全文获取类型
收费全文 | 2096篇 |
免费 | 82篇 |
国内免费 | 15篇 |
专业分类
化学 | 1582篇 |
晶体学 | 20篇 |
力学 | 18篇 |
数学 | 146篇 |
物理学 | 427篇 |
出版年
2023年 | 11篇 |
2021年 | 25篇 |
2020年 | 29篇 |
2019年 | 43篇 |
2018年 | 27篇 |
2017年 | 21篇 |
2016年 | 51篇 |
2015年 | 41篇 |
2014年 | 56篇 |
2013年 | 90篇 |
2012年 | 133篇 |
2011年 | 161篇 |
2010年 | 85篇 |
2009年 | 78篇 |
2008年 | 104篇 |
2007年 | 131篇 |
2006年 | 136篇 |
2005年 | 124篇 |
2004年 | 86篇 |
2003年 | 118篇 |
2002年 | 93篇 |
2001年 | 39篇 |
2000年 | 44篇 |
1999年 | 32篇 |
1998年 | 24篇 |
1997年 | 25篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 21篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1973年 | 10篇 |
1972年 | 11篇 |
排序方式: 共有2193条查询结果,搜索用时 15 毫秒
1.
2.
XPS measurement revealed that the original state of TiO2 was changed to Ti2O3 and TiO by ion bombardment. TiO2 decreased and Ti2O3 increased at the initial stage. TiO increased at a later stage than Ti2O3. Each of them saturated after enough sputtering time.A formulation was proposed in order to explain the change of XPS spectra for oxides as a function of ion sputtering time. This formulation was based on reaction equations that contain two reduction processes (from TiO2 to Ti2O3 and from Ti2O3 to TiO), and sputtering effects. Using four fitting parameters (two reduction coefficients, sputtering yield and information depth), the present formula was fitted to the experimental results. The fitting results agree satisfactorily with the experimental results. The calculation shows that the reduction coefficient from TiO2 to Ti2O3 is about ten times larger than that from Ti2O3 to TiO. This calculation predicts that surface composition of an oxide that is changed by ion bombardment will reach a different value depending on its bulk composition. Moreover, the present formulation can determine the chemical states of compounds changed by ion bombardment. 相似文献
3.
Using a single variable theta identity, which is similar to the Jacobi Triple Product identity, we produce the generating functions for values of certain expressions of Hurwitz zeta functions at non-positive integers. 相似文献
4.
We have investigated the spin-1 Ising model on the simple cubic lattice with bilinear, biquadratic interaction and anisotropic energy (BEG model). We have been specially interested in the case of antiferro biquadratic interaction, because the interaction will cause the competition with bilinear interaction and anisotropy. A two-sublattice ordering, so called the staggered quadrupole (SQ) phase, occurs as long as biquadratic interaction is negative large enough. We have obtained a full phase diagram in the whole interaction parameter space (for the positive bilinear interaction) by the Bethe approximation, and found several kinds of phase transitions, such as successive, re-entrant and double re-entrant transitions. These transitions are also confirmed by Monte Carlo simulations on simple cubic lattices. 相似文献
5.
Ken Ono 《Mathematische Annalen》1998,312(2):251-260
6.
T Kusama T Soga Y Ono E Kumazawa E Shioya Y Osada S Kusumoto T Shiba 《Chemical & pharmaceutical bulletin》1991,39(8):1994-1999
Two novel analogs of a biosynthetic precursor of lipid A (2) were synthesized. The one analog (3) has acyl groups identical to those of 2, and the other (4) has tetradecanoyl groups in place of the (R)-3-hydroxytetradecanoyl groups of 2. Both 3 and 4 possess an alpha-glycosidically-bound phosphonooxyethyl group in place of the alpha-glycosyl phosphate group of 2. Compounds 3 and 4 exhibited definite antitumor activity against Meth A fibrosarcoma and low toxicity in rabbits, as the original compound 2 does. The replacement of the hydroxytetradecanoyl groups with tetradecanoyl groups barely affected the antitumor activity, but slightly enhanced the toxicity in rabbits. 相似文献
7.
Masayuki Kuzuya Akihiro Noguchi Hideki Ito Shin-Ichi Kondo Nahoko Noda 《Journal of polymer science. Part A, Polymer chemistry》1991,29(1):1-7
Plasma-induced polystyrene radicals were first studied by electron spin resonance (ESR). The room temperature ESR spectrum was compared with those obtained by γ-irradiation, UV-irradiation, and mechanical fracture. It was found that even less than a few seconds of plasma-irradiation gave rise to a large amount of polystyrene radicals and the ESR spectrum consisted of two types of spectra, a triplet and a single broad line. The spectral feature of the triplet was nearly identical with that of γ-irradiated polystyrene. Thus, it was assigned to the structure of a cyclohexadienyl-type radical formed by a nearly random addition of a hydrogen atom to the aromatic ring. The single broad line, thought to be an outline of multicomponent spectrum, was assigned to an immobilized dangling-bond sites at the plasma-induced crosslinked portion of the polystyrene surface. 相似文献
8.
9.
10.
Yoshitomo Ono Naoyuki Kawashima Hiroto Kudo Tadatomi Nishikubo Takabumi Nagai 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2978-2988
The ring‐opening copolymerization of a glycidyl ester derivative having a benzophenone group and the donor–acceptor norbornadiene (D‐A NBD) dicarboxylic acid, 5‐(4‐methoxyphenyl)‐1,4,6,7,7‐pentamethyl‐2,5‐norbornadiene‐2,3‐dicarboxylic acid, monoglycidyl ester derivatives with D‐A NBD dicarboxylic anhydride using tetraphenylphosphonium bromide as a catalyst proceeded smoothly to give novel self‐photosensitizing NBD polymers in good yields. The molecular weight of these polyesters was about 4,000, and lower than that of analogous NBD polymers having no benzophenone group. All the synthesized NBD polymers isomerized smoothly to the corresponding quadricyclane (QC) polymers upon UV irradiation in tetrahydrofuran (THF) solution and in the film state. The rate of the photoisomerization of the D‐A NBD moieties in these polymers was higher than that of the D‐A NBD moieties in the polymer having no photosensitizing group. Furthermore, the rate of the photoisomerization of the D‐A NBD moieties in these polymers was also higher than that of the NBD polymer with low molecular weight photosensitizer in dilute solution. The photo‐irradiated polymers having QC moieties released thermal energies of 146–180 J/g. The D‐A NBD moieties contained in these NBD polymers possessed fair to good fatigue resistance. The degradation of the NBD moieties in these polymers was 15–30% after 50 repeated cycles of interconversion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2978–2988, 2007 相似文献