全文获取类型
收费全文 | 2592篇 |
免费 | 48篇 |
国内免费 | 5篇 |
专业分类
化学 | 1664篇 |
晶体学 | 10篇 |
力学 | 25篇 |
数学 | 501篇 |
物理学 | 445篇 |
出版年
2020年 | 27篇 |
2019年 | 27篇 |
2016年 | 39篇 |
2015年 | 23篇 |
2014年 | 38篇 |
2013年 | 78篇 |
2012年 | 54篇 |
2011年 | 78篇 |
2010年 | 58篇 |
2009年 | 42篇 |
2008年 | 68篇 |
2007年 | 74篇 |
2006年 | 55篇 |
2005年 | 90篇 |
2004年 | 72篇 |
2003年 | 52篇 |
2002年 | 35篇 |
2001年 | 37篇 |
2000年 | 39篇 |
1999年 | 36篇 |
1998年 | 22篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 35篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 36篇 |
1990年 | 21篇 |
1989年 | 30篇 |
1988年 | 28篇 |
1987年 | 32篇 |
1986年 | 40篇 |
1985年 | 40篇 |
1984年 | 39篇 |
1983年 | 36篇 |
1982年 | 45篇 |
1981年 | 50篇 |
1980年 | 44篇 |
1979年 | 32篇 |
1978年 | 45篇 |
1977年 | 40篇 |
1976年 | 34篇 |
1975年 | 25篇 |
1974年 | 32篇 |
1973年 | 24篇 |
1972年 | 28篇 |
1971年 | 34篇 |
1970年 | 29篇 |
1968年 | 22篇 |
1967年 | 37篇 |
排序方式: 共有2645条查询结果,搜索用时 15 毫秒
21.
M. Grexa G. Hermann G. Lasnitschka A. Scharmann 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,2(2):157-158
The hyperfine splittings and isotope shifts of n2PJ-levels in203,205Tl have been measured by high resolution two-photon spectroscopy with a cw dye-laser and an actively stabilized marker cavity for laser frequency scancalibration. 相似文献
22.
23.
Barbara Dogan Hans-Dieter Beckhaus Hermann Birkhofer Christoph Rüchardt 《欧洲无机化学杂志》1990,123(6):1365-1368
Effects of Substituents on the Strength of C - C Bonds, 81. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L .-1,2-Dimethyl-l,2-diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol -1, s. d. in parentheses) ΔH°c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 ΔHv = 14.3 (± 0.3) and the heat of sublimation of 2 ΔHsub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation ΔH°t(g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy (s) of 15.9 and 8.0 kcal mol-1, respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group. 相似文献
24.
Rudovsky J Hermann P Botta M Aime S Lukes I 《Chemical communications (Cambridge, England)》2005,(18):2390-2392
A marked increase of relaxivity has been observed upon rigidifying the internal frame of Gd-containing PAMAM dendrimers: the effect has been attained by either protonation of the dendrimer or by forming supramolecular adducts with cationic polyaminoacids. 相似文献
25.
Hermann M. Niemeyer 《Tetrahedron》1978,34(18):2757-2762
Chelates formed by carbocations and cyclic polyethers and polyamines are studied with semiempirical and ab initio MO methods. 相似文献
26.
Study of the development of thermoresistance in human pancreatic carcinoma cell lines using proteome analysis 总被引:3,自引:0,他引:3
In order to find candidate proteins that are potentially associated with the thermoresistant phenotype in combination with drug resistance, we analyzed the differential protein expression in vitro in the human pancreatic cancer cell line EPP85-181-P and classical and atypical multidrug-resistant variants and their thermoresistant counterparts using proteomics. This study identifies sets of proteins that may lead to the development of thermoresistance. These results provide a fundamental basis to elucidate the molecular mechanism of thermoresistance and chemoresistance phenomena that may assist the therapy of inoperable cancers. 相似文献
27.
