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221.
222.
Phan TD Kistler LM Klecker B Haerendel G Paschmann G Sonnerup BU Baumjohann W Bavassano-Cattaneo MB Carlson CW DiLellis AM Fornacon KH Frank LA Fujimoto M Georgescu E Kokubun S Moebius E Mukai T Oieroset M Paterson WR Reme H 《Nature》2000,404(6780):848-850
Magnetic reconnection is a process that converts magnetic energy into bi-directional plasma jets; it is believed to be the dominant process by which solar-wind energy enters the Earth's magnetosphere. This energy is subsequently dissipated by magnetic storms and aurorae. Previous single-spacecraft observations revealed only single jets at the magnetopause--while the existence of a counter-streaming jet was implicitly assumed, no experimental confirmation was available. Here we report in situ two-spacecraft observations of bi-directional jets at the magnetopause, finding evidence for a stable and extended reconnection line; the latter implies substantial entry of the solar wind into the magnetosphere. We conclude that reconnection is determined by large-scale interactions between the solar wind and the magnetosphere, rather than by local conditions at the magnetopause. 相似文献
223.
224.
Determining the architectures of macromolecular assemblies 总被引:1,自引:0,他引:1
Alber F Dokudovskaya S Veenhoff LM Zhang W Kipper J Devos D Suprapto A Karni-Schmidt O Williams R Chait BT Rout MP Sali A 《Nature》2007,450(7170):683-694
To understand the workings of a living cell, we need to know the architectures of its macromolecular assemblies. Here we show how proteomic data can be used to determine such structures. The process involves the collection of sufficient and diverse high-quality data, translation of these data into spatial restraints, and an optimization that uses the restraints to generate an ensemble of structures consistent with the data. Analysis of the ensemble produces a detailed architectural map of the assembly. We developed our approach on a challenging model system, the nuclear pore complex (NPC). The NPC acts as a dynamic barrier, controlling access to and from the nucleus, and in yeast is a 50 MDa assembly of 456 proteins. The resulting structure, presented in an accompanying paper, reveals the configuration of the proteins in the NPC, providing insights into its evolution and architectural principles. The present approach should be applicable to many other macromolecular assemblies. 相似文献
225.
Alber F Dokudovskaya S Veenhoff LM Zhang W Kipper J Devos D Suprapto A Karni-Schmidt O Williams R Chait BT Sali A Rout MP 《Nature》2007,450(7170):695-701
Nuclear pore complexes (NPCs) are proteinaceous assemblies of approximately 50 MDa that selectively transport cargoes across the nuclear envelope. To determine the molecular architecture of the yeast NPC, we collected a diverse set of biophysical and proteomic data, and developed a method for using these data to localize the NPC's 456 constituent proteins (see the accompanying paper). Our structure reveals that half of the NPC is made up of a core scaffold, which is structurally analogous to vesicle-coating complexes. This scaffold forms an interlaced network that coats the entire curved surface of the nuclear envelope membrane within which the NPC is embedded. The selective barrier for transport is formed by large numbers of proteins with disordered regions that line the inner face of the scaffold. The NPC consists of only a few structural modules that resemble each other in terms of the configuration of their homologous constituents, the most striking of these being a 16-fold repetition of 'columns'. These findings provide clues to the evolutionary origins of the NPC. 相似文献
226.
When attempting to understand evolution, we traditionally rely on analysing evolutionary outcomes, despite the fact that unseen intermediates determine its course. A handful of recent studies has begun to explore these intermediate evolutionary forms, which can be reconstructed in the laboratory. With this first view on empirical evolutionary landscapes, we can now finally start asking why particular evolutionary paths are taken. 相似文献
227.
Hessell AJ Hangartner L Hunter M Havenith CE Beurskens FJ Bakker JM Lanigan CM Landucci G Forthal DN Parren PW Marx PA Burton DR 《Nature》2007,449(7158):101-104
Most successful vaccines elicit neutralizing antibodies and this property is a high priority when developing an HIV vaccine. Indeed, passively administered neutralizing antibodies have been shown to protect against HIV challenge in some of the best available animal models. For example, antibodies given intravenously can protect macaques against intravenous or mucosal SHIV (an HIV/SIV chimaera) challenge and topically applied antibodies can protect macaques against vaginal SHIV challenge. However, the mechanism(s) by which neutralizing antibodies afford protection against HIV is not understood and, in particular, the role of antibody Fc-mediated effector functions is unclear. Here we report that there is a dramatic decrease in the ability of a broadly neutralizing antibody to protect macaques against SHIV challenge when Fc receptor and complement-binding activities are engineered out of the antibody. No loss of antibody protective activity is associated with the elimination of complement binding alone. Our in vivo results are consistent with in vitro assays indicating that interaction of Fc-receptor-bearing effector cells with antibody-complexed infected cells is important in reducing virus yield from infected cells. Overall, the data suggest the potential importance of activity against both infected cells and free virus for effective protection against HIV. 相似文献
228.
