全文获取类型
收费全文 | 800篇 |
免费 | 41篇 |
专业分类
林业 | 52篇 |
农学 | 128篇 |
基础科学 | 22篇 |
147篇 | |
综合类 | 54篇 |
农作物 | 61篇 |
水产渔业 | 36篇 |
畜牧兽医 | 263篇 |
园艺 | 11篇 |
植物保护 | 67篇 |
出版年
2021年 | 12篇 |
2020年 | 22篇 |
2019年 | 14篇 |
2018年 | 18篇 |
2017年 | 30篇 |
2016年 | 24篇 |
2015年 | 19篇 |
2014年 | 21篇 |
2013年 | 51篇 |
2012年 | 43篇 |
2011年 | 38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 |
1967年 | 6篇 |
排序方式: 共有841条查询结果,搜索用时 968 毫秒
111.
Aditya Pratap Umashanker Prajapati Chandra Mohan Singh Sanjeev Gupta Meenal Rathore Nupur Malviya Rakhi Tomar Ajeet Kumar Gupta Swapnila Tripathi Narendra Pratap Singh 《Plant Breeding》2018,137(3):235-249
Grain legumes, the important constituents of sustainability‐based cropping systems and energy‐limited vegetarian diets have long been the subject of scientific research. Tremendous technological strides were made in the so‐called orphan crops, in terms of both varietal improvement and generation of basic information. Despite recalcitrancy and high genotype dependency, in vitro culture techniques such as organogenesis, in vitro mutagenesis, embryo rescue and in vitro gene transfer have been deployed for improvement of several grain legumes and these played an important role in introgression of desirable genes from related and distant species and creation of additional genetic variability. Stable and reproducible regeneration protocols resulted in the development of genetically modified chickpea, pigeon pea, cowpea, mungbean, etc., while embryo rescue was deployed successfully for recovery of interspecific recombinants, a few of them exploited for the development of commercial cultivars. Nevertheless, doubled haploidy witnessed limited success and protoplast regeneration and in vitro mutagenesis remained of academic interest. The present review focuses on the progress, achievements, constraints and perspectives of using in vitro technology in grain legume improvement. 相似文献
112.
C. M. Mehta D. Yu R. Srivastava A. Sinkkonen J. M. Kurola V. Gupta 《Compost science & utilization》2016,24(2):105-116
The present study aimed to investigate microbial communities in seven Indian composts and their potential for biocontrol of Fusarium oxysporum f. sp. lycopersici. In addition, identification of bioactive substances in disease suppressive composts was also attempted. Composts were chosen based on disease suppressiveness and subjected to molecular microbial analyses. Total genomic DNA from the composts was extracted and amplified with polymerase chain reaction using primers targeting the 18S rRNA and 16S rRNA genes of fungi and bacteria, respectively. Denaturing gradient gel electrophoresis (DGGE) fingerprinting and DNA sequencing were used to identify the fungal and bacterial targets. Phylogenetic analysis of the fungal 18S rRNA ITS gene sequences showed that phylum Ascomycota was dominant in all composts, while in the bacterial 16S rRNA gene sequences, the phylum Proteobacteria was dominant. Some fungi in disease suppressive composts grouped phylogenetically close to F. oxysporum. Bacterial sequences with close similarity (>95% identity) with Actinobacterium showed a strong presence only in disease suppressive composts. Disease suppressive composts formed a separate group in the cluster analysis of 18S rRNA ITS and 16S rRNA gene sequences. Gas chromatography-time of flight-mass spectrometry was performed with compost extracts to determine if bioactive substances were present in disease suppressive composts. The analysis of compost organic matter showed a negative association of disease suppressiveness with phloroglucinol, sitosterol, and monoenoic fatty acid, while cholesterol and certain organic acids were positively associated with suppressiveness. 相似文献
113.
Anjula Pandey D. P. Semwal K. C. Bhatt Rita Gupta S. P. Ahlawat 《Genetic Resources and Crop Evolution》2016,63(8):1447-1455
114.
