全文获取类型
收费全文 | 1895篇 |
免费 | 404篇 |
国内免费 | 201篇 |
专业分类
化学 | 1342篇 |
晶体学 | 6篇 |
力学 | 106篇 |
综合类 | 19篇 |
数学 | 239篇 |
物理学 | 788篇 |
出版年
2024年 | 2篇 |
2023年 | 45篇 |
2022年 | 43篇 |
2021年 | 79篇 |
2020年 | 82篇 |
2019年 | 87篇 |
2018年 | 68篇 |
2017年 | 60篇 |
2016年 | 76篇 |
2015年 | 83篇 |
2014年 | 109篇 |
2013年 | 119篇 |
2012年 | 185篇 |
2011年 | 203篇 |
2010年 | 151篇 |
2009年 | 107篇 |
2008年 | 136篇 |
2007年 | 115篇 |
2006年 | 123篇 |
2005年 | 103篇 |
2004年 | 69篇 |
2003年 | 55篇 |
2002年 | 67篇 |
2001年 | 48篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 32篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1969年 | 2篇 |
1957年 | 2篇 |
1906年 | 1篇 |
排序方式: 共有2500条查询结果,搜索用时 15 毫秒
101.
通过熔融共混法制备了一系列等比例聚左旋乳酸(PLLA)/聚右旋乳酸(PDLA)共混试样,采用差示扫描量热法(DSC)、核磁共振(13C-NMR)及广角X射线衍射(WAXD)等方法对共混产物进行了表征和研究分析.结果表明,等比例PLLA和PDLA熔融共混生成了立构复合物(stereocomplex,sc),同时部分均聚物发生酯交换反应,生成了立体嵌段物(stereoblock,sb),从而在DSC升温曲线上sc晶体处出现特殊的熔融双峰现象;随着熔融共混温度升高,sc晶体的生成率和结晶度逐渐下降;聚乳酸立构复合物的加工稳定性较好,二次加工后,sc晶体熔点基本不变,生成率和结晶度提高;由于sc晶体的存在,PLLA/PDLA共混物的耐热性能提高,退火热处理后耐热性能得到进一步提高.这对于开发高耐热聚乳酸及其加工应用具有重要的应用价值. 相似文献
102.
In this paper, we derive the asymptotic expansions of the moments of normalized partial maxima for general error distribution. A byproduct is to deduce the convergence rates of the moments of normalized maxima to the moments of the corresponding extreme value distribution. 相似文献
103.
Genetic profile characterization and population study of 21 autosomal STR in Chinese Kazak ethnic minority group 下载免费PDF全文
Xiao‐Ye Wang Chun‐Mei Shen Wen‐Juan Liu Jiang‐Wei Yan Hong‐Dan Wang Hong‐Wei Pu Yan‐Li Wang Guang Yang Yu‐Dang Zhang Hao‐Tian Meng Hang Jing Bo‐Feng Zhu 《Electrophoresis》2014,35(4):503-510
Short tandem repeat loci have been recognized as useful tools in the routine forensic application and in recent decades, more and more new short tandem repeat (STR) loci have been constantly discovered, studied, and applied in forensic caseworks. In this study, we investigated the genetic polymorphisms of 21 STR loci in the Kazak ethnic minority as well as the genetic relationships between the Kazak ethnic minority and other populations. Allelic frequencies of 21 STR loci were obtained from 114 unrelated healthy Kazak individuals in the Ili Kazak Autonomous Prefecture, Xinjiang Uigur Autonomous Region of China. We observed a total of 159 alleles in the group with the allelic diversity values ranging from 0.0044 to 0.5088. The highest polymorphism was found at D19S433 locus and the lowest was found at D1S1627. Statistical analysis of the generated data indicated no deviation from Hardy–Weinberg equilibriums at all 21 STR loci. In order to estimate the population differentiation, allelic frequencies of all STR loci of the Kazak were compared with those of other neighboring populations using analysis of molecular variance method. Statistically significant differences were found between the studied population and other populations at 2–7 STR loci. A neighbor‐joining tree was constructed based on allelic frequencies of the 21 STR loci and phylogenetic analysis indicates that the Kazak has a close genetic relationship with the Uigur ethnic group. The present results may provide useful information for forensic sciences and population genetics studies, and can also increase our understanding of the genetic background of this group. The present findings showed that all the 21 STR loci are highly genetically polymorphic in the Kazak group, which provided valuable population genetic data for the genetic information study, forensic human individual identification, and paternity tests. 相似文献
104.
105.
Dongliang Tang Changtao Wang Zeyu Zhao Yanqin Wang Mingbo Pu Xiong Li Ping Gao Xiangang Luo 《Laser \u0026amp; Photonics Reviews》2015,9(6):713-719
Conventional optics is diffraction limited due to the cutoff of spatial frequency components, and evanescent waves allow subdiffraction optics at the cost of complex near‐field manipulation. Recently, optical superoscillatory phenomena were employed to realize superresolution lenses in the far field, but suffering from very narrow working wavelength band due to the fragility of the superoscillatory light field. Here, an ultrabroadband superoscillatory lens (UBSOL) is proposed and realized by utilizing the metasurface‐assisted law of refraction and reflection in arrayed nanorectangular apertures with variant orientations. The ultrabroadband feature mainly arises from the nearly dispersionless phase profile of transmitted light through the UBSOL for opposite circulation polarization with respect to the incident light. It is demonstrated in experiments that subdiffraction light focusing behavior holds well with nearly unchanged focal patterns for wavelengths spanning across visible and near‐infrared light. This method is believed to find promising applications in superresolution microscopes or telescopes, high‐density optical data storage, etc.
