全文获取类型
收费全文 | 1854篇 |
免费 | 261篇 |
国内免费 | 157篇 |
专业分类
化学 | 873篇 |
晶体学 | 11篇 |
力学 | 89篇 |
综合类 | 20篇 |
数学 | 87篇 |
物理学 | 1192篇 |
出版年
2024年 | 1篇 |
2023年 | 42篇 |
2022年 | 43篇 |
2021年 | 62篇 |
2020年 | 63篇 |
2019年 | 62篇 |
2018年 | 44篇 |
2017年 | 61篇 |
2016年 | 91篇 |
2015年 | 64篇 |
2014年 | 123篇 |
2013年 | 138篇 |
2012年 | 143篇 |
2011年 | 138篇 |
2010年 | 100篇 |
2009年 | 122篇 |
2008年 | 117篇 |
2007年 | 124篇 |
2006年 | 96篇 |
2005年 | 89篇 |
2004年 | 73篇 |
2003年 | 64篇 |
2002年 | 62篇 |
2001年 | 29篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 43篇 |
1997年 | 30篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 14篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 3篇 |
排序方式: 共有2272条查询结果,搜索用时 16 毫秒
1.
2.
《Arabian Journal of Chemistry》2022,15(10):104145
In the present study, novel representatives of the important group of biologically-active, dehydroabietic acid-bearing dithiocarbamate moiety, were synthesized and characterized by 1H NMR, 13C NMR, HR-MS. The in vitro antiproliferative activity evaluation (MTT) indicated that these compounds exhibited potent inhibitory activities in various cancer cell lines (HepG-2, MCF-7, HeLa, T-24, MGC-803). Particularly, compound III-b possessed extraordinary cytotoxicity with low micromolar IC50 values ranging from 4.07 to 38.84 µM against tested cancer cell lines, while displayed weak cytotoxicity on two normal cell lines (LO-2 and HEK 293 T). Subsequently, the potential mechanisms of representative compound III-b were elementarily investigated by Transwell experiment, which showed III-b can inhibit cancer cells migration. Annexin-V/PI dual staining showed that the compound can induce HepG-2 cells apoptosis in a dose-dependent manner. Meanwhile this apoptosis may be related to the upregulated protein expression of cleaved-caspase 3, cleaved-caspase 9, Bax and downregulated of Bcl-2 indicated by Western Blot. Later study further confirmed that ROS levels in HepG-2 cells increased significantly with the rise of concentrations. In addition, through the network pharmacology data analyzing, the core targets and signaling pathways of compound III-b for treatment of liver neoplasms were forecasted. Molecular docking model showed that compound III-b had high affinity with hub targets (CASP3, EGFR, HSP90AA1, MAPK1, ERBB2, MDM2), suggesting that compound III-b might target the hub protein to modulate signaling activity. Taken together, these data indicated that dehydroabietic acid structural modification following the “Molecular hybridization” principle is a feasible way to discover the potential multi-targeted antitumor compounds. 相似文献
3.
Julián Bravo-Castillero Ariel Ramírez-Torres Catherine García-Reimbert Raúl Guinovart-Díaz Reinaldo Rodríguez-Ramos 《Waves in Random and Complex Media》2020,30(4):593-613
ABSTRACT The asymptotic homogenization method is applied to complex dielectric periodic composites. An equivalence to coupled dielectric problems with real coefficients is shown. This is similar to a piezoelectric problem: an out-plane mechanical displacement and an in-plane electric potential establishing a correspondence principle. Closed-form formulas for the complex dielectric effective tensor in the case of a square array of circular inclusions embedded in a matrix are given. These formulas are written in terms of a real and symmetric matrix which facilitates the implementation of the computational scheme. We also get similar formulas for multilayered complex dielectric composites. The real closed-form formulas are advantageous for estimating gain and loss enhancement properties of active and passive composites in certain volume fraction intervals. Numerical computations are performed and the results are compared with other approaches showing the usefulness of the obtained formulas. This may be of interest in the context of metamaterials. 相似文献
4.
