全文获取类型
收费全文 | 159193篇 |
免费 | 29692篇 |
国内免费 | 16098篇 |
专业分类
化学 | 124477篇 |
晶体学 | 1757篇 |
力学 | 8087篇 |
综合类 | 873篇 |
数学 | 17582篇 |
物理学 | 52207篇 |
出版年
2024年 | 452篇 |
2023年 | 2538篇 |
2022年 | 4569篇 |
2021年 | 4837篇 |
2020年 | 6076篇 |
2019年 | 6967篇 |
2018年 | 5405篇 |
2017年 | 4770篇 |
2016年 | 9061篇 |
2015年 | 9086篇 |
2014年 | 10548篇 |
2013年 | 13166篇 |
2012年 | 14125篇 |
2011年 | 13739篇 |
2010年 | 10669篇 |
2009年 | 10307篇 |
2008年 | 10396篇 |
2007年 | 9022篇 |
2006年 | 8265篇 |
2005年 | 7206篇 |
2004年 | 5764篇 |
2003年 | 4774篇 |
2002年 | 5282篇 |
2001年 | 4075篇 |
2000年 | 3627篇 |
1999年 | 2987篇 |
1998年 | 2254篇 |
1997年 | 2063篇 |
1996年 | 2004篇 |
1995年 | 1772篇 |
1994年 | 1562篇 |
1993年 | 1274篇 |
1992年 | 1164篇 |
1991年 | 1009篇 |
1990年 | 851篇 |
1989年 | 643篇 |
1988年 | 483篇 |
1987年 | 426篇 |
1986年 | 435篇 |
1985年 | 334篇 |
1984年 | 222篇 |
1983年 | 198篇 |
1982年 | 157篇 |
1981年 | 102篇 |
1980年 | 68篇 |
1979年 | 32篇 |
1978年 | 26篇 |
1976年 | 24篇 |
1975年 | 26篇 |
1957年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
951.
基于Prony算法的Delsuc谱预测是目前NMR LPSVD(Linear Prediction SingularValue Decomposition)法中比较实用的方法。但在高噪声的条件下,时有失峰和假峰出现且要事先知道谱的峰数。本文通过跟踪迭代过程发现Delsuc法的判别因子r_(mis) 很难选定。如果它太小会失峰,而过大又会出现假峰。同时,由于噪声的影响,弱信号的采样点之间的相关性比强信号小,从而在迭代过程中会增加数值不稳定性。文中引入峰面积判据来改善Delsuc法,经模拟与实验均证明结果有效。 相似文献
952.
表面粗糙度测量的磁光位相调制和锁相干涉 总被引:1,自引:0,他引:1
提出了一种表面粗糙度测量的新方法,该方法采用了微分偏振干涉的原理,利用由法拉第磁光调制器所组成的调制系统对偏振干涉光路的位相进行调制,利用锁相干涉原理对位相进行探测,该方法可实现无参考面快速非接触测量,在普通实验条件下,也可保持良好的稳定恶性循环 ,实验装置即可给出表面的轮廓又可给出其它统计数据,其横向分辨率为1.2μm纵向为2nm。 相似文献
953.
K. C. Nicolaou Dionisios Vourloumis Tianhu Li Joaquin Pastor Nicolas Winssinger Yun He Sacha Ninkovic Francisco Sarabia Hans Vallberg Frank Roschangar N. Paul King M. Ray V. Finlay Pareskevi Giannakakou Pascal Verdier-Pinard Ernest Hamel 《Angewandte Chemie (International ed. in English)》1997,36(19):2097-2103
954.
利用莫尔条纹的准正弦特性的三维轮廓术 总被引:5,自引:0,他引:5
分析了两个矩形光栅迭合产生的莫尔条纹的光强分布特性,通过选择适当的光栅参数,可得到一个近似的正弦分划板,并把它用于三维面形测量中,实验结果表明,这种方法简单,易于自动处理,有广泛的实用价值。 相似文献
955.
