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51.
分析了基站天线室内测量系统的误差源,理论证明微波暗室是影响测量结果(电压驻波比,隔离度)的重要因素.根据对测试结果的分析,得出了关于微波暗室对天线性能参数影响的几点结论.最后指出了所用方法的不足之处,提出了新的分析方法. 相似文献
52.
Schwarz-Linek U Werner JM Pickford AR Gurusiddappa S Kim JH Pilka ES Briggs JA Gough TS Höök M Campbell ID Potts JR 《Nature》2003,423(6936):177-181
Staphylococcus aureus and Streptococcus pyogenes, two important human pathogens, target host fibronectin (Fn) in their adhesion to and invasion of host cells. Fibronectin-binding proteins (FnBPs), anchored in the bacterial cell wall, have multiple Fn-binding repeats in an unfolded region of the protein. The bacterium-binding site in the amino-terminal domain (1-5F1) of Fn contains five sequential Fn type 1 (F1) modules. Here we show the structure of a streptococcal (S. dysgalactiae) FnBP peptide (B3) in complex with the module pair 1F12F1. This identifies 1F1- and 2F1-binding motifs in B3 that form additional antiparallel beta-strands on sequential F1 modules-the first example of a tandem beta-zipper. Sequence analyses of larger regions of FnBPs from S. pyogenes and S. aureus reveal a repeating pattern of F1-binding motifs that match the pattern of F1 modules in 1-5F1 of Fn. In the process of Fn-mediated invasion of host cells, therefore, the bacterial proteins seem to exploit the modular structure of Fn by forming extended tandem beta-zippers. This work is a vital step forward in explaining the full mechanism of the integrin-dependent FnBP-mediated invasion of host cells. 相似文献
53.
Hans Kuhn 《Cellular and molecular life sciences : CMLS》1946,2(2):64-65
Summary The permeability of jellies of known structure can be determined by experiments on models by application of a principle of hydrodynamical similarity. 相似文献
54.
55.
A new approach to isotonic agglomerative hierarchical clustering 总被引:1,自引:1,他引:0
Hierarchical clustering methods must be isotonic for the construction of ultrametric. We present a general strategy to widen
the class of isotonic methods implemented by agglomerative algorithms. At each step of the agglomeration we allow one of several
admissible pairs to be chosen. Then under mild assumptions an appropriate definition of admissibility guarantees isotony.
Moreover we consider the use of the new methods to compute locally optimal ultrametrics. Two examples demonstrate the ability
to define new agglomerative methods superior to their traditional competitors. 相似文献
56.
The xylosyltransferases I and II (XT-I, XT-II, EC 2.4.2.26) catalyze the transfer of xylose from UDP-xylose to selected serine
residues in the proteoglycan core protein, which is the initial and ratelimiting step in glycosaminoglycan biosynthesis. Both
xylosyltransferases are Golgi-resident enzymes and transfer xylose to similar core proteins acceptors. XT-I and XT-II are
differentially expressed in cell types and tissues, although the reason for the existence of two xylosyltransferase isoforms
in all higher organisms remains elusive. Serum xylosyltransferase activity was found to be a biochemical marker for the assessment
of disease activity in systemic sclerosis and for the diagnosis of fibrotic remodeling processes. Furthermore, sequence variations
in the XT-I and XT-II coding genes were identified as risk factors for diabetic nephropathy, osteoarthritis or pseudoxanthoma
elasticum. These findings point to the important role of the xylosyltransferases as disease modifiers in pathologies which
are characterized by an altered proteoglycan metabolism. The present review discusses recent advances in mammalian xylosyltransferases
and the impact of xylosyltransferases in proteoglycan-associated diseases.
Received 9 February 2007; accepted 5 March 2007 相似文献
57.
Werner Brückner 《Cellular and molecular life sciences : CMLS》1945,1(5):157-158
Ohne Zusammenfassung 相似文献
58.
Werner Kuhn 《Cellular and molecular life sciences : CMLS》1948,4(1):23-24
Summary A thermodynamic consideration shows that SiO2 may be reduced to Si by hydrogen at the temperatures present in the earth's interior. The reaction can be expected to involve a rapid change of viscosity with depth inside the earth, required for the explanation of the seismic discontinuity at 2,900 km. 相似文献
59.
It is a long-standing puzzle that the Sun's photosphere--its visible surface--rotates differentially, with the equatorial regions rotating faster than the poles. It has been suggested that waves analogous to terrestrial Rossby waves, and known as r-mode oscillations, could explain the Sun's differential rotation: Rossby waves are seen in the oceans as large-scale (hundreds of kilometres) variations of sea-surface height (5-cm-high waves), which propagate slowly either east or west (they could take tens of years to cross the Pacific Ocean). Calculations show that the solar r-mode oscillations have properties that should be strongly constrained by differential rotation. Here we report the detection of 100-m-high 'hills' in the photosphere, spaced uniformly over the Sun's surface with a spacing of (8.7 +/- 0.6) x 10(4) km. If convection under the photosphere is organized by the r-modes, the observed corrugated photosphere is a probable surface manifestation of these solar oscillations. 相似文献
60.
New concepts in regulation and function of the insulin-like growth factors: implications for understanding normal growth and neoplasia 总被引:12,自引:1,他引:11
The insulin-like growth factors (IGFs) are a ubiquitous family of growth factors, binding proteins and receptors that are involved in normal growth and development. They are also implicated in numerous pathological states, including malignancy. IGF-II is a commonly expressed growth factor in many tumors and may enhance tumor growth, acting via the overexpressed IGF-I receptor, a cell-surface tyrosine kinase receptor. The IGF-I receptor may be overexpressed due to mutations in tumor suppression gene products such as p53 and WT-1 or growth factors such as bFGF and PDGF. Thus, this family of growth factors, especially the IGF-I receptor, may present an excellent target for new therapeutic agents in the treatment of cancer and other disorders of excessive cellular proliferation. 相似文献