全文获取类型
收费全文 | 3278篇 |
免费 | 230篇 |
国内免费 | 4篇 |
专业分类
3512篇 |
出版年
2023年 | 21篇 |
2022年 | 32篇 |
2021年 | 67篇 |
2020年 | 30篇 |
2019年 | 52篇 |
2018年 | 58篇 |
2017年 | 55篇 |
2016年 | 119篇 |
2015年 | 181篇 |
2014年 | 198篇 |
2013年 | 241篇 |
2012年 | 304篇 |
2011年 | 264篇 |
2010年 | 131篇 |
2009年 | 119篇 |
2008年 | 195篇 |
2007年 | 215篇 |
2006年 | 169篇 |
2005年 | 167篇 |
2004年 | 142篇 |
2003年 | 128篇 |
2002年 | 122篇 |
2001年 | 38篇 |
2000年 | 28篇 |
1999年 | 34篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1974年 | 14篇 |
1971年 | 6篇 |
1964年 | 6篇 |
1952年 | 4篇 |
排序方式: 共有3512条查询结果,搜索用时 15 毫秒
991.
992.
Maria Pedrera-Canal Jose M. Moran Vicente Vera Raul Roncero-Martin Jesus M. Lavado-Garcia Ignacio Aliaga Juan D. Pedrera-Zamorano 《PloS one》2015,10(9)
A longitudinal study was conducted to investigate the relation between a polymorphism in the vitamin D receptor (VDR) gene and changes in bone mineral density (BMD) and quantitative ultrasound of the phalanges (QUS) over a five-year period. The subjects were 456 postmenopausal women with osteoporosis undergoing treatment, aged 59.95±7.97 years (mean±standard deviation [SD]) at baseline. BMD was measured at the hips and lumbar spine by dual-energy X-ray absorptiometry, and QUS was measured by means of amplitude-dependent speed of sound (Ad-SoS) at the phalanges. Lifestyle information was obtained via a questionnaire. The genotype frequencies of the BsmI (rs1544410) gene polymorphism were 29.4%, 47.1%, and 23.5% for bb, Bb, and BB, respectively. After five years, BMD (annual change in %/year) at the femoral neck (FN) showed a significant modification based on the rs1544410 genotype (BB vs Bb); there was an overall decrease in bone mass (-0.70±2.79%/year; P = 0.025). An analysis of covariance with adjustments for age, weight, height, percentage of weight change per year, baseline BMD and calcium intake showed that the observed associations were no longer significant (P = 0.429). No significant associations were found between the QUS measurements and the rs1544410 genotype after the five-year period. Our study limitations includes lack of information about type and length of duration of the osteoporosis treatment. Our results indicate that rs1544410 polymorphisms do not account significantly for the changes in bone mass in Spanish women with osteoporosis undergoing treatment. 相似文献
993.
Valeria Musella Maurizio Callari Eleonora Di Buduo Manuela Scuro Matteo Dugo Patrizia Miodini Giampaolo Bianchini Biagio Paolini Luca Gianni Maria Grazia Daidone Vera Cappelletti 《PloS one》2015,10(4)
To obtain gene expression profiles from samples collected in clinical trials, we conducted a pilot study to assess feasibility and estimate sample attrition rates when profiling formalin-fixed, paraffin-embedded specimens. Ten matched fresh-frozen and fixed breast cancer samples were profiled using the Illumina HT-12 and Ref-8 chips, respectively. The profiles obtained with Ref 8, were neither technically nor biologically reliable since they failed to yield the expected separation between estrogen receptor positive and negative samples. With the use of Affymetrix HG-U133 2.0 Plus chips on fixed samples and a quantitative polymerase chain reaction -based sample pre-assessment step, results were satisfactory in terms of biological reliability, despite the low number of present calls (M = 21%±5). Compared with the Illumina DASL WG platform, Affymetrix data showed a wider interquartile range (1.32 vs 0.57, P<2.2 E-16,) and larger fold changes. The Affymetrix chips were used to run a pilot study on 60 fixed breast cancers. By including in the workflow the sample pre-assessment steps, 96% of the samples predicted to give good results (44/46), were in fact rated as satisfactory from the point of view of technical and biological meaningfulness. Our gene expression profiles showed strong agreement with immunohistochemistry data, were able to reproduce breast cancer molecular subtypes, and allowed the validation of an estrogen receptor status classifier derived in frozen samples. The approach is therefore suitable to profile formalin-fixed paraffin-embedded samples collected in clinical trials, provided that quality controls are run both before (sample pre-assessment) and after hybridization on the array. 相似文献
994.
