全文获取类型
收费全文 | 6355篇 |
免费 | 521篇 |
国内免费 | 32篇 |
专业分类
林业 | 330篇 |
农学 | 437篇 |
基础科学 | 54篇 |
973篇 | |
综合类 | 695篇 |
农作物 | 275篇 |
水产渔业 | 387篇 |
畜牧兽医 | 3019篇 |
园艺 | 93篇 |
植物保护 | 645篇 |
出版年
2020年 | 62篇 |
2019年 | 113篇 |
2018年 | 210篇 |
2017年 | 218篇 |
2016年 | 173篇 |
2015年 | 193篇 |
2014年 | 190篇 |
2013年 | 347篇 |
2012年 | 260篇 |
2011年 | 313篇 |
2010年 | 245篇 |
2009年 | 207篇 |
2008年 | 301篇 |
2007年 | 266篇 |
2006年 | 232篇 |
2005年 | 198篇 |
2004年 | 192篇 |
2003年 | 194篇 |
2002年 | 144篇 |
2001年 | 234篇 |
2000年 | 179篇 |
1999年 | 169篇 |
1998年 | 69篇 |
1997年 | 74篇 |
1996年 | 53篇 |
1995年 | 59篇 |
1994年 | 44篇 |
1993年 | 51篇 |
1992年 | 103篇 |
1991年 | 105篇 |
1990年 | 108篇 |
1989年 | 106篇 |
1988年 | 85篇 |
1987年 | 80篇 |
1986年 | 74篇 |
1985年 | 58篇 |
1984年 | 64篇 |
1983年 | 52篇 |
1981年 | 44篇 |
1980年 | 48篇 |
1979年 | 72篇 |
1978年 | 52篇 |
1977年 | 52篇 |
1976年 | 59篇 |
1975年 | 52篇 |
1974年 | 61篇 |
1973年 | 75篇 |
1972年 | 44篇 |
1971年 | 45篇 |
1969年 | 43篇 |
排序方式: 共有6908条查询结果,搜索用时 0 毫秒
91.
The inheritance of buckwheat (Fagopyrum esculentum Moench) seed storage proteins was investigated by control crosses between accessions containing different SDS‐PAGE protein patterns in the range of 38–48 kDa. Analysis of segregation of individual F1 and F2 seeds obtained by 17 crosses showed segregation of eight electrophoretic bands, from which 12‐banding variants were inferred. Two variants contained one band, nine contained two bands and one variant contained three bands and behaved as a single co‐dominant unit. The segregation of banding variants fits the expected ratios and thus supports the hypothesis of single Mendelian gene inheritance and that alleles are co‐dominant. The results therefore suggest that the genes controlling globulin subunits are tightly linked and inherited as a single locus. The locus was designated Glob‐1 and the twelve segregated protein variants as alleles a‐l. This is the first buckwheat globulin locus identified with multiple alleles, phenotypically expressed as groups of protein bands and thus applicable as a functional marker in buckwheat genomic studies. 相似文献
92.
Pre-harvest sprouting (PHS) reduces the quality of wheat (Triticum aestivum L.) and the economic value of the grain. The objective of this study was to evaluate the diversity of the Viviparous-1B (Vp-1B) gene associated with PHS tolerance in a collection of 490 widely grown winter wheat varieties from central and northern
Europe. Four alleles of Vp-1B were found in the wheat varieties tested, three of which (Vp-1Ba, Vp-1Bb and Vp-1Bc) had previously been identified in Chinese wheat varieties. The fourth was a new allele which had a 25-bp of deletion in
the third intron region compared with the nucleotide sequence of Vp-1Ba, and was designated as Vp-1Bd. The frequencies of different alleles in this set of European wheat germplasm were: Vp-1Ba (54%) > Vp-1Bc (21%) > Vp-1Bd (20%) > Vp-1Ba + c (4%) > Vp-1Bb (1%), with Vp-1Bb being present only in two French varieties, ‘Altria’ and ‘Recital’. In addition, the frequencies of the alleles differed
in varieties from different European countries. For example, Vp-1Ba had the highest frequency (76%) in varieties included in the UK National List (NL), but was least frequent in the Recommended
List (RL) of Sweden (19%). Similarly, Vp-1Bc was present with the highest frequency (58%) in wheat varieties from Sweden, and the lowest in UK NL varieties (8%) while
Vp-1Bd had the highest frequency of 32% in German varieties, and the lowest in Sweden varieties with only 8%. The Vp-1Ba allele was present in over half of the UK wheat varieties tested but the frequency was lower in RL varieties than in NL ones.
