全文获取类型
收费全文 | 2769篇 |
免费 | 207篇 |
国内免费 | 9篇 |
专业分类
2985篇 |
出版年
2022年 | 17篇 |
2021年 | 56篇 |
2020年 | 28篇 |
2019年 | 35篇 |
2018年 | 49篇 |
2017年 | 36篇 |
2016年 | 64篇 |
2015年 | 90篇 |
2014年 | 120篇 |
2013年 | 167篇 |
2012年 | 209篇 |
2011年 | 192篇 |
2010年 | 129篇 |
2009年 | 109篇 |
2008年 | 138篇 |
2007年 | 134篇 |
2006年 | 124篇 |
2005年 | 107篇 |
2004年 | 122篇 |
2003年 | 122篇 |
2002年 | 93篇 |
2001年 | 29篇 |
2000年 | 33篇 |
1999年 | 32篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 25篇 |
1994年 | 25篇 |
1993年 | 32篇 |
1992年 | 39篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 22篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1973年 | 14篇 |
1972年 | 15篇 |
1970年 | 21篇 |
排序方式: 共有2985条查询结果,搜索用时 15 毫秒
111.
Background
One of the most common symptoms of speech deficits in individuals with Parkinson''s disease (PD) is significantly reduced vocal loudness and pitch range. The present study investigated whether abnormal vocalizations in individuals with PD are related to sensory processing of voice auditory feedback. Perturbations in loudness or pitch of voice auditory feedback are known to elicit short latency, compensatory responses in voice amplitude or fundamental frequency.Methodology/Principal Findings
Twelve individuals with Parkinson''s disease and 13 age- and sex- matched healthy control subjects sustained a vowel sound (/α/) and received unexpected, brief (200 ms) perturbations in voice loudness (±3 or 6 dB) or pitch (±100 cents) auditory feedback. Results showed that, while all subjects produced compensatory responses in their voice amplitude or fundamental frequency, individuals with PD exhibited larger response magnitudes than the control subjects. Furthermore, for loudness-shifted feedback, upward stimuli resulted in shorter response latencies than downward stimuli in the control subjects but not in individuals with PD.Conclusions/Significance
The larger response magnitudes in individuals with PD compared with the control subjects suggest that processing of voice auditory feedback is abnormal in PD. Although the precise mechanisms of the voice feedback processing are unknown, results of this study suggest that abnormal voice control in individuals with PD may be related to dysfunctional mechanisms of error detection or correction in sensory feedback processing. 相似文献112.
E Villa R Vukotic C Cammà S Petta A Di Leo S Gitto E Turola A Karampatou L Losi V Bernabucci A Cenci S Tagliavini E Baraldi N De Maria R Gelmini E Bertolini M Rendina A Francavilla 《PloS one》2012,7(9):e44624
Introduction
Chronic hepatitis C is the main cause of death in patients with end-stage liver disease. Prognosis depends on the increase of fibrosis, whose progression is twice as rapid in men as in women. Aim of the study was to evaluate the effects of reproductive stage on fibrosis severity in women and to compare these findings with age-matched men.Materials and Methods
A retrospective study of 710 consecutive patients with biopsy-proven chronic hepatitis C was conducted, using data from a clinical database of two tertiary Italian care centers. Four age-matched groups of men served as controls. Data about demographics, biochemistry, liver biopsy and ultrasonography were analyzed. Contributing factors were assessed by multivariate logistic regression analysis.Results
Liver fibrosis was more advanced in the early menopausal than in the fully reproductive (P<0.0001) or premenopausal (P = 0.042) group. Late menopausal women had higher liver fibrosis compared with the other groups (fully reproductive, P<0.0001; premenopausal, P = <0.0001; early menopausal, P = 0.052). Multivariate analyses showed that male sex was independently associated with more severe fibrosis in the groups corresponding to premenopausal (P = 0.048) and early menopausal (P = 0.004) but not late menopausal pairs. In women, estradiol/testosterone ratio decreased markedly in early (vs. reproductive age: P = 0.002 and vs. premenopausal: P<0.0001) and late menopause (vs. reproductive age: P = 0.001; vs. premenopausal: P<0.0001). In men age-matched with menopausal women, estradiol/testosterone ratio instead increased (reproductive age group vs. early: P = 0.002 and vs. late M: P = 0.001).Conclusions
The severity of fibrosis in women worsens in parallel with increasing estrogen deprivation and estradiol/testosterone ratio decrease. Our data provide evidence why fibrosis progression is discontinuous in women and more linear and severe in men, in whom aging-associated estradiol/testosterone ratio increase occurs too late to noticeably influence the inflammatory process leading to fibrosis. 相似文献113.
Kazmi RH Khan N Willems LA VAN Heusden AW Ligterink W Hilhorst HW 《Plant, cell & environment》2012,35(5):929-951
Seed quality in tomato is associated with many complex physiological and genetic traits. While plant processes are frequently controlled by the action of small‐ to large‐effect genes that follow classic Mendelian inheritance, our study suggests that seed quality is primarily quantitative and genetically complex. Using a recombinant inbred line population of Solanum lycopersicum × Solanum pimpinellifolium, we identified quantitative trait loci (QTLs) influencing seed quality phenotypes under non‐stress, as well as salt, osmotic, cold, high‐temperature and oxidative stress conditions. In total, 42 seed quality traits were analysed and 120 QTLs were identified for germination traits under different conditions. Significant phenotypic correlations were observed between germination traits under optimal conditions, as well as under different stress conditions. In conclusion, one or more QTLs were identified for each trait with some of these QTLs co‐locating. Co‐location of QTLs for different traits can be an indication that a locus has pleiotropic effects on multiple traits due to a common mechanistic basis. However, several QTLs also dissected seed quality in its separate components, suggesting different physiological mechanisms and signalling pathways for different seed quality attributes. 相似文献
114.
