全文获取类型
收费全文 | 1591篇 |
免费 | 51篇 |
国内免费 | 7篇 |
专业分类
化学 | 914篇 |
晶体学 | 8篇 |
力学 | 20篇 |
数学 | 213篇 |
物理学 | 494篇 |
出版年
2021年 | 10篇 |
2020年 | 25篇 |
2019年 | 17篇 |
2018年 | 16篇 |
2016年 | 31篇 |
2015年 | 21篇 |
2014年 | 21篇 |
2013年 | 60篇 |
2012年 | 63篇 |
2011年 | 86篇 |
2010年 | 40篇 |
2009年 | 39篇 |
2008年 | 67篇 |
2007年 | 54篇 |
2006年 | 52篇 |
2005年 | 55篇 |
2004年 | 55篇 |
2003年 | 45篇 |
2002年 | 55篇 |
2001年 | 31篇 |
2000年 | 28篇 |
1999年 | 22篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 41篇 |
1995年 | 40篇 |
1994年 | 31篇 |
1993年 | 43篇 |
1992年 | 45篇 |
1991年 | 32篇 |
1990年 | 33篇 |
1989年 | 35篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 21篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 24篇 |
1982年 | 18篇 |
1981年 | 20篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 8篇 |
1975年 | 19篇 |
1974年 | 25篇 |
1973年 | 26篇 |
1972年 | 10篇 |
1970年 | 13篇 |
排序方式: 共有1649条查询结果,搜索用时 15 毫秒
171.
I. Usman Z. Buthelezi J. Carter G.R.J. Cooper R.W. Fearick S.V. Förtsch H. Fujita Y. Fujita Y. Kalmykov P. von Neumann-Cosel R. Neveling P. Papakonstantinou A. Richter R. Roth A. Shevchenko E. Sideras-Haddad F.D. Smit 《Physics letters. [Part B]》2011
The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at Ep=200 MeV. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon–nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for 40Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle–two-hole (2p–2h) states. 相似文献
172.
173.
174.
The environment-assisted cracking (EAC) susceptibility of some aluminum alloys used for airplane structural components currently limits their use in the peak strength condition. Understanding the mechanism of EAC will facilitate the development of crack-resistant alloys with optimum mechanical properties. One component towards understanding the fundamental processes responsible for EAC is a comprehensive knowledge of the chemical conditions within cracks. The present work uses capillary electrophoresis (CE) to quantify the crack chemistry in order to provide insight into the nature of the mechanism controlling cracking. The highly restricted geometry of cracks in metals means that a crack typically contains less than 10 μl of solution. The high mass sensitivity combined with the inherently robust nature of CE makes it an ideal analytical technique for this application. Complicating factors in the accurate determination of the crack environment include high levels of sodium present from the test solution. Low sample volume and analyte matrix complexity necessitated the development of specific sampling, extraction and analysis methods. Analysis of the crack solutions in EAC-susceptible material revealed high levels of Al3+, Mg2+, Zn2+, and Cl− near the crack tip. Cations arise from the anodic dissolution of the alloy, whereas chloride ingress from the external environment occurs to maintain solution electroneutrality within the crack. In contrast, EAC-resistant material exhibited significantly lower concentrations of dissolution products. 相似文献
175.
The configurational distribution of all the cobalt(III) complexes containing a 14-membered tetra-aza macrocyclic backbone in the Cambridge Structural Database was determined by cluster analysis, and the reason for some of the complexes adopting their configuration was established by molecular mechanics. 相似文献
176.
Colin Cooper 《Discrete Applied Mathematics》2009,157(9):2010-2014
A random recursive tree on n vertices is either a single isolated vertex (for n=1) or is a vertex vn connected to a vertex chosen uniformly at random from a random recursive tree on n−1 vertices. Such trees have been studied before [R. Smythe, H. Mahmoud, A survey of recursive trees, Theory of Probability and Mathematical Statistics 51 (1996) 1-29] as models of boolean circuits. More recently, Barabási and Albert [A. Barabási, R. Albert, Emergence of scaling in random networks, Science 286 (1999) 509-512] have used modifications of such models to model for the web and other “power-law” networks.A minimum (cardinality) dominating set in a tree can be found in linear time using the algorithm of Cockayne et al. [E. Cockayne, S. Goodman, S. Hedetniemi, A linear algorithm for the domination number of a tree, Information Processing Letters 4 (1975) 41-44]. We prove that there exists a constant d?0.3745… such that the size of a minimum dominating set in a random recursive tree on n vertices is dn+o(n) with probability approaching one as n tends to infinity. The result is obtained by analysing the algorithm of Cockayne, Goodman and Hedetniemi. 相似文献
177.
Dr. Xavier Ragàs Laurie P. Cooper Dr. John H. White Prof. Santi Nonell Dr. Cristina Flors 《Chemphyschem》2011,12(1):161-165
Fluorescent proteins are increasingly becoming actuators in a range of cell biology techniques. One of those techniques is chromophore‐assisted laser inactivation (CALI), which is employed to specifically inactivate the function of target proteins or organelles by producing photochemical damage. CALI is achieved by the irradiation of dyes that are able to produce reactive oxygen species (ROS). The combination of CALI and the labelling specificity that fluorescent proteins provide is useful to avoid uncontrolled photodamage, although the inactivation mechanisms by ROS are dependent on the fluorescent protein and are not fully understood. Herein, we present a quantitative study of the ability of the red fluorescent protein TagRFP to produce ROS, in particular singlet oxygen (1O2). TagRFP is able to photosensitize 1O2 with an estimated quantum yield of 0.004. This is the first estimation of a quantum yield of 1O2 production value for a GFP‐like protein. We also find that TagRFP has a short triplet lifetime compared to EGFP, which reflects relatively high oxygen accessibility to the chromophore. The insight into the structural and photophysical properties of TagRFP has implications in improving fluorescent proteins for fluorescence microscopy and CALI. 相似文献
178.
Begin with a set of four points in the real plane in general position. Add to this collection the intersection of all lines
through pairs of these points. Iterate. Ismailescu and Radoičić (Comput. Geom. 27:257–267, 2004) showed that the limiting set is dense in the plane. We give doubly exponential upper and lower bounds on the number of points
at each stage. The proof employs a variant of the Szemerédi–Trotter Theorem and an analysis of the “minimum degree” of the
growing configuration. 相似文献
179.
180.
Validation and generalization of DEA and its uses 总被引:3,自引:0,他引:3
R. D. Banker W. W. Cooper E. Grifell-Tajté Jesús T. Pastor Paul W. Wilson Eduardo Ley C. A. K. Lovell 《TOP》1994,2(2):249-314
Summary Rapidly expanding uses of DEA have been accompanied by developments which have enhanced its power and enlarged its utility
for additional applications. Developments covered in the present paper include simulation studies comparing DEA with competing
forms of statistical regressions. Other studies covered show how these two approaches can be combined in complementary fashion.
Another part of this paper deals with Chance Constrained Programming formulations which incorporate probabilistic elements
into DEA. Included also are discussions of statistical characterizations with accompanying tests of statistical significance
for DEA efficiency evaluations. This paper concludes with uses of DEA in “discovery processes”-processes that need strengthening
(and encouragemnt) in contemporary social science and management science research. Suggestions are made for additional research
on further developments which extend to uses of DEA to provide new approaches in economics (including econometrics), management
and psychology and an Appendix introduces new or recently developed efficiency measures for use in DEA.
Invited by J. T. Pastor 相似文献