Furthermore, heterogeneities were found between Vp-1Ba and Vp-1Bc in the varieties from Sweden, Netherlands, Germany and UK. 相似文献
93.
Arthropod predators are abundant in turfgrass systems, and they play an important role in managing pests. Understanding the vertical distribution of predation is critical to developing cultural strategies that enhance and conserve predatory services. However, little is known on how the predation is vertically distributed within the turfgrass canopy. Thus, the objective of this study was to determine the vertical distribution of predation within the turfgrass canopy. Clay models were used to emulate the general appearance of Noctuidae caterpillars, to estimate the predatory activity. The choice and no-choice experiments were conducted by placing clay models at 2.54, 5.08, and 7.62 cm from the thatch surface and denoted as lower, intermediate, and upper levels, respectively, within turfgrass canopy. The predator-mediated impressions, paired mark, scratch, deep cut mark, deep distortion, prick, dent, stacked surface impression, scooped mark, granulation, and U-shaped mark, were identified on clay models. The incidence and severity of impressions were significantly greater on clay models placed at the lower canopy level than on those placed at the intermediate and upper canopy levels in the choice and no-choice experiments (P < 0.05). Thus, predators are more likely to find their prey at the soil level. This information can be used to refine management strategies, such as mowing height and insecticide use for effectively managing soil-borne and foliar-feeding arthropod pests and beneficial arthropods. 相似文献
94.
Distribution of light and heavy fractions of soil organic carbon as related to land use and tillage practice 总被引:10,自引:0,他引:10
Mass distributions of different soil organic carbon (SOC) fractions are influenced by land use and management. Concentrations of C and N in light- and heavy fractions of bulk soils and aggregates in 0–20 cm were determined to evaluate the role of aggregation in SOC sequestration under conventional tillage (CT), no-till (NT), and forest treatments. Light- and heavy fractions of SOC were separated using 1.85 g mL−1 sodium polytungstate solution. Soils under forest and NT preserved, respectively, 167% and 94% more light fraction than those under CT. The mass of light fraction decreased with an increase in soil depth, but significantly increased with an increase in aggregate size. C concentrations of light fraction in all aggregate classes were significantly higher under NT and forest than under CT. C concentrations in heavy fraction averaged 20, 10, and 8 g kg−1 under forest, NT, and CT, respectively. Of the total SOC pool, heavy fraction C accounted for 76% in CT soils and 63% in forest and NT soils. These data suggest that there is a greater protection of SOC by aggregates in the light fraction of minimally disturbed soils than that of disturbed soil, and the SOC loss following conversion from forest to agriculture is attributed to reduction in C concentrations in both heavy and light fractions. In contrast, the SOC gain upon conversion from CT to NT is primarily attributed to an increase in C concentration in the light fraction. 相似文献
95.
Pejsak Z Kusior G Pomorska-Mól M Podgórska K 《Polish journal of veterinary sciences》2012,15(1):37-42
The objective of the study was to evaluate an efficacy of sows vaccination protocols in the herd with serious problems affecting efficacy of reproduction. The study was performed in a large pig herd with about 1200 sows. Before vaccination against PCV2, farrowing rate in this farm was about 65%. Sows, boar and replacement gilts were immunized using Circovac vaccine (Merial, France) according to producer's recommendations. Parameters of production were analyzed since 2007 until 2010 in selected batches of sows inseminated at the same weeks of the year (17th, 18th, 19th and 20th) to eliminate seasonal variability. In total, 940 sows were subjected to the study. No significant changes in management during these years were introduced. The applied protocol of sow herd long-term vaccination proved to be very efficient. All measured production parameters: reproduction rate, number of piglets born alive, birth weight of piglets and number of piglets weaned per a litter improved after implementation of immunization program. Moreover, further improvement was observed with vaccination in the following reproduction cycles. The most spectacular effect of vaccination regarded average farrowing rate that increased from 64.76% in control group to 86.93% after basic vaccination. Two years after implementation of vaccination program this parameter reached 93.6%. Number of piglets weaned per sow per a litter improved from 10.31 to 11.74 after one year of vaccination and remained relatively stable through the following year. Simultaneously, the percentage of newborn piglets with birth weight < 1 kg decreased significantly (p < 0.05). To summarize, vaccination against PCV2 influenced positively the insemination rate, number of piglets born alive and weaned per litter as well as birth body weight and percentage of piglets weighing < 1 kg. 相似文献
96.
