全文获取类型
收费全文 | 22066篇 |
免费 | 2938篇 |
国内免费 | 3300篇 |
专业分类
化学 | 11276篇 |
晶体学 | 176篇 |
力学 | 1883篇 |
综合类 | 360篇 |
数学 | 5585篇 |
物理学 | 9024篇 |
出版年
2024年 | 15篇 |
2023年 | 576篇 |
2022年 | 710篇 |
2021年 | 789篇 |
2020年 | 955篇 |
2019年 | 650篇 |
2018年 | 758篇 |
2017年 | 889篇 |
2016年 | 888篇 |
2015年 | 1001篇 |
2014年 | 1412篇 |
2013年 | 1627篇 |
2012年 | 1841篇 |
2011年 | 1872篇 |
2010年 | 1529篇 |
2009年 | 1489篇 |
2008年 | 1322篇 |
2007年 | 1654篇 |
2006年 | 1481篇 |
2005年 | 947篇 |
2004年 | 692篇 |
2003年 | 601篇 |
2002年 | 546篇 |
2001年 | 545篇 |
2000年 | 485篇 |
1999年 | 504篇 |
1998年 | 359篇 |
1997年 | 231篇 |
1996年 | 173篇 |
1995年 | 219篇 |
1994年 | 169篇 |
1993年 | 199篇 |
1992年 | 199篇 |
1991年 | 152篇 |
1990年 | 149篇 |
1989年 | 122篇 |
1988年 | 92篇 |
1987年 | 91篇 |
1986年 | 92篇 |
1985年 | 104篇 |
1984年 | 48篇 |
1983年 | 46篇 |
1982年 | 22篇 |
1981年 | 29篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1958年 | 2篇 |
1957年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
带滩槽地形的连续弯道中纵向流速横向分布解析 总被引:1,自引:0,他引:1
本文基于沿水深积分的动量方程,假定二次流项和弯道附加应力项沿横断面呈线性分布,提出了预测弯道垂线平均纵向流速的解析计算方法,进一步提出了河槽区和河滩区垂线平均纵向流速沿断面分布的求解模式,并将其应用于带滩槽地形的反向连续弯道水槽中. 根据实测数据率定计算参数,该模式可计算不同出口水深条件下断面垂线平均纵向流速分布,计算结果与实测数据吻合良好.分析了线性分布假设中参数随水深变化的取值规律和沿横断面分布特点,并对参数进行了敏感性分析,分析表明线性假设中一次项系数分区位置对流速峰值的大小和位置影响较大,常数项根据地形横比降变化进行分区取值,流速计算值对常数项在水平段和斜坡段分区位置较为敏感,并根据参数的敏感度提出了参数沿水槽的均值作为参考值.讨论了动量方程中二次流项和弯道附加应力项沿弯道的横向分布规律,进一步认识线性假设的适用范围,结果表明线性假设在本文试验水槽中适用于弯道沿程.研究成果有助于认识带滩槽地形的连续弯道纵向流速分布特征及其形成机制. 相似文献
2.
In this article,we study the initial boundary value problem of coupled semi-linear degenerate parabolic equations with a singular potential term on manifolds with corner singularities.Firstly,we introduce the corner type weighted p-Sobolev spaces and the weighted corner type Sobolev inequality,the Poincare′inequality,and the Hardy inequality.Then,by using the potential well method and the inequality mentioned above,we obtain an existence theorem of global solutions with exponential decay and show the blow-up in finite time of solutions for both cases with low initial energy and critical initial energy.Significantly,the relation between the above two phenomena is derived as a sharp condition.Moreover,we show that the global existence also holds for the case of a potential well family. 相似文献
3.
Nonlinear Dynamics - The hybrid neural model provides a computationally effective and biophysics-based neuron behavior model, which maintains its simplicity by incorporating the dynamics... 相似文献
4.
Orientation dependence in high harmonics of ZnO with polarization corrections to counteract the birefringent effect 下载免费PDF全文
《中国物理 B》2021,30(7):74204-074204
We investigate the influence of the birefringence on the high-order harmonics in an a-cut Zn O crystal with midinfrared laser pulses. The high harmonics exhibit strong dependence on the alignment of the crystal with respect to the laser polarization. We introduce the Jones calculus to counteract the birefringent effect and obtain the harmonics with polarization corrections in Zn O. We show that the birefringent effect plays an important role in the orientation dependence of HHG. 相似文献
5.
Song Zi-Long Zhu Yun Liu Jing-Rui Guo Shu-Ke Gu Yu-Cheng Han Xinya Dong Hong-Qiang Sun Qi Zhang Wei-Hua Zhang Ming-Zhi 《Molecular diversity》2021,25(1):205-221
Molecular Diversity - Based on the strategy of diversity-oriented synthesis and the structures of natural product pimprinine and streptochlorin, two series of novel pimprinine derivatives... 相似文献
6.
Photo-catalytic elimination of organic contaminants plays a significant role in wastewater treatment. Developing a highly efficient photo-catalyst is one of the leading research topic. Herein, we reported the fabrication of a novel nanoporous NiO@SiO2 photo-catalyst by a simple ion-exchange method to eliminate the reactive dyes. The synthesized NiO@SiO2 catalyst exhibited fast photo-degradation and excellent adsorption capability and could efficiently remove Red FN-3GL dye from wastewater, due to a high loading of NiO and a large specific surface area, abundant electron-withdrawing groups, as well as narrow bandgap energy. In addition, the NiO@SiO2 photo-catalyst also displayed a high capability to remove reactive dyes over a wide range of pH values (pH 3–9). The prominent adsorption and photo-degradation of dyes were strongly dependent on the surface charge of the catalyst and the generation of hydroxyl radicals (OH?) by the catalyst, respectively. Furthermore, the NiO@SiO2 photo-catalyst also exhibited excellent recyclability, thus demonstrating the feasibility of practical applications in industries. The strategy of covering the metal oxide to nanoporous silica is a promising method for developing active photo-catalysts and applying them in the wastewater treatments. 相似文献
7.
8.
9.
BIT Numerical Mathematics - In this paper, we introduce a novel class of embedded exponential-type low-regularity integrators (ELRIs) for solving the KdV equation and establish their optimal... 相似文献
10.
《Indagationes Mathematicae》2022,33(4):801-815
We consider the irreducibility of polynomial where is a negative integer. We observe that the constant term of vanishes if and only if . Therefore we assume that where is a non-negative integer. Let and more general polynomial, let where with are integers such that . Schur was the first to prove the irreducibility of for . It has been proved that is irreducible for . In this paper, by a different method, we prove: Apart from finitely many explicitly given possibilities, either is irreducible or is linear factor times irreducible polynomial. This is a consequence of the estimate whenever has a factor of degree and . This sharpens earlier estimates of Shorey and Tijdeman and Nair and Shorey. 相似文献