全文获取类型
收费全文 | 135614篇 |
免费 | 7186篇 |
国内免费 | 109篇 |
专业分类
林业 | 6464篇 |
农学 | 4506篇 |
基础科学 | 826篇 |
15476篇 | |
综合类 | 24691篇 |
农作物 | 5308篇 |
水产渔业 | 6515篇 |
畜牧兽医 | 68806篇 |
园艺 | 1733篇 |
植物保护 | 8584篇 |
出版年
2018年 | 1786篇 |
2017年 | 1894篇 |
2016年 | 1748篇 |
2015年 | 1572篇 |
2014年 | 1936篇 |
2013年 | 4865篇 |
2012年 | 3448篇 |
2011年 | 4199篇 |
2010年 | 2853篇 |
2009年 | 2827篇 |
2008年 | 4254篇 |
2007年 | 4068篇 |
2006年 | 3874篇 |
2005年 | 3626篇 |
2004年 | 3616篇 |
2003年 | 3627篇 |
2002年 | 3395篇 |
2001年 | 4144篇 |
2000年 | 4157篇 |
1999年 | 3393篇 |
1998年 | 1469篇 |
1997年 | 1411篇 |
1995年 | 1517篇 |
1994年 | 1352篇 |
1993年 | 1345篇 |
1992年 | 2743篇 |
1991年 | 2827篇 |
1990年 | 3007篇 |
1989年 | 2839篇 |
1988年 | 2678篇 |
1987年 | 2581篇 |
1986年 | 2664篇 |
1985年 | 2612篇 |
1984年 | 2168篇 |
1983年 | 1959篇 |
1982年 | 1282篇 |
1979年 | 2081篇 |
1978年 | 1630篇 |
1977年 | 1436篇 |
1976年 | 1364篇 |
1975年 | 1507篇 |
1974年 | 1815篇 |
1973年 | 1885篇 |
1972年 | 1872篇 |
1971年 | 1781篇 |
1970年 | 1690篇 |
1969年 | 1621篇 |
1968年 | 1347篇 |
1967年 | 1434篇 |
1966年 | 1348篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
41.
H M Syme J C Scott-Moncrieff N G Treadwell M F Thompson P W Snyder M R White J W Oliver 《Journal of the American Veterinary Medical Association》2001,219(12):1725-8, 1707-8
An 11-year-old spayed female Labrador Retriever and a 9-year-old castrated male miniature Poodle were evaluated because of clinical signs of hyperadrenocorticism. Cortisol testing did not support a diagnosis of hypercortisolemia in either dog; however, imaging studies revealed unilateral adrenal tumors in both dogs. Serum concentrations of 17-hydroxyprogesterone, progesterone, and estradiol were high in both dogs, and androstenedione concentrations were also high in 1 dog. It is suspected that sex hormone secretion by the adrenal tumors in these dogs resulted in clinical signs of hyperadrenocorticism. Clinical signs and hormonal abnormalities resolved in the male dog after surgical resection of the tumor. There was no improvement in clinical signs after treatment with mitotane in the female dog, which died 2 months after diagnosis. Histologic evaluation confirmed the presence of adrenocortical carcinoma in both dogs. 相似文献
42.
To determine whether turkey herpesvirus (HVT) impairs the aspecific and specific defense against an avian pneumovirus (APV) infection, specific-pathogen-free turkeys were inoculated at 7 days of age with HVT and 1, 5, or 7 wk later with APV. Clinical signs, APV replication, and development of antibodies against APV were evaluated. No differences were found between the birds that received both HVT and APV and those that received only APV. 相似文献
43.
44.
M D Pérez Alenza E Tabanera L Pe?a 《Journal of the American Veterinary Medical Association》2001,219(8):1110-1114
OBJECTIVE: To determine epidemiologic, clinical, and pathologic characteristics of inflammatory mammary carcinoma (IC) in dogs. DESIGN: Retrospective study. ANIMALS: 33 dogs with IC and 153 dogs with malignant mammary tumors other than IC. PROCEDURES: Medical records were reviewed, and signalment, history, physical examination findings, and results of thoracic radiography and necropsy were obtained. RESULTS: 33 of 436 (7.6%) dogs examined at a veterinary teaching hospital because of dysplasia or tumors of the mammary glands and 33 of 186 (17.7%) dogs with at least 1 malignant tumor had IC. Thirty-two of the 33 dogs were sexually intact. Dogs with IC were significantly older than were dogs with other malignant mammary tumors, and in dogs with IC, the tumor was initially noticed a mean of 52 days after the beginning of the last observed estrus, whereas in dogs with other mammary tumors, the tumor was initially noticed a mean of 137 days after the beginning of the last observed estrus. Dogs with IC were more likely to be anorectic and to have generalized weakness, weight loss, and thoracic metastases. Dogs with IC survived a mean of 25 days with palliative treatment. Histologically, involvement of dermal lymphatic vessels was identified in 14 of 19 (74%) dogs with IC. Two clinical forms of IC (primary and secondary) were identified. Dogs with primary IC had a worse clinical condition. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that IC is an uncommon but distinct entity in dogs. A histologic finding of dermal lymphatic involvement should be considered a hallmark for the pathologic diagnosis of IC in dogs. 相似文献
45.
