全文获取类型
收费全文 | 2535篇 |
免费 | 305篇 |
国内免费 | 240篇 |
专业分类
化学 | 1166篇 |
晶体学 | 11篇 |
力学 | 133篇 |
综合类 | 20篇 |
数学 | 139篇 |
物理学 | 1611篇 |
出版年
2024年 | 4篇 |
2023年 | 51篇 |
2022年 | 51篇 |
2021年 | 77篇 |
2020年 | 63篇 |
2019年 | 78篇 |
2018年 | 55篇 |
2017年 | 82篇 |
2016年 | 103篇 |
2015年 | 92篇 |
2014年 | 157篇 |
2013年 | 187篇 |
2012年 | 186篇 |
2011年 | 184篇 |
2010年 | 148篇 |
2009年 | 172篇 |
2008年 | 162篇 |
2007年 | 190篇 |
2006年 | 159篇 |
2005年 | 132篇 |
2004年 | 115篇 |
2003年 | 96篇 |
2002年 | 79篇 |
2001年 | 50篇 |
2000年 | 55篇 |
1999年 | 49篇 |
1998年 | 56篇 |
1997年 | 37篇 |
1996年 | 31篇 |
1995年 | 28篇 |
1994年 | 27篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
排序方式: 共有3080条查询结果,搜索用时 15 毫秒
51.
受激拉曼散射(stimulated Raman scattering,SRS)具有激光的特性,并且容易获取不同波长的激光,从而成为调谐激光频率的重要途径之一。然而,由于其转化效率低,限制了它的实际应用。金属纳米粒子具有很强的表面增强效应,曾被广泛地用于增强拉曼散射而获得良好的效果。本文提出将金属纳米粒子的这种性质用于增强SRS。把Au纳米粒子混合于拉曼介质丙酮中,以532nm的纳秒脉冲激光作为激发光,研究了Au纳米粒子在丙酮中的浓度对丙酮SRS一阶Stokes光强的影响,并通过仿真计算对实验结果进行了解释和分析。 相似文献
52.
A new resolution improving method of enhancing the interference stripes, which can achieve better reconstruction of the recorded object of infrared digital holography has been proposed in this paper. The experiment is conducted under near infrared illuminance. We create poor quality holograms with very low-resolution interference stripes and enhance it with our new method. The processed holograms have much higher-resolution interference stripes. This method is based on interpolation theory, and we make it works fast, stable and easy to apply. Both the forward and backward interpolation of the oriental and portrait direction of the source pixels have been calculated, and have been used to realize the final aim of resolution improvement. During the experiment, since the responsivity of the CCD is not satisfied with the illuminance laser, which is by design, we also give specific analysis on the experimental setup of our work to make sure the object information can be fully recorded by the optical setup but cannot be reconstructed because of the low-resolution and unobvious of the interference stripes. After the resolution improvement process of the original hologram, the object information can then be fully reconstructed, which is very clear in the paper. Figures and dataflow give evidence and demonstrate the good performance of our method. 相似文献
53.
《Comptes Rendus Chimie》2016,19(10):1310-1314
Irregularly shaped and inorganic fullerene-like MoS2 compounds were characterized by Resonance Raman spectroscopy using an exciting line at 633 nm. It was shown that the relative intensity of the longitudinal acoustic mode at 226 cm−1 and its overtone strongly depends on the MoS2 crystallite size but not on the size of the particles made of agglomerated crystallites. This technique appeared as a promising probe to characterize in situ very small crystallites that are not observed by XRD. 相似文献
54.
