全文获取类型
收费全文 | 33748篇 |
免费 | 5493篇 |
国内免费 | 5068篇 |
专业分类
化学 | 25456篇 |
晶体学 | 457篇 |
力学 | 2046篇 |
综合类 | 404篇 |
数学 | 3632篇 |
物理学 | 12314篇 |
出版年
2024年 | 108篇 |
2023年 | 597篇 |
2022年 | 1135篇 |
2021年 | 1203篇 |
2020年 | 1313篇 |
2019年 | 1319篇 |
2018年 | 1110篇 |
2017年 | 1047篇 |
2016年 | 1567篇 |
2015年 | 1683篇 |
2014年 | 1993篇 |
2013年 | 2633篇 |
2012年 | 2968篇 |
2011年 | 3219篇 |
2010年 | 2218篇 |
2009年 | 2096篇 |
2008年 | 2252篇 |
2007年 | 2065篇 |
2006年 | 1942篇 |
2005年 | 1613篇 |
2004年 | 1403篇 |
2003年 | 1085篇 |
2002年 | 1024篇 |
2001年 | 906篇 |
2000年 | 786篇 |
1999年 | 692篇 |
1998年 | 569篇 |
1997年 | 451篇 |
1996年 | 465篇 |
1995年 | 434篇 |
1994年 | 402篇 |
1993年 | 308篇 |
1992年 | 305篇 |
1991年 | 259篇 |
1990年 | 241篇 |
1989年 | 177篇 |
1988年 | 128篇 |
1987年 | 106篇 |
1986年 | 103篇 |
1985年 | 98篇 |
1984年 | 58篇 |
1983年 | 60篇 |
1982年 | 44篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 13篇 |
1977年 | 6篇 |
1975年 | 8篇 |
1973年 | 6篇 |
1957年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm 下载免费PDF全文
A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles. 相似文献
62.
63.
64.
Mid-infrared generation based on a periodically poled LiNbO3 optical parametric oscillator 下载免费PDF全文
We report a nanosecond Nd:YVO_4-pumped optical parametric oscillator (OPO) based on periodically poled LiNbO_3 (PPLN). Tuning is achieved in this experiment by varying the temperature and period of the PPLN. The design of double-pass singly resonant oscillator (DSRO) and confocal cavity enables the OPO threshold to be lowered considerably, resulting in a simple, compact, all-solid-state configuration with the mid-infrared idler powers of up to 466mW at 3.41μm. 相似文献
65.
本对于全局优化问题提出一个改进的进化规划算法,该算法以概率p接收基于电磁理论求出合力方向作为随机搜索方向,以概率1-p接收按正态分布产生的随机搜索方向。改进算法不仅克服了传统进化规划算法随机搜索的盲目性,而且保留了传统进化规划算法全局搜索性。本算法应用于几个典型例题,数值结果表明本算法是可行的,有效的。 相似文献
66.
67.
68.
We study the spectral characteristics theoretically and experimentally in the Fraunhofer diffraction pattern formed by the diffraction of a spatially coherent, polychromatic light through a slit. It is found that the spectrum in some diffraction directions close to the singular direction is redshifted, compared to the spectrum of the incident polychromatic light, and blueshifted in other directions, and splits into two lines at the singular direction. We show that the experimental results are consistent with the theoretical expectations. 相似文献
69.
Ping Li Fei Rong Yibing Xie Van Hu Chunwei Yuan 《Journal of Analytical Chemistry》2004,59(10):939-944
S-naproxen imprinted polymer was prepared with acrylamide as a functional monomer, 1,4-butanediyl diacrylate as a new kind of crossliner, and 2,4,6-trimethylbenzoylphenyl-phosphinic acid ethyl ester as photoinitiator. Their UV and IR spectra were applied to study the interactions between the template and the monomer. Binding experiments showed that the S-naproxen imprinted polymer had better recognition capability for the template than that of a blank polymer. The adsorption distribution coefficient KD of S-naproxen on molecularly-imprinted polymer was 153.2 g/mL, and the separation factor was 1.95 when the initial concentration of substrate was 2.0 mmol/L. Scatchard curves suggested that there were two classes of binding sites in the imprinted polymer and only one class in the blank polymer. Computer simulation using Hyperchem showed the existence of the interactions between the template and the functional monomer as well as the models of the complexes formed by the template and the monomer. 相似文献
70.
Efforts are made to explore the hysteresis characteristics of vortex shedding in a pipe flow, whose velocity varies periodically in time. Results obtained show that during acceleration of the flow, the vortex strength tends to be stronger, whereas during deceleration of the flow, the situation is reversed. As reconstructed from the velocity signals measured at a point in the flow field, the shed vortex arrays appear to possess uneven vortex strengths in response to periodically-varying incoming flows. Furthermore, in the hysteresis range, the streamwise spacings between the vortices appear to be unequal. 相似文献