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31.
32.
Marilyn Breen 《Geometriae Dedicata》1991,37(3):287-294
Let S be an open set in R
3 such that: (1) whenever three points x, y, z in S see each other via S, then conv{x, y, z}
S, and (2) every seven points in S see via S a common point. Then S is finitely starlike. The proof uses the topological version of Helly's theorem. 相似文献
33.
Marilyn Breen 《Journal of Geometry》1988,32(1-2):1-12
Let S be a subset of the plane. In case (int cl S) S = , then S is finitely starlike if and only if every 4 points of S see via S a common point. In case (int cl S) S has at most countably many components, each a singleton set, then S is finitely starlike if and only if every 5 points of S see via S a common point. Each of the numbers 4 and 5 is best possible. Examples show that these results fail without suitable restrictions on (int cl S) S. Moreover, a final example shows that if a general Krasnosel'skii number . exists to characterize finitely starlike sets in the plane, then > 9. 相似文献
34.
Marilyn Breen 《Journal of Geometry》1990,37(1-2):48-54
For eachk andd, 1kd, definef(d, d)=d+1 andf(d, k)=2d if 1kd–1. The following results are established:Let
be a uniformly bounded collection of compact, convex sets inR
d
. For a fixedk, 1kd, dim {MM in
}k if and only if for some > 0, everyf(d, k) members of
contain a commonk-dimensional set of measure (volume) at least.LetS be a bounded subset ofR
d
. Assume that for some fixedk, 1kd, there exists a countable family of (k–l)-flats {H
i
:i1} inR
d
such that clS S {Hi i 1 } and for eachi1, (clS S) H
i
has (k–1) dimensional measure zero. Every finite subset ofS sees viaS a set of positivek-dimensional measure if and only if for some>0, everyf(d,k) points ofS see viaS a set ofk-dimensional measure at least .The numbers off(d,d) andf(d, 1) above are best possible.Supported in part by NSF grant DMS-8705336. 相似文献
35.
Marilyn Breen 《Journal of Geometry》1986,27(2):175-179
We will establish the following improved Krasnosel'skii theorems for the dimension of the kernel of a starshaped set: For each k and d, 0 k d, define f(d,k) = d+1 if k = 0 and f(d,k) = max{d+1,2d–2k+2} if 1 k d.Theorem 1. Let S be a compact, connected, locally starshaped set in Rd, S not convex. Then for a k with 0 k d, dim ker S k if and only if every f(d, k) lnc points of S are clearly visible from a common k-dimensional subset of S.Theorem 2. Let S be a nonempty compact set in Rd. Then for a k with 0 k d, dim ker S k if and only if every f (d, k) boundary points of S are clearly visible from a common k-dimensional subset of S. In each case, the number f(d, k) is best possible for every d and k. 相似文献
36.
Marilyn Breen 《Journal of Geometry》1986,27(1):1-23
The following Krasnosel'skii-type theorem is proved: Let S be a nonempty set in R2 whose closure cl S is convex and bounded. Assume that for every 9 point subset T of cl S there correspond points p1 and p2 (depending on T) such that each point of T is clearly visible via S from at least one of p1 or p2. Then S is a union of two starshaped sets. The number 9 is best possible.Moreover, a related result yields a piercing number for families of segments in Rd: Let £ be a collection of at least 6 one-dimensional convex sets in Rd such that for every line M in Rd, at most finitely many members of £ are collinear with M. Assume that every 6 members of £ may be partitioned into two sets £1 and £2 so that L L in £i , i = 1,2. Then £ itself has such a 2-partition. The number 6 is best possible as well.Dedicated to Professor M. Barner on his 65th birthday 相似文献
37.
Marilyn Breen 《Geometriae Dedicata》1982,13(2):201-213
Let Sø be a bounded connected set in R
2, and assume that every 3 or fewer lnc points of S are clearly visible from a common point of S. Then for some point p in S, the set A{s : s in S and [p, s] S} is nowhere dense in S. Furthermore, when S is open, then S in starshaped. 相似文献
38.
Let S be a compact set in R
2. For S simply connected, S is a union of two starshaped sets if and only if for every F finite, F
bdry S, there exist a set G
bdry S arbitrarily close to F and points s, t depending on G such that each point of G is clearly visible via S from one of s, t. In the case where S has at most finitely many components, the necessity of the condition still holds while the sufficiency fails. 相似文献
39.
Iresha D. Herath Dr. Colum Breen Dr. Sarah H. Hewitt Dr. Thomas R. Berki Dr. Ahmad F. Kassir Dr. Charlotte Dodson Martyna Judd Dr. Shereen Jabar Dr. Nicholas Cox Prof. Gottfried Otting Dr. Stephen J. Butler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(51):13009-13023
A lanthanide-binding tag site-specifically attached to a protein presents a tool to probe the protein by multiple spectroscopic techniques, including nuclear magnetic resonance, electron paramagnetic resonance and time-resolved luminescence spectroscopy. Here a new stable chiral LnIII tag, referred to as C12 , is presented for spontaneous and quantitative reaction with a cysteine residue to generate a stable thioether bond. The synthetic protocol of the tag is relatively straightforward, and the tag is stable for storage and shipping. It displays greatly enhanced reactivity towards selenocysteine, opening a route towards selective tagging of selenocysteine in proteins containing cysteine residues. Loaded with TbIII or TmIII ions, the C12 tag readily generates pseudocontact shifts (PCS) in protein NMR spectra. It produces a relatively rigid tether between lanthanide and protein, which is beneficial for interpretation of the PCSs by single magnetic susceptibility anisotropy tensors, and it is suitable for measuring distance distributions in double electron–electron resonance experiments. Upon reaction with cysteine or other thiol compounds, the TbIII complex exhibits a 100-fold enhancement in luminescence quantum yield, affording a highly sensitive turn-on luminescence probe for time-resolved FRET assays and enzyme reaction monitoring. 相似文献
40.