全文获取类型
收费全文 | 491393篇 |
免费 | 5275篇 |
国内免费 | 1779篇 |
专业分类
化学 | 259815篇 |
晶体学 | 7495篇 |
力学 | 21790篇 |
综合类 | 8篇 |
数学 | 58520篇 |
物理学 | 150819篇 |
出版年
2020年 | 3488篇 |
2019年 | 3726篇 |
2018年 | 4410篇 |
2017年 | 4232篇 |
2016年 | 7192篇 |
2015年 | 5180篇 |
2014年 | 7759篇 |
2013年 | 21841篇 |
2012年 | 16495篇 |
2011年 | 20416篇 |
2010年 | 13530篇 |
2009年 | 13437篇 |
2008年 | 18788篇 |
2007年 | 19023篇 |
2006年 | 18249篇 |
2005年 | 16538篇 |
2004年 | 15039篇 |
2003年 | 13334篇 |
2002年 | 13164篇 |
2001年 | 14832篇 |
2000年 | 11374篇 |
1999年 | 9119篇 |
1998年 | 7491篇 |
1997年 | 7346篇 |
1996年 | 7221篇 |
1995年 | 6580篇 |
1994年 | 6323篇 |
1993年 | 6250篇 |
1992年 | 6735篇 |
1991年 | 6740篇 |
1990年 | 6298篇 |
1989年 | 6097篇 |
1988年 | 6443篇 |
1987年 | 6012篇 |
1986年 | 5746篇 |
1985年 | 8134篇 |
1984年 | 8319篇 |
1983年 | 6855篇 |
1982年 | 7267篇 |
1981年 | 7227篇 |
1980年 | 6913篇 |
1979年 | 7195篇 |
1978年 | 7240篇 |
1977年 | 7203篇 |
1976年 | 7189篇 |
1975年 | 6864篇 |
1974年 | 6781篇 |
1973年 | 6953篇 |
1972年 | 4443篇 |
1971年 | 3487篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
R. Suntz H. Becker P. Monkhouse J. Wolfrum 《Applied physics. B, Lasers and optics》1988,47(4):287-293
Two-dimensional laser-induced fluorescence (2D-LIF) imaging of OH radicals, excited at 308 nm, has been employed to visualize the flame front in an internal combustion engine burning air/propane mixtures. Light sheet thicknesses down to 70 m have been attained for excitation. Hydroxyl radicals were detected up to pressures of 7.5 bar at engine speeds of 500 rpm. An upper limit of 300 m for the flame front thickness was obtained from line intensity profiles. 相似文献
992.
L. Käubler W. Enghardt H. Prade P. Carlé L. O. Norlin K. -G. Rensfelt U. Rosengård 《Zeitschrift für Physik A Hadrons and Nuclei》1988,329(2):143-150
Using the reaction138Ba(α,2n)140Ce the magnetic moment of the 10 1 + isomer atE x =3714.7 keV in theN=82 nucleus140Ce has been determined by means of the TDPAD method toμ=+10.3(4)μ N . Measuredg-factors in140Ce are compared to calculations within the shell model with configuration mixing. For the 10 1 + isomer in140Ce the four proton configuration π(1g 7 2/2 ,2d 5 2/2 ) has been found to be dominant. From theg-factor measurement strong contributions of multiparticle excitations to thegp2d 3/2,π3s 1 2 or π1h 11 2 shells and admixtures of neutron excitations to the wave function of the 10 1 + state could be excluded. The strongE1γ-branch of the deexcitation of the 10 1 + isomer in140Ce can be explained by means of small admixtures of configurations which contain the outer subshell excitationsπ2f 7/2 andπ1h 9/2. On this basisE1 transitions experimentally observed in theN=82 nuclei140Ce,141Pr and145Eu may be understood. 相似文献
993.
K. -H. Speidel M. Knopp W. Karle U. Kilgus M. -L. Dong H. -J. Simonis F. Hagelberg J. Gerber 《Zeitschrift für Physik A Hadrons and Nuclei》1988,331(1):29-36
Transient field precessions have been measured with the first excited 2 1 + -state as probe for ions of28Si traversing Fe at vion?1v0 and 13v0(v0=c/137) and62Ni being stopped in Fe. The degree of polarization deduced for the Si ions, p1s=0.19(6), is consistent with low-velocity data. There is clear evidence that the field strength is attenuated by heavy ion beams. For the62Ni(2 1 + ) state at 1.173 MeV a g-factor value of g=0.34(7) was obtained in good agreement with a previous result. 相似文献
994.
