全文获取类型
收费全文 | 280814篇 |
免费 | 16058篇 |
国内免费 | 688篇 |
专业分类
林业 | 24122篇 |
农学 | 14132篇 |
基础科学 | 2990篇 |
45163篇 | |
综合类 | 30720篇 |
农作物 | 17543篇 |
水产渔业 | 17582篇 |
畜牧兽医 | 113977篇 |
园艺 | 6443篇 |
植物保护 | 24888篇 |
出版年
2021年 | 2533篇 |
2020年 | 2948篇 |
2019年 | 3761篇 |
2018年 | 4340篇 |
2017年 | 4778篇 |
2016年 | 4985篇 |
2015年 | 4408篇 |
2014年 | 5772篇 |
2013年 | 16352篇 |
2012年 | 7409篇 |
2011年 | 9704篇 |
2010年 | 7910篇 |
2009年 | 8423篇 |
2008年 | 9074篇 |
2007年 | 8137篇 |
2006年 | 8486篇 |
2005年 | 7820篇 |
2004年 | 7580篇 |
2003年 | 7367篇 |
2002年 | 6569篇 |
2001年 | 7053篇 |
2000年 | 6844篇 |
1999年 | 6144篇 |
1998年 | 4236篇 |
1997年 | 4294篇 |
1996年 | 4003篇 |
1995年 | 4666篇 |
1994年 | 4019篇 |
1993年 | 3718篇 |
1992年 | 4834篇 |
1991年 | 5009篇 |
1990年 | 4715篇 |
1989年 | 4698篇 |
1988年 | 4152篇 |
1987年 | 4181篇 |
1986年 | 4181篇 |
1985年 | 4425篇 |
1984年 | 4002篇 |
1983年 | 3719篇 |
1982年 | 3030篇 |
1981年 | 2880篇 |
1980年 | 2876篇 |
1979年 | 3566篇 |
1978年 | 3128篇 |
1977年 | 2870篇 |
1976年 | 2739篇 |
1975年 | 2665篇 |
1974年 | 2851篇 |
1973年 | 2830篇 |
1972年 | 2470篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
661.
G. B. J. Chapola 《Wood Science and Technology》1989,23(2):131-138
Summary The aim of this study was to investigate the influence of temperature, alkali and cement set on the visco-elastic properties of chip mattresses made in cement and calcium hydroxide, respectively. Two temperatures were used, room temperature and 78°C, believed to represent the limits of the range of temperatures experienced industrially in the manufacture of cement composites. Calcium hydroxide and cement were used to find the effect of alkali and the effect of cement set. The temperature affected the visco-elastic properties by increasing the unrecovered strain, and alkali also increased the unrecoverable strain. The effect of heat and alkali increased when the two were used in combination. In cement chip composites, the effect of cement set was the most dominant that the effect of heat and alkali could not be observed.I am indebted to Dr. A. J. Bolton of the University College of North Wales, Bangor, for his assistance. This study was carried out at this university as an Honours Project 相似文献
662.
D A Benz F M Byers G T Schelling L W Greene D K Lunt S B Smith 《Journal of animal science》1989,67(9):2393-2399
The effects of ionophores on liver weight and function were determined in finishing steers (n = 24; avg weight 440 kg). Steers were group-fed one of three treatments (control, lasalocid or monensin at 33 mg/kg feed) for 46 d prior to slaughter. Three days prior to slaughter, blood was collected for the determination of serum Ca and Mg. At slaughter, the liver was removed, weighed, sampled, frozen in liquid nitrogen and subsequently analyzed for concentrations of carbohydrate metabolites and minerals. Liver weight (5.9 kg) was unaffected by treatment. Serum and hepatic Ca and Mg were not affected by ionophore treatment. Hepatic glycogen levels in steers fed ionophores were unaffected by treatment. Fructose 1,6-bisphosphate was 21% lower (P less than .10) in hepatic tissue of steers fed ionophores, whereas dihydroxyacetone phosphate was 15 to 37% greater in hepatic tissue of steers fed monensin (P less than .20) or lasalocid (P less than .10). Glyceraldehyde 3-phosphate was elevated more extensively by lasalocid than by monensin with increases of 72 (P less than .05) and 132% (P less than .001), respectively, over controls. Glycerol 3-phosphate levels were 37% (P less than .05) and 12% (NS) greater with these ionophores. Hepatic levels of pyruvate were elevated 12 (NS) to 36% (P less than .17) for monensin and lasalocid. Fructose 2,6-bisphosphate levels were 25% lower (P less than .25) in hepatic tissue of steers fed ionophores than in hepatic tissue from control steers. Other metabolites of carbohydrate metabolism in hepatic tissue were not altered appreciably. Changes in levels of intermediary metabolites of carbohydrate metabolism suggest alterations in hepatic carbohydrate metabolism favoring gluconeogenesis in steers fed ionophores. 相似文献
663.
Age at death from natural scrapie in a flock of Suffolk sheep 总被引:1,自引:0,他引:1
This study deals with natural scrapie in a flock of Suffolk sheep being bred to maximise the incidence of the disease and shows that with succeeding generations the incubation period of the disease became progressively shorter until the flock died out. The most likely explanation for this phenomenon is considered to be an increase in the load of infection. 相似文献
664.
