全文获取类型
收费全文 | 140284篇 |
免费 | 24439篇 |
国内免费 | 23939篇 |
专业分类
化学 | 100528篇 |
晶体学 | 2427篇 |
力学 | 8442篇 |
综合类 | 2201篇 |
数学 | 18687篇 |
物理学 | 56377篇 |
出版年
2024年 | 312篇 |
2023年 | 2389篇 |
2022年 | 3944篇 |
2021年 | 4777篇 |
2020年 | 5411篇 |
2019年 | 5148篇 |
2018年 | 4800篇 |
2017年 | 4822篇 |
2016年 | 6278篇 |
2015年 | 6541篇 |
2014年 | 8048篇 |
2013年 | 10667篇 |
2012年 | 12173篇 |
2011年 | 12904篇 |
2010年 | 9697篇 |
2009年 | 9716篇 |
2008年 | 10293篇 |
2007年 | 9229篇 |
2006年 | 8876篇 |
2005年 | 7534篇 |
2004年 | 5967篇 |
2003年 | 4604篇 |
2002年 | 4382篇 |
2001年 | 3996篇 |
2000年 | 3788篇 |
1999年 | 3210篇 |
1998年 | 2416篇 |
1997年 | 2130篇 |
1996年 | 2068篇 |
1995年 | 1807篇 |
1994年 | 1680篇 |
1993年 | 1426篇 |
1992年 | 1254篇 |
1991年 | 1075篇 |
1990年 | 935篇 |
1989年 | 788篇 |
1988年 | 603篇 |
1987年 | 518篇 |
1986年 | 509篇 |
1985年 | 376篇 |
1984年 | 320篇 |
1983年 | 272篇 |
1982年 | 210篇 |
1981年 | 172篇 |
1980年 | 127篇 |
1979年 | 74篇 |
1978年 | 54篇 |
1977年 | 31篇 |
1976年 | 35篇 |
1975年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
本文通过定义本原逆半群在集合上的部分作用及其整体化,给出了E*-酉范畴逆半群的结构. 相似文献
952.
953.
Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs. 相似文献
954.
Optical Recording Properties of Metal-Azo Dye as Recording Medium with Super-Resolution Near-Field Structure
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A novel metallized azo dye has been synthesized. The absorption spectra of the thin film and thermal characteristic are measured. Static optical recording properties with and without the Bi mask layer super-resolution near-field structure (Super-RENS) of the metal-azo dye are investigated. The results show that the metal-azo dye film has a broad absorbance band in the region of 450-650 nm and the maximum absorbance wavelength is located at 603 nm. It is also found that the new metallized azo dye occupies excellent thermal stability, initiatory decomposition temperature is at 270℃ and the mass loss is about 48% in a narrow temperature region (15℃). The complex refractive index N (N = n + iκ) is measured. High refractive index (n = 2.45) and low extinction coefficient (κ = 0.2) at the recording wavelength 65Ohm are attained. Static optical recording tests with and without Super-RENS are carried out using a 65Ohm semiconductor diode laser with recording power of 7mW and laser pulse duration of 200ns. The AFM images show that the diameter of recording mark on the dye film with the Bi mask layer is reduced about 42%, compared to that of recorded mark on the dye film without Super-RENS. It is indicated that Bi can well performed as a mask layer of the dye recording layer and the metallized azo dye can be a promising candidate for recording media with the super-resolution near-field structure. 相似文献
955.
A multisymplectic variational internal energy corresponding equation, its associated local framework for the nonlinear elastic wave equation is presented. The modified to the approximate nonlinea.r elastic wave equation is derived, we obtain the energy and momentum conservation laws as well as the multisymplectic form simultaneously directly from the variational principle 相似文献
956.
An economical magnetocardiogram (MCG) system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device (SQUID) magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements. 相似文献
957.
采用基于识别的分割方法进行手写数字串分割.在识别的过程中,运用反例样本估计分类器参数,实验数据表明,这种运用反例样本训练的分类器与没有经过反例样本训练的分类器相比,将提高拒识率到19%左右,从而保证了较高的识别率,验证了只有经过反例训练的分类器的输出结果才是可信赖的. 相似文献
958.
We consider in this paper the Lagrangian dual method for solving general integer programming. New properties of Lagrangian
duality are derived by a means of perturbation analysis. In particular, a necessary and sufficient condition for a primal
optimal solution to be generated by the Lagrangian relaxation is obtained. The solution properties of Lagrangian relaxation
problem are studied systematically. To overcome the difficulties caused by duality gap between the primal problem and the
dual problem, we introduce an equivalent reformulation for the primal problem via applying a pth power to the constraints. We prove that this reformulation possesses an asymptotic strong duality property. Primal feasibility
and primal optimality of the Lagrangian relaxation problems can be achieved in this reformulation when the parameter p is larger than a threshold value, thus ensuring the existence of an optimal primal-dual pair. We further show that duality
gap for this partial pth power reformulation is a strictly decreasing function of p in the case of a single constraint.
Dedicated to Professor Alex Rubinov on the occasion of his 65th birthday. Research supported by the Research Grants Council
of Hong Kong under Grant CUHK 4214/01E, and the National Natural Science Foundation of China under Grants 79970107 and 10571116. 相似文献
959.
We propose an irreversible binary coagulation model with a constant-reaction-number kernel, in which, among all the possible binary coagulation reactions, only p reactions are permitted to take place at every time. By means of the generalized rate equation we investigate the kinetic behaviour of the system with the reaction rate kernel K(i;j) = (ij)^w (0 ≤w〈1/2), at which an i-mer and a j-mer coagulate together to form a large one. It is found that for such a system there always exists a gelation transition at a finte time to, which is in contrast to the ordinary binary coagulation with the same rate kernel. Moreover, the pre-gelation behaviour of the cluster size distribution near the gelation point falls in a scaling regime and the typical cluster size grows as (to - t)-1/(1-2w). On the other hand, our model can also provide some predictions for the evolution of the cluster distribution in multicomponent complex networks. 相似文献
960.
Compact Single-Stage Femtosecond Multipass Ti:Sapphire Amplifier at 1 kHz with High Beam Quality
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A compact femtosecond Ti:sapphire amplifier system is reported using single-stage multipass configuration with high beam quality. A high dispersion glass stretcher and a pair of double prisms for compression are introduced based on broadband femtosecond seed pulses. The non-grating-based pulse stretcher and compressor are advantageous to increase high beam quality and to reduce the high-order dispersion. A Gaussian filter is used to reduce the gain narrowing effect in amplification. The compact femtosecond Ti:sapphire nine-pass amplifier delivers pulses with a duration of 26 fs and an energy of 800μJ at 7mJ pumping pulses energy at I kHz. The 1-kHz femtosecond amplifier with high beam quality and high stability is very suitable for ultrafast physics research applications, such as attosecond science, ultra-precision micromachining, and THz wave generation. 相似文献