全文获取类型
收费全文 | 52289篇 |
免费 | 5471篇 |
国内免费 | 3374篇 |
专业分类
化学 | 17660篇 |
晶体学 | 599篇 |
力学 | 7562篇 |
综合类 | 292篇 |
数学 | 3752篇 |
物理学 | 13985篇 |
综合类 | 17284篇 |
出版年
2024年 | 114篇 |
2023年 | 427篇 |
2022年 | 885篇 |
2021年 | 946篇 |
2020年 | 1225篇 |
2019年 | 1158篇 |
2018年 | 1209篇 |
2017年 | 1443篇 |
2016年 | 1684篇 |
2015年 | 1867篇 |
2014年 | 2207篇 |
2013年 | 3850篇 |
2012年 | 2812篇 |
2011年 | 3008篇 |
2010年 | 2307篇 |
2009年 | 2668篇 |
2008年 | 2677篇 |
2007年 | 3043篇 |
2006年 | 2774篇 |
2005年 | 2527篇 |
2004年 | 2390篇 |
2003年 | 2239篇 |
2002年 | 2239篇 |
2001年 | 1722篇 |
2000年 | 1778篇 |
1999年 | 1547篇 |
1998年 | 1335篇 |
1997年 | 1215篇 |
1996年 | 1082篇 |
1995年 | 1031篇 |
1994年 | 882篇 |
1993年 | 741篇 |
1992年 | 747篇 |
1991年 | 614篇 |
1990年 | 515篇 |
1989年 | 466篇 |
1988年 | 405篇 |
1987年 | 313篇 |
1986年 | 247篇 |
1985年 | 190篇 |
1984年 | 151篇 |
1983年 | 78篇 |
1982年 | 129篇 |
1981年 | 54篇 |
1980年 | 48篇 |
1979年 | 45篇 |
1978年 | 20篇 |
1976年 | 11篇 |
1973年 | 19篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Summary This paper is concerned with the problem of developing numerical integration algorithms for differential equations that, when
viewed as equations in some Euclidean space, naturally evolve on some embedded submanifold. It is desired to construct algorithms
whose iterates also evolve on the same manifold. These algorithms can therefore be viewed as integrating ordinary differential
equations on manifolds. The basic method “decouples” the computation of flows on the submanifold from the numerical integration
process. It is shown that two classes of single-step and multistep algorithms can be posed and analyzed theoretically, using
the concept of “freezing” the coefficients of differential operators obtained from the defining vector field. Explicit third-order
algorithms are derived, with additional equations augmenting those of their classical counterparts, obtained from “obstructions”
defined by nonvanishing Lie brackets. 相似文献
33.
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
34.
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
35.
36.
37.
本文定义了二阶微分方程的弱 Carathéodory解 ,在不涉及紧型条件的情形下 ,直接用迭代法证明了 Banach空间二阶非线性常微分方程两点边值问题存在唯一解 ,并给出逼近解迭代序列的误差估计 ,对周期边值问题得到类似的结果 相似文献
38.
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
39.
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
40.
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