全文获取类型
收费全文 | 76380篇 |
免费 | 3785篇 |
国内免费 | 52篇 |
专业分类
林业 | 3595篇 |
农学 | 2341篇 |
基础科学 | 392篇 |
7913篇 | |
综合类 | 15522篇 |
农作物 | 3080篇 |
水产渔业 | 3394篇 |
畜牧兽医 | 38507篇 |
园艺 | 904篇 |
植物保护 | 4569篇 |
出版年
2018年 | 856篇 |
2017年 | 925篇 |
2016年 | 856篇 |
2015年 | 779篇 |
2014年 | 952篇 |
2013年 | 2600篇 |
2012年 | 1676篇 |
2011年 | 2068篇 |
2010年 | 1359篇 |
2009年 | 1285篇 |
2008年 | 2036篇 |
2007年 | 2076篇 |
2006年 | 1894篇 |
2005年 | 1831篇 |
2004年 | 1751篇 |
2003年 | 1780篇 |
2002年 | 1690篇 |
2001年 | 2215篇 |
2000年 | 2219篇 |
1999年 | 1846篇 |
1998年 | 700篇 |
1997年 | 698篇 |
1995年 | 812篇 |
1993年 | 696篇 |
1992年 | 1489篇 |
1991年 | 1551篇 |
1990年 | 1666篇 |
1989年 | 1644篇 |
1988年 | 1527篇 |
1987年 | 1477篇 |
1986年 | 1527篇 |
1985年 | 1515篇 |
1984年 | 1247篇 |
1983年 | 1144篇 |
1982年 | 771篇 |
1981年 | 717篇 |
1979年 | 1248篇 |
1978年 | 979篇 |
1977年 | 848篇 |
1976年 | 803篇 |
1975年 | 913篇 |
1974年 | 1201篇 |
1973年 | 1240篇 |
1972年 | 1255篇 |
1971年 | 1182篇 |
1970年 | 1102篇 |
1969年 | 1003篇 |
1968年 | 863篇 |
1967年 | 906篇 |
1966年 | 837篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Brito LF Barth AD Rawlings NC Wilde RE Crews DH Mir PS Kastelic JP 《Domestic animal endocrinology》2007,33(1):1-18
The objective of the present study was to characterize the effects of nutrition on circulating concentrations of metabolic hormones, gonadotropins, and testosterone during sexual development in bulls. Nutrition regulated the hypothalamus-pituitary-testes axis through effects on the GnRH pulse generator in the hypothalamus and through direct effects on the testes. Pituitary function (gonadotropin secretion after GnRH challenge) was not affected by nutrition. However, nutrition affected LH pulse frequency and basal LH concentration during the early gonadotropin rise (10-26 weeks of age). There were close temporal associations between changes in insulin-like growth factor-I (IGF-I) concentrations and changes in LH pulse frequency, suggesting a role for IGF-I in regulating the early gonadotropin rise in bulls. The peripubertal increase in testosterone concentration was delayed in bulls with lesser serum IGF-I concentrations (low nutrition), suggesting a role for IGF-I in regulating Leydig cell function. Serum IGF-I concentrations accounted for 72 and 67% of the variation in scrotal circumference and paired-testes volume, respectively (at any given age), indicating that IGF-I may regulate testicular growth. Bulls with a more sustained elevated LH pulse frequency during the early gonadotropin rise (high nutrition) had greater testicular mass at 70 weeks of age relative to the control group (medium nutrition), despite no differences in metabolic hormone concentrations after 26 weeks of age. Therefore, gonadotropin-independent mechanism regulating testicular growth might be dependent on previous gonadotropin milieu. 相似文献
992.
993.
Taeymans O Peremans K Saunders JH 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2007,21(4):673-684
This review describes the advantages and disadvantages of radiography, ultrasonography, and nuclear medicine in the 2 most frequent thyroid pathologies of the dog: acquired primary hypothyroidism and thyroid neoplasia. Ultrasonography and scintigraphy remain the 2 most indicated imaging modalities for these thyroid abnormalities. However, as in human medicine, computed tomography and magnetic resonance imaging also have potential indications. This is especially the case in the evaluation of the extent, local invasiveness, and local or distant metastases of thyroid neoplasia. Based on experience with different imaging modalities in people, we suggest future directions in the imaging of the canine thyroid gland. 相似文献
994.
