全文获取类型
收费全文 | 1414篇 |
免费 | 53篇 |
国内免费 | 14篇 |
专业分类
化学 | 970篇 |
晶体学 | 11篇 |
力学 | 42篇 |
数学 | 266篇 |
物理学 | 192篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 46篇 |
2021年 | 55篇 |
2020年 | 26篇 |
2019年 | 30篇 |
2018年 | 29篇 |
2017年 | 20篇 |
2016年 | 58篇 |
2015年 | 46篇 |
2014年 | 56篇 |
2013年 | 91篇 |
2012年 | 95篇 |
2011年 | 115篇 |
2010年 | 44篇 |
2009年 | 52篇 |
2008年 | 85篇 |
2007年 | 94篇 |
2006年 | 79篇 |
2005年 | 61篇 |
2004年 | 52篇 |
2003年 | 58篇 |
2002年 | 34篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1974年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有1481条查询结果,搜索用时 15 毫秒
31.
32.
Alan R. Katritzky Subbu Perumal Wojciech Kuzmierkiewicz Ping Lue John V. Greenhill 《Helvetica chimica acta》1991,74(8):1924-1930
tert- Alkyl sulfides are conveniently prepared from α-(1H-benzotriazol-1-yl)alkyl sulfides by displacement of the 1H-benzotriazol-1-yl group with Grignard reagents. The 1-[α-(alkylthio)alkyl]- and 1-[α-(arylthio)alkyl]-1H-benzotriazole intermediates are easily available by several routes: (i) displacement of the halogen from appropriate halides by sodium salts of thiols, (ii) condensation of 1H-benzotriazole and thiols with carbonyl compounds, or (iii) lithiation of N-substituted 1H-benzotriazoles and subsequent treatment with electrophiles. 相似文献
33.
34.
A. Okruszek P. Guga Wojciech J. Stbc 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract It has been recently demonstrated in our laboratory CD that ribonucleoside cyclic 3′,5′-phosphorothioates react with epoxides to give as a major product corresponding cyclic 5′,3′-phosphates, We now report the results OF our ste-reochemical studies OF this reaction. WE have Found that the diastereomerically pure (Sp) 3′.5′-CUFLPS when treated with styrene [10O]-oxide in ethanol gives the same isotopomer OF 2′,3′-[10O]cUMP as that obtained From the reaction of endo-2′.3′-cUMPS with styrene [10O]-oxide. This result strongly supports our previous assumption that reaction of 3′,5′-cNMPS with epoxides proceeds via 3′-oxathiaphosphorylated intermediate (L) which is Formed with inversion and decomposes to 2′,3′-cNMP with retention of configuration at phosphorus atom. 相似文献
35.
Andrzej Okruszek Mandalena Olesiak Wojciech J. Stec 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Nucleoside 3′-0- and 5′-O-phosphorodithioates have been recently described by Caruthers et al.1 as a new type of nucleotide analogues. These compounds have also been obtained in our Laboratory by one-pot dithiaphospholane approach.2 We now report on the transformation of some of these derivatives into new class of dinucleotide analogues. We have found that nucleoside 3′-O-phosphorodithioates (1) react in DMF solution with 5′-bromo-5′-deoxythymidine to give in high yield corresponding dinucleoside (5′→3′)-O,S-phosphorodithioates (2) - first examples of a new class of dinucleotide analogues possessing the internucleotide phosphorothioate linkage with one of the sulfur atoms in a 3′-bridging position. 相似文献
36.
Agnes M Modro Tom A Modro P. Bernatowicz Wojciech Schilf Lech Stefaniak 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract A series of phosphoric amidodiesters, diamidoesters and triamides was prepared and their 31P and15 N NMR spectra were recorded in order to evaluate the major structural factors that determine the chemical shifts and coupling contants values. Considering the equation expressing the structural effects on shielding[1]. 相似文献
37.
