全文获取类型
收费全文 | 22153篇 |
免费 | 3609篇 |
国内免费 | 1690篇 |
专业分类
化学 | 9862篇 |
晶体学 | 590篇 |
力学 | 3568篇 |
综合类 | 194篇 |
数学 | 5347篇 |
物理学 | 7891篇 |
出版年
2024年 | 53篇 |
2023年 | 236篇 |
2022年 | 471篇 |
2021年 | 590篇 |
2020年 | 950篇 |
2019年 | 697篇 |
2018年 | 609篇 |
2017年 | 741篇 |
2016年 | 1034篇 |
2015年 | 923篇 |
2014年 | 1145篇 |
2013年 | 1639篇 |
2012年 | 1152篇 |
2011年 | 1299篇 |
2010年 | 1176篇 |
2009年 | 1237篇 |
2008年 | 1364篇 |
2007年 | 1487篇 |
2006年 | 1327篇 |
2005年 | 1201篇 |
2004年 | 1094篇 |
2003年 | 1133篇 |
2002年 | 872篇 |
2001年 | 760篇 |
2000年 | 667篇 |
1999年 | 574篇 |
1998年 | 466篇 |
1997年 | 406篇 |
1996年 | 303篇 |
1995年 | 240篇 |
1994年 | 204篇 |
1993年 | 197篇 |
1992年 | 157篇 |
1991年 | 137篇 |
1990年 | 120篇 |
1989年 | 78篇 |
1988年 | 74篇 |
1987年 | 73篇 |
1986年 | 67篇 |
1985年 | 77篇 |
1984年 | 68篇 |
1983年 | 44篇 |
1982年 | 49篇 |
1981年 | 52篇 |
1980年 | 28篇 |
1979年 | 40篇 |
1978年 | 44篇 |
1977年 | 34篇 |
1976年 | 20篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this paper, we have developed an analytical model to study the temperature distributions in IR optical materials heated by laser pulses. Our model takes into account the two-photon absorption (TPA). The calculations are based on a three-dimensional model of heat diffusion in solids using the integral transform method. We find out the rigorous analytical expression of the thermal field when one considers both one- and two-photon absorption. The model is valid for any laser–solid system whose interaction can be described by the generalized Beer–Lambert law. Specific results are presented for an application of the model to ZnSe sample. We find out that TPA can produce detectable temperature variation. 相似文献
102.
In this paper, based on the Lame function and Jacobi elliptic function, the perturbation method is appliedto some nonlinear evolution equations to derive their multi-order solutions. 相似文献
103.
Margherita De RosaMaria Rosaria Acocella Rosaria VillanoAnnunziata Soriente Arrigo Scettri 《Tetrahedron letters》2003,44(32):6087-6090
Initial concentration of enantioenriched or enantiopure catalysts proved to be an important factor for the achievement of a more pronounced amplification of ee's in the Ti(IV)/BINOL-catalyzed aldol reaction of an O-silyldienolate. 相似文献
104.
105.
As predicted by Haldane, spin, S=1 one-dimensional (1D) Heisenberg antiferromagnet (HAF) has an energy gap between the singlet ground state and first excited triplet. On application of magnetic field, the triplet state Zeeman splits and the energy of one of the triplet state becomes zero at a critical field, Hc. Above Hc the system recovers magnetism. Then, we expect that a quasi-1D HAF will show a magnetic long-range ordering (LRO) at low temperatures due to the inter-chain coupling. This field-induced LRO has not been observed before due to complication of the crystal structure in the materials studied so far and/or technical difficulty.From a heat capacity measurement on a single crystal of an S=1 quasi-Q1D HAF, Ni(C5H14N2)2N3(PF6), we found an anomaly at a temperature in finite fields indicating a field-induced phase transition. A magnetic LRO is confirmed by a neutron diffraction measurement on the same sample. The temperature versus magnetic field phase diagram of this compound is constructed and discussed. 相似文献
106.
Akhlesh Lakhtakia 《Optik》2004,115(4):151-158
107.
The influence of the parameter of amplitude-phase coupling for nonlinear amplification on the phase-frequency characteristics of an injection laser in the regime of pumping current modulation has been investigated theoretically. The parameter is defined as the coefficient of proportionality between changes in the real and imaginary parts of the refractive index during variation of the density of photons in the cavity. The substantial dependence of the coefficient of phase modulation on the parameter of the amplitude-phase coupling for nonlinear amplification at small modulation frequencies is shown. A technique to determine the indicated parameter based on the frequency dependence of the ratio between the coefficients of phase and amplitude modulation is suggested. 相似文献
108.
N. S. Kazak E. G. Katranji I. A. Utkin A. A. Ryzhevich A. N. Khilo 《Journal of Applied Spectroscopy》2004,71(5):697-701
The phenomenon of self-diffraction of Bessel light beams (BLB) in a nonlinear liquid medium has been studied experimentally and theoretically for the first time. Diffraction maxima which do not correspond to integer orders for an induced periodic structure have been registered. It has been shown that the appearance of these maxima is due to the initial BLB modulation, which can be caused by the departure of the axicon refracting surface from the ideal conical surface, as well as by the imperfection of the form of the Gaussian beam incident on the axicon. 相似文献
109.
110.
本文利用比较原理以及一种特殊变换研究了一类非线性退化方程的混合问题,得到了这类复杂问题解的渐进性质。 相似文献