665.
We studied the ability of lambs to select safe foods in the presence of harmful foods. In a series of feeding experiments, 3- to 6-mo-old lambs were offered a choice between 1) a familiar, safe and a novel, harmful food, 2) a novel, safe and a novel, harmful food and 3) a familiar, harmful and a novel, safe food. All harmful foods were palatable feeds that had been treated with lithium chloride (LiCl), a non-lethal gastrointestinal poison. When lambs ingested a meal composed of a novel food containing LiCl and a familiar, safe food, lambs subsequently avoided the novel food. Lambs avoided the novel food even when the familiar food contained LiCl. The response of lambs varied when lambs were given a choice between a novel, safe food and a novel food containing LiCl. Lambs either avoided the novel food containing LiCl and ingested the safe food or they limited their intake of both novel foods. Their response was dependent on the novelty of the food containing LiCl. When a novel, palatable food contained 2% LiCl, lambs always ate some of the food, even after experiencing illness from ingesting it. Lambs experienced with foods containing LiCl displayed greater food neophobia than lambs naive to LiCl-treated foods. Thus, novelty was the major criterion that lambs used to associate foods with gastrointestinal illness. 相似文献
666.
W. M. PEDERSOLI J. S. SPANO L. M. KRISTA.† J. F. WHITESIDES.† W. R. RAVISH‡ R.J. KEMPPAINEN D. W. YOUNG 《Journal of veterinary pharmacology and therapeutics》1989,12(2):200-208
The effects of single i.v. and p.o. doses (5 mg/kg) of fenbendazole, were evaluated on thyroxine, tri-iodothyronine, corticosterone, hematology, clinical chemistries, and serum proteins in 10 white Pekin ducks. Fenbendazole was administered i.v. (n = 5) as a 3% dimethyl sulfoxide solution and p.o. (n = 5) as a 10% commercial suspension. Serum enzyme concentrations, total protein and protein fractions, glucose, cholesterol, uric acid, sodium, and potassium were unchanged from baseline values. Serum triglycerides decreased consistently in the i.v.-treated group but remained unchanged in the p.o.-treated group. Serum chloride was consistently elevated above baseline values for both i.v.- and p.o.-treated ducks, while inorganic phosphate was consistently decreased only in the i.v.-treated group. Hemoglobin and hematocrit values generally were below baseline values. Leukocyte values varied considerably and were not significantly different from baseline values. Serum thyroxine and tri-iodothyronine values in both the i.v.- and p.o.-treated groups were not changed significantly from baseline values. Serum corticosterone values were not changed in the i.v.-treated groups but they were decreased at various times in the p.o.-treated group. Although there were some sporadic significant changes in the parameters measured versus baseline values all values remained within the physiologic limits for ducks. The safety of fenbendazole has been previously demonstrated for several species. 相似文献
667.
M. A. Gomez J. A. Navarro S. Gomez P. Camara J. C. Gomez A. Bernabé 《Anatomia, histologia, embryologia》1989,18(4):305-315
The structure and ultrastructure of the adenohypophyseal pars distalis in kids of the Murciano-granadiana breed (18 males and 12 females), aged 2-3 months and with an average carcass weight of 8 kg has been studied. Techniques of staining (Tetrachrome Herlant's, and Cleveland-Wolfe) and histochemistry (PAS, PAS-OG and BA-PAS-OG) contrasted with immunolabelling (PAP) have been used. In addition an ultrastructural study has been made and nucleus and cytoplasm, secretory granules, mitochondria and lysosomes have been measured with a semiautomatic image analyzer (IBAS-1). TSH cells are found in sagittal section in the anterior area and in an antero-caudodorsal band, and transversally in the ventral and medial region; they are 6% and their average size is 14.15 microns. Ultrastructurally they are a single cellular type with spherical granules whose size is 195 nm in males and 149 in females; these granules are characterized by a clear halo and a variable electronic density. The rough endoplasmic reticulum is found as slightly enlarged vesicles with a homogeneous and moderately electro-dense content or in concentric stratifications. 相似文献
668.
M J Corbel F A Stuart R A Brewer M Jeffrey R Bradley 《The British veterinary journal》1989,145(4):347-355
Attempts to reproduce in calves the arthropathy associated with Brucella abortus strain 19 (S19) vaccination by direct intra-articular injection of S19 or virulent Brucella cells were unsuccessful. Intra-articular injection of rabbits and a calf with immune complexes isolated from the synovial fluid of a field case produced clinical and histological signs of arthropathy accompanied by the development of rheumatoid factor. 相似文献
669.
670.
M.L. Castor BS R.E. Wooley DVM PhD E.B. Shotts PhD J. Brown DVM PhD J.B. Payeur DVM PhD 《Journal of Equine Veterinary Science》1989,9(5)
During an outbreak of equine salmonellosis in a veterinary teaching hospital 20 Salmonella isolates were cultured from sick horses (13 isolates) or from the hospital environment (7 isolates). Three serotypes were isolated from the environment including: S. give, S. newportand S. agona. The serotypes isolated from horses included: S. give, S. newport and S. anatum. Examination of antibiotic profiles, presence of plasmids, production of bacteriocins and hemagglutination of erythrocytes implied a common origin for the equine and environmental isolates. 相似文献