全文获取类型
收费全文 | 430篇 |
免费 | 72篇 |
国内免费 | 39篇 |
专业分类
化学 | 298篇 |
晶体学 | 4篇 |
力学 | 17篇 |
综合类 | 1篇 |
数学 | 55篇 |
物理学 | 166篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 21篇 |
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 29篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 21篇 |
2015年 | 20篇 |
2014年 | 39篇 |
2013年 | 25篇 |
2012年 | 38篇 |
2011年 | 36篇 |
2010年 | 24篇 |
2009年 | 25篇 |
2008年 | 24篇 |
2007年 | 21篇 |
2006年 | 26篇 |
2005年 | 28篇 |
2004年 | 8篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有541条查询结果,搜索用时 21 毫秒
61.
This work deals with the interaction between urea and DNA bases (adenine, thymine, guanine, and cytosine). The optimized geometries,
binding energies, and harmonic vibrational frequencies are calculated using the DFT/B3LYP functional combined with the 6–31+G(d,p) basis set. Their interactions are studied aiming to understand more about the nature of the intercalation binding forces
between urea and DNA. Fourteen stable complexes are found on the potential energy surface. The structures are cyclic; they
are stabilized by NH...O/N and CH...O interactions. The binding energies range from −19.9 kJ·mol−1 to −74.0 kJ·mol−1. The obtained formation energies indicate that Urea:G and Urea:C are more favorable than Urea:T and Urea:A. In addition,
the Atoms in Molecules theory is performed to study the hydrogen bonds in the complexes. 相似文献
62.
63.
On <Emphasis Type="Italic">s</Emphasis>-Elementary Super Frame Wavelets and Their Path-Connectedness
A super wavelet of length n is an n-tuple (ψ 1,ψ 2,…,ψ n ) in the product space \(\prod_{j=1}^{n} L^{2}(\mathbb{R})\), such that the coordinated dilates of all its coordinated translates form an orthonormal basis for \(\prod_{j=1}^{n} L^{2} (\mathbb{R})\). This concept is generalized to the so-called super frame wavelets, super tight frame wavelets and super normalized tight frame wavelets (or super Parseval frame wavelets), namely an n-tuple (η 1,η 2,…,η n ) in \(\prod_{j=1}^{n}L^{2} (\mathbb{R})\) such that the coordinated dilates of all its coordinated translates form a frame, a tight frame, or a normalized tight frame for \(\prod_{j=1}^{n} L^{2}(\mathbb{R})\). In this paper, we study the super frame wavelets and the super tight frame wavelets whose Fourier transforms are defined by set theoretical functions (called s-elementary frame wavelets). An m-tuple of sets (E 1,E 2,…,E m ) is said to be τ-disjoint if the E j ’s are pair-wise disjoint under the 2π-translations. We prove that a τ-disjoint m-tuple (E 1,E 2,…,E m ) of frame sets (i.e., η j defined by \(\widehat{\eta_{j}}=\frac{1}{\sqrt{2\pi}}\chi_{E_{j}}\) is a frame wavelet for L 2(?) for each j) lead to a super frame wavelet (η 1,η 2,…,η m ) for \(\prod_{j=1}^{m} L^{2} (\mathbb{R})\) where \(\widehat{\eta_{j}}=\frac{1}{\sqrt{2\pi}}\chi_{E_{j}}\). In the case of super tight frame wavelets, we prove that (η 1,η 2,…,η m ), defined by \(\widehat{\eta_{j}}=\frac{1}{\sqrt{2\pi}}\chi_{E_{j}}\), is a super tight frame wavelet for ∏1≤j≤m L 2(?) with frame bound k 0 if and only if each η j is a tight frame wavelet for L 2(?) with frame bound k 0 and that (E 1,E 2,…,E m ) is τ-disjoint. Denote the set of all τ-disjoint s-elementary super frame wavelets for ∏1≤j≤m L 2(?) by \(\mathfrak{S}(m)\) and the set of all s-elementary super tight frame wavelets (with the same frame bound k 0) for ∏1≤j≤m L 2(?) by \(\mathfrak{S}^{k_{0}}(m)\). We further prove that \(\mathfrak{S}(m)\) and \(\mathfrak{S}^{k_{0}}(m)\) are both path-connected under the ∏1≤j≤m L 2(?) norm, for any given positive integers m and k 0. 相似文献
64.
65.
重组家蚕核多角体病毒(rBmNPV)的复制及所载HuIFN-α基因的表达 总被引:3,自引:0,他引:3
报道了重组家蚕核多角体病毒(BombyxmorinuclearPolyhedrosisVirusBmNPV)在家蚕细胞BmN中复制的细胞病理学变化,除了不形成多角体以外,与野生型病毒相同.研究了病毒感染复数、细胞接种密度和细胞生长阶段对重组病毒复制和α-干扰素(IFN-α)表达量的影响.在一定低感染复数时,α-干扰素的产量较高.对于重组病毒的复制,最适的细胞接种密度为3.6~7.0×105细胞/瓶.在细胞指数生长前期(48~60h)接种重组病毒,对于获得较高的重组病毒复制效价和α-干扰素的产量都是有利的. 相似文献
66.
