全文获取类型
收费全文 | 9208篇 |
免费 | 1233篇 |
国内免费 | 740篇 |
专业分类
化学 | 6749篇 |
晶体学 | 122篇 |
力学 | 412篇 |
综合类 | 49篇 |
数学 | 838篇 |
物理学 | 3011篇 |
出版年
2024年 | 26篇 |
2023年 | 177篇 |
2022年 | 264篇 |
2021年 | 309篇 |
2020年 | 352篇 |
2019年 | 322篇 |
2018年 | 252篇 |
2017年 | 229篇 |
2016年 | 437篇 |
2015年 | 377篇 |
2014年 | 453篇 |
2013年 | 657篇 |
2012年 | 838篇 |
2011年 | 846篇 |
2010年 | 508篇 |
2009年 | 510篇 |
2008年 | 592篇 |
2007年 | 572篇 |
2006年 | 489篇 |
2005年 | 456篇 |
2004年 | 304篇 |
2003年 | 206篇 |
2002年 | 224篇 |
2001年 | 190篇 |
2000年 | 181篇 |
1999年 | 157篇 |
1998年 | 145篇 |
1997年 | 112篇 |
1996年 | 108篇 |
1995年 | 136篇 |
1994年 | 119篇 |
1993年 | 90篇 |
1992年 | 79篇 |
1991年 | 70篇 |
1990年 | 67篇 |
1989年 | 34篇 |
1988年 | 45篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A new gelator of urea‐containing triazine derivatives was synthesized and tested in order to explore the gelation potential in different organic solvents. This compound has been found to form organogels with a variety of organic solvents such as decalin and other solvents. The resulting thermo‐reversible gel was characterized by using the dropping ball method and a number of other instruments. The melting temperature of the gel increased with the gel concentration. The intermolecular hydrogen bonding of gelation was demonstrated through an FT‐IR spectrometer. UV‐Vis and fluorescence analysis showed that the gel displayed various optical effects in different organic solvents. The blue fluorescence of the gel in decalin and the quenched effect of gel in CHCl3 were displayed, respectively. Morphological features in decalin and CHCl3 were studied by applying atomic force microscopy (AFM), and the morphological features demonstrated that there were different aggregations in different solvents. In conductivity electrolyte experiments, the organogel electrolytes indicated high conductivity (σ) comparable to the corresponding NaClO4/THF solution. The conductivity of gel electrolytes was increased with electrolyte salt. 相似文献
993.
Chong Jia Yong Su Qingtao Zhou Minjun Xin Yousheng Lv Weihai Kong 《Applied Surface Science》2008,254(8):2331-2335
Large scale flower-like ZnO nanosheets have been synthesized on Zinc foil by a simple hydrothermal method. Their morphology and microstructures were characterized and analyzed by X-ray spectroscopy (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). The as-synthesized flower-like nanosheets are hexagonal phase single crystal with 200-300 nm in width, 50 nm in thickness. The growth process follows the liquid phase epitaxial growth mechanism. In this approach, the ZnO buffer is used as substrate for the growth of flower-like ZnO nanosheets. The growth direction of the nanosheets is the preferential [0 0 0 1] growth direction of ZnO. The photoluminescence spectrum of the sample exhibits only a sharp and strong UV emission centered at 386 nm, which indicates that the flower-like ZnO nanosheets on Zn foil are of good optical property. 相似文献
994.
Su Wang Nanfei Chen Chin-Sheng Chen Xinxiong Zhu 《Finite Elements in Analysis and Design》2009,45(8-9):592-596
Advances in materials and rapid prototyping technology, makes developing rapid-prototype heterogeneous parts possible. This paper proposes a finite element-based approach for modeling heterogeneous parts to facilitate rapid prototyping. In this approach, traditional geometrical and topological data are blended with materials information in the CAD model. It builds on a CAD system to create parts’ geometry which is then subdivided into a set of tetrahedral finite elements. With this, the design problem of material distribution in the whole body can be handled at the finite element level. The material composition of each point inside a finite element is formulated in terms of four control nodes of the finite element and a blending function. Moreover, design rules for modeling heterogeneous parts are introduced in the paper, making the modeling solution more robust. 相似文献
995.
