全文获取类型
收费全文 | 10068篇 |
免费 | 696篇 |
国内免费 | 45篇 |
专业分类
林业 | 798篇 |
农学 | 410篇 |
基础科学 | 96篇 |
2648篇 | |
综合类 | 399篇 |
农作物 | 585篇 |
水产渔业 | 1013篇 |
畜牧兽医 | 3888篇 |
园艺 | 218篇 |
植物保护 | 754篇 |
出版年
2023年 | 69篇 |
2022年 | 126篇 |
2021年 | 229篇 |
2020年 | 228篇 |
2019年 | 247篇 |
2018年 | 381篇 |
2017年 | 421篇 |
2016年 | 403篇 |
2015年 | 319篇 |
2014年 | 403篇 |
2013年 | 658篇 |
2012年 | 740篇 |
2011年 | 775篇 |
2010年 | 439篇 |
2009年 | 431篇 |
2008年 | 605篇 |
2007年 | 592篇 |
2006年 | 481篇 |
2005年 | 424篇 |
2004年 | 449篇 |
2003年 | 403篇 |
2002年 | 312篇 |
2001年 | 250篇 |
2000年 | 251篇 |
1999年 | 221篇 |
1998年 | 68篇 |
1997年 | 53篇 |
1996年 | 45篇 |
1995年 | 51篇 |
1994年 | 32篇 |
1993年 | 28篇 |
1992年 | 45篇 |
1991年 | 41篇 |
1990年 | 42篇 |
1989年 | 59篇 |
1988年 | 28篇 |
1987年 | 44篇 |
1986年 | 32篇 |
1985年 | 35篇 |
1984年 | 24篇 |
1983年 | 26篇 |
1980年 | 14篇 |
1979年 | 25篇 |
1978年 | 18篇 |
1976年 | 18篇 |
1973年 | 18篇 |
1972年 | 14篇 |
1968年 | 14篇 |
1967年 | 15篇 |
1966年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
1. The aim of the present study was to investigate whether grain type (barley or oats) and ss-glucanase inclusion influence the performance and the gastrointestinal ecosystem of broiler chickens, taking the concentrations of short-chain fatty acids and lactic acid, pH, ileal viscosity, and the weight of the caeca and liver into consideration. 2. The inclusion of beta-glucanase in the oat-based diet improved body weight gains. Enzyme supplementation of barley-based diets improved feed conversion efficiency and reduced intestinal viscosity. 3. Irrespective of the type of cereal, beta-glucanase supplementation increased the lactic acid concentration and lowered the pH of the crop contents. No such changes in fermentation were observed in the contents of the gizzard and ileum. 4. Larger amounts of total dietary fibre and its fractions (arabinoxylans and beta-glucans) in oats decreased the weight of the caeca. 5. Molar ratios of acetate, propionate and butyrate in the caecal chyme were affected by cereal type but not by enzyme supplementation. The barley-based diet increased the butyrate:propionate ratio but the opposite effect was observed with the oat-based diet. 相似文献
992.
Castillo C Benedito JL Méndez J García-Partida P Vázquez P Pereira V López-Alonso M Hernández J 《Berliner und Münchener tier?rztliche Wochenschrift》2006,119(11-12):480-485
The aim of this study was to evaluate the effects of two dietary supplements (monensin and a live yeast culture) on acid-base balance in steers maintained in a commercial feedlot system, considering effects over the growing period (14 to 23 weeks of age). A 63-day feedlot study was performed using 42 double-muscled Belgian Blue steers. Steers were allotted randomly to one of the three study groups: (1) control group [no supplementation, C], (2) monensin supplementation [MON] at a concentration of 30 mg/kg (DM basis), and (3) live Saccharomyces cerevisiae strain supplementation [SACC] at a dose of 500 mg/kg (DM basis).Venous blood samples were collected for the measurement of acid-base parameters and L-lactate. Production parameters were also used as a complementary tool for understanding the internal changes associated with supplementation. Our results show that during the study period no statistical differences were observed between supplemented and control steers, although non-supplemented animals tended to gain more efficiently than those fed monensin or yeast. Nevertheless, taking into account blood parameters, these control animals showed a greater risk of acid overload due to a more marked decline in blood buffer levels over time in comparison with supplemented steers although no differences were observed between monensin or yeast supplemented animals. Additionally, significant effect of supplementation was observed in packed cell volume (PCV) values. 相似文献
993.
