全文获取类型
收费全文 | 2197篇 |
免费 | 182篇 |
国内免费 | 1篇 |
出版年
2023年 | 12篇 |
2022年 | 11篇 |
2021年 | 50篇 |
2020年 | 22篇 |
2019年 | 24篇 |
2018年 | 54篇 |
2017年 | 40篇 |
2016年 | 58篇 |
2015年 | 101篇 |
2014年 | 92篇 |
2013年 | 155篇 |
2012年 | 150篇 |
2011年 | 183篇 |
2010年 | 108篇 |
2009年 | 106篇 |
2008年 | 141篇 |
2007年 | 113篇 |
2006年 | 113篇 |
2005年 | 119篇 |
2004年 | 121篇 |
2003年 | 112篇 |
2002年 | 85篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 22篇 |
1998年 | 26篇 |
1997年 | 18篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有2380条查询结果,搜索用时 15 毫秒
91.
Marcin Moch Reinhard Windoffer Nicole Schwarz Raphaela Pohl Andreas Omenzetter Uwe Schnakenberg Fabian Herb Kraisorn Chaisaowong Dorit Merhof Lena Ramms Gloria Fabris Bernd Hoffmann Rudolf Merkel Rudolf E. Leube 《PloS one》2016,11(3)
The keratin intermediate filament cytoskeleton protects epithelial cells against various types of stress and is involved in fundamental cellular processes such as signaling, differentiation and organelle trafficking. These functions rely on the cell type-specific arrangement and plasticity of the keratin system. It has been suggested that these properties are regulated by a complex cycle of assembly and disassembly. The exact mechanisms responsible for the underlying molecular processes, however, have not been clarified. Accumulating evidence implicates the cytolinker plectin in various aspects of the keratin cycle, i.e., by acting as a stabilizing anchor at hemidesmosomal adhesion sites and the nucleus, by affecting keratin bundling and branching and by linkage of keratins to actin filament and microtubule dynamics. In the present study we tested these hypotheses. To this end, plectin was downregulated by shRNA in vulvar carcinoma-derived A431 cells. As expected, integrin β4- and BPAG-1-positive hemidesmosomal structures were strongly reduced and cytosolic actin stress fibers were increased. In addition, integrins α3 and β1 were reduced. The experiments furthermore showed that loss of plectin led to a reduction in keratin filament branch length but did not alter overall mechanical properties as assessed by indentation analyses using atomic force microscopy and by displacement analyses of cytoplasmic superparamagnetic beads using magnetic tweezers. An increase in keratin movement was observed in plectin-depleted cells as was the case in control cells lacking hemidesmosome-like structures. Yet, keratin turnover was not significantly affected. We conclude that plectin alone is not needed for keratin assembly and disassembly and that other mechanisms exist to guarantee proper keratin cycling under steady state conditions in cultured single cells. 相似文献
92.
Interspecific reproductive barriers between sympatric populations of wild tomato species (Solanum section Lycopersicon) 下载免费PDF全文
93.
94.
95.
Carmen Núñez-Lahuerta Gloria Cuenca-Bescós Víctor Sauqué Julia Galán 《Historical Biology》2016,28(6):774-786
Aves are represented by abundant fossil remains in Quaternary sites. Birds are well adapted to the environment they inhabit, so they make very good paleoenvironmental indicators for Quaternary sites. Here we analyse the avian remains from the Late Pleistocene (probably MIS3) site of Aguilón P-7 (AGP-7). The Pleistocene sediments fill up a shallow cave, which is located in the Zaragozan part of the Iberian Range, 55 km south of the city of Zaragoza. We have for the first time provided a taxonomic and taphonomic study of the avian assemblage of AGP-7, as well as a preliminary paleoenvironmental analysis based on these data. Nine avian taxa have been identified: Galliformes indet., Lagopus sp., Aquila chrysaetos, Gyps fulvus, Passeridae indet., Anthus sp., Prunella modularis,Sturnus cf. unicolor and Corvus monedula. The taphonomic analysis did not provide conclusive information. However, it suggests an accumulation of uneaten food remains by diurnal birds of prey. The identified taxa currently inhabit the Iberian Peninsula, populating woodland environments with rocky areas. They are found in areas with an oceanic climate, in contrast to the Mediterranean climate that now prevails in Aguilón. 相似文献
96.
