全文获取类型
收费全文 | 70235篇 |
免费 | 10204篇 |
国内免费 | 6670篇 |
专业分类
化学 | 47065篇 |
晶体学 | 663篇 |
力学 | 4701篇 |
综合类 | 515篇 |
数学 | 8495篇 |
物理学 | 25670篇 |
出版年
2024年 | 228篇 |
2023年 | 1402篇 |
2022年 | 2289篇 |
2021年 | 2404篇 |
2020年 | 2533篇 |
2019年 | 2431篇 |
2018年 | 2194篇 |
2017年 | 1950篇 |
2016年 | 2983篇 |
2015年 | 3097篇 |
2014年 | 3665篇 |
2013年 | 4858篇 |
2012年 | 5903篇 |
2011年 | 6039篇 |
2010年 | 4085篇 |
2009年 | 4031篇 |
2008年 | 4205篇 |
2007年 | 3796篇 |
2006年 | 3582篇 |
2005年 | 3102篇 |
2004年 | 2489篇 |
2003年 | 1899篇 |
2002年 | 1686篇 |
2001年 | 1526篇 |
2000年 | 1425篇 |
1999年 | 1570篇 |
1998年 | 1338篇 |
1997年 | 1176篇 |
1996年 | 1231篇 |
1995年 | 1074篇 |
1994年 | 1007篇 |
1993年 | 865篇 |
1992年 | 771篇 |
1991年 | 668篇 |
1990年 | 555篇 |
1989年 | 483篇 |
1988年 | 366篇 |
1987年 | 349篇 |
1986年 | 297篇 |
1985年 | 300篇 |
1984年 | 202篇 |
1983年 | 176篇 |
1982年 | 145篇 |
1981年 | 112篇 |
1980年 | 82篇 |
1978年 | 56篇 |
1977年 | 52篇 |
1976年 | 50篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
Yan-hua WANG & Xiao-wu CHEN Department of Applied Mathematics Shanghai University of Finance Economics Shanghai China Department of Mathematics University of Science Technology of China Hefei China 《中国科学A辑(英文版)》2007,50(3):450-456
Using the quiver technique we construct a class of non-graded bi-Frobenius algebras. We also classify a class of graded bi-Frobenius algebras via certain equations of structure coefficients. 相似文献
153.
文章讨论无界区域上GBBM方程的Cauchy问题,对方程的解进行了先验估计,并证明了在H1弱拓扑中整体吸引子的存在性. 相似文献
154.
155.
Z.J. Liu H.H. Long W.C. Ye X.X. Zou Z.L. Qin E.P. Li J.S. Chen 《Journal of magnetism and magnetic materials》2006
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated. 相似文献
156.
Nickel and cobalt films illustrate alternative Bloch lines with cap switches. The strip magnetic domains become zigzag and bubbling cells for Ni and Co films, respectively, under an external field of 1.5 T. The magnetoresistances (MR) for currents parallel (CIW) to the domain walls is 15% less than those of the perpendicular (CPW) case. We also studied the magneto size effect by applying the magnetic field normal to the surface, from which the Sondheimer oscillation appears attributing to periodic striking of the surface for electrons traveling in circular motion on a plane canting to the surface. The experiments can be expressed by the magneto size effect inherited with very small specularity parameters. 相似文献
157.
In this paper, we discuss the local and global existence ofweak solutions for some hyperbolicparabolic systems modellingchemotaxis. 相似文献
158.
In general, we will use the numerical differentiation when dealing with the differential equations. Thus the differential equations can be transformed into algebraic equations and then we can get the numerical solutions. But as we all have known, the numerical differentiation process is very sensitive to even a small level of errors. In contrast it is expected that on average the numerical integration process is much less sensitive to errors. In this paper, based on the Sinc method we provide a new method using Sinc method incorporated with the double exponential transformation based on the interpolation of the highest derivatives (SIHD) for the differential equations. The error in the approximation of the solution is shown to converge at an exponential rate. The numerical results show that compared with the exiting results, our method is of high accuracy, of good convergence with little computational efforts. It is easy to treat nonhomogeneous mixed boundary condition for our method, which is unlike the traditional Sinc method. 相似文献
159.
Enantioselective biocatalysis in nonaqueous media is becoming increasingly important in preparative synthetic chemistry. This article discusses (1) the general catalytic properties of enzymes in nonaqueous environments, (2) the basic principles that govern lipase-catalyzed enantioselective esterification and transesterification reactions in organic media for the preparation of optically active acids and alcohols, (3) the determination of kinetic and thermodynamic parameters, and (4) the quantitative analysis of published data. 相似文献
160.
Yangyang Jiang Chen Guo Huizhou Liu 《中国颗粒学报》2007,5(1):130-133
A magnetically rotational reactor (MRR) has been developed and used in absorbing benzene emissions. The MRR has a permanent magnet core and uses magnetic ionic liquid [bmim]FeCl4 as absorbent. Benzene emissions were carried by N2 into the MRR and were absorbed by the magnetic ionic liquid. The rotation of the permanent magnet core provided impetus for the agitation of the magnetic ionic liquid, enhancing mass transfer and making benzene better dispersed in the absorbent. 0.68 g benzene emissions could be absorbed by a gram of [bmim]FeCl4, 0.27 and 0.40 g/g higher than that by [bmim]PF6 and [bmim]BF4, respectively. The absorption rate increased with increasing rotation rate of the permanent magnet. 相似文献