全文获取类型
收费全文 | 508篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
林业 | 74篇 |
农学 | 10篇 |
基础科学 | 1篇 |
184篇 | |
综合类 | 61篇 |
农作物 | 12篇 |
水产渔业 | 12篇 |
畜牧兽医 | 109篇 |
园艺 | 12篇 |
植物保护 | 47篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 20篇 |
2011年 | 30篇 |
2010年 | 24篇 |
2009年 | 10篇 |
2008年 | 27篇 |
2007年 | 35篇 |
2006年 | 37篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 23篇 |
2002年 | 23篇 |
2001年 | 15篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1991年 | 4篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 3篇 |
1966年 | 7篇 |
排序方式: 共有522条查询结果,搜索用时 0 毫秒
41.
42.
Milling fractions from conventional and transgenic corn were prepared at laboratory scale and used to study the influence of sample composition and heat-induced DNA degradation on the relative quantification of genetically modified organisms (GMO) in food products. Particle size distributions of the obtained fractions (coarse grits, regular grits, meal, and flour) were characterized using a laser diffraction system. The application of two DNA isolation protocols revealed a strong correlation between the degree of comminution of the milling fractions and the DNA yield in the extracts. Mixtures of milling fractions from conventional and transgenic material (1%) were prepared and analyzed via real-time polymerase chain reaction. Accurate quantification of the adjusted GMO content was only possible in mixtures containing conventional and transgenic material in the form of analogous milling fractions, whereas mixtures of fractions exhibiting different particle size distributions delivered significantly over- and underestimated GMO contents depending on their compositions. The process of heat-induced nucleic acid degradation was followed by applying two established quantitative assays showing differences between the lengths of the recombinant and reference target sequences (A, deltal(A) = -25 bp; B, deltal(B) = +16 bp; values related to the amplicon length of the reference gene). Data obtained by the application of method A resulted in underestimated recoveries of GMO contents in the samples of heat-treated products, reflecting the favored degradation of the longer target sequence used for the detection of the transgene. In contrast, data yielded by the application of method B resulted in increasingly overestimated recoveries of GMO contents. The results show how commonly used food technological processes may lead to distortions in the results of quantitative GMO analyses. 相似文献
43.
Ulrich?F?rstnerEmail author Susanne?Heise René?Schwartz Bernhard?Westrich Wolfgang?Ahlf 《Journal of Soils and Sediments》2004,4(4):247-260
Background, Aims, and Scope
Data from the Elbe River and its tributaries indicate, despite extensive improvement in water quality during the last 15 years, that the respective sediment situation of many priority pollutants has not reached an acceptable level. For the coming decades, risks for downstream sites and stakeholders will persist, mainly due to secondary sources originating from historical pollution of soils and sediments in the catchment area. In practice, a catchment-wide assessment of historical contaminated soil and sediment should apply a three-step approach: (i) Identification of substances of concern (s.o.c.) and their classification into ’hazard classes of compounds’; (ii) identification of areas of concern (a.o.c.) and their classification into ‘hazard classes of sites’; (iii) identification of areas of risk (a.o.r.) and their assessment relative to each other with regard to the probability of polluting the sediments in the downstream reaches. The conversion of this concept has to consider the underlying philosophy of the EU Water Framework Directive, particularly with respect to the analysis and monitoring of priority substances in solid matrices. However, major deficiencies are still in the assessment and prognosis of resuspension processes, and potential approaches to fill this gap are described both in theory and from examples of the Elbe River. 相似文献44.
