全文获取类型
收费全文 | 29978篇 |
免费 | 144篇 |
国内免费 | 280篇 |
专业分类
化学 | 11249篇 |
晶体学 | 273篇 |
力学 | 1427篇 |
综合类 | 12篇 |
数学 | 9063篇 |
物理学 | 8378篇 |
出版年
2021年 | 52篇 |
2020年 | 51篇 |
2019年 | 46篇 |
2018年 | 1209篇 |
2017年 | 1463篇 |
2016年 | 744篇 |
2015年 | 586篇 |
2014年 | 501篇 |
2013年 | 697篇 |
2012年 | 3204篇 |
2011年 | 2394篇 |
2010年 | 1866篇 |
2009年 | 1605篇 |
2008年 | 657篇 |
2007年 | 673篇 |
2006年 | 649篇 |
2005年 | 4489篇 |
2004年 | 3957篇 |
2003年 | 2333篇 |
2002年 | 531篇 |
2001年 | 299篇 |
2000年 | 124篇 |
1999年 | 195篇 |
1998年 | 128篇 |
1997年 | 79篇 |
1996年 | 51篇 |
1995年 | 50篇 |
1994年 | 51篇 |
1993年 | 31篇 |
1992年 | 176篇 |
1991年 | 160篇 |
1990年 | 136篇 |
1989年 | 110篇 |
1988年 | 104篇 |
1987年 | 60篇 |
1986年 | 42篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 32篇 |
1979年 | 33篇 |
1976年 | 83篇 |
1975年 | 38篇 |
1974年 | 44篇 |
1973年 | 52篇 |
1972年 | 41篇 |
1970年 | 38篇 |
1969年 | 38篇 |
1968年 | 36篇 |
1967年 | 30篇 |
1966年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
942.
Dorota Majda Wac?aw Makowski Maria Mańko 《Journal of Thermal Analysis and Calorimetry》2012,109(2):663-669
Thermoporosimetry, i.e., DSC measurements of melting point depression of water and heptane confined in mesopores, has been used for determination the pore size distribution of several mesoporous silicas synthesized with the use of micelle templates. Porosity of these materials was additionally characterized by low-temperature nitrogen adsorption and quasi-equilibrated thermodesorption of nonane. The pore size distributions obtained using the water thermoporosimetry were similar to those determined using the other methods, but the pore size values found for the narrow pore materials were underestimated by ca 1?nm. Too large pore sizes obtained for the wide pore silica from heptane thermoporosimetry were attributed to nonlinear dependence of the melting point depression on the reciprocal of the pore size. 相似文献
943.
944.
We construct a representation of the infinite dimensional complex Clifford algebra on the Hilbert space of square-integrable
complex-valued functions on the Cantor set, which we show to be equivalent to the classical Fock representation. 相似文献
945.
946.
The p-median model is used to locate P centers to serve a geographically distributed population. A cornerstone of such a model is the measure of distance between a service center and demand points, i.e. the location of the population (customers, pupils, patients, and so on). Evidence supports the current practice of using Euclidean distance. However, we find that the location of multiple hospitals in a rural region of Sweden with a non-symmetrically distributed population is quite sensitive to distance measure, and somewhat sensitive to spatial aggregation of demand points. 相似文献
947.
DNA methylation is the most promising biomarker for estimating human age. There are various methods used for analyzing DNA methylation. Among those, the SNaPshot assay-based method provides a semi-quantitative measurement of DNA methylation using capillary electrophoresis on genetic analyzers. However, DNA methylation measures produced using different types of genetic analyzers have never been compared, although differences in methylation values can directly affect age estimates. To evaluate the differences between the results generated by different genetic analyzers, we analyzed the same blood, saliva, and control methylated DNA using three genetic analyzers—the Applied Biosystems 3130, 3500, and SeqStudio—and compared the methylation values at five CpG sites: ELOVL2, FHL2, KLF14, MIR29B2C, and TRIM59. The methylation value at each of the five CpG sites decreased in the order 3130, 3500, and SeqStudio. The differences in the results produced by the different genetic analyzers resulted in significant errors when applying the 3500 and SeqStudio data to a previous age estimation model constructed using the 3130 Genetic Analyzer data. Therefore, DNA methylation measurements from 3500 and SeqStudio were corrected using the regression functions obtained by plotting the DNA methylation data of one instrument versus the other to facilitate the application of DNA methylation data from one instrument to the age prediction model based on other instruments. The age prediction accuracy obtained by applying corrected 3500 and SeqStudio data to the existing age estimation model was as high as observed in the 3130 data. 相似文献
948.
Collective behaviours can be observed in both natural and man-made systems composed of a large number of elemental subsystems. Typically, each elemental subsystem has its own dynamics but, whenever interaction between individuals occurs, the individual behaviours tend to be relaxed, and collective behaviours emerge. In this paper, the collective behaviour of a large-scale system composed of several coupled elemental particles is analysed. The dynamics of the particles are governed by the same type of equations but having different parameter values and initial conditions. Coupling between particles is based on statistical feedback, which means that each particle is affected by the average behaviour of its neighbours. It is shown that the global system may unveil several types of collective behaviours, corresponding to partial synchronisation, characterised by the existence of several clusters of synchronised subsystems, and global synchronisation between particles, where all the elemental particles synchronise completely. 相似文献
949.
Tomá? Ligursky 《Applications of Mathematics》2012,57(3):263-295
A discrete model of the two-dimensional Signorini problem with Coulomb friction and a coefficient of friction F depending on the spatial variable is analysed. It is shown that a solution exists for any F and is globally unique if F is sufficiently small. The Lipschitz continuity of this unique solution as a function of F as well as a function of the load vector f is obtained. Furthermore, local uniqueness of solutions for arbitrary F > 0 is studied. The question of existence of locally Lipschitz-continuous branches of solutions with respect to the coefficient F is converted to the question of existence of locally Lipschitz-continuous branches of solutions with respect to the load vector f. A condition guaranteeing the existence of locally Lipschitz-continuous branches of solutions in the latter case and results for determining their directional derivatives are given. Finally, the general approach is illustrated on an elementary example, whose solutions are calculated exactly. 相似文献
950.
Karel Kolomazník Ji?í Pecha Veronika Friebrová Dagmar Janá?ová Vladimír Va?ek 《Heat and Mass Transfer》2012,48(9):1505-1512
Biostimulators are substances able to enhance the immune system of cultivated crops and support plant metabolism. Their utilization helps to reduce the amount of chemicals used in agriculture. To perform the desired effect, a biostimulator must be able to penetrate into the plant tissue. The time of penetration however, is limited, since the biostimulator must remain in a liquid state. This is of great importance—especially in field conditions, where the treated plants are exposed to different weather condition and other extrinsic factors. A mathematical model based on diffusion mechanisms has been elaborated to describe the biostimulator transport process from penetration of the leaves into the plant’s inner tissues. By means of the effective diffusion coefficient of the prepared specific protein hydrolyzate, this model can be used to estimate the time necessary for the uptake of the minimal active amount of the biostimulator. 相似文献