全文获取类型
收费全文 | 13126篇 |
免费 | 850篇 |
国内免费 | 47篇 |
专业分类
林业 | 1140篇 |
农学 | 546篇 |
基础科学 | 128篇 |
3443篇 | |
综合类 | 452篇 |
农作物 | 712篇 |
水产渔业 | 1368篇 |
畜牧兽医 | 4898篇 |
园艺 | 249篇 |
植物保护 | 1087篇 |
出版年
2024年 | 21篇 |
2023年 | 95篇 |
2022年 | 174篇 |
2021年 | 318篇 |
2020年 | 300篇 |
2019年 | 295篇 |
2018年 | 553篇 |
2017年 | 566篇 |
2016年 | 568篇 |
2015年 | 440篇 |
2014年 | 543篇 |
2013年 | 824篇 |
2012年 | 960篇 |
2011年 | 944篇 |
2010年 | 571篇 |
2009年 | 509篇 |
2008年 | 782篇 |
2007年 | 762篇 |
2006年 | 629篇 |
2005年 | 561篇 |
2004年 | 533篇 |
2003年 | 488篇 |
2002年 | 376篇 |
2001年 | 304篇 |
2000年 | 307篇 |
1999年 | 260篇 |
1998年 | 67篇 |
1997年 | 68篇 |
1996年 | 55篇 |
1995年 | 54篇 |
1994年 | 34篇 |
1993年 | 32篇 |
1992年 | 76篇 |
1991年 | 58篇 |
1990年 | 56篇 |
1989年 | 64篇 |
1988年 | 51篇 |
1987年 | 54篇 |
1986年 | 52篇 |
1985年 | 63篇 |
1984年 | 42篇 |
1983年 | 44篇 |
1982年 | 27篇 |
1979年 | 48篇 |
1978年 | 42篇 |
1977年 | 31篇 |
1974年 | 32篇 |
1973年 | 55篇 |
1972年 | 37篇 |
1971年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Benigno González-Rivas Mulualem Tigabu Guillermo Castro-Marín Per Christer Odén 《林业研究》2009,20(2):99-104
A study was conducted to examine the germination requirements of Cedrela odorata, Guaiacum sanctum and Calycophyllum candidissimum seeds, and the effect of light intensity on survival and growth of C. Odorata and G. Sanctum seedlings planted on open, partially-open and beneath the canopy of a dry forest in Nicaragua. The results show that germination of C. Candidissimum seeds was significantly higher in light than darkness at constant temperatures ranging from 20–35oC. Both C. Odorata and G. Sanctum seeds germinated in light and darkness to a varying extent, and the optimal germination temperature was around 20-25oC. Alternating temperature regimes did not improve germination. Survival of G. Sanctum seedlings was 70% beneath the canopy and 80% in the open, and its relative growth rate in collar diameter was 1.88 mm/month in the open and 1.42 mm/month in the understory. Survival was generally poor for C. Odorata, particularly in the understory. We concluded that light is an absolute requirement for the germination of C. Candidissimum seeds while germination of C. Odorata and G. Sanctum seeds are more sensitive to temperature. Owing to its high survival rate on open site, G. Sanctum could serve as a candidate species for reforestation of degraded sites. 相似文献
992.
Juan A. Oliet María Tejada K. Francis Salifu Aleyda Collazos Douglass F. Jacobs 《European Journal of Forest Research》2009,128(3):253-263
Holm oak (Quercus ilex L.) seedlings were exponentially (E) nutrient loaded using incremental increases in fertilizer addition or conventionally
(C) fertilized using a constant fertilizer rate during nursery culture. The fertility treatments (mg N plant−1) were control (0), 25E, 100E, and 100C. Subsequently, 1-year-old plants were transplanted under simulated soil fertility
gradients in a greenhouse to evaluate effects of nutrient loading and post-transplant fertility on seedling performance. Post-transplant
fertility consisted of fertilizing plants at two rates (0 vs. 200 mg N plant−1). A water-soluble fertilizer 20-20-20 was supplied in both nursery and post-transplant experiments. Nutrient loading increased
plant N content by 73% in 100E and by 75% in 100C relative to controls, although no significant differences were detected
between constant and exponential fertilization regimes at the 100 mg N plant−1 rate. When transplanted, nutrient loading promoted post-transplant root growth relative to shoot, implicating potential to
confer competitive advantage to loaded holm oak seedlings after trans-planting. In contrast, post-transplant fertility increased
new shoot dry mass by 140% as well as N, P and K content relative to controls. Results suggest that holm oak seedlings can
be successfully nutrient loaded in the nursery at higher fertility rates, improving its potential to extend new roots, but
alternative fertilization regimes and schedules that better fit nutrient availability to the growth rhythm and conservative
strategy of this species must be tested. 相似文献
993.
