全文获取类型
收费全文 | 20738篇 |
免费 | 3743篇 |
国内免费 | 2984篇 |
专业分类
化学 | 14994篇 |
晶体学 | 364篇 |
力学 | 1138篇 |
综合类 | 198篇 |
数学 | 1894篇 |
物理学 | 8877篇 |
出版年
2024年 | 79篇 |
2023年 | 452篇 |
2022年 | 776篇 |
2021年 | 875篇 |
2020年 | 961篇 |
2019年 | 930篇 |
2018年 | 801篇 |
2017年 | 788篇 |
2016年 | 1075篇 |
2015年 | 1139篇 |
2014年 | 1389篇 |
2013年 | 1782篇 |
2012年 | 1975篇 |
2011年 | 2020篇 |
2010年 | 1431篇 |
2009年 | 1340篇 |
2008年 | 1490篇 |
2007年 | 1208篇 |
2006年 | 1089篇 |
2005年 | 890篇 |
2004年 | 731篇 |
2003年 | 526篇 |
2002年 | 491篇 |
2001年 | 393篇 |
2000年 | 356篇 |
1999年 | 348篇 |
1998年 | 251篇 |
1997年 | 214篇 |
1996年 | 263篇 |
1995年 | 177篇 |
1994年 | 185篇 |
1993年 | 173篇 |
1992年 | 150篇 |
1991年 | 133篇 |
1990年 | 91篇 |
1989年 | 106篇 |
1988年 | 70篇 |
1987年 | 60篇 |
1986年 | 65篇 |
1985年 | 52篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1970年 | 3篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
计算全息图产生的锥面波在激光准直中的应用 总被引:1,自引:0,他引:1
本文提出了用计算全息图产生锥面波的方法.将全息图置于激光光路中,它的衍射图样中心在空间形成了一条准直线.文中对锥面波的传播、准直精度及准直距离作了理论分析,给出了实验结果. 相似文献
32.
33.
Gu Chaohao 《数学年刊B辑(英文版)》1994,15(4):385-400
COMPLETEEXTREMALSURFACESOFMIXEDTYPEIN3-DIMENSIONALMINKOWSKISPACE¥GUCHAOHAO(InstituteofMathematics,FudanUniversity,Shanghai200... 相似文献
34.
35.
YBa2Cu3O7-δ and Tl2Ba2CaCu2O8 thin films for microwave filters were synthesized by pulsed laser deposition and the two-step thalliation process. Substrate
quality requirements and the relation of thin film morphology, microstructure with microwave surface resistance were discussed. 相似文献
36.
37.
Super-Wavelets and Decomposable Wavelet Frames 总被引:4,自引:0,他引:4
A wavelet frame is called decomposable whenever it is equivalent to a superwavelet frame of length greater than one. Decomposable
wavelet frames are closely related to some problems on super-wavelets. In this article we first obtain some necessary or sufficient
conditions for decomposable Parseval wavelet frames. As an application of these conditions, we prove that for each n > 1 there
exists a Parseval wavelet frame which is m-decomposable for any 1 < m ≤ n, but not k-decomposable for any k > n. Moreover,
there exists a super-wavelet whose components are non-decomposable. Similarly we also prove that for each n > 1, there exists
a Parseval wavelet frame that can be extended to a super-wavelet of length m for any 1 < m ≤ n, but can not be extended to
any super-wavelet of length k with k > n. The connection between decomposable Parseval wavelet frames and super-wavelets is
investigated, and some necessary or sufficient conditions for extendable Parseval wavelet frames are given. 相似文献
38.
ZhengBin Zhang Chunying Liu Peifeng Li Zhenzhen Wu Cai Lin Huawei Huang Lei Xing Liansheng Liu 《Frontiers of Chemistry in China》2006,1(1):86-97
Many food algae and red tide algae were cultivated in the f/2 medium, and the nitric oxide (NO) concentration of the medium
and the cell density were determined. The experiments on algae were conducted when different concentrations of NO were added
into the medium using two methods. The results show that low concentrations of NO were self-produced by marine algae during
the exponential growth period and were about nmol/L level. But at the end of the period, i.e., 2 or 3 days before the cell
density reaches the maximum, an NO peak appeared, with the NO concentration reaching 10 nmol/L. The NO threshold concentration
exists according to the influence of exogenous NO on the marine phytoplankton growth. One type is the threshold concentration
that can promote algae growth, and its value is between 10 and 1 nmol level, or even lower. The other type can inhibit the
phytoplankton growth, which is about μmol level or higher. The results indicate that red tide algae are far more sensitive
to NO than are food algae. The fundamental experimental outcome above may provide a new clue for red tide chemical forecast
by inspecting the NO change. 相似文献
39.
R. Silvennoinen K. -E. Peiponen T. Asakura Yan-Fang Zhang Cong Gu K. Ikonen E. J. Morley 《Optics and Lasers in Engineering》1992,17(2)
The specular reflectance of cold-rolled aluminum surface is studied using a fiber optic system. An approximation for the determination of surface roughness is presented. 相似文献
40.
In this article, the linear and nonlinear shear rheological behaviors of polylactide (PLA)/clay (organophilic‐montmorillonite) nanocomposites (PLACNs) were investigated by an Advanced Rheology Expanded System rheometer. The nanocomposites were prepared by master batch method using a twin‐screw extruder with poly(ε‐caprolactone) (PCL) as a compatibilizer. The presence of org‐MMT leads to obvious pseudo‐solid‐like behaviors of nanocomposite melts. The behaviors caused by the formation of a “percolating network” derived from the reciprocity among the strong related sheet particles. Therefore, the storage moduli, loss moduli, and dynamic viscosities of PLACNs show a monotonic increase with MMT content. Nonterminal behaviors exists in PLACNs nanocomposites. Besides the PLACNs melts show a greater shear thinning tendency than pure PLA melt because of the preferential orientation of the MMT layers. Therefore, PLACNs have higher moduli but better processibility compared with pure PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3189–3196, 2007 相似文献