全文获取类型
收费全文 | 476篇 |
免费 | 92篇 |
国内免费 | 71篇 |
专业分类
化学 | 369篇 |
晶体学 | 12篇 |
力学 | 16篇 |
综合类 | 5篇 |
数学 | 34篇 |
物理学 | 203篇 |
出版年
2024年 | 8篇 |
2023年 | 21篇 |
2022年 | 40篇 |
2021年 | 39篇 |
2020年 | 32篇 |
2019年 | 40篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 32篇 |
2015年 | 18篇 |
2014年 | 25篇 |
2013年 | 45篇 |
2012年 | 29篇 |
2011年 | 28篇 |
2010年 | 27篇 |
2009年 | 33篇 |
2008年 | 25篇 |
2007年 | 29篇 |
2006年 | 23篇 |
2005年 | 24篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有639条查询结果,搜索用时 31 毫秒
41.
分别在苏打石灰玻璃、Mo箔、无择优取向的Mo薄膜以及(110)择优取向的Mo薄膜四种不同衬底上,采用共蒸发工艺沉积约2 μm厚的Cu(In,Ga)Se2薄膜,用X射线衍射仪测量薄膜的织构,研究衬底对Cu(In,Ga)Se2薄膜织构的影响.在以上四种衬底上沉积的Cu(In,Ga)Se2薄膜的(112)衍射峰强度依次逐渐减弱,(220/204)衍射峰从无到有且强度逐渐增强.在苏打石灰玻璃和Mo箔衬底上的Cu(In,Ga)Se2关键词:
择优取向
Cu(In
2薄膜')" href="#">Ga)Se2薄膜
太阳电池 相似文献
42.
制备了Nd28Fe66B6/Fe50Co50多层纳米复合磁性薄膜,对溅射态和650℃退火处理15 min试样的相成分分析和微结构的观察显示,溅射态薄膜呈非晶态,经650℃退火处理15 min后,薄膜主要相成分为硬磁性Nd2Fe14B相和软磁性相FeCo(110)相.Nd2Fe14B相呈柱状,其易磁化c轴垂直于膜面,尺寸约10 nm.在硬磁性相和软磁性相之间存在少量富Nd相和非晶态,富Nd相大小约7 nm.磁性测量和分析表明,1)该系列薄膜退火态具有垂直于膜面的磁晶各向异性.2)对于固定厚度(10 nm)层Nd-Fe-B和不同厚度(tFeCo=1—100 nm)层FeCo多层纳米复合膜,剩磁随软磁相FeCo 厚度的增加快速增加,而矫顽力则减小.当tFeCo=5 nm时,最大磁能积达到200 kJ/m3. 3)硬磁相Nd-Fe-B层和软磁相FeCo层之间交换耦合导致剩磁和磁能积增强.
关键词:
Nd-Fe-B/FeCo多层纳米复合膜
交换耦合
磁各向异性 相似文献
43.
A class of optimal adaptive multi-arm clinical trial designs is proposed based on an extended generalized Pólya urn (GPU) model. The design is applicable to both the qualitative and quantitative responses and achieves, asymptotically, some pre-specified optimality criterion. Such criterion is specified by a functional of the response distributions and is implemented through the relationship between the design matrix and its first eigenvector. The asymptotic properties of the design are studied using the existing methods on GPU. Some examples for commonly used clinical designs are given as illustration. 相似文献
44.
Nanocrystalline mesoporous titania was synthesized via a combined sol–gel process with surfactant-assisted templating method using cetyltrimethyl ammonium bromide (CTAB) as the structure-directing agent. The process was catalyzed by different acid (hydrochloric acid, nitric acid, sulfuric acid, or phosphoric acid). The prepared samples were characterized by XRD, TEM, BET and FT-IR. The photocatalytic activity of the samples was determined by degradation of phenol in aqueous solution. Results showed that different acid had different effect on the structure and crystal phase of the samples. The sample adjusted by phosphoric acid showed highest surface area and photocatalytic activity. The formation mechanism of the samples catalyzed by different acid was also discussed. 相似文献
45.
