全文获取类型
收费全文 | 2124篇 |
免费 | 123篇 |
国内免费 | 62篇 |
专业分类
林业 | 240篇 |
农学 | 69篇 |
基础科学 | 23篇 |
380篇 | |
综合类 | 184篇 |
农作物 | 115篇 |
水产渔业 | 214篇 |
畜牧兽医 | 841篇 |
园艺 | 76篇 |
植物保护 | 167篇 |
出版年
2024年 | 4篇 |
2023年 | 24篇 |
2022年 | 34篇 |
2021年 | 64篇 |
2020年 | 48篇 |
2019年 | 44篇 |
2018年 | 93篇 |
2017年 | 85篇 |
2016年 | 81篇 |
2015年 | 47篇 |
2014年 | 77篇 |
2013年 | 151篇 |
2012年 | 119篇 |
2011年 | 131篇 |
2010年 | 102篇 |
2009年 | 92篇 |
2008年 | 102篇 |
2007年 | 106篇 |
2006年 | 77篇 |
2005年 | 99篇 |
2004年 | 56篇 |
2003年 | 95篇 |
2002年 | 98篇 |
2001年 | 95篇 |
2000年 | 64篇 |
1999年 | 47篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 29篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1972年 | 5篇 |
1967年 | 9篇 |
1966年 | 6篇 |
排序方式: 共有2309条查询结果,搜索用时 19 毫秒
941.
B.E. Söderström 《Soil biology & biochemistry》1979,11(2):149-154
Metabolically-active fungal biomass, as determined with fluorescein diacetate (FDA) staining, was studied during a 27-month period (21 samplings) in three horizons of a podzolized pine-forest soil. Recurrent definite biomass peaks were registered in autumn and early spring. Biomass increase was also noted during the winter with soil temperatures below 0°C. Only a minor fraction (2.4–4.3%) of the total fungal biomass was found to be active. The FDA-active biomass m?2 was equally distributed between the organic (5 cm) and mineral (15 cm) soil horizons, and varied between 0.5 and 2.4 g d.w. m?2. The amount of FDA-active biomass was correlated with soil moisture content. 相似文献
942.
943.
944.
K E Johansson J G Mattsson K Jacobsson C Fernandez K Bergstr?m G B?lske P Wallgren U B G?bel 《Research in veterinary science》1992,52(2):195-204
Mycoplasma is the common name for the smallest free-living microorganisms, the Mollicutes. Mycoplasma hyopneumoniae is of great importance in veterinary medicine, causing enzootic pneumonia in pigs. M hyorhinis can cause polyserositis and may cause pneumonia in piglets. Oligonucleotides complementary to variable regions of 16S rRNA from these mycoplasmas were designed and used as probes for detection and identification of these mycoplasmas. The probe complementary to 16S rRNA of M hyorhinis gave a very weak cross-hybridisation with M hyosynoviae in filter hybridisation experiments, but not with any of the other porcine mycoplasmas tested. Three oligonucleotide probes complementary to M hyopneumoniae 16S rRNA were tested. One of the probes (Mhp6/30) was found to be specific to M hyopneumoniae, but the other two gave cross-hybridisation with M flocculare. Using the Mhp6/30 probe in direct filter hybridisation experiments, it proved possible to detect M hyopneumoniae in lung biopsies from experimentally infected pigs. 相似文献
945.
946.
Cell-bound immunity to autologous and syngeneic mouse tumors induced by methylcholanthrene and plastic discs 总被引:2,自引:0,他引:2
A colony-inhibition assay, was lused to demonstrate specific immunity in vitro against syngeneic mouse sarcomas induced by mlethlylcholanthrene or implanted Dictabelt plastic discs. An immunity to methylcholanthrene-induced tumors could also be demonstrated with lymphocytes derived from the autologous primary tumor-bearing host 3 to 8 days after removal of the primary tumor. 相似文献
947.
Effects of stress on concentrations of cortisol and corticosteroid-binding globulin (CBG) in blood plasma and on glucocorticoid receptor concentrations in muscle cytosol were studied in pigs representing three Halothane (Hal) genotypes (NN, Nn, nn). At 12 wk of age, animals were divided into four groups: pigs subjected to transport (5 h in a truck), pigs treated with amperozide prior to transport, pigs not transported but treated with amperozide and pigs neither transported nor given amperozide. Animals were slaughtered the week they reached 100 kg live weight (3 mo later). The Hal gene showed no major influence on the variables studied except for cortisol concentrations (P = .06) measured directly after transport at 12 wk of age (NN = 66.8 nM, Nn = 61.4 nM, nn = 69.4 nM). However, the response in each Hal genotype differed, depending on whether or not the pigs had been exposed to transport. Two weeks after transport, NN pigs developed higher cortisol concentrations than untransported animals, whereas the response was reversed in nn animals; Nn pigs showed no difference in this regard. At slaughter, the effect of transport (12 wk of age) on cortisol and CBG was still apparent. In NN pigs cortisol and CBG concentrations were elevated (P less than or equal to .05, P = .08, respectively), whereas concentrations tended to be lower in nn pigs (P = .17, P = .07, respectively) when compared with untransported pigs. Transported pigs had lower receptor concentrations at slaughter (P less than or equal to .01) than untransported pigs. However, pigs given amperozide in connection with transport had a receptor concentration comparable to that in untransported pigs. Our study shows conclusively that transport stress had long-term effects on cortisol, CBG and glucocorticoid receptor concentrations. In addition, amperozide had long-term effects on cortisol and receptor concentrations. 相似文献
948.
949.
950.
Summary A qualitative analysis is presented of failure, perpendicular to the grain, in laminated timber reinforced with a glass fibre composite. The study is focused on beams with holes of different shape. The stress by corners, infinitesimal cracks and finite cracks are investigated. An initial crack model is suggested that brings about some of the phenomena observed in earlier performed experiments. A crack appears to propagate in the wood but is retarded in the reinforced beams. Eventually, the composite will fracture and failure of the beam follows. Finite element computations suggest that the reinforcement decreases the stress intensity at cracks in the wood and acts as a crack stopper. The reinforcing effect increases with the crack length. A point stress criterion is used to predict failure in the fibre composite. 相似文献