全文获取类型
收费全文 | 1450篇 |
免费 | 36篇 |
国内免费 | 7篇 |
专业分类
化学 | 981篇 |
晶体学 | 10篇 |
力学 | 16篇 |
数学 | 201篇 |
物理学 | 285篇 |
出版年
2023年 | 9篇 |
2021年 | 14篇 |
2020年 | 21篇 |
2019年 | 16篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 42篇 |
2015年 | 31篇 |
2014年 | 32篇 |
2013年 | 74篇 |
2012年 | 69篇 |
2011年 | 81篇 |
2010年 | 52篇 |
2009年 | 39篇 |
2008年 | 61篇 |
2007年 | 63篇 |
2006年 | 67篇 |
2005年 | 73篇 |
2004年 | 58篇 |
2003年 | 37篇 |
2002年 | 38篇 |
2001年 | 21篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 18篇 |
1990年 | 13篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1973年 | 9篇 |
1967年 | 9篇 |
1966年 | 11篇 |
排序方式: 共有1493条查询结果,搜索用时 0 毫秒
1.
2.
Bryan B. Sauer Richard Beckerbauer Lixiao Wang 《Journal of Polymer Science.Polymer Physics》1993,31(12):1861-1872
The high sensitivity of the thermally stimulated current, thermal sampling (TS) method is emphasized in a study of the breadth of the glass transition in several liquid-crystalline polymers (LCPs). Differential scanning calorimetry (DSC) was performed on all samples to further quantify the glass transition regions. For “random” copolyester LCPs with widely varying degrees of crystallinity, including highly amorphous samples, very broad glass tran-sition regions were observed. One semicrystalline alternating copolyester and a series of semicrystalline azomethine LCPs were studied as examples of structurally regular polymers. These exhibited relatively sharp glass transitions more comparable to ordinary isotropic amorphous or semicrystalline polymers. The broad glass transitions in the random copolyesters are attributed to structural heterogeneity of the chains. In one example of a moderate-crystallinity random copolyester LCP (Vectra), glass transitions ranging up to ca. 150°C in breadth were determined by the thermal sampling (TS) method and DSC. In other lower crystallinity copolyester LCPs, the main glass transition temperature as determined by DSC was comparable to that determined by TSC although cooperative relaxations of a minor fraction of the overall relaxing species were detected well below the main Tg, by the TS method and not by DSC. Rapid quenches from the isotropic melt to an isotropic glass were possible with one LCP. The anisotropic and isotropic glassy states for this LCP were found to have the same breadth of the glass transition as was determined by the TS method, although TSC and DSC show that Tg is shifted downward by ca. 15°C in the anisotropic glass as compared to the isotropic glass. © 1993 John Wiley & Sons, Inc. 相似文献
3.
4.
5.
6.
Cornelia Bohne Adelaide Faljoni-Alario Giuseppe Cilento 《Photochemistry and photobiology》1988,48(3):341-347
Abstract— The interaction of serum albumin-bound acceptors with enzyme-generated and protected triplet species was studied in two types of systems. Chlorophyll-a bound to bovine and human serum albumins is efficiently excited by enzymatically generated triplet acetone and acetaldehyde. When the Chl-a concentration is much lower than that of the albumin the interaction occurs with chlorophyll in an aggregate in which one Chl-a is surrounded by several protein molecules. When the Chl-a concentration is higher than that of the protein, the aggregate contains the proteins and fluorescent chlorophylls in a 1:1 ratio. The excess chlorophylls, although able to interact with the donors, are not fluorescent.
In another study, probes bound to various specific sites of serum albumins were used as quenchers of the enzymatically generated triplet acetone. The efficiency of quenching by all the bound probes is equal and in one case even stronger than for the free probes.
A model for the interaction of the excited species contained in the enzyme with the acceptor(s) located in the protein is proposed.
The present results provide further evidence that enzyme-generated and protected triplet carbonyl species can interact through a collisional process with acceptors bound to or constituents of macromolecules. 相似文献
In another study, probes bound to various specific sites of serum albumins were used as quenchers of the enzymatically generated triplet acetone. The efficiency of quenching by all the bound probes is equal and in one case even stronger than for the free probes.
A model for the interaction of the excited species contained in the enzyme with the acceptor(s) located in the protein is proposed.
The present results provide further evidence that enzyme-generated and protected triplet carbonyl species can interact through a collisional process with acceptors bound to or constituents of macromolecules. 相似文献
7.
8.
The emission Mössbauer spectra of 125I labeled iodobenzene, methyl iodide, and of their dilute solutions in benzene and hexane, were computer analyzed. Two species were observed, in one of which tellurium is presumably attached to two organic moieties, while in the other, tellurium is attached to a single organic moiety. 相似文献
9.
Wolfgang A. Herrmann Cornelia Weber Manfred L. Ziegler Orhan Serhadli 《Journal of organometallic chemistry》1985,297(2):245-254
The diazoolefines of composition N2CCR2 (R/R = CH3/CH3 and(-CH2-)5) are suitable precursors of the corresponding vinylidene ligands CCR2. Thus, treatment of the RhRh complex [(η5-C5Me5)Rh(μ-CO)]2 (1) with the N-nitrosourethanes 2a and 2b, resp., in the presence of lithium t-butoxide yields the otherwise inaccessible μ-vinylidene complexes (μ-CCR2)[(η5-C5Me5)Rh(CO)]2 (R = CH3 (3a), R,R = (-CH2-)5 (3b)). The analogous cobalt compound (μ-CCMe2)[(η5-C5Me5)Co(CO)]2 (5a) is obtained similarly. This procedure extends the well-documented diazoalkane method for the synthesis of μ-alkylidene complexes to the less stable diazoalkenes. A single-crystal X-ray diffraction study of the dimethylvinylidene derivative 3a shows the CMe2 ligand to adopt an almost symmetrically metal-bridging position (d(RhC) 197.8(1) and 204.3(1) pm), with a rhodium-rhodium single bond completing a three-membered Rh2C-metallacycle (d(RhRh) 268.4(0) pm) analogous with cyclopropane. 相似文献
10.
The parallel between orbital first and second electric moments and statistical first and second central moments is noted. Three measures of orbital spatial distribution in terms of their moments are proposed, and applied to the LMO's in a series of ten-electron hydrides. Consistent differences between bond and lone pair distributions are found. Using the statistical interpretation, for each LMO an effective solid angle around the central atom is postulated. 相似文献