全文获取类型
收费全文 | 1534篇 |
免费 | 98篇 |
专业分类
林业 | 138篇 |
农学 | 37篇 |
基础科学 | 5篇 |
278篇 | |
综合类 | 141篇 |
农作物 | 48篇 |
水产渔业 | 120篇 |
畜牧兽医 | 735篇 |
园艺 | 40篇 |
植物保护 | 90篇 |
出版年
2023年 | 7篇 |
2022年 | 13篇 |
2021年 | 37篇 |
2020年 | 29篇 |
2019年 | 44篇 |
2018年 | 32篇 |
2017年 | 40篇 |
2016年 | 33篇 |
2015年 | 25篇 |
2014年 | 39篇 |
2013年 | 85篇 |
2012年 | 83篇 |
2011年 | 111篇 |
2010年 | 45篇 |
2009年 | 45篇 |
2008年 | 92篇 |
2007年 | 68篇 |
2006年 | 75篇 |
2005年 | 71篇 |
2004年 | 65篇 |
2003年 | 58篇 |
2002年 | 60篇 |
2001年 | 38篇 |
2000年 | 29篇 |
1999年 | 31篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 14篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 28篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1972年 | 12篇 |
1969年 | 7篇 |
1968年 | 7篇 |
排序方式: 共有1632条查询结果,搜索用时 15 毫秒
81.
This paper proposes an evolutionary reading of rural development referred to cases of rapid industrial growth, where a strong concentration process has involved the main urban centers and the successful industrial districts. This territorial development pattern has gradually extinguished rural society and its institutional basis, creating a clear separation between new central and peripheral areas. The consequent effects on local economy and social dynamics reveal the long‐term risks raised in terms of development sustainability. An empirical study of two Italian provinces is also carried out to show how this framework can be helpful in interpreting real historical patterns. 相似文献
82.
Two populations of common bean, Phaseolus vulgaris L., were used to make three independent location-specific selections at Palmira, Quilichao, and Popayán, Colombia. Also, three across-location selections were made by alternating generations between Palmira and Popayan, between Quilichao and Popayán, and among Palmira, Quilichao, and Popayán. The seven highest yielding lines selected from each environment and population along with 14 parents and two checks were evaluated for seed yield, seed weight, maturity, and reaction to an-thracnose, angular leaf spot, and common bacterial blight. Mean squares due to evaluation and selection environments, selected lines, and their interactions were significant for all traits. Mean yields of selected lines were higher than the mean of parents in both populations. Among location-specific selections, lines yielded higher at their respective selection site. Moreover, selections made at Popayán were higher yielding than those made at Quilichao or Palmira when tested across locations and years. Use of Popayán, a relatively wetter and cooler site, either alone or in combination with other locations resulted in higher yield, higher seed weight, and higher resistance to anthracnose. On the average, location-specific selections were lower yielding than the across-location selections. Among across-location selections, those selected between Palmira and Popayán were the highest yielding in both populations. Selections at Palmira and across all three locations resulted in greater stability. 相似文献
83.
Summary In this study, the application of molecular markers to optimise genetic diversity in a polycross breeding program of perennial
ryegrass (Lolium perenne L.) was evaluated. The genetic diversity among 98 potential parental plants from three maturity groups (early, intermediate
and late flowering) was investigated using amplified fragment length polymorphism (AFLP) markers. For each maturity group,
two polycrosses of six parental plants with contrasting levels of genetic diversity were composed. Average genetic diversity
among parents selected for narrow polycrosses was 36% lower than among parents selected for wide polycrosses. Diversity within
first generation synthetic progenies (Syn1) was proportional to the diversity within the respective parental polycrosses.
However, differences were less pronounced with Syn1 progenies from narrow polycrosses showing 16% reduced diversity when compared
to Syn1 progenies from wide polycrosses. Multivariate analyses allowed for a clear separation of the six Syn1 progenies based
on AFLP markers and demonstrated their genetic distinctness. Evaluation of dry matter yield, date of ear emergence and stem
length of Syn1 and Syn2 progenies showed progenies from wide polycrosses to be constantly higher yielding when compared to
progenies from narrow polycrosses. On the other hand, there was no significant difference in variability for the two morphological
traits between progenies of narrow- and wide polycrosses. The results presented here provide evidence for an efficient application
of molecular markers to select genetically diverse polycross parents which resulted in an average yield increase of 3.8%. 相似文献
84.
