全文获取类型
收费全文 | 724篇 |
免费 | 12篇 |
国内免费 | 4篇 |
专业分类
化学 | 458篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 115篇 |
物理学 | 150篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 10篇 |
2013年 | 33篇 |
2012年 | 36篇 |
2011年 | 36篇 |
2010年 | 29篇 |
2009年 | 21篇 |
2008年 | 52篇 |
2007年 | 38篇 |
2006年 | 22篇 |
2005年 | 40篇 |
2004年 | 27篇 |
2003年 | 30篇 |
2002年 | 28篇 |
2001年 | 28篇 |
2000年 | 13篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1969年 | 3篇 |
排序方式: 共有740条查询结果,搜索用时 15 毫秒
141.
Natural enantiomers of unique tricyclic sesquiterpenoids, valeriananoids A-C 1-3, have been synthesized starting from bicyclo[2.2.2]octane-2,5-dione derivative 11, which was obtained by diastereoselective catalytic domino Michael reaction of oxophorone 5 with 8-phenylmenthyl acrylate 10 by LDA or silica-gel-base (NMAP-Li). The tricyclic ring was closed selectively by intramolecular 6-endo-trig mode cyclization of the ketyl radical, which was generated from keto-allylether 25 by either lithium or sodium naphthalenide. 相似文献
142.
143.
Mitsuhashi S Fukushima T Tomiya M Santa T Imai K Toyo'oka T 《Analytica chimica acta》2007,584(2):315-321
Kynurenine (KYN), a tryptophan metabolite, is a crucial compound for modulating neurotransmission because it can be metabolized in vivo into both quinolinic acid and kynurenic acid, which are the agonist and antagonist, respectively, of N-methyl-d-aspartate receptor. For the highly sensitive detection of KYN by high-performance liquid chromatography (HPLC), a fluorescence derivatization of KYN with a benzofurazan-type fluorogenic reagent, 4-N,N-dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (DBD-F) was investigated in the present study. KYN was derivatized with DBD-F (DBD-KYN) at 60 °C for 30 min, and separated on an octadecylsilica column with a gradient elution of the mobile phase, which consists of 0.1% formic acid in acetonitrile/methanol/water. DBD-KYN was detected fluorimetrically at 553 nm with an excitation wavelength of 431 nm. The limits of detection and quantification were approximately 0.30 pmol [signal-to-noise ratio (S/N) 3] and 1.0 pmol (S/N, 10) on column, respectively. Plasma KYN levels were successfully determined using 10 μL of rat plasma with satisfactory precision and accuracy. Intra- and inter-day precisions and accuracies were 1.7-6.8%, and −10 to 9.6%, respectively. KYN levels in plasma of male Sprague-Dawley rats (7 weeks old) were approximately 2.4 ± 0.32 μmol L−1 (n = 4). The proposed HPLC method was applied to determine KYN levels in the plasma of ketamine-treated rats—the animal model of schizophrenia. 相似文献
144.
Testing Parallel Variable Transformation 总被引:2,自引:0,他引:2
This paper studies performance of the parallel variable transformation (PVT) algorithm for unconstrained nonlinear optimization through numerical experiments on a Fujitsu VPP500, one of the most up-to-date vector parallel computers. Special attention is paid to a particular form of the PVT algorithm that is regarded as a generalization of the block Jacobi algorithm that allows overlapping of variables among processors. Implementation strategies on the VPP500 are described in detail and results of numerical experiments are reported. 相似文献
145.
Proton plays a critical role in electrochemical systems to control electrochemical reactivity or isotopic enrichment. Graphene is intensively investigated owing to its unique electronic structure and device fabrication. Through the structural tunability of graphitic materials by chemical or physical modification of the surface, graphene is revealed to be an ideal material for proton manipulation. Here, we review the use of graphene or graphitic materials toward the manipulation of proton with regard to the following three points. (1) Electronic properties of graphene: The electronic band structure of graphene can be modified by metal contacts owing to the interaction with a metal surface. (2) Molecular control of graphitic interface: The chemical structure of graphene can be modified, as is done in molecular chemistry, and can be used as a catalytic platform. (3) Proton conduction by graphene: Proton transport through a graphene layer occurs with a unique mechanism such as tunneling. We provide a perspective on the use of graphitic materials toward controlling the behavior of protons on the basis of the aforementioned points. From the above, graphene can be used as a platform for proton manipulation. 相似文献
146.
Baosong?WuEmail authorView authors OrcID profile Stephen?A.?Altobelli Eiichi?Fukushima 《Applied magnetic resonance》2017,48(7):739-747
We describe and apply a scheme to obtain nuclear magnetic resonance (NMR) signals from multiple regions in space with a single pulse sequence in systems with strong, usually unavoidable, gradient magnetic fields. This is accomplished with multiple frequency irradiation and reception. Applications described include dual-slice NMR of a fluid to enhance S/N, T 2 measurements of two different samples, and efficient T 1 measurement sequence by interleaving shorter delays within a longer delay for different slices. 相似文献
147.
148.
Biodegradation of poly(lactic acid) and its nanocomposites 总被引:2,自引:0,他引:2
PLA nanocomposites based on organically modified montmorillonites at 5% w/w loading were prepared by melt blending using an internal mixer and then degraded in a commercial compost. The addition of nanoclays was found to increase the PLA degradation rate, especially for the highest dispersed clay in the polymer matrix. Biodegradation by microorganisms isolated from the compost showed the bacterium Bacillus licheniformis as one of the responsible for PLA biodegradation in compost. It was also found that clays can influence the polymer bacterial degradation depending on their chemical structure and affinity of the bacterium towards the clay. 相似文献
149.
We consider the stochastic linear complementarity problem (SLCP) involving a random matrix whose expectation matrix is positive semi-definite. We show that the expected residual minimization (ERM) formulation of this problem has a nonempty and bounded solution set if the expected value (EV) formulation, which reduces to the LCP with the positive semi-definite expectation matrix, has a nonempty and bounded solution set. We give a new error bound for the monotone LCP and use it to show that solutions of the ERM formulation are robust in the sense that they may have a minimum sensitivity with respect to random parameter variations in SLCP. Numerical examples including a stochastic traffic equilibrium problem are given to illustrate the characteristics of the solutions. 相似文献
150.
Hiroshi Fukushima 《Journal of Algebra》2009,321(1):312-315
Isaacs conjectured that if G is solvable and α and β are faithful characters of G such that αβ is irreducible, then G is cyclic. In this paper, we shall prove that the conjecture holds if either G is an M-group or G has Fitting height at most 4. 相似文献