Zubrzak P Williams H Coast GM Isaac RE Reyes-Rangel G Juaristi E Zabrocki J Nachman RJ 《Biopolymers》2007,88(1):76-82
Insect neuropeptides of the insect kinin class share a common C-terminal pentapeptide sequence F(1)X(1)(2)X(2)(3)W(4)G(5)-NH(2) (X(2)(3) = P, S, A) and regulate such critical physiological processes as water balance and digestive enzyme release. Analogs of the insect kinin class, in which the critical residues of F(1), P(3), and W(4) were replaced with beta(3)-amino acid or their beta(2)-homo-amino acid variants, have been synthesized by the solid phase peptide strategy. The resulting single- and double-replacement analogs were evaluated in an insect diuretic assay and enzyme digestion trials. Analogs modified in the core P(3) position produce a potent and efficacious diuretic response that is not significantly different from that obtained with the endogenous achetakinin peptides. The analogs also demonstrate enhanced resistance to hydrolysis by ACE and NEP, endopeptidases that inactivate the natural insect neuropeptides. This paper describes the first instance of beta-amino acids analogs of an arthropod peptide that demonstrate significant bioactivity and resistance to peptidase degradation. 相似文献
97.
Burnett KG Bain LJ Baldwin WS Callard GV Cohen S Di Giulio RT Evans DH Gómez-Chiarri M Hahn ME Hoover CA Karchner SI Katoh F Maclatchy DL Marshall WS Meyer JN Nacci DE Oleksiak MF Rees BB Singer TD Stegeman JJ Towle DW Van Veld PA Vogelbein WK Whitehead A Winn RN Crawford DL 《Comparative biochemistry and physiology. Part D, Genomics & proteomics》2007,2(4):257-286
A strong foundation of basic and applied research documents that the estuarine fish Fundulus heteroclitus and related species are unique laboratory and field models for understanding how individuals and populations interact with their environment. In this paper we summarize an extensive body of work examining the adaptive responses of Fundulus species to environmental conditions, and describe how this research has contributed importantly to our understanding of physiology, gene regulation, toxicology, and ecological and evolutionary genetics of teleosts and other vertebrates. These explorations have reached a critical juncture at which advancement is hindered by the lack of genomic resources for these species. We suggest that a more complete genomics toolbox for F. heteroclitus and related species will permit researchers to exploit the power of this model organism to rapidly advance our understanding of fundamental biological and pathological mechanisms among vertebrates, as well as ecological strategies and evolutionary processes common to all living organisms. 相似文献
98.
Lambertucci C Cristalli G Dal Ben D Kachare DD Bolcato C Klotz KN Spalluto G Volpini R 《Purinergic signalling》2007,3(4):339-346
A new series of 2,6,9-trisubstituted adenines (5–14) have been prepared and evaluated in radioligand binding studies for their affinity at the human A1, A2A and A3 adenosine receptors and in adenylyl cyclase experiments for their potency at the human A2B subtype. From this preliminary study the conclusion can be drawn that introduction of bulky chains at the N
6 position of 9-propyladenine significantly increased binding affinity at the human A1 and A3 adenosine receptors, while the presence of a chlorine atom at the 2 position resulted in a not univocal effect, depending
on the receptor subtype and/or on the substituent present in the N
6 position. However, in all cases, the presence in the 2 position of a chlorine atom favoured the interaction with the A2A subtype. These results demonstrated that, although the synthesized compounds were found to be quite inactive at the human
A2B subtype, adenine is a useful template for further development of simplified adenosine receptor antagonists with distinct
receptor selectivity profiles. 相似文献
99.
Reina C Padoani G Carotti C Merico A Tripodi G Ferrari P Popolo L 《FEMS yeast research》2007,7(4):585-594
Na,K-ATPase is a crucial enzyme for ion homeostasis in human tissues. Different isozymes are produced by assembly of four alpha- and three beta-subunits. The expression of the alpha3/beta1 isozyme is confined to brain and heart. Its heterologous production has so far never been attempted in a lower eukaryote. In this work we explored whether the methylotrophic yeast Pichia pastoris is capable of expressing the alpha3/beta1 isoform of human Na,K-ATPase. cDNAs encoding the alpha(3) and the beta(1)-subunits were cloned under the control of the inducible promoter of Pichia pastoris alcohol oxidase 1. Pichia pastoris could express the single alpha3- and beta1-subunits and even coexpress them after methanol induction. beta1-subunit was produced as a major 44-kDa glycosylated polypeptide and alpha3 as a 110-kDa unglycosylated polypeptide. Expression at the plasma membrane was limited in shaking flask cultures but by cultivating P. pastoris cells in a fermenter there was a 10-fold increase of the number of ouabain binding sites per cell. The exported enzyme was estimated to be about 0.230 mg L(-1) at the end of a bioreactor run. Na,K-ATPase proved active and the dissociation constant of the recombinant enzyme-ouabain interaction was determined. 相似文献