全文获取类型
收费全文 | 22554篇 |
免费 | 3766篇 |
国内免费 | 2191篇 |
专业分类
化学 | 15948篇 |
晶体学 | 738篇 |
力学 | 899篇 |
综合类 | 182篇 |
数学 | 662篇 |
物理学 | 10082篇 |
出版年
2024年 | 30篇 |
2023年 | 149篇 |
2022年 | 412篇 |
2021年 | 472篇 |
2020年 | 668篇 |
2019年 | 659篇 |
2018年 | 631篇 |
2017年 | 770篇 |
2016年 | 1028篇 |
2015年 | 967篇 |
2014年 | 1019篇 |
2013年 | 2334篇 |
2012年 | 1333篇 |
2011年 | 1408篇 |
2010年 | 1210篇 |
2009年 | 1247篇 |
2008年 | 1299篇 |
2007年 | 1335篇 |
2006年 | 1258篇 |
2005年 | 1145篇 |
2004年 | 1141篇 |
2003年 | 998篇 |
2002年 | 1084篇 |
2001年 | 747篇 |
2000年 | 747篇 |
1999年 | 621篇 |
1998年 | 529篇 |
1997年 | 425篇 |
1996年 | 389篇 |
1995年 | 401篇 |
1994年 | 307篇 |
1993年 | 264篇 |
1992年 | 255篇 |
1991年 | 178篇 |
1990年 | 159篇 |
1989年 | 122篇 |
1988年 | 124篇 |
1987年 | 112篇 |
1986年 | 98篇 |
1985年 | 90篇 |
1984年 | 83篇 |
1983年 | 37篇 |
1982年 | 58篇 |
1981年 | 31篇 |
1980年 | 34篇 |
1979年 | 39篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
11.
12.
M. Hanson 《Chromatographia》1994,39(7-8):431-437
Summary Pressure/temperature variation in SFC was shown to influence selectivity towards steroids. Major changes were observed for polar column packings compared to non-polar packings and variation of the amount of modifier showed that this is valid over the whole investigated range. The effect is underlined by a fall in resolution in the low density range (low pressure/high temperature) for polar stationary phases and appears to be significantly larger than for non-polar phases. Major selectivity shifts induced by variation of the physical properties of the mobile phase are considered to be due to the greater effect of polar modifiers on the nature of polar stationary phases than on non-polar phases. 相似文献
13.
14.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6. 相似文献
15.
The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent
state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour
of the nuclear ground states using the coherent states. 相似文献
16.
根据GaN氢化物气相外延生长(HVPE)的原理,设计制作了双温区卧式HVPE系统.根据实际生长中出现的问题和CaN样品的测试情况,对系统进行了逐步的调试和改进. 相似文献
17.
根据Pegg-Barnett位相定义, 计算了一种新的奇偶非线性相干态的位相概率分布函数, 利用数值计算方法研究了它们的位相统计性质. 数值计算结果表明:新的奇偶非线性相干态的位相特性与通常奇偶相干态的位相特性截然不同. 相似文献
18.
Qipeng Guo Fei Chen Ke Wang Ling Chen 《Journal of Polymer Science.Polymer Physics》2006,44(21):3042-3052
An amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006 相似文献
19.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
20.
新疆玛纳斯湖水蒸发过程研究 总被引:3,自引:0,他引:3
本文依据Na^ ,K^ ,Mg^2 //Cl^-,SO4^2--H2O五元水盐体系相图,对新疆玛纳斯盐湖水进行原料分析、理论研究、25℃等温蒸发实验和自然蒸发实验,研究了该湖水蒸发过程中盐类的析出规律及湖水中各组分浓度变化的规律,为进行工艺实验及将来的综合开发利用提供了可靠依据。 相似文献