全文获取类型
收费全文 | 285篇 |
免费 | 38篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 14篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 22篇 |
2013年 | 15篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 17篇 |
2009年 | 16篇 |
2008年 | 18篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 11篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1976年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有323条查询结果,搜索用时 453 毫秒
21.
22.
23.
Alvarez M Huygens D Díaz LM Villanueva CA Heyser W Boeckx P 《Plant, cell & environment》2012,35(1):126-135
Acid phosphatase (ACP) enzymes are involved in the mobilization of soil phosphorus (P) and polyphosphate accumulated in the fungal tissues of ectomycorrhizal roots, thereby influencing the amounts of P that are stored in the fungus and transferred to the host plant. This study evaluated the effects of ectomycorrhizal morphotype and soil fertility on ACP activity in the extraradical mycelium (ACP(myc)), the mantle (ACP(mantle)) and the Hartig net region (ACP(Hartig)) of ectomycorrhizal Nothofagus obliqua seedlings. ACP activity was quantified in vivo using enzyme-labelled fluorescence-97 (ELF-97) substrate, confocal laser microscopy and digital image processing routines. There was a significant effect of ectomycorrhizal morphotype on ACP(myc), ACP(mantle) and ACP(Hartig), while soil fertility had a significant effect on ACP(myc) and ACP(Hartig). The relative contribution of the mantle and the Hartig net region to the ACP activity on the ectomycorrhizal root was significantly affected by ectomycorrhizal morphotype and soil fertility. A positive correlation between ACP(Hartig) and the shoot P concentration was found, providing evidence that ACP activity at the fungus:root interface is involved in P transfer from the fungus to the host. It is concluded that the spatial distribution of ACP in ectomycorrhizas varies as a function of soil fertility and colonizing fungus. 相似文献
24.
Simon Maier Anna Szalkowski Susanne Kamphausen Evgeniy Perlov Bernd Feige Jens Blechert Alexandra Philipsen Ludger Tebartz van Elst Raffael Kalisch Oliver Tüscher 《PloS one》2012,7(11)
Recent studies have begun to carve out a specific role for the rostral part of the dorsal medial prefrontal cortex (dmPFC) and adjacent dorsal anterior cingulate cortex (dACC) in fear/anxiety. Within a novel general framework of dorsal mPFC/ACC areas subserving the appraisal of threat and concomitant expression of fear responses and ventral mPFC/ACC areas subserving fear regulation, the rostral dmPFC/dACC has been proposed to specifically mediate the conscious, negative appraisal of threat situations including, as an extreme variant, catastrophizing. An alternative explanation that has not been conclusively ruled out yet is that the area is involved in fear learning. We tested two different fear expression paradigms in separate fMRI studies (study 1: instructed fear, study 2: testing of Pavlovian conditioned fear) with independent groups of healthy adult subjects. In both paradigms the absence of reinforcement precluded conditioning. We demonstrate significant BOLD activation of an identical rostral dmPFC/dACC area. In the Pavlovian paradigm (study 2), the area only activated robustly once prior conditioning had finished. Thus, our data argue against a role of the area in fear learning. We further replicate a repeated observation of a dissociation between peripheral-physiological fear responding and rostral dmPFC/dACC activation, strongly suggesting the area does not directly generate fear responses but rather contributes to appraisal processes. Although we succeeded in preventing extinction of conditioned responding in either paradigm, the data do not allow us to definitively exclude an involvement of the area in fear extinction learning. We discuss the broader implications of this finding for our understanding of mPFC/ACC function in fear and in negative emotion more generally. 相似文献
25.
