全文获取类型
收费全文 | 22531篇 |
免费 | 1415篇 |
国内免费 | 1694篇 |
专业分类
林业 | 1218篇 |
农学 | 1870篇 |
基础科学 | 270篇 |
2907篇 | |
综合类 | 9101篇 |
农作物 | 1817篇 |
水产渔业 | 1921篇 |
畜牧兽医 | 4357篇 |
园艺 | 1067篇 |
植物保护 | 1112篇 |
出版年
2024年 | 134篇 |
2023年 | 350篇 |
2022年 | 716篇 |
2021年 | 804篇 |
2020年 | 868篇 |
2019年 | 966篇 |
2018年 | 727篇 |
2017年 | 1041篇 |
2016年 | 1175篇 |
2015年 | 962篇 |
2014年 | 1092篇 |
2013年 | 1450篇 |
2012年 | 1704篇 |
2011年 | 1741篇 |
2010年 | 1325篇 |
2009年 | 1354篇 |
2008年 | 1161篇 |
2007年 | 1313篇 |
2006年 | 1045篇 |
2005年 | 792篇 |
2004年 | 624篇 |
2003年 | 506篇 |
2002年 | 443篇 |
2001年 | 379篇 |
2000年 | 368篇 |
1999年 | 334篇 |
1998年 | 270篇 |
1997年 | 248篇 |
1996年 | 266篇 |
1995年 | 231篇 |
1994年 | 190篇 |
1993年 | 158篇 |
1992年 | 155篇 |
1991年 | 160篇 |
1990年 | 134篇 |
1989年 | 138篇 |
1988年 | 82篇 |
1987年 | 59篇 |
1986年 | 33篇 |
1985年 | 35篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1962年 | 7篇 |
1956年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
102.
Brewers' spent grain (BSG) is the insoluble residue generated from the production of wort in the brewing industry. This plant-derived by-product is known to contain significant amounts of valuable components, which remain unexploited in the brewing processes. Therefore, it is essential to develop a more detailed characterization of BSG in order to highlight its potential in developing new value-added products and simultaneously solve the environmental problems related to its discharge. The content of BSG in several biologically active compounds (fatty acids, polyphenols, flavonoids, antioxidant capacity) as well as its volatile fingerprint were assessed and compared with the composition of barley, malt and wheat flour samples. The obtained results emphasized the importance and the opportunities of the re-use of this agro-industrial by-product. 相似文献
103.
The effects of long-term fertilization of acidic soils on ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities and its ecological implications remain poorly understood. We chose an acidic upland soil site under long-term (27-year) fertilization to investigate ammonia oxidizer communities under four different regimes: mineral N fertilizer (N), mineral NPK fertilizer (NPK), organic manure (OM) and an unfertilized control (CK). Soil net nitrification rates were significantly higher in OM soils than in CK, N or NPK soils. Quantitative analysis of the distribution of amoA genes by DNA-based stable isotope probing revealed that AOA dominate in CK, N and NPK soils, while AOB dominate in OM soils. Denaturing gradient gel electrophoresis and clone library analyses of amoA genes revealed that Group 1.1a-associated AOA (also referred to as Nitrosotalea) were the most dominant active AOA population (>92%), while Nitrosospira Cluster 3 and Cluster 9 were predominant among active AOB communities. The functional diversity of active ammonia oxidizers in acidic soils is affected by long-term fertilization practices, and the responses of active ammonia oxidizers to mineral fertilizer and organic manure are clearly different. Our results provide strong evidence that AOA are more highly adapted to growth at low pH and low substrate availability than AOB, and they suggest that the niche differentiation and metabolic diversity of ammonia oxidizers in acidic soils are more complex than previously thought. 相似文献
104.
