全文获取类型
收费全文 | 73301篇 |
免费 | 4134篇 |
国内免费 | 32篇 |
专业分类
林业 | 3173篇 |
农学 | 2399篇 |
基础科学 | 466篇 |
8680篇 | |
综合类 | 12016篇 |
农作物 | 2818篇 |
水产渔业 | 3522篇 |
畜牧兽医 | 38583篇 |
园艺 | 835篇 |
植物保护 | 4975篇 |
出版年
2018年 | 966篇 |
2017年 | 1075篇 |
2016年 | 1001篇 |
2015年 | 845篇 |
2014年 | 1047篇 |
2013年 | 2745篇 |
2012年 | 1943篇 |
2011年 | 2267篇 |
2010年 | 1535篇 |
2009年 | 1558篇 |
2008年 | 2324篇 |
2007年 | 2224篇 |
2006年 | 2035篇 |
2005年 | 1970篇 |
2004年 | 1848篇 |
2003年 | 1989篇 |
2002年 | 1807篇 |
2001年 | 2239篇 |
2000年 | 2191篇 |
1999年 | 1748篇 |
1998年 | 714篇 |
1997年 | 776篇 |
1996年 | 685篇 |
1995年 | 867篇 |
1994年 | 734篇 |
1993年 | 734篇 |
1992年 | 1493篇 |
1991年 | 1634篇 |
1990年 | 1602篇 |
1989年 | 1606篇 |
1988年 | 1493篇 |
1987年 | 1456篇 |
1986年 | 1536篇 |
1985年 | 1449篇 |
1984年 | 1270篇 |
1983年 | 1063篇 |
1982年 | 748篇 |
1979年 | 1171篇 |
1978年 | 887篇 |
1977年 | 840篇 |
1976年 | 799篇 |
1975年 | 829篇 |
1974年 | 1030篇 |
1973年 | 1070篇 |
1972年 | 1018篇 |
1971年 | 951篇 |
1970年 | 927篇 |
1969年 | 899篇 |
1968年 | 754篇 |
1967年 | 844篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
E.M. Ibeagha-Awemu & G. Erhardt 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2005,122(1):12-20
Level of genetic differentiation, gene flow and genetic structuring of nine Bos indicus and three Bos taurus cattle breeds in Cameroon and Nigeria were estimated using the genetic information from 16 microsatellite, five blood protein and seven milk protein markers. The global heterozygote deficit across all populations (Fit) amounted to 11.7% (p < 0.001). The overall significant (p < 0.001) deficit of heterozygotes because of inbreeding within breeds (Fis) amounted to 6.1%. The breeds were moderately differentiated (Fst = 6%, p < 0.001) with all loci except CSN1S2 contributing significantly to the Fst value. The 12 populations belong to two genetic clusters, a zebu and a taurine cluster. While inferred sub‐clusters within the taurine group corresponded extremely well to predefined breed categorizations, no real sub‐clusters, corresponding to predefined breeds, existed within the zebu cluster. With the application of prior population information, cluster analysis achieved posterior probabilities from 0.962 to 0.994 of correctly assigning individuals to their rightful populations. High gene flow was evident between the zebu populations. Positive and negative implications of the observed genetic structure of the breeds on their development, improvement and conservation are discussed. The study shows that the breeds are threatened by uncontrolled breeding and therefore are at risk to become genetically uniform in the future. This situation can be avoided by putting in place effective breeding and management measures aimed at limiting uncontrolled mating between the breeds and to preserve special characteristics, genetic as well as breed biodiversity. The first step towards realizing these goals might be to geographically demarcate the breeds. 相似文献
993.
Valérie Sauvé DMV Kenneth J. Drobatz DVM MSCE DACVIM DACVECC Amy B. Shokek VMD Alexia L. McKnight DVM DACVR Lesley G. King MVB DACVIM DACVECC 《Journal of Veterinary Emergency and Critical Care》2005,15(1):38-47
Objective: Correlate the necropsy diagnosis with the history, diagnostic findings, and clinical course of dyspneic cats with primary lung parenchymal disease. Design: Retrospective study. Setting: Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania. Animals: Client‐owned cats over 6 months of age hospitalized in the Intensive Care Unit (ICU) with a primary problem of respiratory distress that had pulmonary parenchymal disease on thoracic radiographs, and a complete necropsy. Interventions: None. Measurements and main results: Cats included were assigned into 2 groups based on the pulmonary histopathology: inflammatory (n=8) and neoplastic (n=7) disease. No statistical difference was found between the groups with regard to age, body weight, clinical signs, duration of clinical signs, physical examination findings, thoracic radiography, duration of hospitalization, treatment, and outcome. Cats with neoplasia had a statistically higher mean total white blood cell count (26.60 k/μL±10.41) than those with inflammatory lung disease (11.59 k/μL±4.49; P=0.026). Cats with bacterial or viral pulmonary disease had a significantly shorter median duration of illness (5 days, range 1–7 days) than all other cats (30 days, range 7–365 days; P=0.0042). Ultrasound guided pulmonary fine‐needle aspiration (FNA) provided an accurate diagnosis in 5/5 cases. Conclusions: Forty‐seven percent of cats with pulmonary parenchymal disease had neoplasia. The clinical diagnosis was difficult to obtain ante‐mortem; lung FNA appeared to be the most helpful diagnostic tool in these cases. 相似文献
994.