Based on the consideration of Boolean dynamics, it has been hypothesized that cell types may correspond to alternative attractors of a gene regulatory network. Recent stochastic Boolean network analysis, however, raised the important question concerning the stability of such attractors. In this paper a detailed numerical analysis is performed within the framework of Langevin dynamics. While the present results confirm that the noise is indeed an important dynamical element, the cell type as represented by attractors can still be a viable hypothesis. It is found that the stability of an attractor depends on the strength of noise related to the distance of the system to the bifurcation point and it can be exponentially stable depending on biological parameters. 相似文献
46.
Ao Feng Hongxiang Li Zixi Liu Yuanjiang Luo Haibo Pu Bin Lin Tao Liu 《Entropy (Basel, Switzerland)》2021,23(6)
The thousand grain weight is an index of size, fullness and quality in crop seed detection and is an important basis for field yield prediction. To detect the thousand grain weight of rice requires the accurate counting of rice. We collected a total of 5670 images of three different types of rice seeds with different qualities to construct a model. Considering the different shapes of different types of rice, this study used an adaptive Gaussian kernel to convolve with the rice coordinate function to obtain a more accurate density map, which was used as an important basis for determining the results of subsequent experiments. A Multi-Column Convolutional Neural Network was used to extract the features of different sizes of rice, and the features were fused by the fusion network to learn the mapping relationship from the original map features to the density map features. An advanced prior step was added to the original algorithm to estimate the density level of the image, which weakened the effect of the rice adhesion condition on the counting results. Extensive comparison experiments show that the proposed method is more accurate than the original MCNN algorithm. 相似文献
47.
Bing Liang Shujuan Yu Jie Li Fan Wang Gaolin Liang Ao Zhang Chunyong Ding 《Tetrahedron letters》2017,58(19):1822-1825
A novel catalyst-free Csp3-H aryloxylation approach allowing for rapid installation of a wide range of aryloxyl groups regioselectively at the C-4 position of Tanshinone IIA under simple and mild conditions was developed. This unique protocol exhibited atom-/step-economy, low cost, high efficiency and robust functional-group tolerance, which will greatly facilitate to diversify the A-ring of the bioactive natural product. 相似文献
48.
Jiang-Tao Li Yu-Fei Ao Qi-Qiang Wang De-Xian Wang Mei-Xiang Wang 《Tetrahedron letters》2017,58(38):3708-3711
Reaction of azacalix[4]pyridine and azacalix[1]arene[3]pyridine with methyl iodide afforded N-methylated products selectively and highly efficiently. Crystal structures revealed that the modified electronic nature of the pyridines could change the conjugation between the bridging nitrogen and the neighbouring aromatics. 相似文献
49.
A simple method for large-scale preparation of ZnS nanoribbon film and its photocatalytic activity for dye degradation 总被引:2,自引:0,他引:2
Chao Wang Yanhui Ao Peifang Wang Songhe Zhang Jin Qian Jun Hou 《Applied Surface Science》2010,256(13):4125-4128
ZnS nanoribbon film has been successfully prepared by solvothermal treating of Zn foil and S powder in hydrazine hydrate without any surfactant and post-high temperature treatment. The prepared samples were characterized by XRD, SEM and PL. Results show that the obtained films were with high crystallinity and uniformity. The obtained samples were used as a photocatalyst for degradation of dye X-3B, and results show that the dye can be photocatalytically degraded with high rate by as-prepared ZnS nanoribbon film under UV light irradiation. 相似文献
50.
Although it has been long that spacecraft observed the anisotropy of velocity protons in the solar wind, there is still not a reasonable explanation. In this paper we try to give an explanation from the diffusion plateau of protoncyclotron resonance predicted by the quasi-linear theory for the resonance between the protons and the parallel propagating waves. We consider the effect of dispersion relation on diffusion plateau and notice that the diffusion plateau we have got by using cold plasma dispersion relation accords with the density contours in the velocity phase space detected at 0.3 AU in fast solar wind. For explaining proton distributions obtained in the fast solar wind from 0.7 AU to 1 AU hot plasma dispersion relation should be considered. We also give a theoretical relation of proton thermal anisotropy A and plasma parameter β. 相似文献