1文字说明详略得当、言简意赅
文字说明能反映解题思路,展示思维过程.写文字说明时,应根据题意,弄清哪些文字必要,需要写,哪些不必要,可以忽略,做到详略得当,言简意赅。必要的文字说明,有以下几项: 相似文献
67.
混合超图是含有两类超边的超图,一类称为C-超边,一类称为D-超边,它们的区别主要体现在染色要求上.混合超图的染色,要求每一C-超边至少有两个点染相同的颜色,而每一D-超边至少有两个点染不同的颜色.所用的最大颜色数称为对应混合超图的上色数,所用的最小颜色数称为对应混合超图的下色数.上、下色数与边数有密切关系.作者在文献[2]中证明了具有最小上色数的3一致C-超图边数的一个下界为‘n(n-2)/3’,其中n为对应混合超图的顶点数.该文证明当n=2k 1时,该下界是可以达到的. 相似文献
68.
采用甚高频等离子体增强化学气相沉积(VHF-PECVD)法,成功制备出从非晶到微晶过渡区 域的硅薄膜. 样品的微结构、光电特性及光致变化的测量结果表明这些处于相变域的硅薄膜 兼具非晶硅优良的光电性质和微晶硅的稳定性. 用这种两相结构的材料作为本征层制备了p- i-n太阳能电池,并测量了其稳定性. 结果在AM15(100mW/cm2) 的光强下曝光 800—5000min后,开路电压略有升高,转换效率仅衰退了29%.
关键词:
相变域硅薄膜
光电特性
太阳能电池 相似文献
69.
The co-transfection of p16(INK4a) and p14(ARF) genes into human lung cancer cell line A549 and the effects on cell growth and chemosensitivity 总被引:2,自引:0,他引:2
Xie QC Hu YD Wang LL Chen ZT Diao XW Wang ZX Guan HJ Zhu B Sun JG Duan YZ Chen FL Nian WQ 《Colloids and surfaces. B, Biointerfaces》2005,46(3):188-196
Two functionally and structurally different proteins, p16(INK4a) and p14(ARF), encoded by the gene INK4a/ARF located at 9p21 are cyclin-dependent kinase (cdk) inhibitors and important cell cycle regulators. More and more evidences have been accumulated to show that the exogenous p16(INK4a) or p14(ARF) can inhibit the cell growth and/or induce the apoptosis. But it is still unclear if they can play positive role when combine with the conventional chemotherapy in cancer treatment. Here we show that cationic liposome-mediated gene transfection of INK4a/ARF into lung cancer cell line A549, in which the INK4a/ARF locus was lost, suppressed the growth and induced apoptosis. When treated with five different chemotherapy drugs with different mechanism after the transfection, A549 got an increased chemosensitivity for adriamycin and cisplatin and an unchanged result for topotecan, taxol or vinorelbine. The results indicated that cell cycle redistribution and increased apoptosis index after transfection might be the main explanation for the enhanced chemosensitivity. The combination of gene therapy with conventional chemotherapy is not always better than single chemotherapy. This trial will be of benefit to the treatment of lung cancer when combine the conventional chemotherapy and gene therapy in the future. 相似文献
70.
Partitionally assembled organosulfur monolayers were prepared by using an electrochemically assisted assembly method on gold films that were preseparated into two regions insulated from each other. Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the n-dodecanethiol (DDT) and the 11-mercaptoundecanoic acid (MUA) monolayers, which were separately assembled on different substrate regions. CV results indicated that both the DDT- and MUA-coated gold electrodes showed a blocking property toward the negatively charged redox probe Fe(CN)6(3-). However, when positively charged Ru(NH3)6(3+) was used as the redox probe, the MUA- and DDT-modified electrodes showed quasireversible and blocking CV features, respectively. These phenomena were attributed to different interactions between the negatively charged MUA surface and the negatively or positively charged redox probes. XPS spectra obtained on the MUA modified region exhibited an O(1s) peak and a small discrete C(1s) peak, which arose from the oxygen and the carbon atoms in the carboxylic acid groups, respectively. For the DDT-modified region, these two peaks were absent. CV and XPS experimental results provided strong evidence that different SAMs were selectively deposited onto different regions of the preexisting patterns of the substrate by electrochemically partitioned assembly. The partitionally assembled sulfur-based monolayers with different terminal groups were used to form location-selective nanoparticle assemblies. This electrochemically partitioned assembly technique has great potential in controllable constructions of molecular layers and nanostructures on different surface microarchitectures that are closely integrated on one substrate but insulated from each other. 相似文献