全文获取类型
收费全文 | 4428篇 |
免费 | 652篇 |
国内免费 | 233篇 |
专业分类
化学 | 936篇 |
晶体学 | 19篇 |
力学 | 1027篇 |
综合类 | 110篇 |
数学 | 1760篇 |
物理学 | 1461篇 |
出版年
2024年 | 6篇 |
2023年 | 42篇 |
2022年 | 84篇 |
2021年 | 104篇 |
2020年 | 131篇 |
2019年 | 113篇 |
2018年 | 119篇 |
2017年 | 153篇 |
2016年 | 186篇 |
2015年 | 137篇 |
2014年 | 221篇 |
2013年 | 301篇 |
2012年 | 232篇 |
2011年 | 268篇 |
2010年 | 206篇 |
2009年 | 216篇 |
2008年 | 224篇 |
2007年 | 252篇 |
2006年 | 277篇 |
2005年 | 264篇 |
2004年 | 235篇 |
2003年 | 202篇 |
2002年 | 190篇 |
2001年 | 121篇 |
2000年 | 140篇 |
1999年 | 135篇 |
1998年 | 119篇 |
1997年 | 95篇 |
1996年 | 89篇 |
1995年 | 63篇 |
1994年 | 65篇 |
1993年 | 49篇 |
1992年 | 38篇 |
1991年 | 26篇 |
1990年 | 25篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 24篇 |
1983年 | 4篇 |
1982年 | 18篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有5313条查询结果,搜索用时 46 毫秒
971.
HUANG Wen-Hua LIU Yu-Lu MA Zheng-Yi 《理论物理通讯》2007,47(3):397-402
Using the variable separation approach, we obtain a general exact solution with arbitrary variable separation functions for the (2+ 1)-dimensional Maccari system. By introducing Jacobi elliptic functions dn and nd in the seed solution, two types of doubly periodic propagating wave patterns are derived. We invest/gate the wave patterns evolution along with the modulus k increasing, many important and interesting properties are revealed. 相似文献
972.
The internal modes of incoherent vector solitons (IVSs) in
photovoltaic photorefractive materials are investigated in the
framework of coupled nonlinear Schr\"{o}dinger equations. It is found
that there is a pair of internal modes corresponding to a
bright--bright IVS. The propagation dynamics of the bright-bright IVS
perturbed by the internal modes is simulated by numerical method. 相似文献
973.
Hong Zhang Ethan Tumarkin Ruby May A. Sullan Gilbert C. Walker Eugenia Kumacheva 《Macromolecular rapid communications》2007,28(5):527-538
Polymer microgels in the size range from several micrometers to hundreds of micrometers are used in the pharmaceutical, cosmetics, nutrition, pesticide, and food industries, as well as in the encapsulation of cells. To date, a broad range of strategies for the generation of polymer microgels exist, however, these methods involve multistage processes, do not utilize biocompatible components or do not allow precise control of the dimensions and internal structure of the microgels. Recently, microfluidic strategies for the production of polymer particles have offered precise control over the shapes, morphologies, and size distributions of polymer colloids. This paper discusses the most recent results obtained by the authors in the area of the microfluidic production of biopolymer microgels. It provides a brief review of the microfluidic methods for the continuous synthesis and fabrication of microgels, sets the criteria for the successful microfluidic generation of biomicrogels, and describes two methods for the preparation of microgels by microfluidic means. The article concludes with a summary and an outlook.
974.
用多极方法数值研究构成六重对称全内反射型光子晶体光纤各种结构参数对基模零色散点的调节.数值结果表明,在相对孔径较大时,包层空气孔柱层数不影响零色散点,在其它结构参数相同的条件下,空气孔直径越大,零色散点波长越短,而在其它结构参数相同的条件下,空气孔孔距越大,零色散点波长越长,当空气孔直径与空气孔孔距都很小时,零色散点出现在长波区域,当空气孔直径与空气孔孔距大到一定程度时,色散曲线在零色散线出现振荡特性,并出现多个零色散点,在包层空气柱层数一定的条件下,中央纤芯缺省空气孔层数对零色散点的调节范围大. 相似文献
975.
