全文获取类型
收费全文 | 909篇 |
免费 | 61篇 |
国内免费 | 68篇 |
专业分类
化学 | 455篇 |
晶体学 | 3篇 |
力学 | 95篇 |
综合类 | 11篇 |
数学 | 136篇 |
物理学 | 338篇 |
出版年
2024年 | 1篇 |
2023年 | 22篇 |
2022年 | 22篇 |
2021年 | 38篇 |
2020年 | 36篇 |
2019年 | 35篇 |
2018年 | 32篇 |
2017年 | 32篇 |
2016年 | 32篇 |
2015年 | 36篇 |
2014年 | 58篇 |
2013年 | 72篇 |
2012年 | 53篇 |
2011年 | 53篇 |
2010年 | 58篇 |
2009年 | 60篇 |
2008年 | 58篇 |
2007年 | 60篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 30篇 |
2003年 | 20篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1038条查询结果,搜索用时 15 毫秒
1.
Anna Luise Grab Dirk Hose Patrick Horn Elisabetta Ada Cavalcanti-Adam Anja Seckinger Martin Müller 《Particle & Particle Systems Characterization》2021,38(3):2000263
In the malignant plasma cell disease multiple myeloma (MM), bone lesions and resulting fractures caused by MM cell (MMC) accumulation represent a major cause of morbidity and mortality. Despite recent advantages in systemic treatment, residual MMCs remain, especially in bone lesions. Therefore an interfacial delivery system for local treatment of MM and induced bone disease based on polyelectrolyte complex nanoparticles (PEC NP) loaded with bone morphogenetic protein 6 (BMP-6) inducing de-novo bone formation and MMC apoptosis is presented herein. BMP-6 loaded PEC NP are fabricated by defined mixing bio-related cationic and anionic polysaccharides and BMP-6 according to molar ratio of BMP-6/PEC-NP of 1/3. BMP-6/PEC NP bound to a model substrate releases 10% BMP-6 sustainably within two weeks as accessed by infrared spectroscopy. BMP-6 loaded PEC NP adheres to cell membranes of MMCs and MSCs and activated phosphorylation of Smad 1/5. Osteogenic differentiation (ALP-concentration) is enhanced in MSCs (p < 0.05). All patient samples (10/10) of MMCs show significant induction of apoptosis (median 84%, p < 0.05). Finally, BMP-6/PEC NP are successfully integrated in a commercial hyaluronic acid based hydrogel material revealing MMC death as principal proof for the local treatment of MM induced bone lesions. 相似文献
2.
In order to investigate the effects of thermoultrasonic treatment (TUT) on the formation of colloidal micro-nano particles (MNPs) and the quality of halibut bone soup, nutrients, particle characteristics, and flavor characteristics were analyzed. The morphology of MNPs was studied using an optical microscope. Results showed that TUT could increase the nutrient content (total sugars, 22.15 mg/100 mL; water soluble proteins, 173.24 mg/mL; fatty acids, 1779.7 mg/100 mL; solids, 3.16 g/100 mL), reduce the particle size (605.92 nm) and interfacial tension. Meanwhile, TUT make the halibut bone soup has better emulsifying characteristics and stability. The contents of flavor substances, such as esters, 5′-nucleotides, organic acids in the halibut bone soup were more abundant, while the contents of hexanal and 1-octen-3-ol and fishy off-flavor were reduced in TUT group. The overall odor and taste outline were more harmonious. Therefore, TUT can be used in the production of high quality fish bone soup, and TUT could be considered as a good deep processing technology for halibut bone and improve economic efficiency. 相似文献
3.
数字微镜阵列(DMD)作为空间调制元件常用于投影光学系统,入射光为长波红外时产生的衍射效应会影响进入系统的能量分布,该文主要讨论光源入射角度对衍射效应的影响,将DMD作为闪耀光栅模型,研究其在长波红外波段产生的衍射效应。从光程差的角度分析在主、副对角线分别处于“开态”情况下的衍射效应,发现衍射效应与入射角度有关;将DMD作为闪耀光栅模型,采用矢量衍射理论计算7.7μm~9.5μm波段下DMD处于“开态”下的衍射效率。计算结果表明:当TM偏振光以44°角照射时,1级衍射达到闪耀状态,衍射效率可达到70%。 相似文献
4.
《Discrete Mathematics》2022,345(12):113083
Let G be a graph, the order of G, the connectivity of G and k a positive integer such that . Then G is said to be k-extendable if it has a matching of size k and every matching of size k extends to a perfect matching of G. A Hamiltonian path of a graph G is a spanning path of G. A bipartite graph G with vertex sets and is defined to be Hamiltonian-laceable if such that and for every pair of vertices and , there exists a Hamiltonian path in G with endpoints p and q, or and for every pair of vertices , there exists a Hamiltonian path in G with endpoints p and q. Let G be a bipartite graph with bipartition . Define to be a maximum integer such that and (1) for each non-empty subset S of X, if , then , and if , then ; and (2) for each non-empty subset S of Y, if , then , and if , then ; and (3) if there is no non-negative integer satisfying (1) and (2).Let G be a bipartite graph with bipartition such that and . In this paper, we show that if , then G is Hamiltonian-laceable; or if , then for every pair of vertices and , there is an -path P in G with . We show some of its corollaries in k-extendable, bipartite graphs and a conjecture in k-extendable graphs. 相似文献
5.
