全文获取类型
收费全文 | 28347篇 |
免费 | 4014篇 |
国内免费 | 4480篇 |
专业分类
化学 | 21160篇 |
晶体学 | 581篇 |
力学 | 1347篇 |
综合类 | 446篇 |
数学 | 3464篇 |
物理学 | 9843篇 |
出版年
2024年 | 52篇 |
2023年 | 387篇 |
2022年 | 701篇 |
2021年 | 792篇 |
2020年 | 950篇 |
2019年 | 971篇 |
2018年 | 842篇 |
2017年 | 940篇 |
2016年 | 1098篇 |
2015年 | 1261篇 |
2014年 | 1480篇 |
2013年 | 2016篇 |
2012年 | 2274篇 |
2011年 | 2548篇 |
2010年 | 1996篇 |
2009年 | 1916篇 |
2008年 | 2133篇 |
2007年 | 2043篇 |
2006年 | 1859篇 |
2005年 | 1497篇 |
2004年 | 1254篇 |
2003年 | 1005篇 |
2002年 | 1040篇 |
2001年 | 910篇 |
2000年 | 767篇 |
1999年 | 528篇 |
1998年 | 369篇 |
1997年 | 294篇 |
1996年 | 338篇 |
1995年 | 266篇 |
1994年 | 282篇 |
1993年 | 203篇 |
1992年 | 198篇 |
1991年 | 158篇 |
1990年 | 158篇 |
1989年 | 121篇 |
1988年 | 127篇 |
1987年 | 100篇 |
1986年 | 97篇 |
1985年 | 118篇 |
1984年 | 84篇 |
1983年 | 80篇 |
1982年 | 67篇 |
1981年 | 52篇 |
1980年 | 55篇 |
1979年 | 46篇 |
1977年 | 40篇 |
1976年 | 42篇 |
1974年 | 51篇 |
1973年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
21.
Rongzhen Wu Hongyu Chen Dr. Ninghui Chang Yuzhi Xu Prof. Dr. Jiao Jiao Prof. Dr. Hailong Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1166-1195
Bryostatins are a class of naturally occurring macrocyclic lactones with a unique fast developing portfolio of clinical applications, including treatment of AIDS, Alzheimer's disease, and cancer. This comprehensive account summarizes the recent progress (2014–present) in the development of bryostatins, including their total synthesis and biomedical applications. An emphasis is placed on the discussion of bryostatin 1 , the most-studied analogue to date. This review highlights the synthetic and biological challenges of bryostatins and provides an outlook on their future development. 相似文献
22.
23.
Uhm H.S. Lee P.H. Kim Y.I. Kim J.H. Chang H.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1995,23(4):628-635
A theory is developed for the density profile of low temperature plasmas confined by applied magnetic field and an experiment of the electron-cyclotron-resonance (ECR) plasma is conducted to compare the theoretical prediction and experimental measurements. Due to a large electron mobility along the magnetic field, electrons move quickly out of the system, leaving ions behind and building a space charge potential, which leads to the ambipolar diffusion of ions. In a steady-state condition, the plasma generation by ionization of neutral molecules is in balance with plasma loss due to the diffusion, leading to the electron temperature equation, which is expressed in terms of the plasma size, chamber pressure, and the ionization energy and cross section of neutrals. The power balance condition leads to the plasma density equation, which is also expressed in terms of the electron temperature, the input microwave power and the chamber pressure. It is shown that the plasma density increases, reaches its peak and decreases, as the chamber pressure increases from a small value (0.1 mTorr). These simple expressions of electron temperature and density provide a scaling law of ECR plasma in terms of system parameters. After carrying out an experimental observation, it is concluded that the theoretical predictions of the electron temperature and plasma density agree remarkably well with experimental data 相似文献
24.
设γM(G)是连通图G=(V,E)的最大亏格,记EM^-(G)={e∈E(G)|G\e连通,且γM(G\e)=γM(G)}。若EM^-(G)≠0,则称G是γ(G)-可约的;否则称G是γM(G)-不可约的。本文证明了边的剖分不改变图的最大亏格可约性,点的扩张不改变上可嵌入图的最大亏格可约性;并给出了两类满足EM^-(G)=E(G)的非4-边连通图。 相似文献
25.
A new method for controlling the quantum coherence of atom laser by applying input light with strong strength is presented
within the framework of quantum dynamical theory. Unlike the case of rotating wave approximation(RWA), we show that the non-classical
properties, such as sub-Poisson distribution and quadrature squeezed effect, can appear in the output atom laser beam with
time. By choosing suitable initial RF phase, a steady and brighter output of squeezed coherent atom laser is also available. 相似文献
26.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
27.
一类机器人系统的最优控制 总被引:1,自引:1,他引:0
王辉 《数学的实践与认识》2002,32(3):455-459
本文通过把结构阻尼系数当作控制变量来讨论一类弹性机器人系统的最优控制问题 ,并利用Banach空间几何性质证明了最优控制元的存在唯一性 相似文献
28.
Jun-tao Chang Joerg Evers Marian O. Scully M. Suhail Zubairy 《量子光学学报》2006,12(B08):77-77
We propose a scheme to obtain the distance of two identical atoms placed inside the standing wave field by monitoring the collective resonance fluorescence spectrum emitted by the two particles. We find three different parameter ranges, depending on the distance of the atoms as compared to the transition wavelength. For large interparticle distances, dipole-dipole coupling is negligible, and the main system evolution arises from the interaction with the standing wave field. In the small-distance limit, the dynamics is dominated by the dipole-dipole interaction. Finally, in the intermediate region, a rich interplay of the various couplings arises, which however is lifted for strong driving laser fields. The present measurement procedure allows us to distinguish the three cases. In each of the cases, we show how to determine the distance of the two particles and their respective positions relative to the nodes of the standing wave field with fractional-wavelength precision. 相似文献
29.
溴酸钾-亚甲蓝催化光度法测定硝酸盐和亚硝酸盐 总被引:16,自引:1,他引:15
用镉柱将NO-3 还原为NO-2 ,利用在磷酸介质中NO-2 对溴酸钾氧化亚甲蓝这一褪色反应具有强烈的催化作用而建立了同时测定痕量硝酸盐和亚硝酸盐的新方法。本方法简便、快速、灵敏 ,对亚硝酸盐和硝酸盐测定的线性范围分别为 0~ 2 0 0 μg·L-1和 0 0 0 3~ 310 μg·L-1,用于测定各种水样中痕量NO-2 和NO-3 的含量均获得满意结果 相似文献
30.
小波变换在金融数据分析中的应用 总被引:11,自引:0,他引:11
市场上的数据,从本质上讲都是一种时间序列。它和小波分析中的信号具有相同的特性。因此,完全可以将这些经济时间序列看成信号,应用小波变换进行分析和预测。 相似文献