Ecophysiological characteristics of five weeds and a wheat crop in the Indo‐Gangetic Plains,India 下载免费PDF全文
Vartika Singh Sweta Gupta Hema Singh Akhilesh Singh Raghubanshi 《Weed Biology and Management》2015,15(3):102-112
The objective of this research was to compare selected ecophysiological parameters for a wheat crop found in the Indo‐Gangetic Plains of India and its five dominant weeds. The dominant and regionally ubiquitous weeds in the wheat field that was selected for the study were Anagallis arvensis, Chenopodium album, Melilotus albus, Phalaris minor and Rumex dentatus. Taller weeds, such as C. album and P. minor, constituted one group along with the crop, with a low photosynthetic rate, specific leaf area, leaf nitrogen mass basis, chlorophyll content, photosynthetic nitrogen‐use efficiency and leaf area ratio, in comparison to shorter weeds, such as A. arvensis, M. albus and R. dentatus, which formed another group with a high photosynthetic rate, specific leaf area, leaf nitrogen mass basis, chlorophyll content, photosynthetic nitrogen‐use efficiency and leaf area ratio. Interspecific variations in the photosynthetic rate were driven mainly by variability in the specific leaf area and leaf nitrogen content. The taller weeds and the crop had a low specific leaf area later in the season, whereas the smaller weeds had a relatively high specific leaf area, which might be an adaptation to the shaded environment below the canopy. The result indicates that any weed management in the wheat fields of the Indo‐Gangetic Plains will need two different approaches because of the different strategies followed by the two weed groups that were identified in the present study. 相似文献
115.
116.
提高蛋壳质量的技术途径 总被引:1,自引:1,他引:0
Lokesh Gupta 《中国家禽》2009,31(1)
编者按:蛋壳质量是衡量种鸡、蛋鸡生产成绩好坏的一项十分重要的指标,它与种蛋入孵率、孵化率、鸡苗质量以及商品蛋鸡的鲜蛋产量、经济效益密切相关. 相似文献
117.
Rani SS Chaturvedi VK Gupta PK Joseph S Nair BC Pandey KD 《Acta veterinaria Hungarica》2006,54(4):449-453
Pasteurella multocida B:2 is responsible for haemorrhagic septicaemia in cattle and buffaloes, causing severe economic losses in the developing countries. In the present study, the ahpA gene of P. multocida B:2 (P52) was cloned, sequenced and compared with the previously reported ahpA gene sequence in P. multocida A:1, which is responsible for its haemolytic phenotype. E. coli DH5a cells were further transformed with recombinant plasmid carrying the ahpA gene from P. multocida B:2 (P52) but SDS-PAGE analysis failed to show the expression of haemolysin protein. Slight haemolysis was albeit observed in horse blood agar plates streaked with recombinant E. coli carrying the ahpA gene. Our study indicates that there is 99.6% similarity and 0.4% divergence between ahpA gene of P. multocida B:2 (P52) and P. multocida A: 1, while membrane topology analysis has predicted that ahpA is an inner membrane protein with two strong hydrophobic regions at the N and C terminals. The presence of significant homology in ahpA sequence in A: 1 and B:2 perhaps suggests a common mechanism of pathogenesis in different species of animals. 相似文献
118.
The poplar based agroforestry system improves aggregation of soil through huge amounts of organic matter in the form of leaf
biomass. The extent of improvement may be affected by the age of the poplar trees and the soil type. The surface and subsurface
soil samples from agroforestry and adjoining non-agroforestry sites with different years of poplar plantation (1, 3 and 6 years)
and varying soil textures (loamy sand and sandy clay) were analyzed for soil organic carbon, its sequestration and aggregate
size distribution. The average soil organic carbon increased from 0.36 in sole crop to 0.66% in agroforestry soils. The increase
was higher in loamy sand than sandy clay. The soil organic carbon increased with increase in tree age. The soils under agroforestry
had 2.9–4.8 Mg ha−1 higher soil organic carbon than in sole crop. The poplar trees could sequester higher soil organic carbon in 0–30 cm profile
during the first year of their plantation (6.07 Mg ha−1 year−1) than the subsequent years (1.95–2.63 Mg ha−1 year−1). The sandy clay could sequester higher carbon (2.85 Mg ha−1 year−1) than in loamy sand (2.32 Mg ha−1 year−1). The mean weight diameter (MWD) of soil aggregates increased by 3.2, 7.3 and 13.3 times in soils with 1, 3 and 6 years plantation,
respectively from that in sole crop. The increase in MWD with agroforestry was higher in loamy sand than sandy clay soil.
