全文获取类型
收费全文 | 3734篇 |
免费 | 735篇 |
国内免费 | 1384篇 |
专业分类
化学 | 2912篇 |
晶体学 | 169篇 |
力学 | 252篇 |
综合类 | 90篇 |
数学 | 553篇 |
物理学 | 1877篇 |
出版年
2024年 | 3篇 |
2023年 | 49篇 |
2022年 | 165篇 |
2021年 | 166篇 |
2020年 | 136篇 |
2019年 | 139篇 |
2018年 | 147篇 |
2017年 | 198篇 |
2016年 | 163篇 |
2015年 | 204篇 |
2014年 | 239篇 |
2013年 | 365篇 |
2012年 | 309篇 |
2011年 | 323篇 |
2010年 | 327篇 |
2009年 | 348篇 |
2008年 | 380篇 |
2007年 | 298篇 |
2006年 | 320篇 |
2005年 | 268篇 |
2004年 | 209篇 |
2003年 | 159篇 |
2002年 | 153篇 |
2001年 | 153篇 |
2000年 | 169篇 |
1999年 | 97篇 |
1998年 | 62篇 |
1997年 | 36篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 30篇 |
1993年 | 23篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有5853条查询结果,搜索用时 15 毫秒
1.
2.
The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr2·6H2O formed. In addition to this double salt, the three single salts LiBr·2H2O, KBr and MgBr2·6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer's electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones. 相似文献
3.
The acoustic and perceptive characteristics of discourse units, including clauses, simple sentences, compound sentences and paragraphs, were studied. The acoustic characteristics were based on the analysis of a speech corpus consisted of ten monologues. The Perceived Boundary Strength (PBS) of the monologues was labeled on a five-point scale by 25 participants. The main results are as follows: (1) There is a significant difference in the PBS of clauses (corresponding to intonational phrase), sentences (including simple sentences and compound sentences) and paragraphs. But the PBS of simple sentences and compound sentences is the same, and the pitch reset and pause are also not significantly different between these two kinds of boundaries. (2) The pitch-based cue used to distinguish clauses, sentences and paragraphs appears to be the difference between pre- and post-boundary syllables, but not simply the pitch value of either syllable alone. (3) Declination mainly occurs within intonational phrases, whereas there is no consistent global declination in sentences or in paragraphs. (4) Pauses are longer and more varied at the boundary of larger discourse units. Moreover, there is a significant positive correlation between pause duration and degree of pitch reset at clause boundaries, but not at sentence or paragraph boundaries. 相似文献
4.
5.
6.
采用同步辐射能量色散X射线衍射技术、激光加热技术和金刚石对顶砧(DAC)高压装置,在温度为2 000 K和压力为23 GPa的范围内,对采自地幔二辉橄榄岩中的顽火斜方辉石,进行了原位的高温高压能量色散X射线衍射(EDXRD)测量。实验结果表明:当压力为15.3 GPa、温度为1 600 K时(相当于地球内部410 km处的地震波不连续界面的温压环境),顽火斜方辉石转变为橄榄石的β相——瓦兹利石(Wadsleyite)相;继续加温加压至2 000 K、23 GPa时(相当于地球内部670 km处的地震波不连续界面的温压环境),顽火斜方辉石相变为钛铁矿(Ilmenite)结构和钙钛矿(Perovskite)结构的混和相。实验结果进一步证明,在地幔中存在的两个地震波不连续界面是由橄榄石、顽火斜方辉石等矿物的相变引起的。 相似文献
7.
GAO Xiaoyan CAI Xiao CAO Zeng CUI Chenghe 《核工业西南物理研究院年报(英文版)》2004,(1):54-56
HL-2A is the first divertor tokamak in China. The vacuum system is one of the important parts of the HL-2A tokamak, which has to be work well during the physics campaign in 2004. As the tokamak machine is separated from the operation staff during discharges, to guarantee the safe and reliable operation of the vacuum system, it is necessary to watch the vacuum system outside the machine hall with an automatic monitoring system. The paper describes the design and manufacture of the monitoring system. 相似文献
8.
The vacuum system of today's tokamak devices is designed to meet the operational requirements of the experiments. The operation can be divided into five modes, (1) pumping down and leak detecting of the vacuum vessel, (2) baking, (3) plasma-facing component (PFC) conditioning, (4)evacuating and controlling of the particles at plasma edge, (5) plasma discharge experiments. 相似文献
9.
10.
Gujie Qian S. Baccaro M. Falconieri Jiafang Bei A. Cecilia Guorong Chen 《Journal of Non》2008,354(40-41):4626-4629
Glasses in SiO2–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF2/BaO ratio on structure of glasses. 相似文献