全文获取类型
收费全文 | 8787篇 |
免费 | 544篇 |
国内免费 | 50篇 |
专业分类
林业 | 541篇 |
农学 | 447篇 |
基础科学 | 82篇 |
1590篇 | |
综合类 | 632篇 |
农作物 | 444篇 |
水产渔业 | 663篇 |
畜牧兽医 | 4048篇 |
园艺 | 124篇 |
植物保护 | 810篇 |
出版年
2023年 | 82篇 |
2022年 | 144篇 |
2021年 | 269篇 |
2020年 | 256篇 |
2019年 | 323篇 |
2018年 | 289篇 |
2017年 | 310篇 |
2016年 | 325篇 |
2015年 | 222篇 |
2014年 | 306篇 |
2013年 | 488篇 |
2012年 | 495篇 |
2011年 | 546篇 |
2010年 | 274篇 |
2009年 | 301篇 |
2008年 | 454篇 |
2007年 | 439篇 |
2006年 | 394篇 |
2005年 | 362篇 |
2004年 | 339篇 |
2003年 | 305篇 |
2002年 | 340篇 |
2001年 | 243篇 |
2000年 | 245篇 |
1999年 | 204篇 |
1998年 | 60篇 |
1997年 | 58篇 |
1996年 | 58篇 |
1995年 | 52篇 |
1994年 | 38篇 |
1993年 | 40篇 |
1992年 | 81篇 |
1991年 | 53篇 |
1990年 | 62篇 |
1989年 | 68篇 |
1988年 | 62篇 |
1987年 | 52篇 |
1986年 | 47篇 |
1985年 | 58篇 |
1984年 | 39篇 |
1983年 | 44篇 |
1982年 | 31篇 |
1980年 | 24篇 |
1979年 | 38篇 |
1978年 | 21篇 |
1977年 | 21篇 |
1974年 | 24篇 |
1973年 | 26篇 |
1972年 | 24篇 |
1970年 | 26篇 |
排序方式: 共有9381条查询结果,搜索用时 0 毫秒
71.
Raúl E. Cian Silvina R. Drago Fermín Sánchez de Medina Olga Martínez-Augustin 《Marine drugs》2015,13(8):5358-5383
Based on their composition, marine algae, and namely red seaweeds, are good potential functional foods. Intestinal mucosal barrier function refers to the capacity of the intestine to provide adequate containment of luminal microorganisms and molecules. Here, we will first outline the component of seaweeds and will summarize the effects of these on the regulation of mucosal barrier function. Special attention will be paid to unique components of red seaweeds: proteins and derived peptides (e.g., phycobiliproteins, glycoproteins that contain “cellulose binding domains”, phycolectins and the related mycosporine-like amino acids) together with polysaccharides (e.g., floridean starch and sulfated galactans, such as carrageenans, agarans and “dl-hybrid”) and minerals. These compounds have been shown to exert prebiotic effects, to regulate intestinal epithelial cell, macrophage and lymphocyte proliferation and differentiation and to modulate the immune response. Molecular mechanisms of action of peptides and polysaccharides are starting to be elucidated, and evidence indicating the involvement of epidermal growth factor receptor (EGFR), insulin-like growth factor receptor (IGFR), Toll-like receptors (TLR) and signal transduction pathways mediated by protein kinase B (PKB or AKT), nuclear factor-κB (NF-κB) and mitogen activated protein kinases (MAPK) will also be summarized. The need for further research is clear, but in vivo experiments point to an overall antiinflammatory effect of these algae, indicating that they can reinforce membrane barrier function. 相似文献
72.
Ana Flavia Camara Bezerra Laura Hecker de Carvalho Wilma Sales Cavalcanti Antonio Gilson Barbosa 《Fibers and Polymers》2016,17(11):1908-1915
Composites were prepared with 13, 23 30 and 40 % fiber and evaluated the mechanical performance in tensile, flexural and impact. The mechanical properties of these composites were also evaluated function of time at 110 °C thermal exposure. Caroa fibers were characterized by techniques such as thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the best mechanical properties were achieved for composites containing 23 to 30 % fiber. The incorporation of 23 % fiber caroa increased both the modulus of elasticity in the tensile test as the flexural strength and impact, the composite with 30 % fiber caroa showed higher tensile strength. The results show that the tensile and flexural strength of the composite decreased with time of thermal exposure. The thermal aging at 110 °C caused a decrease in tensile properties of the composites. 相似文献
73.
