全文获取类型
收费全文 | 201959篇 |
免费 | 2236篇 |
国内免费 | 501篇 |
专业分类
化学 | 110525篇 |
晶体学 | 3647篇 |
力学 | 7996篇 |
综合类 | 11篇 |
数学 | 19193篇 |
物理学 | 63324篇 |
出版年
2020年 | 1725篇 |
2019年 | 1917篇 |
2018年 | 2236篇 |
2017年 | 2355篇 |
2016年 | 3515篇 |
2015年 | 2190篇 |
2014年 | 3546篇 |
2013年 | 9078篇 |
2012年 | 6504篇 |
2011年 | 8008篇 |
2010年 | 5696篇 |
2009年 | 5654篇 |
2008年 | 7154篇 |
2007年 | 7066篇 |
2006年 | 6693篇 |
2005年 | 6050篇 |
2004年 | 5519篇 |
2003年 | 5099篇 |
2002年 | 4867篇 |
2001年 | 6141篇 |
2000年 | 4622篇 |
1999年 | 3518篇 |
1998年 | 2745篇 |
1997年 | 2702篇 |
1996年 | 2591篇 |
1995年 | 2440篇 |
1994年 | 2330篇 |
1993年 | 2165篇 |
1992年 | 2826篇 |
1991年 | 2730篇 |
1990年 | 2672篇 |
1989年 | 2690篇 |
1988年 | 2713篇 |
1987年 | 2721篇 |
1986年 | 2591篇 |
1985年 | 3303篇 |
1984年 | 3313篇 |
1983年 | 2598篇 |
1982年 | 2709篇 |
1981年 | 2763篇 |
1980年 | 2533篇 |
1979年 | 2875篇 |
1978年 | 2860篇 |
1977年 | 2980篇 |
1976年 | 2816篇 |
1975年 | 2553篇 |
1974年 | 2509篇 |
1973年 | 2465篇 |
1972年 | 1702篇 |
1968年 | 1703篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The surface electromigration (SE) of ultrathin In films on Si(111)4 × 1-In surfaces has been investigated using experimental techniques based on μ-electron beams. On the basis of the finding that the SE velocity enhances as the strength of the electrostatic field (EF) fed through the substrate enhances, it is strongly suggested that the driving force of SE is an EF rather than a DC current fed through the substrate. It is found that a patch of ultrathin In film changes to an In patch of 1 × 1 periodicity during SE which is accompanied by spotty parts (named fine-polygons) at both the cathode and anode sides of the In patch. It is found that the fine-polygons are created at the cathode side and are stationary but grow in size to be eventually incorporated into the In-patch. A few In-islands are found on the cathode side of the In-patch and they show no translation but cycles of appearance, growth, decay, and disappearance during SE, by which mass-transportation is achieved. A plausible microscopic model for the SE is presented based on these findings. 相似文献
993.
The amounts of d-limonene, ethanol and indomethacin (IMC) which were transferred from aqueous gel ointments to the skin were determined in rats. The concentration of IMC in the skin correlated well with the plasma concentration of IMC percutaneously absorbed from the gel ointment. The increase of d-limonene concentration in the gel ointments was directly proportional to the accumulation of ethanol in the skin. The amount of ethanol in the skin was closely associated with the percutaneous absorption of IMC. As a possible mechanism for enhancement action of d-limonene and ethanol, it was considered that, at first, d-limonene penetrates into the skin under coexistence with ethanol and may change the barrier structure of the stratum corneum. The transfer of ethanol to the skin is thereby enhanced under the coexistence of d-limonene in the skin. Thus, the permeation of IMC can be promoted due to its affinity with ethanol. 相似文献
994.
For sequences of rational functions, analytic in some domain, a theorem of Montel's type is proved. As an application, sequences of rational functions of the best L
p
-approximation with an unbounded number of finite poles are considered. 相似文献
995.
The dependence of the formation of a p-n or p-p+ junction in semiconducting TiO2 as a function of various parameters is investigated through a computer model. The effect of the polarizing conditions on
the I–V characteristics is also discussed and related to experimental results.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Sept. 15–22, 1996 相似文献
996.
A data set of 29 experimentally determined Newby shifts in rare-earth nuclei is examined for the reliability of each values.
Using this data set, Newby shifts are obtained which are free from the Coriolis and the particle-particle coupling effects.
These new empirical values help resolve the failure of a recently proposed rule for the sign of the Newby shift in the {5/2[413]p − 5/2[642]n} configuration of160Tb and the {5/2[402]p − 5/2[512]n} configuration of174Lu. Also the Newby shifts are significantly modified in two other cases namely the {1/2[411]p − 1/2[521]n} configuration in168Tm and the {1/2[541]p − 1/2[521]n} configuration in172Lu. Only marginal changes are seen in the rest of the cases in the rare-earth nuclei. 相似文献
997.
Perfluorocarboxylic thioesters RFC(O)SR (RF=CF3(CF2)j, R=CH3(CH2)i, i andj=0–5) were studied for the first time by GLC on packed columns using SE-30, SKTFT-50X, and XE-60 as the stationary phase.
The values of thermodynamics functions of sorption were calculated. The correlations between these functions and the molecular
structures as well as the conditions of analysis were established. The insertion of the S atom into the molecules of derivatives
of perfluorocarboxylic acids causes a decrease in the contribution of the orientation interaction and an increase in the dispersion
interaction of thioesters with the stationary phases compared to esters and amides of perfluorocarboxylic acids studied previously.
For Part 1, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1168, June, 1997. 相似文献
998.
K. Liao 《Experimental Techniques》1994,18(5):33-38
Hip prostheses made from thick laminated composite material were cyclically tested under biaxial compressive loading. Fatigue damage was studied using X-ray radiography, a surface replication, and sectioning of the specimens. It has been shown that damage in the neck region occurred predominantly in form of matrix cracking along fiber directions in the major load-carrying plies. These matrix cracks initiated from the surface of the medial-posterior corner, as a result of local high compressive stress, extended to the lateral side, and distributed toward the anterior side, with an increase of applied cycles. We also briefly outlined a life-prediction model for predicting the remaining life and strength of the composite prosthesis based on a "critical element" concept, as well as how laboratory test results can be used in the model. 相似文献
999.
We present Helmholtz's argument against Weber's electrodynamics. It is related with a fixed charged nonconducting spherical shell and a charged particle moving inside it. Then we utilize Weber's electrodynamics plus Schrödinger's expression for gravitational interactions in order to obtain the equation of motion and to study this situation. We show that this approach avoids the problems pointed out by Helmholtz. Moreover, it indicates that the effective inertial mass of the charged particle will depend not only on the electrostatic potential of the shell but also on its velocity. This is a relevant aspect of Weber's theory. 相似文献
1000.
In 1987 the Canadian Department of National Defence enunciated the Total Force concept. The Total Force is comprised of Regular and Reserve components. The intention is to make maximum use of the Reserve to reduce defence expenditures and at the same time to ensure that military capability remains adequate to support national policy objectives. This paper discusses some of the governing parameters that affect the modelling of the composition of the Total Force and analyses the mix of regular and reserve forces. The interplay between the key factors and their marginal costs will be stressed. The models are employed to study two units in the Canadian Forces, a maintenance support unit and a tactical unit with high operational activity cost. The lessons drawn from these studies are highlighted. 相似文献