全文获取类型
收费全文 | 865篇 |
免费 | 69篇 |
专业分类
934篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 23篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 22篇 |
2017年 | 16篇 |
2016年 | 25篇 |
2015年 | 40篇 |
2014年 | 38篇 |
2013年 | 70篇 |
2012年 | 88篇 |
2011年 | 69篇 |
2010年 | 45篇 |
2009年 | 47篇 |
2008年 | 66篇 |
2007年 | 57篇 |
2006年 | 41篇 |
2005年 | 42篇 |
2004年 | 47篇 |
2003年 | 45篇 |
2002年 | 37篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有934条查询结果,搜索用时 15 毫秒
931.
Macrofauna secondary responses to controlled eutrophication within two MARICULT/MAST-III projects, EULIT and COMWEB, are compared. EULIT utilises a nutrient gradient established in eight hard bottom mesocosms, whereas the data from COMWEB originate from a whole-ecosystem study – the case of experimental nutrient addition to Hopavågen lagoon. In both systems, nutrient addition started in May 1998, after initial studies of the background macrofauna communities, thus allowing application of Before-After-Control-Impact-Pairs techniques (BACIP). The main objectives have been to investigate the macrofauna responses to eutrophication in littoral rocky shore ecosystems and to evaluate if similar responses could occur in mesocosm and `field' systems, despite their inherent differences. Apart from a distinct increase in numbers of Littorina littorea L. and some indications of increased abundance of the genus Jaera, no significant changes, caused by 2.5 years of nutrient addition, could be detected in the mesocosm fauna. It is interesting, however, that these two possibly stimulated animal groups have two things in common: (1) both belong to the rather few mobile taxa, which are not flushed out of the system through the mesocosm outlets, (2) both feed on microalgae and green algae in the upper littoral zone, i.e., algal groups that have shown the clearest response to the nutrient addition. In Hopavågen, 1.5 years of nutrient addition only caused modest plant and animal responses in the rocky shore ecosystem, although there was a markedly increased settlement of Mytilus edulis L. at one lagoon site. This increase was probably due to elevated levels of digestible particles (increased phytoplankton production) caused by the nutrient addition. There were also some indications of increased production of filamentous algae at this same lagoon site. All in all, both studies demonstrate only minor responses to increased nutrient levels within the littoral community (both plants and animals). One explanation to this may be that longer time-scales are needed in order for clear-cut changes to occur. Several observations also indicate that wave exposure (significant in both systems) may largely modulate the impact of increased nutrient load on the structure of littoral communities. Another explanation is the high degree of stability among littoral macroalgae-dominated communities with internal biological regulation factors (like grazing) possibly being able to counteract effects. 相似文献
932.
Steven C. Nichols Jolyon P. Mitchell Dennis Sandell Patrik U. Andersson Manfred Fischer Markus Howald Roy Pengilley Phillip Krüger 《AAPS PharmSciTech》2016,17(6):1383-1392
Fine particle dose (FPD) is a critical quality attribute for orally inhaled products (OIPs). The abbreviated impactor measurement (AIM) concept simplifies its measurement, provided there is a validated understanding of the relationship with the full resolution pharmacopoeial impactor (PIM) data for a given product. This multi-center study compared fine particle dose determined using AIM and PIM for five dry powder inhaler (DPIs) and two pressurized metered-dose inhaler (pMDI) products, one of which included a valved holding chamber (VHC). Reference measurements of FPDPIM were made by each organization using either the full-resolution Andersen 8-stage non-viable impactor (ACI) or Next Generation Impactor (NGI). FPDAIM was determined for the same OIP(s) with their choice of abbreviated impactor (fast screening impactor (FSI), fast screening Andersen (FSA), or reduced NGI (rNGI)). Each organization used its validated assay method(s) for the active pharmaceutical ingredient(s) (APIs) involved. Ten replicate measurements were made by each procedure. The upper size limit for FPDAIM varied from 4.4 to 5.0 μm aerodynamic diameter, depending upon flow rate and AIM apparatus; the corresponding size limit for FPDPIM was fixed at 5 μm in accordance with the European Pharmacopoeia. The 90% confidence interval for the ratio [FPDAIM/FPDPIM], expressed as a percentage, was contained in the predetermined 85–118% acceptance interval for nine of the ten comparisons of FPD. The average value of this ratio was 105% across all OIPs and apparatuses. The findings from this investigation support the equivalence of AIM and PIM for determination of FPD across a wide range of OIP platforms and measurement techniques. 相似文献
933.
The secondary metabolites of 150 specimens belonging to 29 species of Teloschistes were analysed with HPLC. Seven anthraquinones were detected of which parietin dominated with minor proportions of emodin,
teloschistin, fallacinal and parietinic acid. The depsidones vicanicin, caloploicin, and isofulgidin occurred together with
some compounds of unknown identity in varying proportions in T. flavicans, T. peruensis, T. stellatus, and one unnamed taxon. Nine chemosyndromes were found in the genus. Most species had only one chemosyndrome, but T. flavicans s. lat. had six syndromes. The geographical distribution patterns of these chemosyndromes in T. flavicans are discussed as well as the applicability of chemical characters for species delimitation in Teloschistes. 相似文献
934.
Fredrik C. Aronsson Patrik Magnusson Björn Andersson Stanislav L. Karsten Yoshiro Shibasaki Corinne L. Lendon Alison M. Goate A. J. Brookes 《Human genetics》1998,103(3):340-345
Full exon-intron structures are presented for the NIK serine/threonine protein kinase gene and a novel gene termed C17orf1.
By in situ hybridisation and radiation hybrid mapping, a cosmid (cDD-Z) that contains regions of both of these genes has been
localised between markers D17S800 and D17S791 at chromosome 17q21. The two genes are thus positional candidates for the mutant
locus underlying frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), a disease for which NIK is also
a good biological candidate. Using exon-intron maps, a genomic DNA sequencing based mutation screen has been performed for
the NIK and C17orf1 genes in a chromosome 17-linked FTDP-17 pedigree. Two silent single-base variations were detected in C17orf1.
No alterations were restricted to DNA samples from patients, thus excluding the C17orf1 and NIK genes as likely sites of mutation
FTDP-17.
Received: 23 December 1997 / Accepted: 23 June 1998 相似文献