全文获取类型
收费全文 | 2105篇 |
免费 | 61篇 |
国内免费 | 5篇 |
专业分类
化学 | 1608篇 |
晶体学 | 24篇 |
力学 | 7篇 |
数学 | 138篇 |
物理学 | 394篇 |
出版年
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 29篇 |
2020年 | 20篇 |
2019年 | 29篇 |
2018年 | 26篇 |
2017年 | 20篇 |
2016年 | 31篇 |
2015年 | 39篇 |
2014年 | 46篇 |
2013年 | 94篇 |
2012年 | 110篇 |
2011年 | 137篇 |
2010年 | 72篇 |
2009年 | 75篇 |
2008年 | 119篇 |
2007年 | 138篇 |
2006年 | 116篇 |
2005年 | 123篇 |
2004年 | 127篇 |
2003年 | 109篇 |
2002年 | 92篇 |
2001年 | 39篇 |
2000年 | 31篇 |
1999年 | 19篇 |
1998年 | 21篇 |
1997年 | 22篇 |
1996年 | 26篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 25篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 28篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1985年 | 32篇 |
1984年 | 33篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 20篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2171条查询结果,搜索用时 15 毫秒
121.
122.
Solution properties,unperturbed dimensions,and chain flexibility of poly(1‐adamantyl acrylate)
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wei Lu Panchao Yin Masashi Osa Weiyu Wang Nam‐Goo Kang Kunlun Hong Jimmy W. Mays 《Journal of Polymer Science.Polymer Physics》2017,55(20):1526-1531
Poly(1‐adamantyl acrylate) (PAdA) exhibits much higher glass transition and degradation temperatures than other polyacrylates. However, the quantitative evaluation of the stiffness of this polymer chain has not been reported previously. In this study, the dilute solution properties and conformational characteristics of PAdA were evaluated using viscometry and scattering techniques. The unperturbed dimensions of this polymer were evaluated using the Burchard–Stockmayer–Fixman extrapolation and the touched‐bead wormlike chain model. The PAdA chain has a comparable persistence length, diameter per bead and characteristic ratio to poly(methyl methacrylate) and polystyrene. All these results indicate that PAdA is less flexible than common polyacrylates. In addition, the second virial coefficients (A2) of PAdA in different solvents obtained by static light scattering were compared. Among the solvents investigated, tetrahydrofuran is a moderate solvent. Radius of gyration of a polymer sample in the various solvents ranged from 16.8 to 30.3 nm. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1526–1531 相似文献
123.
Abstract In this study, the formation of polyion complex micelles from a pair of poly(L-lysine) homopolymers (P(Lys)) and poly(ethylene glycol)-poly(aspartic acid) block copolymers (PEG-P(Asp)) with varying chain length was demonstrated in aqueous medium. There exists the lower critical chain length in the charged segments of both P(Lys) and PEG-P(Asp) to form stable polyion complex micelles in nanometric scale. The scaled average characteristic line width (ΓTK2) was independent on the detection angles for all combinations, suggesting that the formed polyion complex micelles may have a spherical shape. Furthermore, the transitional diffusion coefficient (DT) had no concentration dependence, indicating the micelle system was free from secondary aggregates (the cluster of micelles). It is of interest that the micellar size was almost constant (ca. 50 nm) regardless of the change in the chain length of the charged segments. Size distribution was extremely narrow, and the values of variance μ2/Γ 2) were always less than 0.1. Laser-Doppler electrophoresis measurements revealed that the polyion complex micelles were electrically neutral, suggesting that the PEG corona surrounding the polyion complex core may contribute to their stable dispersion in an aqueous medium through steric repulsion of the tethered hydrophilic chain, in this case, PEG. This system was considerably stable against the change in ionic strength, and it maintained a constant diameter in the region below 0.4 M NaCl. However, they dissociated under high ionic strength condition as 0.6 M NaCl. The system may have potential utility to include charged peptides and nucleotides in the core, delivering these biologically useful substances into a target site in the body. 相似文献
124.
