全文获取类型
收费全文 | 1926篇 |
免费 | 140篇 |
出版年
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 28篇 |
2017年 | 16篇 |
2016年 | 28篇 |
2015年 | 50篇 |
2014年 | 62篇 |
2013年 | 105篇 |
2012年 | 118篇 |
2011年 | 131篇 |
2010年 | 76篇 |
2009年 | 65篇 |
2008年 | 111篇 |
2007年 | 117篇 |
2006年 | 113篇 |
2005年 | 119篇 |
2004年 | 109篇 |
2003年 | 87篇 |
2002年 | 101篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 30篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 27篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1985年 | 13篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1973年 | 11篇 |
1970年 | 8篇 |
1968年 | 9篇 |
1966年 | 9篇 |
排序方式: 共有2066条查询结果,搜索用时 31 毫秒
81.
Marlène Jagut Patricia Hamminger Alexander Woglar Sophia Millonigg Luis Paulin Martin Mikl Maria Rosaria Dello Stritto Lois Tang Cornelia Habacher Angela Tam Miguel Gallach Arndt von Haeseler Anne M. Villeneuve Verena Jantsch 《PLoS biology》2016,14(3)
During the first meiotic division, crossovers (COs) between homologous chromosomes ensure their correct segregation. COs are produced by homologous recombination (HR)-mediated repair of programmed DNA double strand breaks (DSBs). As more DSBs are induced than COs, mechanisms are required to establish a regulated number of COs and to repair remaining intermediates as non-crossovers (NCOs). We show that the Caenorhabditis elegans RMI1 homolog-1 (RMH-1) functions during meiosis to promote both CO and NCO HR at appropriate chromosomal sites. RMH-1 accumulates at CO sites, dependent on known pro-CO factors, and acts to promote CO designation and enforce the CO outcome of HR-intermediate resolution. RMH-1 also localizes at NCO sites and functions in parallel with SMC-5 to antagonize excess HR-based connections between chromosomes. Moreover, RMH-1 also has a major role in channeling DSBs into an NCO HR outcome near the centers of chromosomes, thereby ensuring that COs form predominantly at off-center positions. 相似文献
82.
Qingzhi An Qing Sun Andreas Weu David Becker‐Koch Fabian Paulus Sebastian Arndt Fabian Stuck A. Stephen K. Hashmi Nir Tessler Yana Vaynzof 《Liver Transplantation》2019,9(33)
Four π‐extended phosphoniumfluorene electrolytes (π‐PFEs) are introduced as hole‐blocking layers (HBL) in inverted architecture planar perovskite solar cells with the structure of ITO/PEDOT:PSS/MAPbI3/PCBM/HBL/Ag. The deep‐lying highest occupied molecular orbital energy level of the π‐PFEs effectively blocks holes, decreasing contact recombination. It is demonstrated that the incorporation of π‐PFEs introduces a dipole moment at the PCBM/Ag interface, resulting in significant enhancement of the built‐in potential of the device. This enhancement results in an increase in the open‐circuit voltage of the device by up to 120 mV, when compared to the commonly used bathocuproine HBL. The results are confirmed both experimentally and by numerical simulation. This work demonstrates that interfacial engineering of the transport layer/contact interface by small molecule electrolytes is a promising route to suppress nonradiative recombination in perovskite devices and compensates for a nonideal energetic alignment at the hole‐transport layer/perovskite interface. 相似文献
83.
84.
Ann‐Christin Moritzer Hartmut H. Niemann 《Protein science : a publication of the Protein Society》2019,28(12):2112-2118
Flavin‐dependent halogenases require reduced flavin adenine dinucleotide (FADH2), O2, and halide salts to halogenate their substrates. We describe the crystal structures of the tryptophan 6‐halogenase Thal in complex with FAD or with both tryptophan and FAD. If tryptophan and FAD were soaked simultaneously, both ligands showed impaired binding and in some cases only the adenosine monophosphate or the adenosine moiety of FAD was resolved, suggesting that tryptophan binding increases the mobility mainly of the flavin mononucleotide moiety. This confirms a negative cooperativity between the binding of substrate and cofactor that was previously described for other tryptophan halogenases. Binding of substrate to tryptophan halogenases reduces the affinity for the oxidized cofactor FAD presumably to facilitate the regeneration of FADH2 by flavin reductases. 相似文献
85.
