全文获取类型
收费全文 | 3313篇 |
免费 | 230篇 |
国内免费 | 1篇 |
专业分类
林业 | 647篇 |
农学 | 79篇 |
基础科学 | 13篇 |
635篇 | |
综合类 | 287篇 |
农作物 | 119篇 |
水产渔业 | 114篇 |
畜牧兽医 | 1443篇 |
园艺 | 53篇 |
植物保护 | 154篇 |
出版年
2023年 | 21篇 |
2022年 | 20篇 |
2021年 | 31篇 |
2020年 | 51篇 |
2019年 | 21篇 |
2018年 | 111篇 |
2017年 | 112篇 |
2016年 | 112篇 |
2015年 | 74篇 |
2014年 | 106篇 |
2013年 | 209篇 |
2012年 | 225篇 |
2011年 | 190篇 |
2010年 | 94篇 |
2009年 | 88篇 |
2008年 | 173篇 |
2007年 | 171篇 |
2006年 | 168篇 |
2005年 | 164篇 |
2004年 | 162篇 |
2003年 | 160篇 |
2002年 | 141篇 |
2001年 | 99篇 |
2000年 | 105篇 |
1999年 | 54篇 |
1998年 | 29篇 |
1997年 | 27篇 |
1996年 | 20篇 |
1995年 | 58篇 |
1994年 | 17篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1990年 | 29篇 |
1989年 | 27篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 10篇 |
1980年 | 17篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 16篇 |
1973年 | 12篇 |
1972年 | 11篇 |
1970年 | 10篇 |
1969年 | 9篇 |
排序方式: 共有3544条查询结果,搜索用时 31 毫秒
31.
32.
33.
34.
35.
Marine Remize Frdric Planchon Matthieu Garnier Ai Ning Loh Fabienne Le Grand Antoine Bideau Christophe Lambert Rudolph Corvaisier Aswani Volety Philippe Soudant 《Marine drugs》2022,20(1)
The production of polyunsaturated fatty acids (PUFA) in Tisochrysis lutea was studied using the gradual incorporation of a 13C-enriched isotopic marker, 13CO2, for 24 h during the exponential growth of the algae. The 13C enrichment of eleven fatty acids was followed to understand the synthetic pathways the most likely to form the essential polyunsaturated fatty acids 20:5n-3 (EPA) and 22:6n-3 (DHA) in T. lutea. The fatty acids 16:0, 18:1n-9 + 18:3n-3, 18:2n-6, and 22:5n-6 were the most enriched in 13C. On the contrary, 18:4n-3 and 18:5n-3 were the least enriched in 13C after long chain polyunsaturated fatty acids such as 20:5n-3 or 22:5n-3. The algae appeared to use different routes in parallel to form its polyunsaturated fatty acids. The use of the PKS pathway was hypothesized for polyunsaturated fatty acids with n-6 configuration (such as 22:5n-6) but might also exist for n-3 PUFA (especially 20:5n-3). With regard to the conventional n-3 PUFA pathway, Δ6 desaturation of 18:3n-3 appeared to be the most limiting step for T. lutea, “stopping” at the synthesis of 18:4n-3 and 18:5n-3. These two fatty acids were hypothesized to not undergo any further reaction of elongation and desaturation after being formed and were therefore considered “end-products”. To circumvent this limiting synthetic route, Tisochrysis lutea seemed to have developed an alternative route via Δ8 desaturation to produce longer chain fatty acids such as 20:5n-3 and 22:5n-3. 22:6n-3 presented a lower enrichment and appeared to be produced by a combination of different pathways: the conventional n-3 PUFA pathway by desaturation of 22:5n-3, the alternative route of ω-3 desaturase using 22:5n-6 as precursor, and possibly the PKS pathway. In this study, PKS synthesis looked particularly effective for producing long chain polyunsaturated fatty acids. The rate of enrichment of these compounds hypothetically synthesized by PKS is remarkably fast, making undetectable the 13C incorporation into their precursors. Finally, we identified a protein cluster gathering PKS sequences of proteins that are hypothesized allowing n-3 PUFA synthesis. 相似文献
36.
Väli Ülo Mirski Paweł Sein Gunnar Abel Urmas Tõnisalu Grete Sellis Urmas 《Landscape Ecology》2020,35(7):1667-1681
Landscape Ecology - Biodiversity is closely related to landscape heterogeneity, but both are difficult to evaluate directly. Apex predators, such as raptors, are potential surrogate indicators of... 相似文献
37.
