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   317篇
  免费   13篇
林业   25篇
农学   8篇
基础科学   2篇
  83篇
综合类   20篇
农作物   11篇
水产渔业   31篇
畜牧兽医   119篇
园艺   11篇
植物保护   20篇
  2023年   2篇
  2022年   7篇
  2021年   15篇
  2020年   15篇
  2019年   18篇
  2018年   9篇
  2017年   8篇
  2016年   7篇
  2015年   10篇
  2014年   6篇
  2013年   13篇
  2012年   21篇
  2011年   35篇
  2010年   20篇
  2009年   10篇
  2008年   18篇
  2007年   19篇
  2006年   18篇
  2005年   9篇
  2004年   19篇
  2003年   16篇
  2002年   6篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1992年   3篇
  1989年   3篇
  1986年   1篇
  1982年   2篇
  1980年   1篇
  1973年   1篇
  1970年   1篇
  1964年   2篇
排序方式: 共有330条查询结果,搜索用时 31 毫秒
321.
Activated carbon was derived from waste wood pallets in Hong Kong via phosphoric acid activation and applied to adsorption of basic dye (methylene blue), acid dyes (acid blue 25 and acid red 151), and reactive dye (reactive red 23). The results showed that respective adjustment in phosphoric acid concentration, impregnation ratio, activation temperature, and activation time could maximize the surface area and pore volume of activated carbon. An increase of impregnation ratio or activation temperature significantly influenced the pore size distribution by expanding the porous structure and creating more macropores than micropores. The characterization of the carbon surface chemistry using Fourier-transform infrared (FTIR) spectroscopy, however, revealed a decrease in the amount of several functional groups with increasing activation temperature. The physical properties (surface area and pore volume) of the wood waste-derived activated carbon (using 36% phosphoric acid with an impregnation ratio of 1.5 at an activation temperature of 550°C for 1.5 h) were comparable to those of commercial activated carbon (Calgon F400). The contrasting pH effects on the adsorption of different classes of dyes signified the importance of both electrostatic interaction and chemical adsorption, which correlated to pH-dependent dissociation of surface functional groups. It is noteworthy that the physical properties of activated carbon were insufficient to account for the observed dye adsorption behavior, whereas the surface chemistry of activated carbon and the nature and chemical structure of dyes were more important. The fast kinetics and high capacity of dye adsorption of wood waste-derived activated carbon suggest that production of activated carbon from different types of wood waste should merit further investigation.  相似文献   
322.
Completion of cell division during cytokinesis requires temporally and spatially regulated communication from the microtubule cytoskeleton to the actin cytoskeleton and the cell membrane. We identified a specific inhibitor of nonmuscle myosin II, blebbistatin, that inhibited contraction of the cleavage furrow without disrupting mitosis or contractile ring assembly. Using blebbistatin and other drugs, we showed that exit from the cytokinetic phase of the cell cycle depends on ubiquitin-mediated proteolysis. Continuous signals from microtubules are required to maintain the position of the cleavage furrow, and these signals control the localization of myosin II independently of other furrow components.  相似文献   
323.
Humans have more than doubled the amount of reactive nitrogen (Nr) added to the biosphere, yet most of what is known about its accumulation and ecological effects is derived from studies of heavily populated regions. Nitrogen (N) stable isotope ratios ((15)N:(14)N) in dated sediments from 25 remote Northern Hemisphere lakes show a coherent signal of an isotopically distinct source of N to ecosystems beginning in 1895 ± 10 years (±1 standard deviation). Initial shifts in N isotope composition recorded in lake sediments coincide with anthropogenic CO(2) emissions but accelerate with widespread industrial Nr production during the past half century. Although current atmospheric Nr deposition rates in remote regions are relatively low, anthropogenic N has probably influenced watershed N budgets across the Northern Hemisphere for over a century.  相似文献   
324.
European Journal of Plant Pathology - Volatile fatty acids (VFAs) play a role in suppression of plant pathogens during anaerobic soil disinfestation (ASD), but it is unclear how VFAs in anaerobic...  相似文献   
325.
Okara (a byproduct of the soy milk industry) is rich in proteins (24.5-37.5 g/100 g of dry matter (dm)), lipids (9.3-22.3 g/100 g of dm), and dietary fiber (DF) (14.5-55.4 g/100 g of dm). It also contains isoflavones (0.14 g/100 g of dm). In the present study we fed female healthy Wistar rats either a standard rat diet or a supplemented 10% DF-rich okara (DFRO) diet for 4 weeks, and then we assessed several health parameters in the serum and the cecum compartments. In comparison to the control group, rats fed DFRO showed a significant decrease in weight gain (5.00 +/- 1.22 g vs 2.00 +/- 1.46 g, P < 0.03, during week 4) and in total cholesterol (65 +/- 8 mg/dL vs 51 +/- 5 mg/dL, P < 0.05) and a significantly increased antioxidant status (36.71 +/- 15.31 micromol of Trolox equivalents (TEs)/g vs 69.75 +/- 16.11 micromol of TEs/g, P < 0.0003) and butyrogenic effect (39.37%, P < 0.003) in the cecum. In addition, a significant enhancement in the apparent absorption (41.89 +/- 1.64% vs 47.02 +/- 2.51%, P < 0.004) and in the true retention (41.62 +/- 1.60% vs 46.68 +/- 2.55%, P < 0.005) of calcium was appreciated. In summary, these findings show for the first time that a concentrate DF from a soybean byproduct protects the gut environment in terms of antioxidant status and prebiotic effect. These results may highlight the development of an innovative soybean byproduct rich in DF which could be useful as a functional ingredient with health-promoting attributes.  相似文献   
326.
