全文获取类型
收费全文 | 2067篇 |
免费 | 30篇 |
国内免费 | 5篇 |
专业分类
化学 | 1471篇 |
晶体学 | 34篇 |
力学 | 20篇 |
数学 | 92篇 |
物理学 | 485篇 |
出版年
2021年 | 17篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 36篇 |
2015年 | 24篇 |
2014年 | 24篇 |
2013年 | 99篇 |
2012年 | 84篇 |
2011年 | 95篇 |
2010年 | 66篇 |
2009年 | 53篇 |
2008年 | 105篇 |
2007年 | 106篇 |
2006年 | 112篇 |
2005年 | 115篇 |
2004年 | 107篇 |
2003年 | 72篇 |
2002年 | 66篇 |
2001年 | 64篇 |
2000年 | 43篇 |
1999年 | 37篇 |
1998年 | 21篇 |
1997年 | 27篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 20篇 |
1993年 | 19篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 24篇 |
1989年 | 18篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1986年 | 23篇 |
1985年 | 35篇 |
1984年 | 38篇 |
1983年 | 35篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 21篇 |
1975年 | 20篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1967年 | 11篇 |
排序方式: 共有2102条查询结果,搜索用时 10 毫秒
991.
Masayoshi Itoh Kenji Iwata Jun‐Ichi Ishikawa Hiroshi Sukawa Hideaki Kimura Koichi Okita 《Journal of polymer science. Part A, Polymer chemistry》2001,39(15):2658-2669
Nine new kinds of thermosetting polymers with the Si(H)? C?C unit were synthesized by dehydrogenative polycondensation reactions between hydrosilanes and diethynyl compounds in the presence of a magnesia catalyst. Phenylsilane, silane, vinylsilane, and n‐octylsilane were used as the hydrosilanes, and 1,3‐diethynylbenzene, 1,4‐diethynylbenzene, 4,4′‐diethynyldiphenyl ether, and 1,3‐diethynyl‐1,1,3,3‐tetramethyldisiloxane were used as the diethynyl compounds. All the polymers were thermosetting, highly heat‐resistant, easily soluble in a solvent, and moldable. In particular, ? Si(R)H? C?C? C6H4? C?C? (R = H or CH?CH2) showed high thermal stability; the temperature of 5% weight loss was greater than 800 °C, and the residue at 1000 °C was over 90%. The thermal stabilities of the polymers were attributed to the crosslinking reaction of the Si? H and C?C bonds. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2658–2669, 2001 相似文献
992.
Toshio Sugizaki Mikihiro Kashio Atsuko Kimura Shin‐ichi Yamamoto Osamu Moriya 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4212-4221
Polysilsesquioxane with phenyl and chloromethylphenyl groups (PCPSQ) was prepared readily from phenyltrimethoxysilane and [2‐(chloromethylphenyl)ethyl]trimethoxysilane under acidic conditions. Polymerization with chloromethylphenyl groups on PCPSQ with methyl methacrylate (MMA) was conducted in the presence of a catalytic amount of copper(I) bromide and (−)‐sparteine. Atom transfer radical polymerization yielded a graft polymer (PCPSQ‐g‐MMA) efficiently, and no gelation was observed. The process was also applied to the preparation of graft block copolymers on PCPSQ with several methacrylate monomers. An advantage of the graft hybrid polymers was shown in improved thermal behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4212–4221, 2004 相似文献
993.
Xiaobo Su Satoshi Kimura Masahisa Wada Shigenori Kuga 《Cellulose (London, England)》2011,18(3):531-537
Highly crystalline cellulose samples from green algae (cellulose I) and mercerized ramie (cellulose II) were treated with
anhydrous hydrazine and the resulting complexes were analyzed by synchrotron X-ray diffraction and thermogravimetry. Cellulose
I-hydrazine complex could be fully described by a two-chain monoclinic unit cell, a = 0.879 nm, b = 1.076 nm, c = 1.038 nm, and γ = 122.0°, with space group P21. Cellulose II-hydrazine complex prepared from mercerized ramie gave a different two-chain monoclinic unit cell, a = 1.042 nm, b = 1.046 nm, c = 1.038 nm, γ = 129.7°, also with space group P21. Though having different crystal structures, the number of hydrazine molecules per glucopyranoside residue was 0.82 for cellulose
I-complex and 0.93 for cellulose II-complex, probable stoichiometric value of 1.0. Hydrazine could be extracted from the complexes
by organic solvents retaining the crystalline orders, resulting in the allomorphic conversion to cellulose IIII and cellulose IIIII, both having non-staggered chain arrangements. These features are similar to those of cellulose-ethylenediamine complexes. 相似文献
994.
Yuji Shibahara Yoko Akiyama Yoshinobu Izumi Shigehiro Nishijima Yoshihide Honda Norio Kimura Seiichi Tagawa Goro Isoyama 《Journal of Polymer Science.Polymer Physics》2008,46(1):1-7
The thermal degradation of Nafion membrane was analyzed with age‐momentum correlation (AMOC) measurement and four‐electrode AC impedance measurement. In the heated sample, the decrease in proton conductivity was observed. The lifetimes and corresponding relative intensities showed fairly good agreement between heated and nonheated samples within the experimental error. In the analysis of the photopeak of annihilation γ‐ray, on the other hand, the difference between those two kinds of samples was observed, and this difference was found to be caused by the annihilation of free positrons with low energy electrons by using AMOC method. The decrease in proton conductivity was caused by the low energy electrons, namely sulfonic radicals. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1–7, 2008 相似文献
995.