Kaleczyc J Pidsudko Z Franke-Radowiecka A Sienkiewicz W Majewski M Lakomy M Timmermans JP 《Polish journal of veterinary sciences》2004,7(3):199-201
The present study investigated the chemical coding of neurons in the celiac-superior mesenteric ganglion complex supplying the normal (n=4) and inflamed (n=4) ileum (chemically-induced inflammation) in juvenile pigs using retrograde tracing combined with immunohistochemistry. Ileum-projecting neurons (IPN) were predominantly distributed in the left and right superior mesenteric pools of the ganglion. The majority of them were adrenergic (tyrosine hydroxylase-positive) and also contained neuropeptide Y, somatostatin or galanin. No clear-cut differences in the distribution and chemical coding of IPN were found between normal and inflamed pigs. However, in the inflamed group, the density of peptidergic, IPN-associated nerve fibres was higher than that found in the control group. 相似文献
97.
The effects of fermentation and adsorption using lactic acid bacteria culture broth on the feed quality of rice straw 总被引:1,自引:0,他引:1
LIU Jing-jing LIU Xiao-ping REN Ji-wei ZHAO Hong-yan YUAN Xu-feng WANG Xiao-fen Abdelfattah Z M Salem CUI Zong-jun 《中国农业科学(英文版)》2015,(3):503-513
To improve the nutritional value and the palatability of air-dried rice straw, culture broth of the lactic acid bacteria community SFC-2 was used to examine the effects of two different treatments, fermentation and adsorption. Air-dried and chopped rice straw was treated with either fermentation for 30 d after adding 1.5 L nutrient solution(50 m L inocula L–1, 1.2×1012 CFU m L–1 inocula) kg–1 straw dry matter, or spraying a large amount of culture broth(1.5 L kg–1 straw dry matter, 1.5×1011 CFU m L–1 culture broth) on the straw and allowing it to adsorb for 30 min. The feed quality and aerobic stability of the resulting forage were examined. Both treatments improved the feed quality of rice straw, and adsorption was better than fermentation for preserving nutrients and improving digestibility, as evidenced by higher dry matter(DM) and crude protein(CP) concentrations, lower neutral detergent fiber(NDF), acid detergent fiber(ADF) and NH3-N concentrations, as well as higher lactic acid production and in vitro digestibility of DM(IVDMD). The aerobic stability of the adsorbed straw and the fermented straw was 392 and 480 h, respectively. After being exposed to air, chemical components and microbial community of the fermented straw were more stable than the adsorbed straw. 相似文献
98.
99.
We present a 650-year Antarctic ice core record of concentration and isotopic ratios (δ(13)C and δ(18)O) of atmospheric carbon monoxide. Concentrations decreased by ~25% (14 parts per billion by volume) from the mid-1300s to the 1600s then recovered completely by the late 1800s. δ(13)C and δ(18)O decreased by about 2 and 4 per mil (‰), respectively, from the mid-1300s to the 1600s then increased by about 2.5 and 4‰ by the late 1800s. These observations and isotope mass balance model results imply that large variations in the degree of biomass burning in the Southern Hemisphere occurred during the last 650 years, with a decrease by about 50% in the 1600s, an increase of about 100% by the late 1800s, and another decrease by about 70% from the late 1800s to present day. 相似文献
100.
Z. Hedayatnasab R. Eslami-Farsani S. M. R. Khalili N. Soleimani 《Fibers and Polymers》2013,14(10):1650-1656
This paper focuses on the influence of temperature conditions and the clay contents on enhancement of mechanical characterization of polypropylene (PP) nanocomposites. The nanocomposites were prepared using the melt mixing technique in a co-rotating intermeshing twin screw extruder followed by injection moulding. Nanocomposites properties such as impact strength and ultimate tensile strength, yield strength, failure strain, Young’s modulus and toughness are calculated. The addition of clay to PP matrix was showed remarkable enhancement in mechanical properties at the temperature of 25 oC and 120 °C. Nearly 36 % and 160 % increase in the Young’s modulus and about 45 % and 62 % increase in the impact strength were observed at both room temperature (RT) and high temperature (HT), respectively. But, the tensile strength was not affected much. The basal spacing of clay in the composites was measured by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to assess the surface morphology of the fractured surfaces and dispersion of the nanoclay. 相似文献