B. Ulrich 《植物养料与土壤学杂志》1981,144(3):289-305
Ecological grouping of soils according to their chemical soil state On the base of the solubility of carbonic acid, calcium carbonate, as well as the oxidic compounds of Al and Fe existing in soils, the following buffer ranges are defined and separated from each other by pH values in the soil solution: Carbonic acid/Carbonate buffer range (pH 6.2 to 8.6), Carbonic acid/Silicate buffer range (pH 5.0 to 6.2), Exchanger buffer range (pH 4.2 to 5.0), Aluminium buffer range (pH 2.8 to 4.2), Iron buffer range (pH 2.4 to 3.8). The buffer capacities are calculated and literature indications regarding buffer rates are compiled. The characteristical chemical soil state is demonstrated for the various buffer ranges with aid of a soil collection. With increasing soil acidification the Ca/Al mole ratio in fine roots decreases from values > 1 to values around 0.3; this is taken as evidence for increasing disposition for Al-toxicity. It is suggested to attach soil horizons to buffer ranges on the base of pH(H2O) measurements made on field fresh samples. The measurement of pH in salt solution is taken as measure for the amplitude of the chemical soil state in case of H-ion or salt stress. 相似文献
45.
The concentrations of trace and toxic metals in soil solutions are explained by several authors either in terms of adsorption—desorption or precipitation—dissolution reactions in soils. Data have been given for zinc to test the applicability of both concepts. The results show that the concentrations of zinc in equilibrium solutions with soil clay fractions and whole soil samples at pH values below 7 are determined exclusively by adsorption—desorption reactions for various pH's, contents of bound zinc and compositions of soils. At neutral to alkaline pH values precipitation—dissolution reactions of zinc may take place. There is some evidence that formation of zinc silicates may control the zinc concentration in solution provided natural complexing agents are absent, the affinity of the soil for zinc is low and the content of reaching zinc is high (> ~ 100 ppm). Even at pH values above 7, the formation of other zinc compounds is unlikely in most soils because additions of large amounts of zinc are required to ensure saturation of the adsorption sites of different soil components before the zinc concentration in the soil solution can increase sufficiently to bring about the precipitation of definite compounds. Model experiments in CaCO3-buffered systems showed that the adsorption capacity for specifically adsorbed zinc (in μmole/g) by the following components increased in the order CaCO3 (0.44), bentonite (44), humic acid (842), amorphous Fe- and Al-oxides (1190, 1310) and δ -MnO2 (1540) and demonstrated the importance of Mn-, Fe-, and Al-oxides and humic substances for the binding of zinc in soils containing carbonates, and thus indicate the special role of these components in limiting precipitation reactions. 相似文献
46.
47.
von Andrian UH 《Science (New York, N.Y.)》2002,296(5574):1815-1817
48.
Donnelly SE Birtcher RC Allen CW Morrison I Furuya K Song M Mitsuishi K Dahmen U 《Science (New York, N.Y.)》2002,296(5567):507-510
High-resolution transmission electron microscopy images of room-temperature fluid xenon in small faceted cavities in aluminum reveal the presence of three well-defined layers within the fluid at each facet. Such interfacial layering of simple liquids has been theoretically predicted, but observational evidence has been ambiguous. Molecular dynamics simulations indicate that the density variation induced by the layering will cause xenon, confined to an approximately cubic cavity of volume approximately 8 cubic nanometers, to condense into the body-centered cubic phase, differing from the face-centered cubic phase of both bulk solid xenon and solid xenon confined in somewhat larger (>/=20 cubic nanometer) tetradecahedral cavities in face-centered cubic metals. Layering at the liquid-solid interface plays an important role in determining physical properties as diverse as the rheological behavior of two-dimensionally confined liquids and the dynamics of crystal growth. 相似文献
49.
The passage of large-sized herpesviral capsids through the nuclear lamina and the inner nuclear membrane to leave the nucleus requires a dissolution of the nuclear lamina. Here, we report on the functions of M50/p35, a beta-herpesviral protein of murine cytomegalovirus. M50/p35 inserts into the inner nuclear membrane and is aggregated by a second viral protein, M53/p38, to form the capsid docking site. M50/p35 recruits the cellular protein kinase C for phosphorylation and dissolution of the nuclear lamina, suggesting that herpesviruses target a critical element of nuclear architecture. 相似文献
50.