全文获取类型
收费全文 | 123829篇 |
免费 | 6221篇 |
国内免费 | 75篇 |
专业分类
林业 | 5464篇 |
农学 | 3877篇 |
基础科学 | 861篇 |
13966篇 | |
综合类 | 24337篇 |
农作物 | 4780篇 |
水产渔业 | 5625篇 |
畜牧兽医 | 62192篇 |
园艺 | 1459篇 |
植物保护 | 7564篇 |
出版年
2018年 | 1462篇 |
2017年 | 1558篇 |
2016年 | 1488篇 |
2015年 | 1280篇 |
2014年 | 1579篇 |
2013年 | 4234篇 |
2012年 | 3015篇 |
2011年 | 3607篇 |
2010年 | 2418篇 |
2009年 | 2461篇 |
2008年 | 3715篇 |
2007年 | 3468篇 |
2006年 | 3449篇 |
2005年 | 3243篇 |
2004年 | 3240篇 |
2003年 | 3300篇 |
2002年 | 3129篇 |
2001年 | 3553篇 |
2000年 | 3505篇 |
1999年 | 2865篇 |
1998年 | 1353篇 |
1997年 | 1263篇 |
1995年 | 1338篇 |
1994年 | 1305篇 |
1993年 | 1239篇 |
1992年 | 2577篇 |
1991年 | 2645篇 |
1990年 | 2841篇 |
1989年 | 2742篇 |
1988年 | 2565篇 |
1987年 | 2467篇 |
1986年 | 2516篇 |
1985年 | 2445篇 |
1984年 | 2071篇 |
1983年 | 1853篇 |
1982年 | 1251篇 |
1979年 | 1944篇 |
1978年 | 1576篇 |
1977年 | 1408篇 |
1976年 | 1344篇 |
1975年 | 1465篇 |
1974年 | 1769篇 |
1973年 | 1757篇 |
1972年 | 1792篇 |
1971年 | 1716篇 |
1970年 | 1637篇 |
1969年 | 1532篇 |
1968年 | 1226篇 |
1967年 | 1401篇 |
1966年 | 1253篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
J Jieyuan P B Spradbrow 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1992,39(5):388-390
Chickens were given various fowlpox vaccines on food pellets--a commercial vaccine (strain M), and the same strain after a single passage on chorio-allantoic membrane or in chicken embryo fibroblasts. All three oral vaccines induced antibodies at levels similar to those induced by commercial strain M administered to the wingweb. The oral vaccine derived from chorio-allantoic membrane gave protection similar to that obtained with vaccine administered by the wingweb, but this required a thousandfold more virus. 相似文献
42.
A W Mills 《Veterinary Clinics of North America: Small Animal Practice》1992,22(6):1297-1307
The impact and relevance of dentistry in a general feline practice is detailed. Hospital policy and protocol are described for client education, preanesthetic evaluation, dental procedures, and recall programs. A discussion of commonly observed feline dental problems is included. 相似文献
43.
Water-stable macro-aggregate size fractions (>2.0 mm, 1.0–2.0 mm, 0.5–1.0 mm and 0.25–0.5 mm) and non-aggregated soil from a sandy loam under long-term clover-based pasture and from grass pasture were analysed to determine the role of acid- and water-extractable carbohydrate C, total hyphal length, microbial biomass, organic C and total and mycorrhizal root length in stabilization of the aggregates. Aggregates were examined by scanning electron microscopy (SEM) and the particle-size distribution of the size fractions was also determined. Macro-aggregation increased under grass, relative to clover-based pasture; however, the properties of the aggregate fractions measured did not reflect this difference. Microbial-biomass C, extractable-carbohydrate C, hyphal length, total and mycorrhizal root length and organic C content of the soils were poorly correlated with macro-aggregation. Within the aggregates, the proportion of 250–1000-km sand was smaller and clay, silt and fine sand (20–250 μm) were greater relative to non-aggregated soil, suggesting that the >250-μm sand in the non-aggregated soil limited the stabilization of macro-aggregates. Under SEM, no enmeshment of aggregates by hyphae and roots was apparent. Although 50–160 m hyphae g?1 soil was found within the aggregates, calculations showed that on average only 5 to 13 lengths of hyphae were associated with each 250-μm cube of soil within the aggregates, and suggested little potential to stabilize the aggregates by enmeshing. On average, all >2.0-mm aggregates contained less than 3.6 mm of roots and less than 50% by weight of <2.0-mm aggregates contained a single length of root. The findings cast doubt about the role of hyphae and fine roots in the stabilization of macro-aggregates through an enmeshing mechanism in sandy soils. 相似文献
44.
W Schulze 《Berliner und Münchener tier?rztliche Wochenschrift》1989,102(7):233-235
The paper gives an overview of the history of the school of vet. med. technicians at the School of Veterinary medicine Hannover. 相似文献
45.
The plants of field bean var. Nadwiślaνski were detopped after about 1 month since the beginning of flowering and after that all flower buds were removed from some plants. The effect of a change in the trophic balance on the setting and subsequent growth of root nodules was studied.
The removal of pods had the greater effect on the increase in the weight of the remaining organs than the detopping of plants. Detopping retarded the ageing of the plants and delayed the phase of the greatest reduction of the number of pods. The detopping of plants revealed their considerable compensative possibilities in terms of production of the pod weight and the potential of leaves for biomass production. The data obtained indicate that plant detopping may disturb the root–bacteria exchange of signals, necessary to initiate the nodule development, while the further growth of nodules depends, above all, on the amount of available photosynthates.