By using a Bäcklund transformation and the multi-linear variable separation approach, we find a new general
solution of a (2+1)-dimensional generalization of the nonlinear
Schrödinger system. The new “universal” formula is defined, and then, rich coherent structures can be found by selecting corresponding
functions appropriately. 相似文献
976.
Bayesian latent variable regression (BLVR) aims to utilize all available information for empirical modeling via a Bayesian framework. Such information includes prior knowledge about the underlying variables, model parameters and measurement error distributions. This paper improves upon the existing optimization‐based BLVR (BLVR‐OPT) method [1] by developing a sampling‐based Bayesian latent variable regression (BLVR‐S) method that relies on Gibbs sampling. Use of the sampling‐based framework not only provides point estimates, but its ability to generate samples that represent the posterior distribution of the unknown variables, also readily provides error bounds. Features and advantages of this method are demonstrated via examples based on simulated data and real Near‐Infrared (NIR) spectroscopy data. Practical aspects of Bayesian modeling such as determining when the extra computation may be worth the effort are addressed by an empirical study of the effects of the amount of training data and signal to noise ratio (SNR). The benefits of BLVR seem to be most significant when the number of measurements is limited and when noise in output variables is relatively large. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
977.
TiAl过渡层对电弧离子镀沉积TiAlN膜层的影响 总被引:6,自引:0,他引:6
利用电弧离子镀,在不锈钢和SiCP增强2024铝基复合材料基底上沉积TiAlN薄膜.结果表明:TiAlN膜层直接沉积在不锈钢基底上,膜层呈[111]择优取向;然而,TiAlN膜层沉积在不锈钢基底的TiAl过渡层上,膜层呈[220]方向择优取向;并且随着过渡层从零开始增厚,TiAlN膜层的织构系数T(111)逐渐减小,而T(200)逐渐增大,但膜层一直以[220]方向择优取向,内应力的存在可能是膜层产生[220]方向择优取向的原因.在复合材料基底TiAl过渡层上沉积,随着负脉冲偏压的增加,TiAlN膜层的择优取向由[111]向[200]转变.在不锈钢基底上,没有TiAl过渡层时,膜层表面相对光滑,大颗粒较少;有了TiAl过渡层,表面大颗粒较多;TiAl过渡层不同沉积时间对膜层表面影响不大,颗粒尺寸相差无几.没有TiAl过渡层时,膜层结合强度很差,有了TiAl过渡层,结合强度明显增加,但结合强度的大小随过渡层沉积时间(厚度)变化. 相似文献
978.
The antiplane problem of circular arc rigid line inclusions under antiplane concentrated force and longitudinal shear loading was dealt with. By using RiemannSchwaz‘s symmetry principle integrated with the singularity analysis of complex functions, the general solution of the problem and the closed form solutions for some important practical problems were presented. The stress distribution in the immediate vicinity of circular arc rigid line end was examined in detail. The results show that the singular stress fields near the rigid inclusion tip possess a square-root singularity similar to that for the corresponding crack problem under antiplane shear loading, but no oscillatory character. Furthermore, the stresses are found to depend on geometrical dimension, loading conditions and materials parameters. Some practical results concluded are in agreement with the previous solutions. 相似文献
979.
变厚度正交各向异性矩形板非线性非对称弯曲问题的基本方程 总被引:1,自引:1,他引:0
在不计体力,考虑了薄膜力引起在z方向的分力,导出了厚度线性变化的正交各向异性矩形板非线性非对称弯曲问题的本构方程;在引进无量纲变量和引入三个小参数的条件下,给出了挠度函数W(x,y)和应力函数Φ(x,y)的无量纲化的支配方程形式. 相似文献
980.
SHENShou-Feng PANZu-Liang ZHANGJun 《理论物理通讯》2004,42(4):565-567
The variable separation approach method is very useful to solving (2 1)-dimensional integrable systems.But the (1 1)-dimensional and (3 1)-dimensional nonlinear systems are considered very little. In this letter, we extend this method to (1 1) dimensions by taking the Redekopp system as a simp!e example and (3 1)-dimensional Burgers system. The exact solutions are much general because they include some arbitrary functions and the form of the (3 1)-dimensional universal formula obtained from many (2 1)-dimensional systems is extended. 相似文献