全文获取类型
收费全文 | 4076篇 |
免费 | 210篇 |
国内免费 | 422篇 |
专业分类
化学 | 3096篇 |
晶体学 | 74篇 |
力学 | 34篇 |
综合类 | 26篇 |
数学 | 604篇 |
物理学 | 874篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 64篇 |
2021年 | 101篇 |
2020年 | 75篇 |
2019年 | 180篇 |
2018年 | 234篇 |
2017年 | 73篇 |
2016年 | 100篇 |
2015年 | 80篇 |
2014年 | 123篇 |
2013年 | 259篇 |
2012年 | 149篇 |
2011年 | 228篇 |
2010年 | 214篇 |
2009年 | 309篇 |
2008年 | 274篇 |
2007年 | 259篇 |
2006年 | 242篇 |
2005年 | 214篇 |
2004年 | 207篇 |
2003年 | 150篇 |
2002年 | 206篇 |
2001年 | 117篇 |
2000年 | 84篇 |
1999年 | 66篇 |
1998年 | 76篇 |
1997年 | 51篇 |
1996年 | 63篇 |
1995年 | 57篇 |
1994年 | 70篇 |
1993年 | 62篇 |
1992年 | 50篇 |
1991年 | 29篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 4篇 |
排序方式: 共有4708条查询结果,搜索用时 31 毫秒
71.
M. G. El-Shaarawy 《Journal of Thermal Analysis and Calorimetry》1998,53(1):247-254
The crystallization kinetics of the γ-irradiated and the unirradiated glass Ag7I4VO4 was studied dynamically by means of DTA,
and isothermally via electrical conductivity measurements. The influence of doping with alkali metal ions (Li+, Na+, K+, Rb+
or Cs+) on the crystallization process in the glass was also investigated. The results showed that the rate of crystallization
depends on the nature of the added metal ion and on the crystallization growth mechanism. The latter is a two-dimensional
process for both the pure and the alkali metal-doped glasses. The effects of irradiation and additive ions on the crystallization
process are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
72.
2-(8-羟基喹啉-5-磺酸-7-偶氮)-1,8-二羟基-3,6-萘二磺酸与牛血清白蛋白的相互作用 总被引:5,自引:0,他引:5
用平衡透析法和分光光度法研究了 2 (8 羟基喹啉 5 磺酸 7 偶氮 ) 1,8 二羟基 3,6 萘二磺酸与牛血清白蛋白 (BSA)在酸性溶液中的结合反应 ,认为 8Q5SAC与BSA之间的结合力是以静电引力为主的非共键作用力 ,并探讨了其结合模型。在 2 98K下 ,测得这一反应的最大结合数为 35~ 40 ,结合常数为 6 .1× 10 5L mol。还研究了溶液基本条件如酸度和离子强度等对 8Q5SAC与牛血清白蛋白分子复合物形成的影响 ,在pH =3.34条件下 ,标准工作曲线的线性范围为 0 .2 0~ 46 .90mg L。 相似文献
73.
During the heating of YBCO a peritectic reaction takes place at 1020C, which can be described by: 2YBa2Cu3O7–xY2BaCuO5+L+(1-2x)/2O2 (1) whereL = 3BaCuO2 +2CuO is a fluid with limited amount of yttrium.It has been reported, that many parameters can influence the reaction. From one side not only the starting size of grains but also the heating rate have an influence on the resulting Y2BaCuO5-phase. From the other side, there is a change of the peritectical temperature caused by changing of the partial pressure of O2 and the presence of parasitic phase.From general kinetic consideration one can draw the conclusion, that different mechanisms (nucleation, phase-boundary reaction and diffusion) can control the reaction.Using DTA/TG measurements, the peritectic reaction has been examined. Classical kinetic methods (Kissinger and Friedman) has been used. The Friedman method has given the dependence of the activation energy from reaction degree. This suggests many steps reactions. The dependence of the DTA-peaks from the heat rate suggest a parallel steps of reaction. This assumption can be motivated by evaluation of free O2, one solid and liquid phase formation. Amount of this phases depends on the heating rate. Additionally X-ray and microscopic methods has been used. In this way was shown, that the perovskit structure is stable up to peritectical temperature and than is dramatically destroyed. From microscopic observations has been got information about shape and size of solid phase and it's creation as a function of temperature, time and starting grain size.
Die Arbeit wurde BMBF gefördert und durch Land NRW unterschtützt. 相似文献
74.
在pH4.5的 0.015 mol/L HAc-NaAc介质中,In铟(Ⅲ)-7-(1-苯偶氮)-8-羟基喹啉-5-磺酸钠(BQ)在滴汞电极上于-0.665-0.70 V(vs.SCE)电位处得到络合物的吸附还原波,其一阶导数峰电流I'p与In(Ⅲ)浓度在4.0× 10~(-8)~3.5 × 10~(-6)mol/L范围内呈良好的线性关系,检测限为1.6 × 10~(-8)mol/L In(Ⅲ).应用该法测定了铅粉和氢氧化铝样品中的微量铟,结果令人满意。对电极反应机理进行了探讨。 相似文献
75.
