全文获取类型
收费全文 | 281篇 |
免费 | 13篇 |
专业分类
化学 | 221篇 |
晶体学 | 4篇 |
数学 | 31篇 |
物理学 | 38篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 26篇 |
2012年 | 16篇 |
2011年 | 19篇 |
2010年 | 16篇 |
2009年 | 10篇 |
2008年 | 15篇 |
2007年 | 19篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1939年 | 1篇 |
1938年 | 1篇 |
1935年 | 2篇 |
1909年 | 1篇 |
排序方式: 共有294条查询结果,搜索用时 31 毫秒
91.
The crosslinking of poly(vinyl alcohol) (PVA) with glutaraldehyde at 80 °C was characterized by viscosity and pulse field gradient (PFG) nuclear magnetic resonance (NMR) techniques. NMR signified an initial dormant period of approximately 6 hr, in which the self‐diffusion coefficient of PVA was found to be constant and independent of time. During the next 7 hr (the “primary” gel period), this induction period was succeeded by a fast decay of the self‐diffusion coefficient of rate (9.13 ± 0.45) × 10−5 sec−1 followed by a slower decay rate of (3.22 ± 0.30) × 10−5 sec−1 (the “secondary” gel period). The viscosity of the solution showed the same time behavior, i.e. an initial dormant period (∼ 6 hrs), followed by a fast increase of the viscosity for the next 7 –8 hr. During the “secondary” gel regime, the viscosity became too large to be reliably determined. However, within the time regime where both techniques produced reliable data, they gave identical information regarding the kinetics of the gel process, suggesting that PFG NMR enables in situ monitoring of gelation within porous materials (for instance sandstone). Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
92.
Lay E Song YH Chiu YC Lin YM Chi Y Carty AJ Peng SM Lee GH 《Inorganic chemistry》2005,44(20):7226-7233
Volatile low-melting CuII metal complexes Cu[OC(CF3)2CH2C(Me)=NMe]2 (4) and Cu[OC(CF3)2CH2CHMeNHMe]2 (5) were synthesized and characterized by spectroscopic methods. A single-crystal X-ray diffraction study on complex 4 shows the anticipated N2O2 square-planar geometry with the imino alcoholate ligand arranged in the all-trans orientation. In contrast, a highly distorted N2O2 geometry with a dihedral angle of 33 degrees was observed for complex 5, suggesting that the fully saturated amino alcoholate ligand produces a much greater steric congestion around the metal ion. Metal CVD experiments were conducted, showing that both complexes, 4 and 5, are capable of depositing copper metal at temperatures of 275-300 degrees C using an inert argon carrier gas mixed with low concentrations (2-8%) of O2. The best copper thin film showed a purity of approximately 96 at. % and a resistivity of 2.11 microOmega cm versus that of the bulk standard (1.7 microOmega cm), as revealed by XPS and four-point probe analyses, respectively. We speculate that the low concentration of O2 promotes partial ligand oxidation, thus releasing the reduced copper on the substrate and affording the high-purity copper deposit. 相似文献
93.
In closed, cerium-catalyzed glyoxylic acid Belousov-Zhabotinsky systems we found a new dynamic behavior, viz. the observation of two oscillatory regimes separated by a nonoscillatory region. Mechanisms for this intermediate nonoscillatory domain are discussed.
- , , , . .相似文献
94.
Nasr G Guerlin A Dumur F Beouch L Dumas E Clavier G Miomandre F Goubard F Gigmes D Bertin D Wantz G Mayer CR 《Chemical communications (Cambridge, England)》2011,47(38):10698-10700
Two iridium(III) soft salts based on ion-paired dinuclear cationic and mononuclear anionic complexes were designed and investigated as phosphorescent emitters for solution processed OLEDs. New dinuclear cationic complexes were prepared with two different bridging ligands, a carbazole and a phenylene spacer. Best devices were designed with the soft salt bearing a carbazole moiety. 相似文献
95.
We establish a correspondence between the invariant subsets of a non-degenerate symmetric set-theoretical solution of the quantum Yang–Baxter equation and the parabolic subgroups of its structure group, equipped with its canonical Garside structure. Moreover, we introduce the notion of a foldable solution, which extends the one of a decomposable solution. 相似文献
96.
Md Lutfor Rahman Shaheen M. Sarkar Eddy M. Farid Sazmal E. Arshad M. S. Sarjadi N. Wid 《Journal of Macromolecular Science: Physics》2018,57(2):83-99
Poly(acrylonitrile)/cellulose block copolymer (PAN-b-cell) was prepared by using a free radical initiating process and then the nitrile functional groups of the PAN blocks of the copolymers were transformed into amidoxime ligands. The resulting poly(amidoxime) ligands could complex with heavy metal ions; for example, the reflectance spectra of the [Cu -ligand]n+ was found to be at the highest absorbance, about 94%, at pH 6. The pH was the key parameter for metal ions sensing by the ligand. The adsorption capacity for copper was very good, 272 mg g?1, with a fast adsorption rate (t1/2 = 10 min). The adsorption capacities for other heavy metal ions such as Fe3+, Cr3+, Co3+ and Ni2+ were also good, being 242, 219, 201 and 195 mg g?1, respectively, at pH 6. The heavy metal ions removal efficiency from water was 98% at low concentration. The data proved that the heavy metal ions adsorption onto the polymer ligands were well fitted with the Langmuir isotherm model (R2>0.99), which suggests that the cellulose-based adsorbent surface namely the poly(amidoxime) ligand, was homogenous and a monolayer. The reusability was examined by a sorption/desorption process for six cycles and the extraction efficiency was determined. This new adsorbent could be reused for 6 cycles without any significant loss in its original removal function. 相似文献
97.
98.
99.
Francisco Rego Elwin de Weerdt Eddy van Oort Erik-Jan van Kampen Qiping Chu António M. Pascoal 《Mathematics in Computer Science》2014,8(3-4):425-442
The computation of the reachable set of states of a given dynamic system is an important step to verify its safety during operation. There are different methods of computing reachable sets, namely interval integration, capture basin, methods involving the minimum time to reach function, and level set methods. This work deals with interval integration to compute subpavings to over or under approximate reachable sets of low dimensional systems. The main advantage of this method is that, compared to guaranteed integration, it allows to control the amount of over-estimation at the cost of increased computational effort. An algorithm to over and under estimate sets through subpavings, which potentially reduces the computational load when the test function or the contractor is computationally heavy, is implemented and tested. This algorithm is used to compute inner and outer approximations of reachable sets. The test function and the contractors used in this work to obtain the subpavings involve guaranteed integration, provided either by the Euler method or by another guaranteed integration method. The methods developed were applied to compute inner and outer approximations of reachable sets for the double integrator example. From the results it was observed that using contractors instead of test functions yields much tighter results. It was also confirmed that for a given minimum box size there is an optimum time step such that with a greater or smaller time step worse results are obtained. 相似文献