Abstract Chiral crystals of tryptamine and achiral carboxylic acids such as p-chlorobenzoic acid, cinnamic acid, p-chlorocinnarnic acid and p-methylcinnamic acid were prepared by crystallization from the solutions of both components. All the crystals belonged to typical chiral space group P212121. The crystal chirality is generated through the formation of a unidirectional twofold helix between the two components through quaternary ammonium salt interaction and hydrogen bonding in the lattice. This kind of spontaneous crystallization necessarily gives crystals of both clockwise and counterclockwise helicites. Here, pseudo-seeding based on utilizing these crystals as seed crystals was examined, resulting in successful helicity control in crystallization from solutions of tryptamine and different carboxylic acids. 相似文献
125.
Dr. Masashi Nakamura Yo Nakajima Prof. Dr. Nagahiro Hoshi Dr. Hiroo Tajiri Dr. Osami Sakata 《Chemphyschem》2013,14(11):2426-2431
The oxidation processes of a Pt(111) electrode in alkaline electrolytes depend on non‐specifically adsorbed ions according to in situ X‐ray diffraction and infrared spectroscopic measurements. In an aqueous solution of LiOH, an OHad adlayer is formed in the first oxidation step of the Pt(111) electrode as a result of the strong interaction between Li+ and OHad, whereas Pt oxidation proceeds without OHad formation in CsOH solution. Structural analysis by X‐ray diffraction indicates that Li+ is strongly protective against surface roughening caused by subsurface oxidation. Although Cs+ is situated near the Pt surface, the weak protective effect of Cs+ results in irreversible surface roughening due to subsurface oxidation. 相似文献
126.
Pinacol-type coupling reaction products presenting a high meso-diastereoselectivity (the ratio dl/meso was 4/96 up to 1/99) were obtained in fair to good yields (24–69%) using several aromatic aldehydes as starting materials and aluminium powder/copper sulfate as catalysts, in water, under reflux conditions. 相似文献
127.
Alkylesters of orthophosphoric acids have been used for alkylation of phenols1, anilines2, and nitrogen heterocyclic compounds.3 However, no example is reported on their use as an alkoxylating agent for aromatic amines. We have found that alkyl phosphates can act as alkoxylating agents for aromatic diamines in the presence of H2O or aqueous H3PO4. We now report the one-step dialkoxylation of aromatic diamines such as diaminoanthracene and -naphthalene by trialkyl phosphates. 相似文献
128.
129.
Masashi Daido Yukio Kawashima Masanori Tachikawa 《Journal of computational chemistry》2013,34(28):2403-2411
The structure of Watson–Crick‐type adenine‐thymine and guanine‐cytosine pairs has been studied by hybrid Monte Carlo (HMC) and path integral hybrid Monte Carlo (PIHMC) simulations with the use of semiempirical PM6‐DH+ method in the gas phase. We elucidated the nuclear quantum effect and temperature dependency on the hydrogen‐bonded moiety of base pairs. It was shown that the contribution of nuclear quantum effect on the hydrogen‐bonded structure is significant not only at low temperature 150 K but also at temperature as high as 450 K. The relative position of hydrogen‐bonded proton between two heavy atoms and the nuclear quantum nature of the proton are also shown. Furthermore, we have applied principal component analysis to HMC and PIHMC simulations to analyze the nuclear quantum effect on intermolecular motions. We found that the ratio of Buckle mode (lowest vibrational mode from normal mode analysis) decreases due to the nuclear quantum effect, whereas that of Propeller mode (second lowest vibrational mode) increases. In addition, nonplanar structures of base pairs were found to become stable due to the nuclear quantum effect from two‐dimensional free energy landscape along Buckle and Propeller modes. © 2013 Wiley Periodicals, Inc. 相似文献
130.
Yoshihiro Shigemasa Kuninori Oogaki Nasuo Ueda Ruka Hakashima Ken-Ichi Harada Naohito Takeda 《Journal of carbohydrate chemistry》2013,32(3):325-330
Abstract The formose reaction, by which a complex mixture of sugars and sugar alcohols (the so-called formose) are produced by the base-catalyzed condensation of formaldehyde, has received much attention in connection with the prebiotic synthesis of carbohydrates2 and the microbial utilization of formose.3–5 Formose, however, has not been useful yet, because of the complexity of this product mixture (Fig. 1a). Therefore, it seemed desirable to make the reaction more selective. 相似文献