全文获取类型
收费全文 | 73307篇 |
免费 | 4139篇 |
国内免费 | 32篇 |
专业分类
林业 | 3174篇 |
农学 | 2397篇 |
基础科学 | 467篇 |
8668篇 | |
综合类 | 12016篇 |
农作物 | 2818篇 |
水产渔业 | 3526篇 |
畜牧兽医 | 38608篇 |
园艺 | 836篇 |
植物保护 | 4968篇 |
出版年
2018年 | 968篇 |
2017年 | 1075篇 |
2016年 | 1000篇 |
2015年 | 847篇 |
2014年 | 1046篇 |
2013年 | 2745篇 |
2012年 | 1944篇 |
2011年 | 2268篇 |
2010年 | 1534篇 |
2009年 | 1559篇 |
2008年 | 2323篇 |
2007年 | 2223篇 |
2006年 | 2036篇 |
2005年 | 1970篇 |
2004年 | 1847篇 |
2003年 | 1990篇 |
2002年 | 1807篇 |
2001年 | 2239篇 |
2000年 | 2191篇 |
1999年 | 1750篇 |
1998年 | 714篇 |
1997年 | 777篇 |
1996年 | 685篇 |
1995年 | 865篇 |
1994年 | 734篇 |
1993年 | 734篇 |
1992年 | 1493篇 |
1991年 | 1634篇 |
1990年 | 1605篇 |
1989年 | 1606篇 |
1988年 | 1493篇 |
1987年 | 1456篇 |
1986年 | 1536篇 |
1985年 | 1449篇 |
1984年 | 1270篇 |
1983年 | 1063篇 |
1982年 | 748篇 |
1979年 | 1171篇 |
1978年 | 887篇 |
1977年 | 840篇 |
1976年 | 799篇 |
1975年 | 829篇 |
1974年 | 1030篇 |
1973年 | 1070篇 |
1972年 | 1018篇 |
1971年 | 951篇 |
1970年 | 927篇 |
1969年 | 899篇 |
1968年 | 754篇 |
1967年 | 844篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
Karl Gösswald 《Journal of pest science》1943,19(3):30-34
Ohne Zusammenfassung
Mit 10 Abbildungen 相似文献
992.
H. W. Fassbender L. Alpízar J. Heuveldop H. Fölster G. Enríquez 《Agroforestry Systems》1988,6(1-3):49-62
Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems
of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica.
For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference
between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests)
of the system are considered.
The implications of the models are discussed in detail.
Aspects of net primary production in the systems studied are considered.
N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall
patterns and pruning of theE. poeppigiana.
For part I see Vol. 4, No. 3, 1986 For part II see this issue
Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesellschaft für Technische Zusammenarbeit),
Turrialba, Costa Rica 相似文献
993.
Effects of woodland structure on breeding bird populations in stands of coppiced lime (Tilia cordata) in western England over a 10-year period 总被引:1,自引:0,他引:1
Bird populations were estimated in three adjacent stands ofsmall-leaved lime (Tilia cordata) at Shrawley Wood, Worcestershire,between 1984 and 1993. The stands were old coppice, recent coppicecut in the late 1970s and thinned coppice that had been singledprobably in the 1970s. It is thought that the stands were allpreviously coppiced in the 1940s. The study area presented anunusual opportunity to (1) assess effects of woodland structureon bird populations in the absence of any major differencesin tree species, (2) to compare the dynamics of bird populations,and hence assess habitat preferences, within large samples ofeach habitat. Overall densities of birds were consistently lowestin the old coppice and generally highest in the recent coppice.The singled coppice supported the least diverse bird communitiesas measured by a simple diversity index and the expected numbersof species within standardized samples of individuals. Warblers(Sylviidae) were strikingly more abundant in recent coppicethan other habitats, being virtually absent from the old coppice.Wrens were by far the most abundant species in the singled coppice.There was strong evidence that the old coppice was the leastpreferred habitat of wren and robin. The most striking changeduring the study was the collapse of the warbler populationsin the recent coppice after some 11 to 12 years of coppice growth.This was predictable from previous studies, but the timing ofthe warbler decline occurred later than expected and was probablya consequence of the relatively slow canopy closure of the coppiceat Shrawley Wood. Differences between stands, and changes overthe 10 years within stands, were interpreted in terms of habitatstructure and effects of winter weather on survival of residentspecies. The findings are discussed in relation to managementof abandoned coppice; it is suggested that for conservationpurposes thinning should be regarded as a complementary approach,alongside coppicing and non-intervention. 相似文献
994.
Journal of Pest Science - In einem Labortest wurde die Wirksamkeit des NematodenDiplogaster sp. als Prädator der Zweitlarven der WurzelnematodenMeloidogyne javanica undTylenchulus... 相似文献
995.