J. Dobaczewski W. Nazarewicz A. Plochocki K. Rykaczewski J. Zylicz 《Zeitschrift für Physik A Hadrons and Nuclei》1988,329(3):267-273
Selected properties of the Gamow-Teller beta decay of even nuclei near100Sn have been studied. Two theoretical models were used: a self-consistent Hartree-Fock-Bogolyubov approach with the Skyrme interaction and a shell-correction model with a Woods-Saxon average field and monopole pairing residual interaction. Calculations reproduce fairly well both theQ EC values and the average energies of theI π=1+ states fed directly in the decay. It is shown that the observed energy splitting between the 1+ states cannot be associated with a stable deformation of a final doubly-odd nucleus. The calculated pairing factors are used to estimate the 0+ → 1+ GT transition strength in the neighbourhood of doubly-magic 50 100 Sn50. 相似文献
995.
J. C. Delgado J. Andreu G. Sardin J. Esteve J. L. Morenza 《Applied Physics A: Materials Science & Processing》1988,46(3):207-213
Films of a-Si: H have been deposited by means of a dc hot cathode discharge of SiH4 with electrostatic confinement at a pressure as low as 0.4 Pa. The plasma used is quite quiescent as has been observed by means of reproducible Langmuir probe measurements. Substrates have been placed at different locations in between the electrodes, some of them facing the anode and the others facing the cathode.Films deposited on substrates facing the cathode present a granular, non-columnar, structure, an IR spectrum with only SiH absorption peaks, and a very low photoresponse. Films deposited on substrates facing the anode have a similar IR spectrum but are homogeneous, have lower hydrogen content, and present a high photoresponse. The optical absorption coefficient shows in all samples thenE=C(E–E0)
x
behaviour, but with exponentx=3 and notx=2 as is usually considered in a-SiH. 相似文献
996.
J P Liautard 《Journal of chromatography. A》1992,584(1):135-139
Large nucleic acids can be separated by reversed-phase high-performance liquid chromatography. Analysis shows that the retention time depends not only on the chain length but also on the base composition and the secondary structure of the molecule. A model is proposed to interpret their behavior. This model, called "multiple-point interaction theory" is based on the observation that macromolecules are flexible and very large compared to the hydrophobic phase (octadecylsilane) of the column. It explains the behavior of large nucleic acids in terms of an equilibrium of the macromolecule between the two phases through a multiple-point attachment to the chromatographic matrix, the parameters of the equilibrium being both the hydrophobicity of the base and the number of attachment points. This model fits the experimental data and can be applied to all types of flexible macromolecules, especially proteins and nucleic acids, when they are chromatographed on reversed-phase columns. The model is used to explain the separation of nucleic acids of importance in molecular biology. 相似文献
997.
The three proteins phosphorylase b, calmodulin and fibrinogen are adsorbed onto thioalkyl derivatives of Sepharose much more strongly than onto gels carrying the same alkyl residue coupled via a carbamate linkage. This enhancement of binding onto alkyl-S-Sepharoses compared with alkyl-N-agaroses is not primarily due to an increase in the extent of conformational changes of the proteins occurring on the gel surface. This can be shown in experiments with the tripeptide Trp-Trp-Trp. The Trp tripeptide is also adsorbed with a much higher affinity to butyl-S-Sepharose than to butyl-N-Sepharose, showing that the primary interaction between the immobilized alkyl residue and the amino acids of the protein is decisive for adsorption. A model stressing the strong influence of an atom or a group of atoms at the base of an immobilized alkyl residue is described as "base-atom recognition". 相似文献
998.
Reproducibility for successive determinations with a hanging mercury drop electrode is assessed in relation to solution stirring, drop size and back-diffusion to the mercury thread. The effect of experimental parameters such as drop size, deposition time and gallium concentration on the observed stripping current is investigated. The interference of zinc present in a 0.5M NaSCN + 4.2M NaClO(4) supporting electrolyte on the gallium detection limit and calibration plots is described. Formation of an intermetallic compound with a Zn:Ga ratio of 2:3 and its destruction by co-deposition of zinc with Sb are reported. A detection limit of 10(-8)M gallium was obtained in the presence of 10(-5)M Sb(III). 相似文献
999.
The classical Harary-Read numbers for catafusenes (catacondensed simply connected polyhexes) are reproduced without using generating functions. A complete (mathematical) solution is given for the distribution of these numbers over the different symmetry groups to which the catafusenes belong. 相似文献
1000.
The properties of neutrinos,s-leptons,s-quarks as well as the coloured isosinglet \(\tilde D\) and \(\tilde D^c \) are studied in superstring inspired models. Furthermore the neutrinoless double β-decay process is investigated, including light and heavy majorana neutrinos, as well as the contribution of the exotic Higgs scalars of the theory. From the current experimental limits onov-ββ-decay, useful constraints are imposed on the masses and Yukawa couplings of the theory. 相似文献