全文获取类型
收费全文 | 5742篇 |
免费 | 299篇 |
国内免费 | 3篇 |
专业分类
林业 | 278篇 |
农学 | 313篇 |
基础科学 | 15篇 |
1028篇 | |
综合类 | 481篇 |
农作物 | 807篇 |
水产渔业 | 507篇 |
畜牧兽医 | 2210篇 |
园艺 | 87篇 |
植物保护 | 318篇 |
出版年
2023年 | 37篇 |
2022年 | 63篇 |
2021年 | 189篇 |
2020年 | 118篇 |
2019年 | 140篇 |
2018年 | 172篇 |
2017年 | 174篇 |
2016年 | 180篇 |
2015年 | 175篇 |
2014年 | 244篇 |
2013年 | 340篇 |
2012年 | 406篇 |
2011年 | 455篇 |
2010年 | 280篇 |
2009年 | 264篇 |
2008年 | 372篇 |
2007年 | 371篇 |
2006年 | 344篇 |
2005年 | 269篇 |
2004年 | 263篇 |
2003年 | 239篇 |
2002年 | 193篇 |
2001年 | 173篇 |
2000年 | 124篇 |
1999年 | 74篇 |
1998年 | 38篇 |
1997年 | 20篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 34篇 |
1989年 | 29篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1983年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1978年 | 14篇 |
1975年 | 6篇 |
1974年 | 12篇 |
1973年 | 12篇 |
1972年 | 6篇 |
1971年 | 6篇 |
1970年 | 5篇 |
1968年 | 6篇 |
排序方式: 共有6044条查询结果,搜索用时 31 毫秒
991.
Trunks of 8-year-old vigorous ‘Fuyu’ persimmon (Diospyros kaki Thunb.) were girdled to a 1 cm width on April 20 and June 10 2004. Tree growth and fruit characteristics were monitored for two years, with special emphasis on the carry-over effect in 2005. Girdling reduced trunk and shoot growth especially of April-girdled trees over two consecutive years. However, the most significant effect of girdling was in the occurrence of water sprouts: a control tree had 29.5 in 2004 and 27.3 in 2005, whereas the April-girdled trees had only 0.3 and 5.3, respectively. Girdling increased fruit set by nearly 50% and enhanced fruit colour in 2004 only. Girdling date did not significantly affect fruit size and soluble solids for two years. Fruit flesh of girdled trees in 2004, especially in the April-girdled trees, had lower N and P concentrations. The levels of starch, soluble sugars, and inorganic elements in flower-bearing distal buds measured just before new growth in 2005 were not significantly altered by the girdling in 2004. 相似文献
992.
Young Hoon Park Seong Gyu Ahn Young Mi Choi Hye Jeong Oh Dong Chun Ahn Jin Gi Kim Jum Soon Kang Young Whan Choi Byoung Ryong Jeong 《Scientia Horticulturae》2010
The ‘Genome database for Rosaceae (GDR)’ provides a large collection of expressed sequence tags (ESTs) harboring simple sequence repeats (SSRs) from several Rosaceae genera, including Rosa (rose). Primer pairs flanking SSR were designed for 312 unique Rosa ESTs based on GDR database. Eight rose (Rosa hybrida L.) genotypes were tested for PCR amplification, and 287 (92%) of the primer pairs generated allele-specific PCR bands that were readily scored. From 183 (63.7%) primer pairs that evidenced polymorphic alleles among the eight rose cultivars, 20 pairs evidencing EST sequence homology to known gene functions and high levels of polymorphism were selected and utilized for DNA fingerprinting and genetic diversity assessments of 47 rose hybrids. A total of 202 polymorphic bands were scored and generated unique fingerprints for each rose hybrid. The Nei–Li genetic similarity coefficients among 1081 pair-wise comparisons of 47 cultivars exhibited a broad range of genetic variations from 0.30 (‘Grand King’ and ‘Carnival’) to 0.99 (‘First Red’ and ‘Red Champ’). UPGMA cluster analysis divided 47 hybrids into five major groups and two sub-groups. The cross-species transferability of 273 EST-SSR primer pairs was evaluated using four genotypes of the strawberry, a genus member of the Rosaceae family. PCRs on the DNA samples of strawberry were successful for 165 primer pairs; among these, 123 pairs amplified 243 polymorphic bands. As surrogates of the marker transfer, the phenetic relationship among the four strawberry genotypes was evaluated. Genetic similarity coefficients varied from 0.78 (‘Maehyang’ and ‘Janghyee’) to 0.64 (‘Janghyee’ and ‘Pragana’). The results of cluster analysis showed that the three octaploid strawberry cultivars were quite similar, whereas the diploid ‘Pragana’ was related distantly at the genomic DNA level. The EST-SSR markers developed in the present study can be efficiently utilized for genetic diversity studies in Rosaceae. 相似文献
993.
