全文获取类型
收费全文 | 4959篇 |
免费 | 130篇 |
国内免费 | 15篇 |
专业分类
化学 | 3933篇 |
晶体学 | 42篇 |
力学 | 42篇 |
数学 | 239篇 |
物理学 | 848篇 |
出版年
2023年 | 22篇 |
2022年 | 37篇 |
2021年 | 46篇 |
2020年 | 45篇 |
2019年 | 64篇 |
2018年 | 39篇 |
2017年 | 44篇 |
2016年 | 87篇 |
2015年 | 97篇 |
2014年 | 99篇 |
2013年 | 307篇 |
2012年 | 243篇 |
2011年 | 300篇 |
2010年 | 164篇 |
2009年 | 176篇 |
2008年 | 293篇 |
2007年 | 323篇 |
2006年 | 283篇 |
2005年 | 275篇 |
2004年 | 222篇 |
2003年 | 209篇 |
2002年 | 177篇 |
2001年 | 96篇 |
2000年 | 126篇 |
1999年 | 83篇 |
1998年 | 74篇 |
1997年 | 79篇 |
1996年 | 68篇 |
1995年 | 54篇 |
1994年 | 46篇 |
1993年 | 70篇 |
1992年 | 50篇 |
1991年 | 47篇 |
1990年 | 37篇 |
1989年 | 35篇 |
1988年 | 36篇 |
1987年 | 38篇 |
1986年 | 24篇 |
1985年 | 72篇 |
1984年 | 61篇 |
1983年 | 25篇 |
1982年 | 31篇 |
1981年 | 48篇 |
1980年 | 40篇 |
1979年 | 55篇 |
1978年 | 46篇 |
1977年 | 37篇 |
1976年 | 27篇 |
1975年 | 31篇 |
1974年 | 39篇 |
排序方式: 共有5104条查询结果,搜索用时 0 毫秒
901.
D. N. Dybtsev M. P. Yutkin E. V. Peresypkina A. V. Virovets Y. Hasegawa H. Nishihara V. P. Fedin 《Russian Chemical Bulletin》2007,56(9):1782-1786
The reaction of Co(NO3)2·6H2O with 1,3,5-benzenetricarboxylic acid (H3btc, trimesic acid) in DMF at 100 °C afforded the coordination polymer [Co3(dmf)6(btc)(Hbtc)(H2btc)]··9H2O (1) (dmf is N,N′-dimethylformamide, DMF). According to the X-ray diffraction study, the metal-organic coordination polymer is composed of
planar honeycomb (6,3) networks, in which the organic benzenetricarboxylate anions and the inorganic Co2+ cations play a role of three-connected nodes. Disordered water molecules are intercalated between the layers. A study of
the magnetic properties showed the presence of a weak antiferromagnetic coupling between the Co2+ ions (S = 3/2).
Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1719–1723, September, 2007. 相似文献
902.
Haruko Ikeuchi Kaoru Naganuma Marie Ichikawa Hiromichi Ozawa Tomoya Ino Makoto Sato Hiroko Yonezawa Sonomi Mukaida Akihiro Yamamoto Takeshi Hashimoto 《Journal of solution chemistry》2007,36(10):1243-1259
The diffusion coefficients of several tris(β-diketonato) ruthenium complexes in acetonitrile solutions containing a supporting electrolyte were determined by chronoamperometry.
The diffusion coefficients of the charged complexes, which were produced by electrochemical oxidation or reduction, were also
determined by double potential step chronoamperometry. Two kinds of radii of the complexes were evaluated. One was the Van
der Waals radius and the other was the geometric distance from the center of the complex to the outer surface of the farthest
atom. The latter quantity was determined from X-ray diffractometric data. The diffusion coefficients of the neutral complexes
were discussed on the basis of the Stokes-Einstein equation. Those of charged complexes could not be explained by the theoretical
equation presented by Hubbard and Onsager. 相似文献
903.
A new spectroscopic tool for surface layer analysis: multiple-angle incidence resolution spectrometry 总被引:1,自引:0,他引:1
Hasegawa T 《Analytical and bioanalytical chemistry》2007,388(1):7-15
A series of application studies of infrared multiple-angle incidence resolution spectrometry (IR-MAIRS) have been reported
since it was first proposed as a unique technique for analyzing molecular orientation in thin films on an optically transparent
substrate, and both expected and unexpected benefits of IR-MAIRS have been revealed. In this review, cutting-edge application
studies are summarized systematically, and the principle of MAIRS is explained from a new point of view. 相似文献
904.
