全文获取类型
收费全文 | 10677篇 |
免费 | 799篇 |
国内免费 | 50篇 |
专业分类
林业 | 687篇 |
农学 | 497篇 |
基础科学 | 86篇 |
1850篇 | |
综合类 | 704篇 |
农作物 | 573篇 |
水产渔业 | 936篇 |
畜牧兽医 | 5012篇 |
园艺 | 185篇 |
植物保护 | 996篇 |
出版年
2023年 | 96篇 |
2022年 | 198篇 |
2021年 | 343篇 |
2020年 | 371篇 |
2019年 | 436篇 |
2018年 | 410篇 |
2017年 | 433篇 |
2016年 | 430篇 |
2015年 | 292篇 |
2014年 | 401篇 |
2013年 | 630篇 |
2012年 | 651篇 |
2011年 | 701篇 |
2010年 | 361篇 |
2009年 | 398篇 |
2008年 | 544篇 |
2007年 | 528篇 |
2006年 | 462篇 |
2005年 | 415篇 |
2004年 | 392篇 |
2003年 | 341篇 |
2002年 | 380篇 |
2001年 | 278篇 |
2000年 | 278篇 |
1999年 | 222篇 |
1998年 | 72篇 |
1997年 | 66篇 |
1996年 | 69篇 |
1995年 | 59篇 |
1994年 | 41篇 |
1993年 | 41篇 |
1992年 | 85篇 |
1991年 | 57篇 |
1990年 | 67篇 |
1989年 | 74篇 |
1988年 | 70篇 |
1987年 | 54篇 |
1986年 | 47篇 |
1985年 | 62篇 |
1984年 | 42篇 |
1983年 | 46篇 |
1982年 | 31篇 |
1981年 | 23篇 |
1980年 | 27篇 |
1979年 | 39篇 |
1977年 | 23篇 |
1974年 | 23篇 |
1973年 | 27篇 |
1972年 | 25篇 |
1970年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Harmful algal blooms pose a challenge regarding food safety due to their erratic nature and forming circumstances which are yet to be disclosed. The best strategy to protect human consumers is through legislation and monitoring strategies. Global warming and anthropological intervention aided the migration and establishment of emerging toxin producers into Europe’s temperate waters, creating a new threat to human public health. The lack of information, standards, and reference materials delay effective solutions, being a matter of urgent resolution. In this work, the recent findings of the presence of emerging azaspiracids, spirolildes, pinnatoxins, gymnodimines, palitoxins, ciguatoxins, brevetoxins, and tetrodotoxins on European Coasts are addressed. The information concerning emerging toxins such as new matrices, locations, and toxicity assays is paramount to set the risk assessment guidelines, regulatory levels, and analytical methodology that would protect the consumers. 相似文献
103.
Here we report on the frequency of melanized fungal hyphae in 323 soils, covering different land use types. The proportion of total hyphae that was melanized averaged 61%. Arable fields with loamy sand, heathlands and city parks on sandy soils had the highest percentage of melanized hyphae. In addition to the frequency determinations, a microcosm study was performed on the role of melanized hyphae in two different ecosystems: an ex-arable field and a forest. Melanized hyphae appeared to be part of the active hyphae in the forest soil but not in the ex-arable soil. In conclusion, our results indicate that (1) melanized hyphae represent a large proportion of the total fungal biomass in soils and that (2) their function might differ between ecosystems. 相似文献
104.
Airon José da Silva Clístenes Williams Araújo do Nascimento Artur da Silva Gouveia-Neto Elias Arcanjo da Silva-Jr 《Water, air, and soil pollution》2012,223(6):3527-3533
Chlorophyll fluorescence spectral analysis permits detection, monitoring, and evaluation of abiotic stresses upon healthy plants using illumination of a light source in the UV?CVIS spectral range. This technique indirectly assesses the amount of physiological stress caused by photosynthetic damage, specifically damage to photosystem II, in plants. The objective of this study was to detect the toxicity of cadmium in maize plants via spectral analysis of chlorophyll fluorescence. The analysis is noninvasive and nondestructive and is used to follow the temporal evolution of changes in the chlorophyll content and physiological state of Zea mays L. seedlings under cadmium stress. Conventional techniques were also used to evaluate the dry matter production and Cd accumulation in plant leaves. Plants exhibited a notable reduction in dry matter production and chlorophyll levels with the administration of increasing doses of Cd in the nutrient solution. The fluorescence analysis was sensitive to changes caused by Cd in maize plants, detecting damage caused by different treatments before visual symptoms were observed. This technique has a practical application and produces rapid results that can be used in the evaluation of Cd-induced stress in plants and the detection of areas contaminated by this element. 相似文献
105.
