全文获取类型
收费全文 | 105456篇 |
免费 | 5520篇 |
国内免费 | 52篇 |
专业分类
林业 | 4309篇 |
农学 | 3038篇 |
基础科学 | 729篇 |
11682篇 | |
综合类 | 20721篇 |
农作物 | 4294篇 |
水产渔业 | 4619篇 |
畜牧兽医 | 54326篇 |
园艺 | 1195篇 |
植物保护 | 6115篇 |
出版年
2018年 | 1204篇 |
2017年 | 1331篇 |
2016年 | 1284篇 |
2015年 | 1090篇 |
2014年 | 1260篇 |
2013年 | 3931篇 |
2012年 | 2564篇 |
2011年 | 3184篇 |
2010年 | 2077篇 |
2009年 | 2054篇 |
2008年 | 3205篇 |
2007年 | 2937篇 |
2006年 | 2801篇 |
2005年 | 2637篇 |
2004年 | 2745篇 |
2003年 | 2678篇 |
2002年 | 2621篇 |
2001年 | 3272篇 |
2000年 | 3288篇 |
1999年 | 2440篇 |
1998年 | 1070篇 |
1997年 | 1081篇 |
1995年 | 1251篇 |
1994年 | 1164篇 |
1993年 | 1121篇 |
1992年 | 2362篇 |
1991年 | 2530篇 |
1990年 | 2438篇 |
1989年 | 2493篇 |
1988年 | 2272篇 |
1987年 | 2349篇 |
1986年 | 2484篇 |
1985年 | 2394篇 |
1984年 | 1918篇 |
1983年 | 1773篇 |
1982年 | 1165篇 |
1981年 | 1123篇 |
1980年 | 1025篇 |
1979年 | 1762篇 |
1978年 | 1424篇 |
1977年 | 1146篇 |
1976年 | 1130篇 |
1975年 | 1165篇 |
1974年 | 1524篇 |
1973年 | 1610篇 |
1972年 | 1584篇 |
1971年 | 1515篇 |
1970年 | 1408篇 |
1969年 | 1262篇 |
1967年 | 1094篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A technique is described for biopsy of the bovine udder, employing sedation and local anaesthesia. Tissue samples of approximately 5 g were obtained by electrocautery from two quarters of the udder of a cow laterally recumbent. Care was taken to ensure complete haemostasis which was achieved by electrocoagulation and ligation. Postoperative recovery was rapid, and loss of yield was no greater in biopsied glands than in control glands of the same cow. Yield from all quarters returned to preoperative levels within 48 h. 相似文献
52.
The pyrimidine analog 5-bromodeoxyuridine (BUdR) competes with thymidine for incorporation into DNA. Substitution of BUdR for thymidine does not significantly affect cell viability but does block cell differentiation in many different lineages. BUdR substitution in a mouse myoblast line blocked myogenic differentiation and extinguished the expression of the myogenic determination gene MyoD1. Forced expression of MyoD1 from a transfected expression vector in a BUdR-substituted myoblast overcame the block to differentiation imposed by BUdR. Activation of BUdR-substituted muscle structural genes and apparently normal differentiation were observed in transfected myoblasts. This shows that BUdR blocks myogenesis at the level of a myogenic regulatory gene, possibly MyoD1, not by directly inhibiting the activation of muscle structural genes. It is consistent with the idea that BUdR selectively blocks a class of regulatory genes, each member of which is important for the development of a different cell lineage. 相似文献
53.
29 samples of commonly used surfaces were tested for their water characteristics (litre weight, water capacity, water binding, water evaporation) and their contribution to airborne fungal spores (dust formation, dust setting). The results are discussed in comparison to the literature with regard to the environment. The results are: 1. Any surface--no matter of what material--eventually causes air pollution with fungal spores and dust. 2. Correct watering prevents air pollution by any surface. 3. Artificial products have no advantage over natural materials in the parameters tested. 4. The question of proper disposal of old surface material has to be clarified before purchase. The results show that a mixture of sand and wood shavings should be recommended as a surface for indoor arenas, especially in regard to environmental protection and proper disposal. 相似文献
54.
