全文获取类型
收费全文 | 3238篇 |
免费 | 196篇 |
出版年
2023年 | 16篇 |
2022年 | 22篇 |
2021年 | 81篇 |
2020年 | 41篇 |
2019年 | 75篇 |
2018年 | 110篇 |
2017年 | 116篇 |
2016年 | 166篇 |
2015年 | 170篇 |
2014年 | 221篇 |
2013年 | 245篇 |
2012年 | 292篇 |
2011年 | 305篇 |
2010年 | 199篇 |
2009年 | 116篇 |
2008年 | 222篇 |
2007年 | 191篇 |
2006年 | 157篇 |
2005年 | 181篇 |
2004年 | 117篇 |
2003年 | 128篇 |
2002年 | 85篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 5篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1954年 | 2篇 |
1948年 | 1篇 |
1945年 | 1篇 |
排序方式: 共有3434条查询结果,搜索用时 15 毫秒
1.
MethodsWe analyze all women invited to mammography screening in 2005–09, residing in the city of Malmö, Sweden. Information regarding mammography screening attendance was linked to data on area of residence, demographic and socioeconomic characteristics available from Statistics Sweden. The influence of individual and neighborhood factors was assessed by multilevel logistic regression analysis with 29,901 women nested within 212 neighborhoods.ResultsThe prevalence of non-attendance among women was 18.3%. After adjusting for individual characteristics, the prevalence in the 212 neighborhoods was 3.6%. Neighborhood of residence had little influence on non-attendance. The multilevel analysis indicates that 8.4% of the total individual differences in the propensity of non-attendance were at the neighborhood level. However, when adjusting for specific individual characteristics this general contextual effect decreased to 1.8%. This minor effect was explained by the sociodemographic characteristic of the neighborhoods. The discriminatory accuracy of classifying women according to their non-attendance was 0.747 when considering only individual level variables, and 0.760 after including neighborhood level as a random effect.ConclusionOur results suggest that neighborhoods of residence in Malmö, Sweden (as defined by small-area market statistics (SAMS) areas) do not condition women’s participation in population based mammography screening. Thus, interventions should be directed to the whole city and target women with a higher risk of non-attendance. 相似文献
2.
3.
4.
Juana Magdalena Mats Forsman Mauro V. Lenzini Alain Brans Jean Dusart 《FEMS microbiology letters》1992,99(1):101-105
Two beta-lactamase genes called blaL and blaU have been cloned independently in Liège and in Ume?, from Streptomyces cacaoi. Genes blaL and blaU were found to differ largely in their nucleotide sequences, although the encoded proteins both belonged to the class A of beta-lactamases (active-site serine penicillinases). DNA-hybridization and polymerase chain reaction assays have now demonstrated that both blaL and blaU genes were present in the S. cacaoi strains used in Liège and in Ume?. 相似文献
5.
Jacek Kęsy Beata Maciejewska Magdalena Sowa Magdalena Szumilak Krzysztof Kawałowski Maja Borzuchowska Jan Kopcewicz 《Plant Growth Regulation》2008,55(1):43-50
It has been shown that both IAA and ethylene application inhibit flower induction in the short-day plant Pharbitis nil. However application of IAA has elevated ethylene production in this plant, as well. Strong enhancement of ethylene production
is also correlated with the night-break effect, which completely inhibits flowering. In order to determine what the role of
IAA and ethylene is in the photoperiodic flower induction in Pharbitis nil, we measured changes in their levels during inductive and non-inductive photoperiods, and the effects of ethylene biosynthesis
and action inhibitors on inhibition of flowering by IAA. Our results have shown that the inhibitory effect of IAA on Pharbitis nil flowering is not physiological but is connected with its effect on ethylene biosynthesis. 相似文献
6.
The application of fluorescence spectroscopy to organic matter characterisation in drinking water treatment 总被引:7,自引:0,他引:7
John Bridgeman Magdalena Bieroza Andy Baker 《Reviews in Environmental Science and Biotechnology》2011,10(3):277-290
Key to effective disinfection byproduct (DBP) management is source water control and management, and more specifically, organic
matter (OM) control and management. However, the content and character of OM in source waters is spatially and temporally
variable, and the prediction of its composition is challenging. Water treatment companies require adequate analytical techniques
for OM characterisation to maintain the operation of the water supply and treatment systems adjusted to constantly changing
environmental conditions. There is a requirement, therefore, for an improved understanding of OM composition and character
in source water, how that composition and character varies with flow conditions, and how this impacts on drinking water treatment.