Carnitine in Pregnancy 总被引:1,自引:0,他引:1
Alfred?LohningerEmail author H.?Karlic S.?Lohninger A.?Tammaa S.?Jinniate Hermann?Mascher Daniel?Mascher H.?Salzer 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1523-1533
Summary. By the 12th week of gestation, mean whole blood and plasma carnitine levels are already significantly (p<0.01) lower than those of controls, with a further significant (p<0.01) decrease up to parturition. Diminished carnitine levels may cause a downregulation of carnitine palmitoyltransferase1 (CPT1), both the liver isoform (CPT1A) and muscle isoform (CPT1B), carnitine palmitoyltransferase2 (CPT2), and carnitine acetyltransferase (CRAT) in white blood cells of pregnant women, as determined by real time PCR using the LightCyclerSYBR Green technology.L-Carnitine-L-tartrate supplementation of 2 g/d resulted in an up to 10-fold increase of the relative mRNA abundances of CPT1B, CPT2, and OCTN2 and a 5-fold increase of CPT1A, and CRAT.There is a relationship between the relative mRNA levels of CPT1A and CPT1B and the FFA plasma levels. The substitution of 2 g L-carnitine-L-tartrate/d resulted in significant (p<0.001) lower FFA levels compared to untreated controls and the groups substituted with 0.5 and 1 g L-carnitine/d although plasma carnitine levels were not significantly increased. The most substantial effect was the reduced portion of acylcarnitines on total carnitine in those women receiving 2 g L-carnitine-L-tartrate.Carnitine substitution resulted in an enhanced excretion of both, free carnitine and acylcarnitines, whereas acetylcarnitine accounts for 50–65% of total acylcarnitines.The results of the present study provide evidence that L-carnitine supplementation in pregnancy in sufficient doses avoids a striking increase of plasma FFAs, which are thought to be the main cause of insulin resistance and consequently gestational diabetes mellitus (GDM). 相似文献
28.
Hermann M. Niemeyer 《Tetrahedron》1979,35(10):1297-1299
The performance of ab initio STO-3G and CNDO/2 molecular orbital methods in the calculation of properties of polynitromethanes is studied. 相似文献
29.
Wójcik A Naumov S Marciniak B Hermann R Brede O 《The journal of physical chemistry. B》2005,109(31):15135-15144
Addition and elimination interaction of thiyl radicals with the C5-C6 double bond in pyrimidines was studied by the pulse radiolysis technique in aqueous solution with the use of different monitoring systems. For this purpose, p-thiocresol, cysteamine hydrochloride, and mercaptoethanol were used. The rate constants of addition and elimination of thiyl radicals were determined by applying the modified version of ACUCHEM (computer program for modeling complex reaction systems). Aliphatic thiyl radicals add to the pyrimidine C5-C6 double bond with k = 1.0-3.0 x 10(7) dm3 mol(-1) s(-1), whereas elimination takes place with k = 0.7-2.0 x 10(5) s(-1). Quantum chemical calculations at the B3LYP/6-31G(d)/PCM level show that the addition should occur at the C6 position of the pyrimidine ring and that the energy of interaction between thiyl radicals and the pyrimidine double bond C5-C6 is low. 相似文献
30.
The bimolecular electron transfer from secondary aromatic amines to parent radical cations of nonpolar solvents such as alkanes and alkyl chlorides results in the synchronous formation of amine radical cations as well as aminyl radicals, in comparable amounts. If as for cyclic aromatic amines (c-Ar(2)NH) the intramolecular bending motion around the amine group is restricted in varying degrees (acridane, phenothiazine) or completely prevented (carbazole), then this picture is modified. In the free electron transfer, the completely rigid carbazole yields exclusively amine radical cations. Acridane exhibits preferred radical cations, but phenothiazine with the more flexible six-membered ring involving sulfur as a further heteroatom follows the common two-product rule; see above. The phenomenon is reasoned by a peculiarity in the bimolecular free electron transfer where after diffusional approach the actual electron jump proceeds in the ultrashort time range. Therefore, it reflects femtosecond molecular motions which, in the case of free mobility, continuously pass through different molecule conformers, combined with fluctuation of the electrons of the responsible molecular n-orbitals. The rigid systems, however, do not show this effect because of a nonexistent bending motion. 相似文献