55.
56.
A strain of Yersinia enterocolitica of O serogroup 6,30 isolated from the liver of an aborted ovine fetus was inoculated intravenously into a group of pregnant ewes at about 90 days gestation and produced placentitis with abortion or delivery of infected lambs about 50 days later. Y. enterocolitica of the same serogroup was recovered from the necrotic placental cotyledons and most other fetal tissues and could be isolated from vaginal discharges of the ewes for a least 2 weeks after abortion. Histological changes were consistent with an acute bacterial necrotizing placentitis and systemic infection of the fetus. Subsequent pregnancies in the ewes proceeded to term without evidence of infection. 相似文献
57.
PULMONARY MINERALIZATION IN FOUR DOGS WITH CUSHING'S SYNDROME 总被引:1,自引:0,他引:1
Clifford R. Berry DVM Norman Ackerman DVM Kevin Monce DVM 《Veterinary radiology & ultrasound》1994,35(1):10-16
The clinical and imaging features of four dogs with Cushing's syndrome and pulmonary mineralization are reviewed. Three dogs presented with a primary complaint of respiratory distress/dyspnea. Three dogs had pituitary dependent Cushing's syndrome, while the remaining one dog had iatrogenic Cushing's syndrome. Each dog had clinical features typical for Cushing's syndrome. Two of the dogs were euthanized due to progressive hypoxemia. In each dog, the serum calcium, phosphorous, blood urea nitrogen and creatinine were normal.
A generalized increase in unstructured interstitial pulmonary opacity with diffuse mineralization was noted on thoracic radiographs of all dogs. In one dog, an ill-defined nodular interstitial pattern of mineralization was present. Delayed bone phase scintigraphy using99m Technetium methylene diphosphonate documented generalized pulmonary uptake in two dogs. 99m Technetium labeled microaggregated albumin lung perfusion scans were normal in these two dogs. 99m Tc-MDP scintigraphy can provide useful information in diagnosing pulmonary mineralization in Cushingoid dogs. 相似文献
A generalized increase in unstructured interstitial pulmonary opacity with diffuse mineralization was noted on thoracic radiographs of all dogs. In one dog, an ill-defined nodular interstitial pattern of mineralization was present. Delayed bone phase scintigraphy using
58.
In a companion paper we derived the correct analysis for gerechte designs with uncorrected errors. Here we show that this correct analysis cannot be justified by the usual randomization argument. However, when the regions are rectangular there is a randomization procedure which validates an analysis with three separate error terms. We also outline other developments in design and analysis that may be more satisfactory. 相似文献
59.
High-resolution computed tomography (HRCT) was performed in 21 isolated animal lungs, from 4 mammalian species (pigs, rabbits, dogs, sheep). Gross and subgross central and peripheral lung morphology was determined by HRCT. Three distinct types of lungs can be identified, principally based on the extent of interlobular septal development; the relationship of major vessels to airways; and the thickness of the visceral pleura. Type-I lung is found in pigs, sheep, and cattle; type-II lung is found in rabbits, dogs, cats, and monkeys; and type-III lung is found in human beings and horses. These mammalian lungs were compared with human lungs. The potential use of HRCT to investigate specific human lung diseases in the aforementioned species also was considered. 相似文献
60.
Abstract. The effect of Medicago arborea on erosion on a burnt area was studied in experimental plots near Valencia, Spain, between 1989 and 1992. Its growth and development was studied, and its effect was compared with the natural vegetation (matorral) and bare soil. Medicago decreased soil loss by 41.7% and runoff by 25.7% compared with bare soil. However, under natural vegetation soil loss was 27.5% less than under Medicago. 相似文献