Tereza C. Giannini Leandro R. Tambosi André L. Acosta Rodolfo Jaffé Antonio M. Saraiva Vera L. Imperatriz-Fonseca Jean Paul Metzger 《PloS one》2015,10(6)
Ecosystem services provided by mobile agents are increasingly threatened by the loss and modification of natural habitats and by climate change, risking the maintenance of biodiversity, ecosystem functions, and human welfare. Research oriented towards a better understanding of the joint effects of land use and climate change over the provision of specific ecosystem services is therefore essential to safeguard such services. Here we propose a methodological framework, which integrates species distribution forecasts and graph theory to identify key conservation areas, which if protected or restored could improve habitat connectivity and safeguard ecosystem services. We applied the proposed framework to the provision of pollination services by a tropical stingless bee (Melipona quadrifasciata), a key pollinator of native flora from the Brazilian Atlantic Forest and important agricultural crops. Based on the current distribution of this bee and that of the plant species used to feed and nest, we projected the joint distribution of bees and plants in the future, considering a moderate climate change scenario (following IPPC). We then used this information, the bee’s flight range, and the current mapping of Atlantic Forest remnants to infer habitat suitability and quantify local and regional habitat connectivity for 2030, 2050 and 2080. Our results revealed north to south and coastal to inland shifts in the pollinator distribution during the next 70 years. Current and future connectivity maps unraveled the most important corridors, which if protected or restored, could facilitate the dispersal and establishment of bees during distribution shifts. Our results also suggest that coffee plantations from eastern São Paulo and southern Minas Gerais States could suffer a pollinator deficit in the future, whereas pollination services seem to be secured in southern Brazil. Landowners and governmental agencies could use this information to implement new land use schemes. Overall, our proposed methodological framework could help design novel conservational and agricultural practices that can be crucial to conserve ecosystem services by buffering the joint effect of habitat configuration and climate change. 相似文献
995.
Muthuraman Muthuraman Vera Moliadze Kidist Gebremariam Mideksa Abdul Rauf Anwar Ulrich Stephani Günther Deuschl Christine M. Freitag Michael Siniatchkin 《PloS one》2015,10(10)
At the sensor level many aspects, such as spectral power, functional and effective connectivity as well as relative-power-ratio ratio (RPR) and spatial resolution have been comprehensively investigated through both electroencephalography (EEG) and magnetoencephalography (MEG). Despite this, differences between both modalities have not yet been systematically studied by direct comparison. It remains an open question as to whether the integration of EEG and MEG data would improve the information obtained from the above mentioned parameters. Here, EEG (64-channel system) and MEG (275 sensor system) were recorded simultaneously in conditions with eyes open (EO) and eyes closed (EC) in 29 healthy adults. Spectral power, functional and effective connectivity, RPR, and spatial resolution were analyzed at five different frequency bands (delta, theta, alpha, beta and gamma). Networks of functional and effective connectivity were described using a spatial filter approach called the dynamic imaging of coherent sources (DICS) followed by the renormalized partial directed coherence (RPDC). Absolute mean power at the sensor level was significantly higher in EEG than in MEG data in both EO and EC conditions. At the source level, there was a trend towards a better performance of the combined EEG+MEG analysis compared with separate EEG or MEG analyses for the source mean power, functional correlation, effective connectivity for both EO and EC. The network of coherent sources and the spatial resolution were similar for both the EEG and MEG data if they were analyzed separately. Results indicate that the combined approach has several advantages over the separate analyses of both EEG and MEG. Moreover, by a direct comparison of EEG and MEG, EEG was characterized by significantly higher values in all measured parameters in both sensor and source level. All the above conclusions are specific to the resting state task and the specific analysis used in this study to have general conclusion multi-center studies would be helpful. 相似文献
996.
Miriam Schulz Darja Karpova Gabriele Spohn Annette Damert Erhard Seifried Vera Binder Halvard B?nig 《PloS one》2015,10(3)
The genetics responsible for the inter-individually variable G-CSF responsiveness remain elusive. A single nucleotide polymorphism (SNP) in the 3’UTR of CXCL12, rs1801157, was implicated in X4-tropic HiV susceptibility and later, in two small studies, in G-CSR responsiveness in patients and donors. The position of the SNP in the 3’UTR together with in-silico predictions suggested differential binding of micro-RNA941 as an underlying mechanism. In a cohort of 515 healthy stem cell donors we attempted to reproduce the correlation of the CXCL12 3’UTR SNP and mobilization responses and tested the role of miR941 in this context. The SNP was distributed with the expected frequency. Mobilization efficiency for CD34+ cells in WT, heterozygous and homozygous SNP individuals was indistinguishable, even after controlling for gender. miR941 expression in non-hematopoietic bone marrow cells was undetectable and miR941 did not interact with the 3’ UTR of CXCL12. Proposed effects of the SNP rs1801157 on G-CSF responsiveness cannot be confirmed in a larger cohort. 相似文献
997.