995.
Estimation of the ideal ratio of true ileal digestible sulfur amino acids:lysine in 8- to 26-kg nursery pigs 总被引:1,自引:0,他引:1
Gaines AM Yi GF Ratliff BW Srichana P Kendall DC Allee GL Knight CD Perryman KR 《Journal of animal science》2005,83(11):2527-2534
Four experiments were conducted to determine the ideal ratio of true ileal digestible (TID) sulfur AA to Lys (SAA:LYS) in nursery pigs at two different BW ranges using both DL-Met and 2-hydroxy-4-(methylthio)-butanoic acid (HMTBA) as Met sources. In Exp. 1, 1,549 nursery pigs (Triumph 4 x PIC Camborough 22; initial BW 8.3 +/- 0.08 kg) were allotted to one of nine dietary treatments. The basal diet (Diet 1) was a semicomplex corn-soybean meal-based diet (1.32% TID Lys) with no supplemental HMTBA or DL-Met (47.7% TID SAA:LYS). Diets 2 to 9 consisted of the basal diet supplemented with four equimolar levels of DL-Met or HMTBA (52.7, 57.7, 62.7, and 67.7% TID SAA:LYS). In Exp. 2, 330 nursery pigs (Triumph 4 x PIC Camborough 22; initial BW 11.4 +/- 0.10 kg) were allotted to one of nine dietary treatments. The basal diet (Diet 1) was a corn-soybean meal-based diet (1.15% TID Lys) with no supplemental HMTBA or DL-Met (49% TID SAA:LYS). Diets 2 to 9 consisted of the basal diet supplemented with four equimolar levels of DL-Met or HMTBA (54, 59, 64, and 69% TID SAA:LYS). In Exp. 3, 1,544 nursery pigs (Triumph 4 x PIC Camborough 22; initial BW 12.4 +/- 0.13 kg) were allotted to one of nine dietary treatments as in Exp. 2. In Exp. 4, 343 nursery pigs (Genetiporc; initial BW 12.8 +/- 0.56 kg) were allotted to one of six dietary treatments. The basal diet (Diet 1) was a corn-soybean meal-based diet (1.05% TID Lys) with no supplemental DL-Met (49% TID SAA:LYS). Diets 2 to 5 consisted of the basal diet supplemented with four levels of DL-Met (54, 59, 64, and 69% TID SAA:LYS), and Diet 6 was the basal diet supplemented with one equimolar level of HMTBA to satisfy 59% TID SAA:LYS ratio. In all experiments, increasing the TID SAA:LYS ratio resulted in quadratic improvements in ADG (P < or = 0.09) and G:F (P < or = 0.05). Three different methods were used to estimate the optimal TID SAA:LYS ratio for each experiment. The two-slope broken-line regression model, x-intercept value of the broken-line and quadratic curve, and 95% of upper asymptote across the four experiments indicated that the average optimal TID SAA:LYS ratios were 59.3, 60.1, and 57.7% for ADG and 60.6, 61.7, and 60.1% for G:F, respectively. Thus, the optimal TID SAA:LYS ratio for 8- to 26-kg pigs based on the average value of these three estimates was 59.0% for ADG and 60.8% for G:F. 相似文献
996.
A 9-month-old, castrated male domestic shorthair cat with urinary incontinence was referred for surgical correction of an ectopic ureter. Excretory urography revealed hydronephrosis of the right kidney, right hydroureter, and ureterocele. A partial ureterocelectomy and neoureterocystostomy were performed. This report describes the surgical modification of the ureterocele and ectopic ureter to correct ipsilateral hydronephrosis, hydroureter, and urinary incontinence. 相似文献
997.
998.
999.
1000.
Exercise has been shown to increase the production of reactive oxygen species (ROS) to a point that can exceed antioxidant defenses, to cause oxidative stress. The aim of our trials was to evaluate oxidative stress and recovery times in trained dogs during two different hunting exercises, with reactive oxygen metabolites-derivatives (d-ROMs) and biological antioxidant potential (BAP) tests. A group of nine privately owned Italian hounds were included. A 20-min aerobic exercise and a 4-h aerobic exercise, after 30 days of rest, were performed by the dogs. Our results show an oxidative stress after exercise due to both the high concentration of oxidants (d-ROMs) and the low level of antioxidant power (BAP). Besides, the recovery time is faster after the 4-h aerobic exercise than the 20-min aerobic exercise. Oxidative stress monitoring during dogs exercise could become an interesting aid to establish ideal adaptation to training. 相似文献