Malik Salman Haider Jochen Schreiner Sabine Kendl Matthias Kroiss Robert Luxenhofer 《Macromolecular bioscience》2020,20(1)
Adrenocortical carcinoma (ACC) is a rare tumor and prognosis is overall poor but heterogeneous. Mitotane (MT) has been used for treatment of ACC for decades, either alone or in combination with cytotoxic chemotherapy. Even at doses up to 6 g per day, more than half of the patients do not achieve targeted plasma concentration (14–20 mg L?1) even after many months of treatment due to low water solubility, bioavailability, and unfavorable pharmacokinetic profile. Here a novel MT nanoformulation with very high MT concentrations in physiological aqueous media is reported. The MT‐loaded nanoformulations are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and powder X‐ray diffraction which confirms the amorphous nature of the drug. The polymer itself does not show any cytotoxicity in adrenal and liver cell lines. By using the ACC model cell line NCI‐H295 both in monolayers and tumor cell spheroids, micellar MT is demonstrated to exhibit comparable efficacy to its ethanol solution. It is postulated that this formulation will be suitable for i.v. application and rapid attainment of therapeutic plasma concentrations. In conclusion, the micellar formulation is considered a promising tool to alleviate major drawbacks of current MT treatment while retaining bioactivity toward ACC in vitro. 相似文献
55.
56.
By taking the coupling effect into consideration, we study the resonance condition of a photonic wire microring resonator (PWRR) sensor and compare our results with the previous work. Simulation results show that the resonant wavelength and sensitivity strongly depend on the coupling strength. The difference caused by the coupling effect can be up to tens of nanometers for the resonant peak position and tens of nm/RIU for the sensitivity in a silicon-on-insulator (SOI) PWRR. Such a giant influence from coupling effect cannot be disregarded and should be considered seriously for the design and application of PWRRs. It also shows an alternative tuning technique by controlling the coupling strength. 相似文献
57.
We suggest an electrochemical etching method with viscous etchant to enhance the sharpness of tip of scanning probe microscope. The viscosity of the etchant mixed with HCl solution and glycerol was used as a control parameter in addition to the voltage applied to the tip. In order to improve the sharpness of the tip, a nano-scale meniscus formed between the end of the tip and the liquid level was used. The shapes, aspect ratios, and radii of tips were measured depending on the concentration of the etchant. It was found that the tip etched with the mixed liquid with glycerol was sharper than the tip with the pure HCl solution. This can be explained by the fact that the meniscus formed by viscous liquid is maintained with a thinner diameter and causes final etching until the meniscus bridge is ruptured. 相似文献
58.
Image fusion refers to the techniques that integrate complementary information from multiple image sensors’ data in a way that makes the new images more suitable for human visual perception. The paper focuses on the low color contrast problem of linear fusion algorithms with color transfer method. Firstly, the contrast of infrared and visible images is enhanced using local histogram equalization and median filter. Then the two enhanced images are fused into the three components of a Lab image in terms of a simple linear fusion strategy. To enhance the color contrast between the target and the background, the scaling factor is introduced into the transferring equation in the b channel. Experimental results based on three different data sets show that the hot and cold targets are all popped out with intense colors while the background details present natural color appearance. Target detection experiments through target recognition area, detection rate, target-background discrimination also show that the presented method has a better performance than the former methods. 相似文献
59.
Correlation functions of a driven two‐level system embedded in a photonic crystal are analyzed. The spectral density of the photonic bands near a gap makes this system non‐Markovian. The equations of motion for two‐time correlations are derived by two different methods, the quantum regression theorem and the fluctuation dissipation theorem, and found to be the same. 相似文献
60.
Dr. Noam Shemesh Dr. Jean‐Nicolas Dumez Prof. Lucio Frydman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(39):13002-13008
Nuclear magnetic resonance spectroscopy is governed by longitudinal (T1) relaxation. For protein and nucleic acid experiments in solutions, it is well established that apparent T1 values can be enhanced by selective excitation of targeted resonances. The present study explores such longitudinal relaxation enhancement (LRE) effects for molecules residing in biological tissues. The longitudinal relaxation recovery of tissue resonances positioned both down‐ and upfield of the water peak were measured by spectrally selective excitation/refocusing pulses, and compared with conventional water‐suppressed, broadband‐excited counterparts at 9.4 T. Marked LRE effects with up to threefold reductions in apparent T1 values were observed as expected for resonances in the 6–9 ppm region; remarkably, statistically significant LRE effects were also found for several non‐exchanging metabolite resonances in the 1–4 ppm region, encompassing 30–50 % decreases in apparent T1 values. These LRE effects suggest a novel means of increasing the sensitivity of tissue‐oriented experiments, and open new vistas to investigate the nature of interactions among metabolites, water and macromolecules at a molecular level. 相似文献