全文获取类型
收费全文 | 56489篇 |
免费 | 5623篇 |
国内免费 | 33篇 |
专业分类
林业 | 2745篇 |
农学 | 1928篇 |
基础科学 | 217篇 |
6886篇 | |
综合类 | 10153篇 |
农作物 | 2016篇 |
水产渔业 | 4605篇 |
畜牧兽医 | 28823篇 |
园艺 | 559篇 |
植物保护 | 4213篇 |
出版年
2020年 | 749篇 |
2019年 | 1410篇 |
2018年 | 1502篇 |
2017年 | 1579篇 |
2016年 | 1491篇 |
2015年 | 1339篇 |
2014年 | 1456篇 |
2013年 | 2576篇 |
2012年 | 1877篇 |
2011年 | 2057篇 |
2010年 | 1593篇 |
2009年 | 1370篇 |
2008年 | 1816篇 |
2007年 | 1701篇 |
2006年 | 1618篇 |
2005年 | 1532篇 |
2004年 | 1457篇 |
2003年 | 1421篇 |
2002年 | 1365篇 |
2001年 | 1586篇 |
2000年 | 1572篇 |
1999年 | 1222篇 |
1998年 | 455篇 |
1997年 | 484篇 |
1996年 | 474篇 |
1995年 | 527篇 |
1994年 | 475篇 |
1993年 | 487篇 |
1992年 | 922篇 |
1991年 | 917篇 |
1990年 | 911篇 |
1989年 | 918篇 |
1988年 | 865篇 |
1987年 | 899篇 |
1986年 | 892篇 |
1985年 | 895篇 |
1984年 | 723篇 |
1983年 | 654篇 |
1979年 | 647篇 |
1978年 | 546篇 |
1977年 | 463篇 |
1976年 | 463篇 |
1975年 | 503篇 |
1974年 | 693篇 |
1973年 | 606篇 |
1972年 | 675篇 |
1971年 | 671篇 |
1970年 | 602篇 |
1969年 | 590篇 |
1967年 | 511篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Avilés-Nova F Espinoza-Ortega A Castelán-Ortega OA Arriaga-Jordán CM 《Tropical animal health and production》2008,40(7):509-515
Liveweight gain was evaluated in tropical Dorper X Pelibuey lambs under intensive continuous grazing of native grasslands dominated by Paspalum notatum (PN) or Axonopus compressus (AC) in the subtropics of Central Mexico. Two trials were undertaken. Trial 1 lasted 12 weeks with 10 lambs (initial weight 18 +/- 2.57 kg, 3 months old) per treatment in 2002, and Trial 2 for 13 weeks with 8 lambs (initial weight 24.0 +/- 2.0 kg, 4 months old) per treatment. Lambs were weighed once per week, and liveweight change was estimated by linear regression over day of the experiment, using individual regression coefficients as unbiased estimates of daily liveweight change; analysed in a random block design. Lambs on Trial 1 gained 0.061 kg/lamb/day on PN and 0.047 kg/lamb/day on AC (P > 0.05) at an overall mean stocking rate of 25 lambs/ha. In Trial 2, liveweight gain was significantly larger in PN (0.060 kg/lamb/day) than on AC (0.043 kg/lamb/day) (P < 0.05), at a mean stocking rate of 21.5 lambs/ha. It is concluded that intensive continuous grazing of native grasslands in the subtropics of the highlands of Central Mexico enables moderate liveweight gains for weaned lambs during the rainy season; with better results in grasslands dominated by Paspalum notatum. 相似文献
102.
F Bernard R Furneaux C Adrega Da Silva J-F Bardet 《Veterinary and comparative orthopaedics and traumatology》2008,21(1):64-68
rhBMP-2 solution on a collagen sponge was placed along the diaphysis of an atrophicradius, which had a history of recurring fractures. Two months after rhBMP-2 treatment, new mineralized bone was present, which significantly increased the diameter of the radius and allowed the removal of the external skeletal fixator (ESF). Due to carpo-metacarpal joint compromise, a pancarpal arthrodesis was performed seven months later. At follow-up evaluation two years later the dog was only very mildly lame. 相似文献
103.
104.
