全文获取类型
收费全文 | 4017篇 |
免费 | 95篇 |
国内免费 | 17篇 |
专业分类
化学 | 3193篇 |
晶体学 | 51篇 |
力学 | 30篇 |
数学 | 96篇 |
物理学 | 759篇 |
出版年
2022年 | 23篇 |
2021年 | 32篇 |
2020年 | 31篇 |
2019年 | 42篇 |
2018年 | 23篇 |
2017年 | 30篇 |
2016年 | 67篇 |
2015年 | 64篇 |
2014年 | 83篇 |
2013年 | 130篇 |
2012年 | 211篇 |
2011年 | 256篇 |
2010年 | 130篇 |
2009年 | 138篇 |
2008年 | 227篇 |
2007年 | 243篇 |
2006年 | 232篇 |
2005年 | 237篇 |
2004年 | 221篇 |
2003年 | 186篇 |
2002年 | 170篇 |
2001年 | 124篇 |
2000年 | 92篇 |
1999年 | 78篇 |
1998年 | 42篇 |
1997年 | 53篇 |
1996年 | 50篇 |
1995年 | 40篇 |
1994年 | 38篇 |
1993年 | 35篇 |
1992年 | 53篇 |
1991年 | 39篇 |
1990年 | 49篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 42篇 |
1986年 | 25篇 |
1985年 | 44篇 |
1984年 | 48篇 |
1983年 | 31篇 |
1982年 | 47篇 |
1981年 | 46篇 |
1980年 | 31篇 |
1979年 | 44篇 |
1978年 | 29篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1975年 | 22篇 |
1974年 | 21篇 |
1973年 | 16篇 |
排序方式: 共有4129条查询结果,搜索用时 15 毫秒
991.
The magnetic circular dichroism (MCU) spectra of some 3-arylfervenulins and 3-aryltoxo-flavins were measured. From the dependence of the Faraday B values of 3-arylfervenulins and 3-aryltoxoflavins on the Hammet σpara values, it is concluded that the substituent effects on the Faraday B values of 3-aryltoxoflavins are reverse to the substituent effects on the Faraday B values of 3-arylfervenulins and the reverse property of 3-aryltoxoflavins concerning the substituent effects rises from the contribution of the 1,5-dipolar structure of 3-aryltoxoflavins. 相似文献
992.
The absorption spectra of triphenylene (I) and coronene (II) are assigned by using the MCD spectra and the results of the SCF screened potential π-MO CI calculations. The calculated Faraday A/D values for the 1E and 1E1u excited states of I and II are in excellent agreement with the experimental values, in contrast to the calculated Faraday B value for the 1E1u state of II. 相似文献
993.
Oshio H Nihei M Yoshida A Nojiri H Nakano M Yamaguchi A Karaki Y Ishimoto H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(3):843-848
The reaction of 1/3 equivalent of CuCl2.2H2O with MnCl2.4H2O and 5-bromo-2-salicylideneamino-1-propanol (H(2)5-Br-sap) in methanol gave dark brown crystals of [MnIIICuIICl(5-Br-sap)2(MeOH)] (1). Complex 1 has an alkoxo-bridged dinuclear core of MnIII and CuII ions, which have elongated octahedral and square-planar coordination geometries, respectively. In dc magnetic susceptibility measurements, chi(m)T values increased as the temperature was lowered, followed by a sudden decrease below 20 K. This behavior is indicative of the occurrence of intramolecular ferromagnetic interactions, and fitting gave an S=5/2 spin ground state with an exchange coupling constant J(MnCu) of +78 cm(-1). Magnetization data collected as a function of temperature and applied magnetic field were analyzed by using a spin Hamiltonian with isotropic Zeeman and axial zero-field splitting (ZFS) terms, and a negative D(5/2) value (-1.86 cm(-1)) was obtained. A high-field EPR (HFEPR) spectrum (342.0 GHz) at 4.2 K was composed of four peaks, and two additional peaks at higher magnetic field appeared as the temperature was increased. The temperature dependences in the HFEPR spectra are indicative of a negative D(5/2) value, and fitting of the data gave D(5/2)=-1.81 cm(-1). In the ac magnetic susceptibility measurements, frequency dependent in-phase (chi(m)') and out-of-phase (chi(m)') signals with peak maxima at 0.7-1.5 K were observed and small peaks below 0.7 K appeared. The ac susceptibility data supports that 1 is a single-molecule magnet (SMM). Arrhenius plots for the chi(m)' peaks from 0.7-1.5 K gave the re-orientation energy barrier (DeltaE) of 10.5 K with a pre-exponential factor of 8.2x10(-8) s. 相似文献
994.
