全文获取类型
收费全文 | 1149篇 |
免费 | 408篇 |
国内免费 | 91篇 |
出版年
2024年 | 10篇 |
2023年 | 28篇 |
2022年 | 22篇 |
2021年 | 30篇 |
2020年 | 99篇 |
2019年 | 110篇 |
2018年 | 118篇 |
2017年 | 88篇 |
2016年 | 112篇 |
2015年 | 117篇 |
2014年 | 121篇 |
2013年 | 125篇 |
2012年 | 53篇 |
2011年 | 81篇 |
2010年 | 38篇 |
2009年 | 56篇 |
2008年 | 49篇 |
2007年 | 52篇 |
2006年 | 32篇 |
2005年 | 34篇 |
2004年 | 44篇 |
2003年 | 28篇 |
2002年 | 30篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 15篇 |
1998年 | 20篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 15篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1648条查询结果,搜索用时 640 毫秒
181.
Rogers H.R. Norris M.W. James H.A. 《Reviews in Environmental Science and Biotechnology》2004,3(1):23-32
Products and materials used incontact with drinking water have the potentialto cause tainting of drinking water. Whilsthealth effects are not necessarily associatedwith such effects, for consumers, flavour orodour are the main parameters they use toassess the wholesomeness of their drinkingwater. There are a number of possible causes oftainting from products and materials and theseare discussed. In many countries products usedin contact with drinking water are screened toavoid odour or flavour problems. However,despite these safeguards tainting problems canand do still occur. Some relate tomisapplication of products in distributionsystems, poor domestic plumbing practices orthe use of domestic appliances after the pointof supply. 相似文献
182.
1 Introduction Dynamic wind loads can excite potentially de-structive oscillations in plants. Without dissipation ofmechanical energy a resonance catastrophe is likely tooccur in dynamic winds with frequency componentsclose to the resonant frequencies of the plant. Four modesof oscillation damping are considered [1] ? Friction with other members of the plant commu-nity as for instance in the dense stand of bamboos. ? Structural damping: other than in the engineeringscien… 相似文献
183.
184.
获取复配农药最佳增效配方的一种简易方法 总被引:1,自引:0,他引:1
借鉴共毒因子法评价农药复配联合作用的思想,将参与复配的单剂引起25%死亡率的剂量定为零水平,利用二次回归通用旋转组合设计安排实验研究氯氰菊酯和喹硫磷复配对斜纹夜蛾(Spodoptera litura)2龄幼虫的增效作用,得出杀虫剂使用量与斜纹夜蛾幼虫死亡率机率值之间的关系,从共毒系数(CTC)的计算公式推导出共毒系数与杀虫混剂中两单剂使用浓度N1、N2之间的数学关系,CTC=100/N1/α N2/b(α、b分别为氯氰菊酯和喹硫磷的LC50),进而确定最优化问题的目标函数j=N1/α+N2/b,利用国际统计分析软件SAS的NLP过程求最大共毒系数和最优配方,所得结论与共毒系数法一致。 相似文献
185.
186.
Keleher Jason Bashant Jennifer Heldt Nicole Johnson Latasha Li Yuzhuo 《World journal of microbiology & biotechnology》2002,18(2):133-139
Colloidal silver has been known to have unique antimicrobial activity that may be useful in the construction of antibacterial materials (self-cleaning materials) to aid in the fight against bacteria-related infections. In this study, silver-coated TiO2 (Ag/TiO2) particles prepared through the photo-reduction of Ag+ were investigated as an antibacterial agent against Escherichia coli and Staphylococcus aureus. The deposition of Ag onto the surface was confirmed with SEM and EDS analysis of the post-reaction particles. It was also determined that the initial concentration of Ag+ in solution played a significant role in the effective size of the post-irradiation particles. The antibacterial effectiveness of the Ag/TiO2 was evaluated through the determination of the minimum inhibitory concentration (MIC) of AgTiO2 for each species of bacteria. The MIC values for the Ag/TiO2, on both E. coli and S. aureus, were much lower than the MIC values for Ag metal, and quite comparable to the MIC values for AgNO3. A disc diffusion/antibiotic sensitivity test was also performed using the Ag/TiO2 particles and the results compared with the results obtained for Ag metal, AgNO3 and common antibacterial agents; tetracycline, chloramphenicol, erythromycin, and neomycin. The zone of inhibition diameters for the Ag/TiO2 particles were found to be comparable with those of the other antimicrobial agents. 相似文献
187.
188.
Sebastian Polarz Author Vitae Carlos Lizandara Pueyo Author VitaeAuthor Vitae 《Inorganica chimica acta》2010,363(15):4148-4157
In the current article, we present a concept for the synthesis of complex nanoscaled materials. The synthetic strategy involves a stepwise assembly of materials starting from special molecular precursors possessing multiple information. Therefore, the article focuses on a strong pervasion of inorganic materials chemistry, solid-state chemistry and molecular chemistry. The concept introduced is finally highlighted by examples from our current research in the field of zinc oxide materials. 相似文献
189.
Accuracy of genomic selection for age at puberty in a multi‐breed population of tropically adapted beef cattle 下载免费PDF全文
M. M. Farah A. A. Swan M. R. S. Fortes R. Fonseca S. S. Moore M. J. Kelly 《Animal genetics》2016,47(1):3-11
Genomic selection is becoming a standard tool in livestock breeding programs, particularly for traits that are hard to measure. Accuracy of genomic selection can be improved by increasing the quantity and quality of data and potentially by improving analytical methods. Adding genotypes and phenotypes from additional breeds or crosses often improves the accuracy of genomic predictions but requires specific methodology. A model was developed to incorporate breed composition estimated from genotypes into genomic selection models. This method was applied to age at puberty data in female beef cattle (as estimated from age at first observation of a corpus luteum) from a mix of Brahman and Tropical Composite beef cattle. In this dataset, the new model incorporating breed composition did not increase the accuracy of genomic selection. However, the breeding values exhibited slightly less bias (as assessed by deviation of regression of phenotype on genomic breeding values from the expected value of 1). Adding additional Brahman animals to the Tropical Composite analysis increased the accuracy of genomic predictions and did not affect the accuracy of the Brahman predictions. 相似文献
190.
The study presents a mathematical function describing a correlation between the amount of ergosterol and the number of colony-forming units (CFU) of mould contaminating selected building materials such as: a block of cellular concrete, gypsum—carton board and gypsum—carton board covered with emulsion paint. The dependence obtained for a particular material as well as an average dependence for all the investigated materials has been described by means of an exponential equation. It has been found out that there is high, statistically significant correlation between ergosterol content and CFU number of mould in all of the building materials. The correlation coefficients have ranged from r=0.790 to 0.933. The elaborated equation describing the above dependence can be applied to estimate mould contamination by means of culture methods within the range 103–108 CFU/m2 of the surface. In addition, the estimated level of ergosterol in these materials has been shown to be the criterion by which to evaluate the degree of filamentous fungal contamination. It has been assessed that an ergosterol content exceeding the level of 3.96 mg/m2 indicates the active development of mould. This criterion has been applied to evaluate several building materials i.e.: concrete, gypsum board, emulsion coatings, brick, plaster, wallpaper, glass wool, mineral wool and wood. No statistically significant differences have been observed between CFU number of mould calculated from a model equation on the basis of the ergosterol content and CFU number of mould experimentally determined by traditional methods. The results presented in this paper show that the elaborated equation of correlation between the ergosterol content and CFU number of mould can be applied to estimate mould contamination of different building materials, based on the determination of ergosterol. 相似文献