首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   337篇
  免费   37篇
林业   8篇
农学   8篇
基础科学   2篇
  11篇
综合类   49篇
农作物   8篇
水产渔业   1篇
畜牧兽医   281篇
园艺   1篇
植物保护   5篇
  2023年   2篇
  2021年   4篇
  2020年   9篇
  2019年   8篇
  2018年   8篇
  2017年   9篇
  2016年   12篇
  2015年   14篇
  2014年   14篇
  2013年   11篇
  2012年   13篇
  2011年   16篇
  2010年   6篇
  2009年   11篇
  2008年   13篇
  2007年   17篇
  2006年   7篇
  2005年   15篇
  2004年   9篇
  2003年   14篇
  2002年   12篇
  2001年   11篇
  2000年   16篇
  1999年   10篇
  1998年   5篇
  1997年   3篇
  1996年   10篇
  1995年   5篇
  1994年   10篇
  1993年   4篇
  1992年   7篇
  1991年   6篇
  1990年   10篇
  1989年   8篇
  1988年   4篇
  1987年   6篇
  1984年   2篇
  1983年   2篇
  1978年   2篇
  1976年   2篇
  1974年   3篇
  1970年   2篇
  1928年   3篇
  1925年   2篇
  1901年   1篇
  1900年   1篇
  1899年   1篇
  1898年   1篇
  1897年   1篇
  1896年   1篇
排序方式: 共有374条查询结果,搜索用时 15 毫秒
81.
82.
The ballan wrasse (Labrus bergylta) is a marine fish belonging to the family Labridae characterized by 2 main morphotypes that occur in sympatry: spotty and plain. Previous studies have revealed differences in their life‐history traits, such as growth and maturation; however, the genetic relationship between forms is presently unknown. Using 20 recently developed microsatellite markers, we conducted a genetic analysis of 41 and 48 spotty and plain ballan wrasse collected in Galicia (northwest Spain). The 2 morphotypes displayed highly significant genetic differences to each other (FST = 0.018, P < 0.0001). A similar degree of genetic differentiation (FST = 0.025, P < 0.0001) was shown using the STRUCTURE clustering approach with no priors at K = 2. In this case, the frequency of spotty and plain morphotypes was significantly different (χ2 = 9.46, P = 0.002). It is concluded that there is significant genetic heterogeneity within this species, which appears to be highly associated with the spotty and plain forms, but not completely explained by them. Given the previously demonstrated biological differences between morphotypes, and the present genetic analyses, we speculate about the convenience of a taxonomic re‐evaluation of this species.  相似文献   
83.
Pneumocystis carinii pneumonia is a rare disease in dogs. It is primarily reported in cavalier King Charles spaniels and miniature dachshunds with suspected underlying immunodeficiency. This case series reports the findings in five dogs (four cavalier King Charles spaniels and one Bedlington terrier) with confirmed P. carinii pneumonia. Thoracic (CT) revealed ground glass opacity of the pulmonary parenchyma with a diffuse or multifocal distribution. The severity of this pattern was variable. Less consistent imaging findings included parenchymal bands, bronchial dilation and signs consistent with pulmonary hypertension. Four dogs recovered well with treatment and there was resolution of CT abnormalities in all dogs with follow‐up.  相似文献   
84.
OBJECTIVE: A comparison of a parent-completed Willett food-frequency questionnaire (FFQ) and a self-completed Youth/Adolescent Questionnaire (YAQ) has not yet been conducted. SETTING: In the Diabetes Autoimmunity Study in the Young (DAISY), parents report their child's diet on the FFQ annually from birth until age 10 years, when the child begins to report their own diet using the YAQ. SUBJECTS: To determine the comparability of these collection methods, 89 children aged 10-17 years and their parents completed the YAQ and FFQ, respectively, for the child's previous year's diet. DESIGN: We compared reported intakes for energy, the macronutrients and a variety of micronutrients of interest to the DAISY study. RESULTS: Bland-Altman plots of energy-adjusted differences between questionnaire responses against their means suggested that the two collection methods gave similar results. The average Spearman correlation coefficient of all energy-adjusted nutrient intakes was 0.50, and did not differ significantly by gender (males, r=0.48; females, r=0.46) or age (10-11 years, r=0.49; 12-17 years, r=0.51). While correlated, the nutrient values from the FFQ were higher than the nutrient values from the YAQ. CONCLUSIONS: While reported nutrient intakes are correlated, an indicator variable defining which survey method a nutrient was collected with should be included in any longitudinal data analyses examining nutrient intakes collected with the YAQ and the FFQ as independent predictors of a disease outcome.  相似文献   
85.