Sequestration of chemical defenses from host plants is a strategy widely used by herbivorous insects to avoid predation. Larvae of the arctiine moth Utetheisa ornatrix feeding on unripe seeds and leaves of many species of Crotalaria (Leguminosae) sequester N-oxides of pyrrolizidine alkaloids (PAs) from these host plants, and transfer them to adults through the pupal stage. PAs confer protection against predation on all life stages of U. ornatrix. As U. ornatrix also uses other Crotalaria species as host plants, we evaluated whether the PA chemical defense against predation is independent of host plant use. We fed larvae from hatching to pupation with either leaves or seeds of one of eight Crotalaria species (C. incana, C. juncea, C. micans, C. ochroleuca, C. pallida, C. paulina, C. spectabilis, and C. vitellina), and tested if adults were preyed upon or released by the orb-weaving spider Nephila clavipes. We found that the protection against the spider was more effective in adults whose larvae fed on seeds, which had a higher PA concentration than leaves. The exceptions were adults from larvae fed on C. paulina, C. spectabilis and C. vitellina leaves, which showed high PA concentrations. With respect to the PA profile, we describe for the first time insect-PAs in U. ornatrix. These PAs, biosynthesized from the necine base retronecine of plant origin, or monocrotaline- and senecionine-type PAs sequestered from host plants, were equally active in moth chemical defense, in a dose-dependent manner. These results are also partially explained by host plant phylogeny, since PAs of the host plants do have a phylogenetic signal (clades with high and low PA concentrations in leaves) which is reflected in the adult defense. 相似文献
998.
Richard N Greenberg Yadira Hurley Dinh V. Dinh Serena Mraz Javier Gomez Vera Dorothea von Bredow Alfred von Krempelhuber Siegfried Roesch Garth Virgin Nathaly Arndtz-Wiedemann Thomas Peter Meyer Darja Schmidt Richard Nichols Philip Young Paul Chaplin 《PloS one》2015,10(10)
Background
Replicating smallpox vaccines can cause severe complications in individuals with atopic dermatitis (AD). Prior studies evaluating Modified Vaccinia Ankara virus (MVA), a non-replicating vaccine in humans, showed a favorable safety and immunogenicity profile in healthy volunteers.Objective
This Phase II study compared the safety and immunogenicity of MVA enrolling groups of 350 subjects with AD (SCORAD ≤ 30) and 282 healthy subjects.Methods
Subjects were vaccinated twice with MVA, each dose given subcutaneously 4 weeks apart. Adverse events, cardiac parameters, and the development of vaccinia virus humoral immune responses were monitored.Results
The overall safety of the vaccine was similar in both groups. Adverse events affecting skin were experienced significantly more often in subjects with AD, but the majority of these events were mild to moderate in intensity. Seroconversion rates and geometric mean titers for total and neutralizing vaccinia-specific antibodies in the AD group were non-inferior compared to the healthy subjects.Limitations
The size of the study population limited the detection of serious adverse events occurring at a frequency less than 1%.Conclusion
MVA has a favorable safety profile and the ability to elicit vaccinia-specific immune responses in subjects with AD.Trial Registration
ClinicalTrials.gov NCT00316602 相似文献999.
Fernanda de Oliveira Demitto Renata Claro Ribeiro do Amaral Flaviane Granero Maltempe Vera Lúcia Dias Siqueira Regiane Bertin de Lima Scodro Mariana Aparecida Lopes Katiany R. Caleffi-Ferracioli Pedro Henrique Canezin Rosilene Fressatti Cardoso 《PloS one》2015,10(2)
The aim of the present study was to evaluate the effect of the combination of rifampicin (RIF) and verapamil (VP) against the Mycobacterium tuberculosis H37Rv reference strain and six multidrug-resistant (MDR) M. tuberculosis clinical isolates by determining Time-Kill Curves and the ability to efflux drug by fluorometry. The RIF+VP combination showed synergism in one MDR clinical isolate. For the other five MDR clinical isolates, the drug combination showed no interaction. The MDR clinical isolate had lower ethidium bromide (EtBr) accumulation when exposed to the RIF+VP combination, compared with RIF and VP exposure alone. The other MDR clinical isolates showed no significant difference in EtBr accumulation. These results suggest greater efflux action in one of the MDR clinical isolates compared with the M. tuberculosis H37Rv reference strain. The other five MDR isolates may have additional mechanisms of drug resistance to RIF. The use of the RIF+VP combination made one MDR bacillus more susceptible to RIF probably by inhibiting efflux pumps, and this combination therapy, in some cases, may contribute to a reduction of resistance to RIF in M. tuberculosis. 相似文献
1000.
A high‐density,SNP‐based consensus map of tetraploid wheat as a bridge to integrate durum and bread wheat genomics and breeding 下载免费PDF全文
Marco Maccaferri Andrea Ricci Silvio Salvi Sara Giulia Milner Enrico Noli Pier Luigi Martelli Rita Casadio Eduard Akhunov Simone Scalabrin Vera Vendramin Karim Ammar Antonio Blanco Francesca Desiderio Assaf Distelfeld Jorge Dubcovsky Tzion Fahima Justin Faris Abraham Korol Andrea Massi Anna Maria Mastrangelo Michele Morgante Curtis Pozniak Amidou N'Diaye Steven Xu Roberto Tuberosa 《Plant biotechnology journal》2015,13(5):648-663