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   991篇
  免费   14篇
林业   78篇
农学   67篇
基础科学   33篇
  262篇
综合类   61篇
农作物   109篇
水产渔业   78篇
畜牧兽医   235篇
园艺   16篇
植物保护   66篇
  2025年   8篇
  2024年   17篇
  2023年   24篇
  2022年   28篇
  2021年   34篇
  2020年   56篇
  2019年   54篇
  2018年   52篇
  2017年   61篇
  2016年   55篇
  2015年   24篇
  2014年   38篇
  2013年   103篇
  2012年   57篇
  2011年   61篇
  2010年   42篇
  2009年   38篇
  2008年   35篇
  2007年   22篇
  2006年   16篇
  2005年   13篇
  2004年   11篇
  2003年   13篇
  2002年   16篇
  2001年   15篇
  2000年   15篇
  1999年   8篇
  1998年   6篇
  1997年   4篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   7篇
  1990年   8篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1986年   3篇
  1985年   4篇
  1980年   5篇
  1978年   2篇
  1977年   2篇
  1971年   2篇
  1970年   1篇
  1968年   1篇
  1960年   1篇
  1959年   3篇
  1957年   2篇
排序方式: 共有1005条查询结果,搜索用时 21 毫秒
121.
122.
Chaulya  S. K.  Chakraborty  M. K.  Ahmad  M.  Singh  R. S.  Bondyopadhay  C.  Mondal  G. C.  Pal  D. 《Water, air, and soil pollution》2002,140(1-4):21-55
All major mining activities, particularly opencast coal mining,directly or indirectly contribute to the problem of air pollution.Therefore, air quality assessment and prediction arerequired to prevent and minimize the air quality deteriorationdue to various opencast coal mining operations. Determination ofemission rates for these activities is the first and foremostconcern. In view of the above, this study was undertaken to determinate emission rates and to develop empericalformulae to calculate emission rates of various opencast coalmining activities.To achieve the objectives, seven coal mining sites were selectedto generate site-specific emission data by considering miningpractices, method of working, geographical location,accessibility and above all resourceavailability. The study covers various mining activities andlocations including drilling, overburden loading and unloading,coal loading and unloading, the coal handling plant, the exposedoverburden dump, the stock yard, the workshop, the exposed pit surface roadsand haul roads.Based on the study, a set of twelve emperical formulae have beendeveloped for calculation of suspended particulate matter (SPM)emission rates from various opencast coal mining activities. Theemission of gaseous pollutants (sulphur dioxide and nitrogenoxide) has been found negligible for various mining activities.Therefore, observation for gaseous pollutants has been consideredfor overall mine activities and empirical formulae have subsequently beendeveloped.The developed empirical formulae were calculatedby a field study at another coal mine. The measured andcalculated values of emission rate were compared for eachactivity. Average correlation between the measured andcalculated values for different activities was estimated to be 85.6–99.9%, which indicates fairly good accuracy.Validation of the study was also carried out by means of thefugitive dust model (FDM) using the calculated emissionrate data from the empirical formulae for each mining activity of amine, meteorological data and other details as input.The average accuracy between measured and predictedvalues of concentration of SPM at certain receptor locations wasfound to be 79%. A user-friendly emission software called`EmissCalc' was developed to calculate emission rate, whichcan be used as input for different air quality models.  相似文献   
123.
Tropical Animal Health and Production - This study examined the analysis of personal and production performance of broiler farming in 10 cities of central Punjab (Lahore, Sheikhupura, Kasur, Okara,...  相似文献   
124.
The in vivo and in vitro mechanistic anti-inflammatory actions of cucurbitacin E (CE) (Citrullus lanatus var. citroides) were examined. The results showed that LPS/INF-γ increased NO production in RAW264.7 macrophages, whereas L-NAME and CE curtailed it. CE did not reveal any cytotoxicity on RAW264.7 and WRL-68 cells. CE inhibited both COX enzymes with more selectivity toward COX-2. Intraperitoneal injection of CE significantly suppressed carrageenan-induced rat's paw edema. ORAC and FRAP assays showed that CE is not a potent ROS scavenger. It could be concluded that CE is potentially useful in treating inflammation through the inhibition of COX and RNS but not ROS.  相似文献   
125.
Water, Air, & Soil Pollution - A yearlong (December 2003 to February 2005) monitoring program was undertaken for urban roadside measurement of benzene, toluene, ethyl benzene, m- and p-xylene,...  相似文献   
126.
    
Recent advances in sequencing technology have brought several novel platforms for marker development and subsequent genotyping. The high-throughput and cost effective marker techniques have changed the entire scenario of marker applications. The huge genotypic data obtained with next generation sequencing (NGS) also demands analytical tools, statistical advances, and comprehensive understanding to cope with breeding applications. In the present review, we discussed different available marker techniques, their strengths, and limitations. Emphasis was given on software tools, analytical pipelines, workbenches, and online resources available for marker development. Comparison of SNP genotyping involving complexity reduction techniques like GBS, RRL, RAD, and array-based platforms were presented in a view to describe suitability for specific purposes. We found that genotyping by whole genome re-sequencing has great potential, and could be a routine application in the near future with continuously decreasing cost of sequencing. Microsatellites, still a valuable option for breeders, have also advanced with NGS. Here a catalogue of tools for microsatellite evaluation in short sequence reads was provided. The most common applications of molecular marker like QTL mapping, genome-wide association mapping (GWAS), and genomic selection were highlighted. The present review will be helpful for the effective utilization of available resources and for the planning of crop improvement programs employing molecular marker techniques.  相似文献   
127.
    