46.
47.
H Inokuma G Nane T Uechi Y Yonahara P Brouqui M Okuda T Onishi 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(11):1225-1227
Twelve (54.5%) of 22 free-roaming dogs in Ishigaki Island had tick infestation identified as Rhipicephalus sanguineus. There were 121 ticks recovered and consisted of 28 females, 58 males, 22 nymphs and 3 larvae. Infection of dogs possibly with canine ehrlichial pathogens was examined by both indirect immunofluorescence assay and polymerase chain reaction (PCR). Two dogs of the 13 examined were sero-positive for the human granulocytic ehrlichia agent, and one of two dogs was PCR positive for Ehrlichia platys. This dog had platelet numbers slightly lower than normal value, however, no morulae were found within platelet on peripheral blood smear stained with Giemsa. 相似文献
48.
G H Loneragan D A Dargatz P S Morley M A Smith 《Journal of the American Veterinary Medical Association》2001,219(8):1122-1127
OBJECTIVE: To evaluate trends in feedlot cattle mortality ratios over time, by primary body system affected, and by type of animal. DESIGN: Retrospective cohort study. ANIMALS: Approximately 21.8 million cattle entering 121 feedlots in the United States during 1994 through 1999. PROCEDURES: Yearly and monthly mortality ratios were calculated. Numbers of deaths were modeled by use of Poisson regression methods for repeated measures. Relative risks of death over time and by animal type were estimated. RESULTS: Averaged over time, the mortality ratio was 12.6 deaths/1,000 cattle entering the feedlots. The mortality ratio increased from 10.3 deaths/1,000 cattle in 1994 to 14.2 deaths/1,000 cattle in 1999, but this difference was not statistically significant (P = 0.09). Cattle entering the feedlots during 1999 had a significantly increased risk (relative risk, 1.46) of dying of respiratory tract disorders, compared with cattle that entered during 1994, and respiratory tract disorders accounted for 57.1% of all deaths. Dairy cattle had a significantly increased risk of death of any cause, compared with beef steers. Beef heifers had a significantly increased risk of dying of respiratory tract disorders, compared with beef steers. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that although overall yearly mortality ratio did not significantly increase during the study, the risk of death attributable to respiratory tract disorders was increased during most years, compared with risk of death during 1994. The increased rates of fatal respiratory tract disorders may also reflect increased rates of non-fatal respiratory tract disorders, which would be expected to have adverse production effects in surviving animals. 相似文献
49.
The isolation of (+)-totarol as active compound against Mycobacterium tuberculosis is reported from Chamaecyparis nootkatensis outerbark. 相似文献
50.
The morphology of 16–17 days old embryos from virgin heifers (VH) and repeat breeder heifers (RBH) was compared using light and electron microscopy. In addition some embryos transferred from one heifer category to the other were studied. Embryos from VH were elongated blastocysts and the oval embryonic disc had three germ layers. The ectoderm was stratified and many mitoses were seen. The endoderm lining the blastocoelic cavity consisted of almost squamous cells conjoined by tight junctions. Between the ectoderm and the endoderm the mesoderm had developed and expanded laterally and the coelom had formed. The trophoblastic cells adjacent do the embryonic disc were cylindrical, whereas those more peripheral located were cuboidal. The trophoblastic cells were conjoined by tight junctions and they had numerous long microvilli on their peripheral surface. Except in the embryonic disc region, the endodermal cells had filopodial processes towards the trophoblast. The embryos from RBH varied in appearance. One was similar to those from VH whereas the others were, more or less retarded, without formation of mesoderm. The smaller one consisted ot trophoblastic cells only. The transferred embryos (representing surviving embryos: 2 out of 9 in VH-RBH and 5 of 6 in RBH-VH) had a morphology similar to that of VH blastocytes two though, appeared somewhat retarded. It is suggested that the retarded embryos lack the ability to complete embryonic development and that the uterine environment of RBH is not favourable to sustain normal embryonic development. 相似文献