全文获取类型
收费全文 | 34759篇 |
免费 | 620篇 |
国内免费 | 136篇 |
专业分类
化学 | 19562篇 |
晶体学 | 237篇 |
力学 | 1109篇 |
综合类 | 9篇 |
数学 | 5061篇 |
物理学 | 9537篇 |
出版年
2022年 | 412篇 |
2021年 | 508篇 |
2020年 | 499篇 |
2019年 | 457篇 |
2018年 | 530篇 |
2017年 | 469篇 |
2016年 | 809篇 |
2015年 | 685篇 |
2014年 | 765篇 |
2013年 | 1536篇 |
2012年 | 1589篇 |
2011年 | 1874篇 |
2010年 | 1090篇 |
2009年 | 1015篇 |
2008年 | 1582篇 |
2007年 | 1524篇 |
2006年 | 1411篇 |
2005年 | 1793篇 |
2004年 | 1850篇 |
2003年 | 1333篇 |
2002年 | 975篇 |
2001年 | 776篇 |
2000年 | 728篇 |
1999年 | 483篇 |
1998年 | 400篇 |
1997年 | 411篇 |
1996年 | 509篇 |
1995年 | 426篇 |
1994年 | 420篇 |
1993年 | 470篇 |
1992年 | 463篇 |
1991年 | 411篇 |
1990年 | 321篇 |
1989年 | 307篇 |
1988年 | 307篇 |
1987年 | 354篇 |
1986年 | 320篇 |
1985年 | 415篇 |
1984年 | 391篇 |
1983年 | 323篇 |
1982年 | 348篇 |
1981年 | 352篇 |
1980年 | 333篇 |
1979年 | 312篇 |
1978年 | 326篇 |
1977年 | 287篇 |
1976年 | 264篇 |
1975年 | 267篇 |
1974年 | 251篇 |
1973年 | 243篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Vilas-Boas M Freire C de Castro B Christensen PA Hillman AR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(1):139-150
Electrogenerated polymers based on the nickel(II) complex 2,3-dimethyl-N,N'-bis(salicylidene)butane-2,3-diaminatonickel(II), poly[Ni(saltMe)], were characterised by in situ FTIR and UV/Vis spectroscopy and ex-situ EPR spectroscopy in order to gain insights into film structure, electronic states and charge conduction. The role of the nickel ions during film oxidation was probed by using EPR to study naturally abundant Ni and 61Ni-enriched polymers. The data from all the spectroscopic techniques are consistent, and clearly indicate that polymerisation and redox switching are associated with oxidative ligand based processes; coulometry suggests that one positive charge was delocalised through each monomer unit. EPR provided evidence for the non-direct involvement of the metal in polymer oxidation: the polymer is best described as a polyphenylene-type compound (conducting polymer), rather than an aggregation of nickel complexes (redox polymer), and the main charge carriers are identified as polarons. An explanation for the high electrochemical stability and conductivity of poly[Ni(saltMe)] with respect to that of poly[Ni(salen)] is proposed. based on stereochemical repulsion between monomeric units; this can impose a less compact supramolecular structure on polymers with bulkier substituents. 相似文献
102.
The molecular structures of tricyclohexane, norbornane, quadricyclane, and cubane were completely refined by standard ab initio force relaxation on the 4-21G level. The results can be used as a basis to interpret some contradictory experimental reports found in the literature and to establish some hitherto unobserved structural trends involving the C? C and C? H bond distances of the cases studied. Group Delta;E values for C? (H)3(C), C? (H)2(C)2, and C? (H)(C)3 (Benson's notation) derived from the total energies of the completely relaxed 4-21G geometries of a number of unstrained hydrocarbons are also listed. The values are used to estimate the strain energies of the systems studied and of the optimized 4-21G geometries of cyclopropane, cyclobutane, cyclohexane, and bicyclo (2.1.0)pentane. Cooperative effects in the strain energies are discussed. 相似文献
103.
J. Langelaar M.W. Leeuw J.D.W.Van Voorst R.P.H. Rettschnick 《Chemical physics letters》1979,62(1):14-18
S2 and S1 fluorescence of chrysene and 3,4 benzophenanthrene has been observed in the vapour phase under collision free conditions. It is shown that the intermediate strong couplinng model can be applied to these molecules. The efficiency of the transfer of the excess energy to collision partners is given for different gases. 相似文献
104.
P. Van Leuven 《International journal of quantum chemistry》1970,4(4):355-363
A method for the approximate calculation of matrix elements with respect to projected Hartree–Fock wave functions is proposed. The method is tested on some calculations in the many-parameter AMO method. It is found that the approximation reduces the amount of work, involved in the evaluation of the energy, by a factor of five and that it reproduces the exact values to within a few per cent. 相似文献
105.
In order to check if the parametrized crystal field approach is efficient in the analysis of an EPR powder spectrum we study defects of known geometry as if we did not know it. The g tensor of an interstitial V4+ ion in a single crystal of rutile TiO2 can be interpreted without ambiguity, and the optimized parameters compare well with their theoretical values. For an interstitial Ti3+ ion, two solutions are found: both of them correspond to interstitial positions, but they differ in the principal axis orientation. 相似文献
106.
A simple, quick and inexpensive screening method for cocaine and cocaine metabolites has been developed. Drug extraction was achieved using the relatively new technique of solvent microextraction (SME). Complete analysis is achieved in 13 min, using, a 6-min extraction with a 2-microl drop followed by separation on a gas chromatograph. The developed procedure was tested as a screening method for cocaine and cocaine metabolites in spiked urine samples. Using SME, concentrations as low as 0.125 microg ml(-1) of cocaine, ecgonine methyl ester, cocaethylene and anhydroecgonine methyl ester were measurable with relative standard deviation values averaging 9.0%. 相似文献
107.
108.
S. Garrigues F. J. Rambla M. de la Guardia 《Analytical and bioanalytical chemistry》1998,362(1):137-140
A comparative study has been carried out between a horizontal Attenuated Total Reflectance (h-ATR) cell and a Cylindrical Internal Reflection (CIR) cell (CIRCLE cell). Both cells were employed for the determination of glucose, fructose, sucrose and total sugar in soft drinks and fruit juices using absorbance measurements at two resolution values (4 and 8 cm–1). Data were processed by Partial Least Squares regression (PLS). Using a resolution of 4 cm–1, mean relative errors of prediction from 0.6% to 1.3% were obtained using the horizontal-ATR and from 0.6% to 2.8% using the CIRCLE cell resulting in a limit of detection from 0.03% in the case of sucrose to 0.21% for total sugar for the h-ATR and from 0.06% for sucrose to 0.13% for glucose using the CIRCLE cell. Both cells provided appropriate figures of merit, but the analytical sensitivity obtained using the h-ATR cell was three times higher than that obtained using the CIRCLE cell. 相似文献
109.
110.
U R Tjaden J P Langenberg K Ensing W P van Bennekom E A de Bruijn A T van Oosterom 《Journal of chromatography. A》1982,232(2):355-367
The performance of a number of normal phase and reversed-phase systems, with ultraviolet detection at 360 nm, has been investigated with respect to their applicability to pharmacokinetic studies of mitomycin C (MMC). The reversed-phase system developed was also combined with a polarographic detector in order to compare the sensitivity and selectivity of ultraviolet and electrochemical detection. A simple isolation procedure, based on the adsorption of MMC on a non-ionogenic resin, has been developed. The developed assay is applied to a pharmacokinetic study from which some examples are given. 相似文献