The rapidly growing population of Iran and non‐sustainable agricultural development practices have resulted in an increasing demand for irrigation water. This process, along with Iran's water source restrictions, necessitates investigation and research in the field of water productivity. Behbahan (Maroon Irrigation Network) District, which is located in Khuzestan Province, by benefiting from the Maroon River, has been considered a fertile land for agricultural activity for centuries. The access of farmers to the Maroon River within past decades has meant water has been taken for granted. However, since 2007, the land has faced a dramatic decline in rainfall and surface water. Water scarcity and limitation of available water in the region should force farmers to use water as efficiently as possible. Irrigated agriculture is one of the most water‐ consuming sectors in the region. Therefore, improving the productivity of existing water management practices is the most attractive option to produce more food for the increasing population. In this paper, the water productivity of irrigated wheat in Maroon is analysed. Some 125 farmers from the northern and southern parts of the Maroon Irrigation Network were selected by using a stratified random sampling method. Data were collected through surveying techniques such as questionnaires and interviewing. The data were analysed by using a statistical package for social sciences (SPSS16). Based on the research results, most of the farmers were middle‐aged and with a low level of literacy. Water in the Behbahan region was considered as a service rather than an economically high‐value commodity. Also crop per drop (CPD) index in comparison with similar regions (as a result of high water consumption) was lower than the average CPD index in 2007 and 2008 and was 0.48 and 0.41 kg m−3 respectively. The critical role of water in the border‐based provinces of Iran with due respect to sociocultural and political consequences, as for example in Khuzestan, reinforces the need to employ urgent tactics to increase water productivity through improving knowledge and infrastructure‐based systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
128.
An experiment was conducted to access the genetic variability among early vigour and quantitative traits under limited moisture in F2 generation of a 5 × 5 diallel cross of bread wheat. The results indicated that there was significant genotypic variation among the genotypes. Additive dominance model revealed full fitness of the data for RL, DSW, FRW, DRW, spike length, and 1000-grain weight but was partially fit for SL, FSW, R/S, tillers per seedling, plant height, tillers per plant, spikelets per spike, and grain yield per plant. The partially adequate models for these plant characters might be due to the presence of non-allelic interaction, linkage, and non-independent distribution of the genes in the parents. Additive genes coupled with moderate to high narrow sense heritability were involved in the heritage of all the traits, which indicated a higher scope of selection in early generations.  相似文献   
129.
    
This study evaluates factors influencing pregnancy rates per artificial insemination (P/AI) and pregnancy loss in Lohi ewes undergoing laparoscopic AI with frozen–thawed semen under sub-tropical conditions. Data from three experiments comprising ewes (n = 358) of mixed parity (nulliparous; NP and parous; P), various body condition score (BCS) and assigned to long-term (LTP, 11 days) and short-term (STP, 5 days) oestrus synchronization regimen across high breeding season (HBS) and low breeding season (LBS) were analysed. Laparoscopic insemination was conducted 54 h post-sponge removal. Pregnancy diagnosis and loss were evaluated on days 35 and 90 post-insemination via ultrasonography. Results showed parity significantly influenced P/AI, with nulliparous ewes achieving higher pregnancy ratios than parous ewes (p = .001). BCS significantly influenced P/AI (p < .05), with a quadratic relationship observed between BCS and season (BCS*BCS*Season; p = .07). Progestin treatment did not significantly influence the ratio of pregnant ewes (p = .07). Pregnancy losses were significantly higher during LBS than HBS (p < .05), irrespective of progestin treatment. In conclusion, parity and BCS significantly influenced P/AI, with BCS demonstrating a quadratic association with season. Ewes bred during LBS experienced higher pregnancy losses than HBS, irrespective of progestin treatment.  相似文献   
130.
Crude dihydroxystearic acid was prepared from palm based oleic acid and was then solvent purified with isopropyl alcohol in a custom fabricated simultaneous batch crystallizer unit. The crystallized dihydroxystearic acid was a functional ingredient that acted as multipurpose intermediate for synthesis of various fine chemicals, cosmetics and personal care products. The effects of solvent quantity and concentration on particle size distribution, crystal habit and morphology, and resultant crystal purity were studied. The crystals were purer but smaller and the span of the distribution curve was wider at higher solvent quantity and concentration. Through scanning electron microscopy and X-ray diffraction, it was observed that the crystals agglomerated into plate-like (flaky) habit with triclinic crystal structure. Solvent crystallization with 80% IPA at 20 °C and solute:solvent ratio of 1.0:1.0 was the most optimized and efficient, producing β-DHSA crystals that has high resistance against fat exudation during vacuum filtration process.  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