74.
Luiz Henrique Agra Cavalcante-Silva Ana Carolina de Carvalho Correia José Maria Barbosa-Filho Bagnólia Araújo da Silva Bárbara Viviana de Oliveira Santos Daysianne Pereira de Lira Jéssica Celestino Ferreira Sousa George Emmanuel C. de Miranda Fabiana de Andrade Cavalcante Magna Suzana Alexandre-Moreira 《Marine drugs》2013,11(5):1553-1564
In this work, we investigated the spasmolytic effect of caulerpine, a bisindole alkaloid isolated from marine algae of the Caulerpa genus, on guinea pig ileum. Our findings indicated that caulerpine inhibited phasic contractions induced by carbachol (IC50 = 7.0 ± 1.9 × 10−5 M), histamine (IC50 = 1.3 ± 0.3 × 10−4 M) and serotonin (IC50 = 8.0 ± 1.4 × 10−5 M) in a non-selective manner. Furthermore, caulerpine concentration-dependently inhibited serotonin-induced cumulative contractions (pD′2 = 4.48 ± 0.08), shifting the curves to the right with Emax reduction and slope of 2.44 ± 0.21, suggesting a noncompetitive antagonism pseudo-irreversible. The alkaloid also relaxed the ileum pre-contracted by KCl (EC50 = 9.0 ± 0.9 × 10−5 M) and carbachol (EC50 = 4.6 ± 0.7 × 10−5 M) in a concentration-dependent manner. This effect was probably due to inhibition of Ca2+ influx through voltage-gated calcium channels (CaV), since caulerpine slightly inhibited the CaCl2-induced contractions in depolarizing medium without Ca2+, shifting the curves to the right and with Emax reduction. According to these results, the spasmolytic effect of caulerpine on guinea pig ileum seems to involve inhibition of Ca2+ influx through CaV. However, other mechanisms are not discarded. 相似文献
75.
76.
Aparicio-Fernández X Reynoso-Camacho R Castaño-Tostado E García-Gasca T González de Mejía E Guzmán-Maldonado SH Elizondo G Yousef GG Lila MA Loarca-Pina G 《Plant foods for human nutrition (Dordrecht, Netherlands)》2008,63(1):35-40
Jamapa bean is a black Phaseolus vulgaris variety rich in condensed tannins, anthocyanins and flavonols with interesting biological activities. The objective of this
work was to evaluate the antiradical capacity (ARC) of a Jamapa bean methanolic extract (BME) and some of the proanthocyanidin-rich
fractions derived from it, using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The effect of the BME on some proteins involved
in apoptosis on HeLa cells was also evaluated. A strong correlation between proanthocyanidin concentration in BME and antiradical
capacity was found, suggesting that these compounds contribute significantly to antiradical activity. BME was a better radical
scavenger than butylated hydroxytoluene (45.6 and 33.9% ARC at 400 μM, respectively). Two proanthocyanidin-rich fractions
obtained after a preliminary separation of the BME using Toyopearl (TP4 and TP6) exhibited a higher antiradical activity than
the parent extract. The treatment of HeLa cells with 35 μg BME/ml/24 h increased the expression of Bax and Caspase-3, pro-apoptotic
proteins (6.13 and 1.2 times for Caspase-3 and Bax, respectively). The mechanism of action of some proteins involved in apoptosis
was also evaluated, and the results suggest that black Jamapa bean could be an important source of polyphenolic compounds
with potential biological use as antioxidant and anticancer agents. 相似文献
77.
78.
Adriana Vella Sinéad Murphy Joan Giménez Renaud de Stephanis Barbara Mussi Joseph G. Vella Kamel Larbi Doukara Daniela Silvia Pace 《水产资源保护:海洋与淡水生态系统》2021,31(Z1):110-136
- Preservation of endangered species is now recognized as a relevant component of regional and global conservation actions achieved through the maintenance of the remaining populations in a favourable conservation status. The Mediterranean common dolphin (Delphinus delphis) is listed as an Endangered subpopulation in the International Union for Conservation of Nature Red List, with declining numbers in some of the areas where it has been studied for numerous years. Prey depletion, fisheries bycatch, pollution, health risks, and climate change are among the recognized threats that the species is facing in the region.
