全文获取类型
收费全文 | 796篇 |
免费 | 41篇 |
专业分类
林业 | 51篇 |
农学 | 128篇 |
基础科学 | 22篇 |
147篇 | |
综合类 | 53篇 |
农作物 | 61篇 |
水产渔业 | 36篇 |
畜牧兽医 | 262篇 |
园艺 | 11篇 |
植物保护 | 66篇 |
出版年
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 21篇 |
2019年 | 14篇 |
2018年 | 18篇 |
2017年 | 29篇 |
2016年 | 24篇 |
2015年 | 19篇 |
2014年 | 21篇 |
2013年 | 51篇 |
2012年 | 43篇 |
2011年 | 37篇 |
2010年 | 29篇 |
2009年 | 30篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 24篇 |
2004年 | 12篇 |
2003年 | 16篇 |
2002年 | 23篇 |
2001年 | 20篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1996年 | 7篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1975年 | 13篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1970年 | 11篇 |
1969年 | 13篇 |
1968年 | 6篇 |
排序方式: 共有837条查询结果,搜索用时 15 毫秒
751.
Yadvinder-Singh R. K. Gupta H. S. Thind Bijay-Singh Varinderpal-Singh Gurpreet-Singh Jagmohan-Singh J. K. Ladha 《Biology and Fertility of Soils》2009,45(7):701-710
Poultry litter (PL) is an important nutrient source; however, no information is available regarding its value in supplying
N and P in rice–wheat (RW) production. A three-year field study was conducted at Ludhiana, Punjab, India on a loamy sand soil
to identify optimum combination of PL and N and P fertilizers for a sustainable RW production. The litter was applied to rice
at 5 Mg ha−1 as a single application and supplemented with different rates of N. The residual effect of PL and the direct effects of the
different combinations of N and P were studied in the following wheat. Nitrogen and P mineralization from PL was studied under
controlled conditions in the laboratory, and macronutrient input–output balances were estimated from field results. About
46% of the N from PL was released after 60 days of incubation. The release of P from the PL occurred mainly during the initial
20 days after incubation, accounting for 15–17% of the total P. Combining PL with fertilizer N (40 kg ha−1) increased rice yield and nutrient uptake similar to what was obtained with the application of recommended fertilizer N (120 kg
ha−1). In the following wheat, the residual effect of PL was equal to 30 kg N ha−1 and 13 kg P ha−1. After three annual cropping cycles and PL application, mean soil organic C increased by 17%, Olsen-P by 73%, and NH4OAc-extractable-K by 24%. Most treatments had positive P but negative K balances. About 11% of the net P balance was recovered
from the soil as Olsen-P. The study showed that optimum N and P fertilizer doses for an RW system receiving 5 Mg ha−1 of PL are 40 kg N ha−1 for rice and 90 kg N + 13 kg P ha−1 for the following wheat. Safe and effective management of PL should be based on P balance, particularly when regular applications
of PL are to be made in the RW system. 相似文献
752.
Arun Gupta Vinay Mahajan Mukesh Kumar H. S. Gupta 《Genetic Resources and Crop Evolution》2009,56(6):883-889
One hundred ninety four accessions of barnyard millet collected from different eco-geographical regions of India were evaluated
for 14 quantitative traits during kharif 2003 and 2005. These accessions were grouped into 5 groups on the basis of place of collection. These groups differed significantly
in their mean values for quantitative traits and magnitude of correlation among traits indicates origin based association.
The group ‘C’ (source of origin is unknown) was found most diverse group (mean coefficient of variation 17.67%), while rest
of the groups recorded mean coefficient of variation between 12 and 13%. Correlation studies indicate that flag leaf width,
number of racemes along with internode length should be considered while performing selection in segregating generations.
The plotting of first and second principal component axes scores suggests that presence of three distinct morphotypes in the
present study. These morphotypes are quite similar to three botanical varieties viz., var. robusta, var. intermedia and var. stolonifera in their morphological traits, while botanical variety laxa (endemic to Sikkim area of India) was completely absent from the present study. 相似文献
753.
A preliminary genetic analysis of fibre traits and the use of new genomic SSRs for genetic diversity in jute 总被引:1,自引:0,他引:1
Reyazul R. Mir Sachin Rustgi Shailendra Sharma Ravinder Singh Aakash Goyal Jitendra Kumar Anupama Gaur Akhilesh K. Tyagi Haseena Khan Mohit K. Sinha Harindra S. Balyan Pushpendra Kumar Gupta 《Euphytica》2008,161(3):413-427
Jute is one of the most important fibre crops, which is second only to cotton in providing environment-friendly (biodegradable
and renewable) ligno-cellulose fibre. In order to improve this largely neglected crop, we conducted a preliminary study involving
the following: (i) analysis of nature and extent of the genetic variability for fibre yield and four other related traits
in a set of 81 genotypes belonging to two commercially cultivated Corchorus species (45 genotypes of C. olitorius + 36 genotypes of C. capsularis), (ii) development and analysis of a set of simple sequence repeat (SSR) markers from C. olitorius, and (iii) use of a sub-set of SSRs for assessment of genetic diversity in the above set of 81 genotypes. The results suggested
quantitative nature of fibre yield and other related traits, with a preponderance of dominance component in genetic variance.
