全文获取类型
收费全文 | 11483篇 |
免费 | 1760篇 |
国内免费 | 1673篇 |
专业分类
化学 | 8239篇 |
晶体学 | 173篇 |
力学 | 759篇 |
综合类 | 111篇 |
数学 | 1471篇 |
物理学 | 4163篇 |
出版年
2024年 | 46篇 |
2023年 | 262篇 |
2022年 | 385篇 |
2021年 | 406篇 |
2020年 | 476篇 |
2019年 | 490篇 |
2018年 | 410篇 |
2017年 | 419篇 |
2016年 | 532篇 |
2015年 | 551篇 |
2014年 | 622篇 |
2013年 | 870篇 |
2012年 | 940篇 |
2011年 | 1014篇 |
2010年 | 750篇 |
2009年 | 666篇 |
2008年 | 830篇 |
2007年 | 682篇 |
2006年 | 636篇 |
2005年 | 504篇 |
2004年 | 432篇 |
2003年 | 321篇 |
2002年 | 368篇 |
2001年 | 258篇 |
2000年 | 257篇 |
1999年 | 299篇 |
1998年 | 205篇 |
1997年 | 151篇 |
1996年 | 160篇 |
1995年 | 142篇 |
1994年 | 110篇 |
1993年 | 115篇 |
1992年 | 97篇 |
1991年 | 88篇 |
1990年 | 85篇 |
1989年 | 68篇 |
1988年 | 48篇 |
1987年 | 45篇 |
1986年 | 26篇 |
1985年 | 36篇 |
1984年 | 29篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1975年 | 4篇 |
1957年 | 3篇 |
1948年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
碱蓝6B共振光散射法检测DNA 总被引:4,自引:0,他引:4
研究了碱蓝 6B与脱氧核糖核酸在酸性条件下共振光散射特征 ,考察了影响因素和最佳反应条件 ,建立了一种测定纳克级DNA的方法。在四硼酸钠 盐酸 (pH =2 90 )缓冲溶液中 ,线性范围为 10~ 10 0 4 μg·L- 1 ,相关系数为 0 9913,检出限为 4 2 μg·L- 1 ,用于合成样品的测定结果令人满意。 相似文献
32.
Mid-infrared generation based on a periodically poled LiNbO3 optical parametric oscillator 下载免费PDF全文
We report a nanosecond Nd:YVO_4-pumped optical parametric oscillator (OPO) based on periodically poled LiNbO_3 (PPLN). Tuning is achieved in this experiment by varying the temperature and period of the PPLN. The design of double-pass singly resonant oscillator (DSRO) and confocal cavity enables the OPO threshold to be lowered considerably, resulting in a simple, compact, all-solid-state configuration with the mid-infrared idler powers of up to 466mW at 3.41μm. 相似文献
33.
YaoKui ChenZhixiang 《分析论及其应用》2003,19(2):115-120
This paper gives the weighted Lp convergence rate estimations of the Gruenwald interpolatory polynomials based on the zeros of Chebyshev polymomials of the first kind,and proves that the order of the estimations is optimal for p≥1. 相似文献
34.
Pyroelectricity and Spontaneous Polarization in [111] Oriented 0.955 Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 Single Crystals 下载免费PDF全文
We report that the measurements of the pyroelectric current of the pre-poled [111]-oriented 0.955 Pb(Zn1/3Nb2/3) O3-0.045 PbTiO3 (PZN-4.5%PT) single crystals can shed some light on the phase transition and spontaneous polarization characters of this material in a similar way to measures of remanent polarization and dielectric properties. The pyroelectric current is measured and the corresponding spontaneous polarization is calculated as a function of temperature with various poling fields added during cooling the sample from 200℃ to room temperature. Critical electric field of 0.061 k V/cm is found to be essential to induce the intermediate ferroelectric orthorhombic phase between the ferroelectric rhombohedral and tetragonal phases. Below the critical field, the polarization increases almost linearly with the increase of poling field. At the critical field, the polarization at 30OC increases abruptly from 14μC/cm^2 for a poling field of O.06kV/cm to 29.5μC/cm^2 for a poling field of 0.061 kV/cm, and afterwards, increases slowly and saturates to 31 μC/cm^2 for poling fields beyond 0.55 kV/cm. 相似文献
35.
Yu‐Hsiang Hu Chuh‐Yung Chen Chen‐Chien Wang Yao‐Hui Huang Shao‐Ping Wang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4976-4993
The bulk polymerization of styrene initiated by ?‐caprolactam (CL) and n‐dodecyl mercaptan (RSH) has been explored. This novel polymerization system shows living characteristics. For example, the molecular weight of the resulting polymers increases with conversion, and the system has the ability to form diblock copolymers and so forth. The polymer chain end contains thiol and lactam structures, which we have investigated with Fourier transform infrared, 1H NMR, and 13C NMR techniques. Electron spin resonance spectra and theoretical calculations by the Hartree–Fock methods have been used to examine the mechanism. The results reveal that the initial polymerization starts from thiol via a chain‐transfer reaction, and the propagation proceeds by the insertion of a monomer between the terminal group and the intermediate structure of lactam. Finally, the polymerization kinetics have been examined. The polymerization rate varies linearly with the concentration of CL and RSH, and this confirms the mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4976–4993, 2004 相似文献
36.
37.
从激光推进的要求出发,阐述了用于激光推进的高功率激光器的选择原则,即激光器必须满足:(1)高的平均功率和峰值功率;(2)高的单脉冲能量;(3)高的重复频率;(4)优良的大气传输特性。主要分析了目前YAG固体激光器、自由电子激光器和TEA脉冲CO2激光器的特点,通过上述4个方面性能的比较,认为在目前水平下,TEA脉冲CO2激光器是进行激光推进的首选强激光源,其优点表现在:功率可达10kW量级,单脉冲能量可达0.5~1kJ,重复频率为20~40Hz;激光波长处于大气传输窗口,对大气变化不敏感;工作物质快速流动,不存在热透镜效应和破坏阈值;相关光学元件易于制造;光束质量较好;运行成本低。 相似文献
38.
Yao Ping HOU 《数学学报(英文版)》2005,21(4):955-960
A signed graph is a graph with a sign attached to each edge. This paper extends some fundamental concepts of the Laplacian matrices from graphs to signed graphs. In particular, the relationships between the least Laplacian eigenvalue and the unbalancedness of a signed graph are investigated. 相似文献
39.
ROLAND STOUT MARCY HAMBY TOWNS DEBORAH SAUDER THERESA JULIA ZIELINSKI GEORGE LONG 《The Chemical Educator》1997,2(1):1-21
The use of cooperative learning in an online setting is examined using the online segment of a recently offered physical chemistry course as an example. The nature and function of classical, face-to-face cooperative learning are outlined. The online course segment is outlined and is analyzed with regard to the criteria for classical cooperative learning. Though this specific course segment functioned poorly when taught as online cooperative learning, it is possible to structure online courses to take advantage of the strengths of cooperative learning. The possible structure and function of an online cooperative learning community are explored, concluding with a specific model for online cooperative learning. 相似文献
40.