全文获取类型
收费全文 | 74799篇 |
免费 | 6648篇 |
国内免费 | 6033篇 |
专业分类
化学 | 11212篇 |
晶体学 | 964篇 |
力学 | 9775篇 |
综合类 | 579篇 |
数学 | 14991篇 |
物理学 | 13516篇 |
综合类 | 36443篇 |
出版年
2024年 | 206篇 |
2023年 | 710篇 |
2022年 | 1206篇 |
2021年 | 1359篇 |
2020年 | 1639篇 |
2019年 | 1452篇 |
2018年 | 1488篇 |
2017年 | 2010篇 |
2016年 | 2255篇 |
2015年 | 2216篇 |
2014年 | 3651篇 |
2013年 | 4163篇 |
2012年 | 4438篇 |
2011年 | 4891篇 |
2010年 | 3943篇 |
2009年 | 4476篇 |
2008年 | 4218篇 |
2007年 | 4959篇 |
2006年 | 4307篇 |
2005年 | 4090篇 |
2004年 | 3594篇 |
2003年 | 3321篇 |
2002年 | 2930篇 |
2001年 | 2457篇 |
2000年 | 2232篇 |
1999年 | 2046篇 |
1998年 | 1821篇 |
1997年 | 1647篇 |
1996年 | 1443篇 |
1995年 | 1233篇 |
1994年 | 1132篇 |
1993年 | 1012篇 |
1992年 | 952篇 |
1991年 | 804篇 |
1990年 | 746篇 |
1989年 | 626篇 |
1988年 | 555篇 |
1987年 | 389篇 |
1986年 | 215篇 |
1985年 | 147篇 |
1984年 | 119篇 |
1983年 | 53篇 |
1982年 | 72篇 |
1981年 | 50篇 |
1980年 | 27篇 |
1979年 | 43篇 |
1978年 | 31篇 |
1977年 | 37篇 |
1976年 | 14篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
N. S. Mosyagin A. V. Titov R. J. Buenker H.‐P. Liebermann A. B. Alekseyev 《International journal of quantum chemistry》2002,88(5):681-686
Multireference single‐ and double‐excitation configuration interaction (MRD‐CI) calculations of transition energies for the Hg atom and spectroscopic constants for the HgH molecule are carried out with the generalized relativistic effective core potential (GRECP) method. A new selection criterium for the reference configurations is discussed. The calculated spectroscopic constants are compared with experimental data and results of calculations of other groups. Improvement of accuracy is mainly observed for bond lengths from the GRECP/MRD‐CI calculations (without applying the T = 0 correction) with respect to the results of other groups. Analysis of the quality of the approximations employed is carried out. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
932.
933.
934.
Theoretical and Experimental Study on the Adsorption and Desorption of Methane by Granular Activated Carbon at 25 ℃ 总被引:1,自引:0,他引:1 下载免费PDF全文
E. Salehi V. Taghikhani C. Ghotbi E. Nemati Lay A. Shojaei 《天然气化学杂志》2007,16(4):415-422
A theoretical and experimental study was conducted to accurately determine the amount of adsorption and desorption of methane by various Granular Activated Carbon(GAC)under different physical conditions.To carry out the experiments,the volumetric method was used up to 500 psia at constant temperature of 25℃.In these experiments,adsorption as well as desorption capacities of four different GAC in the adsorption of methane,the major constituent of natural gas,at various equilibrium pressures and a constant temperature were studied.Also,various adsorption isotherm models were used to model the experimental data collected from the experiments.The accuracy of the results obtained from the adsorption isotherm models was compared and the values for the regressed parameters were reported.The results shows that the physical characteristics of activated carbons such as BET surface area,micropore volume,packing density,and pore size distribution play an important role in the amount of methane to be adsorbed and desorbed. 相似文献
935.
936.
937.
以共沉淀法得到的类球形MnCO3为前驱物,制备了类球形正交LiMnO2(So-LiMnO2),采用XRD、SEM和N2吸附技术对样品进行表征;与非球形正交LiMnO2(No-LiMnO2)进行了对比研究。结果表明:o-LiMnO2的堆垛层错度、结晶状况、颗粒形貌和大小与前驱物的微结构密切相关;在80次电化学循环测试过程中,So-LiMnO2经15次循环可达最大的放电容量152 mAh·g-1,其容量衰减平均每次循环0.58 mAh·g-1;而No-LiMnO2要经过38次循环才能达到最大放电容量128 mAh·g-1,容量衰减平均每次循环高达1.24 mAh·g-1。TEM和EDS分析证明:由一次粒子团聚的类球形So-LiMnO2能有效地抑制电解液对材料的腐蚀、减少Mn的溶解,从而提高了电化学循环能力。 相似文献
938.
The relation between thermochromism and thermal motion of aromatic rings on model bithiophene and 3-butylbithiophene molecules was studied by molecular dynamics (MD) simulations based on semiempirical AM1 hamiltonian. Theoretical optical spectra at various temperatures are generated from the conformations obtained from MD calculations. Alkyl chains have a tendency to tilt bithiophene fragments from co-planarity (connected with blue shift) whereas the unsubstituted systems prefer the higher degree of planarity (connected with red shift) upon the temperature increase. The slope of the linear temperature dependence of the reciprocal maximal wavelengths consists of the above electronic and of the vibrational contribution that (according to Wien’s displacement law) causes always the increase of the above mentioned slope by reciprocal Wien’s constant. This model explains the temperature dependence of experimental UV–vis spectra for dibutylheptathiophene and 3′,3,4′,4-tetrahexylhexathiophene. 相似文献
939.
The preparation of the title compounds was achieved via the ‘azirine/oxazolone method’ starting from the corresponding γ‐hydroxy acids. Upon subjecting the γ‐hydroxy‐N‐[1‐(dimethylcarbamoyl)ethyl]butanamides 4 to the so‐called ‘direct amide cyclization’ (DAC) conditions, chlorinated acids 11 or imino lactones 12 were obtained as the sole products instead of the expected cyclodepsipeptides A or their cyclodimers (Scheme 4). Variation of the substituents in 4 did not affect the outcome of the reaction and a mechanism for the formation of both products from the intermediate oxazolone 13 has been proposed. Under the acidic conditions of the DAC, the imino lactones are formed as their HCl salts 12 , which, in polar solvents or on silica gel, reacted further to give the chlorinated acids 11 . Stabilization of the imino lactones was achieved by increasing the substitution in the five‐membered ring, and their structure, in the form of the hydrochlorides, was established independently by X‐ray crystallography (Fig. 4). A derivative 15 of the imino lactone 12a was prepared by the reaction with the 2H‐azirin‐3‐amine 10a ; its structure was also established by an X‐ray crystal‐structure determination (Fig. 3). Furthermore, the structures of the ω‐chloro acids 11a and 11b were determined by X‐ray crystallography (Fig. 2). 相似文献
940.