全文获取类型
收费全文 | 3038篇 |
免费 | 123篇 |
国内免费 | 11篇 |
专业分类
化学 | 1931篇 |
晶体学 | 143篇 |
力学 | 103篇 |
数学 | 304篇 |
物理学 | 691篇 |
出版年
2023年 | 24篇 |
2022年 | 67篇 |
2021年 | 64篇 |
2020年 | 53篇 |
2019年 | 69篇 |
2018年 | 70篇 |
2017年 | 58篇 |
2016年 | 107篇 |
2015年 | 93篇 |
2014年 | 99篇 |
2013年 | 269篇 |
2012年 | 172篇 |
2011年 | 168篇 |
2010年 | 128篇 |
2009年 | 111篇 |
2008年 | 141篇 |
2007年 | 126篇 |
2006年 | 102篇 |
2005年 | 104篇 |
2004年 | 87篇 |
2003年 | 73篇 |
2002年 | 77篇 |
2001年 | 34篇 |
2000年 | 26篇 |
1999年 | 27篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 28篇 |
1994年 | 19篇 |
1993年 | 34篇 |
1992年 | 34篇 |
1991年 | 34篇 |
1990年 | 32篇 |
1989年 | 41篇 |
1988年 | 26篇 |
1987年 | 24篇 |
1986年 | 31篇 |
1985年 | 29篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 34篇 |
1980年 | 28篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 32篇 |
1976年 | 20篇 |
1975年 | 24篇 |
1974年 | 21篇 |
排序方式: 共有3172条查询结果,搜索用时 15 毫秒
11.
12.
Y. Shi L. Sun J. E. S. Venart R. C. Prasad 《Journal of Thermal Analysis and Calorimetry》2006,86(3):585-590
The transient hot-wire technique is widely used for absolute measurements
of the thermal conductivity and thermal diffusivity of fluids. It is well
established that fluid radiation effects significantly influence these measurements,
especially those for the thermal diffusivity. Corrections for radiation effects
are based on the models developed and deviations of the measured data from
the ideal line source model. In this paper, the effect of fluid radiation
on the measurements of the thermal conductivity of n-pentane
is presented. For comparison, the influence of thermal radiation effect on
measurement of transparent fluids, such as argon is also shown. The difference
between the influence of natural convection and thermal radiation is also
demonstrated. 相似文献
13.
Selenocystine ([Sec]2) and aryl-substituted selenocysteine (Sec) derivatives are synthesized, starting from commercially available amino acid l-serine. These compounds are characterized by a number of analytical techniques such as NMR (1H, 13C and 77Se) and TOF mass spectroscopy. This study reveals that the introduction of amino/imino substituents capable of interacting with selenium may stabilize the Sec derivatives. This study further suggests that the oxidation-elimination reactions in Sec derivatives could be used for the generation of biologically active selenols having internally stabilizing substituents. 相似文献
14.
M. Durga Prasad 《Theoretical chemistry accounts》1994,88(5):383-388
Summary Finite order expressions are derived for expectation values and transition matrix elements within the framework of the coupled cluster method. 相似文献
15.
Signs of the dipole moment derivatives, ?px/?S4 and ?px/?S5 where px is the dipole moment vector along an axis perpendicular to the CO bond in the plane of the molecule and Sj are the symmetry coordinates for the B1 vibrations of Br2CO have been re-evaluated from the reported ?p/?Qi values (p being the dipole moment of the molecule and Qi the normal coordinates) and the L matrix elements. The new set of dipole moment derivatives fits well with similar parameters for Cl2CO and F2CO. 相似文献
16.
The exchange part of the usual Hartree-Fock potential in the unrestricted Hartree-Fock (UHF) theory is suitablyaveraged to construct an, average one-electron model Hamiltonian which generates a set of spin-restricted one-electron orbitals in
a self-consistent manner. These orbitals are then used to calculate the electronic energy of the open-shell system by using
the proper functional form for the energy which handles the exchange terms correctly. The eigenvalues ofF
av can be used for calculating either the spin-polarised or spin-averaged ionisation potentials of different orbitals at theKoopmans’ theorem level of approximation. Comparison ofE
ac with the UHF-energy shows thatE
UHF<E
ac in each case revealing some kind of an upper bound nature ofE
ac. An approximate variational argument is given. Relationship of our model with the hyper-Hartree-Fock theory of slater is
explored and the general problem of eliminating ‘self-interaction’ terms in average Fock-operator based theories is discussed. 相似文献
17.
A microwave-assisted click chemistry synthesis of 1,4-disubstituted 1,2,3-triazoles via a copper(I)-catalyzed three-component reaction 总被引:4,自引:0,他引:4
A microwave-assisted three-component reaction was used to prepare a series of 1,4-disubstituted-1,2,3-triazoles from corresponding alkyl halides, sodium azide, and alkynes. This procedure eliminates the need to handle organic azides, as they are generated in situ, making this already powerful click process even more user-friendly and safe. 相似文献
18.
19.
[reaction: see text] A wide range of substituted isoquinolines were synthesized via a highly efficient nickel-catalyzed annulation of the tert-butyl imines of 2-iodobenzaldehydes and various alkynes; examination of the regiochemistry of isoquinolines synthesized indicates that there are two different alkyne insertion pathways for the catalytic reactions. 相似文献
20.
The isolation and the X-ray crystal structure of physiological copper(II)-L-histidine complex are reported. The neutral five-coordinate complex shows distorted square pyramidal geometry with bidentate and tridentate L-histidine ligands. The basic character of the pendent imidazole group and H-bonding interactions of bidentate L-histidine ligand are important for copper transport. The unique structural features help explain the origin of its thermodynamic stability and kinetic reactivity in human blood along with the ternary copper(II)-amino acid complexes. The role of L-histidine in interaction with copper(II)-albumin, in cellular uptake of copper, and in treatment of Menkes disease can be studied using these results. 相似文献