The magnetic resonance (MR) imaging features of central nervous system lymphoma in eight dogs and four cats are described. Intracranial lesions affected the rostrotentorial structures in six dogs and caudotentorial structures in two cats. Lesions affected the spinal cord in two dogs and in two cats. One dog and one cat with intracranial lymphoma had signs of local extracranial extension and lymphadenopathy. Lesions were considered extraparenchymal in four dogs and three cats, intraparenchymal in two dogs and one cat, and appeared to have both intra- and extraparenchymal components in two dogs. All lesions were hyperintense in T2-weighted images when compared to white matter, most were hypointense in T1-weighted images (7/12), and most were hyperintense in fluid-attenuated inversion recovery (FLAIR) images (5/9). When compared to grey matter, these lesions appear either isointense (5/12) or hyperintense (7/12) on T2-weighted images, half of them were hypointense in T1-weighted images (6/12), and most were isointense in FLAIR images (7/9). Lesion margins were usually indistinct in T2-weighted images (10/12) and had perilesional hyperintensity in FLAIR images (7/9). The majority of lesions (10/12) had abnormal meninges around the lesion and half (6/12) had generalized contrast enhancement. Mass effect was evident in all lesions. Although not specific, when combined with the history and neurologic signs, MR features aid presumptive diagnosis that should be confirmed by cytology or histopathology.  相似文献   
86.
The Iberian lynx is considered the most endangered felid species. Therefore, an ex situ conservation program was initiated to protect this species from extinction. Additional knowledge on lynx reproduction biology and reliable methods for reproductive monitoring are important for developing a captive breeding program. The aim of this study in lynx was to implement transrectal ultrasonography to visualize ovarian structures (follicles, corpora lutea) and to assess ovarian activity in addition to analysis of serum progesterone and oestradiol. Because of limited access to Iberian lynxes, the less-endangered Eurasian lynx and bobcat were also studied in this comparative study. Recent endocrinological studies based on faecal and urinary progesterone and oestrogen metabolites revealed that steroid profiles in both these species were alike and did not follow the typical pattern of other felids. Pregnancy diagnosis was not possible, since progesterone concentrations did not differ between pregnant and pseudopregnant animals. Progesterone was also detected after parturition as well as after weaning until the onset of a new oestrous cycle. In the present study, the presence of corpora lutea during the non-breeding season was confirmed by ultrasonography and by elevated serum levels of progesterone averaging 3.56 ± 1.3 ng/ml in Eurasian and 6.1 ± 0.26 ng/ml in Iberian lynx, respectively. The ultrasonographical findings on the ovarian structures suggest strongly that corpora lutea developed after ovulation stay active until November and regress before the onset of the next oestrus.  相似文献   
87.
