全文获取类型
收费全文 | 12926篇 |
免费 | 1091篇 |
国内免费 | 1595篇 |
专业分类
化学 | 6807篇 |
晶体学 | 93篇 |
力学 | 1452篇 |
综合类 | 104篇 |
数学 | 3393篇 |
物理学 | 3763篇 |
出版年
2024年 | 19篇 |
2023年 | 173篇 |
2022年 | 272篇 |
2021年 | 480篇 |
2020年 | 644篇 |
2019年 | 427篇 |
2018年 | 378篇 |
2017年 | 394篇 |
2016年 | 536篇 |
2015年 | 436篇 |
2014年 | 659篇 |
2013年 | 1035篇 |
2012年 | 585篇 |
2011年 | 670篇 |
2010年 | 538篇 |
2009年 | 733篇 |
2008年 | 737篇 |
2007年 | 769篇 |
2006年 | 722篇 |
2005年 | 592篇 |
2004年 | 489篇 |
2003年 | 613篇 |
2002年 | 591篇 |
2001年 | 423篇 |
2000年 | 448篇 |
1999年 | 320篇 |
1998年 | 371篇 |
1997年 | 186篇 |
1996年 | 176篇 |
1995年 | 163篇 |
1994年 | 127篇 |
1993年 | 116篇 |
1992年 | 127篇 |
1991年 | 66篇 |
1990年 | 54篇 |
1989年 | 48篇 |
1988年 | 70篇 |
1987年 | 61篇 |
1986年 | 56篇 |
1985年 | 86篇 |
1984年 | 60篇 |
1983年 | 23篇 |
1982年 | 40篇 |
1981年 | 21篇 |
1980年 | 11篇 |
1979年 | 25篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
Details are given of a new method allowing an exact calculation of the spontaneous magnetization in the corner as well as along the edge at an arbitrary distance of the corner for a rectangular planar Ising ferromagnet. 相似文献
82.
After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results. 相似文献
83.
Hans C. Fogedby 《Journal of statistical physics》1992,69(1-2):411-425
We elaborate in some detail on a new phase space approach to complexity, due to Y.-C. Zhang. We show in particular that the connection between maximal complexity and power law noise or correlations can be derived from a simple variational principle. For a 1D signal we find 1/f noise, in accordance with Zhang. 相似文献
84.
S. Chen H. Büttner 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):15-18
We generalize the Shastry-Sutherland model to three dimensions. By representing the model as a sum of the semidefinite positive
projection operators, we exactly prove that the model has exact dimer ground state. Several schemes for constructing the three-dimensional
Shastry-Sutherland model are proposed.
Received 20 February 2002 / Received in final form 27 May 2002 Published online 17 September 2002 相似文献
85.
1IntroductionConsiderthelinearregressioumodelcensoredfromtheleft:K=m{K,0}=rnax{Z:W ei,0},1Si5n,(1.1)whereZi=(1,X:),,15i5n,7o=(ac,P6)'(1'2)ThedimensionalityofXiisd21.WeobBerve(Xi,K)',1SiSn.Basedontheseobservations,wetrytogivesomeestimationofac,ortesthypothesisonit.Themodelwasfirstconsideredbycabin[llundertheassumptionthatelfe2,''arelid.withacommonnormaldistributionN(0,rs:).HedefinedtheMLEof7o,whichnowisusuallyknownastheTobinestimator.TheconsistencyOfthisestimatorwasestablishedbyAmend… 相似文献
86.
To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA, incorporating a dynamic model of the human body with a finite element model of the seat structure was used. Modifications were performed in the program for reconstruction of an occupant's head impact with the interior walls or bulkhead. A viscoelastic-type contact force model was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft. 相似文献
87.
Richard O. LaMaire 《Queueing Systems》1992,11(4):357-375
We define and analyze anM/G/1/N vacation model that uses a service discipline that we call theE-limited with limit variation discipline. According to this discipline, the server provides service until either the system is emptied (i.e. exhausted) or a randomly chosen limit ofl customers has been served. The server then goes on a vacation before returning to service the queue again. The queue length distribution and the Laplace-Stieltjes transforms of the waiting time, busy period and cycle time distributions are found. Further, an expression for the mean waiting time is developed. Several previously analyzed service disciplines, including Bernoulli scheduling, nonexhaustive service and limited service, are special cases of the general varying limit discipline that is analyzed in this paper. 相似文献
88.
Bernard Bialecki 《Numerical Algorithms》1994,8(2):167-184
Cyclic reduction and Fourier analysis-cyclic reduction (FACR) methods are presented for the solution of the linear systems which arise when orthogonal spline collocation with piecewise Hermite bicubics is applied to boundary value problems for certain separable partial differential equations on a rectangle. On anN×N uniform partition, the cyclic reduction and Fourier analysis-cyclic reduction methods requireO(N
2log2
N) andO(N
2log2log2
N) arithmetic operations, respectively. 相似文献
89.
In this paper various ensemble learning methods from machine learning and statistics are considered and applied to the customer choice modeling problem. The application of ensemble learning usually improves the prediction quality of flexible models like decision trees and thus leads to improved predictions. We give experimental results for two real-life marketing datasets using decision trees, ensemble versions of decision trees and the logistic regression model, which is a standard approach for this problem. The ensemble models are found to improve upon individual decision trees and outperform logistic regression. 相似文献
90.
Inhibition of the reduction of Cr(VI) at the magnetite–water interface by calcium carbonate coatings
The effect of calcium carbonate coatings on the reduction of aqueous chromate on the magnetite(1 1 1) surface has been investigated using a combination of synchrotron based X-ray photoemission spectroscopy (PES) and X-ray absorption near edge structure (XANES) spectroscopy, along with laboratory-based powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO3 coatings (dominantly calcite with minor quantities of aragonite and vaterite) of thicknesses ranging from 10 Å to 20 m were grown on magnetite(1 1 1) surfaces by exposure to supersaturated aqueous solutions followed by evaporation of the solution—a process that mimics pore-water evaporation in vadose zones leading to the formation of caliche and calcium carbonate coatings on mineral grains. Coating thicknesses were determined from attenuation of the Fe 2p photoemission signal by the carbonate coating. For coatings less than 15 Å thick, Cr 2p photoemission and Cr LII, LIII-edge XANES spectra show that chromate is reduced by the underlying magnetite surface; however, as the minimum coating thickness increases beyond 15 Å, the magnetite surface becomes passivated and further chromate reduction ceases. Our findings suggest that carbonate coatings on natural magnetite grains can significantly reduce or eliminate their ability to reduce Cr(VI), which is a toxic and highly mobile environmental contaminant. 相似文献