全文获取类型
收费全文 | 3119篇 |
免费 | 94篇 |
国内免费 | 10篇 |
专业分类
化学 | 1991篇 |
晶体学 | 27篇 |
力学 | 76篇 |
数学 | 325篇 |
物理学 | 804篇 |
出版年
2023年 | 28篇 |
2022年 | 60篇 |
2021年 | 60篇 |
2020年 | 66篇 |
2019年 | 81篇 |
2018年 | 81篇 |
2017年 | 72篇 |
2016年 | 126篇 |
2015年 | 75篇 |
2014年 | 118篇 |
2013年 | 240篇 |
2012年 | 182篇 |
2011年 | 206篇 |
2010年 | 137篇 |
2009年 | 140篇 |
2008年 | 208篇 |
2007年 | 177篇 |
2006年 | 145篇 |
2005年 | 125篇 |
2004年 | 90篇 |
2003年 | 71篇 |
2002年 | 63篇 |
2001年 | 38篇 |
2000年 | 37篇 |
1999年 | 15篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 30篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 34篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 18篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 11篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1965年 | 7篇 |
排序方式: 共有3223条查询结果,搜索用时 15 毫秒
1.
In this paper, we consider linear combinations of modified Baskakov operators. By use of several lemmas, we obtain the inverse
theorem (Theorem 1.1) and the saturation (Theorem 1.2) for those linear combinations. 相似文献
2.
The stereoselective intramolecular cyclizations of bis(cinnamyl)tosylamides and dimethyl bis(cinnamyl)malonates mediated by cerium(IV) ammonium nitrate leading to the synthesis of 3,4-trans-disubstituted pyrrolidines and cyclopentanes are described. 相似文献
3.
An efficient synthesis of isothiazolidines in good yields is described. 相似文献
4.
5.
Absolute total electron scattering cross sections for carbon dioxide have been measured at low electron energies using a photoelectron
source. The measurements have been carried out at 27 electron energies varying from 0.91–9.14 eV with an accuracy of ±3%.
The cross sections obtained in the present experiment have been compared with other measurements and theoretical computations. 相似文献
6.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
7.
We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam,
which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive
relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and
focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has
been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are
elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius
of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed
to convert a circular Gaussian beam into an elliptic Gaussian beam. 相似文献
8.
Vijay Balasubramanian Donald Marolf Moshe Rozali 《General Relativity and Gravitation》2006,38(11):1529-1536
We argue that if black hole entropy arises from a finite number of underlying quantum states, then any particular such state
can be identified from infinity. The finite density of states implies a discrete energy spectrum, and, in general, such spectra
are non-degenerate except as determined by symmetries. Therefore, knowledge of the precise energy, and of other commuting
conserved charges, determines the quantum state. In a gravitating theory, all conserved charges including the energy are given
by boundary terms that can be measured at infinity. Thus, within any theory of quantum gravity, no information can be lost
in black holes with a finite number of states. However, identifying the state of a black hole from infinity requires measurements
with Planck scale precision. Hence observers with insufficient resolution will experience information loss.
First Award in the 2006 Essay Competition of the Gravity Research Foundation. 相似文献
9.
A method for the construction of the second constant of motion in fourth order is carried out. Correspondingly the fourth order potential equation is obtained whose solutions directly provide the classical integrable systems. Second constant of motion is obtained for a large class of potentials. Quantum invariants are also obtained with second order quantum corrections of the order O(?2) to the corresponding classical invariants. The phase space diagrams for these cases are drawn using a mathematical computer software package in two dimensions. 相似文献
10.
D. Behera T. Mohanty S. K. Dash T. Banerjee D. Kanjilal N. C. Mishra 《Radiation measurements》2003,36(1-6):125-129
Swift heavy ions (SHI) with electronic energy loss exceeding a value of 14.4 keVnm−1 create amorphized latent tracks in YBCO type superconductors. In the low fluence regime of an ion beam where tracks do not overlap, a decrease of the superconducting transition temperature as probed through resistivity studies, is not expected due to availability of percolating current paths. The present study however shows Tc decrease by about 1–3 K in thin films of YBCO when irradiated by 250 MeVAg ions at 79 K at a fluence of 5×1010–1×1012 ionscm−2. The highest fluence used in the present study is three times less than the fluence where track overlapping becomes significant. The Tc tends to increase towards the preirradiation value on annealing the films at room temperature. To explain this unusual result, we consider the effect of ion irradiation in inducing materials modification not only through creation of amorphized latent tracks along the ion path, but also through creation of atomic disorder in the oxygen sublattice in the Cu–O chains of YBCO by the secondary electrons. These electrons are emitted radially from the tracks during the passage of the SHI. Considering the correlation between the charge state of copper and its oxygen coordination, we show in particular that the latter process is a consequence of the inelastic interaction of the SHI induced low-energy secondary electrons with the YBCO lattice, which result in chain oxygen disorder and Tc decrease. 相似文献