全文获取类型
收费全文 | 1934篇 |
免费 | 48篇 |
国内免费 | 2篇 |
专业分类
化学 | 1400篇 |
晶体学 | 7篇 |
力学 | 66篇 |
数学 | 184篇 |
物理学 | 327篇 |
出版年
2021年 | 24篇 |
2020年 | 12篇 |
2019年 | 20篇 |
2018年 | 24篇 |
2016年 | 33篇 |
2015年 | 33篇 |
2014年 | 41篇 |
2013年 | 93篇 |
2012年 | 65篇 |
2011年 | 82篇 |
2010年 | 66篇 |
2009年 | 47篇 |
2008年 | 75篇 |
2007年 | 76篇 |
2006年 | 78篇 |
2005年 | 89篇 |
2004年 | 59篇 |
2003年 | 73篇 |
2002年 | 43篇 |
2001年 | 43篇 |
2000年 | 34篇 |
1999年 | 17篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 31篇 |
1995年 | 34篇 |
1994年 | 33篇 |
1993年 | 37篇 |
1992年 | 26篇 |
1991年 | 25篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 16篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 19篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1978年 | 18篇 |
1977年 | 20篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1967年 | 16篇 |
1966年 | 20篇 |
1965年 | 39篇 |
1964年 | 45篇 |
排序方式: 共有1984条查询结果,搜索用时 15 毫秒
91.
92.
Hesam Makki Koen N. S. Adema Elias A. J. F. Peters Jozua Laven Leendert G. J. van der Ven Rolf A. T. M. van Benthem Gijsbertus de With 《Journal of Polymer Science.Polymer Physics》2016,54(6):659-671
In this article we studied the evolution of thermomechanical properties of a polyester‐urethane coating during degradation under different degradation conditions, i.e., aerobic and anaerobic conditions with and without dry/wet cycling during degradation. Dynamic mechanical and thermal analyses show that under aerobic conditions the coatings become stiffer and more brittle in the glassy state. This stiffening is probably due to the increase in the amount of hydrogen bonding and the formation of oxidized groups which increase the polarity of the material and enhance the interactions of the polymer segments. However, oxidation reactions result in a considerable decrease in cross‐link density and stiffness in the rubbery state. Both changes, in the glassy and rubbery states, give rise to development of internal stresses. These stresses increase as the degradation process proceeds. Nevertheless, for samples exposed to anaerobic conditions, the stiffness remains constant in the glassy state and the cross‐link density slightly increases as a result of degradation. This reconfirms the dominance of the effect of oxidation reactions on the mechanical failure of the coatings. Oxygen permeation measurements show a more‐or‐less time‐independent diffusion coefficient and a gradual decrease in solubility of oxygen as a function of exposure time. This results in a slight decrease in oxygen permeation (mainly in the early stage of the degradation) as degradation proceeds. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 659–671 相似文献
93.
Accurate quantification of polymer distributions is one of the main challenges in polymer analysis by liquid chromatography. The response of contemporary detectors is typically influenced by compositional features such as molecular weight, chain composition, end groups, and branching. This renders the accurate quantification of complex polymers of which there are no standards available, extremely challenging. Moreover, any (programmed) change in mobile‐phase composition may further limit the applicability of detection techniques. Current methods often rely on refractive index detection, which is not accurate when dealing with complex samples as the refractive‐index increment is often unknown. We review current and emerging detection methods in liquid chromatography with the aim of identifying detectors, which can be applied to the quantitative analysis of complex polymers. 相似文献
94.
Edward N. Peters 《高分子科学杂志,C辑:聚合物评论》2013,53(2):173-208
The need for elastomeric polymers which will maintain their elastic properties at high temperatures has led to a wide interest in inorganic-based polymers [l]. The development of carborane-siloxane polymers in the early 1960s was a breakthrough in the search for a high-temperature elastomer. Incorporation of a carborane moiety into the siloxane backbone significantly enhanced the overall thermal stability [2]. 相似文献
95.
96.
97.
98.