Wang Jingxiu Zhang Jun Deng Yuanyong Li Jingqun Tian Lirong Yang Xiulan 《中国科学A辑(英文版)》2002,45(1):57-64
Based on the studies on the source regions of a group of coronal mass ejections, we have identified two types of large-scale magnetic structures, and suggested that they are intrinsic components of solar magnetism, their destabilization, expansion, and eruption into the interplanetary space are the basic physical processes which lead to the coronal mass ejections. These two types of large-scale structures are giant magnetic loops connecting the two active belts on the opposite hemispheres of the Sun, and the giant filaments (filament channels) and their related magnetic structures. The latter often appear as two parallel rows of sunspots and plage fields, which align side by side in the full disk daily and synoptic magnetograms. The magnetic neutral lines of these large-scale structures are usually longer than 50 heliographic degrees. We name this type of structure “super A configuration”. Sometimes, they are shown as very long filaments and related large-scale magnetic fields. As these magnetic structures are of very large scale, they extend to a great altitude into the corona, they are not easily recognized in magnetic field observations which are usually aimed at solar flare studies. To identify these large-scale structures becomes a key to understanding and predicting coronal mass ejections. 相似文献
956.
采用紫外线、同平板梯度浓度亚硝基肌,纯铜蒸气激光诱变去甲基金霉素生产菌金霉素链霉菌的原生质体,结果表明原生质体对各种诱变剂的敏感性较高.正变幅度较大.原生质体经紫外线、同平板梯度浓度亚硝墓肌复合诱变后,筛选到一菌株,重新制备原生体,经激光诱变,选育出高产菌株S. A. HU02,去甲基金霉素效价从2831u/ml提高到4337u/ml,提高了53. 2,经多次传代产量性状非常稳定. 相似文献
957.
简述了聚氧化乙烯介质中的铽、铕、铥、钆、钇、镓、锰掺杂的硫化锌纳米晶的制备方法以及紫外吸收光谱、激发光谱和光激发发射光谱.制成的硫化锌纳米晶直径为3.0~3.5nm. 相似文献
958.
A fifth-order theory for solving the problem of interaction between Stokes waves and exponential profile currents is proposed.
The calculated flow fields are compared with measurements. Then the errors caused by the linear superposition method and approximate
theory are discussed. It is found that the total wavccurrent field consists of pure wave, pure current and interaction components.
The shear current not only directly changes the flow field, but also indirectly does so by changing the wave parameters due
to wave-current interaction. The present theory can predict the wave kinematics on shear currents satisfactorily. The linear
superposition method may give rise to more than 40% loading error in extreme conditions. When the apparent wave period is
used and the Wheeler stretching method is adopted to extrapolate the current, application of the approximate theory is the
best.
Project supported by the Chinese Academy of Sciences. 相似文献
959.
Y. -S. Xiong L. Yi K. -L. Yao Z. -G. Li 《Zeitschrift für Physik B Condensed Matter》1994,96(2):261-265
By means of the generalized static replica symmetric spin glass theory, a quantum HeisenbergS=1/2 spin glass model with the infinite-ranged random Dzyaloshinskii-Moriya (DM) interaction and ferromagnetic coupling is investigated. The dependence of entropy, specific heat, susceptibility and the corresponding order parameters on temperature is studied numerically for different ferromagnetic interactions and fixed anisotropy. Two spin glass phases has been found including transverse and mixed spin glass phases. It has been shown that the local susceptibility exhibits double-cusp features for different ferromagnetic coupling (J
0). Phase transition poins are found in the specific heat-temperature plane at various ferromagnetic coupling values. Additionally, the dependence of the spontaneous moment on temperature is calculated. 相似文献
960.
Polyethylene oxide (PEO) based polymer electrolytes with BaTiO3 as filler and Li(C2F5SO2)2N as salt have been examined in lithium polymer batteries. The aluminum disolution potential in PEO-Li(C2F5SO2)2N was estimated to be 4.1 V vs. Li/Li+ at 80 °C, which was compared to that of 3.8 V vs. Li/Li+ in PEO-Li(CF3SO2)2N. The electrical conductivity of the system was measured as a function of O/Li ratio. The highest conductivity was observed
in O/Li=8. The conductivity was 1.65×10−3 S/cm at 80 °C and 1.5×10−5 S/cm at 25 °C. The interfacial resistance of Li/polymer electrolyte/Li annealed at 80 °C for 15 days was lower than 100 Ωcm2.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001. 相似文献