全文获取类型
收费全文 | 25907篇 |
免费 | 2275篇 |
国内免费 | 1381篇 |
专业分类
化学 | 9840篇 |
晶体学 | 175篇 |
力学 | 7571篇 |
综合类 | 254篇 |
数学 | 4847篇 |
物理学 | 6876篇 |
出版年
2024年 | 23篇 |
2023年 | 260篇 |
2022年 | 362篇 |
2021年 | 498篇 |
2020年 | 626篇 |
2019年 | 483篇 |
2018年 | 530篇 |
2017年 | 671篇 |
2016年 | 789篇 |
2015年 | 791篇 |
2014年 | 991篇 |
2013年 | 1693篇 |
2012年 | 1296篇 |
2011年 | 1608篇 |
2010年 | 1228篇 |
2009年 | 1562篇 |
2008年 | 1467篇 |
2007年 | 1491篇 |
2006年 | 1325篇 |
2005年 | 1150篇 |
2004年 | 1075篇 |
2003年 | 979篇 |
2002年 | 810篇 |
2001年 | 673篇 |
2000年 | 681篇 |
1999年 | 577篇 |
1998年 | 562篇 |
1997年 | 562篇 |
1996年 | 540篇 |
1995年 | 482篇 |
1994年 | 399篇 |
1993年 | 377篇 |
1992年 | 327篇 |
1991年 | 271篇 |
1990年 | 248篇 |
1989年 | 218篇 |
1988年 | 247篇 |
1987年 | 181篇 |
1986年 | 181篇 |
1985年 | 224篇 |
1984年 | 210篇 |
1983年 | 115篇 |
1982年 | 203篇 |
1981年 | 144篇 |
1980年 | 114篇 |
1979年 | 126篇 |
1978年 | 78篇 |
1976年 | 34篇 |
1973年 | 21篇 |
1972年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 357 毫秒
81.
This research extends previous work with dynamic models to manage groundwater quality by using the consumptive nitrate use rate instead of the nitrate application rate. The analysis indicates that misspecification results in overestimation of economic benefits, and supra-optimum nitrogen fertilizer application rates and groundwater nitrate stocks at a steady state. 相似文献
82.
83.
Jean-Franç ois Coulombel Thierry Goudon 《Transactions of the American Mathematical Society》2007,359(2):637-648
We construct global smooth solutions to the multidimensional isothermal Euler equations with a strong relaxation. When the relaxation time tends to zero, we show that the density converges towards the solution to the heat equation.
84.
K. Rßner M. Hümmer A. Benkert A. Forchel 《Physica E: Low-dimensional Systems and Nanostructures》2005,30(1-2):159-163
We have successfully fabricated and characterized room temperature continuous wave (cw) GaInAsSb/AlGaAsSb distributed feedback lasers emitting in the wavelength region between 2.499 and 2.573 μm. To the best of our knowledge, this is the longest emission wavelength realized with a GaSb-based DFB laser diode. The laser structure used for DFB processing was grown by solid source molecular beam epitaxy. A DFB concept requiring no subsequent overgrowth step was used by defining first-order Cr-Bragg gratings laterally patterned to a ridge waveguide. Threshold currents smaller than 60 mA and room temperature cw output powers up to 6.5 mW were obtained. The laser diodes show single mode emission with side mode suppression ratios (SMSR) of up to 32 dB. 相似文献
85.
We consider the isothermal flow through a cylindrical flat chamber, a model of some particular heat exchanger, for which LDV measurements and a numerical simulation have been performed. Experimental results show the establishment of an important vortex zone, the secondary flow extending all along the chamber radius. This observation leads to an expected significant increase of the fluid mixing. Results issued from the numerical simulation appear to be in close agreement with experimental data. Nevertheless, the k–ε model used here must be improved to obtain a better approach near the vortex centre. To cite this article: S. Petitot et al., C. R. Mecanique 330 (2002) 593–599. 相似文献
86.
运输网络中最小饱和流的求解 总被引:4,自引:0,他引:4
运输网络中常常由于流量的不可控易发生堵塞现象.网络发生堵塞时的饱和流值达不到最大流值.最小饱和流是运输网络,尤其是紧急疏散网络设计中很重要的一个参数.通过建立网络的割集矩阵来确定网络的堵塞截面,基于此提出了求解最小饱和流的线性规划模型及算法.举例分析表明,利用该算法计算网络最小饱和流更加简便、更加实用. 相似文献
87.
88.
A model for the flow of a fluid through a channel with parallel plates is investigated. The channel is narrow, so that the lubrication approximation may be applied. The channel walls are maintained at a constant temperature. Shear heating effects are included and the fluid viscosity decreases exponentially with temperature. When the flow is driven solely by shear stress or imposed velocity at the top, analytical progress is possible. When pressure gradient also drives the flow the problem is solved numerically. 相似文献
89.
90.
In this note, we study convergence rates in the law of large numbers for independent and identically distributed random variables under sublinear expectations. We obtain a strong L^p-convergence version and a strongly quasi sure convergence version of the law of large numbers. 相似文献