A sub-set of 45 SSRs derived from C. olitorius, when used for a study of DNA polymorphism and genetic diversity, showed high transferability of these C. olitorius SSRs to C. capsularis. The average number of alleles for individual SSRs was surprisingly low (3.04 for both species, 2.02 for C. capsularis and 2.51 for C. olitorius), and so was the average polymorphic information content (PIC; 0.23 and 0.24 in two species). In the dendrogram obtained
using a similarity matrix, the 81 genotypes were grouped into three clusters, which largely corresponded to the two species,
Cluster I belonging mainly to C. capsularis and the other two closely related clusters (clusters II and III) belonging to C. olitorius. It was also shown that a minimum of 15 SSRs could give the same information as 41 SSRs, thus making many SSRs redundant.
The SSR markers developed during the present study and to be developed in future will prove useful not only for evaluation
of genetic diversity, but also for molecular mapping/QTL analysis, and for comparative genome analysis of the two Corchorus species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
754.
Guriqbal Singh Harpreet Kaur Virk Navneet Aggarwal R K Gupta Veena Khanna 《Archives of Agronomy and Soil Science》2019,65(3):411-420
Field experiments evaluated the effects of integrated nutrient management on symbiotic parameters, growth, nutrient accumulation, productivity and profitability of lentil (Lens culinaris Medikus). Application of recommended dose of nutrients (RDN, 12.5 kg N ha?1 + 40 kg P2O5 ha?1) + 25 kg ZnSO4 ha?1 + seed inoculation with biofertilizers [Rhizobium + phosphate solubilizing bacteria (PSB) + plant growth promoting rhizobacteria (PGPR)] + 1.0 g ammonium molybdate kg?1 seed recorded the highest number & dry weight of nodules, leghaemoglobin content, root & shoot dry weight, plant height, number of pods plant?1 and 100-seed weight. The next best treatment was RDN + seed inoculation with biofertilizers + 1.0 g ammonium molybdate kg?1 seed. On the basis of mean of three-year data, the treatment of RDN + 25 kg ZnSO4 ha?1 + seed inoculation with biofertilizers + 1.0 g ammonium molybdate kg?1 seed proved the best in realizing the highest grain yield (34.0%), gross returns (34.0%) and net returns (54.8% higher over control). Nitrogen, phosphorus and potassium in the grains and straw were significantly improved where RDN was applied in combination with seed inoculation, basal application of ZnSO4 and seed treatment with 1 g ammonium molybdate than their single applications. 相似文献
755.
An attempt has been made to assess the productivity as well as the carbon sequestration potential of this mixture. The grain as well as straw yields were significantly lower in poplar block plantations than in the open (14 to 64% and 13 to 66% grain and straw yield, respectively under one to six year plantation). The annual productivity of poplars was recorded maximum after fourth year and later the annual wood increment decreased (42.4, 39.8 and 35.6 m^3/ha/yr after 4^th, 5^th and 6^th year, respectively). The enrichment of soil through litter and roots enhanced the organic carbon in the surface layer of soil (0-15 cm) under poplar blocks as compared to open fields with wheat crop only. The carbon storage potential in agroforestry system was recorded very high in comparison to sole crop. The carbon storage in agroforestry system increased with the age of the plantation and the major contribution came from the timber, roots and litter (37.30 mg/ha after six years). However, wheat crop yield decreased under poplar but this may be compensated by the poplar trees in terms of biomass, economic returns and the carbon sequestration potential. 相似文献
756.