A very high correlation between the dry weight of the whole plant to the dry weight of leaves ratio and the weight of nodules was observed. It proves the importance of the trophic balance of the plant for the root nodule weight production. 相似文献
The removal of pods had the greater effect on the increase in the weight of the remaining organs than the detopping of plants. Detopping retarded the ageing of the plants and delayed the phase of the greatest reduction of the number of pods. The detopping of plants revealed their considerable compensative possibilities in terms of production of the pod weight and the potential of leaves for biomass production. The data obtained indicate that plant detopping may disturb the root–bacteria exchange of signals, necessary to initiate the nodule development, while the further growth of nodules depends, above all, on the amount of available photosynthates.
A very high correlation between the dry weight of the whole plant to the dry weight of leaves ratio and the weight of nodules was observed. It proves the importance of the trophic balance of the plant for the root nodule weight production. 相似文献
46.
David F. Edwards DVM John W. Parker DVM J. Erby Wilkinson DVM PhD R. Gayman Helman DVM PhD 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1993,7(3):169-176
Plasma cell myelomas in horses have been reported infrequently. Data from 10 cases, 9 from the literature and 1 new case, are used to characterize the disease in the horse. Hot-blooded horses (7/10), specifically Quarter Horses (4/10), were most often affected. Median age at diagnosis was 11 years (range, 3 mo-22 yr) and both male (5) and female horses (5) were represented equally. Clinical findings included weight loss (6/8), anorexia (4/8), fever (4/8), limb edema (4/8), pneumonia (3/8), rear leg paresis/ataxia (3/8), epistaxis (3/8), palpable lymphadenopathy (2/8), and bone pain (2/8). Anemia (8/8) was present routinely, and in three horses, RBCs were macrocytic. Leukopenia (2/8), thrombocy-topenia (2/8), and circulating plasma cells (3/8) were variable findings. Except for abnormal protein concentrations and hyponatremia (3), abnormal results from serum biochemical analysis including hypo-cholesterolemia (1), hypercalcemia (1), and azotemia (1) were reported infrequently. Hyperproteinemia (8/9), hypoalbuminemia (7/9), and hyperglobulinemia (8/9) were characteristic but not invariable findings. Monoclonal proteins (7/7) were detected in the α2, β, or γ region by serum electrophoresis. The paraprotein's heavy chain, determined in four horses, was a subclass of IgG. Three horses had decreased concentrations of normal immunoglobulins. Variable proteinuria (trace to 4+) was detected by routine urinalysis in four of six horses. Bence Jones proteinuria was detected in one of five horses (heat precipitation) and monoclonal proteins were detected in two of three electrophoresed urine samples. Three of the horses had lytic bone lesions detected radiographically. Bone marrow aspirates were diagnostic in two of five horses. Atypical plasma cells or increased numbers of plasma cells or both were present in histologic sections of bone marrow in six of eight horses. Common extraosseous sites of plasma cell infiltration included lymph nodes (8/8), kidney (5/8), spleen (5/8), liver (3/8), lung (3/8), brain (2/8), and orbit (2/8). Two horses had intracellular and extracellular crystalline deposits. 相似文献
47.
In this clinical study, a diaphragmatic peritoneo-pericardial hernia in an eight month-old Persian cat is reported. The diagnostic procedure is described, and the clinical symptoms and diagnostic possibilities are discussed. 相似文献
48.
49.
F Urayama T Sato H Shibuya W Shirai M Matsutani R Yamazaki 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(11):1249-1252
An apocrine adenocarcinoma was observed in the subcutis of the abdomen of golden hamster. Histologically, the tumor cells irregularly formed multiple layers of cysts and some detached cells were presented in the cystic space. PAS stain with alpha-amylase digestion revealed PAS-positive alpha-amylase-resistant granules in the cytoplasm. Immunohistochemically, cytokeratin was demonstrated in the tumor cells. By electron microscopy, the tumor cells had an oval nucleus with invagination, abundant cytoplasmic organelles and microvilli protruding into the intercellular spaces. 相似文献
50.
P. Banik 《Journal of Agronomy and Crop Science》1996,176(5):289-294
A field experiment was conducted during the winter season of 1992–93 and 1993–94 at Agricultural Experimental Farm, Giridih, Bihar to evaluate the intercropping systems of legumes, gram ( Cicer arietinum L.), pea ( Pisum sativum ) and lentil ( Lens culinaris ) with wheat ( Triticum aestivum ) in 1:1 and 2:1 'row replacement series'. Intercropping systems were assessed on the basis of new indices termed as actual yield loss (AYL) and intercropping advantage (IA). This paper highlights the comparative effectiveness of evaluating the intercropping systems through the existing intercropping indices like LER, RCC, aggressivity. The indices AYL and IA seem to be more appropriate particularly when per plant yield is considered. Intercropping reduced the yield of component crops compared with respective pure stands. Wheat + pea in 1:1 row replacement series gave the highest wheat yield equivalent value (3.02 t ha−1 ) followed by wheat + lentil (2.91 tha−1 ). When the actual sown proportion was considered wheat + lentil (1:1) resulted in maximum AYL (+0.610) and IA (+0.279) values. This treatment also gave the maximum monetary advantage (Rs 5985.45 ha−1 ). 相似文献