全文获取类型
收费全文 | 1264篇 |
免费 | 106篇 |
专业分类
林业 | 23篇 |
农学 | 13篇 |
基础科学 | 4篇 |
56篇 | |
综合类 | 367篇 |
农作物 | 116篇 |
水产渔业 | 40篇 |
畜牧兽医 | 666篇 |
园艺 | 14篇 |
植物保护 | 71篇 |
出版年
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 15篇 |
2017年 | 20篇 |
2016年 | 27篇 |
2015年 | 22篇 |
2014年 | 24篇 |
2013年 | 26篇 |
2012年 | 36篇 |
2011年 | 39篇 |
2010年 | 25篇 |
2009年 | 39篇 |
2008年 | 58篇 |
2007年 | 29篇 |
2006年 | 38篇 |
2005年 | 41篇 |
2004年 | 47篇 |
2003年 | 35篇 |
2002年 | 43篇 |
2001年 | 35篇 |
2000年 | 34篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1994年 | 16篇 |
1992年 | 11篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1973年 | 11篇 |
1947年 | 11篇 |
1946年 | 13篇 |
1936年 | 13篇 |
1907年 | 18篇 |
1906年 | 22篇 |
1905年 | 19篇 |
1904年 | 19篇 |
1903年 | 14篇 |
1902年 | 10篇 |
1901年 | 13篇 |
1900年 | 10篇 |
1899年 | 13篇 |
1898年 | 19篇 |
1897年 | 13篇 |
1896年 | 16篇 |
排序方式: 共有1370条查询结果,搜索用时 15 毫秒
91.
92.
93.
E Stauber M Papageorges R Sande L Ward 《Journal of the American Veterinary Medical Association》1990,196(6):939-940
A 10-year-old female cockatiel in a thin and depressed condition and with a 1 X 2-cm soft abdominal swelling was hospitalized. Radiography revealed a well-circumscribed mass containing punctate areas of mineralization, displacing the gizzard cranially in the caudodorsal portion of the abdomen. There was bilateral, symmetric, generalized, increased medullary opacity of the radius, ulna, carpometacarpus, femur, tibiotarsus, and tarsometatarsus. These findings were compatible with polyostotic hyperostosis secondary to an estrogen-secreting tumor. Euthanasia and necropsy were requested. A small area of neoplastic cells in the oviduct was identified histologically, but most of the tissue mass consisted of necrotic cellular debris. There was no metastasis. Sagittal secretions of decalcified radiopaque bones revealed up to 60% filling of medullary cavities with bone spicules. Although clinical and radiographic findings were compatible with an estrogen-secreting tumor, osteopetrosis, metastatic neoplasia, hypertrophic osteopathy, and metabolic bone disease were included in the initial differential diagnosis. The absence of metastasis and the confinement of the tumor within the oviduct would have made surgical removal a possible approach to treatment. 相似文献
94.
Grazing trials were conducted utilizing individually supplemented lactating beef cows in a 2-yr study to determine the effect of supplemental escape protein (EP) on cow/calf performance during the active growth periods of smooth brome and big bluestem. Graded levels (0, .11, .23, and .34 kg of EP/animal from an equal-protein-basis mixture of blood meal and corn gluten meal were offered daily, replacing corn starch and molasses, which was used as the energy control. All cows received 582 g of supplemental DM/d. Analyses for the smooth brome study indicated a cubic response (P less than .05) to milk production and calf daily gain. No response to EP supplementation (P greater than .10) was observed for the big bluestem study. Analysis of esophageal extrusa samples collected throughout the grazing seasons for both years demonstrated that quality of forage selected by the animal decreased as the trial progressed. Using a 16-h modified dacron bag technique that did not adjust for microbial attachment, protein escaping degradation for smooth brome and big bluestem was estimated to range from 7.0 to 14.5% and 22.2 to 30.3%, respectively. There was limited response to a moderate level of EP supplementation of lactating cows grazing smooth brome, but calf gains were depressed by both the low and the high levels of EP. Lactating cows grazing big bluestem did not respond to EP supplementation, but added energy supplement depressed calf gains. 相似文献
95.
