全文获取类型
收费全文 | 22706篇 |
免费 | 287篇 |
国内免费 | 835篇 |
专业分类
林业 | 4344篇 |
农学 | 2169篇 |
基础科学 | 546篇 |
3559篇 | |
综合类 | 3012篇 |
农作物 | 2574篇 |
水产渔业 | 2103篇 |
畜牧兽医 | 1962篇 |
园艺 | 1315篇 |
植物保护 | 2244篇 |
出版年
2024年 | 31篇 |
2023年 | 67篇 |
2022年 | 183篇 |
2021年 | 259篇 |
2020年 | 216篇 |
2019年 | 210篇 |
2018年 | 2874篇 |
2017年 | 2908篇 |
2016年 | 1347篇 |
2015年 | 284篇 |
2014年 | 241篇 |
2013年 | 322篇 |
2012年 | 1202篇 |
2011年 | 2518篇 |
2010年 | 2504篇 |
2009年 | 1643篇 |
2008年 | 1657篇 |
2007年 | 1953篇 |
2006年 | 413篇 |
2005年 | 419篇 |
2004年 | 266篇 |
2003年 | 349篇 |
2002年 | 337篇 |
2001年 | 290篇 |
2000年 | 257篇 |
1999年 | 184篇 |
1998年 | 114篇 |
1997年 | 103篇 |
1996年 | 86篇 |
1995年 | 94篇 |
1994年 | 93篇 |
1993年 | 91篇 |
1992年 | 76篇 |
1991年 | 56篇 |
1990年 | 46篇 |
1989年 | 39篇 |
1988年 | 39篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 4篇 |
1969年 | 1篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
Cuprous oxide-modified diatomite waste (Cu2O-DW) as a low-cost and effective adsorbent was prepared via a hydrothermal route combined with acid-alkali treatment. The microstructure and surface properties of the obtained Cu2O-DW composite was characterized by Brunauer-Emmett-Teller, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The adsorption behaviors of three different types of dyes such as cationic dye methyl blue (MB), anionic dye acid orange (AO), and reactive dye reactive yellow (RY) onto the as-prepared Cu2O-DW were investigated. Several experimental parameters such as contact time, adsorbent dosage, initial dye concentration, and initial pH values were systematically estimated. The experimental results indicated that as-prepared Cu2O-DW have a better adsorption performance for MB, AO, and RY. Moreover, the kinetic and isotherm models were also used to account for the adsorption mechanism of dye molecules onto Cu2O-DW. The results demonstrated that three different dyes are all fitted well with pseudo-first-order kinetic model. Additionally, the Langmuir and Freundlich isotherm model is more suitable for describing the adsorption process of RY and MB on the as-prepared Cu2O-DW, respectively, and the AO adsorption is propitious to the D-R isotherm model. The value of adsorption energy (E?<?8 kJ mol?1) confirmed that the physical adsorption is dominator during the adsorption process. The findings of the study demonstrated that the synthesized Cu2O-DW composite can be a promising adsorbent for the removal of organic dyes from wastewater and it provided a sustainable development method for cycling the diatomite waste from the brewery. 相似文献
182.
Lanqing Hong Zhi-Sheng Ye Ran Ling 《Journal of Agricultural, Biological & Environmental Statistics》2018,23(3):390-409
The degradation behavior of an emerging contaminant is a key factor in its environmental risk assessment. Existing risk assessment methods based on EC degradation data commonly neglect the time-varying volatility of the degradation, the possible correlations in degradation between different ECs, and the estimation errors. To fill the gaps, this paper proposes an EC risk assessment framework based on the Wiener process. We first focus on degradation data from competitive experiments, which are adopted to evaluate a useful risk indicator, i.e., the bimolecular rate constant of a degradation reaction. A two-dimensional Wiener process model is developed to capture the degradation behaviors of the target EC and a reference contaminant in the experiment. Point and interval estimations of desired quantities, including the rate constant and the degradation half-life, are developed. We further extend the model to the multivariate case, which is applicable to waste water treatment where multiple ECs degrade in a mixed solution. A risk indicator for the mixed solution is proposed, based on which a minimal treatment time can be determined. Both point and interval estimation procedures of the risk indicator and the minimal treatment time are proposed. Two EC degradation datasets are used to demonstrate the proposed methodologies. Supplementary materials accompanying this paper appear on-line. 相似文献
183.
Reducing CH<Subscript>4</Subscript> and CO<Subscript>2</Subscript> emissions from waterlogged paddy soil with biochar 总被引:1,自引:0,他引:1
Yuxue Liu Min Yang Yimin Wu Hailong Wang Yingxu Chen Weixiang Wu 《Journal of Soils and Sediments》2011,11(6):930-939
Purpose
A potential means to diminish increasing levels of CO2 in the atmosphere is the use of pyrolysis to convert biomass into biochar, which stabilizes the carbon (C) that is then applied to soil. Before biochar can be used on a large scale, especially in agricultural soils, its effects on the soil system need to be assessed. This is especially important in rice paddy soils that release large amounts of greenhouse gases to the atmosphere. 相似文献184.
叶脉是植物水和养分运输的重要通道,其网络结构具有植物种的特异性,也具有环境的适应性。利用LEAF GUI软件定量获取枣、过渡型和酸枣的叶面积、周长、闭合度、节点数等叶脉网络结构特征值,研究其分布规律和变异趋势,并比较了三者之间的差异。结果表明,酸枣的叶脉网络结构特征与枣和过渡型有显著差异;叶脉网络结构特征的变异具有连续性;酸枣的叶面积、网眼数、节点数等特征较枣小,是其对干旱、瘠薄等生长环境的长期适应的结果。 相似文献
185.
