全文获取类型
收费全文 | 329529篇 |
免费 | 3436篇 |
国内免费 | 931篇 |
专业分类
化学 | 164773篇 |
晶体学 | 5374篇 |
力学 | 15531篇 |
综合类 | 7篇 |
数学 | 38467篇 |
物理学 | 109744篇 |
出版年
2021年 | 3127篇 |
2020年 | 3330篇 |
2019年 | 3760篇 |
2018年 | 5198篇 |
2017年 | 5440篇 |
2016年 | 7368篇 |
2015年 | 4139篇 |
2014年 | 7029篇 |
2013年 | 15904篇 |
2012年 | 12375篇 |
2011年 | 14824篇 |
2010年 | 11012篇 |
2009年 | 10913篇 |
2008年 | 13235篇 |
2007年 | 13192篇 |
2006年 | 12137篇 |
2005年 | 10520篇 |
2004年 | 9832篇 |
2003年 | 8686篇 |
2002年 | 8673篇 |
2001年 | 10394篇 |
2000年 | 7655篇 |
1999年 | 5967篇 |
1998年 | 4973篇 |
1997年 | 4811篇 |
1996年 | 4479篇 |
1995年 | 3864篇 |
1994年 | 3820篇 |
1993年 | 3701篇 |
1992年 | 4096篇 |
1991年 | 4306篇 |
1990年 | 4096篇 |
1989年 | 4008篇 |
1988年 | 3779篇 |
1987年 | 3917篇 |
1986年 | 3683篇 |
1985年 | 4629篇 |
1984年 | 4681篇 |
1983年 | 3885篇 |
1982年 | 3973篇 |
1981年 | 3697篇 |
1980年 | 3647篇 |
1979年 | 3913篇 |
1978年 | 3901篇 |
1977年 | 3906篇 |
1976年 | 3879篇 |
1975年 | 3675篇 |
1974年 | 3615篇 |
1973年 | 3651篇 |
1972年 | 2604篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Explosion-produced plasma jets formed in free spece are experimentally investigated. The feasibility of emitting pulsed electromagnetic signals by plasma jets is shown, and the emitting conditions are studied. Comparison is made between the results of experiments with short and long plasma jets. When the jet passes through the field of a helix, a short-term increase in the emitted signal is detected. A linear parametric model of interaction between the plasma jet and an exciting electromagnetic signal is proposed. The operating performance of instrumentation developed for the investigation is presented. 相似文献
992.
We considered the kaon absorption from atomic states into the nucleus. We found that the nuclear density probed by the atomic
kaon significantly depends on the kaon orbit. Then, we re-examined the meanings of the observed strengths of one-body and
two-body kaon absorption, and investigated the effects to the formation spectra of kaon bound states by in-flight (K
-, p) reactions. As a natural consequence, if the atomic kaon probes a smaller nuclear density, the ratio of the two-body absorption
at nuclear center is larger than the observed value in kaonic atoms, and the depth of the imaginary potential is deeper even
at smaller kaon energies as in kaonic nuclear states because of the large phase space for the two-body processes. This deeper
imaginary potential makes the signals of kaonic nucleus formation more unclear in the (K
-, p) spectra. 相似文献
993.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献
994.
Barannikov V. P. Guseinov S. S. V'ugin A. I. 《Russian Journal of Coordination Chemistry》2002,28(3):153-162
A review of the experimental and theoretical studies of the crown ether complexes with polar molecules in their crystals, solutions, and in a gas phase is given. The type of the molecular bonds in the complexes, their stoichiometry, and the change in the macrocycle conformation during complex formation are considered, as well as the effect of the macrocycle structure and the nature of the medium on the efficiency of the molecular bonding. New data are given on the enthalpies of transfer of the crown ethers from tetrachloromethane into solvents capable of forming hydrogen bonds. The enthalpies of specific interactions of macrocycles with the molecules of the solvents in the medium of the same solvents are characterized. The conformations of the crown ethers in the media under study are discussed. 相似文献
995.
996.
997.
Thomas M. F. Case G. S. Bland J. Herring A. D. F. Stirling W. G. Tixier S. Boni P. Ward R. C. C. Wells M. R. Langridge S. 《Hyperfine Interactions》2002,141(1-4):471-476
Hyperfine Interactions - Multilayers of Ce/Fe and U/Fe were fabricated by sputtering and studied by X-ray diffraction and reflectivity, Mössbauer spectroscopy and polarised neutron... 相似文献
998.
A method of four-dimensional Lie group integration of the Fock–Klein equation is described in the present paper. The method is based on the formalism of co-adjoint representation orbits and on the non-commutative integration method. Right-invariant metrics being solutions of the Einstein equation are also classified for manifolds of four-dimensional Lie groups. 相似文献
999.
Benzildithiosemicarbazone (BDTSC) is proposed as a sensitive and selective analytical reagent for the extractive spectrophotometric determination of copper(II). BDTSC reacts with copper(II) in the pH range 1.0-7.0 to form a yellowish complex. Beer's law is obeyed in the concentration range 0.5-0.4 microg cm(-3). The yellowish Cu(II)-BDTSC complex in chloroform shows a maximum absorbance at 380 nm, with molar absorptivity and Sandell's sensitivity values of 1.63 x 10(4) dm3 mol(-1) cm(-1) and 0.00389 microg cm(-2), respectively. A repetition of the method is checked by finding the relative standard deviation (RSD) (n = 10), which is 0.6%. The composition of the Cu(II)-BDTSC complex is established as 1:1 by slope analysis, molar ratio and Asmus' methods. An excellent linearity with a correlation coefficient value of 0.98 is obtained for the Cu(II)-BDTSC complex. The instability constant of the complex calculated from Edmond and Birnbaum's method is 7.70 x 10(-4) and that of Asmus' method is 7.66 x 10(-4), at room temperature. The method is successfully employed for the determination copper(II) in pharmaceutical and environmental samples. The reliability of the method is assured by analyzing the standard alloys (BCS 5g, 10g, 19e, 78, 32a, 207 and 179) and by inter-comparison of experimental values, using an atomic absorption spectrometer. 相似文献
1000.
S. B. Gashkov 《Moscow University Mathematics Bulletin》2007,62(3):87-89
It is shown that Lozhkin’s method (1981) for minimization of the depth of formulas with a bounded number of changing types of elements in paths from input to output and Hoover-Klawe-Pippenger’s method (technical report in 1981, journal publication in 1984) for minimization of the depth of circuits with unbounded branching by insertion of trees from buffers with bounded branching of outputs for each buffer are dual to each other and can be proved by one and the same method. 相似文献