To expand the application of cellulose in the field of fluorescence techniques, the cotton cellulose was labeled with norfloxacin
(Cell-NF) via a three-step reaction, involving alkali treatment, epoxy activation, and opening of the epoxy rings with norfloxacin
molecules. And the coordination complexes of Cell-NF with rare earth ions terbium (Cell-NF-Tb) and europium (Cell-NF-Eu) were
obtained. The products were detected by IR, TG, XPS, UV and fluorescence spectra. Results showed that the norfloxacin content
of the labeled cellulose was about 6.73 w% and the start temperature of decomposition of the Cell-NF was raised by 40°C compared
with the stock cotton cellulose. When excited at 340 nm, the Cell-NF, Cell-NF-Tb, and Cell-NF-Eu in the solid state could
emit violet (430 nm), green (549 nm) and red (620 nm) light, respectively. 相似文献
996.
Protocatechualdehyde (PCA) is one of the effective ingredients extracted from Danshen (Radix Salviae Miltiorrhizae) and was employed to modify the silk fibroin (SF) by graft polymerization and surface adsorption. The surface composition of modified SF was characterized by attenuated total reflectance Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and UV spectrophotometer. The anticoagulant activity of modified SF was assessed by in vitro coagulation test and platelet adhesion measurement. The endothelial cell affinity was evaluated by a parallel plate flow chamber. The test results indicated that with the introduction of PCA into SF, the anticoagulant activity has been improved obviously. And the SF surface composition altered by PCA, but did not disturb its β-sheet conformation. Moreover, the adsorbed PCA on SF surface can enhance the endothelial cell affinity. 相似文献
997.
X.-M. Su Z.-C. Zhuo Z.-H. Kang L.-J. Wang J.-Y. Gao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):395-398
We investigate the conditions in which the propagation of an electromagnetic wave is changed from transparency to cutoff in
a non-uniform plasma. The allowed frequency range of the driving wave is obtained for the case that the probe frequency is
above the plasma frequency. The effect of the power of the driving field on the range is analyzed.
Received 23 May 2001 相似文献
998.
Zhang Su Wang Cheng-Yu Sun Yun-Fu Pan Li-Jin Liang Dong-Bai Lin Li-Wn 《Hyperfine Interactions》1986,28(1-4):941-944
Iron supported catalysts were investigated by in situ Mössbauer spectroscopy. Results showed that MSI can be vell Interpreted as a combination of the dispersion effect and the chemical interaction effect. 相似文献
999.
A theoretical investigation on the structure, stability, and aromaticity of M‐subphthalocyanine (M? SubPc; M?B, Al, and Ga) was performed at the B3LYP/6‐31+G*//B3LYP/6‐31G* level. The comparison between M? SubPc and the corresponding M? phthalocyanine (M? Pc) was considered. The geometry optimization of the M? SubPc shows that in the Al? SubPc and Ga? SubPc, the steric repulsions among the three azacoupled isoindole moieties increase, as to their macrocycles tend to be far from planarity. The binding energies of Cl? M … aza‐coupled isoindole corrected by the basis set superposition error (BSSE), and the nucleus‐independent chemical shift (NICS) values at the ring center, which are a simple and effective local aromaticity probe, were calculated. The results show that Al? SubPc is less stable than both B? SubPc and Al? Pc for larger steric repulsion, smaller binding energy, and weaker aromaticity. In the same way, Ga? SubPc is less stable than both B? SubPc and Ga? Pc. In addition, the ring expansion reactivity occurring in B? SubPc was confirmed by the global aromaticity mirrored by the electrophilicity index ω values. Therefore, the Al? SubPc and Ga? SubPc remain unknown, while the corresponding compounds Al? Pc and Ga? Pc are known experimentally. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
1000.
Determination of Fatty Acid Methyl Esters in Biodiesel Produced from Yellow Horn Oil by LC 总被引:2,自引:0,他引:2
Yu-Jie Fu Yuan-Gang Zu Li-Li Wang Nai-Jing Zhang Wei Liu Shuang-Ming Li Su Zhang 《Chromatographia》2008,67(1-2):9-14
A simple and accurate HPLC method with refractive index detection was developed to determine the main fatty acid methyl esters
in biodiesel produced from yellow horn oil. Methyl linoleate, methyl linolenate, methyl arachidate, methyl stearate, methyl
palmitate and methyl oleate were separated on a HIQ SIL C18W column using methanol as mobile phase. The method has good repeatability
and precision, the intraday and interday RSD for both retention time and peak area was less than 3.2%. The LOD (S/N = 3) and
LOQ (S/N = 9) were less than 0.004 and 0.015 mg mL−1, respectively. 相似文献