以热带柱花草和黑籽雀稗为材料,通过盆栽试验,研究不同磷水平对其根际酸性磷酸酶、微生物数量及根系活力的影响。结果表明:2种牧草根际酸性磷酸酶(ACP)活性随着磷浓度的增加而降低,在低磷(P0)处理时达最高,柱花草的ACP活性为603.24 mg/(kg·h),黑籽雀稗为367.21 mg/(kg·h)。当高磷浓度处理时,柱花草根际ACP活性较黑籽雀稗低。各处理中,柱花草的根际微生物总量较黑籽雀稗高,柱花草根际真菌的数量随磷浓度的增加而减少,处理间差异达极显著水平,低磷处理时土壤真菌数量较多,这有利于根瘤菌的形成。2种牧草的根系活力随着施磷浓度的增加而递减。黑籽雀稗根系活力P0处理极显著高于P3和P4处理,显著高于P2处理。黑籽雀稗根系活力受供磷水平的影响大于柱花草。 相似文献
105.
[目的] 进一步探讨牛磺鹅去氧胆酸(taurochenodeoxycholic acid,TCDCA)在抗炎免疫方面的潜在调节作用。[方法] 以AA大鼠成纤维样滑膜细胞作为研究对象,采用ELISA方法检测TCDCA和IL-1β作用下AA大鼠成纤维样滑膜细胞上清液中PGE2的含量,分析TCDCA对IL-1β刺激下AA大鼠成纤维样滑膜细胞中PGE2分泌情况的影响。[结果] TCDCA能够对IL-1β刺激下AA大鼠纤维样滑膜细胞PGE2的分泌产生下调作用(P<0.05)。[结论] TCDCA对IL-1β刺激下AA大鼠成纤维样滑膜细胞中PGE2的分泌具有抑制作用,为TCDCA在兽医临床应用提供依据。 相似文献
106.
The effect of 0, 0.05 or 0.1 mm abscisic acid treatment on chilling tolerance and salicylic acid‐related responses was investigated in young maize seedlings (Zea mays L., hybrid Norma). Although the pre‐treatment of maize seedlings with abscisic acid slightly decreased the chlorophyll content, it also reduced the level of chilling injury caused by 6 days of cold treatment at 5 °C. Under normal growth conditions, increased levels of bound salicylic acid and of bound ortho‐hydroxycinnamic acid were observed in the leaves during abscisic acid treatment. In the roots, abscisic acid did not affect the free and bound salicylic acid levels, but increased the amount of free and bound ortho‐hydroxycinnamic acid. The activity of glutathione‐S‐transferase increased on the 3rd day of abscisic acid treatment, whereas it did not change when followed by cold stress, compared with the control leaves. In the roots, the activities of glutathione reductase, glutathione‐S‐transferase and ascorbate peroxidase increased during the abscisic acid treatment, and those of glutathione‐S‐transferase and ascorbate peroxidase were also stimulated when abscisic acid pre‐treatment was followed by cold stress, compared with the control roots. Our results suggest that an overlap may exist between the abscisic acid‐induced cold acclimation and the salicylic acid‐related stress response. 相似文献
107.
D. Liu Z. F. Pei M. S. Naeem D. F. Ming H. B. Liu F. Khan W. J. Zhou 《Journal of Agronomy and Crop Science》2011,197(4):284-295
The present study assesses the effects of 5‐aminolevulinic acid (ALA, 0, 0.1, 1 and 10 mg l?1) on the growth of oilseed rape (Brassica napus L. cv. ZS758) seedlings under water‐deficit stress induced by polyethylene glycol (PEG 6000, 0 and ?0.3 MPa). Water‐deficit stress imposed negative effects on seedling growth by reducing shoot biomass, cotyledon water potential, chlorophyll content and non‐enzymatic antioxidants (glutathione and ascorbic acid) levels. On the other hand, water‐deficit stress enhanced the malondialdehyde (MDA) content, reactive oxygen species (ROS) production, enzymatic antioxidants activities, reduced/oxidized glutathione ratio (GSH/GSSG) and reduced/oxidized ascorbic acid (ASA/DHA) ratio in seedlings. Application of ALA at lower dosages (0.1 and 1 mg l?1) improved shoot weight and chlorophyll contents, and decreased MDA in rape seedlings, whereas moderately higher dosage of ALA (10 mg l?1) hampered the growth. The study also indicated that 1 mg l?1 ALA improved chlorophyll content, but reduced MDA content and ROS production significantly under water‐deficit stress. Lower dosages of ALA (0.1 and 1 mg l?1) also enhanced GSH/GSSG and ASA/DHA as compared to the seedlings under water‐deficit stress. The antioxidant enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase and superoxide dismutase) enhanced their activities remarkably with 1 mg l?1 ALA treatment under water‐deficit stress. It was also revealed that 1 mg l?1 ALA treatment alone induced the expression of APX, CAT and GR substantially and under water‐deficit stress conditions ALA treatment could induce the expression of POD, CAT and GR to a certain degree. These results indicated that 0.1–1 mg l?1 ALA could enhance the water‐deficit stress tolerance of oilseed seedlings through improving the biomass accumulation, maintaining a relative high ratio of GSH/GSSG and ASA/DHA, enhancing the activities of the specific antioxidant enzymes and inducing the expression of the specific antioxidant enzyme genes. 相似文献
108.