Laurent S Vander Elst L Thirifays C Muller RN 《European biophysics journal : EBJ》2008,37(6):1007-1014
Nuclear magnetic relaxation dispersion (NMRD) profiles of unilamellar DPPC liposomes incorporating Gd-DTPA-bisamides with alkyl chains of 12 to 18 C atoms in their external and internal layers were recorded in order to study the influence that the chain length and structure of Gd-bisamides incorporated in the liposomal membrane have on their proton relaxivity. The NMRD profiles recorded at 310 K show that the relaxivity reaches a minimum value when the carbon chain lengths of the phospholipid and of the Gd complex match and is at a maximum in the presence of a carbon-carbon double bond. For these DPPC paramagnetic liposomes, the longer the aliphatic chains of the complex, the larger will be its immobilization in the membrane. In addition, the presence of an unsaturated carbon-carbon bond in the alkyl chain of the Gd complex induces an increase of its mobility and of its water exchange rate with, as a result, a much greater efficiency as an MRI contrast agent. 相似文献
26.
27.
Kevin Lambeets Frederik Hendrickx Stijn Vanacker Kris Van Looy Jean-Pierre Maelfait Dries Bonte 《Biodiversity and Conservation》2008,17(13):3133-3148
We assessed the composition of spider and carabid beetle assemblages along river banks from the Common Meuse (Belgium) to
determine their relationships with local topographical and landscape-related characteristics. Data were gathered with pitfall
traps in 1998 and explored by ordination and grouping methods. Our analysis revealed that the presence of xerothermic spider
species was limited to scarcely covered, less dynamic gravel banks. Riparian spider species were found on frequently flooded
as well as on rather elevated and high gravel banks, while riparian carabid beetles were dominant on all sampled banks. The
level of flooding disturbance, the vegetation density and the presence of silt appeared to be the most important environmental
determinants of spider and carabid beetle assemblage structure. Consequently, local environmental factors influence species
occurrence patterns in a similar way for the two investigated arthropod groups. Nevertheless, distinct ecological groups are
differently ordered along the prime environmental gradients. Nature management should therefore consider the conservation,
restoration and connectivity of both dynamic and more elevated banks in order to obtain a high degree of local and regional
heterogeneity throughout the river system. 相似文献
28.
Luce Vander Elst Florence Chapelle Sophie Laurent Robert N. Muller 《Journal of biological inorganic chemistry》2001,6(2):196-200
The water proton relaxation rate enhancement of the hepatospecific Gd-(S)-EOB-DTPA (Eovist) and of its (R) isomer in aqueous solutions free of protein, in serum and in 4% human serum albumin solution, are compared. In the absence of proteins, both compounds exhibit, as expected, the same proton relaxivity, as measured by the nuclear magnetic relaxation dispersion (NMRD) profiles. In serum and albumin solution, non-covalent binding of the paramagnetic complexes to macromolecules is observed. Both isomers are likely to bind to the same site of human serum albumin, but the affinity of the (S) isomer is larger than for the (R) isomer. 相似文献
29.
Solid-phase synthesis of the nucleopeptide fragment H-Asp-Ser[pAAAGTAAGCC]-Glu-OH from the nucleoprotein of Bacillus subtilis phage phi 29. 下载免费PDF全文
C M Dreef-Tromp J C van der Maarel H van den Elst G A van der Marel J H van Boom 《Nucleic acids research》1992,20(15):4015-4020
The naturally occurring DNA-nucleopeptide H-Asp-Ser[5'-pAAAGTAAGCC-3']-Glu-OH was prepared via a solid-phase phosphite triester approach using N-2-(tert-butyldiphenylsilyloxymethyl)benzoyl protected nucleosides. The oligonucleotide was linked via the extremely base-labile oxalyl ester anchor to the solid support. 相似文献
30.
H M Rajh J H Uitzetter L W Westerhuis C L van den Dries G I Tesser 《International journal of peptide and protein research》1979,14(1):68-79
In order to investigate the special function of tryptophan in peptide hormones, six tryptophan analogues have been synthesized, in which structural resemblance has been grossly retained and potentially essential properties have only partially been varied. The L-enantiomers have been isolated after enzymatic digestion of racemic dipeptide derivatives, and charge-transfer properties of the compounds have been studied. 相似文献