全文获取类型
收费全文 | 34177篇 |
免费 | 3435篇 |
国内免费 | 4010篇 |
专业分类
化学 | 25988篇 |
晶体学 | 432篇 |
力学 | 1849篇 |
综合类 | 290篇 |
数学 | 5626篇 |
物理学 | 7437篇 |
出版年
2024年 | 46篇 |
2023年 | 375篇 |
2022年 | 774篇 |
2021年 | 969篇 |
2020年 | 1144篇 |
2019年 | 1099篇 |
2018年 | 958篇 |
2017年 | 1235篇 |
2016年 | 1352篇 |
2015年 | 1197篇 |
2014年 | 1608篇 |
2013年 | 2468篇 |
2012年 | 1875篇 |
2011年 | 2138篇 |
2010年 | 1772篇 |
2009年 | 2240篇 |
2008年 | 2069篇 |
2007年 | 2049篇 |
2006年 | 1846篇 |
2005年 | 1709篇 |
2004年 | 1713篇 |
2003年 | 1316篇 |
2002年 | 1613篇 |
2001年 | 1002篇 |
2000年 | 828篇 |
1999年 | 698篇 |
1998年 | 615篇 |
1997年 | 529篇 |
1996年 | 579篇 |
1995年 | 535篇 |
1994年 | 487篇 |
1993年 | 348篇 |
1992年 | 354篇 |
1991年 | 218篇 |
1990年 | 192篇 |
1989年 | 176篇 |
1988年 | 175篇 |
1987年 | 148篇 |
1986年 | 105篇 |
1985年 | 121篇 |
1984年 | 91篇 |
1983年 | 41篇 |
1982年 | 89篇 |
1981年 | 112篇 |
1980年 | 123篇 |
1979年 | 132篇 |
1978年 | 98篇 |
1977年 | 73篇 |
1976年 | 68篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
51.
52.
采用甚高频等离子体增强化学气相沉积技术制备了系列微晶硅薄膜太阳电池,指出了气体总流量和背反射电极的类型对电池性能参数的影响.电池的I-V测试结果表明:随反应气体总流量的增加,对应电池的短路电流密度、开路电压和填充因子都有很大程度的提高,结果使得电池的光电转换效率得以提高.另外,ZnO/Ag/Al背反射电极能明显提高电池的短路电流密度,进而也提高了电池的光电转换效率.对气体总流量和背反射电极类型影响电池效率的原因进行了分析.
关键词:
微晶硅薄膜太阳电池
气体流量
ZnO/Ag/Al背反射电极 相似文献
53.
基于校园网的实验管理系统的设计 总被引:2,自引:1,他引:1
主要讨论了应用实验室管理系统的必要性,并从用户需求分析、系统总体设计、功能模块的设计等方面对B/S实验室管理系统的开发进行了详细的阐述。 相似文献
54.
All-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity
Fei Wang 《Optics Communications》2006,257(2):334-339
A novel scheme for all-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity is proposed and investigated numerically. The results show, for a 2.5 GHz driving pulse train, it can be generated 5-25 GHz repetition rate pulse trains with low clock amplitude jitter, polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence signal can be realized based on the proposed scheme. 相似文献
55.
An admissible minimax estimator of a bounded scale-parameter in a subclass of the exponential family under scale-invariant squared-error loss 总被引:3,自引:0,他引:3
Mohammad Jafari Jozani Nader Nematollahi Khalil Shafie 《Statistics & probability letters》2002,60(4):437-444
A subclass of the scale-parameter exponential family is considered and for the rth power of the scale parameter, which is lower bounded, an admissible minimax estimator under scale-invariant squared-error loss is presented. Also, an admissible minimax estimator of a lower-bounded parameter in the family of transformed chi-square distributions is given. These estimators are the pointwise limits of a sequence of Bayes estimators. Some examples are given. 相似文献
56.
By using the quasi-Lyapunov function, some sufficient conditions of global exponential stability for impulsive systems are established, which is the basis for the following discussion. Then, by employing Riccati inequality and Hamilton-Jacobi inequality approach, some sufficient conditions of robust exponential stability for uncertain linear/nonlinear impulsive systems are derived, respectively. Finally, some examples are given to illustrate the applications of the theory. 相似文献
57.
Statistical Inference with Fractional Brownian Motion 总被引:3,自引:1,他引:2
Kukush Alexander Mishura Yulia Valkeila Esko 《Statistical Inference for Stochastic Processes》2005,8(1):71-93
We give a test between two complex hypothesis; namely we test whether a fractional Brownian motion (fBm) has a linear trend against a certain non-linear trend. We study some related questions, like goodness-of-fit test and volatility estimation in these models. 相似文献
58.
The usual tool for modelling bond ratings migration is a discrete, time‐homogeneous Markov chain. Such model assumes that all bonds are homogeneous with respect to their movement behaviour among rating categories and that the movement behaviour does not change over time. However, among recognized sources of heterogeneity in ratings migration is age of a bond (time elapsed since issuance). It has been observed that young bonds have a lower propensity to change ratings, and thus to default, than more seasoned bonds. The aim of this paper is to introduce a continuous, time‐non‐homogeneous model for bond ratings migration, which also incorporates a simple form of population heterogeneity. The specific form of heterogeneity postulated by the proposed model appears to be suitable for modelling the effect of age of a bond on its propensity to change ratings. This model, called a mover–stayer model, is an extension of a Markov chain. This paper derives the maximum likelihood estimators for the parameters of a continuous time mover–stayer model based on a sample of independent continuously monitored histories of the process, and develops the likelihood ratio statistic for discriminating between the Markov chain and the mover–stayer model. The methods are illustrated using a sample of rating histories of young corporate issuers. For these issuers the default probabilities predicted by the Markov chain and mover–stayer models are different. In particular for 1–4 years old bonds the mover–stayer model estimates substantially lower default probabilities from rating C than a Markov chain. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
59.
The modification of the number field sieve which Joux and Lercier recently used to compute logarithms in a prime field of a record 120 decimal digits makes use of the notion of a virtual logarithm of a prime ideal in a number ring. We provide necessary and sufficient conditions for their method to succeed and give an explicit formula for the virtual logarithm of an ideal. 相似文献
60.
MATLAB/SIMULINK在电力系统仿真中的应用 总被引:2,自引:0,他引:2
介绍了Matlab/Simulink仿真工具在电力系统仿真中的应用方法. 相似文献