全文获取类型
收费全文 | 3866篇 |
免费 | 261篇 |
国内免费 | 4篇 |
专业分类
4131篇 |
出版年
2023年 | 15篇 |
2022年 | 22篇 |
2021年 | 41篇 |
2020年 | 32篇 |
2019年 | 36篇 |
2018年 | 56篇 |
2017年 | 51篇 |
2016年 | 101篇 |
2015年 | 152篇 |
2014年 | 195篇 |
2013年 | 253篇 |
2012年 | 289篇 |
2011年 | 302篇 |
2010年 | 198篇 |
2009年 | 155篇 |
2008年 | 229篇 |
2007年 | 238篇 |
2006年 | 212篇 |
2005年 | 230篇 |
2004年 | 180篇 |
2003年 | 226篇 |
2002年 | 214篇 |
2001年 | 45篇 |
2000年 | 32篇 |
1999年 | 48篇 |
1998年 | 43篇 |
1997年 | 42篇 |
1996年 | 41篇 |
1995年 | 38篇 |
1994年 | 30篇 |
1993年 | 32篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 18篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1973年 | 13篇 |
1972年 | 13篇 |
1971年 | 8篇 |
排序方式: 共有4131条查询结果,搜索用时 0 毫秒
161.
Dennis S. Nielsen Łukasz Krych Karsten Buschard Camilla H.F. Hansen Axel K. Hansen 《FEBS letters》2014
Type 1 diabetes (T1D) is an autoimmune disease ultimately leading to destruction of insulin secreting β-cells in the pancreas. Genetic susceptibility plays an important role in T1D etiology, but even mono-zygotic twins only have a concordance rate of around 50%, underlining that other factors than purely genetic are involved in disease development. Here we review the influence of dietary and environmental factors on T1D development in humans as well as animal models. Even though data are still inconclusive, there are strong indications that gut microbiota dysbiosis plays an important role in T1D development and evidence from animal models suggests that gut microbiota manipulation might prove valuable in future prevention of T1D in genetically susceptible individuals. 相似文献
162.
Koji Yoshida Karsten VogttZunbeltz Izaola Margarita RussinaToshio Yamaguchi Marie-Claire Bellissent-Funel 《Biochimica et Biophysica Acta - Proteins and Proteomics》2012,1824(3):502-510
Structural and dynamic properties of β-lactoglobulin (β-LG) were revealed as a function of alcohol concentration in ethanol- and trifluoroethanol(TFE)-water mixtures with circular dichroism (CD), small-angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS). The CD spectra showed that an increase in TFE concentration promotes the formation of the β-sheet structure of β-LG. The SANS-intensities were fitted using form factors for two attached spheres for the native and native-like states of the protein. At higher alcohol concentrations, where aggregation takes place, a form factor modelling diffusion limited colloidal aggregation (DLCA) was employed. The QENS-data were analyzed in terms of internal motions for all alcohol concentrations. While low concentrations of TFE (10% (v/v)) lead to an increase of the mean square amplitudes of vibrations < u2> and a retention of a native-like structure — but not to an increase of the characteristic radius of proton diffusion processes a. Addition of 20% (v/v) of TFE induces aggregation, going along with a further increase of < u2>. Further increase of TFE concentration to 30% (v/v) changes the nanoscale structure of the oligomeric nucleate, but induces no further significant changes in < u2>. The present study underlines the necessity of methods sensitive to the dynamics of a system to obtain a complete picture of a molecular process. 相似文献
163.
Phylogeny of Passerida (Aves: Passeriformes) based on nuclear and mitochondrial sequence data 总被引:10,自引:0,他引:10
Passerida is a monophyletic group of oscine passerines that includes almost 3500 species (about 36%) of all bird species in the world. The current understanding of higher-level relationships within Passerida is based on DNA-DNA hybridizations [C.G. Sibley, J.E. Ahlquist, Phylogeny and Classification of Birds, 1990, Yale University Press, New Haven, CT]. Our results are based on analyses of 3130 aligned nucleotide sequence data obtained from 48 ingroup and 13 outgroup genera. Three nuclear genes were sequenced: c-myc (498-510 bp), RAG-1 (930 bp), and myoglobin (693-722 bp), as well one mitochondrial gene; cytochrome b (879 bp). The data were analysed by parsimony, maximum-likelihood, and Bayesian inference. The African rockfowl and rockjumper are found to constitute the deepest branch within Passerida, but relationships among the other taxa are poorly resolved--only four major clades receive statistical support. One clade corresponds to Passeroidea of [C.G. Sibley, B.L. Monroe, Distribution and Taxonomy of Birds of the World, 1990, Yale University Press, New Haven, CT] and includes, e.g., flowerpeckers, sunbirds, accentors, weavers, estrilds, wagtails, finches, and sparrows. Starlings, mockingbirds, thrushes, Old World flycatchers, and dippers also group together in a clade corresponding to Muscicapoidea of Sibley and Monroe [op. cit.]. Monophyly of their Sylvioidea could not be corroborated--these taxa falls either into a clade with wrens, gnatcatchers, and nuthatches, or one with, e.g., warblers, bulbuls, babblers, and white-eyes. The tits, penduline tits, and waxwings belong to Passerida but have no close relatives among the taxa studied herein. 相似文献
164.