Sehm J Lindermayer H Dummer C Treutter D Pfaffl MW 《Journal of animal physiology and animal nutrition》2007,91(7-8):289-296
Alternative food ingredients, e.g. secondary plant compounds, are discussed to have beneficial effects and improve gut health. In this study, the effect of three different diets - normal piglets starter without additives, with apple pomace or with red-wine pomace - on the intestinal morphology was investigated from 3 days prior to weaning to 4 weeks post-weaning. At five time points, six piglets from each treatment group were slaughtered; at first time point only six animals from control group were slaughtered. Villus height, crypt depth and breadth of villi and crypts were determined in the jejunum, ileum and colon in 78 piglets. Additionally, the area of the Peyer's patches in the ileum was measured. In jejunum (p < 0.01) and ileum (p < 0.001) the villus length in the control group decreased after weaning but increased over the entire feeding experiment (p < 0.001). In the two-pomace groups, no decrease was measured after weaning. In jejunum, an increase in villi breadth occurred, 73% in the control group and approximately 10% in both treatment groups. A 35% increase was found in the ileum in all groups. Peyer's patches area increased approximately 21% in the control group over 26 days of treatment, whereas in other groups no significant differences were found. Different polyphenol rich pomaces have diverse effects in the gastrointestinal tract. Red-wine pomace has an inhibitory effect on the jejunum villi growth, whereas apple and red-wine pomace have stimulating effect on crypt size in piglet colon. Apple and red-wine pomace can reduce the GALT activation via the Peyer's patches in the ileum. In conclusion, the flavanoids rich feeding regimen showed positive effects on villi morphology, GALT activation and can improve pig health. 相似文献
995.
Swai ES Karimuribo ED French NP Fitzpatrick JL Bryant MJ Kambarage DM Ogden NH 《Journal of the South African Veterinary Association》2007,78(1):15-20
Variations in the seroprevalence of antibody to Babesia bigemina infection by farm and animal level risk factors were investigated for 2 contrasting regions of Tanga and Iringa in Tanzania. Tanga is situated in the eastern part of the country and has typical tropical coast climate while Iringa is situated in the Southern Highlands and has a tropical highland climate. Two hundred farms from each region were selected using simple random sampling procedure and visited once between January 1999 and April 1999. Blood samples were collected from 1329 smallholder dairy animals on selected farms for harvesting serum which was subsequently used for serodiagnosis of B. bigemina using an indirect enzyme linked immuno-sorbent assay (ELISA). Of the 1329 sera samples screened, 34.9 % were positive for B. bigemina. The prevalence was higher in Iringa Region [43%, 95% confidence intervals (CI) = 39.5-47.3] than in Tanga Region (27%, CI = 23.6-30.5). Using a logistic binomial regression model as an analytical method for predicting the likelihood of animal seropositivity, we found (in both regions) that the risk of positive reaction varied with the animal's age, history of grazing and geographical location. Seroprevalence increased with age (beta = 0.01 and 0.01 per year of age, P < 0.005 in Tanga and Iringa, respectively). Animals located in Lushoto and Iringa urban district were associated with increased risk of seropositivity [Odds ratio (OR) = 4.24, P = 0.001, for Lushoto, and OR = 1.81, P = 0.040, for Iringa Urban, respectively). Animals grazed 3 months prior to sampling had higher odds for seropositivity than zero/semi-grazed, despite farmer-reported high frequency of tick control (OR = 2.71, P = 0.0087, for Tanga, and OR = 4.53, P = 0.001, for Iringa). Our study suggests that even though herd sizes are small, B. bigemina infection is widespread in many smallholder dairy farms and endemic stability with respect to this disease has not yet been attained, but the observed levels are sufficiently high to ensure that clinical disease would be a risk. 相似文献
996.
Marais HJ Nel P Bertschinger HJ Schoeman JP Zimmerman D 《Journal of the South African Veterinary Association》2007,78(3):145-148
There are no reports in the literature describing any tumours, and specifically sarcoids, in zebras. The equine sarcoid, a locally aggressive, fibroblastic skin tumour, is the most common dermatological neoplasm reported in horses. The Cape mountain zebra (CMZ) has been described as one of the most vulnerable mammals in South Africa with current populations existing in isolated units. All South African CMZ are descendants from no more than 30 individual animals originating from 3 populations, namely the Mountain Zebra National Park, and Kammanassie and Gamka Mountain Nature Reserves near Cradock. The possibility therefore exists that the existing populations arose from a very small gene pool and that they are considerably inbred. A reduction in major histocompatibility complex diversity due to genetic bottlenecks and subsequent inbreeding probably contributed to uniform population sensitivity and the subsequent development of sarcoid in two CMZ populations, namely in the Bontebok National Park and Gariep Nature Reserve. The entire population of CMZ in the Bontebok National Park was observed and sampled during 2002 to document the prevalence and body distribution of sarcoids. During the same year, a comparative study was carried out on an outbred population of Burchell's zebra in the Kruger National Park. The prevalence in CMZ in the Bontebok National Park was 53 %, while the Burchell's zebra in Kruger National Park had a prevalence of 1.9 %. The most common sites for sarcoid in CMZ were the ventral abdomen and limbs. Prevalence of sarcoids in horses recorded in the literature varies between 0.5 % and 2 %. The Gariep Nature Reserve recently reported a prevalence of almost 25 % in CMZ in the reserve. 相似文献
997.
