全文获取类型
收费全文 | 991篇 |
免费 | 14篇 |
专业分类
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 |
出版年
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.
Rahman Naeem Ur Mehmood Shahid Ahmad Sohail Javid Arshad Mahmud Athar Hussain Jibran Shaheen Muhammad Shabir Usman Muhammad Mohayud Din Hashmi Syed Ghulam 《Tropical animal health and production》2020,52(3):1125-1131
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.
Abdelwahab SI Hassan LE Sirat HM Yagi SM Koko WS Mohan S Taha MM Ahmad S Chuen CS Narrima P Rais MM Hadi AH 《Fitoterapia》2011,82(8):1190-1197
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.
Conesa Héctor M. Moradi Ahmad B. Robinson Brett H. Jiménez-Cárceles Francisco J. Schulin Rainer 《Water, air, and soil pollution》2009,201(1-4):379-388
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.
Sajad Majeed Zargar Bodo Raatz Humira Sonah MuslimaNazir Javid A. Bhat Zahoor Ahmad Dar Ganesh Kumar Agrawal Randeep Rakwal 《Journal of Crop Science and Biotechnology》2015,18(5):293-308
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.
Shahid Iqbal Awan Muhammad Shahzad Ahmed Jehanzeb Farooq Syed Dilnawaz Ahmad Muhammad Ilyas Asad Hussain Shah Muhammad Fareed Khan Sardar Ali Lutful Hasan 《Frontiers of Agriculture in China》2011,5(4):486-496
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.
Muhammad Tayyab Khan;Ejaz Ahmad;Ali Husnain;Muhammad Rizwan Yousaf;Muhammad Oneeb;Tanveer Ahmad;Muhammad Irfan-ur-Rehman Khan; 《Reproduction in domestic animals》2024,59(5):e14579
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.
Gregory F.L. Koay Teong-Guan Chuah Sumaiya Zainal-Abidin Salmiah Ahmad Thomas S.Y. Choong 《Industrial Crops and Products》2011,34(1):1135-1140
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