以聚L-谷氨酸苄酯(PBLG)为原料, 通过溶剂浇铸与粒子沥滤法分别构建PBLG单层致密和PBLG单层多孔膜, 利用乙醇胺对薄膜表面改性, 构筑双层引导骨再生膜. 研究了不同胺解改性时间对PBLG-s-PHEG双层膜亲水性和力学性能的影响, 结果表明, 随着PBLG分子量的增大, 薄膜的力学性能增强而降解速率减缓. 延长胺解改性时间可提高薄膜亲水性和体内外降解速率. 细胞实验结果表明, 双层薄膜的致密结构能够有效阻隔成纤维细胞的侵入, 多孔结构能够支持细胞贴壁黏附和铺展. 体外生物活性评价结果表明, 表面改性的PBLG基材料可用于体内骨缺损修复. 本文所构建的双层引导骨再生膜在体外具有良好的力学性能和降解性能, 与组织具有一定的贴合性, 同时可有效阻碍成纤维细胞侵入, 具有潜在应用价值. 相似文献
6.
《Macromolecular bioscience》2018,18(6)
The combination of bioactive components such as calcium phosphates and fibrous structures are encouraging niche‐mimetic keys for restoring bone defects. However, the importance of hemocompatibility of the membranes is widely ignored. Heparin‐loaded nanocomposite poly(ε‐caprolactone) (PCL)‐α‐tricalcium phosphate (α‐TCP) fibrous membranes are developed to provide bioactive and hemocompatible constructs for bone tissue engineering. Nanocomposite membranes are optimized based on bioactivity, mechanical properties, and cell interaction. Consequently, various concentrations of heparin molecules are loaded within nanocomposite fibrous membranes. In vitro heparin release profiles reveal a sustained release of heparin over the period of 14 days without an initial burst. Moreover, heparin encapsulation enhances mesenchymal stem cell (MSC) attachment and proliferation, depending on the heparin content. It is concluded that the incorporation of heparin within TCP–PCL fibrous membranes provides the most effective cellular interactions through synergistic physical and chemical cues. 相似文献
7.
8.
Sajeesh Kumar Madhurakkat Perikamana Sang Min Lee Jinkyu Lee Taufiq Ahmad Min Suk Lee Hee Seok Yang Heungsoo Shin 《Macromolecular bioscience》2019,19(4)
Plant derived flavonoids have not been well explored in tissue engineering applications due to difficulties in efficient formulations with biomaterials for controlled presentation. Here, the authors report that surface coating of epigallocatechin gallate (EGCG) on polymeric substrates including poly (L‐lactic acid) (PLLA) nanofibers can be performed via oxidative polymerization of EGCG in the presence of cations, enabling regulation of biological functions of multiple cell types implicated in bone regeneration. EGCG coating on the PLLA nanofiber promotes osteogenic differentiation of adipose‐derived stem cells (ADSCs) and is potent to suppress adipogenesis of ADSCs while significantly reduces osteoclastic maturation of murine macrophages. Moreover, EGCG coating serves as a protective layer for ADSCs against oxidative stress caused by hydrogen peroxide. Finally, the in vivo implantation of EGCG‐coated nanofibers into a mouse calvarial defect model significantly promotes the bone regeneration (61.52 ± 28.10%) as compared to defect (17.48 ± 11.07%). Collectively, the results suggest that EGCG coating is a simple bioinspired surface modification of polymeric biomaterials and importantly can thus serve as a promising interface for tuning activities of multiple cell types associated with bone fracture healing. 相似文献
9.
特征提取是太赫兹光谱识别的关键处理步骤,通常利用降维方法作为特征提取手段。然而,当一些化合物的太赫兹光谱曲线整体差异度较小时,降维方法往往会缺失样本差异的重要特征信息,从而导致分类错误。如果不采用降维方法提取特征,传统机器学习分类算法对维数较高的原始太赫兹光谱数据又不能很好的分类。针对此问题,提出了一种基于双向长短期记忆网络(BLSTM-RNN)自动提取太赫兹光谱特征的识别方法。BLSTM-RNN作为一种特殊的循环神经网络,利用其LSTM单元可以有效解决原始太赫兹光谱数据维数较高使得模型难以训练问题。再结合模型的双向频谱信息利用架构模式,可以增强模型对复杂光谱数据自动提取有效特征信息的能力。采用三类、15种化合物太赫兹透射光谱作为测试对象,首先利用S-G滤波和三次样条插值对Anthraquinone,Benomyl和Carbazole等十五种化合物在0.9~6 THz内的太赫兹透射光谱数据进行归一化处理,然后通过构建一个具有双向长短期记忆的循环神经网络对太赫兹光谱的全频谱信息进行自动特征提取并利用Softmax分类器进行分类。通过试验优化网络结构和各项参数,最终获得了针对复杂太赫兹透射光谱数据的预测模型,并与传统机器学习算法SVM,KNN及神经网络算法MLP,CNN进行对比实验。结果表明,dataset-1和dataset-2分别作为差异度较大和无明显峰值特征的五种化合物太赫兹透射光谱数据集,其平均识别率分别为100%和98.51%,与其他方法相比识别率有所提高;最重要的是,dataset-3作为5种化合物谱线极为相似的太赫兹透射光谱数据集,其平均识别率为96.56%,与其他方法相比识别率提高显著;dataset-4作为dataset-1,dataset-2和dataset-3的透射光谱数据集集合,其平均识别率为98.87%。从而验证了BLSTM-RNN模型能自动提取有效的太赫兹光谱特征,同时又能保证复杂太赫兹光谱的预测精度。在选择模型训练优化算法方面,使用Adam优化算法要好于RMSProp,SGD和AdaGrad,其模型的目标函数损失值收敛速度最快。同时随着模型训练迭代次数增加,相似太赫兹透射光谱数据集的预测准确率也不断提升。可为复杂太赫兹光谱数据库的光谱识别检索提供一种新的识别方法。 相似文献
10.