全文获取类型
收费全文 | 198篇 |
免费 | 52篇 |
国内免费 | 49篇 |
专业分类
系统科学 | 5篇 |
丛书文集 | 1篇 |
教育与普及 | 9篇 |
现状及发展 | 7篇 |
研究方法 | 34篇 |
综合类 | 243篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 12篇 |
2015年 | 6篇 |
2014年 | 16篇 |
2013年 | 8篇 |
2012年 | 25篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 22篇 |
2007年 | 21篇 |
2006年 | 20篇 |
2005年 | 18篇 |
2004年 | 21篇 |
2003年 | 13篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 19篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有299条查询结果,搜索用时 15 毫秒
201.
The structural characteristics and optical and electrical properties of molecular-beam-epitaxy (MBE) grown ZnS0.8Se0.2 thin films on indium-tin-oxide (ITO) glass substrates were investigated in this work. The X-ray diffraction (XRD) results indicated that high quality polycrystalline ZnS0.8Se0.2 thin film grown at the optimized temperature had a preferred orientation along the (111) planes. The transmission electron microscopy (TEM) cross-sectional micrograph of the sample showed a well defined columnar structure with lateral crystal dimension in the order of a few hundred angstroms. Ultraviolet(UV) photoresponsivity as high as 0.01 A/W had been demonstrated and for wavelengths longer than 450 nm, the response was down from the peak response by more than 3 orders of magnitude. The thin ZnS0.8Se0,2 photosensor layer, with a wide energy gap and anisotropic electrical property, makes a transmission UV liquid crystal light valve (LCLV) with high resolution feasible. 相似文献
202.
A modified complex coacervation-co-precipitation method was used to prepare bone morphogenetic protein (BMP)-loaded nanospheres. Three natural polymers were used as packing materials to obtain nanoscale delivery device for BMP, in the presence of phosphatidylcholine functioning as stabilizer. Positively charged polysaccharide, N,N-diethylaminoethyl dextran (DEAE-dextran) tended to form stable, uniform and smaller size particles carrying BMP. Negatively charged bovine serum albumin (BSA) induced precipitation of the produced BMP particles due to its weak interaction with BMP molecules, although it produced nanosized BMP spheres. While collagen, a weakly positively charged protein shaped larger particles due to the strong interaction among themselves. A mechanism of co-precipitation process was also deduced to depict the formation of stable nanospheres. 相似文献
203.
204.
Cuk T Shen ZX Gromko AD Sun Z Dessau DS 《Nature》2004,432(7015):1 p following 291; discussion following 291
In conventional superconductivity, sharp phonon modes (oscillations in the crystal lattice) are exchanged between electrons within a Cooper pair, enabling superconductivity. A critical question in the study of copper oxides with high critical transition temperature (Tc) is whether such sharp modes (which may be more general, including, for example, magnetic oscillations) also play a critical role in the pairing and hence the superconductivity. Hwang et al. report evidence that sharp modes (either phononic or magnetic in origin) are not important for superconductivity in these materials, but we show here that their conclusions are undermined by the insensitivity of their experiment to a crucial physical effect. 相似文献
205.
Shen Junxian 《中国科学基金(英文版)》2007,15(1):49-50
Animals have special solution to the problem of communication in high levels of background noise. A small group of vertebrates (bats, dolphins and whales,and some rodents )that use ultrasound for communication.Our research first demonstrated that the conc 相似文献
206.
The expression of the Escherichia coli DNA polymerases pol V (UmuD'2C complex) and pol IV (DinB) increases in response to DNA damage. The induction of pol V is accompanied by a substantial increase in mutations targeted at DNA template lesions in a process called SOS-induced error-prone repair. Here we show that the common DNA template lesions, TT (6-4) photoproducts, TT cis-syn photodimers and abasic sites, are efficiently bypassed within 30 seconds by pol V in the presence of activated RecA protein (RecA*), single-stranded binding protein (SSB) and pol III's processivity beta,gamma-complex. There is no detectable bypass by either pol IV or pol III on this time scale. A mutagenic 'signature' for pol V is its incorporation of guanine opposite the 3'-thymine of a TT (6-4) photoproduct, in agreement with mutational spectra. In contrast, pol III and pol IV incorporate adenine almost exclusively. When copying undamaged DNA, pol V exhibits low fidelity with error rates of around 10(-3) to 10(-4), with pol IV being 5- to 10-fold more accurate. The effects of RecA protein on pol V, and beta,gamma-complex on pol IV, cause a 15,000- and 3,000-fold increase in DNA synthesis efficiency, respectively. However, both polymerases exhibit low processivity, adding 6 to 8 nucleotides before dissociating. Lesion bypass by pol V does not require beta,gamma-complex in the presence of non-hydrolysable ATPgammaS, indicating that an intact RecA filament may be required for translesion synthesis. 相似文献
207.
KE Shen QI Zhongtian YANG Ziyi SHI Ming WANG Jianan YAO Zhijian SHEN Beifen 《自然科学进展(英文版)》2000,10(6):446-450
Three mouse monoclonal antibodies (mAb) specific to E2 antigen of human hepatitis G virus (HGV) were used to bio-panning of a phage displayed random peptide library of 15 amino acid residues. After 3 rounds of screening, the ratio of output to input increased to 1.1 x 10" and the false positive rate reduced to 0.2% , which means the enrichment was effective. At the third round of screening, 15 plage clones were selected for the use in binding and competitive inhibition tests. Thirteen of them could specifically react with the mAb M6. The inhibition rates of phage 10 clones out of 15 were over 60% . From the deduced insert sequence in the coat protein VIII, the core sequence NPLWP was found in 6 phage clones which are homologeous to the amino acids 301—305 of HGV E2.The sera from the mice immunized with the phage clone C2 containing motif sequence were found positive for anti-HGV. These indicate the possibility that NPLWP motif in the short peptide is the mimic of HGV E2 epitope that can be recognized by HGV mAb M6. 相似文献
208.
Nodal signalling in vertebrate development 总被引:9,自引:0,他引:9
Communication between cells during early embryogenesis establishes the basic organization of the vertebrate body plan. Recent work suggests that a signalling pathway centering on Nodal, a transforming growth factor beta-related signal, is responsible for many of the events that configure the vertebrate embryo. The activity of Nodal signals is regulated extracellularly by EGF-CFC cofactors and antagonists of the Lefty and Cerberus families of proteins, allowing precise control of mesoderm and endoderm formation, the positioning of the anterior-posterior axis, neural patterning and left-right axis specification. 相似文献
209.
210.
Preparation and electrochemical performance of double perovskite La<Subscript>2</Subscript>CoMnO<Subscript>6</Subscript> nanofibers
下载免费PDF全文
![点击此处可从《矿物冶金与材料学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Through electrospinning, La2CoMnO6 nanofibers were prepared from a polyvinylpyrrolidone/lanthanum nitrate–cobalt acetate–manganese acetate (PVP/LCM) precursor and were used as electrode materials. The morphologies and structures of the samples were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) specific surface area analysis. The results show that the prepared La2CoMnO6 nanofibers are stable, one-dimensional structures formed from interconnected La2CoMnO6 nanoparticles with a diamond-like crystal structure. The specific surface area of the fibers is 79.407 m2·g-1. Electrochemical performance tests with a three-electrode system reveal the specific capacitance of the La2CoMnO6 nanofibers as 109.7 F·g-1 at a current density of 0.5 A·g-1. After 1000 charge-discharge cycles at a current density of 1 A·g-1, the specific capacitance maintains 90.9% of its initial value, demonstrating a promising performance of the constraint capacitance and good cyclic stability. 相似文献