全文获取类型
收费全文 | 18262篇 |
免费 | 110篇 |
国内免费 | 12篇 |
专业分类
林业 | 3759篇 |
农学 | 1383篇 |
基础科学 | 162篇 |
3221篇 | |
综合类 | 862篇 |
农作物 | 2178篇 |
水产渔业 | 1910篇 |
畜牧兽医 | 1781篇 |
园艺 | 1147篇 |
植物保护 | 1981篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 39篇 |
2020年 | 60篇 |
2019年 | 56篇 |
2018年 | 2782篇 |
2017年 | 2744篇 |
2016年 | 1231篇 |
2015年 | 114篇 |
2014年 | 98篇 |
2013年 | 133篇 |
2012年 | 907篇 |
2011年 | 2249篇 |
2010年 | 2183篇 |
2009年 | 1342篇 |
2008年 | 1446篇 |
2007年 | 1687篇 |
2006年 | 129篇 |
2005年 | 187篇 |
2004年 | 191篇 |
2003年 | 231篇 |
2002年 | 160篇 |
2001年 | 38篇 |
2000年 | 59篇 |
1999年 | 16篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 28篇 |
1994年 | 10篇 |
1993年 | 24篇 |
1992年 | 18篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 18篇 |
1987年 | 10篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1971年 | 4篇 |
1968年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A study was conducted to investigate the effects of skid trail slope and traffic levels on soil disturbances at two soil depths
(0–10 and 10–20 cm). The treatments were set at four traffic levels (2, 7, 12 and 20), two slope classes (<20% and >20%) and
two soil depths (0–10 and 10–20 cm). Results show that skidder traffic, longitudinal slope and soil depth have significant
effect on soil bulk density in skid trail. Comparison of average soil bulk density in different traffic levels shows that
there are significant differences in average bulk density between different traffic levels and control (p<0.05). The average bulk densities in different slopes and soil depths are significantly increased with increase in traffic
levels, maximized at 12 passes (p<0.05), but there are no significant differences between 12 and 20 passes. The interaction effects between traffic and soil
depth are significant (F
0.05,3=0.109, p<0.001). For all traffic treatments, there are significant differences in soil moisture content between the two slope classes
and the two depths (p<0.001). However, the interaction effects between traffic levels and slope classes are not significant (p >0.05), although skidder traffic and slope affected soil moisture content. 相似文献
92.
Mir-M Seyedbagheri 《Potato Research》2010,53(4):341-349
Since 1900, soil organic matter (SOM) in farmlands worldwide has declined drastically as a result of carbon turnover and cropping
systems. Over the past 17 years, research trials were established to evaluate the efficacy of different commercial humates
products on potato production. Data from humic acid (HA) trials showed that different cropping systems responded differently
to different products in relation to yield and quality. Important qualifying factors included: source; concentration; processing;
chelating or complexing capacity of the humic acid products; functional groups (Carboxyl; Phenol; Hydroxyl; Ketone; Ester;
Ether; Amine), rotation and soil quality factors; consistency of the product in enhancing yield and quality of potato crops;
mineralization effect; and influence on fertilizer use efficiency. Properties of humic substances, major constituents of soil
organic matter, include chelation, mineralization, buffer effect, clay mineral-organic interaction, and cation exchange. Humates
increase phosphorus availability by complexing ions into stable compounds, allowing the phosphorus ion to remain exchangeable
for plants’ uptake. Collectively, the consistent use of good quality products in our replicated research plots in different
years resulted in a yield increase from 11.4% to the maximum of 22.3%. Over the past decade, there has been a major increase
in the quality of research and development of organic and humic acid products by some well-established manufacturers. Our
experimentations with these commercial products showed an increase in the yield and quality of crops. 相似文献
93.
The hollowness of crosslinked hollow phenolic fibers was regulated successfully from 9 % to 80 % by adjusting the curing temperature
of the partially crosslinked fibers. The partially crosslinked fibers was studied in detail by mass gained, tensile strength,
solvent dissolution, SEM, IR, and TG analysis, and the prepared hollow phenolic fibers with different degrees of hollowness
were characterized with SEM, tensile strength, TG-DSC and TG-MS. The results show that the factor determining the hollowness
is the crosslinked extent of the partially crosslinked fibers and the hollow fibers with different degrees of hollowness have
similar crosslinkage, mechanical properties and thermal stability. 相似文献
94.
