全文获取类型
收费全文 | 34313篇 |
免费 | 213篇 |
国内免费 | 291篇 |
专业分类
化学 | 13706篇 |
晶体学 | 288篇 |
力学 | 1497篇 |
综合类 | 12篇 |
数学 | 9552篇 |
物理学 | 9762篇 |
出版年
2020年 | 69篇 |
2018年 | 1228篇 |
2017年 | 1477篇 |
2016年 | 794篇 |
2015年 | 624篇 |
2014年 | 545篇 |
2013年 | 884篇 |
2012年 | 3346篇 |
2011年 | 2556篇 |
2010年 | 1944篇 |
2009年 | 1653篇 |
2008年 | 794篇 |
2007年 | 883篇 |
2006年 | 854篇 |
2005年 | 4702篇 |
2004年 | 4162篇 |
2003年 | 2491篇 |
2002年 | 635篇 |
2001年 | 401篇 |
2000年 | 208篇 |
1999年 | 239篇 |
1998年 | 160篇 |
1997年 | 136篇 |
1996年 | 121篇 |
1995年 | 100篇 |
1994年 | 115篇 |
1993年 | 104篇 |
1992年 | 285篇 |
1991年 | 226篇 |
1990年 | 220篇 |
1989年 | 179篇 |
1988年 | 154篇 |
1987年 | 126篇 |
1986年 | 110篇 |
1985年 | 147篇 |
1984年 | 128篇 |
1983年 | 105篇 |
1982年 | 96篇 |
1981年 | 107篇 |
1980年 | 84篇 |
1979年 | 104篇 |
1978年 | 97篇 |
1977年 | 84篇 |
1976年 | 135篇 |
1975年 | 107篇 |
1974年 | 116篇 |
1973年 | 133篇 |
1972年 | 97篇 |
1971年 | 67篇 |
1970年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
4.
5.
The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported. 相似文献
6.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
7.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
8.
We investigate the linear stability of the Bickley jet in the framework of the beta-plane approximation. Because singular inviscid neutral modes exist in the retrograde case , it is necessary to add viscosity to interpret them. One of these modes was found in closed form by Howard and Drazin [1] . However, its critical point is at the center of the jet and it was therefore not possible for these authors to ascertain the relationship of this mode to the stability problem or to discuss how to continue the eigenfunction across the singularity.
The viscous critical layer problem associated with this singularity is considerably more difficult than the usual one (which leads to integrals of the Airy function) because and, consequently, a second-order turning point is involved. Our analysis shows that the Howard–Drazin mode is degenerate in the domain where it is valid as a limit of the viscous problem (wavenumber α2 ≤ 9/2 ), that is, it corresponds to both an odd and an even mode. This conclusion is confirmed by direct numerical solution of the Orr–Sommerfeld equation which shows, in addition, that viscosity is destabilizing along portions of the stability boundary. For a retrograde jet, instability is found to occur beyond the inviscid critical value of β, that is, in the region where the flow would be stable according to the Rayleigh–Kuo condition. 相似文献
The viscous critical layer problem associated with this singularity is considerably more difficult than the usual one (which leads to integrals of the Airy function) because and, consequently, a second-order turning point is involved. Our analysis shows that the Howard–Drazin mode is degenerate in the domain where it is valid as a limit of the viscous problem (wavenumber α
9.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
10.
Let
d−1{(x1,…,xd)
d:x21+···+x2d=1} be the unit sphere of the d-dimensional Euclidean space
d. For r>0, we denote by Brp (1p∞) the class of functions f on
d−1 representable in the formwhere dσ(y) denotes the usual Lebesgue measure on
d−1,
and Pλk(t) is the ultraspherical polynomial.For 1p,q∞, the Kolmogorov N-width of Brp in Lq(
d−1) is given bythe left-most infimum being taken over all N-dimensional subspaces XN of Lq(
d−1).The main result in this paper is that for r2(d−1)2,where ANBN means that there exists a positive constant C, independent of N, such that C−1ANBNCAN.This extends the well-known Kashin theorem on the asymptotic order of the Kolmogorov widths of the Sobolev class of the periodic functions. 相似文献