全文获取类型
收费全文 | 58426篇 |
免费 | 2953篇 |
国内免费 | 778篇 |
专业分类
化学 | 37016篇 |
晶体学 | 376篇 |
力学 | 1221篇 |
综合类 | 50篇 |
数学 | 10162篇 |
物理学 | 13332篇 |
出版年
2023年 | 526篇 |
2022年 | 636篇 |
2021年 | 828篇 |
2020年 | 1067篇 |
2019年 | 1015篇 |
2018年 | 1234篇 |
2017年 | 1133篇 |
2016年 | 2200篇 |
2015年 | 1843篇 |
2014年 | 1930篇 |
2013年 | 3857篇 |
2012年 | 3882篇 |
2011年 | 3744篇 |
2010年 | 2443篇 |
2009年 | 2178篇 |
2008年 | 3145篇 |
2007年 | 2921篇 |
2006年 | 2593篇 |
2005年 | 2591篇 |
2004年 | 2145篇 |
2003年 | 1726篇 |
2002年 | 1557篇 |
2001年 | 1201篇 |
2000年 | 1209篇 |
1999年 | 870篇 |
1998年 | 694篇 |
1997年 | 586篇 |
1996年 | 714篇 |
1995年 | 582篇 |
1994年 | 634篇 |
1993年 | 552篇 |
1992年 | 576篇 |
1991年 | 477篇 |
1990年 | 527篇 |
1989年 | 407篇 |
1988年 | 425篇 |
1987年 | 378篇 |
1986年 | 363篇 |
1985年 | 485篇 |
1984年 | 452篇 |
1983年 | 349篇 |
1982年 | 359篇 |
1981年 | 365篇 |
1980年 | 290篇 |
1979年 | 286篇 |
1978年 | 284篇 |
1977年 | 274篇 |
1976年 | 283篇 |
1974年 | 259篇 |
1973年 | 269篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
111.
The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004 相似文献
112.
Sándor G?r?g 《Analytical sciences》2004,20(5):767-782
The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis. 相似文献
113.
Su Nee Tan Daniel Fornasiero Rossen Sedev John Ralston 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):307-315
The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol−1). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability. 相似文献
114.
借助电子动量谱学结合量子化学理论和其他方法可以给出轨道电子在整个空间的分布信息,由此给出电子运动的完备描述[1,2 ] .清华大学电子动量谱学实验室近几年已成功地对甲烷[3] 、异丁烷[4 ] 、环戊烷[5] 、二乙酰等[6 ] 分子的轨道电子动量分布进行了测量.我们利用第二代电子动量谱仪首次对CH2 F2 分子3a1和2b2 轨道的电子动量谱进行测量,并与理论计算结果作了比较.同时还计算了坐标空间和动量空间中电子在x - y平面的密度分布.电子动量谱学最基本的过程是(e ,2e)反应,即电子与靶粒子碰撞而发生的电离过程.而对于(e ,2e)反应,含有大量信… 相似文献
115.
116.
117.
The exponential functional of simple, symmetric random walks with negative
drift is an infinite polynomial Y = 1 + ξ1 + ξ1ξ2 + ξ1ξ2ξ3 + ⋯ of independent
and identically distributed non-negative random variables. It has moments that are
rational functions of the variables μ
k
= E(ξ
k
) < 1 with universal coefficients. It
turns out that such a coefficient is equal to the number of permutations with descent
set defined by the multiindex of the coefficient. A recursion enumerates all numbers
of permutations with given descent sets in the form of a Pascal-type triangle.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
118.
Periodica Mathematica Hungarica - In our paper we study the usage of partially defined Boolean functions (PDBFs) for generating cryptographically strong Boolean functions. A PDBF can be considered... 相似文献
119.
A note on a generalized Douglas space 总被引:1,自引:0,他引:1
Periodica Mathematica Hungarica - 相似文献
120.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献