The water stable aggregates (WSA >0.25 mm) increased by 14.4, 32.6 and 56.9 times in soils with 1, 3 and 6 years plantation,
respectively, from that in sole crop. The WSA >0.25 mm were 6.02 times higher in loamy sand and 2.2 times in sandy clay than
in sole crop soils. 相似文献
119.
Anil Kumar Nidhi Gupta Atul Kumar Gupta Vikram Singh Gaur 《Journal of Crop Science and Biotechnology》2009,12(4):183-194
Worldwide, the nitrogen use efficiency (NUE) for crop plants is of great concern. The burgeoning world population needs crop genotypes that respond to higher nitrogen and show a direct relationship to yield with use of nitrogen inputs, i.e. high nitrogen-responsive genotypes. However, for fulfilling the high global demand of organic produce, it requires the low nitrogen responsive genotypes with greater NUE and grain yields. The lack of knowledge about precise regulatory mechanisms to explain NUE in crop plants hampers the goal of agricultural productivity. Understanding the molecular basis of NUE will enable to provide handle for crop improvement through biotechnological means. With the advent of modern genomics and proteomics approaches such as subtractive hybridization, differential display, and microarray techniques are revolutionizing to identify the candidate genes which play a pivotal role in the regulation of NUE. Beside it, quantitative real-time polymerase chain reaction technology is also being used to establish marker-trait association for NUE. The identification of potential candidate genes/proteins in the regulation of NUE will serve as biomarker(s) for screening genotypes for their nitrogen responsiveness for optimization of nitrogen input in agriculture. This paper describes the molecular basis of NUE with respect to nitrogen metabolism and its intimate relationship with carbon metabolism, use of molecular-physiological-genetics approaches for understanding the role of various genes/proteins, and their validation to use as biomarker(s) for determining genotypic potential for NUE. Since NUE in plants is a complex trait which not only involves the primary process of nitrogen uptake and assimilatory pathways but also a series of events, including metabolite partitioning, secondary remobilization, C-N interactions, as well as molecular signalling pathways and regulatory control outside the metabolic cascades. Therefore, identification of novel nitrogen responsive genes and their cis- and trans-acting gene elements is essential. Thus, fishing out a single gene, biomarker or a master regulator controlling complex trait of NUE could serve as an appropriate strategy for nitrogen management in agriculture. 相似文献
120.
The nontarget effects of three plant growth stimulants (gibberellic acid, Siapton and triacontanol) and two plant growth retardants
(chlormequat chloride and mepiquat chloride) on the survivorship and developmental parameters of Spilarctia obliqua Walker (Lepidoptera: Arctiidae) were studied. For each compound, various concentrations (0.125×, 0.25×, 0.5×, × , 2× and
4×; × = labeled dose) bracketing the labeled dose were prepared by serial dilution and mixed with an artificial diet for the
insect. Gibberellic acid caused an increase in the larval period at × − 4×, but no marked difference was observed in the pupal
period or in larval survival at any concentration. Siapton induced a significant increase in larval period at the two highest
doses but caused significant reduction in pest survival at × − 4×. Interestingly, triacontanol induced a significant reduction
in pest survivorship at almost all doses. The LC50 for triacontanol was 0.206% and LT50 was 266.5 hours at the labeled dose. However, triacontanol did not cause any significant difference in larval or pupal periods
at any dose tested. Chlormequat chloride and mepiquat chloride caused significant reduction of larval survivorship at concentrations
higher than the labeled doses, and no effect on the larval period. Intriguingly, a significant reduction in pupal period was
observed with chlormequat chloride at × and 0.25×. Based on the marked effect of triacontanol on pest survivorship, this study
suggests incorporating triacontanol in integrated pest management modules for S. obliqua. Caution in the use of gibberellic acid and Siapton for pest infestations is also indicated. 相似文献