This paper demonstrates that fluorescence spectroscopy offers a potential alternative to other analytical methods of OM characterisation.
The advantages of fluorescence include rapid, sensitive and selective characterisation of OM, no sample pre-treatment, small
sample volume, and the potential for on-line monitoring incorporation. Fluorescence can provide useful information on OM reactivity
and treatability together with an indication of the OM sources (allochthonous or autochthonous). The paper discusses a body
of literature which has identified relationships between fluorescence spectra and OM physico-chemical properties (i.e. degree
of hydrophobicity, microbial content), has applied fluorescence spectroscopy to characterise the changes in OM upon disinfection,
and has related the fluorescence properties to DBP formation. Further work is required in the robust management of data arising
from fluorescence spectroscopy analysis and, in particular, Excitation Emission Matrices. Consideration must be given as to
how the data might best be employed to greatest effect on a routine basis at WTW. 相似文献
7.
8.
Magdalena Brzezowska Francesca Bernardi Nicola Gaggelli Gianni Valensin 《Journal of inorganic biochemistry》2010,104(2):193-198
Teicoplanin, a member of the “last chance” antibiotic family has a similar structure and the same mechanism of action as parent drug vancomycin, which is proved to be an effective binder of Cu(II) ions. However, the potentiometric and spectroscopic studies (UV-visible, CD, NMR) have shown that the modification of the N-terminal structure of the peptide backbone in teicoplanin affects considerably the binding ability towards Cu(II) ions. While vancomycin forms almost instantly the stable 3 N complex species involving the N-terminal and two amide nitrogen donors, in case of teicoplanin only two nitrogen donors derived from the N-terminal amino group and adjacent peptide bond are coordinated to Cu(II) ion within the whole pH range studied. The major factor influencing the binding mode is most likely the structure of the N-terminus of the peptide unit in the antibiotic ligand. 相似文献
9.
10.
Joanna Kajzer Magdalena Lenda Andrzej Kośmicki Rafał Bobrek Tomasz Kowalczyk Rafał Martyka Piotr Skórka 《Journal of Biogeography》2012,39(2):371-381
Aim This study investigated whether habitat fragmentation at the landscape level influences patch occupancy and abundance of the black‐headed gull, Chroicocephalus ridibundus, and whether the response of the species to environmental factors is consistent across replicated landscape plots. Location Water bodies (habitat patches) in southern Poland. Methods Surveys were conducted in two landscape types (four plots in each): (1) more‐fragmented landscape, in which habitat patches were small (mean size 2.2–6.2 ha) and far apart (mean distance 2.5–3.1 km); and (2) less‐fragmented landscape, in which habitat patches were large (mean size 9.2–16.5 ha) and separated by short distances (mean 0.9–1.4 km). Observations were performed twice in 284 potential habitat patches during the 2007 breeding season. Results Colonies were significantly more frequent and larger in the less‐fragmented landscapes than in the more‐fragmented ones. Probability of patch occupancy and number of breeding birds were positively related with patch size and these relationships were especially strong in the more‐fragmented landscapes. In the less‐fragmented landscapes, the occurrence of black‐headed gulls was negatively related to the distance to the nearest local population, but in the more‐fragmented landscapes such a relationship was not detected. As distance to the nearest habitat patch increased, the probability of the patch occupancy decreased in the more‐fragmented landscapes. Moreover, abundance was negatively influenced by distance to the nearest habitat patch, especially strongly in more‐fragmented landscapes. Proximity of corridors (rivers) positively influenced the occupation of patches regardless of landscape type. The number of islets positively influenced occupancy and abundance of local populations, and this relationship was stronger in the more‐fragmented landscapes. Main conclusions Our results are in agreement with predictions from metapopulation theory and are the first evidence that populations of black‐headed gulls may have a metapopulation structure. However, patch occupancy and abundance were differentially affected by explanatory variables in the more‐fragmented landscapes than in the less‐fragmented ones. This implies that it is impossible to derive, a priori, predictions about presence/abundance patterns based on only a single landscape. 相似文献