LI Chun-Bao Chen Yi LI Song-Lin ZHANG Wen-Qin CUI Yi JI Xiu-Jie ZHENG Peng-Wu 《结构化学》2002,21(5):470-472
1 INTRODUCTION (9S,13R,14S)-7,8-Didehydro-3,7-dimethoxy-4-hydroxy-17-methylmorphinan-6-one I is an impor- tant natural product that was used to ease pain, decrease blood pressure and diminish inflammation. In order to study the stereochemistry of the reduction of I with potassium boronhydride, the crystal structure of the title compound II was determined by X-ray diffraction method. 2 EXPERIMENTAL 2. 1 Instrument The melting point was measured on a Yanagimoto MP-500 apparatus… 相似文献
76.
From methyl-5-acetylamino-7,8-anhydro-4,9-O-bis-(t-butyldimethylsilyl)-3,5-dideoxy--D-glycero-D-galacto-2-nonulopyranosidonic acid methylester (1) the derivatives1 a and1 b were obtained by removing the 9-O-(t-butyldimethylsilyl)group withBu
4NF, followed by acetylation. Treatment of1 b with 80% acetic acid and acetanhydride/pyridine yields the 8-epi-N-acetylneuraminic acid derivative2 a and the 7-epi-N-acetylneuraminic acid derivative3 a in a ratio of 3:1 (Scheme 1). The structure elucidation of2 b was achieved by converting2 b via the 4,9-bis-O-(tBDMSi)-8-O-tosyl-derivative2 d into the epoxide1 (Scheme 2). Using the same sequence the epoxides4 and5 were transformed into theN-acetylneuraminic acid derivative6 a and the 7,8-bis-epi-N-acetylneuraminic acid derivative7 a (Scheme 3). After treatment with sodium hydroxide and 0.025m HCl and Dowex 50 H+ the 8-epi-, 7-epi- and 7,8-bis-epi-N-acetylneuraminic acids2,3, and7 were obtained. These three compounds were tested withCMP-N-acetylneuraminic acid synthetase.
Herrn KollegenK. Schlögl mit den besten Wünschen zum 60. Geburtstag. 相似文献
77.
Halfsandwich Complexes of Chromium with the Trifluoromethyl Isocyanide Ligand The synthesis and properties of the halfsandwich complexes [η6-1,3,5-C6H3(CH3)3]Cr(CO)2(CNCF3), [η6-1,3,5-C6H3(CH3)3]Cr(CO)(CNCH3)(CNCF3) und [η6-1,3,5-C6H3(CH3)3]Cr(CNCF3)3 is reported. The vibrational spectroscopic data proof the strong π accepting character of the trifluoromethyl isocyanide ligand. 相似文献
78.
Valerio Magnasco Massimo Ottonelli Giuseppe Figari Marina Rui Camilla Costa 《Journal of Molecular Structure》1998,430(1-3):231-239
The real spherical tensor theory of long-range intermolecular coefficients developed in previous papers is applied to derive explicit formulae for the first three dispersion coefficients for like centrosymmetric linear molecules. The expansion of angle-dependent coefficients in associated Legendre polynomials allows one to identify the isotropic and anisotropic components of the dispersion interaction in terms of London dispersion constants, the treatment of higher coefficients being simplified by the coupling of the elementary (l, l′)-polarizations to resultant angular momenta LA and LB onto each molecule. The contributions from all coupling schemes are given explicitly for C6, C8, C10, and numerical results are presented for H2-H2 using two-term reduced spectra values from the Kaiserlautern group. 相似文献
79.
V. V. Lipson V. V. Borodina M. G. Shirobokova S. M. Desenko O. V. Shishkin R. I. Zubatyuk 《Chemistry of Heterocyclic Compounds》2007,43(4):490-495
Interaction of 3-amino-5-methylpyrazole, 3-amino-5-methylthio-, and 3,5-diamino-1,2,4-triazole with Meldrum’s acid, acetone,
ethyl methyl ketone, and cyclohexanone leads to alkyl-substituted pyrazolo[3,4-b]pyridin-6-ones and 1,2,4-triazolo[1,5-a]pyrimidin-7-ones
respectively. The structure of 5,5-dimethyl-2-methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-7-one was demonstrated
by an X-ray structural investigation.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 595–601, April, 2007. 相似文献
80.
The catalysts prepared sequentiallyvia the interaction of C3H5PdC5H5 with the surface of evacuated Pr4O7/C and reduction with H2 at 573 K, contain 20–30 Pd particles and Pr4O7 particles<20 . The catalysts obtained have two-order of magnitude higher specific activity in the CH3OH synthesis than Pd/C. 相似文献