The equilibrium constants, K
2, have been determined for the proton-transfer reactions of 1-phenacylquinolinium ion, PHQ+, with several amines {triethylamine (TEA), N,N,N′,N′-tetramethylethylenediamine (ED), N,N,N′, N′-tetramethylpropanediamine (PD), N,N,N′,N′-tetramethylbutanediamine (BD), and 1,8-bis(dimethylamino-naphthalene (DMAN)} in acetonitrile (AN), AN-tetrahydrofuran (THF)
and AN-ethanol (EtOH) mixtures. The reaction was followed spectrophotometrically using a stopped-flow technique. The K
2 value decreased for DMAN and increased for TEA with increasing vol-% of THF in AN-THF mixtures. The changes in the K
2 value for ED, PD and BD changed in the order: ED, PD and BD from a pattern similar to TEA to a pattern similar to DMAN. The
change in the K
2 value for DMAN with increasing vol-% of THF in AN-THF mixtures was explained by the effect of polarity on the stability of
P−Q+ (the deprotonated product of PHQ+). The effect of THF on the K
2 value is consistent with that of the peak wavelength of the absorption spectrum of P−Q+. The change in the K
2 value for TEA, ED, PD and BD depended on the structures of the protonated bases, one of the products for this reaction. The
effect of EtOH on the K
2 value for DMAN was examined in ternary EtOH-THF-AN mixtures that contain different amounts of EtOH and whose relative permittivities
were adjusted to that of EtOH. The K
2 value increased with increasing vol-% of EtOH because of the stabilization of P−Q+ upon the formation of the hydrogen-bonded complex with EtOH. The absorption spectrum of P−Q+ demonstrated a blue shift as the vol-% of EtOH increased. 相似文献
905.
Sayaka Taji Takeshi Yamada Yasuko In Shun‐ichi Wada Yoshihide Usami Kazuo Sakuma Reiko Tanaka 《Helvetica chimica acta》2007,90(11):2047-2057
Three new lanostane‐type triterpenoids, inonotsulides A, B, and C ( 1 – 3 , resp.) were isolated from the sclerotia of Inonotus obliquus (Pers .: Fr.) (Japanese name: Kabanoanatake; Russian name: Chaga). Their structures were determined to be (20R,24S)‐3β,25‐dihydroxylanost‐8‐en‐20,24‐olide ( 1 ), (20R,24R)‐3β,25‐dihydroxylanost‐8‐en‐20,24‐olide ( 2 ), and (20R,24S)‐3β,25‐dihydroxylanosta‐7,9(11)‐dien‐20,24‐olide ( 3 ) on the basis of chemical transformation, NMR spectroscopy including 1D and 2D (1H,1H‐COSY, NOESY, HMQC, HMBC), EI‐MS, and single‐crystal X‐ray analysis. 相似文献
906.
907.
Takeshi Yanai Robert J. Harrison Takahito Nakajima Yasuyuki Ishikawa Kimihiko Hirao 《International journal of quantum chemistry》2007,107(6):1382-1389
A new, practical implementation of double‐group symmetry to relativistic Gaussian spinors is presented for four‐component relativistic molecular calculations. We show that the systematic adaptability to irreducible representations under arbitrary point‐group symmetry, as well as Kramers (time‐reversal) symmetry, is inherent in the present basis spinors, which possess the analytic structure of Dirac atomic spinors. The implementation of double‐group symmetry entails significant computational efficiencies in the relativistic second‐order Møller–Plesset perturbation calculation on Au2 and the density functional theory (DFT) calculation with the B3LYP functional on octahedral UF6, in which the highest symmetries used are, respectively, C and D. The four‐component B3LYP equilibrium geometry of UF6 is reported. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
908.
909.
A reactivity difference based on the position of substituents on cyclohexa-1,3- diene was observed for the title reaction. The effect of water as solvent was more distinct for 1-methyl-4-isopropylcyclohexa-1,3-diene than for 2-methyl-5-isopropylcyclohexa- 1,3-diene or non-substituted cyclohexa-1,3-diene. The effect of NaCl (salting-out) and guanidium chloride (salting-in) was also large for 1-methyl-4-isopropylcyclohexa-1,3- diene. 相似文献
910.
[chemical reaction: see text]. The stereocontrolled total synthesis of (-)-spirofungin A (1) and (+)-spirofungin B (2a), polyketide-type antibiotics having various antifungal activities, has been achieved employing the Weinreb amide 8, the alkyne 9, and the vinyl boronate 5 readily available from the common intermediate 10. The first synthesis proceeded with a longest linear sequence of 31 steps, affording (-)-1 and (+)-2a in 7.9% and 5.2% overall yields, respectively. 相似文献