) contains 1,25‐dihydroxyvitamin D3 (1,25‐(OH)2D3) glycosides. We investigated the effect of SG on hypocalcemia in cows. Serum levels of 1,25‐(OH)2D3, total calcium and phosphorus dose‐relatedly increased after feeding with SG, while serum magnesium and chloride levels fell (P < 0.05). We also performed an ethylenediaminetetraacetic acid (EDTA) infusion to induce artificial hypocalcemia. Cows that had been fed 4.0 mg/kg body weight of SG daily for 2 weeks had a higher serum concentration of total calcium at the end of EDTA infusion than those not fed SG (P < 0.05). In a field trial, multiparous cows were assigned to one of four groups: (1) no SG, (2) 1.3 g or (3) 2.6 g of SG daily from 14 days before the estimated calving day until 3 days after calving, or (4) a single feed of 35.75 g SG at 3 days before the estimated calving day. The concentrations of serum total calcium after the calving in each treatment group were (1) 7.4, (2) 7.9, (3) 8.0 and (4) 8.9 mg/dL and higher for (4) than for (1) (P < 0.05). The data suggests that feeding a high dose of SG before the calving may maintain higher concentrations of serum calcium after the calving.  相似文献   
6.
In this study, the effect of fibronectin on the neurite outgrowth from embryoid bodies (EBs) in neurodifferentiated embryonal carcinoma P19 cells was examined. The neurite outgrowth on fibronectin was maintained for a longer time in comparison with those on collagen or laminin. Quantitative RT-PCR revealed that mRNA level corresponding to sonic hedgehog (Shh) in neurodifferentiated P19 cells was upregulated on fibronectin, whereas collagen or laminin did not affect. Further knockdown of integrin αv subunit in P19 cells demonstrated that expression of Shh was mediated through interaction between fibronectin and integrin. Additionally, exogenous Shh agonist accelerated neurite outgrowth from embryonic stem cell-derived EBs without large change of neuronal phenotype expression. Taken together, fibronectin could maintain neurite outgrowth via increased Shh expression.  相似文献   
7.
The objective of this study was to investigate the toxicokinetic characteristics of melamine in broilers due to the limited information available for livestock. Melamine was then administered to broiler chickens at an intravenous (i.v.) or oral (p.o.) dosage of 5.5 mg/kg of body weight, and plasma samples were collected up to 48 h. The concentration of melamine in each plasma sample was analyzed using liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Melamine was measurable up to 24 h after i.v. and p.o. administration. A one‐compartment model was developed to describe the toxicokinetics of melamine in broilers. Following i.v. administration, the values for the elimination half‐life (t1/2β), the volume of distribution (Vd), and the clearance (CL) were 4.42 ± 1.02 h, 00.52 ± 0.18 L/kg, and 0.08 ± 0.01 L/h/kg, respectively. The absolute oral bioavailability (F) was 95.63 ± 3.54%. The results suggest that most of the administered melamine is favorably absorbed from the alimentary tract and rapidly cleared by the kidneys in broiler chickens.  相似文献   
8.
9.
The sesame crop is highly susceptible to infection by phytoplasmas, a class of cell wall-less plant pathogenic bacteria (Mollicutes), which is responsible for widespread loss of sesame crops in both North and South India in recent years. Therefore, characterizing the pathogen population is required before the control measures can be devised and implemented. With molecular tools based on nested polymerase chain reaction (PCR) assays, sequencing, restriction profiling, and phylogenetic analysis, phyllody-affected sesame plants collected from nine different states of India were found to be infected by phytoplasmas belonging to two 16Sr groups, namely 16SrI and II. Two subgroups of phytoplasma −16SrI-B and 16SrII-D— were prevalent in symptomatic sesame samples collected from North India, whereas phytoplasma of only the 16SrII group was found in South India. However, the latter samples were diverse, belonging to three different subgroups (16SrII-A, II-C, and II-D). In addition, yearly phyllody-affected sesame samples from Delhi for 4 consecutive years (2007–2010) showed variation in the infecting phytoplasma: the subgroup 16SrII-D was detected in samples collected in 2007, and 16SrI-B was predominantly found in the samples collected in the subsequent years. The study also provides molecular evidence for the association between 16SrI-B phytoplasma and different symptoms in sesame crops such as fasciation, little leaf, and stunting. This is the first study to report the association of the phytoplasma subgroups 16SrII-A and II-D with sesame crops in India. This study provides a baseline for designing specific detection and molecular analysis strategies for quarantine purposes. It also highlights the need for examining the dynamics of seasonal or location-specific variation in vector populations to determine the pattern of infection outbreaks.  相似文献   
10.
Methane (CH4) is a potent greenhouse gas and the huge CH4 fluxes emitted from paddy fields can prejudice the eco-compatibility of rice cultivation. CH4 production in submerged rice crops is known to be highly influenced by water temperature. Hence, lowering ponding water temperature (LPWT) could be an option to mitigate CH4 emissions from paddy environments when it is possible either to irrigate with slightly colder water or to increase ponding water depth. However, paddy soil is a complex environment in which many processes are simultaneously influenced by temperature, leading to a difficult prediction of LPWT effects. For this reason, LPWT efficiency is here theoretically investigated with a one-dimensional process-based model that simulates the vertical and temporal dynamics of water temperature in soil and the fate of chemical compounds that influence CH4 emissions. The model is validated with literature measured data of CH4 emissions from a paddy field under time-variable temperature regime. Based on modeling results, LPWT appears promising since the simulated reduction of CH4 emissions reaches about −12% and −49% for an LPWT equal to −5 °C during the ripening stage only (last 30 days of growing season, when rice is less sensitive to temperature variations) and −2 °C over the whole growing season, respectively. LPWT affects CH4 emissions either directly (decreasing methanogenic activity), indirectly (decreasing activity of bacteria using alternative electron acceptors), or both. The encouraging results provide the theoretical ground for further laboratory and field studies aimed to investigate the LPWT feasibility in paddy environments.  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