全文获取类型
收费全文 | 27502篇 |
免费 | 617篇 |
国内免费 | 107篇 |
专业分类
化学 | 15671篇 |
晶体学 | 171篇 |
力学 | 827篇 |
综合类 | 9篇 |
数学 | 3808篇 |
物理学 | 7740篇 |
出版年
2023年 | 122篇 |
2022年 | 288篇 |
2021年 | 477篇 |
2020年 | 432篇 |
2019年 | 395篇 |
2018年 | 458篇 |
2017年 | 425篇 |
2016年 | 738篇 |
2015年 | 602篇 |
2014年 | 693篇 |
2013年 | 1128篇 |
2012年 | 1438篇 |
2011年 | 1645篇 |
2010年 | 926篇 |
2009年 | 901篇 |
2008年 | 1364篇 |
2007年 | 1331篇 |
2006年 | 1213篇 |
2005年 | 1616篇 |
2004年 | 1613篇 |
2003年 | 1146篇 |
2002年 | 772篇 |
2001年 | 641篇 |
2000年 | 583篇 |
1999年 | 392篇 |
1998年 | 320篇 |
1997年 | 320篇 |
1996年 | 383篇 |
1995年 | 326篇 |
1994年 | 329篇 |
1993年 | 344篇 |
1992年 | 337篇 |
1991年 | 279篇 |
1990年 | 229篇 |
1989年 | 222篇 |
1988年 | 193篇 |
1987年 | 183篇 |
1986年 | 180篇 |
1985年 | 236篇 |
1984年 | 220篇 |
1983年 | 188篇 |
1982年 | 196篇 |
1981年 | 192篇 |
1980年 | 176篇 |
1979年 | 157篇 |
1978年 | 180篇 |
1977年 | 148篇 |
1976年 | 141篇 |
1974年 | 134篇 |
1973年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
81.
Mathilde Kammerer-Colin de Verdière 《Comptes Rendus Mathematique》2004,339(9):625-629
For generic families of vector fields or transformations, normally hyperbolic invariant products of spheres appear near partially elliptic rest points. To cite this article: M. Kammerer-Colin de Verdière, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献
82.
What features characterize complex system dynamics? Power laws and scale invariance of fluctuations are often taken as the hallmarks of complexity, drawing on analogies with equilibrium critical phenomena. Here we argue that slow, directed dynamics, during which the system's properties change significantly, is fundamental. The underlying dynamics is related to a slow, decelerating but spasmodic release of an intrinsic strain or tension. Time series of a number of appropriate observables can be analyzed to confirm this effect. The strain arises from local frustration. As the strain is released through “quakes,” some system variable undergoes record statistics with accompanying log‐Poisson statistics for the quake event times. We demonstrate these phenomena via two very different systems: a model of magnetic relaxation in type II superconductors and the Tangled Nature model of evolutionary ecology and show how quantitative indications of aging can be found. © 2004 Wiley Periodicals, Inc. Complexity 10: 49–56, 2004 相似文献
83.
This paper describes an application of statics to geometrical proofs in the classroom. The aim of the study was to find out whether the use of concepts and arguments from statics can help students understand and produce proofs of geometrical theorems. The two theorems studied were (1) that the medians in a triangle meet at a single point which is the centre of gravity of the triangle, and (2) the Varignon theorem, that the lines joining the midpoints of successive sides of a quadrilateral form a parallelogram. The classroom experiment showed that most students were successful in using arguments from statics in their proofs, and that they gained a better understanding of the theorems. These findings lend support to the claim that the introduction of statics helps students produce proofs and grasp their meaning. 相似文献
84.
85.
We perform three tests on our proposal to implement diffeomorphism invariance in the non-abelian D0-brane DBI action as a base-point independence constraint between matrix Riemann normal coordinate systems. First, we show that T-duality along an isometry correctly interchanges the potential and kinetic terms in the action. Second, we show that the method to impose base-point independence using an auxiliary dN2-dimensional nonlinear sigma model also works for metrics which are curved along the brane, provided a physical gauge choice is made at the end. Third, we show that without alteration this method is applicable to higher order in velocities. Testing specifically to order 4, we elucidate the range of validity of the symmetrized trace approximation to the non-abelian DBI action. 相似文献
86.