Douglas C. Doehlert Jae‐Bom Ohm Michael S. McMullen Neil R. Riveland 《Cereal Chemistry》2009,86(2):239-246
Test weight and groat proportion are two very important quality characteristics of oat grain. In this study, we pose the hypothesis that these two characteristics are related through characteristics of grain density. Test weight is defined as the product of kernel density and packing proportion. Groat proportion, in theory, is the ratio of the groat mass to the kernel mass. We present two theoretical constructions expressing test weight in terms of groat proportion, packing proportion and kernel density components. To test these, we have applied measurements of test weight, groat proportion, kernel density components, and packing proportion of 18 oat cultivars grown at six environments. Whereas the groat proportion alone accounted for only 34% of the variation in test weight, our theoretical constructions that included groat proportion could account for ≤82% of variation in test weight. Also, we present previously undescribed variation in oat kernel density components across genotypes and environments. Although the kernel density alone could account for most of the variation in test weight across genotypes, packing proportion appeared to be more important in describing variation in test weight of a genotype across different environments. We observed significant variation in both groat and hull density which, together with groat proportion, described most of the variation in kernel density. 相似文献
105.
Phillip F. Steyn BVSc MRCVS MS David Twedt DVM Wanda Toombs CVT 《Veterinary radiology & ultrasound》1995,36(4):327-331
The gastric emptying half-time of solid food in normal cats was determined using a scintigraphic technique. 99m Tc-sulfur colloid was applied to dry food. Sequential images were acquired post prandial, and the gastric emptying half-time was determined for several different acquisition and processing parameters. Good correlation was found between different acquisition and processing methods, some of which made use of edge detection applications, while others used different views, or number of views from which the gastric emptying half-time was calculated. The mean ± standard deviation, (range) and median of the gastric emptying half-time determined using the geometric mean of total counts in hand-drawn regions of interest from the lateral and ventral images were 2.47 × 0.71, (1.42–3.61) and 2.37 hours respectably. 相似文献
106.
107.
108.
109.
Engelsma KA Veerkamp RF Calus MP Windig JJ 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2011,128(6):473-481
Up to now, prioritization of animals for conservation has been mainly based on pedigree information; however, genomic information may improve prioritization. In this study, we used two Holstein populations to investigate the consequences for genetic diversity when animals are prioritized with optimal contributions based on pedigree or genomic data and whether consequences are different at the chromosomal level. Selection with genomic kinships resulted in a higher conserved diversity, but differences were small. Largest differences were found when few animals were prioritized and when pedigree errors were present. We found more differences at the chromosomal level, where selection based on genomic kinships resulted in a higher conserved diversity for most chromosomes, but for some chromosomes, pedigree-based selection resulted in a higher conserved diversity. To optimize conservation strategies, genomic information can help to improve the selection of animals for conservation in those situations where pedigree information is unreliable or absent or when we want to conserve diversity at specific genome regions. 相似文献
110.
Real R González-Lobato L Baro MF Valbuena S de la Fuente A Prieto JG Alvarez AI Marques MM Merino G 《Journal of animal science》2011,89(12):4325-4338
In commercial dairy production, the risk of drug residues and environmental pollutants in milk from ruminants has become an outstanding problem. One of the main determinants of active drug secretion into milk is the ATP-binding cassette transporter G2/breast cancer resistance protein (ABCG2/BCRP). It is located in several organs associated with drug absorption, metabolism, and excretion, and its expression is highly induced during lactation in the mammary gland of ruminants, mice, and humans. As a consequence, potential contamination of milk could expose suckling infants to xenotoxins. In cows, a SNP for this protein affecting quality and quantity of milk production has been described previously (Y581S). In this study, our main purpose was to determine whether this polymorphism has an effect on transcellular transport of veterinary drugs because this could alter substrate pharmacokinetics and milk residues. We stably expressed the wild-type bovine ABCG2 and the Y581S variant in Madin-Darby canine kidney epithelial cells (MDCKII) and MEF3.8 cell lines generating cell models in which the functionality of the bovine transporter could be addressed. Functional studies confirmed the greater functional activity in mitoxantrone accumulation assays for the Y581S variant with a greater relative V(MAX) value (P = 0.040) and showed for the first time that the Y581S variant presents greater transcellular transport of the model ABCG2 substrate nitrofurantoin (P = 0.024) and of 3 veterinary antibiotics, the fluoroquinolone agents enrofloxacin (P = 0.035), danofloxacin (P = 0.001), and difloxacin (P = 0.008), identified as new substrates of the bovine ABCG2. In addition, the inhibitory effect of the macrocyclic lactone ivermectin on the activity of wild-type bovine ABCG2 and the Y581S variant was also confirmed, showing a greater inhibitory potency on the wild-type protein at all the concentrations tested (5 μM, P = 0.017; 10 μM, P = 0.001; 25 μM, P = 0.008; and 50 μM, P = 0.003). Differential transport activity depending on the genotype together with the differential inhibition pattern might have clinical consequences, including changes in substrate pharmacokinetics (and subsequently pharmacodynamics) and more specifically, changes in secretion of ABCG2 substrates into milk, potentially implying important consequences to veterinary therapeutics. 相似文献