全文获取类型
收费全文 | 3524篇 |
免费 | 1715篇 |
国内免费 | 949篇 |
专业分类
化学 | 570篇 |
晶体学 | 124篇 |
力学 | 548篇 |
综合类 | 102篇 |
数学 | 352篇 |
物理学 | 4492篇 |
出版年
2024年 | 32篇 |
2023年 | 109篇 |
2022年 | 134篇 |
2021年 | 174篇 |
2020年 | 104篇 |
2019年 | 103篇 |
2018年 | 83篇 |
2017年 | 159篇 |
2016年 | 124篇 |
2015年 | 166篇 |
2014年 | 296篇 |
2013年 | 212篇 |
2012年 | 235篇 |
2011年 | 269篇 |
2010年 | 293篇 |
2009年 | 272篇 |
2008年 | 298篇 |
2007年 | 243篇 |
2006年 | 284篇 |
2005年 | 294篇 |
2004年 | 314篇 |
2003年 | 266篇 |
2002年 | 239篇 |
2001年 | 189篇 |
2000年 | 157篇 |
1999年 | 141篇 |
1998年 | 108篇 |
1997年 | 108篇 |
1996年 | 114篇 |
1995年 | 115篇 |
1994年 | 80篇 |
1993年 | 73篇 |
1992年 | 98篇 |
1991年 | 87篇 |
1990年 | 69篇 |
1989年 | 76篇 |
1988年 | 16篇 |
1987年 | 27篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 3篇 |
排序方式: 共有6188条查询结果,搜索用时 15 毫秒
71.
Nano-Crystalline Diamond Films with Pineapple-Like Morphology Grown by the DC Arcjet vapor Deposition Method 下载免费PDF全文
A nano-crystlline diamond film is grown by the dc arcjet chemical vapor deposition method. The film is characterized by scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) and Ftaman spectra, respectively. The nanocrystalline grains are averagely with 80hm in the size measured by XRD, and further proven by Raman and HRTEM. The observed novel morphology of the growth surface, pineapple-like morphology, is constructed by cubo-octahedral growth zones with a smooth faceted top surface and coarse side surfaces. The as-grown film possesses (100) dominant surface containing a little amorphous sp2 component, which is far different from the nano-crystalline film with the usual cauliflower-like morphology. 相似文献
72.
In this work, we derive the nuclear form factor for the spin-independent collision between the WIMPs and nucleus in terms of the relativistic mean field (RMF) theory. Comparison with the traditional form factors which are commonly used in literature is given and it is found that our results are slightly above that of the 2PF model by 4% to 8%, but deviate from the Helm form factor by 15% to 25% for the whole recoil energy spectrum of 0 ∽ 100keV. Moreover, taking Xe and Ge as examples, we show the dependenceof the form factor on the recoil energy. 相似文献
73.
We report a theoretical study on producing electrically spin-polarized current in the Rashba ring with parallel double dots embedded, which are subject to two time-dependent microwave fields. By means of the Keldysh Green's function method, we present an analytic result of the pumped current at adiabatic limit and demonstrate that the interplay between the quantum pumping effectand spin-dependent quantum interference can lead to an arbitrarily controllable spin-polarized current in the device. The magnitude and direction of the charge and spin current can be effectively modulated by system parameters such as the pumping phase difference, Rashba precession phase, and the dynamic phase difference of electron traveling in two arms of ring; moreover, thespin-polarization degree of the charge current can also be tuned in the range [-∞, +∞]. Our findings may shed light on the all-electric way to produce the controllable spin-polarized charge current in the field of spintronics. 相似文献
74.
The interference of high-order harmonics generated by two successive gas jets within a single laser pulse is discussed by a modeling with the inclusion of macroscopic propagation of the fundamental and harmonic fields in an ionizing medium. Based on the interference, we show that one can extract the laser Rayleigh range from the interference of harmonics and the accuracy of retrieve is independent of carrier-envelope phase while dependent on the pulse duration. Moreover~ we demonstrate that it is possible to optimize the single or range of harmonics with a high ratio relative to the adjacent orders by changing the separation of two gas jets, which is unavailable by using a single gas jet and linear polarized laser pulse. 相似文献
75.
We derive the basic canonical brackets amongst the creation and annihilation operators for a two (1 + 1)- dimensional (2D) gauge field theoretic model of an interacting Hodge theory where a U(1) gauge field (Aμ) is coupled with the fermionic Dirac fields (ψ and ψ). In this derivation, we exploit the spin-statistics theorem, normal ordering and the strength of the underlying six infinitesimal continuous symmetries (and the concept of their generators) that are present in the theory. We do not use the definition of the canonical conjugate momenta (corresponding to the basic fields of the theory) anywhere in our whole discussion. Thus, we conjecture that our present approach provides an alternative to the canonical method of quantization for a class of gauge field theories that are physical examples of Hodge theory where the continuous symmetries (and corresponding generators) provide the physical realizations of the de Rham cohomological operators of differential geometry at the algebraic level. 相似文献
76.
77.
78.
在直流电路中,由于滑动变阻器滑片的移动,或者由于电键的接通与断开,或者由于某一用电器的突然烧坏等因素,导致电路中的总电阻发生变化,从而使电路中的电流、电压和电功率等物理量随之变化,这类问题叫做电路动态变化问题,它是直流电路中最常见的一种题型。 相似文献
79.
A nonmean-field model for the ripening of two-dimensional islands is presented. In this model, the adatom sea is divided into many small cells that are the polygons of a Voronoi network. The chemical potentials of adatom seas surrounding different islands are different. Strain generated by lattice mismatch is introduced into the model.Computer simulation under periodic boundary conditions is carried out to describe the island ripening in two cases (with and without strain), and demonstrates that small islands may grow faster than large islands, which cannot occur in the mean-field model. The simulated results also show that including strain will slow down the evolution of average island size, and an explanation for this is given. 相似文献
80.