全文获取类型
收费全文 | 131797篇 |
免费 | 35065篇 |
国内免费 | 32587篇 |
专业分类
化学 | 62072篇 |
晶体学 | 1955篇 |
力学 | 6876篇 |
综合类 | 1432篇 |
数学 | 13353篇 |
物理学 | 63184篇 |
无线电 | 50577篇 |
出版年
2024年 | 967篇 |
2023年 | 1960篇 |
2022年 | 2891篇 |
2021年 | 2813篇 |
2020年 | 2897篇 |
2019年 | 3952篇 |
2018年 | 3743篇 |
2017年 | 5046篇 |
2016年 | 5102篇 |
2015年 | 6579篇 |
2014年 | 6677篇 |
2013年 | 8852篇 |
2012年 | 9596篇 |
2011年 | 10454篇 |
2010年 | 13774篇 |
2009年 | 13837篇 |
2008年 | 7837篇 |
2007年 | 7224篇 |
2006年 | 6672篇 |
2005年 | 6378篇 |
2004年 | 6505篇 |
2003年 | 5019篇 |
2002年 | 4789篇 |
2001年 | 4787篇 |
2000年 | 4176篇 |
1999年 | 3406篇 |
1998年 | 2690篇 |
1997年 | 2404篇 |
1996年 | 2722篇 |
1995年 | 3080篇 |
1994年 | 3091篇 |
1993年 | 3239篇 |
1992年 | 2813篇 |
1991年 | 2438篇 |
1990年 | 1987篇 |
1989年 | 2096篇 |
1988年 | 1990篇 |
1987年 | 1248篇 |
1986年 | 1273篇 |
1985年 | 909篇 |
1984年 | 1035篇 |
1982年 | 936篇 |
1981年 | 774篇 |
1980年 | 806篇 |
1979年 | 558篇 |
1978年 | 544篇 |
1977年 | 643篇 |
1976年 | 1045篇 |
1972年 | 539篇 |
1971年 | 449篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous. 相似文献
22.
通过对TFM调制技术的研究,修正了其中预调制滤波器冲击响应波形g(f)在时间轴上的位置及其频谱G(w)的表达式.然后将TFM基带信号进行近似,即对TFM的相位路径进行进一步的控制,得到一个改进的TFM调制技术.改进后的TFM调制技术和原TFM调制技术相比,频带压缩能力提高了一倍,误码性能不变,但会出现3 dB的寄生调幅,需要提高发射机的发射功率. 相似文献
23.
针对目前爆轰试验中使用的机械密封射频连接器存在的问题.设计了基于玻璃封接技术的新型密封射频连接器结构,并进行了射频反射补偿计算和强度分析.本项研究为爆轰条件下新型密封射频连接器的研制提供了设计依据. 相似文献
24.
N. A. Anurova V. A. Blatov G. D. Ilyushin O. A. Blatova A. K. Ivanov-Shitz L. N. Demyanets 《Crystallography Reports》2008,53(6):930-936
A new method was developed for studying voids and channels in crystal structures based on the Voronoi-Dirichlet partition
of crystal space, and 822 structurally characterized ternary compounds Li
p
X
q
O
r
were analyzed for the first time. For these compounds, the dimensionality was determined and the migration patterns of channel
systems capable of providing lithium-ion transport were constructed. The calculated coordinates of lithium atoms in the centers
of the voids are consistent (within 0.4 ?) with the known structural data. Among these compounds, 113 compounds have infinite
channel systems, 60 compounds (18 structural types, STs) have been described earlier in the literature as solid electrolytes,
and 53 compounds (23 STs) can be considered as potential one-, two-, or three-dimensional ionic conductors (13, 3, and 7 STs,
respectively).
Original Russian Text ? N.A. Anurova, V.A. Blatov, G.D. Ilyushin, O.A. Blatova, A.K. Ivanov-Shitz, L.N. Dem’yanets, 2008,
published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 987–993. 相似文献
25.
Hiroshi Maruyama Tadao Ishii Naruhiko Bamba Hironobu Maeda Akihisa Koizumi Yuzo Yoshikawa Hitoshi Yamazaki 《Physica C: Superconductivity and its Applications》1989,160(5-6):524-532
The temperature dependence of the extended X-ray absorption fine structure (EXAFS) is studied in the high Tc superconductors, YBa2Cu3O7−δ. The measurements were done at the Cu K-edge for samples of two orthorhombic phases (Tc≈90 K and ≈58 K, respectively) and a nonsuperconducting tetragonal phase. Interatomic distances and mean square relative displacements σ2 for Cu-O bonds are determined by the least squares refinement. The results indicate that values of σ2 increase near Tc for both the orthorhombic samples. It is concluded that this anomalous behavior related to Tc is caused by an anomalous vibration of oxygen atoms in the Ba-O layer. Changes in the Cu-O distances from 300 to 20 K are not found. 相似文献
26.
27.
The concept and application of phase-space reconstructions are reviewed. Fractional derivatives are then proposed for the purpose of reconstructing dynamics from a single observed time history. A procedure is presented in which the fractional derivatives of time series data are obtained in the frequency domain. The method is applied to the Lorenz system. The ability of the method to unfold the data is assessed by the method of global false nearest neighbors. The reconstructed data is used to compute recurrences and correlation dimensions. The reconstruction is compared to the commonly used method of delays in order to assess the choice of reconstruction parameters, and also the quality of results. 相似文献
28.
Jocelyn Sabatier Serge Poullain Patrick Latteux Jean Luc Thomas Alain Oustaloup 《Nonlinear dynamics》2004,38(1-2):383-400
Robust speed control of a low damped electromechanical system with backlash is studied, controlled load angular speed being not measured. The proposed control strategy combines a Luenberger observer (load angular speed and load torque disturbance estimations) and a robust CRONE controller. The observer provides estimation of the load angular speed and of the disturbance torque applied on the load. Through the computation of only three independent parameters (as many as a PID controller), the CRONE controller permits to ensure the robust speed control of the load in spite of plant parametric variations and speed observation errors. The proposed control strategy is applied to a four mass experimental test bench. 相似文献
29.
针对柱面注浆方式,研究了有关渗透注浆的单孔复注及不同方式布孔时多孔注浆的相互影响等问题,推导出一些有价值的岩体注浆理论公式,可用于指导现场注浆工程的设计与施工. 相似文献
30.
Accreditation and Quality Assurance - 相似文献