全文获取类型
收费全文 | 1651篇 |
免费 | 89篇 |
国内免费 | 1篇 |
专业分类
林业 | 228篇 |
农学 | 52篇 |
基础科学 | 11篇 |
425篇 | |
综合类 | 183篇 |
农作物 | 65篇 |
水产渔业 | 70篇 |
畜牧兽医 | 491篇 |
园艺 | 48篇 |
植物保护 | 168篇 |
出版年
2023年 | 15篇 |
2022年 | 27篇 |
2021年 | 33篇 |
2020年 | 39篇 |
2019年 | 35篇 |
2018年 | 53篇 |
2017年 | 67篇 |
2016年 | 46篇 |
2015年 | 38篇 |
2014年 | 51篇 |
2013年 | 76篇 |
2012年 | 112篇 |
2011年 | 131篇 |
2010年 | 76篇 |
2009年 | 79篇 |
2008年 | 112篇 |
2007年 | 109篇 |
2006年 | 79篇 |
2005年 | 84篇 |
2004年 | 72篇 |
2003年 | 71篇 |
2002年 | 71篇 |
2001年 | 26篇 |
2000年 | 14篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1981年 | 5篇 |
1979年 | 7篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1970年 | 7篇 |
1963年 | 3篇 |
1962年 | 3篇 |
排序方式: 共有1741条查询结果,搜索用时 15 毫秒
1.
Abstract. Experiments were conducted for one year on two different soil types. On a clay soil straw was either (a) burnt, (b) baled leaving the stubble, or (c) chopped and spread. The soil was tine cultivated to depths of 5, 10 or 15 cm or ploughed to 20 or 30 cm before winter wheat was sown conventionally. In addition, a direct-drilled crop was sown after each straw treatment. On a silt loam soil the direct-drilled, tine cultivated to 15 cm and ploughed to 30 cm treatments following burning or chopping and spreading straw were repeated.
Tine cultivation incorporated less straw than ploughing, decreased plant establishment and early growth but did not decrease yield. Direct-drilling through chopped straw decreased yield on the silt loam but not on the clay soil. Short straw (< 5 cm) was easier to incorporate than longer straw. Ploughing was the most efficient method of straw incorporation because it inverts soil. Early effects on crop growth and nutrient uptake following straw incorporation were transient and associated with large amounts of straw in the seeded layer of soil. 相似文献
Tine cultivation incorporated less straw than ploughing, decreased plant establishment and early growth but did not decrease yield. Direct-drilling through chopped straw decreased yield on the silt loam but not on the clay soil. Short straw (< 5 cm) was easier to incorporate than longer straw. Ploughing was the most efficient method of straw incorporation because it inverts soil. Early effects on crop growth and nutrient uptake following straw incorporation were transient and associated with large amounts of straw in the seeded layer of soil. 相似文献
2.
Nwaodu Chibuzo Hope Okoro Victor Mela Obinna Uchegbu Martins Chigozie Mbajiorgu Christian Anayochukwu 《Tropical animal health and production》2018,50(4):851-856
Tropical Animal Health and Production - A study was conducted to determine the effects of varied brooding regimes on the performance of small bronze turkey poults and their grow-outs. One hundred... 相似文献
3.
C. Larrigaudière J. Pons R. Torres J. Usall 《The Journal of Horticultural Science and Biotechnology》2013,88(3):314-319
SummaryThe potential of using hot water (2.5 min at 45°C), 2% sodium carbonate or 2% sodium bicarbonate solutions alone or combined with hot water, for control of Penicillium digitatum (green mould) was investigated on commecially ripe clementines. The effect of such treatments on the post-harvest storage life of clementines was determined during two months analysing weight loss, increase in rind deformation and internal maturity. Carbonate and bicarbonate solutions effectively control green mould during storage but hot water does not. Compared with the control and hot-water treated fruits, clementines treated with carbonate and, to a lesser extend with bicarbonate, showed higher weight loss and lower firmness during storage. In contrast, lower increase in ripening index was found when the fruits were treated with carbonate or bicarbonate. Fruits treated with hot water alone or combined with carbonate exhibited no change in ripening during the first month of storage. Rinsing the fruit significantly reduces weight and firmness loss in the fruits treated with carbonate and bicarbonate, but did not change the ripening index. The primary finding of this work was that carbonate and bicarbonate treatments might significantly increase the loss in weight and firmness during storage. Rinsing the fruit immediately after treatment appeared to be a simple solution to avoid these losses in quality. 相似文献
4.