165.
Transformed 3T3 cells have reduced levels and altered subcellular distribution of the major PKC substrate protein marcks 总被引:1,自引:0,他引:1
The MARCKS (myristylated alanine-rich C-kinase substrate) protein is an abundant calmodulin-binding protein that is a major and specific endogenous substrate of protein kinase C (PKC). Stimulation of cells with phorbol esters or other activators of PKC has been shown previously to result in rapid phosphorylation of MARCKS proteins and redistribution of these myristylated C-kinase substrates from membrane to cytosol. Here we show that NIH3T3 murine fibroblasts transformed by p21-HA-C-RAS or pp60-V-SRC oncoproteins have markedly reduced levels of p68-MARCKS and that most of the remaining MARCKS protein is found in the cytosol. 3T3 cells containing a nontransforming oncoprotein p26-BCL2, in contrast, exhibited normal levels and distribution of p68-MARCKS. When taken together with recent evidence that MARCKS proteins are involved in regulating organization of the membrane cytoskeleton, our findings suggest that oncoprotein-mediated alterations in MARCKS protein levels and subcellular distribution may contribute to the development or maintenance of the transformed phenotpe. 相似文献
166.
A search was performed for a periplasmic molecular chaperone which may assist outer membrane proteins of Escherichia coli on their way from the cytoplasmic to the outer membrane. Proteins of the periplasmic space were fractionated on an affinity column with sepharose-bound outer membrane porin OmpF. A 17kDa polypeptide was the predominant protein retained by this column. The corresponding gene was found in a gene bank; it encodes the periplasmic protein Skp. The protein was isolated and it could be demonstrated that it bound outer membrane proteins, following SDS-PAGE, with high selectivity. Among these were OmpA, OmpC, OmpF and the maltoporin LamB. The chromosomal skp gene was inactivated by a deletion causing removal of most of the signal peptide plus 107 residues of the 141-residue mature protein. The mutant was viable but possessed much-reduced concentrations of outer membrane proteins. This defect was fully restored by a plasmid-borne skp gene which may serve as a periplasmic chaperone. 相似文献
167.
The formation of a microbial biofilm on glass surfaces arranged in lamellar piles parallel with circulating sea water (3 cm·sec–1) was studied. The increase in dry weight, protein content, nucleotide content (ATP, ADP), and diatoms was followed over a period of 62 days. Dry weight and protein were estimates of the total biofilm development, whereas the nucleotide measurements revealed the viability of the biofilm and reflected the dynamics in the community structure. 相似文献
168.
Summary Immunohistochemistry with monoclonal and polyclonal antibodies revealed the presence of cytokeratins in epithelial cells of Rathke's cysts in the pars intermedia of the human pituitary gland. With monoclonal antibodies specific for individual cytokeratins, the expression of CK 18, CK 8, CK 7, and CK 19 could be shown in these cells. Within the hypophysis, CK 19 and CK 7 were restricted to Rathke's cysts and a few epithelial cell clusters in the pars tuberalis, whereas other cytokeratins were also present in endocrine cells of the pars distalis. Furthermore, vimentin and, focally, glial fibrillary acidic protein (GFAP) were detected in the cystic epithelia. By double labelling, coexpression of cytokeratin and vimentin, GFAP and cytokeratin, and GFAP and vimentin could be demonstrated. Compiled data of all known cases of coexpression of cytokeratin and vimentin in normal cells reveal physiological correlations and suggest a functional significance of this rare type of coexpression of intermediate filament proteins. 相似文献
169.
Ephyra larvae and small medusae (1.795 mm diameter, 0.01350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 106 µg AFDW cell1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 103 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual1) and mixed zooplankton(mainly copepods and cladocerans, 2.13.1 µg AFDWindividual1). Phytoplankton in natural concentrations(50200 µg C I1) were not utilized by largemedusae (4495 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml"1 were consumed by ephyra larvaeand small medusae (314 mm diameter) at a maximum predationrate of 171 prey day1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100600 prey I1, resulted in daily rations ofephyra larvae (25 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 540%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day"1 in prey concentrationsexceeding 100 I1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential scope for growththat exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species.
1Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway 相似文献
170.