Nadine Hovnanian Liliane G. Hubert-pfalzgraf 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4)
Abstract Phosphorus ylides are known to form σ-metal-carbon bonds of unusual stability. Bis(cyclopentadienyl)niobium derivatives offer a general synthetic approach to niobium phosphorus ylide complexes, the first to be reported. 相似文献
99.
Jorge A. Martínez-Ramírez Juliane Strien Juliane Sanft Gita Mall Grit Walther Frank T. Peters 《Analytical and bioanalytical chemistry》2013,405(26):8443-8450
Cadavers can be colonized by a wide variety of bacteria and fungi. Some of these microbes could change the concentration or the metabolic pattern of drugs present in postmortem samples. The purpose of this study was to identify fungi from human postmortem material and to further assess their potential role in the metabolism of drugs. Aliquots of 252 postmortem samples (heart blood, liver, kidney, and lung) taken from 105 moderately to severely decomposed bodies were streaked on Sabouraud agar for isolation of fungal species. One part of the samples was worked up immediately after autopsy (group I). The second part had previously been stored at ?20 °C for at least 1 year (group II). Identification of the isolates was achieved morphologically by microscopy and molecularly by polymerase chain reaction amplification and sequencing of markers allowing species identification of the respective genera. Depending on the genus, different gene fragments were used: calmodulin for Aspergillus, β-tubulin for Penicillium, translation elongation factor 1α for Fusarium, and the internal transcribed spacer region of the ribosomal DNA for all remaining genera. A total of 156 fungal strains were isolated from 62 % of the postmortem materials. By using these primers, 98 % of the isolates could be identified to the species level. The most common genera were Candida (60.0 %—six species), Penicillium (10.3 %—two species), Rhodotorula (7.1 %—one species), Mucor (6.4 %—four species), Aspergillus (3.2 %—four species), Trichosporon (3.2 %—one species), and Geotrichum (3.2 %—one species). Group I samples contained 53 % more fungal species than stored samples suggesting some fungi did not survive the freezing process. The isolated fungi might be characteristic for decomposed bodies. The proposed methodology proved to be appropriate for the identification of fungi in this type of material. 相似文献
100.
Johannes P. F. G. Helsper Ruud J. B. Peters Lambertus Brouwer Stefan Weigel 《Analytical and bioanalytical chemistry》2013,405(4):1181-1189
This paper describes the characterisation of liposome-type nanoparticles (NPs) dispersed in a beverage matrix. Characterisation is based on a two-step procedure: first, liposomes are separated on the basis of size in the nanometre range by use of hydrodynamic chromatography (HDC); second, chemical characterisation is performed by use of MALDI–TOF mass spectrometry (MS). Characterisation of three types of Coatsome liposome, a commercially available type of empty liposome, was investigated. All three liposome types, Coatsome A?=?anionic, N?=?neutral, and C?=?cationic, gave single peaks in HDC, reflecting diameters of 153, 187, and 205 nm, respectively. Subsequent MALDI–TOF MS in positive mode furnished major signals at m/z?=?734.5 ([M?+?H]+ adduct) and m/z?=?756.6 ([M?+?Na]+ adduct) of l-(α)-dipalmitoylphosphatidylcholine (DPPC) monomer and dimeric adducts at m/z?=?1468.1 and m/z?=?1490.1, respectively. MALDI–TOF MS in negative mode gave a signal at m/z?=?721.3 ([M???H]? adduct) of l-(α)-dipalmitoylphosphatidylglycerol (DPPG), except for Coatsome C which lacks this phospholipid. After HDC separation of Coatsome A NPs the major DPPC and DPPG signals can be detected in the expected fractions by use of MALDI–TOF MS in positive and negative modes, respectively. Validation of the analytical strategy revealed linearity (R 2?>?0.99), repeatability (relative standard deviation <10 %), and reproducibility (relative standard deviation between days <10 %) were good, recovery was 61?±?5 %, and the limit of quantification was 1 mg?mL?1 in this matrix. With 4 mg Coatsome A mL?1 20 out of 20 samples furnished the 734.5 and 756.6 signals typical of DPPC in MALDI–TOF MS characterisation. 相似文献