全文获取类型
收费全文 | 491193篇 |
免费 | 7443篇 |
国内免费 | 1607篇 |
专业分类
化学 | 274976篇 |
晶体学 | 6991篇 |
力学 | 20133篇 |
综合类 | 11篇 |
数学 | 57739篇 |
物理学 | 140393篇 |
出版年
2020年 | 3343篇 |
2019年 | 3353篇 |
2018年 | 3772篇 |
2017年 | 3485篇 |
2016年 | 6861篇 |
2015年 | 5597篇 |
2014年 | 7283篇 |
2013年 | 22080篇 |
2012年 | 16919篇 |
2011年 | 20578篇 |
2010年 | 13022篇 |
2009年 | 12564篇 |
2008年 | 18710篇 |
2007年 | 19005篇 |
2006年 | 18106篇 |
2005年 | 16676篇 |
2004年 | 14977篇 |
2003年 | 13124篇 |
2002年 | 12752篇 |
2001年 | 14307篇 |
2000年 | 11033篇 |
1999年 | 8811篇 |
1998年 | 7027篇 |
1997年 | 6887篇 |
1996年 | 7024篇 |
1995年 | 6318篇 |
1994年 | 6115篇 |
1993年 | 5819篇 |
1992年 | 6680篇 |
1991年 | 6377篇 |
1990年 | 6061篇 |
1989年 | 5963篇 |
1988年 | 6100篇 |
1987年 | 5862篇 |
1986年 | 5566篇 |
1985年 | 7899篇 |
1984年 | 7998篇 |
1983年 | 6536篇 |
1982年 | 7021篇 |
1981年 | 7016篇 |
1980年 | 6656篇 |
1979年 | 6916篇 |
1978年 | 7097篇 |
1977年 | 6937篇 |
1976年 | 6888篇 |
1975年 | 6637篇 |
1974年 | 6460篇 |
1973年 | 6625篇 |
1972年 | 3994篇 |
1968年 | 3425篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in the computer code CFX4.4 is further developed to accommodate the wall nucleation at the heated wall and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Additional comparison using empirical relationships for the active nucelation site density and local bubble diameter is also investigated. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress to circumvent the deficiency through the consideration of additional momentum equations or developing an algebraic slip model to account for bubble separation. 相似文献
994.
995.
Donald J. Wink 《Foundations of Chemistry》2006,8(2):111-151
The rich and ongoing debate about constructivism in chemistry education includes questions about the relationship, for better or worse, between applications of the theory in pedagogy and in epistemology. This paper presents an examination of the potential to use connections of epistemological and pedagogical constructivism to one another. It examines connections linked to the content, processes, and premises of science with a goal of prompting further research in these areas. 相似文献
996.
A model for the flow of a fluid through a channel with parallel plates is investigated. The channel is narrow, so that the lubrication approximation may be applied. The channel walls are maintained at a constant temperature. Shear heating effects are included and the fluid viscosity decreases exponentially with temperature. When the flow is driven solely by shear stress or imposed velocity at the top, analytical progress is possible. When pressure gradient also drives the flow the problem is solved numerically. 相似文献
997.
In this paper we propose a general integration scheme for a Multi-Criteria Decision Making model of the Multi-Attribute Utility
Theory in Constraint Programming. We introduce the Choquet integral as a general aggregation function for multi-criteria optimization
problems and define the Choquet global constraint that propagates this function during the Branch-and-Bound search. Finally the benefits of the propagation
of the Choquet constraint are evaluated on the examination timetabling problem. 相似文献
998.
S.N. Abdulmadjid M.M. Suliyanti K.H. Kurniawan T.J. Lie M. Pardede R. Hedwig K. Kagawa M.O. Tjia 《Applied physics. B, Lasers and optics》2006,82(1):161-166
We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium
ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited
state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark
broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation
respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen
analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration
of the conventional LIBS method.
PACS 51-52 相似文献
999.
We consider three one-dimensional quantum, charged and spinless particles interacting through delta potentials. We derive
sufficient conditions which guarantee the existence of at least one bound state. 相似文献
1000.
G.J. Hager 《Applied Surface Science》2006,252(19):6558-6561
Utilizing Au4004+ primary ions produces large molecular ion yields, some in excess of unity, with minimal surface damage. A surprising observation is the occurrence of Au-analyte adducts as part of the ejecta desorbed by a single Au-cluster impact. We present data that demonstrate that Au and Au-adducts as secondary ions (e.g., AuCN−, AuGly− and AuCsI−) are the result of the interaction between a single primary ion, Au4004+ and the target atoms. 相似文献