D.R. Coventry A. YadavR.K. Gupta R.S. ChhokarS.C. Gill V. KumarA. Kumar A. MehtaS.G.L. Kleemann J.A. Cummins 《Field Crops Research》2011,123(2):80-88
Wheat in Haryana (NW India) is grown as a winter crop in an annual sequence with rice, cotton, pearl millet or cluster bean as the main monsoon crops. Higher wheat yields in Haryana are associated with the use of modern varieties, increase in fertiliser use, improved irrigation practice and conservation tillage, and the recommendation to farmers for N fertiliser rates and timing and irrigation practice have an emphasis on optimising yield and input efficiencies. In India the importance to consumers of product quality does exist and, although the market place presently does not actively reward farmers for better quality wheat, the need for creating suitable and targeted marketing opportunities is now recognised. This paper examines aspects of input efficiencies and focuses on combinations of N-fertiliser and irrigation input in wheat crops grown with these four rotations (rice-wheat, cotton-wheat, pearl millet-wheat and cluster bean-wheat). Management practices that optimise grain production as well targeting grain that achieves best chapatti (Indian flat bread) quality are evaluated within a split-plot experiment where 4 irrigation schedule treatments were split with nitrogen management treatments involving a 2-way or 3-way split of N fertiliser. With the rice-wheat system, there were no differences between different split timings of N with grain yield, however with the 3 other wheat systems the 3 way split of N-fertiliser application, with N applied equally at N-fertiliser applied at seeding, early tillering and first node stage, always gave the highest yield. With all 4 rotations the highest protein level was achieved (range 11.8-12.5%) with this 3-way N application split. Grain yield increased in a step-wise manner as additional irrigation was implemented with all rotations and the highest protein outcomes were achieved with the least irrigations. The apparent recovery of N fertiliser applied was similar and highest with the 3-way split, and the 2-way split that did not include a basal N fertiliser application. Different rates of N fertiliser were included in separate experiments using the 3-way split of N application, and with the rice-wheat rotation the GreenSeeker instrument was used to establish the rate for the third application of N. The application of extra N-fertiliser with the non rice-wheat rotations produced no additional grain yield with an increase in the N-fertiliser input beyond 150 kg N ha−1, although protein and N-content increased incrementally. Grain hardness and chapatti score trended higher with increases in N-fertiliser input but the increases were relatively small. The use of the GreenSeeker instrument with the rice-wheat rotation resulted in N saving of 21-25 kg N ha−1 with similar grain yield, protein and grain hardness to that provided by using the recommended 150 kg N ha−1. Where the GreenSeeker was used the apparent recovery was 70-75% compared with 60% with the wheat receiving the recommended 150 kg N ha−1, suggesting farmers are likely to be over-fertilising their wheat crop. The best yields obtained in these experiments were about 5.5-6.0 t ha−1 and these yields are consistent with a decade-long attainable yield identified for wheat in rice-wheat rotation for Haryana. If farmers can achieve market recognition for chapatti quality, and with the use of appropriate varieties, then farmers can assume that the best practice outlined here for optimising grain yield with integrated nutrient and soil management will be the same practice that optimises chapatti quality. 相似文献
757.
758.
759.
Wool/cotton union fabric was dyed with a direct dye in union shade. The dyeing was performed in a single bath in relation
to four factors: leveling agent (Lyogen SMKI, 0–1.5 % oww), electrolyte (sodium sulfate, 0–10 %), dyeing temperature (85–95
°C), and dyeing time (15–60 min). The dyeing was characterized by dye bath exhaustion (%), color strength (K/S value), washing
fastness, and light fastness of dyed sample. Response surface analysis showed that the exhaustion of direct dye increased
with electrolyte, dyeing temperature, and dyeing time while the K/S value followed a linear shape with leveling agent and
dyeing temperature. An optimized recipe was formulated based on response surface strategy and numerical optimization solution. 相似文献
760.
Manmeet Kumar Ausaf Ahmad Preeti Rawat Mohammad Faheem Khan Naila Rasheed Prasoon Gupta B. Sathiamoorthy Gitika Bhatia Gautam Palit Rakesh Maurya 《Fitoterapia》2010
Oxidative damage is an established outcome of chronic stress. Thus, the present study was designed to investigate the modulatory role of ethanolic extract of Evolvulus alsinoides (EA) in terms of oxidative alterations at peripheral and central level in rats subjected to chronic unpredictable stress (CUS). CUS exposure for 7 days reduced Cu, Zn superoxide dismutase and catalase activity with increase in glutathione peroxidase activity and lipid peroxidation, while decrease in reduced glutathione level in blood plasma, frontal cortex and hippocampus regions of brain. Oral administration of EA extract at 200 mg/kg p.o. normalized these stress induced oxidative alterations with an efficacy similar to that of melatonin. Further, EA extract was taken up for detailed chemical investigation. Two new flavonol-4′-glycoside, kaempferol 4′-O-β-d-glucopyranosyl-(1 → 2)-β-d-glucopyranoside (3) and kaempferol 4′-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside (5) were isolated, along with eight known compounds (1, 2, 4 and 6–10). The structures of new compounds were established by detailed spectroscopic studies, while known compounds were characterized by direct comparison of their reported NMR data. All these compounds were evaluated for their in vitro antioxidant activity. Compounds 3, 5, 9 and 10 at 100 and 200 μg/ml showed significant in vitro antioxidant activity. Therefore, EA may hold great potential in preventing clinical deterioration in stress induced oxidative load and related disorders. 相似文献