全文获取类型
收费全文 | 1660篇 |
免费 | 280篇 |
国内免费 | 175篇 |
专业分类
化学 | 1165篇 |
晶体学 | 18篇 |
力学 | 91篇 |
综合类 | 10篇 |
数学 | 147篇 |
物理学 | 684篇 |
出版年
2024年 | 2篇 |
2023年 | 45篇 |
2022年 | 37篇 |
2021年 | 55篇 |
2020年 | 91篇 |
2019年 | 78篇 |
2018年 | 50篇 |
2017年 | 47篇 |
2016年 | 73篇 |
2015年 | 79篇 |
2014年 | 68篇 |
2013年 | 95篇 |
2012年 | 115篇 |
2011年 | 143篇 |
2010年 | 111篇 |
2009年 | 117篇 |
2008年 | 123篇 |
2007年 | 104篇 |
2006年 | 109篇 |
2005年 | 92篇 |
2004年 | 57篇 |
2003年 | 47篇 |
2002年 | 42篇 |
2001年 | 50篇 |
2000年 | 37篇 |
1999年 | 42篇 |
1998年 | 29篇 |
1997年 | 25篇 |
1996年 | 33篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1982年 | 1篇 |
排序方式: 共有2115条查询结果,搜索用时 484 毫秒
121.
122.
A simple and reliable RP-HPLC method has been developed for the simultaneous determination of ropivacaine and antipyrine in perfusate samples. Samples were analyzed on an ODS column with UV detection at 210 nm after liquid-liquid extraction. The mobile phase consisted of potassium dihydrogenphosphate (25 mM, adjusted to pH 5.0 with phosphoric acid)-acetonitrile (79:21, v/v). The method has been validated to be precise, accurate and linear. It has been applied to the investigation of placental transfer of ropivacaine via a dually perfused cotyledon model of human placenta in vitro. 相似文献
123.
利用液芯光纤技术研究了不同浓度的β-Carotene的CS2溶液的吸收与荧光的特性对CS2的一、二阶Stokes谱线阈值的影响.实验发现随溶液浓度(10-8—10-6 mol/L)增加,CS2的一阶Stokes谱线的激发阈值相对变高;并且与纯CS2芯液的受激拉曼散射相比较,在低抽运能量激发下,就观察到CS2的二阶Stokes谱线.这主要是由于在CS2的受激拉曼谱线产生的过程中,β-Carotene的CS2溶液的吸收和荧光共同影响了CS2的一、二阶Stokes谱线的阈值.我们进行了理论上的拟合与分析,其结果与实验符合很好.
关键词:
2受激拉曼散射阈值')" href="#">CS2受激拉曼散射阈值
液芯光纤
吸收与荧光 相似文献
124.
H.T. Huang J.L. He C.H. Zuo H.J. Zhang J.Y. Wang Y. Liu H.T. Wang 《Applied physics. B, Lasers and optics》2007,89(2-3):319-321
We have demonstrated an efficient diode-pumped passively Q-switched Nd:YVO4 laser at 1342 nm by using an uncoated Co2+:LaMgAl11O19 (Co2+:LMA) crystal as the saturable absorber. With the absorbed pump power of 11.7 W, the pulse width could be as low as 42 ns,
with a corresponding average output power of 580 mW. At around 40 kHz repetition rate, the energy of a single Q-switched pulse
was estimated to be about 14.5 μJ and the peak power was 346 W. The passive Q switching operation for the Co2+:LMA in different polarization states was also investigated.
PACS 42.55.-f; 42.55.Xi; 42.60.Gd; 42.70.Mp 相似文献
125.
利用液芯光纤技术研究了不同浓度的β-Carotene的CS2溶液的吸收与荧光的特性对CS2的一、二阶Stokes谱线阈值的影响.实验发现随溶液浓度(10-8-10-6 mol/L)增加,CS2的一阶Stokes谱线的激发阈值相对变高;并且与纯CCS2芯液的受激拉曼散射相比较,在低抽运能量激发下,就观察到CS2的二阶Stokes谱线.这主要是由于在CS2的受激拉曼谱线产生的过程中,β-Carotene的CS2溶液的吸收和荧光共同影响了CS2的一、二阶Stokes谱线的阈值.我们进行了理论上的拟合与分析,其结果与实验符合很好. 相似文献
126.
