全文获取类型
收费全文 | 1050篇 |
免费 | 138篇 |
专业分类
林业 | 27篇 |
农学 | 24篇 |
基础科学 | 3篇 |
122篇 | |
综合类 | 65篇 |
农作物 | 47篇 |
水产渔业 | 71篇 |
畜牧兽医 | 767篇 |
园艺 | 19篇 |
植物保护 | 43篇 |
出版年
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 26篇 |
2018年 | 23篇 |
2017年 | 23篇 |
2016年 | 38篇 |
2015年 | 19篇 |
2014年 | 36篇 |
2013年 | 63篇 |
2012年 | 49篇 |
2011年 | 52篇 |
2010年 | 27篇 |
2009年 | 28篇 |
2008年 | 45篇 |
2007年 | 43篇 |
2006年 | 32篇 |
2005年 | 26篇 |
2004年 | 47篇 |
2003年 | 45篇 |
2002年 | 39篇 |
2001年 | 42篇 |
2000年 | 33篇 |
1999年 | 31篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1977年 | 7篇 |
1975年 | 11篇 |
1974年 | 17篇 |
1973年 | 12篇 |
1972年 | 10篇 |
1971年 | 7篇 |
1970年 | 7篇 |
1969年 | 7篇 |
1968年 | 8篇 |
1967年 | 7篇 |
1966年 | 11篇 |
排序方式: 共有1188条查询结果,搜索用时 31 毫秒
91.
92.
Jaramillo TF Jørgensen KP Bonde J Nielsen JH Horch S Chorkendorff I 《Science (New York, N.Y.)》2007,317(5834):100-102
The identification of the active sites in heterogeneous catalysis requires a combination of surface sensitive methods and reactivity studies. We determined the active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) by atomically resolving the surface of this catalyst before measuring electrochemical activity in solution. By preparing MoS2 nanoparticles of different sizes, we systematically varied the distribution of surface sites on MoS2 nanoparticles on Au(111), which we quantified with scanning tunneling microscopy. Electrocatalytic activity measurements for hydrogen evolution correlate linearly with the number of edge sites on the MoS2 catalyst. 相似文献
93.
Sequence-selective recognition of DNA by strand displacement with a thymine-substituted polyamide 总被引:105,自引:0,他引:105
A polyamide nucleic acid (PNA) was designed by detaching the deoxyribose phosphate backbone of DNA in a computer model and replacing it with an achiral polyamide backbone. On the basis of this model, oligomers consisting of thymine-linked aminoethylglycyl units were prepared. These oligomers recognize their complementary target in double-stranded DNA by strand displacement. The displacement is made possible by the extraordinarily high stability of the PNA-DNA hybrids. The results show that the backbone of DNA can be replaced by a polyamide, with the resulting oligomer retaining base-specific hybridization. 相似文献
94.
Vanhollebeke B De Muylder G Nielsen MJ Pays A Tebabi P Dieu M Raes M Moestrup SK Pays E 《Science (New York, N.Y.)》2008,320(5876):677-681
The protozoan parasite Trypanosoma brucei is lysed by apolipoprotein L-I, a component of human high-density lipoprotein (HDL) particles that are also characterized by the presence of haptoglobin-related protein. We report that this process is mediated by a parasite glycoprotein receptor, which binds the haptoglobin-hemoglobin complex with high affinity for the uptake and incorporation of heme into intracellular hemoproteins. In mice, this receptor was required for optimal parasite growth and the resistance of parasites to the oxidative burst by host macrophages. In humans, the trypanosome receptor also recognized the complex between hemoglobin and haptoglobin-related protein, which explains its ability to capture trypanolytic HDLs. Thus, in humans the presence of haptoglobin-related protein has diverted the function of the trypanosome haptoglobin-hemoglobin receptor to elicit innate host immunity against the parasite. 相似文献
95.
Chalcocite Oxidation and Coupled Carbon Dioxide Fixation by Thiobacillus ferrooxidans 总被引:1,自引:0,他引:1
The reaction of cell suspensions of Thiobacillus ferrooxidans with pulverized chalcocite (Cu(2)S) in a Warburg manometric apparatus resulted in oxygen uptake accompanied by increased solubilization of copper and fixation of carbon dioxide. Since the only detectable oxidized products were cupric ions and the more oxidized form of the sulfide mineral, that is, digenite or covellite, the apparent source of energy for the carbon dioxide fixation was provided by the oxidation of the cuprous copper of the chalcocite. 相似文献
96.