At geological time scales, the role of continental erosion in the organic carbon (OC) cycle is determined by the balance between recent OC burial and petrogenic OC oxidation. Evaluating its net effect on the concentration of carbon dioxide and dioxygen in the atmosphere requires the fate of petrogenic OC to be assessed. Here, we report a multiscale (nanometer to micrometer) structural characterization of petrogenic OC in the Himalayan system. We show that graphitic carbon is preserved and buried in marine sediments, while the less graphitized forms are oxidized during fluvial transport. Radiocarbon dating indicates that 30 to 50% of the carbon initially present in the Himalayan rocks is conserved during the erosion cycle. Graphitization during metamorphism thus stabilizes carbon in the crust over geological time scales. 相似文献
5.
Community structures of Collembola and their seasonal fluctuations were studied in eight southern Quebec sugar maple (Acer saccharum Marsh.) forests growing on mull, moder and mor humus types. Endogeic species were extracted from soil cores using Berlese-Tullgren funnels while epigeic species were collected using pit-light traps (Luminoc®). Comparisons of species presence, abundance, and dominance among sites and seasons were done using Sorensen's similarity coefficients and CANOCO. A total of 92 species from 7 families and 35 genera were identified. Species dominance and community structure differed according to humus types. Two groups of endogeic species were identified. The mor/mor-moder type group included Folsomia penicula, Hypogastrura (Ceratophysella) spp. Que., Micrisotoma achromata, Onychiurus (Protaphorura)? parvicornis, Onychiurus (Onychiurus) sp. A Que. And Onychiurus (Onychiurus) sp. B Que. The mull/mull-moder type group included Isotoma (Desoria) notabilis, Tullbergia (Tullbergia) silvicola, Tullbergia (Tullbergia) clavata, and Pseudosinella alba. Such clear humus type relationships were not found among the epigeic species, but important seasonal changes in community structures were found for these species. Spring species were Sminthurinus (Katiannina) macgillivrayi, Hypogastrura (Ceratophysella) maheuxi, Hypogastrura (Hypogastrura) sp. A Que. and Sminthurinus (Sminthurinus) latimaculosus. Tomocerus (Pogonognathellus) flavescens, Sminthurinus (Sminthurinus) henshawi, and Orchesella hexfasciata appeared in the summer samples while Dicyrtoma (Dicyrtoma) aurata was found only in fall samples where it was dominant in most sites along with either Sminthurides (Sminthurides) lepus or Sminthurinus (Sminthurinus) quadrimaculatus. No strong seasonal trends were found among the dominant endogeic species. 相似文献
6.
Christian Poll Sven Marhan Joachim Ingwersen Ellen Kandeler 《Soil biology & biochemistry》2008,40(6):1306-1321
Factors determining C turnover and microbial succession at the small scale are crucial for understanding C cycling in soils. We performed a microcosm experiment to study how soil moisture affects temporal patterns of C turnover in the detritusphere. Four treatments were applied to small soil cores with two different water contents (matric potential of ?0.0063 and ?0.0316 MPa) and with or without addition of 13C labelled rye residues (δ13C=299‰), which were placed on top. Microcosms were sampled after 3, 7, 14, 28, 56 and 84 days and soil cores were separated into layers with increasing distance to the litter. Gradients in soil organic carbon, dissolved organic carbon, extracellular enzyme activity and microbial biomass were detected over a distance of 3 mm from the litter layer. At the end of the incubation, 35.6% of litter C remained on the surface of soils at ?0.0063 MPa, whereas 41.7% remained on soils at ?0.0316 MPa. Most of the lost litter C was mineralised to CO2, with 47.9% and 43.4% at ?0.0063 and ?0.0316 MPa, respectively. In both treatments about 6% were detected as newly formed soil organic carbon. During the initial phase of litter decomposition, bacteria dominated the mineralisation of easily available litter substrates. After 14 days fungi depolymerised more complex litter compounds, thereby producing new soluble substrates, which diffused into the soil. This pattern of differential substrate usage was paralleled by a lag phase of 3 days and a subsequent increase in enzyme activities. Increased soil water content accelerated the transport of soluble substrates, which influenced the temporal patterns of microbial growth and activity. Our results underline the importance of considering the interaction of soil microorganisms and physical processes at the small scale for the understanding of C cycling in soils. 相似文献
7.