A new noise-removal technique is applied to scanning laser microscopic (SLM) images to remove clustered spike noise in the images and to recover the shapes of diamond abrasive grains degraded by the noise. For achievement of this purpose, noise points in the SLM image are accurately detected by taking advantage of their properties in the space and spatial-frequency regions. The noise points are removed by a method of smoothing that is based on linear interpolation; that is, their pixel values are replaced by the interpolated values of their non-noise neighboring points. Noise-point information in the space region is acquired from image segmentation based on pixel classification, while noise-point information in the frequency region is derived from redundant wavelet decomposition for the SLM image. Fisher's linear discriminant method is used to yield the two noise-point images. The degraded grain shapes in the SLM images at different noise levels are satisfactorily recovered with a single iteration of smoothing without losses in sharp edges although a single smoothing needed four interpolations. Thus, the present noise-removal technique is shown to be effective for recovering the original shapes of the grains in every SLM image. 相似文献
127.
The robust phase locking of a linear diode array consisting of 49 broad-area emitters was demonstrated.The single lobe in the far field with output power of 0.83 W was observed. The far-field divergence was reduced to 2.0 mrad. The spectral bandwidth was reduced from 1.7 to 0.13 nm. 相似文献
128.
A tunable optical rail is embedded into the cavity of a nonlinear-polarization-rotation(NPR) mode-locked fiber laser to generate a sampling pulse with different repetition frequencies and realize bit-rate-adaptive software synchronous optical sampling.Two ultrashort pulses(20.26677 and 20.22900 MHz) are derived,and a 100-MHz data signal is sampled twice with these pulses based on sum-frequency generation(SFG) in periodically poled lithium niobate(PPLN).The eye diagram is successfully recovered,and an estimated bit rate of 102.22 MHz is derived.This method is feasible for bit rates ranging from 200 MHz to 1 GHz,with <3% relative error. 相似文献
129.
Shi Wang Xue-Hua Ding Jing-Lin Zuo Xiao-Zeng You Wei Huang 《Coordination chemistry reviews》2011,255(15-16):1713-1732
Cyano-bridged molecule-based magnetic materials with reduced dimensionality, such as single-molecule magnets (SMMs) and single-chain magnets (SCMs), have attracted great research interest during the last decade. Among the cyano-based molecular precursors with ample coordinating capability, we note the ability of the tricyanometalate to link various metal ions lead to a wide diversity of structural architectures ranging from discrete polynuclear complexes to various one-dimensional (1D) assemblies. Some of them are promising cyano-bridged SMMs and SCMs. The use of capping tridentate organic ligands results in a number of clusters containing di-, tri-, tetra-, penta-, hexa-, octa-, fourteen-nuclear and various 1D metal-cyanide molecular architectures. Here we review the structural topologies of these complexes and their related magnetic properties, highlight typical examples, and point out the main possible directions that remain to be developed in this field. From the crystal engineering point of view, the compounds reviewed here should provide useful information for further design and investigation on this elusive class of cyano-bridged SMMs and SCMs. 相似文献
130.
Submicron-sized Bi2Fe4O9 crystals were successfully synthesized via the hydrothermal method, while micron-sized Bi2Fe4O9 crystals with rod-like morphologies were obtained in the presence of the mineralizer KNO3. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were employed to characterize the products. According to a series of time-dependent experiments, it was concluded that the likeliest formation mechanism for the microrods was the Ostwald ripening process. It was proposed that the blocking effect of NO3? contributed to the formation of the rod-like powders. Moreover, the optical absorption of the prepared Bi2Fe4O9 crystals was measured using an UV–vis spectrophotometer, indicating that Bi2Fe4O9 powders can be used as effective photocatalysts under visible light. 相似文献