全文获取类型
收费全文 | 121894篇 |
免费 | 13369篇 |
国内免费 | 10763篇 |
专业分类
化学 | 56511篇 |
晶体学 | 861篇 |
力学 | 5479篇 |
综合类 | 741篇 |
数学 | 10310篇 |
物理学 | 30675篇 |
综合类 | 41449篇 |
出版年
2024年 | 481篇 |
2023年 | 1941篇 |
2022年 | 3182篇 |
2021年 | 3623篇 |
2020年 | 3336篇 |
2019年 | 3096篇 |
2018年 | 2927篇 |
2017年 | 2786篇 |
2016年 | 4049篇 |
2015年 | 4553篇 |
2014年 | 5809篇 |
2013年 | 7190篇 |
2012年 | 8327篇 |
2011年 | 8667篇 |
2010年 | 6662篇 |
2009年 | 6648篇 |
2008年 | 7189篇 |
2007年 | 6663篇 |
2006年 | 6142篇 |
2005年 | 5615篇 |
2004年 | 4474篇 |
2003年 | 3666篇 |
2002年 | 3731篇 |
2001年 | 3390篇 |
2000年 | 3028篇 |
1999年 | 3649篇 |
1998年 | 3025篇 |
1997年 | 2886篇 |
1996年 | 2906篇 |
1995年 | 2385篇 |
1994年 | 2251篇 |
1993年 | 1951篇 |
1992年 | 1708篇 |
1991年 | 1514篇 |
1990年 | 1351篇 |
1989年 | 1190篇 |
1988年 | 952篇 |
1987年 | 753篇 |
1986年 | 533篇 |
1985年 | 413篇 |
1984年 | 222篇 |
1983年 | 195篇 |
1982年 | 161篇 |
1981年 | 117篇 |
1980年 | 92篇 |
1978年 | 73篇 |
1977年 | 56篇 |
1976年 | 55篇 |
1975年 | 58篇 |
1973年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Hongwei Hao Minsheng Wu Yifang Chen Jiaowen Tang Qingyu Wu 《Colloids and surfaces. B, Biointerfaces》2004,33(3-4):151-156
To prevent cyanobacterial bloom in eutrophic water by ultrasonic method, ultrasonic irradiations with different parameters were tested to inhibit Spirulina platensis from growth. The experimental result based on cyanobacterial growth, chlorophyll a and photosynthetic activity showed that, the ultrasonic irradiation inhibited cyanobacterial proliferation effectively, furthermore the inhibition effectiveness increased in the order: 200 kHz>1.7 MHz>20 kHz and became saturated with the increased power. The inhibition mechanism can be mainly attributed to the mechanical damage to the cell structures caused by ultrasonic cavitation, which was confirmed by light microscopy and differential interference microscopy. The optimal frequency of 200 kHz in cavition and sonochemistry was also most effective in cyanobacterial growth inhibition. The higher frequency of 1.7 MHz is weaker than 20 kHz in cavitation, but has more effective inhibition because it is nearer to the resonance frequency of gas vesicle. The inhibition saturation with ultrasonic power was due to the ultrasonic attenuation induced by the acoustic shielding of bubbles enclosing the radiate surface of transducer. 相似文献
42.
According to a multiphase mixture theory, we have mathematically developed a multiphysical model with chemoelectromechanical coupling considerations, termed the multieffect‐coupling electric‐stimulus (MECe) model, to simulate the responsive behavior of electric‐sensitive hydrogels immersed in a bath solution under an externally applied electric field. For solutions of the MECe model consisting of coupled nonlinear partial differential governing equations, a meshless Hermite–Cloud method with a hierarchical iteration technique has been used for a one‐dimensional steady‐state analysis of a hydrogel strip. The computed results are compared with the experimental data, and there is very good agreement. Simulations within the domains of both hydrogels and surrounding solutions also present distributions of the ionic concentrations and electric potential as well as the hydrogel displacement. The effects of various physical parameters on the response behavior of electric‐stimulus responsive hydrogels are discussed in detail. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1514–1531, 2004 相似文献
43.
44.
45.
陈刚 《西北大学学报(自然科学版)》1995,(5)
运用深盆气圈闭的基本原理,综合分析了鄂尔多斯盆地下古生界天然气赋存的基本地质因素,论证并提出了盆地腹部下古生界深盆气圈闭的新认识,并依据盆地地质构造特征将其进一步划分为:西部前渊拗陷型和中东部复式向斜型两大深盆气赋存系统. 相似文献
46.
Double-diffusive convection due to a cylindrical source submerged in a salt-stratified solution is numerically investigated
in this study. For proper simulation of the vortex generated around the cylinder, a computational domain with irregular shape
is employed. Flow conditions depend strongly on the thermal Rayleigh number, Ra
T
, and the buoyancy ratio, R
ρ. There are two types of onset of instability existing in the flow field. Both types are due to either the interaction of
the upward temperature gradient and downward salinity gradient or the interaction of the lateral temperature gradient and
downward salinity gradient. The onset of layer instability due to plume convection is due to the former, whereas, the onset
of layer instability of layers around the cylinder is due to the latter. Both types can be found in the flow field. The transport
mechanism of layers at the top of the basic plume belongs to former while that due to basic plume and layer around the cylinder
are the latter. The increase in Ra
T
reinforces the plume convection and reduces the layer numbers generated around the cylinder for the same buoyancy ratio.
For the same Ra
T
, the increase of R
ρ suppresses the plume convection but reinforces the layers generated around the cylinder. The profiles of local Nusselt number
reflects the heat transfer characteristics of plume convection and layered structure. The profiles of averaged Nusselt number
are between the pure conduction and natural convection modes and the variation is due to the evolution of layers.
Received on 13 September 1996 相似文献
47.
Lizeng Wang Chengsong Ma Xiaoli Zhang Yibing Ren Yong Yu 《Fresenius' Journal of Analytical Chemistry》1995,351(7):689-691
The electrochemical behavior of the copper-tyrosine complex has been studied by linear-sweep adsorption voltammetry. In 0.02 mol/L Na2HPO4 buffer solution (pH=9.6), the complex can be adsorped on a hanging mercury drop electrode and reduced at a peak potential of about –0.42 V (vs. SCE). The secondary derivative peak height is linear proportional to the concentration of tyrosine in the range 1.0×10–7–5.0×10–5 mol/L. The detection limit is 5×10–8 mol/L.Project supported by the Provincial Science Foundation of Shandong Province 相似文献
48.
49.
50.
1 工作原理及电路组成图给出电路原理框图.以工作发射频率为时钟脉冲,调制脉冲作为闸门开启时间,将调制脉冲予以延迟作为接收信号的选通脉冲来关闭闸门,这个时间就是声脉冲从换能器发射到采样点,再回到接收换能器所经过的时间,用这个时间来控制时钟脉冲予以汁数、寄存、译码,以数字形 相似文献