Magdalena Mititelu Gabriela Stanciu Doina Drgnescu Ana Corina Ioni Sorinel Marius Neacu Mihaela Dinu Raluca-Ioana Stefan-van Staden Elena Moroan 《Marine drugs》2022,20(1)
(1) Background: The mussel (Mytilus edulis, Mytilus galloprovincialis) is the most widespread lamellibranch mollusk, being fished on all coasts of the European seas. Mussels are also widely grown in Japan, China, and Spain, especially for food purposes. This paper shows an original technique for mussel shell processing for preparation of calcium salts, such as calcium levulinate. This process involves synthesis of calcium levulinate by treatment of Mytilus galloprovincialis shells with levulinic acid. The advantage of mussel shell utilization results in more straightforward qualitative composition. Thus, the weight of the mineral component lies with calcium carbonate, which can be used for extraction of pharmaceutical preparations. (2) Methods: Shell powder was first deproteinized by calcination, then the mineral part was treated with levulinic acid. The problem of shells generally resulting from the industrialization of marine molluscs creates enough shortcomings, if one only mentions storage and handling. One of the solutions proposed by us is the capitalization of calcium from shells in the pharmaceutical industry. (3) Results: The toxicity of calcium levulinate synthesized from the mussel shells was evaluated by the method known in the scientific literature as the Constantinescu phytobiological method (using wheat kernels, Triticum vulgare Mill). Acute toxicity of calcium levulinate was evaluated; the experiments showed the low toxicity of calcium levulinate. (4) Conclusion: The experimental results highlighted calcium as the predominant element in the composition of mussel shells, which strengthens the argument of capitalizing the shells as an important natural source of calcium. 相似文献
38.
Effects of tagging on migration behaviour,survival and growth of hatchery‐reared Atlantic salmon smolts
下载免费PDF全文
![点击此处可从《Fisheries Management and Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
R. Huusko A. Huusko A. Mäki‐Petäys P. Orell J. Erkinaro 《Fisheries Management and Ecology》2016,23(5):367-375
The effects of four different tagging methods (PIT, anchor T‐tag, Carlin tag and dummy radio transmitter) on survival, behaviour and growth of Atlantic salmon smolts during their downstream migration were examined in semi‐natural circular channels during a natural migration period in spring. Survival of smolts was high and tagging wounds healed well in all tagging groups. Tag loss rates were generally low, being the highest (2.5%) in the dummy radio transmitter group. Total length and body mass of the tagged and untagged smolts did not differ at the end of the experiment. Migration activity of smolts generally showed similar patterns among the treatments. However, Carlin‐tagged smolts started their migration slightly later than the PIT‐tagged fish, and smolts tagged with Carlin tag or dummy radio transmitter showed less overall migration activity than fish with PIT tag. 相似文献
39.
Loreida Timberg Kadri Koppel Rain Kuldjärv Edgar Chambers IV Aussama Soontrunnarudrungsri Suntaree Suwonsichon 《Journal Of Aquatic Food Product Technology》2013,22(6):552-566
The aim of the study was to describe and evaluate competitiveness of Estonian spice-cured sprat products in Estonia and Thailand. Sample A was saltiest, Sample B had lowest overall spiciness, and Sample C had highest pepper flavor and sour taste intensity. The main drivers of consumer acceptance for the spice-cured sprat products were different: flavor and appearance in Estonia and appearance and odor in Thailand. In Estonia, one cluster of consumers liked the traditional (Sample A) and lightly spiced (Sample B) sprat products, while the other cluster liked the traditional (Sample A) and the marinated (Sample C) sprat products. In Thailand, all samples scored low, but manual clustering indicated that marinated (Sample C) sprat products are most acceptable. The current study showed that spice-cured sprat products in general can be accepted by Thai consumers, especially as part of meals, if further flavor development is carried out with the products. 相似文献
40.
Environmental effects on soil NO concentrations and root N uptake in beech and spruce forests
下载免费PDF全文
![点击此处可从《植物养料与土壤学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Fang Dong Judy Simon Michael Rienks Jürgen Schäffer Klaus von Wilpert Heinz Rennenberg 《植物养料与土壤学杂志》2016,179(2):244-256
This study aimed to investigate the shifts in net nitrogen (N) uptake and N compounds of fine roots over the vegetation period (i.e., spring, summer, autumn) and correlate this with NO concentration in the soil. Soil NO concentration was measured using gas lysimeters for collection and a chemiluminescence analyzer for quantification. Net N uptake by the roots was determined using the 15N enrichment technique. N pools were quantified using spectrophotometric techniques. Soil NO concentrations at beech and spruce forest sites were highest in spring (June), and lowest in winter (December). Total N of the roots was similar during the seasons and between the two years under study despite considerable variation of different N compounds. Net N uptake generally increased with higher N supply. Correlation analysis revealed a positive relationship between soil NO concentration and net N uptake only for spruce trees. This relationship seemed to be modulated by environmental factors and tree species. 相似文献