Mulinacci N Innocenti M La Marca G Mercalli E Giaccherini C Romani A Erica S Vincieri FF 《Journal of agricultural and food chemistry》2005,53(23):8963-8969
Solid olive residues (SOR) are byproducts of the olive-milling process, but they have an increasing importance in the pharmaceutical industry due to their rich content of biophenols. Such compounds are studied widely for their antioxidant and antimicrobial activities, but there is a lack of information about their quantitative recovery. This research highlighted the key role played both by the selection of the cultivar and by the degree of olive fruit ripening on the phenolic content on the SOR. The extraction methods were selected to reach the best quantitative results mainly using a safe food solvent. In light of the results the Soxhlet extraction with ethanol could be proposed as preferential for a higher recovery of verbascoside and its analogues. 相似文献
85.
Determining some parameters of capillary moisture transport in porous building materials. Part 1: Deriving the material parameters Various relevant material parameters were defined and their mutual correlations pointed out. By means of simple mathematical approaches, one can calculate several characteristic data such as e.g. water absorption and water penetration coefficients, water capacity, capillary rise maximum, velocity of the rising liquid front and post-suction time. 相似文献
86.
Off-vine grape drying effect on volatile compounds and aromatic series in must from Pedro Ximénez grape variety 总被引:1,自引:0,他引:1
Franco M Peinado RA Medina M Moreno J 《Journal of agricultural and food chemistry》2004,52(12):3905-3910
Changes in 36 volatile compounds of must from ripe grapes dried by direct exposure to sun and must from ripe grapes were studied. Compounds not dependent on sampling site in both musts were selected, and their concentration/Brix degree ratio values, were subjected to variance analysis. Only butan-1-ol and isoamyl alcohols showed no differences, while (E)-hex-3-en-1-ol, (Z)-hex-3-en-1-ol, (E)-hex-2-en-1-ol, (E)-hex-2-enal, hexanoic acid, isobutanol, benzyl alcohol, 2-phenylethanol, gamma-butyrolactone, gamma-hexalactone, and 5-methylfurfural, showed significant differences between the two must types, which may be ascribed to the drying process. An approach to describe must odor has been carried out by grouping volatile compounds in aromatic series, increasing their values in the fruity, solvent, sweet, and roasted series and diminishing the herbaceous as a consequence of the drying process. 相似文献
87.
88.
89.
Fabio Donisete Pezzuto de Andrade Sonia Piacente Cosimo Pizza Wagner Vilegas 《Journal of agricultural and food chemistry》2002,50(2):255-261
The isolation of three new triterpene saponins 3beta-O-beta-D-glucopyranosyl-(1-->3)-alpha-L-2-O-acetylarabinopyranosylolean-12-en-28-oic acid 28-O-beta-D-glucopyranosyl ester (2), 3beta-O-beta-D-glucopyranosyl-(1-->2)-alpha-L-O-arabinopyranosylurs-12-en-28-oic acid (3), and 3beta-O-beta-D-glucopyranosyl-(1-->2)-beta-D-O-galactopyranosylurs-12-en-28-oic acid (4) together with five known saponins and one flavonoid glycoside from the aqueous infusion of Ilex amara (Vellozo) Loes. leaves is reported. All structures were elucidated by spectroscopic methods, including the concerted application of one-dimensional (1H, TOCSY, 13C, and 13C DEPT NMR) and two-dimensional NMR techniques (DQF-COSY, HSQC, and HMBC). 相似文献
90.
Characterization of commercial kava-kava herbal drug and herbal drug preparations by means of nuclear magnetic resonance spectroscopy 总被引:1,自引:0,他引:1
Bilia AR Bergonzi MC Lazari D Vincieri FF 《Journal of agricultural and food chemistry》2002,50(18):5016-5025
The efficiency of one- and two-dimensional NMR experiments in characterizing the content of the constituents of both herbal drugs and herbal drug preparations is demonstrated for kava-kava. These experiments directly detect active constituents represented by kavalactones in both a finely powdered herbal drug and a commercial extract. In addition, NMR spectroscopy can detect all other compounds present in the extract. As previously evidenced, NMR experiments can represent a generally applicable technique for rapid screening and are a complement to the classical analytical techniques such as high-performance thin-layer chromatography, high-performance liquid chromatography, capillary gas chromatography, and electrophoresis. These experiments can be considered a very simple and fast analytical method to obtain a fingerprint of the herbal drugs and their preparations, and to quantify the content of the active principles of the extract. 相似文献