Gonzálvez A Armenta S Pastor A de la Guardia M 《Journal of agricultural and food chemistry》2008,56(13):4943-4954
Different sample preparation methods were evaluated for the simultaneous multielement analysis of wine samples by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). Microwave-assisted digestion in closed vessel, thermal digestion in open reactor, and direct sample dilution were considered for the determination of Li, Be, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Y, Mo, Cd, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Tl, Pb, and Bi in 12 samples of red wine from Valencia and Utiel-Requena protected designation of origin. ICP-MS allows the determination of 17 elements in most of the samples, and using ICP-OES, a maximum of 15 elements were determined. On comparing the sample pretreatment methodology, it can be concluded that the three assayed procedures provide comparable results for the concentration of Li, Na, Mg, Al, K, Ca, Mn, Fe, Zn, and Sr by ICP-OES. Furthermore, ICP-MS data found for Cu, Pb, and Ba were comparable. Digestion treatment provides comparable values using both total decomposition in open system and microwave-assisted treatment for Cu by ICP-OES and for Cr, Ni, and Zn by ICP-MS. Open vessel total digestion provides excess values for Cr, Mn, Fe, and Zn by ICP-OES and defect values for Se. However, direct measurement of diluted wine samples provided uncomparable results with the digestion treatment for Mn, Cu, Pb, Zn, Ba, and Bi by ICP-OES and for Mg, Cr, Fe, Ni, and Zn by ICP-MS. Therefore, it can be concluded that microwave-assisted digestion is the pretreatment procedure of choice for elemental analysis of wine by ICP-based techniques. 相似文献
106.
Itamar Cristiano Nava Carla Andréa Delatorre Ismael T. de Lima Duarte Marcelo Teixeira Pacheco Luiz Carlos Federizzi 《Euphytica》2006,148(3):353-358
Summary Aluminum toxicity due to the cation Al+3 is a major factor limiting yields in acid soils. Wide genetic variability to aluminum tolerance is found in oat genotypes. The objectives of this study were to determine the number of genes controlling aluminum tolerance in oats and to verify if any detrimental effects were present of the aluminum tolerance genes on grain yield and grain quality in Al+3free soils. Aluminum tolerance was estimated as the average regrowth of the main root after exposure to toxic levels of Al+3 in a hydroponic solution under controlled conditions. The number of genes controlling that trait was estimated from the distribution of the average root regrowth frequencies in a population of 333 recombinant inbred lines (RIL's) in generations F5:6 and F5:7. The effects on grain yield and grain quality were assessed in a subpopulation of 162 RIL's chosen based on their aluminum tolerance response. Aluminum tolerance in the evaluated population was controlled by one dominant major gene with the tolerant genotypes carying Al
a
Al
a
and the sensitive ones al
a
al
a
alleles. No detrimental effects of the Al
a
allele on grain yield or grain quality were detected.Part of the Master of Science dissertation of the first author 相似文献
107.
The mechanism that controls the proportion of cannabichromene (CBC), a potential pharmaceutical, in the cannabinoid fraction
of Cannabis sativa L. is explored. As with tetrahydrocannabinol (THC) and cannabidiol (CBD), CBC is an enzymatic conversion product of the precursor
cannabigerol (CBG). CBC is reported to dominate the cannabinoid fraction of juveniles and to decline with maturation. This
ontogeny was confirmed in inbred lines with different mature chemotypes. A consistent CBC presence was found in early leaves
from a diverse clone collection, suggesting that CBC synthase is encoded by a fixed locus. Morphological variants possessing
a ‘prolonged juvenile chemotype’ (PJC), a substantial proportion of CBC persisting up to maturity, are presented. PJC is associated
with a reduced presence of floral bracts, bracteoles, and capitate-stalked trichomes. Genetic factors causing these features
were independent of the allelic chemotype locus B that was previously postulated and regulates THC and CBD synthesis and CBG accumulation. In contrast to previously described
Cannabis chemotypes, the cannabinoid composition of PJCs showed plasticity in that reduced light levels increased the CBC proportion.
The ability of PJC plants to enable the production of pharmaceutical raw material with high CBC purity is demonstrated. 相似文献
108.
Fabrício Alves Oliveira Derly José Henriques da Silva Germano Leão Demolin Leite Gulab Newandram Jham Marcelo Picanço 《Scientia Horticulturae》2009
The aim of this study was to evaluate resistance to Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) by antixenosis on 57 Lycopersicon esculentum Mill. accessions from the Horticultural Germplasm Bank (HGB) of Universidade Federal de Viçosa and by the three commercial cultivars (Santa Clara, Moneymaker and TOM-601) under greenhouse conditions. A randomized complete block design was used with three replications. Infestations with T. absoluta adults were performed weekly and the following characteristics were evaluated: number of small, large and total mines/leaf and % of leaves mined at days 60, 75 and 90 after planting. Low infestation occurred at days 60 and 75 but at day 90, infestation was sufficient to evaluate insect damage. Based on these data it was concluded that only accessions HGB-674 and HGB-1497 appeared to be the most promising. In addition, to determine possible chemical causes of resistance, hexane extracts were analyzed at day 90 by gas chromatography/mass spectrometry and the major peaks identified by a mass spectral database using similarity index. Nine hydrocarbons, viz., hexadecane, heptadecane, eicosane, tricosane, 2-methyltricosane, tetracosane, hexacosane, octacosane and triacontane were identified in the hexane extracts in many samples. Tricosane, tetracosane and hexacosane presented significant correlations with the leaves mined. Only tricosane presented a negative correlation with the number of small mines (r = −0.28), total number of mines (r = −0.27) and % of leaves mined (r = −0.22). However, tetracosane and hexacosane presented significant positive correlations (r = 0.25 and 0.24, respectively) with the % of leaves mined. 相似文献
109.
110.
Antoine LF Gady Freddy WK Hermans Marion HBJ Van de Wal Eibertus N van Loo Richard GF Visser Christian WB Bachem 《Plant methods》2009,5(1):13-14