Arencibia A Rivero MA De Miguel I Contreras S Cabrero A Orós J 《Research in veterinary science》2006,81(2):165-169
The heads of three loggerhead sea turtles were disarticulated and imaged immediately to minimize postmortem changes and then frozen and sectioned. For computed tomography (CT) imaging, the heads were positioned in ventral recumbency. Transverse CT images with soft-tissue window were obtained from the olfactory sac region to the temporomandibular joint region. After CT imaging, the heads were sectioned and the gross sections were compared to CT images, to assist in the accurate identification of the anatomic structures. Different clinically relevant anatomic structures were identified and labelled in two series of photographs (CT images and anatomic cross-sections). CT images provided good differentiation between the bones and the soft tissues of the head. The information presented in this paper should serve as an initial reference to evaluate CT images of the head of the loggerhead sea turtle and to assist in the interpretation of lesions of this region. 相似文献
994.
Brucellosis is a highly infectious disease which is diagnosed using serological and microbiological methods. The objective of this study was to assess the viability of using conventional and real-time PCR assays as potential diagnostic tools for the detection of Brucella abortus in naturally infected cows. PCR assays that amplify various regions of the Brucella genome, IS711 genetic element, 31kDa outer membrane protein and 16S rRNA, were optimised using nine known Brucella strains. Real-time PCR was used to examine the detection efficiency of the IS711 assay which was estimated at 10 gene copies. Milk, blood and lymph tissue samples were collected from naturally infected animals. B. abortus was not detected in blood samples collected from naturally infected cows by conventional or real-time PCR, but was detected in a proportion of the culture-positive milk (44%) and lymph tissue (66% - retropharyngeal, 75% - supramammary) samples by the same methods. There was no difference between PCR and bacteriological detection methods. It is unlikely that conventional or real-time PCR will supersede current diagnostic methods for detection of B. abortus in clinical samples. 相似文献
995.
Horizontal Maedi-Visna virus (MVV) infection in adult dairy-sheep raised under varying MVV-infection pressures investigated by ELISA and PCR 总被引:2,自引:0,他引:2
Leginagoikoa I Daltabuit-Test M Alvarez V Arranz J Juste RA Amorena B de Andrés D Luján LL Badiola JJ Berriatua E 《Research in veterinary science》2006,80(2):235-241
A three year long experimental study was carried out to investigate horizontal MVV-infection by PCR and ELISA, in 191 one year-old latxa dairy-sheep raised in two separate groups under low and high MVV-infection pressure, respectively. Sheep originated from a previous MVV-transmission study in lambs and seroprevalence among one year-old sheep in both groups was 15% approximately. The high infection-pressure group (H-group) consisted of 147 replacement ewes that joined a milk-producing, housed dairy-flock with 42-66% MVV-seroprevalence and the low infection-pressure group (L-group) were castrated males raised in a separate shed. In contrast to results obtained when infection was investigated in lambs, the overall degree of agreement between ELISA and PCR results was very good and there was some indication that it increased further as sheep became older. MVV-prevalence did not change in the L-group and increased to 57% in three year-old sheep in the H-group (p<0.001). Random effects logistic regression confirmed seroconversion was significantly higher in the H-group compared to the L-group and was highest during the year after the sheep were introduced in the dairy flock and did not increase with age as in previous studies using less sensitive antibody assays. The evidence that horizontal transmission can be very low in spite of prolonged close contact between infected and non-infected sheep is valuable for MVV-control purposes. Furthermore it highlights the need to investigate virus excretion dynamics in infected animals and animal to animal transmission to improve our overall understanding of horizontal MVV transmission in MVV endemic populations. 相似文献
996.
Zafra-Gómez A Garballo A Morales JC García-Ayuso LE 《Journal of agricultural and food chemistry》2006,54(13):4531-4536
A fast, simple, and reliable method for the isolation and determination of the vitamins thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, folic acid, cyanocobalamin, and ascorbic acid in food samples is proposed. The most relevant advantages of the proposed method are the simultaneous determination of the eight more common vitamins in enriched food products and a reduction of the time required for quantitative extraction, because the method consists merely of the addition of a precipitation solution and centrifugation of the sample. Furthermore, this method saves a substantial amount of reagents as compared with official methods, and minimal sample manipulation is achieved due to the few steps required. The chromatographic separation is carried out on a reverse phase C18 column, and the vitamins are detected at different wavelengths by either fluorescence or UV-visible detection. The proposed method was applied to the determination of water-soluble vitamins in supplemented milk, infant nutrition products, and milk powder certified reference material (CRM 421, BCR) with recoveries ranging from 90 to 100%. 相似文献
997.