Florian Chain Gérard Riault Maxime Trottet Emmanuel Jacquot 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(1):35-43
Serial passage experiments (SPE) of a Barley yellow dwarf virus-PAV (BYDV-PAV) isolate were performed on Zhong ZH and TC14 wheat lines to evaluate the durability of their resistance to BYDV. At different passage numbers (from the 2nd to the 114th), biological properties of the produced isolates were recorded either by monitoring infection percentages and virus titers of the first 3 weeks of viral infection or by measuring their impact on yield components. Statistical analyses using the area under pathogen progress curves and the area under concentration progress curves demonstrated that these two resistant lines induce, after only a few passages, a selection of variant(s) with significantly modified infection abilities. Isolates resulting from SPE performed on these lines induced important decreases of yield components. These results indicate that the use of Zhong ZH and TC14 lines in BYDV-resistant breeding programmes should be approached with caution. 相似文献
186.
187.
Masabumi Komatsu Machiko Taniguchi Norihisa Matsushita Yukiko Takahashi Taizo Hogetsu 《Journal of General Plant Pathology》2010,76(6):363-369
Taphrina wiesneri, the pathogen of witches’ broom of cherry, is highly pathogenic to Cerasus × yedoensis, the most widely planted ornamental cherry species in Japan. For adequate control of this disease, it is necessary to understand
the life history of T. wiesneri. However, sites inhabited by T. wiesneri within infected trees are little understood, except during flowering and leafing periods in spring. Therefore, we attempted
to detect the location of T. wiesneri in shoots of witches’ broom before flowering and leafing in spring using PCR with a T. wiesneri-specific primer pair that was designed from 69 sequences in rDNA-internal transcribed spacer region of 32 Taphrina species. DNA extracted from symptomatic and asymptomatic C. × yedoensis sampled before leafing was amplified by PCR. T. wiesneri was detected in every bud and 5-mm stem segment of symptomatic shoots, except for one stem segment, and locally inside buds
and the inner bark of stem segments. These results indicate that T. wiesneri overwinters inside symptomatic shoots. Fungal hyphae were observed with an epifluorescence microscope in intercellular spaces
of young leaves in symptomatic buds but not in asymptomatic ones in thin sections stained with fluorescein-isothiocyanate-conjugated
concanavalin A. This observation supports the results of PCR detection. 相似文献
188.
Taissir Abou Al Fadil Alain Jauneau Yves Martinez Martina Rickauer Grégory Dechamp-Guillaume 《European journal of plant pathology / European Foundation for Plant Pathology》2009,124(1):93-103
Phoma macdonaldii, the causal agent of black stem disease of sunflower (Helianthus annuus), also attacks roots and collars of the plants, resulting in early death. Totally resistant lines do not exist for infection
of the aerial parts, but tolerant lines have been characterised. This paper presents a study on colonisation of a partially
resistant and a susceptible sunflower line by P. macdonaldii. The fungus was transformed with a constitutively expressed reporter gene encoding the jellyfish green fluorescent protein
via Agrobacterium tumefaciens, and colonisation of sunflower roots by this transformed strain was studied by various microscopy techniques including confocal
and scanning electron microscopy. The results show that penetration of the fungus into the root occurred through natural fissures
or through the epidermis and was similar in both lines. In contrast, the colonisation rate of the stele was reduced in the
partially resistant line, and the morphology of the fungal hyphae was also affected. The effect on hyphal morphology was strongest
in the stele, indicating a localised production of defence compounds in this line. 相似文献
189.
Mestorino N Formentini EA Lucas MF Fernandez C Modamio P Hernández EM Errecalde JO 《Veterinary research communications》2008,32(1):21-33
A comparative pharmacokinetic study was conducted to determine the order and the rate of absorption of triclabendazole (TCBZ)
in cattle and sheep. A commercial suspension of TCBZ (Biofasiolex, Biogénesis S.A., Argentina) was administered at a dose
rate of 10 mg/kg by the oral route to six Holstein female calves and six Corriedale female sheep. The plasma concentration
profiles of the metabolites triclabendazole sulfoxide (TCBZ-SO) and triclabendazole sulfone (TCBZ-SO2) were analysed by means of the non-compartmental method. The order of the absorption process of the active metabolite, TCBZ-SO,
was determined by construction of curves of cumulative absorbed fraction of the drug by means of the Wagner-Nelson method.
The appearance of TCBZ-SO in plasma of cattle and sheep resembles the entry of a constant quantity of drug into the organism
per unit time. This is explained by the reservoir effect of the rumen, which acts as a biological slow-release system for
TCBZ-SO and its precursor TCBZ to the posterior digestive tract where they are absorbed. The plasma concentration profiles
of TCBZ-SO in both species were well described by a one-compartment open model with zero-order process of absorption and first-order
process of elimination. The values of AUC0-∞ and C
max of TCBZ-SO did not differ between species, while other kinetic parameters except for λ
z
had higher values in calves than in sheep. In the case of TCBZ-SO2, t
max was the only parameter that did not differ between species, while other kinetic parameters except for λ
z
had higher values in calves than in sheep. 相似文献
190.
FlordeFátima Rosas-Cárdenas Noé Durán-Figueroa Jean-Philippe Vielle-Calzada Andrés Cruz-Hernández Nayelli Marsch-Martínez Stefan de Folter 《Plant methods》2011,7(1):4