Körner C Asshoff R Bignucolo O Hättenschwiler S Keel SG Peláez-Riedl S Pepin S Siegwolf RT Zotz G 《Science (New York, N.Y.)》2005,309(5739):1360-1362
Whether rising atmospheric carbon dioxide (CO2) concentrations will cause forests to grow faster and store more carbon is an open question. Using free air CO2 release in combination with a canopy crane, we found an immediate and sustained enhancement of carbon flux through 35-meter-tall temperate forest trees when exposed to elevated CO2. However, there was no overall stimulation in stem growth and leaf litter production after 4 years. Photosynthetic capacity was not reduced, leaf chemistry changes were minor, and tree species differed in their responses. Although growing vigorously, these trees did not accrete more biomass carbon in stems in response to elevated CO2, thus challenging projections of growth responses derived from tests with smaller trees. 相似文献
8.
During our screening of plant materials to find new natural fragrance and flavor ingredients, we discovered two series of 3-sulfanylalkyl alkanoates in a peel extract of fruits of wild-growing Poncirus trifoliata (L.) Raf. (Rutaceae), a species closely related to Citrus. The two series belong to alkanoates of 3-methyl-3-sulfanylbutan-1-ol and 3-sulfanylhexan-1-ol, respectively, and thus are members of a family of natural molecules having in common a 1,3-positioned O,S moiety. The alkanoate residues comprise all even-numbered saturated fatty acids from C2 (acetate) to C18 (octadecanoate). Among the 20 sulfur-containing compounds identified, 14 are described for the first time as naturally occurring in a botanical species. Several cysteine-S-conjugates were synthesized as hypothetical precursors of the new volatile sulfur-containing constituents, where after S-(3-hydroxy-1,1-dimethylpropyl)-L-cysteine, S-[3-(acetyloxy)-1,1-dimethylpropyl]-L-cysteine, and S-[1-(2-hydroxyethyl)butyl]-L-cysteine were identified in the fruit peel. No cysteine-S-conjugates were detected in the fruit juice. 相似文献
9.
Belayneh Ayalew Desalegne Kifle Dagne Gedil Melaku Boukar Ousmane Christian A. Fatokun 《Journal of Crop Science and Biotechnology》2017,20(2):107-128
The extent of genetic diversity and relatedness of cowpea germplasm from East Africa are poorly understood. A set of 13 microsatellites (SSR) and 151 single nucleotide polymorphisms (SNPs) markers were applied to assess the levels of genetic diversity in a sample of 95 accessions of local cowpea germplasm and inbred lines of Vigna unguiculata. The average genetic diversity (D), as quantified by the expected heterozygosity, was higher for SSR loci (0.52) than for SNPs (0.34). The polymorphic information content was 0.48 for SSR and 0.28 for SNP while the fixation index was 0.095 for SSR and 0.15 for SNPs showing moderate differentiation and high gene flow among cowpea accessions from East African countries. The results of data analysis of both SSR and SNP markers showed similar clustering patterns suggesting a substantial degree of association between origin and genotype. Principal coordinate analysis (PCoA) with SSR and SNP markers showed that accessions were grouped into two and three broad groups across the first two axes, respectively. Our study found that SNP markers were more effective than SSR in determining the genetic relationship among East African local cowpea accessions and IITA inbred lines. Based on this analysis, five local cowpea accessions Tvu-13490, Tvu-6378, Tvu-13448, Tvu-16073, and 2305675 were identified to be tightly clustered sharing several common alleles with the drought tolerant variety Danila when analyzed with SSR and SNP markers. The findings will assist and contribute to future genetic diversity studies aimed at the genetic improvement of local Eastern Africa cowpea accessions for improved overall agronomic performance in general and breeding for drought tolerant in particular. 相似文献
10.
Nazgol Emrani Mario Hasler Dilan S. R. Patiranage Maldonado-Taipe Nathaly Elodie Rey Christian Jung 《Plant Breeding》2020,139(6):1190-1200
Quinoa offers a promising alternative for staple food, considering its outstanding nutritional value and tolerance to abiotic stresses. To develop breeding programmes in quinoa, a reliable crossing method for increasing the genetic variation is required. In the following study, we aimed to develop segregating populations in quinoa. We tested the efficiency of three different crossing methods (hand emasculation, warm water emasculation and no emasculation). Moreover we developed a two-stage selection strategy based on morphological traits and molecular markers for the selection of hybrid plants. We reported hand emasculation to be the most efficient crossing method, followed by warm water emasculation and no emasculation. Our results demonstrated that crosses in quinoa can be successfully performed, despite its complicated flower structure and high self-pollination rate. Additionally, we developed 30 segregating populations from crosses between accessions of different origins with varying phylogenetic relationship, which offers a promising perspective for quinoa breeding programmes in the future. 相似文献