E.D. Aydin C.R.E. de Oliveira 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(3):247-260
In this paper, we solve the steady-state form of the Boltzmann transport equation in homogeneous and heterogeneous tissue-like media with a finite element-spherical harmonics (FE-PN) radiation transport method. We compare FE-transport and diffusion solutions in terms of the ratio of absorption to reduced scattering coefficient, (μa/μs′) and the anisotropy factor g. Two different scattering phase function formulas are employed to model anisotropic scattering in the slab media with high g-value. Influence of void-like heterogeneities, and of their boundaries with the surrounding medium on the transport of photons are also examined. 相似文献
87.
We show that reductions of KP hierarchies related to the loop algebra of SLn with homogeneous gradation give solutions of the Darboux-Egoroff system of PDE's. Using explicit dressing matrices of the Riemann-Hilbert problem generalized to include a set of commuting additional symmetries, we construct solutions of the Witten– Dijkgraaf–E. Verlinde–H. Verlinde equations. 相似文献
88.
报道Ar^q Ne(q=8,9,11,12)碰撞体系中多电子转移过程,得到了多组实验测量电荷交换截面数据,讨论入射离子电荷交换截面、反冲离子产生截面与入射离子电荷态、能量以及散射离子电荷态的关系,并且将实验结果与Ar^q Ar碰撞体系进行对比研究。在修正分子库仑过垒模型的基础上,对实验现象做了合理的解释。 相似文献
89.
C. S. Munita L. P. Barroso P. M. S. Oliveira 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):335-338
Summary In general, when characterizing samples, such as ceramic samples or other types of samples, for first time by means of chemical
elements, the analyst measures a large number of variables, many of which may not be very informative. In fact, some may even
be unrelated to the issue at hand and blur the picture instead of making it clearer. In subsequent studies the analyst may
wish to measure fewer variables for several reasons, such as being very time consuming; in cases where measurement time is
important, such as on-line monitoring; in order to reduce cost or effort; etc. Therefore, the hope is to determine those variables
that are most relevant without losing essential information and to remove the less productive information. The problem is
how to perform this in an objective way and to capture crucial information using a multivariate analysis. This paper aims
to describe and illustrate a stopping rule for the identification of redundant variables, and the selection of variable subsets,
preserving multivariate data structure using stepwise discriminant analysis, selecting those variables that are in some senses
adequate for discrimination purposes. One illustrative example using data sets obtained via INAA of ceramic samples from two
archaeological sites is provided. 相似文献
90.
Marcos Almeida Bezerra Sérgio Mitihiro do Nascimento Maêda Eliane Padua Oliveira Maria de Fátima Batista de Carvalho Ricardo Erthal Santelli 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
In the present paper a procedure is proposed for the determination of traces of Cd, Co, Mn and Cr in petroleum industry produced water by inductively coupled plasma optical emission spectrometry. The procedure is based on cloud point extraction of these metals, as their dithizonate complexes, into the surfactant-rich phase of octylphenoxypolyethoxyethanol surfactant (Triton X-114). Extractions were carried out in solutions with salinities between 10‰ and 70‰. Since residual salinity in the surfactant-rich phase caused differences in its transport to the plasma, yttrium was used as an internal standard to correct for this effect. The simultaneous metal extraction procedure was optimized by response surface methodology using a Doehlert design and desirability function. Enhancement factors of 21, 21, 9 and 19, along with limits of quantification of 0.093, 0.20, 0.73 and 1.2 μg L− 1, and precision expressed as relative standard deviation (n = 8, 20.0 μg L− 1) of 5.8, 1.2, 1.7 and 5.7% were obtained for Cd, Co, Mn and Cr, respectively. The accuracy was evaluated by spike recovery tests on the high salinity water samples with salinity of 40 and 63‰. 相似文献