全文获取类型
收费全文 | 20044篇 |
免费 | 4268篇 |
国内免费 | 3940篇 |
专业分类
化学 | 9051篇 |
晶体学 | 865篇 |
力学 | 602篇 |
综合类 | 179篇 |
数学 | 2495篇 |
物理学 | 15060篇 |
出版年
2024年 | 74篇 |
2023年 | 171篇 |
2022年 | 443篇 |
2021年 | 490篇 |
2020年 | 539篇 |
2019年 | 478篇 |
2018年 | 509篇 |
2017年 | 806篇 |
2016年 | 980篇 |
2015年 | 798篇 |
2014年 | 1239篇 |
2013年 | 2054篇 |
2012年 | 1684篇 |
2011年 | 1605篇 |
2010年 | 1264篇 |
2009年 | 1402篇 |
2008年 | 1594篇 |
2007年 | 1490篇 |
2006年 | 1342篇 |
2005年 | 1197篇 |
2004年 | 1022篇 |
2003年 | 906篇 |
2002年 | 861篇 |
2001年 | 792篇 |
2000年 | 688篇 |
1999年 | 626篇 |
1998年 | 529篇 |
1997年 | 478篇 |
1996年 | 399篇 |
1995年 | 383篇 |
1994年 | 331篇 |
1993年 | 235篇 |
1992年 | 194篇 |
1991年 | 127篇 |
1990年 | 106篇 |
1989年 | 81篇 |
1988年 | 74篇 |
1987年 | 52篇 |
1986年 | 35篇 |
1985年 | 36篇 |
1984年 | 32篇 |
1983年 | 18篇 |
1982年 | 26篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
The implementation of a nonzero-order joint transform correlator using the double port Mach-Zehnder interferometric technique is proposed and demonstrated. This approach provides on-line processing for directly removing the zero-order components of a joint power spectrum in one step and performs the nonzero-order optical correlation. Experimental results are presented and discussed. 相似文献
24.
Hirohisa Yokota Kenji Kamoto Jun-ichi Igarashi Norihiko Mouri Yutaka Sasaki 《Optical Review》2002,9(1):9-12
A new configuration for an ASE reduction filter in EDFA repeaters for WDM optical transmission systems using optical fiber grating couplers (FGCs) was proposed and first demonstrated. The filtering characteristics of the proposed filter for amplified single wavelength signal and 2-channel WDM signals using EDFA were identified. It was found that the filter was effective to improve SNR in optical domain by reducing ASE noise. The required FGC characteristics for the filter were theoretically predicted under the condition that the total filter loss did not exceed 3 dB. More than 70% of drop efficiency was required in each FGC for the application of the proposed filter to an 8-channel WDM system using EDFA repeaters. 相似文献
25.
Tunable properties of light propagation in photonic crystal fibers filled with liquid crystals, called photonic liquid crystal
fibers (PLCFs) are presented. The propagation properties of PLCFs strongly depend on contrast between refractive indices of
the solid core (pure silica glass) and liquid crystals (LCs) filing the holes of the fiber. Due to relatively strong thermo-optical
effect, we can change the refractive index of the LC by changing its temperature. Numerical analysis of light propagation
in PLCF, based on two simulation methods, such as finite difference (FD) and multipole method (MM) is presented. The numerical
results obtained are in good agreement with our earlier experimental results presented elsewhere [1]. 相似文献
26.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
27.
功能性丙烯酸/MBAM体系共聚产物的研制 总被引:2,自引:0,他引:2
以丙烯酸和MBAM为主要原料,经聚合,合成了一种高性能的具有良好保水性能的聚合产物,其保水量达到750~1000倍.50℃以下有良好的保水性能,28℃以下有极好的保水性能,并研究了工艺条件对该产品性能的影响因素. 相似文献
28.
Monodisperse polyaniline nanoparticles (PAPSSA) were synthesized from an oxidative dispersion polymerization using poly(sodium 4-styrenesulfonate) (PSSA) as both a polymeric stabilizer and a dopant agent due to its acidity. The nanoparticles were being stabilized with two different molecular weight of PSSA. Size effect of PAPSSA particles were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The d.c. electrical conductivity of composite films on the glass substrate was measured by a four-probe method. It was found that the electrical properties of the composite films are affected by the content of nano-sized polyaniline and different molecular weights of stabilizer in the poly(vinyl alcohol) (PVA) matrix. 相似文献
29.
30.
We propose a new approach towards proving that the fixed point property for ordered sets is preserved by products. This approach uses a characterization of fixed points in products via isotone relations. First explorations of classes of isotone relations are presented. These first explorations give us hope that this approach could lead to advances on the Product Problem. 相似文献