全文获取类型
收费全文 | 34885篇 |
免费 | 853篇 |
国内免费 | 131篇 |
专业分类
化学 | 20910篇 |
晶体学 | 175篇 |
力学 | 905篇 |
综合类 | 10篇 |
数学 | 5469篇 |
物理学 | 8400篇 |
出版年
2022年 | 259篇 |
2021年 | 414篇 |
2020年 | 428篇 |
2019年 | 397篇 |
2018年 | 455篇 |
2017年 | 402篇 |
2016年 | 804篇 |
2015年 | 682篇 |
2014年 | 825篇 |
2013年 | 1355篇 |
2012年 | 1503篇 |
2011年 | 1675篇 |
2010年 | 1017篇 |
2009年 | 961篇 |
2008年 | 1469篇 |
2007年 | 1435篇 |
2006年 | 1352篇 |
2005年 | 1758篇 |
2004年 | 1758篇 |
2003年 | 1307篇 |
2002年 | 973篇 |
2001年 | 786篇 |
2000年 | 721篇 |
1999年 | 460篇 |
1998年 | 399篇 |
1997年 | 420篇 |
1996年 | 489篇 |
1995年 | 432篇 |
1994年 | 429篇 |
1993年 | 471篇 |
1992年 | 465篇 |
1991年 | 383篇 |
1990年 | 345篇 |
1989年 | 340篇 |
1988年 | 318篇 |
1987年 | 316篇 |
1986年 | 293篇 |
1985年 | 450篇 |
1984年 | 412篇 |
1983年 | 308篇 |
1982年 | 356篇 |
1981年 | 342篇 |
1980年 | 365篇 |
1979年 | 346篇 |
1978年 | 376篇 |
1977年 | 367篇 |
1976年 | 319篇 |
1975年 | 283篇 |
1974年 | 266篇 |
1973年 | 307篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
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
102.
103.
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
104.
105.
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
106.
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
107.
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
108.
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
109.
Alvaro P. Raposo Hans J. Weber David E. Alvarez-Castillo Mariana Kirchbach 《Central European Journal of Physics》2007,5(3):253-284
We briefly review the five possible real polynomial solutions of hypergeometric differential equations. Three of them are
the well known classical orthogonal polynomials, but the other two are different with respect to their orthogonality properties.
We then focus on the family of polynomials which exhibits a finite orthogonality. This family, to be referred to as the Romanovski
polynomials, is required in exact solutions of several physics problems ranging from quantum mechanics and quark physics to
random matrix theory. It appears timely to draw attention to it by the present study. Our survey also includes several new
observations on the orthogonality properties of the Romanovski polynomials and new developments from their Rodrigues formula. 相似文献
110.
Hamid Olia Erich Russi Hans Thomann 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1992,43(3):581-583
Summary An atomizer had been designed that could create an aerosol of a liquid with high viscosity. The amount of additional driving gas that had to be used was very low. In a cooperation with the University Hospital in Zurich the atomizer was miniaturized and used for treating six patients. 相似文献