全文获取类型
收费全文 | 10821篇 |
免费 | 1272篇 |
国内免费 | 604篇 |
专业分类
化学 | 2730篇 |
晶体学 | 37篇 |
力学 | 718篇 |
综合类 | 245篇 |
数学 | 5229篇 |
物理学 | 3738篇 |
出版年
2024年 | 22篇 |
2023年 | 165篇 |
2022年 | 421篇 |
2021年 | 419篇 |
2020年 | 286篇 |
2019年 | 258篇 |
2018年 | 208篇 |
2017年 | 349篇 |
2016年 | 398篇 |
2015年 | 334篇 |
2014年 | 588篇 |
2013年 | 883篇 |
2012年 | 644篇 |
2011年 | 633篇 |
2010年 | 598篇 |
2009年 | 734篇 |
2008年 | 717篇 |
2007年 | 729篇 |
2006年 | 542篇 |
2005年 | 407篇 |
2004年 | 377篇 |
2003年 | 353篇 |
2002年 | 337篇 |
2001年 | 244篇 |
2000年 | 247篇 |
1999年 | 199篇 |
1998年 | 201篇 |
1997年 | 176篇 |
1996年 | 197篇 |
1995年 | 123篇 |
1994年 | 153篇 |
1993年 | 124篇 |
1992年 | 86篇 |
1991年 | 58篇 |
1990年 | 62篇 |
1989年 | 40篇 |
1988年 | 35篇 |
1987年 | 25篇 |
1986年 | 47篇 |
1985年 | 49篇 |
1984年 | 41篇 |
1983年 | 12篇 |
1982年 | 47篇 |
1981年 | 25篇 |
1980年 | 22篇 |
1979年 | 29篇 |
1978年 | 16篇 |
1977年 | 16篇 |
1976年 | 8篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
101.
102.
本文讨论了在带有截断情况的线性回归模型中 ,响应变量均值的估计问题 .将经验似然的方法应用到带有截断情况的回归模型中 ,在估计响应变量的均值时构造了调整的经验似然统计量 ,证明了在一定的条件下 ,该统计量渐近服从 χ2 分布 ,给出了均值的置信区间 ,并与正态下得到的结果进行了比较 ,模拟的结果说明了经验似然的优良性 . 相似文献
103.
ρ混合、φ混合、ψ混合线性模型M估计的强相合性 总被引:5,自引:3,他引:2
研究了 ρ混合、φ混合、ψ混合样本线性模型中回归参数M估计的强相合性 ,在条件不变的情况下 ,获得与独立情形一样的M估计是强相合的充分条件 ,推广了文 [1 ]定理 2 . 相似文献
104.
Testing goodness of fit for the distribution of errors in multivariate linear models 总被引:2,自引:0,他引:2
M.D. Jimnez Gamero J. Muoz García R. Pino Mejías 《Journal of multivariate analysis》2005,95(2):301-322
In this paper, to test goodness of fit to any fixed distribution of errors in multivariate linear models, we consider a weighted integral of the squared modulus of the difference between the empirical characteristic function of the residuals and the characteristic function under the null hypothesis. We study the limiting behaviour of this test statistic under the null hypothesis and under alternatives. In the asymptotics, the rank of the design matrix is allowed to grow with the sample size. 相似文献
105.
采用AMI方法研究了10种新型的磺酰脲类除草剂的电子结构,并以原子的Mulliken净电荷和除草剂在不同浓度(100,10mg/L)下对油菜、稗草两种作物的根、茎部位的抑制率为训练样本集。构造并训练得到具有活性预测能力的BP神经网络.结果表明,该BP网络不仅能对训练样本很好拟合。亦能对未知化合物的活性作出很好的预测. 相似文献
106.
The classes ofL
1-matrices,L
2-matrices,L
3-matrices andW-matrices are introduced to study solvability of a linear complementarity problem via solving a linear program. Three sufficient
conditions are presented to guarantee that a linear complementarity problem is solvable via a linear program. The new sufficient
conditions are weaker than the ones introduced by Mangasarian. This fact is also illustrated by an example.
Partially supported by NSFC.
This author is also with College of Business Administration of Human University as a Lotus chair professor. 相似文献
107.
108.
面对多样化的市场需求,企业的销售渠道也变得异常复杂,利用网络图可以简化实际问题,并能形象地描述它。本根据网络知识建立了产品分销模型,探求企业在市场需求固定和随机时的最优收益。最后,章还进行实例验算,并做出相应的结果分析。 相似文献
109.
Kojima T. Inoue E. Tsuchiya M. Ishimaru K. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):737-742
TG, swelling, and viscometric studies are presented for the residues, PTHF/IPDI polymer networks, and the extracts, the linear
polymers and unreacted IPDI, after Soxhlet extraction of PTHF/IPDI reaction products. The products are obtained by reacting
PTHF with 650, 1400, (2×650+1×2900), or 2900 of molecular mass with IPDI at various concentrations in bulk. The results on
the swelling and the viscosity experiments suggest that the PTHF/IPDI reaction products have a usual expectable structure.
All the TG curves are a double stage curve. The initial stage and the last stage seem to reflect decomposition of PTHF chains
and vaporization of the remainder, IPDI, respectively. These are analyzed by a trial-and-error construction, supposing double
event behavior. The values of ratio of mass loss associated with the initial event, W01, to the mass loss associated with the last event, W02, are smaller than the expectable those. This suggests that Event 2 involves vaporization of the decomposition products of
PTHF moieties bonded to IPDI in addition to vaporization of IPDI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
110.
A flow model in combination with a statistical-dynamical turbulence generator and a linearised Euler time-domain model for sound waves were used to simulate the effect of screen-induced turbulence on the noise level in the acoustical shadow of a screen in wind. Instead of simulating a great number of different frozen turbulence realisations, the concept of transient turbulence was successfully tested and applied. This concept is adequate to the time-domain model and reduces the computational demands. Several two-dimensional simulations allowed to isolate the individual effects of wind and screen on the propagation of 500 Hz sound waves over a 4-m high noise barrier. At a distance of 250 m from the source (240 m behind the screen) the sheltering effect of the screen and the refraction effect of the wind are in the order of 6 and 4 dB, respectively. The screen-induced turbulence leads to fluctuations in the noise level with a standard deviation of 1.2 dB and a maximum amplitude of 3 dB. However, the time averaged effect turned out to be in the order of merely 0.2 dB. The effect of the screen-induced turbulence on the average noise level behind the screen is therefore negligible. 相似文献