We examined the flow behaviors and mixing characteristics of double-concentric jets using laser-assisted smoke flow visualization method to analyze typical flow patterns and binary boundary detection technique to investigate jet spread width. Time-averaged velocity vectors, streamline patterns, velocity distributions, turbulence properties, and vorticity contours were analyzed using Particle Image Velocimetry (PIV). Topological flow patterns were analyzed to interpret the vortical flow structures. Mixing properties were investigated using a tracer-gas concentration detection method. Four characteristic modes were observed: annular flow dominated mode, transition mode, central jet dominated mode-low shear, and central jet dominated mode-high shear. The jets’ mixing properties were enhanced by two major phenomena: the merging of annular flow and central jet at the centerline and the large turbulence fluctuations produced in the flow field. The merging of the jets induced stagnation points on the central axis in the annular flow dominated mode, which caused reverse flow on the central axis and drastic turbulence fluctuations of the near field region. When the central jet penetrated the recirculation region in the other three modes, the stagnation points on the central axis and the reverse flow vanished. Therefore, the mixing behaviors were prominently enhanced in the annular flow dominated mode. 相似文献
5.
针对传统红外图像增强算法中细节模糊及过度增强的问题,提出了一种基于Retinex理论与概率非局部均值相结合的红外图像增强方法.首先通过单尺度Retinex方法调整图像中过暗与过亮部分的灰度级;然后利用概率非局部均值对图像进行分解处理得到基本层与细节层,对基本层采用直方图均衡化拉伸对比度,对细节层采用非线性函数进行增强;最后,将不同层次的结果融合得到对比度与细节增强的红外图像.用该方法对多组不同场景的红外图像进行仿真实验,并将其与多种增强方法进行主、客观对比分析,结果表明所提方法在红外图像的细节及对比度增强方面都获得了更好的效果. 相似文献
6.
Robin van der Veer 《Discrete Mathematics》2019,342(9):2680-2693
7.
Beatriz Pascual-Escudero 《Journal of Pure and Applied Algebra》2019,223(6):2598-2614
Let X be an algebraic variety defined over a field of characteristic zero, and let be a point in the closed subset of maximum multiplicity of X. We provide a criterion, given in terms of arcs, to determine whether ξ is isolated in . More precisely, we use invariants of arcs derived from the Nash multiplicity sequence to characterize when ξ is an isolated point in . 相似文献
8.
设计了由超大口径前置望远系统和超大视场光谱仪组成的超大口径高光谱海洋水色仪.前置望远系统采用同轴三反光学系统结构,口径为4 m,视场为0.64°,焦距为21.6 m,波段范围为400~1 000nm.超大视场光谱仪采用改进的Offner结构,视场为240mm,光谱分辨率为10nm.探测器像元尺寸为15μm×15μm,4片探测器交错拼接实现400km幅宽.超大视场光谱仪在400~1 000nm的宽波段内,点列图半径的均方根值均小于3.9μm,静止轨道高光谱海洋水色仪全系统不同波长的MTF在33.3lp/mm处大于0.52,各项指标均满足应用要求. 相似文献
9.
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
10.
Anneli Kruve Riin Rebane Karin Kipper Maarja-Liisa Oldekop Hanno Evard Koit Herodes Pekka Ravio Ivo Leito 《Analytica chimica acta》2015
This is the part II of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS) and discuss specific issues that arise with MS (and MS–MS) detection in LC (as opposed to the “conventional” detectors). The Part II starts with briefly introducing the main quantitation methods and then addresses the performance related to quantification: linearity of signal, sensitivity, precision, trueness, accuracy, stability and measurement uncertainty. The last section is devoted to practical considerations in validation. With every performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to handle it, specifically in the case of LC–MS methods. 相似文献