全文获取类型
收费全文 | 1722篇 |
免费 | 73篇 |
国内免费 | 6篇 |
专业分类
化学 | 1407篇 |
晶体学 | 17篇 |
力学 | 13篇 |
数学 | 85篇 |
物理学 | 279篇 |
出版年
2023年 | 12篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 16篇 |
2019年 | 31篇 |
2018年 | 17篇 |
2017年 | 27篇 |
2016年 | 36篇 |
2015年 | 36篇 |
2014年 | 50篇 |
2013年 | 92篇 |
2012年 | 85篇 |
2011年 | 129篇 |
2010年 | 55篇 |
2009年 | 54篇 |
2008年 | 122篇 |
2007年 | 122篇 |
2006年 | 104篇 |
2005年 | 95篇 |
2004年 | 95篇 |
2003年 | 85篇 |
2002年 | 91篇 |
2001年 | 16篇 |
2000年 | 32篇 |
1999年 | 20篇 |
1998年 | 18篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1974年 | 10篇 |
排序方式: 共有1801条查询结果,搜索用时 0 毫秒
41.
Masato Doura Hiroyuki Aota Akira Matsumoto 《Journal of polymer science. Part A, Polymer chemistry》2004,42(9):2192-2201
Novel amphiphilic network polymers consisting of nonpolar, short primary polymer chains and polar, long crosslink units were prepared, and the swelling behavior of resulting amphiphilic gels is discussed by focusing on the influence of characteristic dangling chains; that is, benzyl methacrylate (BzMA) was copolymerized with tricosaethylene glycol dimethacrylate [CH2?C(CH3)CO(OCH2CH2)23OCOC(CH3)?CH2, PEGDMA‐23] in the presence of lauryl mercaptan as a chain‐transfer agent because BzMA forms nonpolar, short primary polymer chains and PEGDMA‐23 as a crosslinker contains a polar, long poly(oxyethylene) unit. The enhanced incorporation of dangling chains into the network polymer was brought by shortening the primary polymer chain length, and copolymerization with methoxytricosaethylene glycol methacrylate, a mono‐ene counterpart of PEGDMA‐23, enforced the incorporation of flexible dangling poly(oxyethylene) chains into the network polymer, although the former dangling chains as terminal parts of primary poly(BzMA) chains were rather rigid. Then, the influence of characteristic dangling chains on the swelling behavior of amphiphilic gels was examined in mixed solvents consisting of nonpolar t‐butylbenzene and polar methanol. The profiles of the solvent‐component dependencies of the swelling ratios were characteristic of amphiphilic gels. The introduction of dangling poly(oxyethylene) chains led not only to an increased swelling ratio but also to sharpened swelling behavior of amphiphilic gels. The swelling response of amphiphilic gels was checked by changing the external solvent polarity. The dangling chains with freely mobile end segments influenced the swelling response of gels. The amphiphilic gels with less entangled, collapsed crosslink units exhibited faster swelling response than the ones with more entangled, collapsed primary polymer chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2192–2201, 2004 相似文献
42.
Masato Hasebe Catherine Lazare Paul de Mayo Alan C. Weedon 《Tetrahedron letters》1981,22(51):5149-5152
Irradiation of a number of aromatic hydrocarbons adsorbed on alumina in the presence of ferric chloride leads to monochlorination. 相似文献
43.
44.
Yuji Hayashi Takeshi Matsumoto Motokazu Uemura Masato Koreeda 《Magnetic resonance in chemistry : MRC》1980,14(2):86-91
Carbon-13 NMR signals of the biologically active norditerpenoid dilactones from Podocarpus plants were fully assigned by using selective 1H decoupling, coupling constants (2JCH), spin-lattice relaxation times (T1) and correlation of the spectra of more than thirty dilactone congeners. The spectra of five nagilactones, B, C, D, E and F, which constitute representative members of three major structural types of the dilactones: (A) 8:14, 9:11-dienolide (α-pyrone) type, (B) 7α:8α-epoxy-9:11-enolide type, and (C) 7:8,9:11-dienolide type, were extensively analysed. Some characteristic steric interactions for the substituents on the ring system can be demonstrated from the spectral properties. 相似文献
45.
