全文获取类型
收费全文 | 187554篇 |
免费 | 10605篇 |
国内免费 | 858篇 |
专业分类
林业 | 7796篇 |
农学 | 6080篇 |
基础科学 | 1387篇 |
23833篇 | |
综合类 | 33625篇 |
农作物 | 7477篇 |
水产渔业 | 9223篇 |
畜牧兽医 | 94669篇 |
园艺 | 2680篇 |
植物保护 | 12247篇 |
出版年
2020年 | 1715篇 |
2019年 | 2045篇 |
2018年 | 2873篇 |
2017年 | 3288篇 |
2016年 | 2946篇 |
2015年 | 2615篇 |
2014年 | 3183篇 |
2013年 | 7269篇 |
2012年 | 5948篇 |
2011年 | 7336篇 |
2010年 | 4857篇 |
2009年 | 4819篇 |
2008年 | 6933篇 |
2007年 | 6591篇 |
2006年 | 6072篇 |
2005年 | 5705篇 |
2004年 | 5303篇 |
2003年 | 5436篇 |
2002年 | 4929篇 |
2001年 | 5646篇 |
2000年 | 5752篇 |
1999年 | 4523篇 |
1998年 | 1979篇 |
1997年 | 1856篇 |
1996年 | 1728篇 |
1995年 | 2023篇 |
1994年 | 1778篇 |
1993年 | 1698篇 |
1992年 | 3559篇 |
1991年 | 3819篇 |
1990年 | 3704篇 |
1989年 | 3659篇 |
1988年 | 3344篇 |
1987年 | 3374篇 |
1986年 | 3477篇 |
1985年 | 3283篇 |
1984年 | 2748篇 |
1983年 | 2381篇 |
1979年 | 2485篇 |
1978年 | 1995篇 |
1977年 | 1644篇 |
1976年 | 1708篇 |
1975年 | 1804篇 |
1974年 | 2231篇 |
1973年 | 2220篇 |
1972年 | 2105篇 |
1971年 | 1950篇 |
1970年 | 1911篇 |
1969年 | 1900篇 |
1967年 | 1653篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
M E Olson C J Hannigan P F Gaviller L A Fulton 《The Canadian veterinary journal. La revue veterinaire canadienne》2001,42(11):865-868
Dogs (n = 13), which had failed to be cured of giardiosis following chemotherapeutic measures, were treated with a Giardia vaccine (2-3 injections). Clinical signs resolved between 16 and 42 days postvaccination and cessation of fecal cyst shedding was between 21 and 70 days. Vaccination is a potential method of treating giardiosis in dogs. 相似文献
202.
Fireblight disease, caused by Erwinia amylovora was first detected in Bulgaria on quince in the region of Plovdiv in 1989. The disease was initially localized in that area but, during 1995/1997, due to favourable climate conditions, it became epidemic. Infected trees were grubbed out and destroyed. The main hosts are quince and pear (over 40% of affected trees), then apple, medlar and Cotoneaster. Containment measures undertaken by the Bulgarian NPPO are laid down in the Plant Protection Law, in Phytosanitary Regulation no. 1 for phytosanitary control, and in Phytosanitary Regulation no. 5 of 1996 (amended 1997) for containment of fireblight. Phytosanitary control is mainly focused on fruit‐tree nurseries and on the distribution of healthy plants for planting. In 2003, 41 protected zones and 29 protected sectors within infested areas have been established. 相似文献
203.
L S Pelan-Mattocks B A Pesch M E Kehrli 《American journal of veterinary research》2001,62(11):1740-1744
OBJECTIVE: To develop an efficient and reliable method that accurately differentiates bovine lymphocytes from monocytes in leukograms. SAMPLE POPULATION: Blood samples from 30 healthy cows and 1 calf with bovine leukocyte adhesion deficiency. PROCEDURE: Flow cytometric analysis of intracellular complexity and CD45 expression on bovine leukocytes was compared with results for conventional light microscopy methods. Verification of leukocyte subpopulations determined by intracellular complexity and CD45 expression was conducted, using 2-color phenotypic analysis with selected monoclonal antibodies. RESULTS: The CD45 and side-scatter properties of bovine leukocytes clearly differentiated cell types, including neutrophils, eosinophils, monocytes, and lymphocytes. CONCLUSIONS AND CLINICAL RELEVANCE: This is a rapid assay that is simple to use. More importantly, it is more accurate than the conventional method that involves the use of blood slides and light microscopy, because of the ability of the assay to readily distinguish bovine monocytes and lymphocytes. Rapid preparation of samples and short analysis times allow for efficient and reliable examination of a large number of samples, and the task of viewing slides by light microscopy is eliminated. The labor-savings benefit of this procedure is most apparent in research environments that require frequent processing of batches of blood samples. 相似文献
204.