The objective of the work was to evaluate the effect on the nutrient content of replacing fish meal (FM) with blood meal (BM) in fish supplement. Three isonitrogenous diets (35% crude protein) were formulated using FM as the main source of animal protein (BM0); 50% replacement of FM with blood meal (BM50); or 100% replacement of FM with BM (BM100). The chemical composition (ash, crude protein, crude fat and crude fibre) and amino acid composition were determined. Replacement of FM with BM did not affect the proximate composition of the diet apart from ash content which decreased with the level of substitution. Substituting fish meal with blood meal reduced the levels of methionine, lysine, isoleucine, leucine, proline, valine and increased the levels of arginine, phenylanine and alanine in the diet. Amino acid indices revealed that BM0 had more amino acids with the highest chemical scores followed by BM50 and BM100. In all the diets, methionine was the most limiting amino acid. The essential amino acid index of the diets reduced with the level of replacement of FM (0.94, 0.88 and 0.77). The study showed substitution of up to 50% FM with BM gave a useful protein diet and 100% gave almost a poor protein diet. 相似文献
109.
J. Robison N. Arora Y. Yamasaki M. Saito J. Boone B. Blacklock S. Randall 《Journal of Agronomy and Crop Science》2017,203(6):553-561
Soybean has been considered a cold intolerant species; based largely upon seed germination and soil emergent evaluations. This study reports a distinct acquisition of cold tolerance, in seedlings, following short acclimation periods. Diversity in cold responses was assessed in eight cultivars of Glycine max and six accessions of G. soja. All varieties of soybean significantly increased in freezing tolerance following acclimation. This study indicates soybean seedlings are indeed capable of sensing cold and acquiring cold tolerance. Germination rates after cold imbibition were negatively correlated with maturity group, but positively correlated with cold acclimation potential in G. soja. Seed fatty acid composition was varied between the species, with Glycine soja accessions containing about 2‐times more linolenic acid (18:3) than G. max. Furthermore, high levels of linoleic acid (18:2) in seeds were positively correlated with germination rates following cold imbibition in G. soja only. We suggest that domestication has not impacted the overall ability of soybean to cold acclimate at the seedling stage and that there is little variation within the domesticated species for ability to cold acclimate. Thus, this brief comparative study reduces the enthusiasm for the “wild” species as an additional source of genetic diversity for cold tolerance. 相似文献
110.
土壤中根皮苷和根皮素对桃幼苗的影响 总被引:1,自引:0,他引:1
以一年生桃嫁接苗为试材,在盆栽条件下研究了苹果园土壤中特征酚酸类物质——根皮苷和根皮素对桃苗生物量、根系活力、根系保护性酶活性和MDA含量的影响。结果表明,根皮苷对桃幼苗的伤害显著,与对照相比,鲜质量、干质量分别降低了16.66%和21.58%,根系活力降低了33.04%,SOD、POD活性分别降低了40.80%和31.10%,MDA含量提高了116.34%。根皮素对桃苗的影响不大。高锰酸钾处理明显缓解了根皮苷对桃苗的伤害,苹果园土壤中的根皮苷含量降低了57.80%,提高了桃苗的生物量、根系活力和保护性酶活性,降低了MDA含量。综上,老龄苹果园土壤实测含量的根皮苷(0.343mg·kg~(-1))可降低桃苗的生物量,适量的高锰酸钾能缓解根皮苷的伤害作用。 相似文献