Joanna Augustynowicz Anna M. Ko?ton Agnieszka M. Baran Anna M. Kostecka-Guga?a Wojciech W. Lasek 《Central European Journal of Chemistry》2013,11(2):295-303
The present work focused on the qualitative and quantitative analysis of Cr detoxification strategy of aquatic cosmopolitan plant Callitriche cophocarpa. This plant species has just been described in the context of its unusual accumulation potential of Cr. The emphasis of the work was placed on the redox reaction Cr(VI)→Cr(III) which is considered to be remediation mechanism of highly reactive and mobile Cr(VI) ions. Plants were immersed for 5 days in 1 mM of Cr(VI) (potassium dichromate) or 1 mM of Cr(III) (chromium sulphate) solutions in semi-natural conditions. Cr was effectively removed from the solution up to the extent of ca.58% or 35% of the starting amount, in the case of Cr(III) and Cr(VI), respectively. No plant-induced Cr(VI) reduction accompanying Cr accumulation was observed in Cr(VI) solutions except from the apparent one, noticed at the fourth day of incubation. On the contrary to these results, according to the method of electron paramagnetic resonance spectroscopy (L-band EPR), biphasic signal of Cr(V) attending Cr(VI) to Cr(III) reduction was detected inside the plant tissue every day of investigations. Our results show that phytoextraction but not phytostabilization is the main strategy of Cr detoxification by C. cophocarpa in aquatic systems. 相似文献
38.
Ireneusz W. Bulik Robert Zaleśny Wojciech Bartkowiak Josep M. Luis Bernard Kirtman Gustavo E. Scuseria Aggelos Avramopoulos Heribert Reis Manthos G. Papadopoulos 《Journal of computational chemistry》2013,34(20):1775-1784
A set of exchange‐correlation functionals, including BLYP, PBE0, B3LYP, BHandHLYP, CAM‐B3LYP, LC‐BLYP, and HSE, has been used to determine static and dynamic nonresonant (nuclear relaxation) vibrational (hyper)polarizabilities for a series of all‐trans polymethineimine (PMI) oligomers containing up to eight monomer units. These functionals are assessed against reference values obtained using the Møller–Plesset second‐order perturbation theory (MP2) and CCSD methods. For the smallest oligomer, CCSD(T) calculations confirm the choice of MP2 and CCSD as appropriate for assessing the density functionals. By and large, CAM‐B3LYP is the most successful, because it is best for the nuclear relaxation contribution to the static linear polarizability, intensity‐dependent refractive index second hyperpolarizability, static second hyperpolarizability, and is close to the best for the electro‐optical Pockels effect first hyperpolarizability. However, none of the functionals perform satisfactorily for all the vibrational (hyper)polarizabilities studied. In fact, in the case of electric field‐induced second harmonic generation all of them, as well as the Hartree–Fock approximation, yield the wrong sign. We have also found that the Pople 6–31+G(d) basis set is unreliable for computing nuclear relaxation (hyper)polarizabilities of PMI oligomers due to the spurious prediction of a nonplanar equilibrium geometry. © 2013 Wiley Periodicals, Inc. 相似文献
39.
ABSTRACT Among the known non-symmetrical naturally occurring aminotrehaloses possessing antimicrobial activity, the stereoselective synthesis of α, α-linked D-glucosaminyl-D-glucoside as well as of D-glucosaminyl-D-mannoside has been reported.1 In contrast, the synthesis of the α, β-isomer composed of two 2-amino sugar units occurring in tunicamycin antibiotics 1 has not been studied to the same extent and is not readily obtainable in pure form. 相似文献
40.
Zixin Huang Josie E. Auckett Peter E. R. Blanchard Brendan J. Kennedy Wojciech Miiller Qingdi Zhou Maxim Avdeev Mark R. Johnson Mohamed Zbiri Gaston Garbarino William G. Marshall Qinfen Gu Chris D. Ling 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(13):3482-3485
Pressure‐induced charge transfer from Bi to Ir/Ru is observed in the hexagonal perovskites Ba3+nBiM2+nO9+3n (n=0,1; M=Ir,Ru). These compounds show first‐order, circa 1 % volume contractions at room temperature above 5 GPa, which are due to the large reduction in the effective ionic radius of Bi when the 6s shell is emptied on oxidation, compared to the relatively negligible effect of reduction on the radii of Ir or Ru. They are the first such transitions involving 4d and 5d compounds, and they double the total number of cases known. Ab initio calculations suggest that magnetic interactions through very short (ca. 2.6 Å) M M bonds contribute to the finely balanced nature of their electronic states. 相似文献