全文获取类型
收费全文 | 15434篇 |
免费 | 2771篇 |
国内免费 | 2236篇 |
专业分类
化学 | 11350篇 |
晶体学 | 172篇 |
力学 | 882篇 |
综合类 | 150篇 |
数学 | 1907篇 |
物理学 | 5980篇 |
出版年
2024年 | 39篇 |
2023年 | 318篇 |
2022年 | 566篇 |
2021年 | 602篇 |
2020年 | 646篇 |
2019年 | 718篇 |
2018年 | 559篇 |
2017年 | 535篇 |
2016年 | 772篇 |
2015年 | 817篇 |
2014年 | 970篇 |
2013年 | 1190篇 |
2012年 | 1414篇 |
2011年 | 1416篇 |
2010年 | 996篇 |
2009年 | 1023篇 |
2008年 | 1041篇 |
2007年 | 882篇 |
2006年 | 818篇 |
2005年 | 666篇 |
2004年 | 564篇 |
2003年 | 448篇 |
2002年 | 515篇 |
2001年 | 390篇 |
2000年 | 321篇 |
1999年 | 333篇 |
1998年 | 261篇 |
1997年 | 228篇 |
1996年 | 209篇 |
1995年 | 179篇 |
1994年 | 150篇 |
1993年 | 157篇 |
1992年 | 103篇 |
1991年 | 101篇 |
1990年 | 84篇 |
1989年 | 81篇 |
1988年 | 71篇 |
1987年 | 41篇 |
1986年 | 40篇 |
1985年 | 49篇 |
1984年 | 28篇 |
1983年 | 18篇 |
1982年 | 24篇 |
1981年 | 11篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
An analytical method involving anion exchange high performance liquid chromatographic determination of vitellogenin (Vtg) in fish plasma after postcolumn fluorescence derivatization with o-phthalaldehyde (OPA) was developed. The retention time of Vtg was about 11 min. The reagent variables for derivatization were optimized. The fluorophore was excited at 335 nm and detected at 435 nm. A calibration curve was established ranging from 0.13 to 11.28 microg. The determination limit of Vtg was found to be as low as 0.13 microg. The spiked recovery was 93.6% and interassay variability was less than 4%. The method developed was used to determine Vtg in fish plasma obtained from red sea bream (Pagrosomus major), black porgy (Sparus macrocephalus) and skew band grunt (Hapalogenys nitens), without complicated sample pretreatment. The results confirmed that the method showed advantages of being simple, rapid, reproducible and sensitive. 相似文献
112.
Yi-rang Yuan 《应用数学学报(英文版)》2007,23(2):255-268
For a coupled system of multiplayer dynamics of fluids in porous media,the characteristic finiteelement domain decomposition procedures applicable to parallel arithmetic are put forward.Techniques suchas calculus of variations,domain decomposition,characteristic method,negative norm estimate,energy methodand the theory of prior estimates are adopted.Optimal order estimates in L~2 norm are derived for the error inthe approximate solution. 相似文献
113.
Model and empirical study on some collaboration networks 总被引:8,自引:0,他引:8
Pei-Pei Zhang Kan Chen Yue He Tao Zhou Bei-Bei Su Yingdi Jin Hui Chang Yue-Ping Zhou Li-Cheng Sun Bing-Hong Wang Da-Ren He 《Physica A》2006,360(2):599-616
In this paper we present an empirical study of a few practical systems described by cooperation networks, and propose a model to understand the results obtained. We study four non-social systems, which are the Bus Route Networks of Beijing and Yangzhou, the Travel Route Network of China, Huai-Yang recipes of Chinese cooked food, and a social system, which is the Collaboration Network of Hollywood Actors. In order to explain the results related to the degree distribution, act-degree distribution and act-size distribution (especially about the degree distribution, which may be better fitted using a stretched exponential distribution (SED)), we suggest a simple model to show a possible evolutionary mechanism for the emergence of such networks. The analytic and numerical results obtained from the model are in good agreement with the empirical results. 相似文献
114.
Data in social and behavioral sciences are often hierarchically organized. Multilevel statistical methodology was developed to analyze such data. Most of the procedures for analyzing multilevel data are derived from maximum likelihood based on the normal distribution assumption. Standard errors for parameter estimates in these procedures are obtained from the corresponding information matrix. Because practical data typically contain heterogeneous marginal skewnesses and kurtoses, this paper studies how nonnormally distributed data affect the standard errors of parameter estimates in a two-level structural equation model. Specifically, we study how skewness and kurtosis in one level affect standard errors of parameter estimates within its level and outside its level. We also show that, parallel to asymptotic robustness theory in conventional factor analysis, conditions exist for asymptotic robustness of standard errors in a multilevel factor analysis model. 相似文献
115.
116.
117.
118.
119.
3520ICP发射光谱仪维修二例房毅卓,原力(中国科学院青海盐湖研究所西宁810008)3520型电感耦合等离子顺序扫描发射光谱仪,是由瑞士应用研究实验室(ARL)生产的高速自动分析装置,主要应用于冶金、地质、石油、卫生和科研等部门的元素分析。以下介... 相似文献
120.
根据ΔAp=KΔ(bc)p原理,采用“等滴光度法”测定钼铁中的钼,通过试验确定了最佳测定条件。该方法简便、快速,用于钼铁标准样品中钼的测定,测定结果的精密度为0.196%,与标准值之间的相对误差为0.064%(n=4)。 相似文献