全文获取类型
收费全文 | 585篇 |
免费 | 44篇 |
专业分类
化学 | 445篇 |
晶体学 | 5篇 |
力学 | 26篇 |
数学 | 18篇 |
物理学 | 135篇 |
出版年
2023年 | 15篇 |
2022年 | 5篇 |
2021年 | 18篇 |
2020年 | 33篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 25篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 47篇 |
2012年 | 55篇 |
2011年 | 53篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 39篇 |
2007年 | 25篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 20篇 |
2003年 | 17篇 |
2002年 | 17篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有629条查询结果,搜索用时 15 毫秒
1.
2.
Summary The possible correlation between the self-attenuation correction in gamma-spectrometric assay of uranyl nitrate samples and
spectral line intensity ratios was investigated experimentally and simulated numerically using MCNP code. The characteristic
gamma- and X-lines of uranium were measured using a low energy Ge gamma-spectrometer. The simulation results agreed with the
experimental data and showed obvious correlation between the self-attenuation correction and the intensity ratios [(185.7
keV)/(143.8 keV), (98.44 keV)/(185.7 keV) and (185.7 keV)/(63.23 keV)]. This correlation greatly simplifies the determination
of the self-attenuation correction and reduces the troublesome traditional procedures used to determine this coefficient. 相似文献
3.
By means of exponential laws we show a Bianchi Type I model of the universe where we define overall deceleration and Hubble's parameters that have constant values. We employ a convenient relation for defining the radius of the universe. Pressure and density have constant values, too. 相似文献
4.
Suman Dhami Garry Rumbles Alexander J. MacRobert David Phillips 《Photochemistry and photobiology》1997,65(1):85-90
Abstract— The photophysical properties of cis -disulfonated aluminum phthalocyanine (AlPcS2 ) in unilamellar vesicles (liposomes) of DL-a-dipalmitoyl-phosphatidylcholine have been measured. Both the fluorescence and triplet quantum yields decreased with increasing sensitizer concentration. The time-resolved fluorescence decays, analyzed by both the sum of exponentials and decay time distribution analyses, are compared with those reported for AlPcS2 in leukemic K562 cells. Information on the pho-todynamic transport and localization mechanism has been obtained by drawing correlations between the two systems, indicating active transport of the phthalocyanine into tumor cells involving lysosomal accumulation. 相似文献
5.
6.
Suman L JainBir Sain 《Tetrahedron letters》2003,44(3):575-577
N-Iodo-N-potassio-p-toluenesulphonamide was found to be a convenient nitrene precursor for the aziridination of alkenes in the presence of copper catalysts. 相似文献
7.
K. V. Dinesha Suman B. Iyer Saraswathi Vishveshwara 《International journal of quantum chemistry》1986,30(6):783-790
The matrix elements of the spin-free Hamiltonian between two atomic configuration state functions (CSF 'S ) in the L–S coupling scheme are expressed in terms of the atomic integrals Fk's and Gk's. Using these general expressions, the matrix elements have been obtained for all the atomic configurations with three valence electrons that have not been solved so far by earlier methods. The scope for applying this new approach to obtain the Auger line energies and the promotion energies of metals that involve more than two partially filled shells is indicated. The energy expressions for some of the relevant configurations are tabulated. 相似文献
8.
An efficient construction of a 24-membered macrocyclic hexaoxazole derivative pertinent to the synthesis of analogues of the important natural product telomestatin was developed, which featured a convergent union of two trisoxazole units. 相似文献
9.
Samanta S Ghosh D Mukhopadhyay S Endo A Weakley TJ Chaudhury M 《Inorganic chemistry》2003,42(5):1508-1517
The tridentate dithiocarbazate-based Schiff base ligands H(2)L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocarbazate, R = NO(2), L = L(2); R = Br, L = L(3)) react with [VO(acac)(2)] in the presence of imidazole derivatives as coligands to form oxovanadium(IV) and cis-dioxovanadium(V) complexes. With benzimidazole and N-methylimidazole, the products are oxovanadium(IV) complexes, viz. [VOL(3)(BzIm)].0.5CH(3)CN (1a) and [VOL(N-MeIm)(2)] (L = L(3), 1b; L = L(2), 1c), respectively. In both 1a,b, the O and S donor atoms of the tridentate ligand are cis to the terminal oxo group (in the "equatorial" plane) and mutually trans, but the N donor atom is respectively cis and trans to the oxo atom, as revealed from X-ray crystallography. When imidazole or 4-methylimidazole is used as the ancillary ligand, the products obtained are water-soluble cis-dioxovanadium(V) complexes [VO(2)L(R'-ImH)] (L = L(3) and L(2), R' = H and Me, 2a-d). These compounds have zigzag chain structures in the solid state as confirmed by X-ray crystallographic investigations of 2a,d, involving an alternating array of LVO(2)(-) species and the imidazolium counterions held together by Coulombic interactions and strong hydrogen bonding. Complexes 2a-d are stable in water or methanol. In aprotic solvents, viz. CH(3)CN, DMF, or DMSO, however, they undergo photochemical transformation when exposed to visible light. The putative product is a mixed-oxidation divanadium(IV/V) species obtained by photoinduced reduction as established by EPR, electronic spectroscopy, and dynamic (1)H NMR experiments. 相似文献
10.
Summary The kinetics of the silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate (pdp) was studied in acetate buffers. The rate law as represented by-d[pdp]/dt = {(k
1
K
inf2
sup-1
[H+]2 + k
2[H+] + k
3
K
3)/ ([H+]2/K
2 + [H+] + K
3)}[pdp][Ag(I)] conforms to the proposed mechanism. The rate is independent of malonic acid concentrations. Acetate ions do not affect the rate; however, the rate decreases as the ionic strength increases. A probable portrait of reaction events is suggested. A comparative analysis of the reactivity pattern of malonic acid towards peroxodiphosphate and peroxodisulphate in presence of silver(I) has been made. 相似文献