The evolution of trees of modern size growing together in forests fundamentally changed terrestrial ecosystems. The oldest trees are often thought to be of latest Devonian age (about 380-360 Myr old) as indicated by the widespread occurrence of Archaeopteris (Progymnospermopsida). Late Middle Devonian fossil tree stumps, rooted and still in life position, discovered in the 1870s from Gilboa, New York, and later named Eospermatopteris, are widely cited as evidence of the Earth's 'oldest forest'. However, their affinities and significance have proved to be elusive because the aerial portion of the plant has been unknown until now. Here we report spectacular specimens from Schoharie County, New York, showing an intact crown belonging to the cladoxylopsid Wattieza (Pseudosporochnales) and its attachment to Eospermatopteris trunk and base. This evidence allows the reconstruction of a tall (at least 8 m), tree-fern-like plant with a trunk bearing large branches in longitudinal ranks. The branches were probably abscised as frond-like modules. Lower portions of the trunk show longitudinal carbonaceous strands typical of Eospermatopteris, and a flat bottom with many small anchoring roots. These specimens provide new insight into Earth's earliest trees and forest ecosystems. The tree-fern-like morphology described here is the oldest example so far of an evolutionarily recurrent arborescent body plan within vascular plants. Given their modular construction, these plants probably produced abundant litter, indicating the potential for significant terrestrial carbon accumulation and a detritus-based arthropod fauna by the Middle Devonian period. 相似文献
229.
Anaphase initiation is regulated by antagonistic ubiquitination and deubiquitination activities 总被引:1,自引:0,他引:1
Stegmeier F Rape M Draviam VM Nalepa G Sowa ME Ang XL McDonald ER Li MZ Hannon GJ Sorger PK Kirschner MW Harper JW Elledge SJ 《Nature》2007,446(7138):876-881
The spindle checkpoint prevents chromosome mis-segregation by delaying sister chromatid separation until all chromosomes have achieved bipolar attachment to the mitotic spindle. Its operation is essential for accurate chromosome segregation, whereas its dysregulation can contribute to birth defects and tumorigenesis. The target of the spindle checkpoint is the anaphase-promoting complex (APC), a ubiquitin ligase that promotes sister chromatid separation and progression to anaphase. Using a short hairpin RNA screen targeting components of the ubiquitin-proteasome pathway in human cells, we identified the deubiquitinating enzyme USP44 (ubiquitin-specific protease 44) as a critical regulator of the spindle checkpoint. USP44 is not required for the initial recognition of unattached kinetochores and the subsequent recruitment of checkpoint components. Instead, it prevents the premature activation of the APC by stabilizing the APC-inhibitory Mad2-Cdc20 complex. USP44 deubiquitinates the APC coactivator Cdc20 both in vitro and in vivo, and thereby directly counteracts the APC-driven disassembly of Mad2-Cdc20 complexes (discussed in an accompanying paper). Our findings suggest that a dynamic balance of ubiquitination by the APC and deubiquitination by USP44 contributes to the generation of the switch-like transition controlling anaphase entry, analogous to the way that phosphorylation and dephosphorylation of Cdk1 by Wee1 and Cdc25 controls entry into mitosis. 相似文献
230.
Giridhar Pulletikurthi Bj?rn B?decker Andriy Borodin Bernd Weidenfeller Frank Endres 《自然科学进展(英文版)》2015,25(6):603-611
The addition of 1-butylpyrrolidine to AlCl_3 results in the formation of an electrolyte that is suited to Al deposition.The feasibility of electrodepositing Al from the synthesized electrolyte was investigated.Several compositions of AlCl_3 and 1-butylpyrrolidine were prepared for this purpose.These mixtures show a different phase behavior at various compositions of AlCl_3 and 1-butylpyrrolidine.IR,Raman and NMR spectroscopy were employed to characterize the synthesized liquids.Among the prepared compositions,1:1.2 mol ratio of 1-butylpyrrolidine:AlCl_3 and the upper phase of 1:1.3 mol ratio of 1-butylpyrrolidine:AlCl_3 were found to be suitable for Al electrodeposition at room temperature(RT).Uniform and thick( mm thick) layers of Al were obtained on copper at RT.Al deposition occured from the cationic species of AlCl_3 xLty(where x r 2,y ? 1–2,and L ? 1-butylpyrrolidine) in this electrolyte.This behavior is contrary to the well investigated classic AlCl_3 based ionic liquids,where the deposition of Al occurs mainly from anionic Al2 Cl 7ions. 相似文献