全文获取类型
收费全文 | 7869篇 |
免费 | 412篇 |
国内免费 | 62篇 |
专业分类
化学 | 5539篇 |
晶体学 | 73篇 |
力学 | 302篇 |
数学 | 1034篇 |
物理学 | 1395篇 |
出版年
2023年 | 54篇 |
2022年 | 189篇 |
2021年 | 258篇 |
2020年 | 217篇 |
2019年 | 291篇 |
2018年 | 266篇 |
2017年 | 199篇 |
2016年 | 371篇 |
2015年 | 261篇 |
2014年 | 388篇 |
2013年 | 797篇 |
2012年 | 486篇 |
2011年 | 514篇 |
2010年 | 381篇 |
2009年 | 336篇 |
2008年 | 373篇 |
2007年 | 326篇 |
2006年 | 309篇 |
2005年 | 232篇 |
2004年 | 236篇 |
2003年 | 207篇 |
2002年 | 221篇 |
2001年 | 98篇 |
2000年 | 140篇 |
1999年 | 90篇 |
1998年 | 59篇 |
1997年 | 61篇 |
1996年 | 59篇 |
1995年 | 51篇 |
1994年 | 52篇 |
1993年 | 56篇 |
1992年 | 53篇 |
1991年 | 45篇 |
1990年 | 32篇 |
1989年 | 49篇 |
1988年 | 50篇 |
1987年 | 33篇 |
1986年 | 26篇 |
1985年 | 51篇 |
1984年 | 37篇 |
1983年 | 29篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 32篇 |
1979年 | 23篇 |
1978年 | 25篇 |
1976年 | 21篇 |
1975年 | 23篇 |
1974年 | 20篇 |
1973年 | 17篇 |
排序方式: 共有8343条查询结果,搜索用时 421 毫秒
11.
Umie F.M. Haziz Rosenani A. Haque Shun-Ze Zhan Hassan H. Abdallah Mohd R. Razali 《应用有机金属化学》2020,34(10):e5818
The synthesis and characterizations for a series of dinuclear gold (I)-di-NHC complexes, 1–8 through the trans-metalation method of their respective silver (I)-di-NHC complexes, i–viii are reported (where NHC = N-heterocyclic carbene). The successful complexation of a series of unusual non-symmetrical and symmetrical di-NHC ligands, 3,3'-(ethane-1,2-diyl)-1-alkylbenzimidazolium-1'-butylbenzimidazolium (with alkyl = methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, benzyl) with the gold (I) ions are suggested by elemental analysis, Fourier transform-infrared, 1H- and 13C-NMR data. The 13C-NMR spectra of 1–8 show a singlet sharp peak in the range of 190.00–192.00 ppm, indicating the presence of a carbene carbon that bonded to the gold (I) ion. From single crystal X-ray diffraction data, the structure of complex 6 with the formula of [di-NHC-Au (I)]2·2PF6 is obtained [where NHC = 3,3'-(ethane-1,2-diyl)-1-hexylbenzimidazolium-1'-butylbenzimidazolium]. The photophysical study in solid state of 6 displays an intense photoluminescence with a strong emission maxima, λem = 480 nm, upon excitation at 340 nm at room temperature. Interestingly, the emission maximum at 77 K shows a structural character with a strong peak at 410 nm, a medium at 433 nm and a weak at 387 nm, accompanied by a tail band to about 500 nm. 相似文献
12.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献
13.
14.
15.
Hassan Sedaghat 《Journal of Mathematical Analysis and Applications》2004,291(1):31-39
Each solution {xn} of the equation in the title is either eventually periodic with period 3 or else, it converges to zero—which case occurs depends on whether the ratio of the initial values of {xn} is rational or irrational. Further, the sequence of ratios {xn/xn−1} satisfies a first-order difference equation that has periodic orbits of all integer periods except 3. p-cycles for each p≠3 are explicitly determined in terms of the Fibonacci numbers. In spite of the non-existence of period 3, the unique positive fixed point of the first-order equation is shown to be a snap-back repeller so the irrational ratios behave chaotically. 相似文献
16.
17.
18.
A.R.ELAMROUSS 《数学学报(英文版)》2005,21(1):129-142
This paper contains a generalization of the well-known Palais-Smale and Cerami compactness conditions. The compactness condition introduced is used to prove some general existence theorems for critical points. Some applications are given to differential equations. 相似文献
19.
Habibollah Eskandari Gholam Hassan Imanzadeh Karkaragh Ali Ghanbari Saghseloo Ghadamali Bagherian Dehaghi 《Analytical sciences》2004,20(8):1227-1230
The formed cobalt-a-benzilmonoxime complex was adsorbed onto microcrystalline naphthalene. Then it was determined by zero and first derivative spectrophotometry and by atomic absorption spectrophotometry (AAS) after dissolving into chloroform and methylisobutylketone (MIBK), respectively. Under optimum conditions, cobalt in the range of 1.0 - 20.0, 0.4 - 30.0 and 2.5 - 50.0 microg could be determined by spectrophotometry, first derivative spectrophotometry and AAS method, respectively. By the method, a preconcentration factor equal to approximately 30 for cobalt was obtained. The effect of diverse ions on the determination of 5.0 microg cobalt was also studied. The method was successfully applied to some pharmaceuticals and synthetic alloy samples. 相似文献
20.
Linear complexity and linear complexity profile are important characteristics of a sequence for applications in cryptography
and Monte-Carlo methods.
The nonlinear congruential method is an attractive alternative to the classical linear congruential method for pseudorandom
number generation.
Recently, a weak lower bound on the linear complexity profile of a general nonlinear congruential pseudorandom number generator
was proven by Gutierrez, Shparlinski and the first author. For most nonlinear generators a much stronger lower bound is expected.
Here, we obtain a much stronger lower bound on the linear complexity profile of nonlinear congruential pseudorandom number
generators with Dickson polynomials. 相似文献