全文获取类型
收费全文 | 2917篇 |
免费 | 108篇 |
国内免费 | 13篇 |
专业分类
化学 | 2153篇 |
晶体学 | 8篇 |
力学 | 32篇 |
数学 | 433篇 |
物理学 | 412篇 |
出版年
2022年 | 23篇 |
2021年 | 22篇 |
2020年 | 52篇 |
2019年 | 45篇 |
2018年 | 24篇 |
2016年 | 76篇 |
2015年 | 72篇 |
2014年 | 82篇 |
2013年 | 104篇 |
2012年 | 141篇 |
2011年 | 154篇 |
2010年 | 101篇 |
2009年 | 69篇 |
2008年 | 114篇 |
2007年 | 152篇 |
2006年 | 150篇 |
2005年 | 140篇 |
2004年 | 90篇 |
2003年 | 83篇 |
2002年 | 96篇 |
2001年 | 62篇 |
2000年 | 45篇 |
1999年 | 47篇 |
1998年 | 42篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 42篇 |
1994年 | 41篇 |
1993年 | 32篇 |
1992年 | 48篇 |
1991年 | 29篇 |
1990年 | 25篇 |
1989年 | 31篇 |
1988年 | 42篇 |
1987年 | 41篇 |
1986年 | 33篇 |
1985年 | 45篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 29篇 |
1980年 | 35篇 |
1979年 | 23篇 |
1978年 | 30篇 |
1977年 | 23篇 |
1976年 | 29篇 |
1975年 | 34篇 |
1974年 | 36篇 |
1973年 | 34篇 |
1971年 | 21篇 |
排序方式: 共有3038条查询结果,搜索用时 15 毫秒
91.
Harald Høiland 《Journal of solution chemistry》1977,6(5):291-297
The isentropic coefficients of compressibility of the homologous series of alcohols and diols R
n
CH2OH (n=2–6), CH3CHOHR
n
(n=1–5), 1,2-propanediol, 1,3- 1,4- and 2,3-butanediol, 1,5-pentanediol, and 1,7-heptanediol dissolved in propylene carbonate have been measured at 25°C. Isentropic partial molal compressibilities and group partial molal compressibilities at infinite dilution have been evaluated. The isentropic partial molal compressibilities of these alcohols and diols have been compared with the corresponding values in water. This comparison shows that the values in propylene carbonate are higher than in water by a factor of 10 due to an increased compressibility of the solvation sheath around nonpolar groups in PC. 相似文献
92.
We have examined two-dimensional electrophoresis (2-DE) gel maps of polypeptides from the Gram-negative bacterium Methylococcus capsulatus (Bath) and found the same widespread trains of spots as often reported in 2-DE gels of polypeptides of other Gram-negative bacteria. Some of the trains of polypeptides, both from the outer membrane and soluble protein fraction, were shown to be generated during the separation procedure of 2-DE, and not by covalent post-translational modifications. The trains were found to be regenerated when rerunning individual polypeptide spots. The polypeptides analysed giving this type of trains were all found to be classified as stable polypeptides according to the instability index of Guruprasad et al. (Protein Eng. 1990, 4, 155-161). The phenomenon most likely reflects conformational equilibria of polypeptides arising from the experimental conditions used, and is a clear drawback of the standard 2-DE procedure, making the gel picture unnecessarily complex to analyse. 相似文献
93.
Müller U Rätzsch M Schwanninger M Steiner M Zöbl H 《Journal of photochemistry and photobiology. B, Biology》2003,69(2):97-105
The yellowing and IR-changes of spruce wood as a result of UV-irradiation were studied using two different types of xenon lamps (lambda>300 nm; I(o)=50 mW cm(-2) and lambda>280 nm; I(o)=17.5 mW cm(-2)). Changes in the IR spectra as well as the yellowing of the irradiated wood surfaces show the influence of UV light on the wood modules. The UV-irradiation (72 h; lambda>300 nm; I(o)=50 mW cm(-2)) decreased the lignin content on the surface by up to 20% of the original values. The colour difference of yellowing (deltaE) exhibited a systematic trend to higher values with increasing irradiation time. Our results show that the photoyellowing (UV-Vis detection) correlates very well with lignin degradation (IR detection). This result is in agreement with the quinone formation as the chromophoric reaction product of lignin decay. The degradation, yellowing, and oxidation kinetics differed only little using different light sources. The absorbed light intensity, which depends on wavelength, the intensity distribution of the light source and the absorption spectrum of lignin, influenced the degradation rate. Under the current experimental conditions, the absorption spectrum of lignin was the most important factor. Therefore, irradiation with lambda>280 nm is useful for rapidly monitoring the UV-degradation of wood 相似文献
94.