Yongju Zhao Jiahua Zhang Hong Wei Xinming Sun Biao Mu Mingju Yu Lingbing Wang 《Tropical animal health and production》2010,42(6):1257-1262
Two experiments were undertaken to select the efficient method applied for goat estrous synchronization. In experiment 1,
a total of 120 does (Capra hircus) were divided into five groups with a randomized block design, and the does of treatment 1 were synchronized by intravaginal
sponges impregnated with 30 mg Levonorgestrel inserted for 10 days. Does of treatments 2, 3, and 4 were treated with further
injection of 25 IU follicle-stimulating hormone (FSH), 0.05 mg prostaglandin F2 alpha (PGF2α), and 25 IU FSH + 0.05 mg PGF2α at sponge withdrawal, respectively. The does in the control group (n = 40) without estrous synchronization treatment and natural estrous does were observed. In experiment 2, a total of 140 does
in five goat farms in breeding and non-breeding seasons were treated with the selective efficient procedure. The results presented
that all the employed treatments were capable of inducing and synchronizing estrous goats. According to estrous response and
economy, the use of intravaginal sponges impregnated with 30 mg Levonorgestrel and 0.05 mg PGF2α (treatment 3) is the first choice for estrous synchronization, and 95.0% of synchronized does demonstrated estrus, which
was significantly higher than that of treatment 1 (P < 0.05) and control group (P < 0.01). The percentages of ovulating of treatments 3 and 4 were the same (95.0%), which were significantly higher than that
of treatment 1 (P < 0.01). The ovulation rates among different groups were not significant (P > 0.05). When the selective procedure was applied to five goat farms, 85.7% (120/140) of does demonstrated estrus, and the
kidding percentage, litter size, and prolificacy rate were 53.6%, 0.95, and 177%, respectively. 相似文献
95.
George Rigos Alexandros Samartzis Morgane Henry Eleni Fountoulaki Efthimia Cotou John Sweetman Simon Davies Ioannis Nengas 《Aquaculture International》2010,18(6):1093-1104
The comparative effects of iron-supplemented levels on growth, tissue distribution, haematology and immunology of gilthead
sea bream, Sparus aurata (2 g) were investigated, using four organic (50, 100, 200, 300 mg ORG/kg diet) and one inorganic iron source (200 INOR mg/kg diet).
Fish were treated for 12 weeks with the experimental diets and maintained at a water temperature of 19–22°C. Growth (final
weight and specific growth rate), tissue distribution (spleen, liver and muscle), haematological parameters (red blood cells,
haematocrit, haemoglobin and mean corpuscular haemoglobin concentration) and non-specific immune indexes (respiratory burst
activity and antibacterial activity of serum) were analysed. No significant differences were found in growth and iron tissue
distribution among the tested groups. Red blood cell counting was statistically higher in fish given 50 ORG, 100 ORG, 200
ORG and 200 INOR feeds. However, haematocrit, haemoglobin and mean corpuscular haemoglobin concentration were not significantly
affected by increasing dietary iron. Fish receiving the 100 ORG diet had the best performance with respect to the respiratory
burst activity and significantly higher values for antibacterial activity of serum were obtained in fish fed with the 300
ORG diet. The present findings provided no clear evidence of the optimum iron concentration. However, there was adequate indication
that iron supplementation enhanced the performance of gilthead sea bream, mainly from a haematological and immunological point
of view. 相似文献
96.
