全文获取类型
收费全文 | 23135篇 |
免费 | 3415篇 |
国内免费 | 2564篇 |
专业分类
化学 | 16707篇 |
晶体学 | 272篇 |
力学 | 1499篇 |
综合类 | 160篇 |
数学 | 2874篇 |
物理学 | 7602篇 |
出版年
2024年 | 75篇 |
2023年 | 481篇 |
2022年 | 766篇 |
2021年 | 871篇 |
2020年 | 976篇 |
2019年 | 875篇 |
2018年 | 727篇 |
2017年 | 684篇 |
2016年 | 1112篇 |
2015年 | 1066篇 |
2014年 | 1179篇 |
2013年 | 1677篇 |
2012年 | 1962篇 |
2011年 | 1915篇 |
2010年 | 1369篇 |
2009年 | 1301篇 |
2008年 | 1488篇 |
2007年 | 1269篇 |
2006年 | 1169篇 |
2005年 | 1108篇 |
2004年 | 864篇 |
2003年 | 740篇 |
2002年 | 782篇 |
2001年 | 657篇 |
2000年 | 528篇 |
1999年 | 538篇 |
1998年 | 378篇 |
1997年 | 325篇 |
1996年 | 373篇 |
1995年 | 303篇 |
1994年 | 263篇 |
1993年 | 216篇 |
1992年 | 171篇 |
1991年 | 156篇 |
1990年 | 134篇 |
1989年 | 94篇 |
1988年 | 98篇 |
1987年 | 66篇 |
1986年 | 68篇 |
1985年 | 62篇 |
1984年 | 46篇 |
1983年 | 31篇 |
1982年 | 25篇 |
1981年 | 29篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1971年 | 7篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
12.
Longitudinal study has become one of the most commonly adopted designs in medical research. The generalized estimating equations (GEE) method and/or mixed effects models are employed very often in causal inferences. The related model diagnostic procedures are not yet fully formalized, and perhaps never will be. The potential causes of major problems are the high variety of the dependence within subjects and/or the number of repeated measurements. A single testing procedure, e.g., run test, is not possible to resolve all model diagnostics problems in longitudinal data analysis. Multiple quantitative indexes for model diagnostics are needed to take into account this variety. We propose eight testing procedures for randomness accompanied with some conventional and/or non-conventional plots to remedy model diagnostics in longitudinal data analysis. The proposed issue in this paper is well illustrated with four clinical studies in Taiwan. 相似文献
13.
Zhong‐Zhen Yu Mingshu Yang Qingxin Zhang Chungui Zhao Yiu‐Wing Mai 《Journal of Polymer Science.Polymer Physics》2003,41(11):1234-1243
Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with an alkyl ammonium surfactant pretreated montmorillonite (MMT). The thermal stability of the organic MMT powders was measured by thermogravimetric analysis. The decomposition of the surfactant on the MMT occurred from 200 to 500 °C. The low onset decomposition temperature of the organic MMT is one shortcoming when it is used to prepare polymer nanocomposites at high melt‐compounding temperatures. To provide greater property enhancement and better thermal stability of the polymer/MMT nanocomposites, it is necessary to develop MMT modified with more thermally stable surfactants. The dispersion and spatial distribution of the organic MMT layers in the nylon‐66 matrix were characterized by X‐ray diffraction. The organic MMT layers were exfoliated but not randomly dispersed in the nylon‐66 matrix. A model was proposed to describe the spatial distribution of the organic MMT layers in an injection‐molded rectangular bar of nylon‐66/organic MMT nanocomposites. Most organic MMT layers were oriented in the injection‐molding direction. Layers near the four surfaces of the bar were parallel to their corresponding surfaces; whereas those in the bulk differed from the near‐surface layers and rotated themselves about the injection‐molding direction. The influence of the spatial distribution of the organic MMT on crystallization of nylon‐66 was also investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1234–1243, 2003 相似文献
14.
We establish a self-improving property of the Hardy inequality and an estimate on the size of the boundary of a domain supporting a Hardy inequality.
15.
本文中对一个斜群环为Dubrovin赋值环给出了一系列等价刻画,并且刻画了一个Dubrovin赋值斜群环的所有素理想. 相似文献
16.
Yu-hai WU~ 《中国科学A辑(英文版)》2007,50(7):925-940
This paper concerns the number and distributions of limit cycles in a Z_2-equivariant quintic planar vector field.25 limit cycles are found in this special planar polynomial system and four different configurations of these limit cycles are also given by using the methods of the bifurcation theory and the qualitative analysis of the differential equation.It can be concluded that H(5)≥25=5~2, where H(5)is the Hilbert number for quintic polynomial systems.The results obtained are useful to study the weakened 16th Hilbert problem. 相似文献
17.
18.
A combined programming and iteration algorithm for finite element analysis of three-dimensional contact problems 总被引:3,自引:0,他引:3
Comparing with two-dimensional contact problems, three-dimensional frictional contact problems are more difficult to deal
with, because of the unknown slip direction of the tangential force and enormous computing time. In order to overcome these
difficulties, a combined PQP (Parametric Quadratic Programming) and iteration method is derived in this paper. The iteration
algorithm, which alleviates the difficulty of unknown slip direction, is used along with the PQP method to cut down computing
costs. Numerical example is given to demonstrate the validity of the present algorithm.
The project supported by the Machinary and Electronics Ministry of China 相似文献
19.
Deguang Han 《应用数学学报(英文版)》1994,10(2):213-219
In this paper we will prove some theorems on theM-ideals of compact operators and the best approximation of quasitriangular operator algebras. These results improve and extend the known results in [4, 5, 7].This work is supported in part by the National Natural Science Foundation of China. 相似文献
20.
壳模型计算表明,1/2+[411]出现于157Tm核的基态可能是由非轴对称形变造成的.但是新近从157Yb衰变纲图给出的157Tm低激发谱中,指认了一个建立在1/2+[411]带头上的基态转动带,并认为该带的性质是轴对称的,提取了该带的惯性参数与脱耦合参数.通过对奇ATm核1/2+[411]转动带的系统分析,强调了在157Tm核中非轴对称γ自由度效应的重要性. 相似文献