全文获取类型
收费全文 | 58233篇 |
免费 | 9579篇 |
国内免费 | 6911篇 |
专业分类
化学 | 42308篇 |
晶体学 | 734篇 |
力学 | 3365篇 |
综合类 | 453篇 |
数学 | 6750篇 |
物理学 | 21113篇 |
出版年
2024年 | 126篇 |
2023年 | 1160篇 |
2022年 | 1883篇 |
2021年 | 2143篇 |
2020年 | 2492篇 |
2019年 | 2325篇 |
2018年 | 1989篇 |
2017年 | 1912篇 |
2016年 | 2809篇 |
2015年 | 2821篇 |
2014年 | 3401篇 |
2013年 | 4276篇 |
2012年 | 5275篇 |
2011年 | 5354篇 |
2010年 | 3820篇 |
2009年 | 3582篇 |
2008年 | 3837篇 |
2007年 | 3376篇 |
2006年 | 3061篇 |
2005年 | 2641篇 |
2004年 | 2102篇 |
2003年 | 1675篇 |
2002年 | 1632篇 |
2001年 | 1313篇 |
2000年 | 1139篇 |
1999年 | 1220篇 |
1998年 | 958篇 |
1997年 | 867篇 |
1996年 | 865篇 |
1995年 | 791篇 |
1994年 | 642篇 |
1993年 | 556篇 |
1992年 | 459篇 |
1991年 | 421篇 |
1990年 | 356篇 |
1989年 | 252篇 |
1988年 | 193篇 |
1987年 | 174篇 |
1986年 | 166篇 |
1985年 | 143篇 |
1984年 | 89篇 |
1983年 | 94篇 |
1982年 | 56篇 |
1981年 | 41篇 |
1980年 | 30篇 |
1979年 | 19篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1972年 | 19篇 |
1957年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
261.
本文针对高压陡脉冲测量过程中由于对地电容引起的波形畸变,介绍了一种电感补偿方法,这种补偿回路简便、可靠,可使测量系统的方波响应得到明显的改善。 相似文献
262.
In this paper, we study the existence, uniqueness and regularity of the solutions to Volterra-Fredholm boundary integral equations of second kind in a kind of boundary function spaces. 相似文献
263.
The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and 13C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (Tg) for the in situ blends, contrary to an increase of Tg with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007 相似文献
264.
Optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy was employed to observe the visible absorption spectra of the B^2Σ^+_u-X^2Σ^+_g electronic transition of C^-_2. Four hot bands (0,1), (1,2), (2,3) and (3,4) have been observed and the band (3,4) is measured directly for the first time, so far as we know, by absorption. A rotational analysis was carried out to obtain molecular constants. With the Franck-Condon principle and the vibrational Boltzmann distribution, we have estimated the vibrational temperature of C^-_2 to be about 3000K. 相似文献
265.
The method of demodulation with two parallel matched fiber Bragg gratings( FBGs)system is introduced to enlarge the range of strain that can be detected by the FBG sensor system. 相似文献
266.
After taking into account energy conservation and the particle’s self-gravitation interaction, Hawking radiation of the massive
particle as tunneling from Schwarzshild-anti-de Sitter black hole is studied by using Parikh-Wilczek’s semi-classical quantum
tunneling approach. Meanwhile, Hawking radiation as tunneling from the black hole is reexamined by developing Angheben–Nadalini–Vanzo–Zerbini
(ANVZ) covariant method to cover energy conservation and the particle’s self-gravitation interaction. Both the results perfectly
generalize those obtained by Parikh and Wilczek, and show that the tunneling rate is related to the change of Bekenstein-Hawking
entropy, and the factual emission spectrum is not exactly thermal, but satisfies the underlying unitary theory.
PACS: 04.70-s, 9760. Lf. 相似文献
267.
268.
269.
首先将无线传感器网络的路由问题转化成求解最小Steiner树问题,然后给出了求解无线传感器网络路由的蚁群优化算法,并对算法的收敛性进行了证明.最后对找到最优解后信息素值的变化进行了分析.即在限制信息素取值的条件下,当迭代次数充分大时,该算法能以任意接近于1的概率找到最优解,并且当最优解找到后,最优树边上的信息素单调增加,而最优解以外边上的信息素在有限步达到最小值. 相似文献
270.