Investigations using sustained-release deslorelin implants at various insertion sites have shown that this method consistently induces oestrus in anoestus bitches. However, fertility comparisons between implant insertion sites have not been performed. Anestrous beagle bitches received one 2.1 mg deslorelin implant beneath the vestibular mucosa (VM group; n = 6) or in the subcutaneous tissue between the shoulder blades (SubQ group; n = 8). Vestibular implants were removed when serum progesterone concentrations first exceeded 1.5 ng/ml. Vaginal cytologies and blood samples were collected daily and bitches were inseminated during oestrus. Serum progesterone and deslorelin concentrations were measured and pregnancy status was determined using ultrasonography. There were no differences between groups in the intervals between implant administration and the onset of proestrus, the time of the luteinizing hormone surge and the onset of cytologic diestrus. There were also no differences in the number of corpora lutea or foetuses. However, conception rate was significantly lower in the SubQ group. The pregnancy rate did not differ significantly between the VM and SubQ groups [4 out of 6 (66.7%) and 3 out of 8 (37.5%), respectively]. One bitch (16.7%) in the VM group and three bitches (37.5%) in the SubQ group suffered distinct, premature declines in serum progesterone concentrations starting 1–4 weeks after cytologic diestrus. Serum progesterone concentrations did not recover (premature luteal failure), resulting in abortion. Bitches with premature luteal failure in the SubQ group still had serum deslorelin concentrations >100 pg/ml 20 days after implant insertion, suggesting a possible association between prolonged deslorelin release and luteal failure.  相似文献   
88.
O bjective : To describe in detail the computed tomographic findings in elbows of dogs with fragmentation of the medial coronoid process of the ulna.
M ethods : Retrospective review of computed tomographic images of 58 elbows that had displaced medial coronoid process fragment(s), non-displaced medial coronoid process fragment or a stable fissure in the articular cartilage of the medial coronoid process at arthroscopy.
R esults : Bone fragments were observed in 85 per cent elbows with a displaced fragment at arthroscopy, in 18 per cent elbows with a non-displaced fragment and in 29 per cent elbows with a stable fissure. Fissures in the subchondral bone were observed in computed tomographic images of 43 per cent elbows that had a stable fissure at arthroscopy. Abnormal shape, sclerosis and lucency affecting the medial coronoid process, subchondral sclerosis of the ulna and humerus, irregular radial incisure of the ulna and periarticular osteophytes were observed in a similar proportion in dogs regardless of the arthroscopic findings. Kissing lesions affecting the medial aspect of the humeral condyle were mainly associated with displaced fragments. Signs of joint incongruity were observed in dorsal and sagittal reconstructed computed tomographic images in 24 per cent elbows.
C linical S ignificance : A wide range of abnormalities may be observed in computed tomographic images of dogs with fragmented medial coronoid process. Computed tomographic is moderately sensitive for detection of fragments.  相似文献   
89.
A nine-month-old puppy was presented for investigation of seizures. Neurological deficits were found localising to the prosencephalon, mesencephalon and myelencephalon. Magnetic resonance imaging identified multiple, large lesions involving both cerebral hemispheres. Management with antiepileptic and immunomodulatory drugs was instituted; however, the seizures became progressively refractory and the puppy was euthanased. Histopathology following post-mortem examination found a mixed glial cell tumour with discrete areas where neoplastic cells appeared oligodendroglial or astrocytic. Primary intracranial neoplasia is a rare cause of neurological disease in young dogs. Moreover, this case is unusual in terms of both the mixed glial nature of the neoplasm and also its multi-focal distribution.  相似文献   
90.
Ultrasonographic features of intestinal intussusception in 10 dogs   总被引:2,自引:0,他引:2  
Records of dogs that had abdominal ultrasonography and surgical or pathological diagnosis of intestinal intussusception between February 1992 and June 1997 were reviewed retrospectively. Ultrasound images were reviewed with respect to appearance of the intussusception, suspected location, evidence of predisposing cause and concurrent lesions. Ten intussusceptions were found, affecting a variety of breeds. The mean (range) age of affected dogs was 2·5 (0·3 to seven) years (four females and six males) and the reported duration of clinical signs, 48 (one to 150) days. Intussusceptions were jejunojejunal (five dogs), ileocolic (three), caecocolic (one) and colocolic (one). A concentric ring sign was identified ultrasonographically in each dog and anatomical location predicted correctly in five instances. Additional ultrasonographic findings associated with intussusceptions included intestinal neoplasm in two dogs, enlarged abdominal lymph nodes in two, multiple mesenteric cysts in one and intestinal foreign body in a further dog. Thus, ultrasonography enables accurate diagnosis of intestinal intussusception and is a useful method for searching for concurrent or predisposing lesions.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号