全文获取类型
收费全文 | 19324篇 |
免费 | 3268篇 |
国内免费 | 2831篇 |
专业分类
化学 | 14002篇 |
晶体学 | 265篇 |
力学 | 1110篇 |
综合类 | 245篇 |
数学 | 2190篇 |
物理学 | 7611篇 |
出版年
2024年 | 78篇 |
2023年 | 361篇 |
2022年 | 665篇 |
2021年 | 713篇 |
2020年 | 833篇 |
2019年 | 820篇 |
2018年 | 710篇 |
2017年 | 661篇 |
2016年 | 979篇 |
2015年 | 956篇 |
2014年 | 1170篇 |
2013年 | 1460篇 |
2012年 | 1857篇 |
2011年 | 1827篇 |
2010年 | 1339篇 |
2009年 | 1271篇 |
2008年 | 1455篇 |
2007年 | 1238篇 |
2006年 | 1051篇 |
2005年 | 904篇 |
2004年 | 739篇 |
2003年 | 608篇 |
2002年 | 604篇 |
2001年 | 497篇 |
2000年 | 394篇 |
1999年 | 334篇 |
1998年 | 227篇 |
1997年 | 206篇 |
1996年 | 217篇 |
1995年 | 175篇 |
1994年 | 166篇 |
1993年 | 121篇 |
1992年 | 106篇 |
1991年 | 101篇 |
1990年 | 94篇 |
1989年 | 74篇 |
1988年 | 53篇 |
1987年 | 40篇 |
1986年 | 42篇 |
1985年 | 50篇 |
1984年 | 42篇 |
1983年 | 34篇 |
1982年 | 25篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
We describe one convenient synthesis route to boron nitride (BN) nanotube by the reaction of boron powder, iron oxide, and ammonium chloride at 600 °C for 12 h. Characterized by XRD, FTIR, XPS, TEM and SAED, the composition and morphology of the products are confirmed. The possible reaction mechanism is also discussed. 相似文献
32.
Xia Yin Weiguang Zhang Qijiao Zhang Jun Fan Chian Sing Lai Edward R. T. Tiekink 《应用有机金属化学》2004,18(3):139-140
The centrosymmetric structure of {Cd[S2CN(CH2Ph)2]2}2 features both bridging and chelating dithiocarbamate ligands so that a square pyramidal S5 coordination geometry results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
33.
Yonggang Shangguan Li Zhao Liyang Tao Qiang Zheng 《Journal of Polymer Science.Polymer Physics》2007,45(13):1704-1712
The effects of preparation method, composition, and thermal condition on formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X‐ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α‐iPP and β‐iPP can simultaneity form in the melt‐blended samples, whereas only α‐iPP exists in the solution‐blended samples. The results show that the formation of β‐iPP in the melt‐blended samples is related to the crystallization temperature and the β‐iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β‐iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β‐iPP in iPP/EPR. Furthermore, it was found that the amount of β‐iPP in melt‐blended iPP/EPR samples is dependent on the composition and the maximum amount of β‐iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β‐crystallization of iPP. However, only α‐iPP can be observed in solution‐blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase‐separation happens in both melt‐blended and solution‐blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β‐iPP. It is suggested that the origin of formation of β‐iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007 相似文献
34.
It is shown that the cascaded fifth-order nonlinear phase shifts will increase with energy loss in the cascaded processes. Essentially different from the multi-photon absorption accompanied with inherent material nonlinearities, the loss of fundamental wave in a cascaded process is controllable and suppressible. By introducing difference frequencies generated from the reaction between the fundamental and its second harmonic after the cascaded processes, the fundamental wave can be free of energy loss, while the large cascaded fifth-order nonlinear phase shift is maintained. 相似文献
35.
36.
Supramolecular side chain liquid crystalline polymers (SCLCPs) based on poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane) (PSIX, X=100, 76, 60, 41 or 23, denoting the mole percentage of 3-carboxypropylmethylsiloxane unit in the polymer) and stilbazole derivatives have been obtained through intermolecular hydrogen bonding (H-bonding) interactions between the carboxylic acid and the pyridyl moieties. The formation of H-bonding and self-assembly results in the formation of new mesogenic units, in which H-bonds function as molecular connectors. FTIR shows the existence of H-bonding in the complexes. The polymeric complexes behave as single component liquid crystalline polymers and exhibit stable and enantiotropic mesophases. The liquid crystalline properties of the supramolecular SCLCPs were studied using differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction, and were found to exhibit smectic A phases with focal-conic textures. The thermal stability of the SCLCP increases on increasing the carboxylic acid content in the polysiloxane and the concentration of the stilbazole derivative in the complex. However, the thermal stability decreases on increasing the chain length of the stilbazole derivative. The crystal phase was not formed even on cooling to the glass transition temperature of the polymeric complex. 相似文献
37.
研究了钍与5-(对羧基苯偶氮)-8-羟基喹啉(5-CPAHQ)的显色反应条件:在阳离子表面活性剂十六烷基三甲基溴化铵(CTMAB)存在下,pH4.4-5.4缓冲介质中,形成稳定的橙红色络合物,最大吸收波长为490nm,ε=1.10×105L·mol-1·cm-1,钍在0-9μg/25mL范围内符合比尔定律。用TBP萃淋树脂分离,该方法可用于测定矿石中的微量钍。 相似文献
38.
投资理论告诉人们,应尽量使投资分散化.但许多投资在实际投资中却常常违背这一原则.本从一个调面分析在一个等均值和有一个无风险资产的均方世界里,交易成本的存在,会使投资产生很强的违背分散化原则的动机。 相似文献
39.
40.
This study investigates Chinese teachers’ cultural beliefs concerning effective mathematics teaching through semi-structured interview with nine experienced teachers. For the Chinese teachers, an effective teacher should always be passionate and committed to the teaching profession. She should not only understand the knowledge in the textbook thoroughly but also be able to carefully craft the knowledge from the textbook for teaching by predicting possible students’ difficulties. Although Chinese teachers emphasize student participation and flexible teaching, they tend to see the teacher’s ability to design and lead coherent lessons as the key for facilitating students’ understanding. The result of this study helps researchers and educators understand the teacher-designed and content-oriented teaching model in Chinese classrooms. 相似文献