全文获取类型
收费全文 | 341744篇 |
免费 | 18435篇 |
国内免费 | 731篇 |
专业分类
林业 | 25089篇 |
农学 | 14355篇 |
基础科学 | 3030篇 |
48817篇 | |
综合类 | 51284篇 |
农作物 | 17835篇 |
水产渔业 | 18930篇 |
畜牧兽医 | 148350篇 |
园艺 | 6628篇 |
植物保护 | 26592篇 |
出版年
2019年 | 3834篇 |
2018年 | 4719篇 |
2017年 | 5231篇 |
2016年 | 5286篇 |
2015年 | 4592篇 |
2014年 | 5987篇 |
2013年 | 16594篇 |
2012年 | 8773篇 |
2011年 | 11471篇 |
2010年 | 8537篇 |
2009年 | 8914篇 |
2008年 | 10710篇 |
2007年 | 9955篇 |
2006年 | 10071篇 |
2005年 | 9347篇 |
2004年 | 9074篇 |
2003年 | 8894篇 |
2002年 | 8097篇 |
2001年 | 9343篇 |
2000年 | 9038篇 |
1999年 | 7757篇 |
1998年 | 4514篇 |
1997年 | 4542篇 |
1996年 | 4245篇 |
1995年 | 4978篇 |
1994年 | 4396篇 |
1993年 | 4116篇 |
1992年 | 6372篇 |
1991年 | 6582篇 |
1990年 | 6273篇 |
1989年 | 6310篇 |
1988年 | 5708篇 |
1987年 | 5837篇 |
1986年 | 5941篇 |
1985年 | 5937篇 |
1984年 | 5154篇 |
1983年 | 4714篇 |
1982年 | 3584篇 |
1981年 | 3365篇 |
1980年 | 3300篇 |
1979年 | 4646篇 |
1978年 | 3982篇 |
1977年 | 3558篇 |
1976年 | 3401篇 |
1975年 | 3443篇 |
1974年 | 3937篇 |
1973年 | 3988篇 |
1972年 | 3666篇 |
1971年 | 3550篇 |
1970年 | 3405篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
131.
Margaret C. McEntee DVM Donald E. Thrall DVM PhD 《Veterinary radiology & ultrasound》2001,42(3):221-225
Twenty two dogs with an infiltrative lipoma had computed tomographic (CT) images acquired to evaluate the extent of local disease. Ten dogs had undergone at least one cytoreductive surgical procedure (range = 1-3; median = 2) prior to imaging. Twenty dogs had measurable disease on CT images; 2 dogs had diffuse disease at a previous surgical site that could not be measured. Tumor volume (n = 20) ranged from 20 to 5,632 cm3 (median = 345 cm3; mean = 996 cm3). None of the dogs had evidence of bone involvement on the CT images; 2 of the 22 dogs had tumors that did not come into direct contact with osseous structures. All dogs with measurable disease had evidence of a fat opacity mass with variable degrees of muscle infiltration. Eleven of 22 dogs were given intravenous contrast medium prior to image acquisition and there was not evidence of enhancement of the infiltrative lipoma in any dog. Based on CT images, tumors were classified as well-defined in 9 dogs, moderately well-defined in 4, not well-defined in 3 and a mix of well-defined and not well-defined in 6 dogs. Tumors tended to be less well-defined in regions where the infiltrative lipoma interdigitated with normal body fat. It appears CT imaging allows adequate discrimination of tumor with the caveat that differentiation of normal fat from infiltrative lipoma can be problematic. 相似文献
132.
133.
H E Kennedy S J McCullough D Graham J Cassidy F E Malone W A Ellis 《Journal of veterinary diagnostic investigation》2001,13(1):30-35
Two serological tests (indirect immunofluorescence and enzyme-linked immunosorbent assay) were developed for the detection of fetal antibody to Chlamydia psittaci. Fetal blood and thoracic fluid from 126 field cases of suspected ovine chlamydial abortion were examined using both tests. Placenta and fetal tissues (lung, liver, and kidney) from the same animals were also examined by the following conventional diagnostic methods: isolation in McCoy cells, detection of chlamydial lipopolysaccharide (LPS), modified Ziehl-Nielsen staining, and direct fluorescent antibody staining of chlamydia in frozen cryostat sections. Seventy cases were positive by fetal serology, and of these, 68 were also positive by isolation and/or LPS detection. The remaining 56 cases had negative fetal serology, and of these, 39 were positive by isolation and/or LPS detection. Results indicate that fetal serology, although less sensitive than either isolation in McCoy cells or detection of chlamydial LPS antigen, may be of particular use when placenta is not available. 相似文献
134.
S T Grubbs S A Kania L N Potgieter 《Journal of veterinary diagnostic investigation》2001,13(2):128-132
Subgroup-specific peptide-based enzyme-linked immunosorbent assays from the G-protein of the ovine and bovine respiratory syncytial virus (RSV), respectively, were used to determine the prevalence of the ovine and bovine subgroup strains of RSV infections in cattle. A total of 1,102 bovine serum samples were obtained from 6 diagnostic laboratories located in the northwestern and the southeastern USA and were tested for antibody to either the bovine or ovine subgroups of RSV. Antibody to viruses from each subgroup was present in samples from each region and all states tested. The Southeast had a higher prevalence of the bovine subgroup strains (69.5%). Then did the Northwest (40.9%). The prevalence of the ovine strain was similar for the two regions (16.7% in the southeast, 14.9% in the northwest). The overall prevalence was 56.6% for the bovine strain and 15.9% for the ovine strain. These results suggest members of the ovine subgroup of RSV circulate in the cattle population but with less frequency than those viruses of the bovine subgroup. 相似文献
135.
Hege Kippenes DVM Patrick R. Gavin DVM PhD Susan L. Kraft DVM PhD Ronald D. Sande DVM MS PhD Russell L. Tucker DVM 《Veterinary radiology & ultrasound》2001,42(2):130-133
The pituitary gland was measured from transverse magnetic resonance T1-weighted images after Gadolinium administration in 96 dogs weighing from 13 to 45 kg. The measurements were done by hand with calipers. The mean (+/- standard deviation) pituitary gland height was 5.1 mm (+/-0.9 mm). The mean width was 6.4 mm (+/- 1.1 mm). The correlation coefficient between pituitary and brain measurements, between pituitary measurement and body weight, and brain measurements and body weight was 0.0 to 0.3. A hyperintense region was present on T1-weighted images in the center of the pituitary gland in 64% of the dogs. At necropsy the pituitary glands were grossly and histologically normal. No pituitary gland measurements were performed at necropsy. 相似文献
136.
137.
B. Götz 《Journal of pest science》1938,14(8):92-93
Ohne Zusammenfassung 相似文献
138.
139.
140.