The effects of rosemary, in combination with ascorbic acid, red beet root, and sodium lactate, as well as their mixtures, on the inhibition of both lipid and pigment oxidation of fresh pork sausages packaged in a modified atmosphere were studied. Sausages (240) were packaged in a 80% O2 + 20% CO2 gas mixture and analyzed for CIE a, metmyoglobin, TBARS, psychrotrophic aerobes, and sensory discoloration and off-odor throughout 20 days of storage at 2 +/- 1 degrees C. The mixture of rosemary + ascorbic acid + sodium lactate + red beet root extract extended the shelf life of fresh pork sausages from 8 to 16 days. Results demonstrated that all of the components of the mixture contributed to obtaining the maximum delay in color and/or odor decay, due to a combined inhibitory action on both pigment and lipid oxidation, as well as on microbial growth.  相似文献   
327.
To pursue a systematic approach to the discovery of functional connections among diseases, genetic perturbation, and drug action, we have created the first installment of a reference collection of gene-expression profiles from cultured human cells treated with bioactive small molecules, together with pattern-matching software to mine these data. We demonstrate that this "Connectivity Map" resource can be used to find connections among small molecules sharing a mechanism of action, chemicals and physiological processes, and diseases and drugs. These results indicate the feasibility of the approach and suggest the value of a large-scale community Connectivity Map project.  相似文献   
328.
The vast majority of global freshwater ecosystems are small lakes with less than 100 m2 surface area. These lakes are often unconnected to other water bodies but frequently host fish populations. Existing explanations for how fish colonize such remote habitats often involve birds as vectors transporting fish eggs as propagules. In this study, we aim to quantify the prevalence of these explanations among relevant societal groups as well as their scientific knowledge basis. We analyzed entries in online blogs and forums and surveyed the opinions of local stakeholders and decision makers using a questionnaire. To collect published scientific knowledge, we conducted a structured literature review. Our results reveal a discrepancy between commonly found beliefs and the empirical knowledge supporting those beliefs: Dispersal of fish eggs by water birds was overall the most frequent explanation online and in the questionnaire. In the scientific literature, however, we found hardly any empirical research on passive fish egg dispersal. We propose research directions for how to close this gap of knowledge and suggest that future empirical studies on passive fish egg dispersal may be inspired by existing work on passive dispersal in aquatic invertebrates. Mitigating the belief‐evidence discrepancy on fish dispersal will be essential to better understand the patterns of fish biodiversity across landscapes, to counteract its losses, and inform management strategies for invasive fish species.  相似文献   
329.
In this study changes in hematochemical parameters, milk composition and yield were investigated in buffaloes during the transition period. A total of 93 buffaloes 113.9 ± 8.03 months old and 535 ± 50 kg average body weight were used. Parity was recorded, blood samples were collected from 80 days pre‐partum until 70 days post‐partum; milk samples were collected from 5 days to 70 days post‐partum. On serum samples, the values of non‐esterified fatty acids, β‐hydroxybutyrate, glucose, cholesterol, triglycerides, aspartate aminotransferase, alanine aminotransferase, gamma‐glutamyltransferase, urea, total proteins were evaluated. On milk, percentage of fat, protein and lactose, along with the somatic cell count (SCC), milk yield and daily milk production (DMP) were assessed. The peripartum period significantly (P ≤ 0.01) influenced all studied parameters with the exception of glucose. Milk fat percentage showed decreasing trend from 10 until 40 days post‐partum; DMP significantly (P ≤ 0.01) increased from 1 day post‐partum until 40 days post‐partum. Milk yield significantly (P ≤ 0.01) decreased in animals over the sixth lactation. Our results confirmed the importance of transit period in buffaloes. Blood parameters and milk composition alterations are crucial to predict the energy balance status of buffaloes in order to improve their management and feed intake during the transition period.  相似文献   
330.
Plant growth‐promoting rhizobacteria (PGPR) are soil bacteria that colonize the rhizosphere of plants, enhance plant growth, and may alleviate environmental stress, thus constituting a powerful tool in sustainable agriculture. Here, we compared the capacity of chemical fertilization to selected PGPR strains to promote growth and alleviate salinity stress in tomato plants (Solanum lycopersicum L.). A pot experiment was designed with two main factors: fertilization (chemical fertilization, bacterial inoculation with seven PGPR, or a non‐fertilized non‐inoculated control) and salt stress (0 or 100 mM NaCl). In the absence of stress, a clear promotion of growth, a positive effect on plant physiology (elevated Fv/Fm), and enhanced N, P, and K concentrations were observed in inoculated plants compared to non‐fertilized controls. Salinity negatively affected most variables analyzed, but inoculation with certain strains reduced some of the negative effects on growth parameters and plant physiology (water loss and K+ depletion) in a moderate but significant manner. Chemical fertilization clearly exceeded the positive effects of inoculation under non‐stressed conditions, but conversely, biofertilization with some strains outperformed chemical fertilization under salt stress. The results point at inoculation with selected PGPR as a viable economical and environment‐friendly alternative to chemical fertilization in salinity‐affected soils.  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