Empirical models for predicting the production of wild mushrooms in Scots pine (Pinus sylvestris L.) forests in the Central Pyrenees 总被引:1,自引:0,他引:1
José Antonio Bonet Timo Pukkala Christine R. Fischer Marc Palahí Juan Martínez de Aragón Carlos Colinas 《Annals of Forest Science》2008,65(2):206-206
Mushroom picking has become a widespread autumn recreational activity in the Central Pyrenees and other regions of Spain. Predictive models that relate mushroom production or fungal species richness with forest stand and site characteristics are not available. This study used mushroom production data from 24 Scots pine plots over 3 years to develop a predictive model that could facilitate forest management decisions when comparing silvicultural options in terms of mushroom production. Mixed modelling was used to model the dependence of mushroom production on stand and site factors. The results showed that productions were greatest when stand basal area was approximately 20 m2 ha?1. Increasing elevation and northern aspect increased total mushroom production as well as the production of edible and marketed mushrooms. Increasing slope decreased productions. Marketed Lactarius spp., the most important group collected in the region, showed similar relationships. The annual variation in mushroom production correlated with autumn rainfall. Mushroom species richness was highest when the total production was highest. 相似文献
994.
Miren del Río Rafael Calama Isabel Cañellas Sonia Roig Gregorio Montero 《Annals of Forest Science》2008,65(3):308-308
The effect of different thinning intensities on growth and yield was studied in Pinus sylvestris L. stands at the south-western limit of its distribution area (Central Spain), using five long-term thinning trials. Data were analysed collectively considering several factors (trial, block, plot and period) as random effects. Total volume and volume increment decreased with thinning intensity, this loss being more significant in the case of moderate and heavy thinning. No difference was found among treatments for total basal area or the increment in basal area. The results revealed an optimum basal area (Assmann’s definition) between 85 and 100% of the basal area in unthinned plots. Volume growth loss associated with heavy thinnings (reduction of 18% in volume increment) was smaller than that reported in Central and Northern European regions (greater than 25%). Height increment was not influenced by thinning, whereas dominant and quadratic mean diameter increments increased with the thinning intensity. The response of diameter growth to thinning was greater at younger ages (less than 50 y) and in medium-sized trees. 相似文献
995.
Jaime Puértolas Marta Pardos María Dolores Jiménez Ismael Aranda José Alberto Pardos 《Annals of Forest Science》2008,65(6):611-611
996.
997.
Arnulfo Blanco-García Cuauhtémoc Sáenz-Romero Pedro Alvarado-Sosa Roberto Lindig-Cisneros 《New Forests》2008,36(3):299-305
Under heavily disturbed conditions, the selection of the appropriate native species and of planting and ameliorating techniques
is necessary. Volcanic eruptions create harsh conditions that can preclude native plant establishment. We tested the performance
of two native species Pinus pseudostrobus and P. montezumae for restoration of volcanic ash covered areas. Two age classes of P. pseudostrobus and one of P. montezumae were tested as well as the effect of mulching to ameliorate harsh substrate conditions. Results show that older plants of
P. pseudostrobus (19-month old at planting) have higher survival and growth rates than young plants (8-months at planting). Plants at least
19-months-old at planting of P. pseudostrobus and P. montezumae, are appropriate for restoration of volcanic ash covered areas. Mulching had no effect on plant survival or growth for this
experiment. 相似文献
998.