Genetic diversity within and among 20 herbicide-resistant (HR) and 16 herbicide-susceptible (HS) Avena fatua multi-field populations was determined using 82 polymorphic loci resulting from two intersimple sequence repeat (ISSR) primers and one long-primer random amplified polymorphic DNA (LP-RAPD) primer. Collections from the Red River Valley of North Dakota and Minnesota, sampled in 1964 and 2000, represented A. fatua populations before and after intensive exposure to herbicides. A 1995 collection from south-west North Dakota represented A. fatua exposed to low herbicide selection. Despite differences in years of herbicide exposure among collections, both HR and HS populations from every collection maintained nearly similar levels of ISSR and RAPD diversity. Genetic differentiation among populations (GST) varied from 11% to 13% among HR populations and from 9% to 16% among HS populations, indicating that 84–91% of total variation remained within HS or within HR populations. Minimal difference in gene diversity between HR and HS is consistent with multiple origins of resistance, where HR A. fatua most likely evolved from diverse founding individuals. 相似文献
205.
206.
Canine distal renal tubular acidosis and urolithiasis 总被引:1,自引:0,他引:1
D J Polzin C A Osborne F W Bell 《Veterinary Clinics of North America: Small Animal Practice》1986,16(2):241-250
Distal RTA is characterized by decreased distal renal tubular hydrogen ion secretion, decreased ability to acidify urine, hypercalciuria, hyperphosphaturia, hypocitraturia, and metabolic acidosis. Because of the resulting alterations in urine composition and pH, patients with distal RTA are predisposed to urolithiasis and renal calcification. Diagnosis of distal RTA is important because it is a potentially reversible disorder that, left untreated, may cause nephrocalcinosis, recurrent urolith formation, moderate to severe metabolic acidosis, and renal failure. 相似文献
207.
Abstract – Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974–1991 and in summer (late June to early July) in 1992–2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series. 相似文献
208.
A E van de Braak A T van 't Klooster A Malestein J A Faber 《The Veterinary quarterly》1986,8(1):12-23
Forty-one dairy cows were fed a low (LCa-13 g/d) and a high (HCa-83.5 g/d) calcium ration in the 8 weeks prior to parturition and the effect on the Ca mobilization rate around parturition was studied. Plasma Ca values were stable in the LCa group around parturition. In the older cows of the HCa group a very slight decrease in the mean plasma Ca was observed: 2.58 mmol/l at 12-36 h ante partum decreased to 2.38 mmol/l at parturition. Hypocalcaemia, which commonly occurs around parturition, did not occur in 40 of the cows. A subclinical hypocalcaemia (1.8 mmol/l) occurred in one cow (parity 10) from the HCa group. To assess the efficiency of Ca mobilization, a severe hypocalcaemia (1.0 mmol/l) with clinical signs was induced by means of Na2EDTA infusion (0.90 mmol/min), starting at 10 h post-partum. The older cows in the LCa group required more Na2EDTA than those in the HCa group. Higher urinary hydroxyproline excretion in the week before parturition in the LCa than in the HCa group suggested a higher bone turnover. Plasma PTH levels around parturition were not significantly different between the groups. The amount of colostrum milked out in the first 10 h post-partum did not influence Ca homeostasis around parturition. The results contradict those of many other experiments in which hypocalcaemia was observed in cows ingesting high levels of Ca. It is concluded that the restricted feed intake prepartum possibly had a favourable effect on Ca homeostasis. 相似文献
209.
Serum samples collected from 687 indigenous chickens located in small scattered groups in four states of Nigeria were examined for antibodies to infectious bursal disease (IBD) virus by the agar-gel precipitation (AGPT) and counterimmunoelectrophoresis (CIEOP) tests. 51 of the positive samples were further titrated by each of the two techniques. CIEOP detected more positive reactors (74.59%) than AGPT (58.95%). CIEOP also detected higher antibody levels among the reactors [geometric mean titre (GMT) of 51 samples was 23.02] when compared to AGPT. GMT of the same 51 samples was 21.8. The prevalence of antibodies to IBD virus in the indigenous chickens ranged from 64.7 to 77.7% CIEOP reactors between states. Since reports of IBD outbreaks among these chickens are rare unlike the situation among commercial poultry flocks, it was concluded that local chickens probably act as carriers of IBD virus. 相似文献
210.