Matthias Weiand Paula Ballmaier Christoph Niemietz Hartmut Schmidt Andree Zibert 《Biochemistry and Biophysics Reports》2022
Human primary cells, including urine-derived cells (UCs), are an excellent source for generation of pluripotent stem cells (iPSCs) to model disease. However, replicative senescence starts early and shortens the time window for generation of iPSCs. We addressed the question whether combinations of transgenes allows efficient immortalization of UCs, iPSC generation, and differentiation into hepatocyte-like cells (HLCs). Retroviral transfer of three gene cassettes HPVE6E7 (H), hTERT/p53DD (T), cyclinD1/CDK4R24C (C) encoding five genes was established in primary UCs. Long-term cell proliferation was observed in cells carrying transgenes H, HT, HC, and HCT, whereas cells carrying transgenes C, T and CT showed early senescence similar to UCs. iPSCs could be exclusively generated from immortalized UCs transduced with transgenes HCT and HC. iPSC colonies appeared however later and in smaller number as compared to UCs. Using an established hepatic differentiation protocol, HLCs were obtained with high efficacy. Of note, a high expression of individual transgenes was observed in immortalized UCs, which was down-regulated after reprogramming in four out of five genes. One transgene was re-expressed in HLCs as compared to iPSCs. Our data suggest that individual transgene combinations result in advanced growth rates of immortalized cells and do not prevent iPSC formation and HLC differentiation. Retroviral transgene expression is mostly silenced in iPSCs but can be rarely re-expressed after hepatic differentiation. An extended time window for iPSC establishment can be proposed that allows straightforward functional analyses of differentiated cells. 相似文献
86.
Elizabeth F. Dowler Annette Diehl Peter Schmieder Christoph Brockmann Jonathan Elkins Meera Soundararajan Hartmut Oschkinat Linda J. Ball 《Biomolecular NMR assignments》2007,1(1):95-97
We have assigned 1H, 15N and 13C resonances of the RGS domain from the human RGS14 protein, a multi-domain member of the RGS (Regulators of G-protein signalling)
family of proteins, important in the down-regulation of specific G-protein signalling pathways. 相似文献
87.
Saez-Rodriguez J Simeoni L Lindquist JA Hemenway R Bommhardt U Arndt B Haus UU Weismantel R Gilles ED Klamt S Schraven B 《PLoS computational biology》2007,3(8):e163
Cellular decisions are determined by complex molecular interaction networks. Large-scale signaling networks are currently being reconstructed, but the kinetic parameters and quantitative data that would allow for dynamic modeling are still scarce. Therefore, computational studies based upon the structure of these networks are of great interest. Here, a methodology relying on a logical formalism is applied to the functional analysis of the complex signaling network governing the activation of T cells via the T cell receptor, the CD4/CD8 co-receptors, and the accessory signaling receptor CD28. Our large-scale Boolean model, which comprises 94 nodes and 123 interactions and is based upon well-established qualitative knowledge from primary T cells, reveals important structural features (e.g., feedback loops and network-wide dependencies) and recapitulates the global behavior of this network for an array of published data on T cell activation in wild-type and knock-out conditions. More importantly, the model predicted unexpected signaling events after antibody-mediated perturbation of CD28 and after genetic knockout of the kinase Fyn that were subsequently experimentally validated. Finally, we show that the logical model reveals key elements and potential failure modes in network functioning and provides candidates for missing links. In summary, our large-scale logical model for T cell activation proved to be a promising in silico tool, and it inspires immunologists to ask new questions. We think that it holds valuable potential in foreseeing the effects of drugs and network modifications. 相似文献
88.
89.
Hartmut Arndt Maria Krocker Brigitte Nixdorf Antje Khler 《International Review of Hydrobiology》1993,78(3):379-402
Annual changes of rotifers, copepods, cladocerans, the ciliate Epistylis rotans, and larvae of Dreissena polymorpha were analysed for the period 1908–1990. Though food resources increased 6–10 fold in the course of eutrophication, only rotifers and Epistylis increased accordingly. Probably as a result of increased predation pressure crustaceans increased only twice. The seasonal pattern of metazoans and protozoans (flagellates, sarcodines, ciliates) were analysed for 12 and 3 years, resp. During winter and spring, large heterotrophic flagellates and ciliates dominated the zooplankton and were responsible for a pronounced - formerly underestimated - grazing pressure on phytoplankton. In early summer, metazoan filter-feeders were often able to cause a significant reduction of phyto- and protozooplankton. However, during some years, phytoplankton declined in the absence of a pronounced grazing pressure. Field data and experiments revealed that predators were able to regulate the density of cladocerans in early summer (mainly cyclopoids) and summer (mainly Leptodora, smelt and fish juveniles). 相似文献
90.
Though rotifers play an important role in many pelagic ecosystems, there is a lack for studies on diurnal variations in feeding behaviour. Diurnal feeding rhythms of estuarine populations of Brachionus plicatilis and Keratella cruciformis f. eichwaldi and a pond population of K. cochlearis were investigated using 14C-Chlorella and 14C-labelled natural bacteria populations, respectively, as a tracer food during in situ experiments. A 51Cr/14C double tracer technique was used to determine Assimilation efficiencies. All species had about two times higher feeding rates during day than during dark hours. There was a tendency for higher values during the afternoon. No trend was found regarding diurnal changes in assimilation efficiency. Diurnally segregated niches between microphagous daytime active rotifers and nighttime active crustacean populations in pelagic ecosystems are demonstrated and their ecological significance with special regard to changes in food quality and predation pressure is discussed. 相似文献