全文获取类型
收费全文 | 45882篇 |
免费 | 2470篇 |
国内免费 | 3134篇 |
专业分类
化学 | 24068篇 |
晶体学 | 538篇 |
力学 | 2103篇 |
综合类 | 276篇 |
数学 | 10844篇 |
物理学 | 13657篇 |
出版年
2023年 | 160篇 |
2022年 | 269篇 |
2021年 | 433篇 |
2020年 | 492篇 |
2019年 | 548篇 |
2018年 | 1625篇 |
2017年 | 1831篇 |
2016年 | 1383篇 |
2015年 | 1286篇 |
2014年 | 1352篇 |
2013年 | 1904篇 |
2012年 | 4530篇 |
2011年 | 3771篇 |
2010年 | 2933篇 |
2009年 | 2637篇 |
2008年 | 1902篇 |
2007年 | 1841篇 |
2006年 | 1724篇 |
2005年 | 5352篇 |
2004年 | 4784篇 |
2003年 | 3090篇 |
2002年 | 1387篇 |
2001年 | 1015篇 |
2000年 | 651篇 |
1999年 | 606篇 |
1998年 | 382篇 |
1997年 | 349篇 |
1996年 | 275篇 |
1995年 | 246篇 |
1994年 | 224篇 |
1993年 | 192篇 |
1992年 | 326篇 |
1991年 | 262篇 |
1990年 | 234篇 |
1989年 | 191篇 |
1988年 | 146篇 |
1987年 | 108篇 |
1986年 | 81篇 |
1985年 | 72篇 |
1984年 | 54篇 |
1983年 | 42篇 |
1976年 | 87篇 |
1975年 | 42篇 |
1974年 | 45篇 |
1973年 | 55篇 |
1972年 | 41篇 |
1970年 | 36篇 |
1969年 | 37篇 |
1968年 | 37篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Daniel Pa?ca 《Journal of Mathematical Analysis and Applications》2007,325(1):90-100
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian. 相似文献
92.
93.
The decay process J/ψ→p X X→p P,where p,p and P are the proton,antiproton and pseudoscalar states,respectively,has been studied in terms of the angular distribution and the generalized moment analysis methods.The result shows that we can identify the spin,but cannot determine the parity of the baryon resonance state X produced in the process J/ψ→p X X→p P. 相似文献
94.
新型X射线靶设计为:由SiO2和TiO2组成具有12个周期的一维光子晶体,在它的中间嵌入光靶材料层作为缺陷层,SiO2,TiO2和光靶层的光学厚度分别为λ4、λ4和λ2,λ为抽运激光波长.与普通平板光靶相比,当抽运光垂直照射到这种光靶时,靶层内部的光强将提高2个数量级,所以抽运激光的阈值强度将降低2个数量级,这有利于X射线激光的小型化.在同样的抽运激光照射下,X射线激光的强度将提高4个数量级,转换效率也将提高约4个数量级.由于平均电离度随抽运激光强度的提高而提高,所以采用这种光靶有利于使X射线激光向短波长推进.
关键词:
X射线激光
光子晶体
光波局域 相似文献
95.
96.
Goran Pavi? 《Applied Acoustics》2006,67(9):864-881
A method is formulated for the identification of an unknown physical parameter of a fluid-filled pipe using the measurement of sound speed in the pipe. The method uses a simple formula which provides the relationship between the sound speed and a few physical parameters of the pipe: thickness, diameter, wall material constants and fluid constants. Once the sound speed in the pipe is measured, the simple formula can be used to extract one of the unknown parameters providing the remaining ones are known.The sound speed in the pipe is measured using a 3-transducer array. In order to demonstrate the potential of the technique the results of several measurements obtained in a water-filled steel pipe are presented.The required accuracy of the measurement of sound speed and of the specification of known parameters is analysed. The accuracy depends on the unknown parameter which is to be identified. For example, if the pipe thickness is the unknown parameter, the other parameters have to be known within a very narrow margin of error. On the contrary, if the fluid properties have to be identified the needed accuracy of known parameters gets much lower. 相似文献
97.
ICP-AES测定饮用水源中的Cu、Mn、Pb、Cd、Zn 总被引:7,自引:2,他引:5
用ICP-AES法同时测定饮用水源中的Cu、Mn、Pb、Cd、Zn等重金属元素,具有基体效应小、测量范围宽等优点。检出限为0.2-4.0μg/L,回收率为91.5%-103.9%,相对标准偏差为0.29%-1.5%,测定密码样与实际样品,结果令人满意。 相似文献
98.
A tree T is arbitrarily vertex decomposable if for any sequence τ of positive integers adding up to the order of T there is a sequence of vertex-disjoint subtrees of T whose orders are given by τ. An on-line version of the problem of characterizing arbitrarily vertex decomposable trees is completely solved here. 相似文献
99.
Yah ZHAO Xiao Qing LIU Hong You ZHU Zi Ming YANG Rong HUANG 《中国化学快报》2006,17(12):1543-1546
Bridged bis(β-cyclodextrin)s (CDs), as a very important family of CD derivatives, have been known that they can significantly alter the molecular binding ability and selectivity toward a variety of guests in comparison with parent cyclodextrin. Their two… 相似文献
100.
Improved sample wettability was obtained by oxygen plasma functionalization of pyrolytic graphite. The samples were exposed to highly dissociated oxygen plasma with the density of 1 × 1016 m−3, the electron temperature of about 5.5 eV and the density of neutral oxygen atoms of 8 × 1021 m−3 for 20 s. The surface wettability was measured by a contact angle of water drop. The contact angle dropped from original 112° down to about 1°. The functional groups were detected by XPS analyses. The survey spectrum showed a substantial increase of oxygen concentration on the surface, while high-resolution analyses showed additional oxygen was bonded onto the graphite surface in the form of C-O polar functional group responsible for the increase of the surface energy. 相似文献