95.
Emission and absorption polarization spectra as well as emission lifetimes between room temperature and 5 °K have been measured of [Cr urea6]X3 single crystals, where X stands for ClO
4
–
, J–, NO
3
–
, Br–, Cl–, F–, and X3 for JSO
4
3–
. The strong temperature dependence of the fluorescence/phosphorescence-ratios, and of the emission lifetimes is discussed. The differences between the spectra as well as the emission lifetimes of the various salts can be attributed to an anion dependent trigonal perturbation.
Die Autoren danken dem Verband der Chemischen Industrie für finanzielle Unterstützung dieser Arbeit. 相似文献
96.
The partial molar isentropic pressure coefficients at infinite dilution, K
S,2
o
, have been determined for a number of dipeptides in aqueous solution at 25°C. For a series of dipeptides of sequence gly-X, where X is an amino acid with a neutral side chain, the K
S,2
o
values are all more negative than that for diglycine. The results are discussed in terms of the hydration of the side chains. There are significant differences in the K
S,2
o
values for sequence isomeric dipeptides. These differences can be rationalized in terms of the mutual interactions between the side chain and the ionic end groups in the dipeptides. Possible relationships between K
S,2
o
and V
2
o
, the partial molar volume at infinite dilution, were investigated. For the dipeptides of sequence gly-X there is an interesting linear relationship between K
S,2
o
/V
2
o
and V
2
o
. 相似文献
97.
M. Hampl J. Leitner K. Růžička M. Straka P. Svoboda 《Journal of Thermal Analysis and Calorimetry》2007,87(2):553-556
The heat capacity and the heat content of
bismuth niobate BiNb5O14 were
measured by the relaxation time method, DSC and drop method, respectively.
The temperature dependence of heat capacity in the form C
pm=455.84+0.06016T–7.7342·106/T
2 (J K–1
mol–1) was derived by the least squares method
from the experimental data. Furthermore, the standard molar entropy at 298.15
K S
m=397.17 J K–1
mol–1 was derived from the low temperature
heat capacity measurement. 相似文献
98.
Harald Luschgy 《Probability Theory and Related Fields》1992,93(1):39-66
Summary Let
(Q) be the statistical experiment based on the observation of an unknown function in the presence of an additive noise process with distributionQ. The (possible) loss of information whenQ is replaced by some other noise distributionP is measured by the deficiency of
(P) relative to
(Q). This deficiency and its relation to the variational distance ofP andQ are studied mainly for Gaussian noise processes. Gaussian diffusion processes and special set-indexed processes are treated in detail.Research supported by a Heisenberg grant of the Deutsche Forschungsgemeinschaft 相似文献
99.
Wack H France S Hafez AM Drury WJ Weatherwax A Lectka T 《The Journal of organic chemistry》2004,69(13):4531-4533
We detail the synthesis of a new C(2)-symmetric bis(cyclophane) ligand system that can be thought of as electronically analogous to binol, but which possesses the added "third dimension" of cyclophane chirality. The ligand synthesis involves a spontaneous (but unexpected) atropisomerization to the desired product. We have employed this ligand to form a metal complex that is an effective cocatalyst for the highly enantio- and diastereoselective catalytic asymmetric synthesis of a beta-lactam. 相似文献
100.
Oxidefluorides of Niobium and Tantalum The reaction of NbF5 with SiO2 (silica glass ampules) at 310°C or with SiO2 (Aerosil) at 180°C always leads to NbO2F. To the contrary the reaction with laboratory glass (Jenaer Geräteglas) at 130°C leads to NbOF3. TaF5 reacts in silica glass ampules at 400°C by formation of TaO2F, however at 300°C or 260°C by formation of TaOF3. Silica glass did not react with NbF5 at 130°C, however Nb2O5 and NbF5 gave at 130°C in silica glass ampoules NbOF3. Similarly, TaF5 and Ta2O5 or TaO2F formed at 260°C in nickel ampoules TaOF3. The chemical and the thermochemical behaviour of oxidefluorides have been investigated. The compounds NbOF3 and TaOF3 are isomorphic. Lattice constants are mentioned. 相似文献