Tadatsugu Yamaguchi Manabu HosakaToru Ozeki Masakazu MorimotoMasahiro Irie 《Tetrahedron letters》2011,52(43):5601-5604
Photochromic benzo[b]silole derivatives, 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenylbenzo[b]thien-3-yl)perfluorocyclopentene and 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenyl-1-benzofuran-3-yl)perfluorocyclopentene, were synthesized and their photochromic performance was examined in solution. 相似文献
995.
Kenji Yamaguchi 《Theoretical chemistry accounts》1978,49(2):151-160
A diagrammatic technique was developed for the estimation of the screened potential of -electron systems. The screened potential was expanded in terms of the polarization propagators which were constructed from either the singlet,
, or triplet vertex part,
. These vertex parts correspond to the singlet or triplet excitations, respectively, in the Random Phase Approximation (RPA) containing exchange diagrams. The excitation energies were calculated by using the screened potential in the framework of RPA with exchange. The excitation energies of several conjugated molecules with or without a hetero atom are in agreement with the experimental data. 相似文献
996.
1 : 1 mixtures of aminomethylenehelicene (P)-tetramer and (M)-pentamer with terminal C16 alkyl groups in fluorobenzene showed structural changes between hetero-double-helices B and C and random-coils 2A. Figure-eight thermal hysteresis appeared when the solution was cooled and heated at a constant rate and involved the crossing of cooling and heating curves in Δε/temperature profiles. This unusual thermal hysteresis emerged in the intermediate state between counterclockwise and clockwise thermal hystereses. This phenomenon arose from the competition between self-catalytic reactions to form B and C from 2A. Significant effects of terminal C16 alkyl groups on the thermodynamic and kinetic phenomena are also described.1 : 1 mixtures of aminomethylenehelicene (P)-tetramer and (M)-pentamer with terminal C16 alkyl groups in fluorobenzene showed structural changes between hetero-double-helices B and C and random-coils 2A. 相似文献
997.
Geometry optimization of perepoxide, 1,4-diradicals and dioxetane for the ethylene plus molecular oxygen system is performed using the energy gradients of the HF 4-31G and STO-3G solutions. Perepoxide is less stable than the singlet (σπ) diradical by ≈24 k cal/mole at the 4-31G level, incompatible with the GVB CI plus thermochemical estimations. The rotational barrier of the terminal methylene group around the C-C bond is small. 相似文献
998.
A new optical sensor that uses local plasmon resonance is proposed. A peak that is due to the local plasmon resonance appears in the absorption spectrum of a gold colloid suspension in the visible region, and its height and wavelength depend on the refractive index of the suspension. These properties are used for optical sensors. We used gold colloid monolayers in which colloidal gold particles a few tens of nanometers in diameter were immobilized upon a glass slide by a functional organic coupling agent. We measured the absorption spectra of the the gold colloid monolayers, which were immersed in liquid samples or coated with thin films. We observed increases of both the resonance wavelength and the absorbance as the refractive indices of the sample liquids or the thickness of the coated films increased. The proportional constants of the resonance wavelength to the film thickness were 3.6 and 5.7 for a 13.9- and a 20.2-nm gold colloid monolayer, respectively. 相似文献
999.
1000.
张高龙 叶沿林 江栋兴 郑涛 李智焕 李湘庆 吴翠娥 陈志强 胡青元 庞丹阳 王佳 A.Ozawa Y.Yamaguchi R.Kanungo D.Fang I.Tanihata 《中国物理 C》2005,29(10):940-943
在25MeV/u 6He轰击9Be靶的反应中,用探测器望远镜测得氚碎片,得到了5个角度的能谱,经过仔细的分析取得了高能直接破碎成分的角分布.利用Serber模型进行了破碎反应的理论计算,证实了实验中高能成分的t来自于6He的直接破碎反应.利用Fermi破碎模型计算了6He中各破碎反应道基于相空间的百分比产额,进而估算出6He初态中t+t结构的概率约占1/3, 而4He核心加价中子的组态约占2/3. 相似文献