Ultrathin, large nylon capsules whose porous membranes were corked with charged, synthetic bilayer-forming amphiphiles (cationic, anionic, zwitterionic bilayers) were prepared. The chemically stable, bilayer-corked capsules can selectively retain 0.1 M aqueous acidic (HCl, HNO3, H2SO4, HClO4 and p-toluenesulfonic acid) and alkaline solutions (NaOH, Ba(OH)2, NH4 OH, and N(Et)4OH) in the inner aqueous phase depending on the surface charge of corking bilayers: the capsule corked with positively and negatively charged bilayers could selectively store alkalies and acids, respectively, and could keep a selective pH-gradient across the membrane. The zwitterionic bilayer-corking could retain neither acids nor alkalies in the inner aqueous phase. The permeation of these acids and alkalies to the outer phase (pH gradient decreasing across the capsule membrane) could be reversibly controlled by the phase transition of corking bilayers from gel to liquid crystalline state. The selective storage and permeation of acids and alkalies could be explained by the process of permeation of H+ or OH- counter ions across the charged bilayer-corking. 相似文献
46.
Noguchi H Kondoh A Hattori Y Kanoh H Kajiro H Kaneko K 《The journal of physical chemistry. B》2005,109(29):13851-13853
We measured adsorption and desorption isotherms of methane on [Cu(4, 4'-bipyridine)2(BF4)2] (LPC) at 258, 273, and 303 K. Adsorption proceeds almost vertically at a definite pressure, which is named gate pressure. The lower the measurement temperature, the smaller the gate pressure. The temperature dependence of the gate pressure is expressed by the Clapeyron-Clausius equation, giving a thermodynamic evidence on the clathrate formation between the Cu complex and methane. 相似文献
47.
Y. Uzawa M. Takeda A. Kawakami Z. Wang T. Noguchi 《International Journal of Infrared and Millimeter Waves》2005,26(1):41-54
We describe a novel method of designing a tuning circuit with two half-wave distributed junctions separated by a half-wavelength microstripline, which analytically determines the circuit parameters such as the minimum current density of the junctions and the characteristic impedances of the distributed junctions and the microstripline. The tuning circuit was approximated by simple transmission theory and then simplified with ideal circuit components for analysis. We applied Chebyshevs band-pass filter theory, in part, to optimize the circuit design. The analytical results revealed that a high characteristic-impedance ratio between the distributed junctions and the microstripline is necessary to obtain broadband matching using low-current-density junctions. The experimental results for all-NbN SIS mixers we designed with this method demonstrated double-sideband (DSB) receiver-noise temperatures of 6–10 quanta from 710 to 810 GHz for a mixer with a current density of only 4 kA/cm2 (estimated CJRN product of 37 at 750 GHz). The RF bandwidth was broader than that of a conventional full-wave distributed SIS mixer with the same current density. 相似文献
48.
We introduce a notion ofq-analogue of the perfect numbers. We also define a new zeta function which we call a zeta function ofq-perfect numbers. In this paper, the properties of theq-perfect numbers and the zeta functions are studied. Especially, we determine theq-perfect numbers whenq is a root of unity. 相似文献
49.
A highly efficient, two-step sequence method for the deoxygenation of hydroxyl groups has been developed. The method involves the preparation of the 2-(2-iodophenyl)ethyl methyl phosphite derivative of an alcohol using methyl dichlorophosphite and 2-(2-iodophenyl)ethanol. Treatment of the phosphite intermediate with (n-Bu)3SnH/AIBN in refluxing benzene cleanly produces the deoxygenation product of the original alcohol. 相似文献
50.
Let D be a complex of non-trivial p-subgroups of a finite groupG, closed under G-conjugation. In this paper, a p-local geometryp(G; D) is introduced for G associated with the complex D. Thehomotopy equivalence between p(G; D) and D is also studied.2000 Mathematics Subject Classification 20E15, 51E24. 相似文献