96.
97.
JL Yaniz M Lopez-Bejar P Santolaria J Rutllant & F Lopez-Gatius 《Reproduction in domestic animals》2002,37(2):75-80
This review focuses on factors associated with the development of intraperitoneal insemination in mammals. Findings to date indicate that fertility improves as the sperm cell concentration rises, but that the optimal sperm number differs in each species. Sperm washing before intraperitoneal insemination favours fertility. Peritoneal fluid shows a variable effect on spermatozoa, depending on the hormonal status of the female. The optimal time for insemination appears to be just prior to ovulation. The technique may be performed either through the abdominal or the vaginal wall. Verification of sperm deposition in the proximity of the ovaries improves fertility rates. Although associated with some risk of infection and an immune reaction against spermatozoa, the intraperitoneal technique rarely gives rise to severe anaphylactic shock, peritonitis, adhesion formation and the production of anti‐sperm antibodies and these complications may be prevented by adequate sperm pretreatment and antibiotic therapy. The success of intraperitoneal insemination in humans, with results comparable with those of intrauterine insemination in the treatment of infertility, suggest the potential use of this technique in domestic mammals, especially in those in which intrauterine insemination poses practical difficulties. Some of the methods applied in human intraperitoneal insemination, such as confirming the position of the needle in the peritoneal cavity, and sperm pre‐treatments might also improve results in domestic species. Conversely, the use of the animal model should help to develop some aspects of this technique in humans. 相似文献
98.
A state-transition model based on Leslie matrix formulation was used to investigate the effects of herd immunity and age structure on the infection of a simulated cattle herd with bluetongue viruses under Australian climatic conditions. Increasing duration of immunity decreased the prevalence of infection. A duration of immunity of 33 months was consistent with prevalence estimates made from previous serological studies of bluetongue virus. Herd prevalence displayed slowly dampening cyclical variation over time (most pronounced when a short duration of immunity was simulated). Increasing calving and mortality risk rates in the simulated herd increased prevalence, whereas increasing age at first calving decreased prevalence. Manipulation of calving rates had the greatest effect on the predicted prevalence of infection in the herd. Simulation of a number of herd-management scenarios suggested that management systems in which cattle are bred early and where high calving rates are achieved are likely to contribute to high levels of infection with bluetongue viruses. Results confirm the importance of management factors in influencing the prevalence of infectious diseases in animal populations. 相似文献
99.
100.
Boyer TC Ward MP Wallace RL Singer RS 《American journal of veterinary research》2007,68(11):1212-1219
OBJECTIVE: To estimate seroprevalence of bluetongue virus (BTV) and the geographic distribution of seropositive cattle herds in Illinois and western Indiana. SAMPLE POPULATION: 10,585 serum samples obtained from cattle in 60 herds during 3 transmission seasons (2000 through 2002). PROCEDURES: In a longitudinal study, serum samples were tested for BTV antibodies by use of a competitive ELISA. Four geographic zones were created by use of mean minimum January temperature. A multivariable mixed-effects logistic regression model with a random effect for herd was used to estimate seropositive risk for zone, age of cattle, herd type, and transmission season. RESULTS: Overall, BTV antibodies were detected in 156 (1.5%) samples. Estimated seroprevalence in 2000, 2001, and 2002 was 1.49%, 0.97%, and 2.18%, respectively. Risk of being seropositive for BTV was associated with geographic zone and age. Seroprevalence increased progressively from northern to southern zones, with no evidence of BTV infection in the northernmost zone. In the southernmost zone, annual seroprevalence ranged from 8.65% to 11.00%. Adult cattle were 2.35 times as likely as juvenile cattle to be seropositive. CONCLUSIONS AND CLINICAL RELEVANCE: Overall seroprevalence was lower than has been reported for Illinois cattle. Bluetongue virus antibodies were distributed heterogeneously in this region. Only in the southernmost zone was seroprevalence consistently > 2%. Regionalization of BTV risk based on state borders does not account for such variability. Serologic data could be combined with landscape, climate, and vector data to develop predictive models of BTV risk within transitional regions of the United States. 相似文献