全文获取类型
收费全文 | 98772篇 |
免费 | 10335篇 |
国内免费 | 18972篇 |
专业分类
化学 | 89415篇 |
晶体学 | 2844篇 |
力学 | 2780篇 |
综合类 | 810篇 |
数学 | 7331篇 |
物理学 | 24899篇 |
出版年
2024年 | 96篇 |
2023年 | 1472篇 |
2022年 | 1781篇 |
2021年 | 3218篇 |
2020年 | 3700篇 |
2019年 | 3476篇 |
2018年 | 2937篇 |
2017年 | 3715篇 |
2016年 | 3916篇 |
2015年 | 3506篇 |
2014年 | 4626篇 |
2013年 | 8503篇 |
2012年 | 6165篇 |
2011年 | 6764篇 |
2010年 | 5719篇 |
2009年 | 6779篇 |
2008年 | 6560篇 |
2007年 | 6651篇 |
2006年 | 6166篇 |
2005年 | 5583篇 |
2004年 | 5339篇 |
2003年 | 4297篇 |
2002年 | 4105篇 |
2001年 | 3062篇 |
2000年 | 2858篇 |
1999年 | 2260篇 |
1998年 | 1995篇 |
1997年 | 1790篇 |
1996年 | 1498篇 |
1995年 | 1550篇 |
1994年 | 1405篇 |
1993年 | 1158篇 |
1992年 | 1010篇 |
1991年 | 704篇 |
1990年 | 514篇 |
1989年 | 467篇 |
1988年 | 417篇 |
1987年 | 288篇 |
1986年 | 231篇 |
1985年 | 218篇 |
1984年 | 196篇 |
1983年 | 83篇 |
1982年 | 155篇 |
1981年 | 209篇 |
1980年 | 192篇 |
1979年 | 183篇 |
1978年 | 146篇 |
1977年 | 127篇 |
1976年 | 95篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
温度/应变/扭曲三参量同时测量低成本传感系统 总被引:9,自引:3,他引:6
提出了一种利用布喇格光纤光栅反射光作信号源、高频CO2激光脉冲写入的长周期光纤光栅和超周期光纤光栅作传感器实现温度、应变和扭曲同时测量的全光栅型低成本强度解调传感方案.文中利用长周期光纤光栅边缘滤波效应实现了温度、应变和扭曲传感信号的实时解调.实验结果表明,其温度和应变的测量灵敏度分别为-0.211 dB/℃和-0.012 dB/10με;而扭曲率的测量灵敏度为0.4394 dB/(rad·m-1),是该法写入普通LPFG的4倍以上. 相似文献
122.
使用SAC/SAC-CI方法,利用D95(d),6-311g**以及cc-PVTZ等基组,对B2分子的基态(X3Σg-)和第一激发态(A3Σu-)的平衡结构和谐振频率进行了优化计算.通过对3个基组的计算结果的比较,得出了D95(d)基组为3个基组中的最优基组的结论;使用D95(d)基组,利用SAC的GSUM(Group Sum of Operators)方法对基态(X3Σg-),SAC-CI的GSUM方法对激发态(A3Σu-)进行单点能扫描计算,用正规方程组拟合Murrell-Sorbie函数,得到了相应电子态的完整势能函数;从得到的势能函数计算了与基态(X3Σg-)和第一激发态(A3Σu-)相对应的光谱常数(Be,αe,ωe和ωeχe),结果与实验数据吻合. 相似文献
123.
124.
125.
126.
采用交流法测量大功率商用钛酸钡(BT)陶瓷加热器的电阻和加热功率随温度的变化关系.结果显示,BT陶瓷的电导特性在80℃附近出现了明显的转变,从低温时的极化子跳跃导电转变为高温时的能带导电,此时,电阻出现极小值,而加热功率出现极大值. 相似文献
127.
128.
Shufeng Zuo 《Applied Surface Science》2006,253(5):2508-2514
Al-pillared clays supported rare earths (RE/Al-PILC) are prepared and used as supports of palladium catalysts for deep oxidation of low concentrations of benzene (130-160 ppm). The supports and catalysts are characterized by X-ray powder diffraction (XRD), FT-IR, BET, transmission electron microscopy (TEM) and temperature-programmed reduction (H2-TPR). The results show that Al-pillaring results in a strong increase in the basal spacing (d0 0 1) from about 1.2 to 1.8 nm, and an increase in the BET surface area from 63.6 (±3.2) to 238.8 (±11.9) m2/g. Activity tests of deep oxidation of low concentration benzene show catalysts supported on Al-PILC and RE/Al-PILC are obviously more active than that on raw clay. Pd/6% Ce/Al-PILC, in particular, can catalyze the complete oxidation of low concentration benzene at a temperature as low as about 290 °C. 相似文献
129.
Gang Wang Xiulin Zhu Zhenping Cheng Jian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2912-2921
A series of (di)picolinic acids and their derivates are investigated as novel complexing tridentate or bidentate ligands in the iron‐mediated reverse atom transfer radical polymerization of methyl methacrylate in N,N‐dimethylformamide at 100 °C with 2,2′‐azobisisobutyrontrile as an initiator. The polymerization rates and polydispersity indices (1.32–1.8) of the resulting polymers are dependent on the structures of the ligands employed. Different iron complexes may be involved in iron‐mediated reverse atom transfer radical polymerization, depending on the type of acid used. 1H NMR spectroscopy has been used to study the structure of the resulting polymers. Chain‐extension reactions have been performed to further confirm the living nature of this catalytic system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2912–2921, 2006 相似文献
130.
More than 250 rotationally resolved vibrational bands of the A2B2-X2A1 electronic transition of 15NO2 have been observed in the 14 300-18 000 cm−1 range. The bands have been recorded in a recently constructed setup designed for high resolution spectroscopy of jet cooled molecules by combining time gated fluorescence spectroscopy and molecular beam techniques. The majority of the observed bands has been rotationally assigned and can be identified as transitions starting from the vibrational ground state or from vibrationally excited (hot band) states. An exceptionally strong band is located at 14 851 cm−1 and studied in more detail as a typical benchmark transition to monitor 15NO2 in atmospheric remote sensing experiments. Standard rotational fit routines provide band origins, rotational and spin rotation constants. A subset of 177 vibronic levels of 2B2 vibronic symmetry has been analyzed in the energy range between 14 300 and 17 250 cm−1, in terms of integrated density and using Next Neighbor Distribution. It is found that the overall statistical properties and polyad structure of 15NO2 are comparable to those of 14NO2 but that the internal structures of the polyads are completely different. This is a direct consequence of the X2A1-A2B2 vibronic mixing. 相似文献