Rivas B Torrado A Moldes AB Domínguez JM 《Journal of agricultural and food chemistry》2006,54(20):7904-7911
The recovery of tartaric acid (TA) from distilled vinification lees coming from the white and red winemaking technology was optimized using response surface methodology and Statistica 5.0 software. The sequential treatment of dissolving TA and further calcium tartrate (CaT) precipitation could be used to recover up to 92.4% of the initial TA when distilled white lees were used. The residual lees were employed as economic nutrients for lactic acid production by Lactobacillus pentosus CECT-4023 using hemicellulosic vine shoot hydrolysates as carbon source. Distilled lees after TA extraction used as nutrients provided values of lactic acid (18.4-18.9 g/L), global volumetric productivities (0.82-0.84 g/L.h), and product yields (0.69-0.70 g/g) similar to those achieved when using the general medium for Lactobacilli (18.6 g/L, 1.11 g/L.h, and 0.62 g/g, respectively) or lees without TA extraction (16.4-17.2 g/L, 0.96-1.21 g/L.h, and 0.61-0.66 g/g, respectively). This technology not only avoids pollutant disposal but also represents a commercial source of tartaric acid and economic nutrients for biotechnological processes. 相似文献
998.
Effect of industrial dehydration on the soluble carbohydrates and dietary fiber fractions in legumes
Martín-Cabrejas MA Aguilera Y Benítez V Molla E López-Andréu FJ Esteban RM 《Journal of agricultural and food chemistry》2006,54(20):7652-7657
The effects of soaking, cooking, and industrial dehydration treatments on soluble carbohydrates, including raffinose family oligosaccharides (RFOs), and also on total dietary fiber (TDF), insoluble dietary fiber (IDF), and soluble (SDF) dietary fiber fractions were studied in legumes (lentil and chickpea). Ciceritol and stachyose were the main alpha-galactosides for chickpea and lentil, respectively. The processing involved a drastic reduction of soluble carbohydrates of these legumes, 85% in the case of lentil and 57% in the case of chickpea. The processed legume flours presented low residual levels of alpha-galactosides, which are advisable for people with digestive problems. Processing of legumes involved changes in dietary fiber fractions. A general increase of IDF (27-36%) due to the increase of glucose and Klason lignin was observed. However, a different behavior of SDF was exhibited during thermal dehydration, this fraction increasing in the case of chickpea (32%) and decreasing in the case of lentil (27%). This is probably caused by the different structures and compositions of the cell wall networks of the legumes. 相似文献
999.
Santaclara FJ Espiñeira M Cabado AG Aldasoro A Gonzalez-Lavín N Vieites JM 《Journal of agricultural and food chemistry》2006,54(22):8461-8470
Legislation regarding the labeling of processed products is an important issue in the protection of consumer rights. This labeling is especially important in products that cannot be identified on the basis of their morphological characters, because these are removed from the animal in the transformation process. The goal of this study was the identification of mussel species using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) and Forensically Informative Nucleotide Sequencing (FINS) methodologies. The molecular marker selected was 18S rDNA (nuclear small-subunit rDNA gene), which allows identification at the genus level and at the species level in some cases. The genera included in this study were Mytilus, Perna, Aulacomya, Semimytilus, Brachidontes, Choromytilus, and Perumytilus. Different markers were used for genetic identification at the species level. To identify the species included in the genus Perna and Choromytilus, a fragment of ITS 1 (Internal Transcribed Spacer 1) was amplified by multiplex PCR and digested with restrictases. The species of Mytilus were identified by length polymorphism and RFLP of the polyphenolic adhesive protein gene. This methodology was validated with products manufactured in the authors' pilot plant and applied to commercial samples. Therefore, this sequential method can be completely or partially used to determine the mussel genus or species present in any food product. 相似文献
1000.
Almeida AA Farah A Silva DA Nunan EA Glória MB 《Journal of agricultural and food chemistry》2006,54(23):8738-8743
The in vitro antimicrobial activity of commercial coffee extracts and chemical compounds was investigated on nine strains of enterobacteria. The antimicrobial activity investigated by the disc diffusion method was observed in both the extracts and tested chemical compounds. Even though pH, color, and the contents of trigonelline, caffeine, and chlorogenic acids differed significantly among the coffee extracts, no significant differences were observed in their antimicrobial activity. Caffeic acid and trigonelline showed similar inhibitory effect against the growth of the microorganisms. Caffeine, chlorogenic acid, and protocatechuic acid showed particularly strong effect against Serratia marcescens and Enterobacter cloacae. The IC(50) and IC(90) for the compounds determined by the microtiter plate method indicated that trigonelline, caffeine, and protocatechuic acids are potential natural antimicrobial agents against Salmonella enterica. The concentrations of caffeine found in coffee extracts are enough to warrant 50% of the antimicrobial effect against S. enterica, which is relevant to human safety. 相似文献