全文获取类型
收费全文 | 347篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
化学 | 271篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 36篇 |
物理学 | 51篇 |
出版年
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 16篇 |
2014年 | 8篇 |
2013年 | 29篇 |
2012年 | 26篇 |
2011年 | 30篇 |
2010年 | 18篇 |
2009年 | 24篇 |
2008年 | 20篇 |
2007年 | 15篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1966年 | 1篇 |
1948年 | 1篇 |
1936年 | 2篇 |
1934年 | 1篇 |
1926年 | 1篇 |
1917年 | 3篇 |
排序方式: 共有364条查询结果,搜索用时 0 毫秒
41.
<正>A new practical method for the synthesis of unsymmetrical ureas was achieved by reaction of phenylurea with primary and secondary amines under neutral and mild condition in very good yields.The reaction took place in refluxing dioxane and does not require any catalyst or additives. 相似文献
42.
43.
44.
45.
If a given graphG can be obtained bys vertex identifications from a suitable planar graph ands is the minimum number for which this is possible thens is called the splitting number ofG. Here a formula for the splitting number of the complete graph is derived. 相似文献
46.
A two-step reaction cascade is applied to the sequence-specific detection of DNA by enzymatic amplification of the molecular into an optical signal. 相似文献
47.
We study the electronic density charge topology of CH(5)(+) species 1 (C(s)()), 2 (C(s)()), and 3 (C(2)(v)) at ab initio level using the theory of atoms in molecules developed by Bader. Despite the reports of previous studies concerning carbocationic species, the methane molecule is protonated at the carbon atom, which clearly shows its pentacoordination. In addition to the fact that hydrogen atoms in the methonium molecule behave in a very fluxional fashion and that the energy difference among the species 1, 2, and 3 are very low, is important to point out that two different topological situations can be defined on the basis of our study of the topology of the electronic charge density. Then, the species 1 and 2 present a three-center-two-electron (3c-2e) bond of singular characteristics as compared with other carbocationic species, but in the species 3, the absence of a 3c-2e bond is noteworthy. This structure can be characterized through the three bond critical points found, corresponding to saddle points on the path bonds between the C-H(2,3,5) that lie in the same plane. These nuclei define a four-center interaction where the electronic delocalization produced among the sigma(C-H) bonds provide a stabilization of the three C-H bonds involved in this interaction (the remaining two C-H bonds are similar to those belonging to the nonprotonated species). Our results show that bonding situations with a higher number of atom arrays are possible in protonated hydrocarbons. 相似文献
48.
Combinatorial library screening offers a rapid process for identifying potential therapies to toxins. Hinge peptide libraries,
which rely on conformational diversity rather than traditional molecular diversity, reduce the need for huge numbers of syntheses
and screening steps and greatly expedite the discovery process of active molecules. Hinge peptide libraries having the structures:
Acetyl-X1–X2–hinge–X3–X4–NH2 (capped) and X1–hinge–X2–X3 (uncapped), where X1 through X4 are near-equimolar mixtures of twelve L-amino acids and hinge = 4-aminobutyric acid, were screened for inhibitory activity in bioassays for botulinum neurotoxins
A and B (BoNT/A, BoNT/B) and saxitoxin. The zinc protease activity of the reduced light chains of BoNT/A and /B was assayed
by measuring the cleavage of synthetic substrates. Saxitoxin activity was measured by the restoration of the viability of
neuroblastoma cells treated with ouabain and veratridine. Deconvolution of libraries was accomplished by fixing one position
at a time beginning with the C-terminus. Primary library subsets in which position 4 was fixed showed moderate levels of inhibition
for BoNT/A. Secondary library subsets showed stronger inhibition in the bioassays. In each of the bioassays, inhibitory potency
was stronger when the second position to be fixed was on the opposite side of the hinge, rather than on the same side with
respect to the C-terminus, suggesting that the hinge facilitates the interaction of side chains. Inhibitors for all three
of the toxins studied were discovered within library subsets, although not necessarily in primary subsets. These studies demonstrate
that (1) the best strategy for deconvoluting hinge peptide libraries is by fixing residues alternately on each side of the
hinge moiety, and (2) it is essential to investigate secondary subsets even when primary subsets are inactive. The present
findings support the concept that the increased flexibility imposed by the inclusion of a central hinge residue in small peptides
increases the opportunity for side chain interactions, providing a distinct advantage for hinge peptide libraries over conventional
peptide libraries. Hinge peptide libraries are a rich source of novel ligands for modulation of biomechanisms. The library
subsets uncovered in this study may possess peptides that will lead to effective therapies to neurotoxin poisoning. 相似文献
49.
This paper investigates an enhanced proximal algorithm with interesting practical features and convergence properties for solving non-smooth convex minimization problems, or approximating zeroes of maximal monotone operators, in Hilbert spaces. The considered algorithm involves a recent inertial-type extrapolation technique, the use of enlargement of operators and also a recently proposed hybrid strategy, which combines inexact computation of the proximal iteration with a projection. Compared to other existing related methods, the resulting algorithm inherits the good convergence properties of the inertial-type extrapolation and the relaxed projection strategy. It also inherits the relative error tolerance of the hybrid proximal-projection method. As a special result, an update of inexact Newton-proximal method is derived and global convergence results are established. 相似文献
50.
McKenna J Sayler AM Anis F Gaire B Johnson NG Parke E Hua JJ Mashiko H Nakamura CM Moon E Chang Z Carnes KD Esry BD Ben-Itzhak I 《Physical review letters》2008,100(13):133001
High-order (three-photon or more) above-threshold dissociation (ATD) of H(2)(+) has generally not been observed using 800 nm light. We demonstrate a strong enhancement of its probability using intense 7 fs laser pulses interacting with beams of H(2)(+), HD(+), and D(2)(+) ions. The mechanism invokes a dynamic control of the dissociation pathway. These measurements are supported by theory that additionally reveals, for the first time, an unexpectedly large contribution to ATD from highly excited electronic states. 相似文献