全文获取类型
收费全文 | 39825篇 |
免费 | 6375篇 |
国内免费 | 4407篇 |
专业分类
化学 | 21988篇 |
晶体学 | 349篇 |
力学 | 1802篇 |
综合类 | 136篇 |
数学 | 2984篇 |
物理学 | 12639篇 |
无线电 | 10709篇 |
出版年
2024年 | 189篇 |
2023年 | 1066篇 |
2022年 | 1354篇 |
2021年 | 1818篇 |
2020年 | 1714篇 |
2019年 | 1652篇 |
2018年 | 1385篇 |
2017年 | 1275篇 |
2016年 | 1888篇 |
2015年 | 1930篇 |
2014年 | 2425篇 |
2013年 | 2926篇 |
2012年 | 3474篇 |
2011年 | 3479篇 |
2010年 | 2334篇 |
2009年 | 2329篇 |
2008年 | 2636篇 |
2007年 | 2190篇 |
2006年 | 2134篇 |
2005年 | 1746篇 |
2004年 | 1232篇 |
2003年 | 1032篇 |
2002年 | 1009篇 |
2001年 | 837篇 |
2000年 | 660篇 |
1999年 | 822篇 |
1998年 | 717篇 |
1997年 | 668篇 |
1996年 | 682篇 |
1995年 | 566篇 |
1994年 | 471篇 |
1993年 | 367篇 |
1992年 | 362篇 |
1991年 | 274篇 |
1990年 | 237篇 |
1989年 | 176篇 |
1988年 | 107篇 |
1987年 | 85篇 |
1986年 | 110篇 |
1985年 | 76篇 |
1984年 | 44篇 |
1983年 | 49篇 |
1982年 | 33篇 |
1981年 | 25篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1957年 | 4篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Chengzhe Zhao Guangfeng Wu Chao Zhou Haidong Yang Huixuan Zhang 《Journal of Polymer Science.Polymer Physics》2006,44(4):696-702
A series of acrylic impact modifiers (AIMs) with different particle sizes ranging from 55.2 to 927.0 nm were synthesized by seeded emulsion polymerization, and the effect of the particle size on the brittle–ductile transition of impact‐modified poly(vinyl chloride) (PVC) was investigated. For each AIM, a series of PVC/AIM blends with compositions of 6, 8, 10, 12, and 15 phr AIM in 100 phr PVC were prepared, and the Izod impact strengths of these blends were tested at 23 °C. For AIMs with particle sizes of 55.2, 59.8, 125.2, 243.2, and 341.1 nm, the blends fractured in the brittle mode when the concentration of AIM was lower than 10 phr, whereas the blends showed ductile fracture when the AIM concentration reached 10 phr. It was concluded that the brittle–ductile transition of the PVC/AIM blends was independent of the particle size in the range of 55.2–341.1 nm. When the particle size was greater than 341.1 nm, however, the brittle–ductile transition shifted to a higher AIM concentration with an increase in the particle size. Furthermore, the critical interparticle distance was found not to be the criterion of the brittle–ductile transition for the PVC/AIM blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 696–702, 2006 相似文献
112.
Yan Zhao Xingbin Yang Ru Jiang Xiaoli Sun Wenmin Liu Shengyong Zhang 《Analytical sciences》2006,22(5):747-751
The investigation on capillary electrophoretic enantioseparation of six synthetic compounds containing vicinal diol groups has been undertaken to acquire the optimum conditions using native beta-cyclodextrin (beta-CD) as chiral selector and borate as a background electrolyte. The separation was carried out in an uncoated capillary (58.5 cm x 75 microm i.d., effective length 48.5 cm) and the effects of several important factors were investigated in detail. The results showed that beta-CD as a chiral selector exhibited good enantioselectivity and that the enantioseparation was greatly influenced by the structure of the diols, the borate concentration and the buffer pH. The optimum performance was obtained for the chiral vicinal diols under the conditions of 200 mM borate buffer of pH 9.8 containing 1.7% beta-CD at an applied voltage of 15 kV and a capillary temperature of 20 degrees C. Under the conditions, four diols were baseline separated with fast analysis time and the good theoretical plate numbers (above 10 x 10(4)) and favorable migration-time reproducibilities (RSDs below 3.0%) were obtained. The separation results were satisfactory. 相似文献
113.
Hong Bi Qianwang Chen Yonglong Zhuang Shenqiang Zhao 《Journal of magnetism and magnetic materials》2006
Molecular magnet {NBu4[Fe Cr(ox)3]}x (NBu4+=tetra(n-buty1) ammonium ion; ox2−=oxalate ion) was synthesized under an applied low magnetic field of 0.3 T in comparison to that synthesized without a field. Their crystallinities, morphologies and magnetic properties were characterized by using the X-ray diffractionmeter, the transmission electron microscope, and a superconducting quantum interference device. It is found that the average size of particles synthesized under the applied field appears larger than that synthesized without a field. Moreover, its crystallinity, morphology and magnetic susceptibility have also been improved. However, its chemical structure and ferromagnetic phase transition temperature Tc do not change. Possible reasons to explain this effect are also discussed. 相似文献
114.
115.
The influence of interdiffusion on eigenstates in an interdiffusion-induced GaAs/AlxGa1-xAs single-quantum-well structure is analysed numerically by the finite element method. In this approach, the confinement potential profile of the interdiffused quantum well structure is nonlinear and is modelled by an error function and, in particular, the nature of the effective mass of an electron is considered. The results show that the number of eigenstates and energy levels varies with the extent of the interdiffusion. Numerical results for the quasi-bound states in the quantum well structure with an applied electric field are also presented. 相似文献
116.
117.
118.
119.
本文介绍了一个可对含连接线的电路进行瞬态分析的电路模拟器,该模拟器是在SPICE基础上经修改扩充而成的,连接线的处理采用了文献[1]的方法.文中介绍了方法的基本原理,讨论了数值Laplace反变换时参数的选择与误差的控制.实际VHSIC电路的试算结果表明,该模拟器是相当有效的. 相似文献
120.
我们用扫描电镜观察肠道杆菌种(Enterobacteriaceae)中的四种细菌,大肠埃希氏杆菌(Escherichiacoli),普通变形杆菌(Proteus vulgaris),伤寒沙门氏菌(Salmonella typhi)和福氏志贺氏菌(Shigella Flexneri)。未处理的菌落标本,菌落表面都可形成一层厚薄不同的表膜(Surface film)。四种细菌菌落的表膜,形状不一,千姿百态。适当处理后的菌落标本,则可显示菌体的本来面目。四种细菌菌体在菌落表面的分布和排列,也是各不相同,千差万别。本文根据扫描电镜的观察,对四种不同菌落进行了讨论。 相似文献