全文获取类型
收费全文 | 3797篇 |
免费 | 190篇 |
国内免费 | 30篇 |
专业分类
化学 | 2745篇 |
晶体学 | 20篇 |
力学 | 197篇 |
数学 | 575篇 |
物理学 | 480篇 |
出版年
2023年 | 29篇 |
2022年 | 51篇 |
2021年 | 75篇 |
2020年 | 94篇 |
2019年 | 83篇 |
2018年 | 55篇 |
2017年 | 46篇 |
2016年 | 127篇 |
2015年 | 119篇 |
2014年 | 152篇 |
2013年 | 202篇 |
2012年 | 308篇 |
2011年 | 338篇 |
2010年 | 207篇 |
2009年 | 182篇 |
2008年 | 257篇 |
2007年 | 242篇 |
2006年 | 213篇 |
2005年 | 174篇 |
2004年 | 182篇 |
2003年 | 164篇 |
2002年 | 160篇 |
2001年 | 49篇 |
2000年 | 50篇 |
1999年 | 46篇 |
1998年 | 23篇 |
1997年 | 40篇 |
1996年 | 37篇 |
1995年 | 24篇 |
1994年 | 22篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1968年 | 15篇 |
1967年 | 12篇 |
排序方式: 共有4017条查询结果,搜索用时 15 毫秒
21.
Lionel Joucla Florence Popowycz Olivier Lozach Laurent Meijer Benoît Joseph 《Helvetica chimica acta》2007,90(4):753-763
The syntheses of paullone ( 1a ) and three paullone derivatives, including a sulfur analogue ( 2a ), a tricyclic derivative ( 2b ), and a ring‐enlarged variant ( 2c ), are described, Pd‐catalyzed intramolecular Heck reaction being the key step. The kinase‐inhibitory properties of the novel paullone analogues were investigated. 相似文献
22.
23.
Paolo Battocchio Francesco Menoncin Olivier Scaillet 《Annals of Operations Research》2007,152(1):141-165
In a financial market with one riskless asset and n risky assets whose prices are lognormal, we solve in a closed form the problem of a pension fund maximizing the expected
CRRA utility of its surplus till the (stochastic) death time of a representative agent. We consider a unique asset allocation
problem for both accumulation and decumulation phases. The optimal investment in the risky assets must decrease during the
first phase and increase during the second one. We accordingly suggest it is not optimal to manage the two phases separately,
and outsourcing of allocation decisions should be avoided in both phases.
JEL: G23, G11
MSC 2000: 62P05, 91B28, 91B30, 91B70, 93E20 相似文献
24.
S. Franchoo F. Ibrahim F. Le Blanc M. Lebois A. Olivier C. Phan Viet B. Roussière R. Sifi D. Verney 《Hyperfine Interactions》2006,171(1-3):117-119
The availability of both a tandem deuteron beam and a linac electron beam, the latter converted into Bremsstrahlung, at the
new ALTO facility at IPN-Orsay offers a unique opportunity to compare the performance of a laser ion guide under different
regimes. The ALTO accelerator has delivered its first electron beam at the end of 2005 and a design for a gas-cell prototype
is being studied. 相似文献
25.
26.
Michael Binnewies Marion Jerzembeck Andreas Kornick 《Angewandte Chemie (International ed. in English)》1991,30(7):745-753
One of the modern high technologies which has advanced enormously in the last few years is glass fiber technology. This is used in the manufacture of glass fibers for lighting purposes and for the optical transfer of analog and digital data with a high transfer density. The technical demands made on the glass fibers required for data transfer, the optical waveguides, are extremely high and are already fulfilled to a large extent by industry. At present about four million kilometers of fiber, worth ca. 800 million DM are produced worldwide (10% in the Federal Republic of Germany). Numerous chemical processes take place during the manufacture of optical waveguides. However, in contrast both to the high and constantly growing demands on the quality and to the increasing production volume of such fibers, little is in fact known about the reactions involved. The present article will attempt to develop a picture of the multifarious reactions occurring in the course of this technical process on the basis of literature data and our own studies. 相似文献
27.
N. Huppert Marion Würtele Hermann H. Hahn 《Analytical and bioanalytical chemistry》1998,362(6):529-536
A rapid, inexpensive and solvent-free method for the simultaneous determination of the polyamide plasticizer N-butylbenzenesulfonamide (NBBS) and the widely used pharmaceutical Ibuprofen by solid phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MSD) in wastewater samples was developed. Besides the optimized analytical conditions, results of investigations with varying analytical parameters are reported. Problems, which may occur during the analytical procedure (e.g. salt deposits, adsorption phenomena, carry-over), are discussed. For the determination of Ibuprofen, it is important to carry out the extraction under acidic conditions with sufficiently buffered samples; the GC/MSD system must be very clean and well maintained. SPME allows an extraction of Ibuprofen without derivatization of its carboxylic group. For quantification in complex matrices, the standard addition technique is necessary. Limit of detection and limit of determination are 0.1 μg/L for both analytes. NBBS and Ibuprofen were detected in several raw and treated wastewater samples from municipal wastewater treatment plants in the range from < 0.1 to 3.5 μg/L. 相似文献
28.
29.
Martinho M Banse F Bartoli JF Mattioli TA Battioni P Horner O Bourcier S Girerd JJ 《Inorganic chemistry》2005,44(25):9592-9596
The green complex S=1 [(TPEN)FeO]2+ [TPEN=N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine] has been obtained by treating the [(TPEN)Fe]2+ precursor with meta-chloroperoxybenzoic acid (m-CPBA). This high-valent complex belongs to the emerging family of synthetic models of Fe(IV)=O intermediates invoked during the catalytic cycle of biological systems. This complex exhibits spectroscopic characteristics that are similar to those of other models reported recently with a similar amine/pyridine environment. Thanks to its relative stability, vibrational data in solution have been obtained by Fourier transform infrared. A comparison of the Fe=O and Fe=(18)O wavenumbers reveals that the Fe-oxo vibration is not a pure one. The ability of the green complex to oxidize small organic molecules has been studied. Mixtures of oxygenated products derived from two- or four-electron oxidations are obtained. The reactivity of this [FeO]2+ complex is then not straightforward, and different mechanisms may be involved. 相似文献
30.
Omar El Tall Nicole Jaffrezic‐Renault Monique Sigaud Olivier Vittori 《Electroanalysis》2007,19(11):1152-1159
Boron‐doped Diamond (BDD) electrode has become one of the important tools for heavy metal detection. By studying some analytical parameters of DPASV method, like deposition time and potential in different electrolyte concentrations (acetate buffer), the conditions for detecting very low metal ion levels (Zn, Cd, Pb, and Cu) could be chosen. Diluted electrolyte (0.01 M buffer) was one of the factors favoring low detection and quantification limits, but its quantification range is short in comparison to more concentrated media. For ?1.7 V deposition potential, the detection of single metal at ppb levels was reached in 60 s deposition time. Understanding different metal‐metal interactions shows the limits to the simultaneous determination of heavy metals at BDD. Quantification was possible for the simultaneous determination of Zn, Cd and Pb despite the overlapping of Zn and Cd peaks. The performance of the BDD was compared with that of another C‐based solid electrode: the glassy carbon electrode (without mercury plating). A lower base line current, wider potential range, higher sensitivity (3 to 5 times higher than GC) and longevity of the material were noticed for the BDD. 相似文献