全文获取类型
收费全文 | 21941篇 |
免费 | 3578篇 |
国内免费 | 2632篇 |
专业分类
化学 | 16145篇 |
晶体学 | 252篇 |
力学 | 1573篇 |
综合类 | 201篇 |
数学 | 2549篇 |
物理学 | 7431篇 |
出版年
2024年 | 50篇 |
2023年 | 417篇 |
2022年 | 608篇 |
2021年 | 732篇 |
2020年 | 874篇 |
2019年 | 859篇 |
2018年 | 692篇 |
2017年 | 722篇 |
2016年 | 984篇 |
2015年 | 1002篇 |
2014年 | 1244篇 |
2013年 | 1515篇 |
2012年 | 1972篇 |
2011年 | 2024篇 |
2010年 | 1387篇 |
2009年 | 1264篇 |
2008年 | 1386篇 |
2007年 | 1226篇 |
2006年 | 1199篇 |
2005年 | 997篇 |
2004年 | 790篇 |
2003年 | 700篇 |
2002年 | 702篇 |
2001年 | 623篇 |
2000年 | 447篇 |
1999年 | 469篇 |
1998年 | 375篇 |
1997年 | 328篇 |
1996年 | 378篇 |
1995年 | 281篇 |
1994年 | 263篇 |
1993年 | 193篇 |
1992年 | 191篇 |
1991年 | 197篇 |
1990年 | 145篇 |
1989年 | 135篇 |
1988年 | 96篇 |
1987年 | 78篇 |
1986年 | 92篇 |
1985年 | 66篇 |
1984年 | 56篇 |
1983年 | 48篇 |
1982年 | 40篇 |
1981年 | 33篇 |
1980年 | 32篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1974年 | 20篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
171.
Unsteady mass transfer in a steady flow field of a laminar forced flow against a rotating disk is analyzed by using a very effective solution method. Rigorous numerical solutions have been obtained for steady and unsteady mass transfer for any relative flow strength of external flow and rotation-induced flow for 0.1 ≤Sc ≤ 10000. Simple but very accurate correlation equations of Sherwood number for both the steady and unsteady mass transfer are proposed. 相似文献
172.
This paper is concerned with a class of nonlinear delay partial difference equations with variable coefficients, which may
change sign. By making use of frequency measures, some new oscillatory criteria are established. This is the first time oscillation
of these partial difference equations is discussed by employing frequency measures.
相似文献
173.
Two series of size‐fractionated combusted residues, a bag‐house ash and a scrubber residue, from a municipal solid waste incinerator (MSWI) were prepared and extracted by means of sequential chemical extraction (SCE) procedures proposed by Tessier. Concentrations of water‐soluble phase, exchangeable phase, carbonated phase, Fe/Mn oxide phase, organic matter phase, and residual phase bound amphoteric metals (Pb and Zn) were obtained, and have been compared with those of single batch extraction of toxic characteristic leaching procedure (TCLP). In each size fraction of baghouse ash or scrubber residue, lead or zinc shows a common phenomena that the TCLP value is always lower than the content of the water‐soluble fraction. For lead, baghouse ash has a significant size‐dependent distribution on the water‐soluble phase to perform a size‐dependent test of lead in the TCLP test. The zinc TCLP data having less size dependence might be due to that neither the baghouse ash nor the scrubber residue has a size‐dependent distribution on the water‐soluble zinc phase. 相似文献
174.
This paper tries to introduce the reader to the method of using photochemical re-action to copy holographic optical elements(HOEs)in relief.The holographic blazing gratingso copied is groove depth adjustable phase modulability enlarged through copying and 3.3times the diffraction efficiency(DE)of the original grating.It is expected that the newmethod will lead to the mass production of the light-weight HOEs at low cost. 相似文献
175.
Frame Wavelets with Compact Supports for L^2(R^n) 总被引:1,自引:0,他引:1
De Yun YANG King Wei ZHOU Zhu Zhi YUAN 《数学学报(英文版)》2007,23(2):349-356
The construction of frame wavelets with compact supports is a meaningful problem in wavelet analysis. In particular, it is a hard work to construct the frame wavelets with explicit analytic forms. For a given n × n real expansive matrix A, the frame-sets with respect to A are a family of sets in R^n. Based on the frame-sets, a class of high-dimensional frame wavelets with analytic forms are constructed, which can be non-bandlimited, or even compactly supported. As an application, the construction is illustrated by several examples, in which some new frame wavelets with compact supports are constructed. Moreover, since the main result of this paper is about general dilation matrices, in the examples we present a family of frame wavelets associated with some non-integer dilation matrices that is meaningful in computational geometry. 相似文献
176.
Stephen Z. D. Cheng 《Journal of Thermal Analysis and Calorimetry》1997,50(5-6):907-910
177.
178.
179.
180.
田兴 《新疆大学学报(理工版)》1991,8(1):53-55
本文分析计算了荧光光纤温度传感器的温敏元件——GsAlAs/GaAs双异质结半导体材料的荧光辐射效率与激励光波长的关系。讨论了温度测量范围及温敏元件GaAlAs层铝含量对激励光源的限制,在0~200℃测温范围内,若采用LED作激励光源,其峰值波长应在0.70~0.76μm之间选择。 相似文献