Michal Janáč Luděk Šlapanský Zdenka Valová Pavel Jurajda 《Ecology of Freshwater Fish》2013,22(3):430-438
Several Ponto‐Caspian gobiid species have recently expanded their ranges in Europe and North America. This is the first study to demonstrate passive downstream dispersal (drift) of the round goby (Neogobius melanostomus) and tubenose goby (Proterorhinus semilunaris) in newly colonised areas (River Dyje, Danube basin), a factor that could play an important role in their dispersal. Drift duration (i.e. number of dates on which the species was caught) in round goby was longer than that of both native species and tubenose goby, providing a possible advantage. Size of drifting fish was restricted to a narrow range of 6–8 mm and 5–8 mm for round and tubenose goby, respectively. Drift in both species occurred almost completely during hours of darkness (<1 lux) and fish size did not vary throughout the night. In both species, drift density increased significantly during the first hour after dusk. Round goby density gradually decreased up to dawn, while tubenose goby density varied throughout the night with no clear pattern. Drift of early life stages appears to be an important phenomenon that has not received adequate attention in studies of round and tubenose goby ecology and dispersal. 相似文献
97.
98.
Photochemistry of the herbicide 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) (I) was investigated by irradiating at approximately 313 nm. Aqueous phase photoreactions of 0.078–7.800 × 10?5m solutions of I were carried out at different pH values. Quantum yields for the loss of I in buffered solutions were 0.008 (±0.0004), 0.048 (±0.0024), and 0.044 (±0.0022) at pH 2.6, 7.0, and 11.0, respectively. In neutral and basic conditions, I absorbed more strongly at wavelengths > 290 nm, an environmentally significant region. Phototransformation of I was monitored by HPLC and UV-VIS spectrometry. All photoreactions of I gave rise to the generation of two products, 3-bromo-4-hydroxybenzonitrile and 4-hydroxybenzonitrile. The former photoproduct was tentatively identified from its mass spectral data. The photoproducts can be accounted for with a proposed mechanism involving free radicals. 相似文献
99.
Jan C Ramer Roberto Maria Tim Reichard Peter J Tolson Tai C Chen Michael F Holick 《Journal of zoo and wildlife medicine》2005,36(2):188-191
Calcidiol (25-hydroxyvitamin D) values are reported for 22 wild Ricord's iguanas (Cyclura ricordii) and seven wild rhinoceros iguanas (Cyclura cornuta cornuta). Calcitriol (1,25-hydroxyvitamin D) values are reported for 12 wild Ricord's iguanas and seven wild rhinoceros iguanas. These animals were captured as part of a larger health assessment study being conducted on Ricord's iguanas in Isla Cabritos National Park, Dominican Republic. A total of 13 captive rhinoceros iguanas held outdoors at Parque Zoológico Nacional were also sampled for comparison. Mean concentrations of 25-hydroxyvitamin D were 554 nmol/L (222 ng/ml) with a range of 250-1,118 nmol/L (100-448 ng/ml) for wild Ricord's iguanas, 332 nmol/L (133 ng/ml) with a range of 260-369 nmol/L (104-148 ng/ml) for wild rhinoceros iguanas, and 317 nmol/L (127 ng/ml) with a range of 220-519 nmol/L (88-208 ng/ml) for captive rhinoceros iguanas. On the basis of these results, serum concentrations of at least 325 nmol/L (130 ng/ml) for 25-hydroxyvitamin D should be considered normal for healthy Ricord's and rhinoceros iguanas. 相似文献
100.
Marianne J. Huisman Erik Jongedijk Dinie Posthumus-Lutke Willink Frank Van Der Wilk Ben J. C. Cornelissen 《European journal of plant pathology / European Foundation for Plant Pathology》1992,98(2):29-36
To engineer resistance against potato virus X (PVX), the viral coat protein (CP) gene has been introduced into two potato cultivars. Stable expression of the gene in transgenic clones throughout the growing season has been obtained and resulted in considerably increased virus resistance. With varying frequencies depending on the original cultivar used, true-to-type PVX resistant transgenic clones have been obtained. Since deviant light sprout characteristics were invariably associated with aberrations in plant phenotype, they can be used in procedures to early screen for deviations. Furthermore, it has been possible to unequivocally discriminate between the original untransformed and independent transgenic cultivars. Although no relation has been found between the presence, if any, of the CP of potato virus Y (PVY) or potato leafroll virus (PLRV) in CP gene transgenic potato, appreciable levels of resistance to these viruses has been obtained. This suggests that the mechanism by which a viral CP gene in the potato genome evokes resistance, differs amongst various viruses. 相似文献