全文获取类型
收费全文 | 1789篇 |
免费 | 45篇 |
国内免费 | 11篇 |
专业分类
化学 | 1177篇 |
晶体学 | 6篇 |
力学 | 81篇 |
数学 | 324篇 |
物理学 | 257篇 |
出版年
2022年 | 16篇 |
2021年 | 28篇 |
2020年 | 23篇 |
2019年 | 36篇 |
2018年 | 28篇 |
2017年 | 15篇 |
2016年 | 53篇 |
2015年 | 27篇 |
2014年 | 36篇 |
2013年 | 74篇 |
2012年 | 80篇 |
2011年 | 97篇 |
2010年 | 55篇 |
2009年 | 65篇 |
2008年 | 85篇 |
2007年 | 97篇 |
2006年 | 89篇 |
2005年 | 100篇 |
2004年 | 81篇 |
2003年 | 70篇 |
2002年 | 46篇 |
2001年 | 22篇 |
2000年 | 28篇 |
1999年 | 34篇 |
1998年 | 19篇 |
1997年 | 26篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 13篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1930年 | 6篇 |
1888年 | 8篇 |
排序方式: 共有1845条查询结果,搜索用时 15 毫秒
921.
Maurizio Canetti Fabio Bertini Aurelio De Chirico Guido Audisio 《Polymer Degradation and Stability》2006,91(3):494-498
The influence of lignin on the thermal degradation of isotactic polypropylene, investigated by thermogravimetric analysis, is reported in this article. Polypropylene blends containing 5 and 15 wt% of lignin were prepared by mixing the components in a screw mixer. An increase in the thermal degradation temperature of the blends was observed as a function of lignin content, in both oxidative and non-oxidative conditions. The increase is noticeably marked for the experiments carried out in air atmosphere, where the interactions between the polypropylene and the lignin lead to the formation of a protective surface able to reduce the oxygen diffusion towards the polymer bulk. Morphological analyses were carried out with optical and electronic microscopy, to evaluate the degree of dispersion of the lignin in the polypropylene matrix. X-ray techniques were employed to study the influence of lignin on the structure of the blended polypropylene. 相似文献
922.
Stijn Viaene Mercedes Ayuso Montserrat Guillen Dirk Van Gheel Guido Dedene 《European Journal of Operational Research》2007
Some property and casualty insurers use automated detection systems to help to decide whether or not to investigate claims suspected of fraud. Claim screening systems benefit from the coded experience of previously investigated claims. The embedded detection models typically consist of scoring devices relating fraud indicators to some measure of suspicion of fraud. In practice these scoring models often focus on minimizing the error rate rather than on the cost of (mis)classification. We show that focusing on cost is a profitable approach. We analyse the effects of taking into account information on damages and audit costs early on in the screening process. We discuss several scenarios using real-life data. The findings suggest that with claim amount information available at screening time detection rules can be accommodated to increase expected profits. Our results show the value of cost-sensitive claim fraud screening and provide guidance on how to render this strategy operational. 相似文献
923.
924.
Gianpiero Cattaneo Tiziana Marsico Giuseppe Nisticò Guido Bacciagaluppi 《Foundations of Physics》1997,27(10):1323-1343
We discuss the problem of how a (commutative) generalized observable in a finite-dimensional Hilbert space (communtative effect-valued
resolution of the identity) can be considered as an unsharp realization of some standard observable (projection-valued resolution
of the identity). In particular, we give a concrete procedure for constructing such a standard observable. Some results about
the “uniqueness” of the resulting observable are also examined. 相似文献
925.
926.
The possibility of using feedback to achieve or to enhance system linearity is well known to control engineers since decades ago. A few major breakthroughs, made possible by the application of differential geometric tools to control theoretic issues, have revamped a new interest in all facets of the problem, including the search, the analysis and the computation of suitable approximate solutions. In the present paper, recent developments and new trends in the field are shortly reviewed, with special attention paid to some research issues currently addressed by the authors. Though primarily meant for learned mathematically oriented readers, the presentation focuses on ideas and concepts more than on their most general and mathematically rigorous formulations. On the other hand, it does not assume familiarity with advanced control theory nor modern control technology. 相似文献
927.
Guido Montagna Mauro Moretti Oreste Nicrosini Fulvio Piccinini 《The European Physical Journal C - Particles and Fields》1998,2(3):483-496
The production of an intermediate-mass Higgs boson in processes of the kind fermions at the energies of future linear colliders is studied. The recently developed and fully automatic algorithm/code
ALPHA is used to compute the tree-level scattering amplitudes for the reactions . The code has been interfaced with the Monte Carlo program HIGGSPV/WWGENPV, properly adapted to 6-fermion production, in order to provide realistic results, both in the form of cross sections and
event samples at the partonic level. Phenomenological results, that incorporate the effects of initial-state radiation and
beamstrahlung, are shown and commented, emphasizing the potentials of full six-fermion calculations for precise background
evaluation as well as for detailed studies of the fundamental properties of the Higgs particle.
Received: 22 May 1997 / Published online: 20 February 1998 相似文献
928.
929.
The vanishing of the divergence of the matter stress-energy tensor for General Relativity is a particular case of a general identity, which follows from the covariance of the matter Lagrangian in much the same way as (generalized) Bianchi identities follow from the covariance of the purely gravitational Lagrangian. This identity, holding for any covariant theory of gravitating matter, relates the divergence of the stress tensor with a combination of the field equations and their derivatives. One could thus wonder if, according to a recent suggestion [1], the energy-momentum tensor for gravitating fields can be computed through a suitable rearrangement of the matter field equations, without relying on the variational definition. We show that this can be done only in particular cases, while in general it leads to ambiguities and possibly to wrong results. Moreover, in nontrivial cases the computations turn out to be more difficult than the standard variational technique. 相似文献
930.