Radar soundings of the subsurface of Mars 总被引:2,自引:0,他引:2
Picardi G Plaut JJ Biccari D Bombaci O Calabrese D Cartacci M Cicchetti A Clifford SM Edenhofer P Farrell WM Federico C Frigeri A Gurnett DA Hagfors T Heggy E Herique A Huff RL Ivanov AB Johnson WT Jordan RL Kirchner DL Kofman W Leuschen CJ Nielsen E Orosei R Pettinelli E Phillips RJ Plettemeier D Safaeinili A Seu R Stofan ER Vannaroni G Watters TR Zampolini E 《Science (New York, N.Y.)》2005,310(5756):1925-1928
The martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-circular structure about 250 kilometers in diameter that is interpreted to be an impact basin. In addition, a planar reflector associated with the basin structure may indicate the presence of a low-loss deposit that is more than 1 kilometer thick. 相似文献
97.
98.
99.
An isotope dilution method using [1‐13C]sodium acetate was applied to determine the effect of feeding ensiled hop (Humulus lupulus L.) residues on plasma acetate turnover rate in six adult crossbred sheep. The sheep were fed 63 g/kg body weight (BW)0.75/day of either mixed hay of orchardgrass (Dactylis glomerata L.) and reed canarygrass (Phalaris arundinacea L.) and round bale silage at 3:1 ratio (Hay‐diet), or another where round bale silage was replaced by ensiled hop residues (Hop‐diet) with a crossover design each of a 3‐week period. The isotope dilution method was performed on day 21 of each dietary treatment. Dry matter digestibility was similar between diets, and nitrogen (N) digestibility was lower (P = 0.001) for Hop‐diet than Hay‐diet. However, N retention did not differ between diets. Plasma acetate concentration was lower (P = 0.04) for Hop‐diet than Hay‐diet, and the turnover rate of plasma acetate did not differ between diets. Plasma concentration of lactate and non‐esterified fatty acids were similar between diets. Hop‐diet was found almost comparable to Hay‐diet on plasma acetate turnover rate in the present experimental conditions. Therefore, it could be concluded that hop residues partially could be used as an alternative to traditionally used round bale silage for rearing sheep. 相似文献
100.
Nielsen S Frank C Fruth A Spode A Prager R Graff A Plenge-Bönig A Loos S Lütgehetmann M Kemper MJ Müller-Wiefel DE Werber D 《Zoonoses and public health》2011,58(8):567-572
Infection with sorbitol-fermenting Shiga toxin-producing Escherichia coli O157:H- (sf STEC O157:H-) is rare, but emerging in Europe. The pathogen is typically isolated from paediatric patients with life-threatening haemolytic uraemic syndrome (HUS). It is unclear whether this observation primarily reflects the pathogen's virulence or its complex laboratory diagnosis, not routinely conducted in diarrhoeal patients. In summer 2009, four boys living in the same suburb in Germany developed diarrhoea-associated HUS: three were infected by sf STEC O157:H- and one died. We conducted two analytical epidemiological studies, an extensive search for diarrhoeal cases in potentially exposed groups, and an environmental investigation. Outbreak cases were residents of the suburb diagnosed with HUS, sf STEC O157:H- infection, or both between 24 July 2009 and 25 August 2009. Overall, we ascertained eight cases with a median age of 4 years (range: from 8 months to 9 years). Stool screening of 220 persons led to the identification of only four additional cases: two asymptomatic carriers and two diarrhoeal cases. HUS was strongly associated with visiting a local playground in July, particularly on 16th July (odds ratio = 42.7, P = 0.002). No other commonality, including food, was identified, and all environmental samples (n = 24) were negative. In this localized non-foodborne outbreak, the place of likely infection was a local playground. Sf STEC O157:H- infection apparently limits itself rarely to diarrhoeal illness and progresses frequently to HUS. Therefore, detection of and response to this hypervirulent pathogen primarily relies on HUS surveillance. 相似文献