全文获取类型
收费全文 | 3628篇 |
免费 | 97篇 |
国内免费 | 2篇 |
专业分类
化学 | 2370篇 |
晶体学 | 39篇 |
力学 | 73篇 |
数学 | 263篇 |
物理学 | 982篇 |
出版年
2023年 | 37篇 |
2022年 | 63篇 |
2021年 | 60篇 |
2020年 | 89篇 |
2019年 | 103篇 |
2018年 | 70篇 |
2017年 | 58篇 |
2016年 | 126篇 |
2015年 | 74篇 |
2014年 | 123篇 |
2013年 | 237篇 |
2012年 | 232篇 |
2011年 | 288篇 |
2010年 | 174篇 |
2009年 | 146篇 |
2008年 | 214篇 |
2007年 | 181篇 |
2006年 | 161篇 |
2005年 | 140篇 |
2004年 | 110篇 |
2003年 | 75篇 |
2002年 | 83篇 |
2001年 | 62篇 |
2000年 | 58篇 |
1999年 | 53篇 |
1998年 | 30篇 |
1997年 | 23篇 |
1996年 | 38篇 |
1995年 | 29篇 |
1994年 | 35篇 |
1993年 | 43篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 30篇 |
1980年 | 19篇 |
1979年 | 27篇 |
1978年 | 16篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 11篇 |
1957年 | 13篇 |
排序方式: 共有3727条查询结果,搜索用时 15 毫秒
911.
The synthesis, electrochemical, optical, and metal-cation-sensing properties of ferrocene-glycine conjugates C(30)H(38)O(8)N(8)Fe (2) and C(20)H(24)O(4)N(4)Fe (3) have been documented. Both compounds 2 and 3 behave as very selective redox (ΔE(1/2) = 217 mV for 2 and ΔE(1/2) = 160 mV for 3), chromogenic, and fluorescent chemosensors for Hg(2+) cations in an aqueous environment. The considerable changes in their absorption spectra are accompanied by the appearance of a new low-energy peak at 630 nm (2, ε = 1600 M(-1) cm(-1); 3, ε = 822 M(-1) cm(-1)). This is also accompanied by a strong color change from yellow to purple, which allows a prospective for the "naked eye" detection of Hg(2+) cations. These chemosensors present immense brightness and fluorescence enhancement (chelation-enhanced fluorescence = 91 for 2 and 42 for 3) following Hg(2+) coordination within the limit of detection for Hg(2+) at 7.5 parts per billion. 相似文献
912.
Nanocrystallites of cadmium oxide (CdO) thin films were deposited by sol–gel dip coating technique on glass and Si substrates. XRD and TEM diffraction patterns confirmed the nanocrystalline cubic CdO phase formation. TEM micrograph of the film revealed the manifestation of nano CdO phase with average particle size lying in the range 1.6–9.3 nm. UV–Vis spectrophotometric measurement showed high transparency (nearly 75% in the wavelength range 500–800 nm) of the film with a direct allowed bandgap lying in the range 2.86–3.69 eV. Particle size has also been calculated from the shift of bandgap with that of bulk value for the films for which the particles sizes are comparable to Bohr exitonic radius. The particle size increases with the increase in annealing temperature and also the intensity of XRD peaks increases which implies that better crystallinity takes place at higher temperature. 相似文献
913.
Tejas Patel Goutam Ghosh Vinod Aswal Pratap Bahadur 《Colloid and polymer science》2009,287(10):1175-1181
The effect of polyoxyethylene type nonionic surfactants (C12E
n
n = 3, 4, 5, 6, 7 and 8) on the aqueous solution of sodium dodecyl sulfate (SDS) in absence and presence of NaCl was examined
using small-angle neutron scattering (SANS), dynamic light scattering (DLS), and viscosity measurements. Upon addition of
C12E
n
, micellar size of SDS was found to increase significantly, and such micellar elongation was further enhanced in the presence
of NaCl. Micellar growth is most significant in presence of shorter moieties of C12E
n
(e.g., n = 3, 4) as compared to higher ethereal oxygen content. The results of structural investigations with SANS and DLS to confirm
this assumption are reported. The cloud point of C12E
n
has increased upon addition of SDS and decrease with NaCl, and a typical behavior is observed when both SDS and NaCl were
present. 相似文献
914.