- The existing national, regional, and international legislation pertinent to Mediterranean countries should aid greater science–policy–management integration and support innovative research and monitoring towards effective conservation. The challenges inherent in studying the pelagic D. delphis should not preclude the use of long-term, year-round, multiplatform surveys, side by side with the latest molecular tools, which aid our understanding of its populations' genetic diversity, resistance to diseases, and resilience in a semi-enclosed fast-changing sea.
- Addressing the multiplicity of problems confronting the species requires collaborative effort at all levels to share and merge resources, data, and expertise more efficiently. In this review, we provide an overview of the current knowledge on the Mediterranean common dolphin, the main threats, and knowledge gaps that are priorities for addressing its conservation, while providing clear recommendations for effectively safeguarding the species and its habitat at both local and regional levels.
79.
W.?P.?WaserEmail author A.?Schmitz S.?F.?Perry A.?Wobschall 《Fish physiology and biochemistry》2005,31(1):73-82
The teleost pseudobranch, a reduced mandibular gill arch, morphologically closely resembles a gill hemibranch. It consists
of several filaments bearing numerous lamellae. The vascular system of the pseudobranch also matches that of a gill, with
afferent and efferent filamental arteries and the lamellar blood space. Despite the pseudobranch’s gill-like appearance, however,
a gas exchange function is excluded in many teleosts by overlying opercular epithelium, effectively eliminating diffusional
exchange with the external medium. The physiological function of the pseudobranch is still unknown, though its conspicuously
close association with the ocular choroid rete mirabile, a structure supporting elevated oxygen partial pressures in the eye, suggests a role related to the process of oxygen secretion
into the eyes of teleosts. In this paper we present new stereological data on the pseudobranch of rainbow trout (average weight:
478 ± 114 g, x ± SD, n = 12). The total Cavalieri volume of the pseudobranch was 46.4 μl (97 μl kg−1), consisting of lamellae 49%, connective tissue 43.8%, large blood vessels 4.5%, filamental cartilage 2.3%, and central venous
sinus 1.3%. Lamellae were comprised of pillar and pseudobranchial cells 81%, blood space 12.3%, and lacunar tissue 6.4%. The
inner surface of the blood space in the lamellae was 12.2 cm2 (25.5 cm2 kg−1), and its volume was 2.81 μl (5.88 μl kg−1). The results demonstrate the pseudobranch’s potential for physiological functions requiring a high surface area or surface-to-volume
ratio, i.e. ion transfer, gas exchange and other regulatory processes. More detailed analysis of the function of the pseudobranch,
however, has to remain subject of future morphological and physiological studies. 相似文献
80.
Diego Villaseñor Renato de Mello Prado Gilmara Pereira da Silva Manuel Carrillo Wuellins Durango 《Journal of plant nutrition》2020,43(18):2785-2796
Abstract Foliar analysis is an effective method to diagnose the nutritional status of plants. However, the mineral concentration in foliar tissue has traditionally been evaluated by assessing the activity of each element, without considering the interactions between them. To address this, dual interactions were calculated using the Diagnosis and Recommendation Integrated System (DRIS) to identify which crop nutrients are most influential in nutrient imbalances and which are the most limiting nutrients for the nutritional status of banana crops in Ecuador. To achieve this, a regional survey of the nutritional status and its productivity levels was conducted for 188 different sites during the crop season in 2017–2018, involving banana cultivars ‘Vallery’ and ‘Williams’, from the Cavendish subgroup. The DRIS calculation method was combined with Beaufils and Jones functions. From the initial 188 foliar samples, 83 samples (representing 44% of the population) were considered to represent the high-yield reference population, with yields of 38–60 t ha?1. The DRIS method defined the mean nutritional balance index, which was not found to be statistically correlated (p?>?0.05) with productivity, revealing that there was no significant association with the nutritional status of the plants. Specific DRIS norms were obtained and indicated that deficiencies in K, N, Ca, and Fe, and excesses in Mn, B, Cl, Zn, S, Cu, and Mg were the most limiting nutrients for banana cultivars in the south of Ecuador. 相似文献