全文获取类型
收费全文 | 15141篇 |
免费 | 2832篇 |
国内免费 | 2384篇 |
专业分类
化学 | 6921篇 |
晶体学 | 272篇 |
力学 | 625篇 |
综合类 | 218篇 |
数学 | 1372篇 |
物理学 | 4070篇 |
无线电 | 6879篇 |
出版年
2024年 | 60篇 |
2023年 | 335篇 |
2022年 | 547篇 |
2021年 | 608篇 |
2020年 | 643篇 |
2019年 | 578篇 |
2018年 | 510篇 |
2017年 | 665篇 |
2016年 | 641篇 |
2015年 | 888篇 |
2014年 | 901篇 |
2013年 | 1180篇 |
2012年 | 1259篇 |
2011年 | 1259篇 |
2010年 | 1117篇 |
2009年 | 1135篇 |
2008年 | 1184篇 |
2007年 | 1185篇 |
2006年 | 1047篇 |
2005年 | 876篇 |
2004年 | 635篇 |
2003年 | 452篇 |
2002年 | 501篇 |
2001年 | 424篇 |
2000年 | 392篇 |
1999年 | 248篇 |
1998年 | 120篇 |
1997年 | 105篇 |
1996年 | 118篇 |
1995年 | 92篇 |
1994年 | 71篇 |
1993年 | 86篇 |
1992年 | 76篇 |
1991年 | 45篇 |
1990年 | 48篇 |
1989年 | 39篇 |
1988年 | 45篇 |
1987年 | 20篇 |
1986年 | 26篇 |
1985年 | 35篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
71.
72.
在制作付里叶计算全息过程中,加入适当的二次位相因子,使此种全息图在相干光照明下就可预定的位置上只再现一个像,省略了过去丙现此种计算全息图必要的付里叶透镜,并且使两个互为共轭像分离,从而拓宽了此种计算全息的应用领域,实验结果与理论分析相符。 相似文献
73.
Statistical computer-aided design for microwave circuits 总被引:4,自引:0,他引:4
A useful methodology for microwave circuit design is presented. A statistical technique known as Design of Experiments is used in conjunction with computer-aided design (CAD) tools to obtain simple mathematical expressions for circuit responses. The response models can then be used to quantify response trade-offs, optimize designs, and minimize circuit variations. The use of this methodology puts the designer's intelligence back into design optimization while making “designing for circuit manufacturability” a more systematic and straightforward process. The method improves the design process, circuit performance, and manufacturability. Two design examples are presented in context to the new design methodology 相似文献
74.
本文讨论了用辉光放电法制备氮化硅薄膜时衬底温度、射频功率和气体流量比对薄膜的电导率、介电常数和击穿强度的影响。通过优化生长条件,制备了优质非晶氮化硅薄膜,其介电常数为7.5、击穿强度为5.5MV/cm、电导率为10-13(Ωcm)-1。 相似文献
75.
76.
研究了平台石墨炉原子吸收测定磷的方法,表明以氯化钯和硝酸钙的混合液作为基体改进剂测定生物样品中的磷效果最好,方法特征量为8×10~(-9)g,工作曲线线性范围为0~0.400吸光度,精密度好,抗干扰能力强,方法简单,利用标准曲线即可测定生物样品中磷。 相似文献
77.
In this paper we apply linear control theory to study the effect of various inventory policies on order and inventory variability, which are key drivers of supply chain performance. In particular, we study a two-echelon supply chain with a stationary demand pattern under the influence of three inventory policies: an inventory-on-hand policy that bases orders on the visible inventory at an installation, an installation-stock policy that bases orders on the inventory position (on-hand plus on-order inventory) at an installation, and an echelon-stock policy that bases orders on the inventory position at that installation and all downstream installations. We prove analytically that the inventory-on-hand policy is unstable in practical settings, confirming analytically what has been observed in experimental settings and in practice. We also prove that the installation-stock and echelon-stock policies are stable and analyze their effect on order and inventory fluctuation. Specifically, we show the general superiority of the echelon-stock in our setting and demonstrate analytically the effect of forecasting parameters on order and inventory fluctuations, confirming the results in other research. 相似文献
78.
我国全固态激光技术研发情况及发展趋势 总被引:2,自引:2,他引:0
1 Significance of All Solid State Laser (DPL)Technology in Field of Laser
Because of the advantages of high conversion efficiency, good beam quality, small size and light weight, DPL becomes the hotspot and priority of development of laser technology. It may be the main body of laser in the future and replace gas laser and liquid laser. It is a great revolution of laser technology. 相似文献
79.
80.
We use the PCP-SAFT equation of state, which is of the Van der Waals type and has a sound physical basis, to predict mixture properties, such as vapor–liquid and liquid–liquid equilibria, as well as excess enthalpies. We use molecular properties, such as dipole moment, quadrupole moment, polarizability and dispersion interaction coefficients, that have been determined quantum mechanically in Part I of this publication and adjust the remaining three pure compound parameters to pure compound data. We finally present a new combination rule for the dispersion energy parameter ? that is based on the quantum mechanically determined data. The predictions based on quantum mechanically determined pure compound properties along with the new combination rule show an improved performance compared to the original PCP-SAFT combination rule. 相似文献