106.
ZHANG Tianran YU Huacheng WANG Wenkai BAI Pu JIN Keyan ZHANG Jia-Nan YAN Wenfu 《高等学校化学研究》2022,38(6):1532-1541
It is highly desired yet challenged to find an adsorbent with low cost and excellent performance in the removal of organic dyes from aqueous solution. Here we reported that a layered cationic aluminum oxyhydroxide material hydrothermally synthesized from the low-cost source materials of AlCl3∙6H2O, CaO and H2O, known as JU-111, can meet such criterion in removing methyl orange(MO) and Congo red(CR). JU-111 shows fast adsorption kinetics[especially for CR(15 s)] and high adsorption capacity(MO:>1000 mg/g; CR:>2900 mg/g), surpassing most of the reported adsorbents. Comprehensive characterizations of the adsorption process of MO and CR revealed that both adsorptions were achieved via the anion exchange process. The characteristics of extremely low cost and excellent performance render JU-111 great potential in the practical applications in the removal of anionic dyes. 相似文献
107.
Delocalized \begin{document}$\pi_3^6$\end{document} Bond in OX\begin{document}$_2$\end{document} (X=Halogen) Molecules 下载免费PDF全文
Yi-han Tang Pu Yang Meng-yuan Chen Yu-ru Wang Jia-xin Wang Jia-wei Xu 《化学物理学报(中文版)》2022,35(3):542-550
OX\begin{document}$_2$\end{document} (X=halogen) molecules was studied theoretically. Calculation results show that delocalized \begin{document}$\pi_3^6$\end{document} bonds exist in their electronic structures and O atoms adopt the sp\begin{document}$^2$\end{document} type of hybridization, which violates the prediction of the valence shell electron pair repulsion theory of sp\begin{document}$^3$\end{document} type. Delocalization stabilization energy is proposed to measure the contribution of delocalized \begin{document}$\pi_3^6$\end{document} bond to energy decrease and proves to bring extra-stability to the molecule. These phenomena can be summarized as a kind of coordinating effect. 相似文献
108.
Shuguang Guan Qiaoli Pu Yinan Liu Honghong Wu Wenbo Yu Zifeng Pi Shu Liu Fengrui Song Jingya Li De-An Guo 《Molecules (Basel, Switzerland)》2021,26(11)
Crocins are highly valuable natural compounds for treating human disorders, and they are also high-end spices and colorants in the food industry. Due to the limitation of obtaining this type of highly polar compound, the commercial prices of crocins I and II are expensive. In this study, macroporous resin column chromatography combined with high-speed counter-current chromatography (HSCCC) was used to purify crocins I and II from natural sources. With only two chromatographic steps, both compounds were simultaneously isolated from the dry fruit of Gardenia jasminoides, which is a cheap herbal medicine distributed in a number of countries. In an effort to shorten the isolation time and reduce solvent usage, forward and reverse rotations were successively utilized in the HSCCC isolation procedure. Crocins I and II were simultaneously obtained from a herbal resource with high recoveries of 0.5% and 0.1%, respectively, and high purities of 98.7% and 99.1%, respectively, by HPLC analysis. The optimized preparation method was proven to be highly efficient, convenient, and cost-effective. Crocins I and II exhibited inhibitory activity against ATP citrate lyase, and their IC50 values were determined to be 36.3 ± 6.24 and 29.7 ± 7.41 μM, respectively. 相似文献
109.
Ye Jiang Honglie Shen Tian Pu Chaofan Zheng Quntao Tang Wangyang Yang Jing Wu Chunbao Rui Yufang Li 《固体物理学:研究快报》2016,10(12):870-873
Acid texture is difficult for diamond wire sawn (DWS) multicrystalline silicon (mc‐Si) wafer owing to the inhomogeneous distribution of damage layer on the surface. In this article, metal‐assisted chemical etching (MACE) has been selected for introducing a porous seeding layer to induce acid texturing etching. SEM results show that the oval pit structures coverage get obvious improvement even on the smooth areas. Owing to the further improved light absorption ability by second MACE and nanostructure rebuilding (NSR) process, nanostructured DWS mc‐Si solar cell has exhibited a conversion efficiency of 17.96%, which is 0.45% higher than that of DWS wafer with simple acid texture process. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
110.
The adiabatic approximation is an important concept in quantum mechanics. In linear systems, the adiabatic condition is derived with the help of the instantaneous eigenvalues and eigenstates of the Hamiltonian, a procedure that breaks down in the presence of nonlinearity. Using an explicit example relevant to photoassociation of atoms into diatomic molecules, we demonstrate that the proper way to derive the adiabatic condition for nonlinear mean-field (or classical) systems is through a linearization procedure, using which an analytic adiabatic condition is obtained for the nonlinear model under study. 相似文献