Eugenio Díaz-Pinés Andreas Schindlbacher Michael Pfeffer Robert Jandl Sophie Zechmeister-Boltenstern Agustín Rubio 《European Journal of Forest Research》2010,129(1):101-109
We conducted a trenching experiment in a mountain forest in order to assess the contribution of the autotrophic respiration
to total soil respiration and evaluate trenching as a technique to achieve it. We hypothesised that the trenching experiment
would alter both microbial biomass and microbial community structure and that fine roots (less than 2 mm diameter) would be
decomposed within one growing season. Soil CO2 efflux was measured roughly biweekly over two growing seasons. Root presence and morphology parameters, as well as the soil
microbial community were measured prior to trenching, 5 and 15 months after trenching. The trenched plots emitted about 20
and 30% less CO2 than the control plots in the first and second growing season, respectively. Roots died in trenched plots, but root decay
was slow. After 5 and 15 months, fine root biomass was decreased by 9% (not statistically different) and 30%, (statistically
different) respectively. When we corrected for the additional trenched-plot CO2 efflux due to fine root decomposition, the autotrophic soil respiration rose to ~26% of the total soil respiration for the
first growing season, and to ~44% for the second growing season. Soil microbial biomass and community structure was not altered
by the end of the second growing season. We conclude that trenching can give accurate estimates of the autotrophic and heterotrophic
components of soil respiration, if methodological side effects are accounted for, only. 相似文献
999.
P. Álvarez-Álvarez E. Díaz-Varela A. Cámara-Obregón E. Afif-Khouri 《Agroforestry Systems》2010,79(3):291-301
The growth and nutritional status of 97 hybrid chestnut plantations on former agricultural land and forest land were studied
in relation to site conditions (climatic variables and soil properties). A single family of curves was obtained for classifying
the early height growth of hybrid and sweet chestnut. Soil limitations and nutrient deficiencies were evident in the former
forest land, whereas the agricultural soils were found to be generally suitable for growing chestnut. The stands with highest
growth rates were characterized by high foliar concentrations of K, P and Ca. Successful growth of the plantations was always
related to high summer precipitation, low elevation and absence of long periods of risk of frost. The results confirm the
adaptability of chestnut to most sites where it has been planted for timber production. 相似文献
1000.
L. Di Toto Blessing O. Álvarez Colom S. Popich A. Neske A. Bardón 《Journal of pest science》2010,83(3):307-310
Several species of the large family of tropical plants Annonaceae have been intensely investigated over the last 20 years,
mainly because of the discovery of annonaceous acetogenins. These compounds are powerful cytotoxics, with potential applications
as insecticides, antiparasitics, acaricides, fungicides, and antitumor drugs. Annona montana Macfad. (Annonaceae) grows in Santa Cruz de la Sierra, Bolivia, where an infusion of leaves is used for the treatment of
lice, influenza, and insomnia. The major acetogenins from a Bolivian collection of A. montana, annonacin (1), cis-annonacin-10-one (2), densicomacin-1 (3), gigantetronenin (4), murihexocin-B (5), and tucupentol (6), were evaluated for their antifeedant and toxic effects on Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), a serious pest affecting corn crops in Argentina. All the acetogenins produced 100% mortality
during the larval or pupal stages at 100 μg of treatment per gram of diet. In addition, compounds 2, 3, and 4 deterred more than 80% feeding at the same dose. Relative toxicity values of LD50 for the strongest larvicidal compounds 1, 2, and 4 were determined, indicating that the three compounds are effective natural insecticides. This is the first report on the
antifeedant and toxic effects produced by the particular type of acetogenins, the mono-THF acetogenins, on the lepidopteran
S. frugiperda. No correlation was detected between the toxicity of the mentioned compounds to larvae and the known capacity of the acetogenins
1, 2, and 4 to inhibit the NADH oxidase, indicating that the inhibition of the mitochondrial complex I is not the only cause for larval
mortality of S. frugiperda. 相似文献