M.A. Awal Takeshi Ohta Kazuho Matsumoto Tae Toba Kenichi Daikoku Shigeaki Hattori Tetsuya Hiyama Hotaek Park 《Urban Forestry & Urban Greening》2010,9(3):261-270
Urbanisation is increasing tremendously in some parts of the world. Consequently, many rural forests may become depleted, although many opportunities exist for urban forests to increase. However, few studies have quantified the carbon (C) sequestration capacities of urban and rural forests in specific climatic zones. The present study compared carbon sequestration in two temperate deciduous forests located in Nagoya and Toyota, central Japan. The Nagoya University forest represented an urban forest, and a site in Toyota represented a rural forest. The urban forest at Nagoya University had comparatively smaller areas of green space and larger areas of buildings and roads. Land uses for building and road, which are typical of urban areas, result in smaller diurnal temperature ranges but higher air temperature, vapour pressure deficit, and atmospheric carbon dioxide (CO2) concentration. The urban forest in this study exhibited higher gross ecosystem exchange (GEE), especially in the active growing season from May to September, suggesting the possible effect of CO2 fertilisation. However, higher air temperatures caused comparatively smaller net ecosystem exchange (NEE) because of higher ecosystem respiration (RE). Although both forests functioned as CO2 sinks at annual time scales, the rural Toyota forest site (5.43 t C ha–1 yr–1) had 36% higher net ecosystem production (NEP=–NEE; the negative sign indicates uptake by the forest ecosystem from the atmosphere) than that at the urban forest. The higher normalised respiration (i.e., RE/GPP ratio; GPP=–GEE where GPP represents gross primary production) at the Nagoya University forest might be attributable to factors associated with the degree of urbanisation. Thus, in temperate forests, factors associated with urbanisation may reduce the atmospheric carbon sink function by accelerating respiration. This is an issue of global interest, as many countries are experiencing rapid urbanisation. 相似文献
994.
Kim H Hebelstrup Michael W Christiansen Massimiliano Carciofi Birgitte Tauris Henrik Brinch-Pedersen Preben B Holm 《Plant methods》2010,6(1):15
Background
Cloning of gene casettes and other DNA sequences into the conventional vectors for biolistic or Agrobacterium-mediated transformation is hampered by a limited amount of unique restriction sites and by the difficulties often encountered when ligating small single strand DNA overhangs. These problems are obviated by "The Uracil Specific Excision Reagent (USER™)" technology (New England Biolabs) which thus offers a new and very time-efficient method for engineering of big and complex plasmids. 相似文献995.
Influence of prohexadione-calcium on growth and gibberellins content of Chinese cabbage grown in alpine region of South Korea 总被引:2,自引:0,他引:2
Sang-Mo Kang Jung-Tae Kim Muhammad Hamayun In-Cheon Hwang Abdul Latif Khan Yoon-Ha Kim Joon-Hee Lee In-Jung Lee 《Scientia Horticulturae》2010
We investigated the effect of prohexadione-calcium (Pro-Ca) on growth characteristics and endogenous gibberellins content of Chinese cabbage grown in the alpine region of South Korea. Pro-Ca was applied at the rates of 200 ppm and 400 ppm, after 10, 15 and 20 days of transplanting seedlings in to the field. Application of Pro-Ca through foliage improved quality and quantity of yield by promoting Chinese cabbage head yield, number of head leaves, total soluble sugar content and compactness of head. The leaf size was reduced, while the chlorophyll content increased under the influence of elevated Pro-Ca application, when measured after 40 days of transplantation. The endogenous bioactive GA1 and GA4 contents of Chinese cabbage drastically decreased with elevated Pro-Ca, indicating that gibberellins (GAs) biosynthesis was blocked by this chemical. Current study suggests that both of GAs biosynthesis pathways are operational in Chinese cabbage, although non-C13-hydroxylation pathway was found to be the major pathway. GAs were quantified by gas chromatography/mass spectroscopy-selective ion monitoring (GC/MS-SIM). 相似文献
996.
997.
