全文获取类型
收费全文 | 30340篇 |
免费 | 2920篇 |
国内免费 | 2695篇 |
专业分类
化学 | 28174篇 |
晶体学 | 681篇 |
力学 | 408篇 |
综合类 | 124篇 |
数学 | 1526篇 |
物理学 | 5042篇 |
出版年
2024年 | 61篇 |
2023年 | 384篇 |
2022年 | 1043篇 |
2021年 | 1020篇 |
2020年 | 1233篇 |
2019年 | 958篇 |
2018年 | 794篇 |
2017年 | 749篇 |
2016年 | 1248篇 |
2015年 | 1238篇 |
2014年 | 1332篇 |
2013年 | 2357篇 |
2012年 | 1546篇 |
2011年 | 1382篇 |
2010年 | 1398篇 |
2009年 | 1565篇 |
2008年 | 1625篇 |
2007年 | 1667篇 |
2006年 | 1619篇 |
2005年 | 1479篇 |
2004年 | 1422篇 |
2003年 | 1250篇 |
2002年 | 1864篇 |
2001年 | 728篇 |
2000年 | 655篇 |
1999年 | 601篇 |
1998年 | 563篇 |
1997年 | 470篇 |
1996年 | 643篇 |
1995年 | 584篇 |
1994年 | 277篇 |
1993年 | 233篇 |
1992年 | 249篇 |
1991年 | 147篇 |
1990年 | 111篇 |
1989年 | 107篇 |
1988年 | 127篇 |
1987年 | 96篇 |
1986年 | 79篇 |
1985年 | 153篇 |
1984年 | 144篇 |
1983年 | 74篇 |
1982年 | 109篇 |
1981年 | 112篇 |
1980年 | 74篇 |
1979年 | 60篇 |
1978年 | 65篇 |
1977年 | 42篇 |
1973年 | 33篇 |
1971年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
S. Schweizer M. Secu J. -M. Spaeth L. W. Hobbs A. Edgar G. V. M. Williams 《Radiation measurements》2004,38(4-6):633-638
We found a significant PSL effect in Eu2+-doped fluorozirconate glasses (ZBLAN) which were additionally doped with Br− or Cl− ions. The PSL is attributed to the characteristic emission of Eu2+ present in nano-crystallites of BaBr2 or BaCl2, which form in the glass upon annealing. The metastable hexagonal form of BaX2 (X=Br,Cl) is always formed first before it is converted into the stable orthorhombic form. The particle size increases upon annealing and so does the PSL efficiency of the glass ceramic. However, there is a saturation of the PSL efficiency, which is for Br− doping about 9% and for Cl−-doping about 80% of the Eu-doped BaFBr standard. The particle size was determined by transmission electron microscopy (TEM). The TEM results show a clear tendency for bigger particles for longer annealing at the expense of its number. The particle size for the most efficient phosphor is about 100 nm. 相似文献
52.
The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
53.
For the purpose of testing the spherical uniformity based on i.i.d. directional data (unit vectors) zi, i=1,…,n, Anderson and Stephens (Biometrika 59 (1972) 613–621) proposed testing procedures based on the statistics Smax=maxu S(u) and Smin=minu S(u), where u is a unit vector and nS(u) is the sum of squares of u′zi's. In this paper, we also consider another test statistic Srange=Smax−Smin. We provide formulas for the P-values of Smax, Smin, Srange by approximating tail probabilities of the limiting null distributions by means of the tube method, an integral-geometric approach for evaluating tail probability of the maximum of a Gaussian random field. Monte Carlo simulations for examining the accuracy of the approximation and for the power comparison of the statistics are given. 相似文献
54.
线性规划的符号跟踪算法 总被引:2,自引:1,他引:1
分析了只含一个约束条件的线性规划最优基变量的特征,将其运用到搜寻含m个约束条件的线性规划的最优基变量,从而提出了线性规划的符号跟踪算法,为线性规划求解提供了新途径。 相似文献
55.
Chung-Cherng Lin 《Journal of Physics and Chemistry of Solids》2004,65(5):913-921
The phase transition of a synthetic clinoenstatite in a diamond-anvil cell has been studied by using Raman spectroscopy at various pressures and room temperature. The phenomena observed in clinoenstatite have been compared with that observed in orthoenstatite. It is found that the pressure-induced phase transitions in the two enstatites are reversible, but with different transition pressures and transition behavior. An analysis of Raman spectra has revealed that the two enstatites have different high-pressure polymorphs. This result suggests that the space group of the high-pressure polymorph of orthoenstatite is not of C2/c, and that orthoenstatite and orthoferrosilite have different transition routes at room temperature and high pressure. The compressional behavior of the high-PC2/c enstatite is also discussed according to the pressure dependences of Raman frequencies. 相似文献
56.
Michael C. W. Chan Dr. 《化学:亚洲杂志》2008,3(1):18-27
The notion of weak attractive ligand–polymer interactions is introduced, and its potential application, importance, and conceptual links with “cooperative” ligand–substrate interactions are discussed. Synthetic models of weak attractive ligand–polymer interactions are described, in which intramolecular weak C? H???F? C interactions (the existence of which remains contentious) have been detected by NMR spectroscopy and neutron and X‐ray diffraction experiments. These C? H???F? C interactions carry important implications for the design of catalysts for olefin polymerization, because they provide support for the practical feasibility of ortho‐F???Hβ ligand–polymer contacts proposed for living Group 4 fluorinated phenoxyimine catalysts. The notion of weak attractive noncovalent interactions between an “active” ligand and the growing polymer chain is a novel concept in polyolefin catalysis. 相似文献
57.
给出模糊半群上的模糊同余的概念,并进一步研究它的一些基本代数性质。同时研究带有模糊半群上的模糊同余扩张性质(FCEPF)的半群类,得到一个半群有模糊半群上的模糊同余扩张性质、有模糊同余扩张性质(FCEP)、有同余扩张性质(CEP)三个条件是等价的。 相似文献
58.
从等离子体平板显示器(PDP)的发光原理出发,分析和研究了存贮控制电路的工作原理,提出基于FPGA的电路设计方案,并给出数据整理电路和驱动信号产生电路的具体电路框图,最后给出部分仿真波形. 相似文献
59.
60.
Mathematical Notes - 相似文献