全文获取类型
收费全文 | 104篇 |
免费 | 0篇 |
专业分类
系统科学 | 1篇 |
现状及发展 | 12篇 |
研究方法 | 13篇 |
综合类 | 77篇 |
自然研究 | 1篇 |
出版年
2021年 | 2篇 |
2014年 | 1篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 3篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1967年 | 4篇 |
1966年 | 4篇 |
1965年 | 1篇 |
排序方式: 共有104条查询结果,搜索用时 15 毫秒
41.
42.
One difficulty in the production of allophenic mice by aggregation of preimplantation embryos is that they frequently roll apart before the bonds between the blastomeres have had time to form. One solution to the problem, described here, is to pretreat one of the embryos with rabbit anti-mouse serum just prior to pushing them together. Blastocyst formation is unhampered by antibody treatment, and numerous allophenic mice have already been produced with this new procedure. 相似文献
43.
Vascular endothelial cells synthesize nitric oxide from L-arginine 总被引:155,自引:0,他引:155
Nitric oxide (NO) released by vascular endothelial cells accounts for the relaxation of strips of vascular tissue and for the inhibition of platelet aggregation and platelet adhesion attributed to endothelium-derived relaxing factor. We now demonstrate that NO can be synthesized from L-arginine by porcine aortic endothelial cells in culture. Nitric oxide was detected by bioassay, chemiluminescence or by mass spectrometry. Release of NO from the endothelial cells induced by bradykinin and the calcium ionophore A23187 was reversibly enhanced by infusions of L-arginine and L-citrulline, but not D-arginine or other close structural analogues. Mass spectrometry studies using 15N-labelled L-arginine indicated that this enhancement was due to the formation of NO from the terminal guanidino nitrogen atom(s) of L-arginine. The strict substrate specificity of this reaction suggests that L-arginine is the precursor for NO synthesis in vascular endothelial cells. 相似文献
44.
Experimental lepromatous leprosy 总被引:17,自引:0,他引:17
45.
46.
Li ZY Young NP Di Vece M Palomba S Palmer RE Bleloch AL Curley BC Johnston RL Jiang J Yuan J 《Nature》2008,451(7174):46-48
An unambiguous determination of the three-dimensional structure of nanoparticles is challenging. Electron tomography requires a series of images taken for many different specimen orientations. This approach is ideal for stable and stationary structures. But ultrasmall nanoparticles are intrinsically structurally unstable and may interact with the incident electron beam, constraining the electron beam density that can be used and the duration of the observation. Here we use aberration-corrected scanning transmission electron microscopy, coupled with simple imaging simulation, to determine with atomic resolution the size, three-dimensional shape, orientation and atomic arrangement of size-selected gold nanoclusters that are preformed in the gas phase and soft-landed on an amorphous carbon substrate. The structures of gold nanoclusters containing 3096 atoms can be identified with either Ino-decahedral, cuboctahedral or icosahedral geometries. Comparison with theoretical modelling of the system suggests that the structures are consistent with energetic considerations. The discovery that nanoscale gold particles function as active and selective catalysts for a variety of important chemical reactions has provoked much research interest in recent years. We believe that the detailed structure information we provide will help to unravel the role of these nanoclusters in size- and structure-specific catalytic reactions. We note that the technique will be of use in investigations of other supported ultrasmall metal cluster systems. 相似文献
47.
Blake CH Bloom JS Starr DL Falco EE Skrutskie M Fenimore EE Duchêne G Szentgyorgyi A Hornstein S Prochaska JX McCabe C Ghez A Konopacky Q Stapelfeldt K Hurley K Campbell R Kassis M Chaffee F Gehrels N Barthelmy S Cummings JR Hullinger D Krimm HA Markwardt CB Palmer D Parsons A McLean K Tueller J 《Nature》2005,435(7039):181-184
The explosion that results in a cosmic gamma-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows. Although observations of afterglows continue to refine our understanding of GRB progenitors and relativistic shocks, gamma-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and it was associated with emission from an external shock. Here we report the discovery of infrared emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a (ref. 8). We acquired 21 images during the active phase of the burst, yielding early multi-colour observations. Our analysis of the initial infrared pulse suggests an origin consistent with internal shocks. 相似文献
48.
49.
50.
Yokoyama S Woods SL Boyle GM Aoude LG MacGregor S Zismann V Gartside M Cust AE Haq R Harland M Taylor JC Duffy DL Holohan K Dutton-Regester K Palmer JM Bonazzi V Stark MS Symmons J Law MH Schmidt C Lanagan C O'Connor L Holland EA Schmid H Maskiell JA Jetann J Ferguson M Jenkins MA Kefford RF Giles GG Armstrong BK Aitken JF Hopper JL Whiteman DC Pharoah PD Easton DF Dunning AM Newton-Bishop JA Montgomery GW Martin NG Mann GJ Bishop DT Tsao H Trent JM Fisher DE Hayward NK Brown KM 《Nature》2011,480(7375):99-103