Ji-Hyun?Park Sung-Eun?Cho Mai?Suyama Yousuke?Degawa Hyeon-Dong?ShinEmail author 《European journal of plant pathology / European Foundation for Plant Pathology》2016,146(4):949-961
Hibiscus syriacus, as a national flower of Korea, is most popularly used for ornamental purposes and includes numerous cultivars, and it is widely planted in temperate zones that feature hot summers. We investigated Choanephora flower rot on H. syriacus from 2012 to 2014 in Korea and Japan and confirmed Choanephora infection in several localities in both countries. Here, our objectives were to identify the main causal agent of Choanephora flower rot on H. syriacus and describe its morphological and molecular characteristics. We identified 44 out of 50 isolates as Choanephora cucurbitarum and the remainder as C. infundibulifera based on morphological characterization and phylogenetic analysis. The sequences of the internal transcribed spacer region (ITS) of ribosomal DNA and the D1/D2 region of the large subunit (LSU) rDNA of examined isolates were compared with sequences obtained from GenBank, and the analysis of the results revealed 100 % identity with the corresponding sequences of C. cucurbitarum and C. infundibulifera strains. Classification of the Choanephora species performed here according to the key described by Kirk (1984) corresponded with the results of the phylogenetic analysis of this study. Through intraspecific and interspecific mating tests, the characteristics of zygospore were described in details. Pathogenicity tests using both species showed the same symptoms, causing blossom blight and soft rot on the flowers, which were identical to those observed in the field. All identified causal agents of Choanephora rot were indeed Choanephora species, where C. cucurbitarum was identified in the majority, while the others were in the minority of examined samples. 相似文献
998.
Effect of hydrogen peroxide exposures on mucous cells and lysozymes of gill tissues of olive flounder Paralichthys olivaeceus
下载免费PDF全文
![点击此处可从《Aquaculture Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigated the effects of hydrogen peroxide on mucous cells and lysozymes in gill tissue of olive flounder. Morphological analysis revealed significant changes in the number of mucous cells after exposure to 300 and 500 mg L ? 1 hydrogen peroxide; however, there was no detectable difference in the 100 mg L ? 1 group. Lysozyme activities declined gradually in the gill mucus, but in contrast activities in serum increased significantly following the completion of treatment. The hepatic c‐ and g‐type lysozyme levels showed significant responses, indicating that the liver is a major lysozyme producer in response to stress condition; however, in the head kidney, there were no significant changes in the g‐type lysozyme level in all the groups, while the only detectable difference with the c‐type gene in the 300 mg L ? 1. While the treatments showed no significant changes compared with the control for either branchial lysozyme, there were significant differences in c‐type lysozyme between the 3rd treatment and 5 day. Taken together, our data indicate that hydrogen peroxide treatment may lead to modulation of the innate immune response of olive flounder; therefore, the application of hydrogen peroxide in a field system will require more attention to dose and timing effects. 相似文献
999.
Kim N. Irvine Mary F. Perrelli Ratchadawan Ngoen-klan Ian G. Droppo 《Journal of Soils and Sediments》2009,9(4):328-341
Background, aim and scope Street sediment samples were collected at 50 locations in a mixed land use area of Hamilton, Ontario, Canada, and metal levels
were analyzed using a sequential extraction procedure for different particle size classes to provide an estimate of potential
toxicity as well as the potential for treatment through best management practices (BMPs).
Methodology The street sediment samples were dry sieved into four different particle size categories and a sequential extraction procedure
was done on each size category following the methodology proposed by Tessier et al. 1979 using a Hitachi 180-80 Polarized Zeeman Atomic Absorption Spectrophotometer.
Results and discussion Analysis of variance, post hoc least-significant difference tests, and kriging analysis showed that spatially Mn and Fe levels
were associated with a well-defined heavy industrial area that includes large iron- and steel-making operations; Cu and Pb
were associated with both the industrial and high-volume traffic areas, while Zn tended to be more associated with high-volume
traffic areas. The potential bioavailability of the metals, based on the sum of chemical fractions 1 (exchangeable) and 2
(carbonate-bound), decreased in order: Zn > Cd > Mn > Pb > Cu > Fe. Based on aquatic sediment quality guidelines, there is
some concern regarding the potential impact of the street sediment when runoff reaches receiving waters.
Conclusions It is possible that a combination of BMPs, including street sweeping and constructed wetlands, could help to reduce street
sediment impact on environmental quality in the Hamilton region. The data presented here would be important in developing
and optimizing the design of these BMPs. 相似文献
1000.