Summary The inheritance of five characteristics namely branching behaviour, clustering pattern, growth habit, leaf size and hairiness was studied in clusterbean. All the traits were controlled by single pairs of genes except branching behaviour which exhibited digenic inheritance. Complementary gene effects were involved in the expression of branching in the F1 and F2 generations; the F2 showing a ratio of 9:7 for branched to unbranched genotypes in the cross FS 277 × NC 70 where both the parents were single shooted. The alleles governing branching, discontinuous clustering, indeterminate growth habit, small leaf size and hairiness were dominant over the alleles controlling non-branching, continuous clustering, determinate growth habit, broad leaf and glabrous leaf and stem. 相似文献
996.
Development of B-Genome Chromosome Addition Lines of B. napus Using Different Interspecific Brassica Hybrids 总被引:3,自引:0,他引:3
By interspecific hybridization within the genus Brassica, trigenomic haploids were produced and back-crossed four times with B. napus, variety ‘Andor’. From this material, monosomic B-genome chromosome addition lines were selected with the extra chromosome derived from three different B-genome sources, i.e., B. nigra (BB), B. carinata (BBCC), and B. juncea (AABB). After selfing and/or microspore culture, disomic addition lines were obtained. Meiotic behavior was studied of the trigenomic hybrids, the pentaploid BC1 plants, and the monosomic addition lines. The addition lines were shown to possess cytological stability and good fertility. 相似文献
997.
Summary Diallel crosses were made between 15 tomato genotypes with varying performance under a low energy regime. It appeared that differences between genotypes for 11 vegetative and generative plant characters are determined mainly by additive genetic variation. For breeding cultivars adapted to low energy conditions, crossing genotypes with a high GCA for weight of trusses and fruits (WTF) and genotypes with a high GCA for weight of vegetative plant parts (WVP) seems most promising. Complications may arise from the negative correlation between GCA values for WTF and WVP, and the strong positive correlation between GCA values for fruit number and WTF, causing small fruits. 相似文献
998.
The current study investigated the effects of oyster mushroom Pleurotus ostreatus, extract on immunological and hematological parameters of rainbow trout, Oncorhynchus mykiss. The fish were fed diets containing 0 (control), 1, and 2% supplementation of the oyster mushroom extract for 6 wk. Blood samples were collected weekly for the first 6 weeks. After 6 wk of feeding, the fish were challenged with Lactococcus garvieae and mortality was recorded. The results of this study showed that feeding rainbow trout an oyster mushroom extract–supplemented diet stimulated phagocytic activity of phagocytic cells, lysozyme activity, and myeloperoxidase activity in serum, but it did not significantly affect the total serum immunoglobulin level. At the same time, a significant increase was found in the number of neutrophils, monocytes, and total white blood cells. Fish fed the diet supplemented with oyster mushroom extract showed reduced mortalities following L. garvieae infection compared with controls. These results show that supplementation of fish diets with oyster mushroom extract at 1 and 2% concentrations significantly imrpoves hematological parameters and modulates the immune response against L. garvieae in rainbow trout. 相似文献
999.
Diurnal measurements of sap velocity were made in 50-, 90-, 150- and 230-year-old mountain ash (Eucalyptus regnans F. Muell.) forests in the North Maroondah catchment (southeast Australia) over the periods January 8, 1990 to April 4, 1990 and October 29, 1990 to April 16, 1991. Over the two periods, daily mean sap velocities for the four forests, in order of increasing age, were 11.5, 11.4, 9.9 and 11.8 cm h(-1) respectively. Daily mean sap velocity did not differ significantly among the 50-, 90- and 230-year-old plots. However, in the 150-year-old trees it was significantly smaller by an average of 14%. Sap velocity varied diurnally and also between positions within individual trees and among trees both within and between stands. Despite this variability, the sampling intensity and duration were sufficient to establish that behavior was highly correlated among individuals within plots. There was a significant decline with age in the overstory sapwood conducting area of these forests. In order of increasing age, the values were 6.7, 6.1, 4.2 and 4.0 m(-2) ha(-1), respectively. When combined with daily mean sap velocity, these data allowed the calculation of overstory water use. Over the experimental period, water use of the overstory decreased with age ranging, on average, from 1.86 mm day(-1) for the 50-year-old plot to 0.81 mm day(-1) for the 230-year-old plot. Mean daily water use for the two intermediate-aged forests was 1.67 and 1.00 mm day(-1), respectively. Annual water use decreased with forest age from 679 mm for the 50-year-old stand to 296 mm for the 230-year-old stand. This difference corresponds to 3.8 x 10(3) m(3) ha(-1). The annual water use of the intermediate-aged stands was 610 and 365 mm for the 90- and 150-year-old stands, respectively. 相似文献
1000.
Audrey G. Quentin Elizabeth A. Pinkard Christopher L. Beadle Timothy J. Wardlaw Anthony P. O’Grady Stephen Paterson Caroline L. Mohammed 《Annals of Forest Science》2010,67(2):203-203