Presented is an African giant rat (Cricetomys gambianus) following zinc ingestion. The sick rat was lethargic, withdrawn, had soft, mucus-impregnated faeces and diahorrea, foot twitching and icterus. Comparative age, sex and body weight (b.wt.)-matched analyses were made with a healthy giant rat. Twelve-hourly Urine volume (UV), Haematocrit (Hct), urinary glucose, plasma zinc and Alkaline Phosphatase (ALP) were performed over an 8-week period. Full blood counts were performed and differential WBC counts and microscopic observations were made on blood smears obtained from both healthy and sick rats. Consecutive blood samples were drawn at the end of each week (Weeks <2-6 treatment; Weeks 7-8 post-treatment). Treatment involved oral vitamin B12 supplement at 4 microg/day and 2 ml diethylenetriaminepentaacetic acid (DTPA) intramuscular injections at 1 ml/450g b.wt./5 wks (Week 2 - 6). Day 1 showed neutropaenia, Heinz bodies on RBCs (reticulocytes and immature forms). Zinc (Day 1 - end Week 7), glucose (Day 1 - end Week 4), ALP (Day 1 -Week 4) and UV were elevated (Day 1 - end Week 6). Indications of moderate zinc toxicosis following ingestion and stress-associated glucosuria were concluded. 相似文献
998.
Szalo IM Lassence C Licois D Coudert P Poulipoulis A Vindevogel H Marlier D 《Veterinary journal (London, England : 1997)》2007,173(3):652-657
Epizootic rabbit enteropathy (ERE) is a major cause of economic loss in intensive rabbit production. Since its first recognition in 1997, much work has been done to determine the pathogenic mechanisms of the disease and to identify the aetiological agent(s). Unfortunately, the quest for aetiology has only met with limited success despite the ability to reproduce the syndrome by inoculation of intestinal contents from field cases. These intestinal inocula contain a huge number of microorganisms which could all be involved in the aetiology of ERE. To decrease the number of putative agents, the French reference inoculum TEC3 was fractionated on a discontinuous sucrose gradient so that seven fractions (supernatant, 10%, 20%, 30%, 40%, 50% and pellet) were obtained. Specific-pathogen-free rabbits were inoculated with three out of these seven fractions (supernatant, 30%, and pellet). The objectives were: (1) to characterise the seven fractions by bacteriological examination; (2) to verify whether the aetiological agent was present in the fractions by inoculation of rabbits; (3) to assign the aetiological agent of ERE to a morphological group of pathogens; (4) to identify a fraction which could replace the reference inoculum TEC3 in applications such as cell cultures or egg inoculation. The results strongly suggest that ERE is a bacterial disease and does not have a viral or parasitic aetiology. 相似文献
999.
OBJECTIVE: To describe the clinical symptoms of 10 cases of superficial nonhealing corneal ulcers in horses and to evaluate the results of grid keratotomy in these patients. DESIGN: Retrospective study. ANIMALS: Ten horses with superficial nonhealing corneal ulceration in one eye. PROCEDURE: The signalment, history and clinical symptoms are reported of 10 patients with superficial nonhealing corneal ulcers during the period from August 2003 to February 2005. Grid keratotomy was performed in all cases. In addition, the surgical procedure of grid keratotomy and response to therapy are described. RESULTS: Horses generally responded well to grid keratotomy (eight cases healed after one grid keratotomy and one horse healed after a second grid keratotomy; one case was not available for follow-up). Only 2/10 had discomfort after treatment and only 2/9 had some degree of scarring after treatment. The healing time, which was known in seven cases, averaged 8.4 days (+/- SD 4). CONCLUSIONS AND CLINICAL RELEVANCE: Grid keratotomy is an appropriate option for treatment of superficial nonhealing corneal ulcers in horses. The procedure is simple to perform. It generally induces a rapid and uncomplicated healing of the cornea. Only in a limited number of cases does a small amount of scarring occur. 相似文献
1000.
Thirty-seven bulk tank milk (BTM) and individual milk samples of all contributing cows were tested for Coxiella burnetii detection by a real-time PCR assay and used to assess the relationship between the BTM PCR-response and (i) the within-herd prevalence of milk-shedder cows and (ii) the proportion of heavy milk-shedder cows. The within-herd prevalence of milk-shedder cows (i) was found to be significantly higher in herds with a positive BTM and (ii) increased significantly with the estimated titre in Coxiella burnetii obtained in positive BTM. The proportion of heavy milk-shedder cows among the milk-shedder cows increased significantly with an increased estimated titre in Coxiella burnetii in positive BTM. Therefore, a real-time PCR assay applied to BTM samples collected repeatedly over time appears to be a valuable tool to assess on a larger scale the status of herds towards Coxiella shedding, and to evaluate the efficiency of control actions aimed at controlling and/or preventing Coxiella shedding in dairy herds. 相似文献