We investigate resonant nonlinear optical interactions and demonstrate induced transparency in acetylene molecules in a hollow-core photonic-band-gap fiber at 1.5 mum. The induced spectral transmission window is used to demonstrate slow-light effects, and we show that the observed broadening of the spectral features is due to collisions of the molecules with the inner walls of the fiber core. Our results illustrate that such fibers can be used to facilitate strong coherent light-matter interactions even when the optical response of the individual molecules is weak. 相似文献
915.
A non-linear variation of bandgap energy with Co doping is observed in sputter deposited Co-doped TiO2 thin films. This peculiar behavior is explained on the basis of mechanical stress in the films together with spin polarization due to s,p-d exchange interaction between the localized Co 3d electrons and delocalized electrons. Quantitative analyses of mechanical stress and grain boundary barrier potential due to spin polarization are performed from the below bandgap absorption tail. Furthermore, anomalous variations in both the refractive indices and extinction coefficients with Co doping are noted and are explained on the basis of ab-initio calculations based on density functional theory. 相似文献
916.
T. Mukherjee S. Sur A. S. Ghosh 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1988,9(2):147-151
It is demonstrated that time resolved laser spectroscopy can give atomic lifetime data with an accuracy of better than 0.5%. This is achieved by a single-photon counting delayed coincidence technique, using a mode-locked dye laser for the excitation. Natural radiative lifetimes are measured for the sodium and bismuth atoms. 相似文献
917.
918.
The life-time of the first excited member of the ground-state band in101Zr has been determined to 0.9(3) ns through the measurement of γ-γ-delayed coincidences with Ge detectors at the fission-product separator JOSEF. The result shows that this nucleus is strongly deformed with |ß|=0.32(6). This finding provides further important evidence for the fact that the odd-mass nuclei at A ~ 100 with more than 59 neutrons are good rotors. 相似文献
919.
Sarkar R Ghosh M Shaw AK Pal SK 《Journal of photochemistry and photobiology. B, Biology》2005,79(1):67-78
In this contribution we report studies on enzymatic activity of alpha-chymotrypsin (CHT) upon complexation with cationic cetyltrimethylammonium bromide (CTAB) micelle. With picosecond time resolution, we examined solvation dynamics at the interface of CHT-micelle complex, and rigidity of the binding. We have used 5-(dimethyl amino) naphthalene-1-sulfonyl chloride (dansyl chloride; DC) that is covalently attached to the enzyme at the surface sites. The solvation processes at the surface of CHT in buffer solution are found to be mostly in the sub-50 ps time scale. However, at the interface the solvation correlation function decays with time constant 150 ps (65%) and 500 ps (35%), which is significantly different from those found at the enzyme and micellar surfaces. The binding structure of the enzyme-micelle complex was examined by local orientational motion of the probe DC and compared with the case without micelle. The orientational dynamics of the probe DC in the complex reveals a structural perturbation at the surface sites of CHT upon complexation, consistent with other reported structural studies. We also found possible entanglement of charge transfer dynamics of the probe DC on the measured solvation processes by using time-resolved area normalized emission spectroscopic technique. The interfacial solvation process and complex rigidity elucidate the strong recognition mechanism between CHT and the micelle, which is important to understand the biological function of CHT upon complexation with the micelle. 相似文献
920.
By employing the coupling reaction of trans-PtI2(Et3)2 with C-H bonds in alkynes as the key step, two new 60 degrees organometallic subunits with different size from 3,6-dibromophenanthrene were prepared in reasonable yields. The X-ray structures of both di-Pt(II) diiodide complexes showed that they were indeed suitable candidates for 60 degrees building units. By utilizing these novel linkers as ditopic acceptor subunits, three M3L2 trigonal-bipyramidal (TBP) cages were formed. All three TBP cages were characterized with multinuclear NMR and electrospray ionization mass spectrometry (ESI-MS) along with element analysis. 相似文献