全文获取类型
收费全文 | 52856篇 |
免费 | 8836篇 |
国内免费 | 5656篇 |
专业分类
化学 | 37316篇 |
晶体学 | 641篇 |
力学 | 3077篇 |
综合类 | 328篇 |
数学 | 5955篇 |
物理学 | 20031篇 |
出版年
2024年 | 182篇 |
2023年 | 1120篇 |
2022年 | 2076篇 |
2021年 | 2155篇 |
2020年 | 2270篇 |
2019年 | 2141篇 |
2018年 | 1829篇 |
2017年 | 1777篇 |
2016年 | 2606篇 |
2015年 | 2638篇 |
2014年 | 3100篇 |
2013年 | 3953篇 |
2012年 | 4848篇 |
2011年 | 4785篇 |
2010年 | 3322篇 |
2009年 | 3112篇 |
2008年 | 3339篇 |
2007年 | 2956篇 |
2006年 | 2652篇 |
2005年 | 2276篇 |
2004年 | 1739篇 |
2003年 | 1388篇 |
2002年 | 1275篇 |
2001年 | 1018篇 |
2000年 | 895篇 |
1999年 | 1045篇 |
1998年 | 856篇 |
1997年 | 808篇 |
1996年 | 794篇 |
1995年 | 726篇 |
1994年 | 612篇 |
1993年 | 519篇 |
1992年 | 430篇 |
1991年 | 392篇 |
1990年 | 331篇 |
1989年 | 240篇 |
1988年 | 178篇 |
1987年 | 163篇 |
1986年 | 159篇 |
1985年 | 139篇 |
1984年 | 87篇 |
1983年 | 93篇 |
1982年 | 55篇 |
1981年 | 39篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1977年 | 18篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
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
122.
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
123.
124.
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
125.
126.
The spin coating method was used to assemble polymer (Poly (2,5-dibutoxy-1,4-phenylenevinylene)) (DBO-PPV) into the pores of porous alumina which was prepared by anodization. Four peaks in the photoluminescence (PL) spectra of the composite, with contributions from the DBO-PPV and porous alumina, were found. It was also found that the light emitting from the porous alumina could excite the photoluminescence of DBO-PPV. The nanometer effect of the porous alumina can lead to a blue shift of 90 nm of the PL peaks of DBO-PPV. 相似文献
127.
128.
129.
130.
The possibility of ferromagnetic (FM) and antiferromagnetic (AFM) phase transitions in symmetric nuclear matter is analyzed
within the framework of a Fermi liquid theory with effective Gogny interaction. It is shown that, at some critical density,
nuclear matter with the D1S effective force undergoes a phase transition to the AFM spin state (opposite directions of neutron
and proton spins). The self-consistent equations of spin-polarized nuclear matter with the D1S force have no solutions corresponding
to FM spin ordering (the same direction of neutron and proton spins) and, hence, the FM transition does not appear. The AFM
spin polarization parameter is found for zero and finite temperature. It is shown that the AFM spin polarization parameter
of partially polarized nuclear matter at low enough temperatures increases with temperature. The entropy of the AFM spin state
for some temperature range is larger than the entropy of the normal state. Nevertheless, the free energy of the AFM spin state
is always less than the free energy of the normal state, and the AFM spin-polarized state is preferable for all temperatures
below the critical temperature.
The text was submitted by the authors in English. 相似文献