Shengjing Shi Maureen O’Callaghan E. Eirian Jones Alan E. Richardson Christian Walter Alison Stewart Leo Condron 《Plant and Soil》2012,359(1-2):149-163
Purpose
Understanding of the role of low molecular weight organic anions (OAs) in structuring rhizosphere microbial communities in situ is limited due to challenges associated with sampling. Improved techniques are needed for such studies.Methods
This study used in situ and destructive sampling techniques and compared two exudate extraction methods [anion exchange membrane (AEM) capturing and water extraction] from rhizosphere and non-rhizosphere samples of genetically modified (GM) and control Pinus radiata D. Don trees grown in large-scale rhizotrons for ~10?months. Metabolically active soil microbial communities were analysed using rRNA-DGGE.Results
Recovery of eight out of 12 anions was influenced by extraction methods, and in situ sampling using AEM was shown to be the most efficient method. Only minor differences were detected in OAs in root exudates collected from the GM and control trees. Significant differences in α-Proteobacterial and Pseudomonas communities were associated with the two tree lines in the topsoil at both sampling events. Additional differences in β-Proteobacterial and fungal communities between tree lines were detected in the rhizosphere using destructive sampling.Conclusion
This study demonstrated that in situ sampling was superior to destructive sampling for the efficient collection of root exudates and analysis of associated rhizosphere microbial communities. 相似文献115.
Jenna M. McCullough Leo Joseph Robert G. Moyle Michael J. Andersen 《Zoologica scripta》2019,48(4):411-418
Molecular systematics is bringing taxonomy into the 21st Century by updating our nomenclature to reflect phylogenetic relationships of taxa. This transformation is evidenced by massive changes in avian taxonomy, ranging from ordinal to subspecies changes. In this study, we employ target capture of ultraconserved elements to resolve genus‐level systematics of a problematic group of honeyeaters (Aves: Meliphagidae). With near complete species‐level taxon sampling of the Australo‐Papuan species within the traditionally recognized Meliphaga and Oreornis, we investigate generic limits using a genomic dataset. Likelihood and species tree methods confirm two clades within this group and found the New Guinea endemic Oreornis chrysogenys embedded within one of these clades. Our study supports earlier recommendations that Meliphaga Lewin, 1808 should be restricted to three species, M. aruensis, M. lewinii and M. notata. We make a case for recognizing three genera in the remaining species, Oreornis van Oort, 1910, Microptilotis Mathews, 1912 and Territornis Mathews, 1924. 相似文献
116.
Kelk Steven Pardi Fabio Scornavacca Celine van Iersel Leo 《Journal of mathematical biology》2019,78(1-2):527-547
Journal of Mathematical Biology - Phylogenetic networks are often constructed by merging multiple conflicting phylogenetic signals into a directed acyclic graph. It is interesting to explore... 相似文献
117.
The lipopolysaccharide adjuvant effect on T cells relies on nonoverlapping contributions from the MyD88 pathway and CD11c+ cells 总被引:1,自引:0,他引:1
McAleer JP Zammit DJ Lefrançois L Rossi RJ Vella AT 《Journal of immunology (Baltimore, Md. : 1950)》2007,179(10):6524-6535
Bacterial LPS is a natural adjuvant that induces profound effects on T cell clonal expansion, effector differentiation, and long-term T cell survival. In this study, we delineate the in vivo mechanism of LPS action by pinpointing a role for MyD88 and CD11c(+) cells. LPS induced long-term survival of superantigen-stimulated CD4 and CD8 T cells in a MyD88-dependent manner. By tracing peptide-stimulated CD4 T cells after adoptive transfer, we showed that for LPS to mediate T cell survival, the recipient mice were required to express MyD88. Even when peptide-specific CD4 T cell clonal expansion was dramatically boosted by enforced OX40 costimulation, OX40 only synergized with LPS to induce survival when the recipient mice expressed MyD88. Nevertheless, these activated, but moribund, T cells in the MyD88(-/-) mice acquired effector properties, such as the ability to synthesize IFN-gamma, demonstrating that effector differentiation is not automatically coupled to a survival program. We confirmed this notion in reverse fashion by showing that effector differentiation was not required for the induction of T cell survival. Hence, depletion of CD11c(+) cells did not affect LPS-driven specific T cell survival, but CD11c(+) cells were paramount for optimal effector T cell differentiation as measured by IFN-gamma potential. Thus, LPS adjuvanticity is based on MyD88 promoting T cell survival, while CD11c(+) cells support effector T cell differentiation. 相似文献
118.
119.
120.
Lisa F. P. Ng Angela Chow Yong-Jiang Sun Dyan J. C. Kwek Poh-Lian Lim Frederico Dimatatac Lee-Ching Ng Eng-Eong Ooi Khar-Heng Choo Zhisheng Her Philippe Kourilsky Yee-Sin Leo 《PloS one》2009,4(1)