Takayuki Ikehara Hironori Kimura Toshiyuki Kataoka 《Journal of Polymer Science.Polymer Physics》2010,48(6):706-711
Miscible blends of three crystalline polymers, namely poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), and poly(oxyethylene) (POE), exhibited interpenetrating spherulites, where a spherulite of one component grows inside the spherulites of other components. PBS and PES were immiscible above the melting points, Tm, of these substances, while ternary blends with POE showed miscibility, which depended on the molecular weight of POE. PBS and PES exhibited the same spherulitic growth process as in a miscible binary blend when they were crystallized from a homogeneous ternary melt. Spherulites of PBS, which is the highest‐Tm component, filled the whole volume first when a miscible ternary blend was quenched below Tm of POE, the lowest‐Tm component. Then, the blends showed either two types of crystallization processes. One was successive nucleation and growth of PES and POE spherulites, that is, PES nucleated and developed spherulites inside the PBS spherulites and then POE spherulites grew inside the interlocked spherulites of PBS and PES. The other was simultaneous growth and the formation of interpenetrating spherulites of PES and POE inside the PBS spherulites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 706–711, 2010 相似文献
996.
A French maritime pine bark extract, Flavangenol®, is widely used as a nutritional supplement for protection against atherosclerosis, hypertension, diabetes, etc. Chronic exposure to solar UV radiation damages skin, increasing cutaneous thickness, wrinkling and pigmentation, as well as reducing elasticity, and causes skin cancer. The aim of this study was to examine the effects of flavangenol on skin damage and the incidence of skin tumors caused by long-term UVB irradiation in melanin-possessing hairless mice. The oral administration of flavangenol (60, 200 or 600 mg kg−1, twice daily) significantly inhibited increases in skin thickness, and the formation of wrinkles and melanin granules, as well as increases in the diameter and length of skin blood vessels. Furthermore, it prevented increases in numbers of apoptotic, Ki-67-positive and 8-hydroxy-2′-deoxyguanosine (8-OHdG)-positive cells, and the expression of skin vascular endothelial growth factor (VEGF) induced by chronic UVB irradiation. The effect on these biomarkers was associated with a reduction in the incidence of tumors in mice. The antiphotoaging and anticarcinogenetic activities of flavangenol may be due to inhibition of the expression of Ki-67, 8-OHdG and VEGF through a scavenging effect on reactive oxygen species. 相似文献
997.
Isao Yamaguchi Hideo Higashi Shunsuke Kimura Moriyuki Sato 《Helvetica chimica acta》2010,93(5):819-828
Diacetylenes (DAs) having a dipolar D‐π‐A structure (D=donor: amino group; π=π‐conjugation core; A=acceptor: pyridinium (Py) and bipyridinium (BPy) groups), i.e., 4 (APBPyDA) and 5 (APPyPyDA), or an A‐π‐A structure, i.e., 7 (DBPyDA) and 8 (PyDA(Cl)), were obtained by 1 : 1 and 1 : 2 reactions of 4,4′‐(buta‐1,3‐diyne‐1,4‐diyl)bis[benzenamine] (APDA; 3 ) with 1‐(2,4‐dinitrophenyl)‐1′‐hexyl‐4,4′‐bipyridinium bromide chloride (1 : 1 : 1) ( 1 ), 1‐(2,4‐dinitrophenyl)‐4‐(pyridin‐4‐yl)pyridinium chloride ( 2 ), or 1‐(2,4‐dinitrophenyl)pyridinium chloride ( 6 ) (Schemes 1 and 2). The anion‐exchange reactions of 8 with NaI and Li(TCNQ) (TCNQ?=2,2′‐(cyclohexa‐2,5‐diene‐1,4‐diylidene)bis[propanedinitrile] radical ion (1?)) yielded the corresponding I? and TCNQ? salts 9 (PyDA(I)) and 10 (PyDA(TCNQ)). Compounds 10 and 4 exhibited a UV/VIS absorption due to a charge transfer between the TCNQ? and the pyridinium groups and a strong solute–solvent interaction of a dipolar solute molecule in the polar environment, respectively. Compounds 8 – 10 exhibited photoluminescence in solution, whereas 4 and 7 did not because of the presence of the 4,4′‐bipyridinium quenching groups. Differential‐scanning‐calorimetry (DSC) measurements suggested that the DAs obtained in this study can be converted into poly(diacetylenes) by thermal polymerization. 相似文献
998.
999.
Crystal growth and electric‐property change by rubidium or cesium doping on potassium‐sodium‐niobate
Hideo Kimura Rumi Tanahashi Hongyang Zhao Koji Maiwa 《Crystal Research and Technology》2011,46(1):37-40
Alkali metals (Na, Rb or Cs) co‐doped with fiber‐ and bulk‐shaped KNbO3 single crystals were grown using two original methods by means of doping together of small ionic Na and large ionic Rb or Cs into KNbO3. Single‐phase crystals could be grown with an orthorhombic system at room temperature as well as pure KNbO3. Piezoelectric and ferroelectric property changes by the co‐doping of Rb or Cs with Na were estimated using d33 values and a polarization‐electric field hysteresis curve in fiber‐ and bulk‐shaped crystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
We report the mutually exclusive relationship between carbon nanotube (CNT) yield and crystallinity. Growth conditions were optimized for CNT growth yield and crystallinity through sequential tuning of three input variables: growth enhancer level, growth temperature, and carbon feedstock level. This optimization revealed that, regardless of the variety of carbon feedstock and growth enhancer, the optimum conditions for yield and crystallinity differed significantly with yield/crystallinity, preferring lower/higher growth temperatures and higher/lower carbon feedstock levels. This mutual exclusivity stemmed from the inherent limiting mechanisms for each property. 相似文献