全文获取类型
收费全文 | 3225篇 |
免费 | 133篇 |
国内免费 | 31篇 |
专业分类
化学 | 2332篇 |
晶体学 | 16篇 |
力学 | 143篇 |
数学 | 298篇 |
物理学 | 600篇 |
出版年
2023年 | 27篇 |
2022年 | 44篇 |
2021年 | 112篇 |
2020年 | 120篇 |
2019年 | 114篇 |
2018年 | 123篇 |
2017年 | 94篇 |
2016年 | 152篇 |
2015年 | 115篇 |
2014年 | 155篇 |
2013年 | 342篇 |
2012年 | 219篇 |
2011年 | 229篇 |
2010年 | 180篇 |
2009年 | 143篇 |
2008年 | 168篇 |
2007年 | 127篇 |
2006年 | 120篇 |
2005年 | 68篇 |
2004年 | 87篇 |
2003年 | 81篇 |
2002年 | 57篇 |
2001年 | 29篇 |
2000年 | 34篇 |
1999年 | 24篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 23篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 23篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 22篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 11篇 |
排序方式: 共有3389条查询结果,搜索用时 15 毫秒
991.
We perform self-consistent ab-initio calculations to study the structural, electronic and thermodynamic properties of InAs1-xPx alloy. The full potential-linearized augmented plane wave (FP-LAPW) method was employed within density functional theory (DFT). The ground-state properties are determined for the bulk materials (InAs and InP) as well as for the different concentration of their alloys. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. The gap bowing for the alloy of interest was found to be mainly caused by the charge-exchange contributions. In addition, the thermodynamic stability of InAs1-xPx alloy was investigated by calculating the excess enthalpy of mixing ΔHm and the calculated phase diagram showed a broad miscibility gap with a high critical temperature. 相似文献
992.
Munawar Ali Munawar Muhammad Azad Hamid Latif Siddiqui Faiz‐Ul‐Hassan Nasim 《中国化学会会志》2008,55(2):394-400
The quinolinylpyrimidine derivatives were prepared by the condensation of quinolinyl chalcones with urea (or thiourea) under basic conditions by using both conventional and microwave heating. Their IR, 1H NMR, 13C NMR, mass spectra and CHN analyses confirmed the prepared compounds. The newly prepared quinolinylpyrimidine derivatives were screened for antimicrobial activities against the bacterial strains viz. S. aureus, Shigella, Salmonela, P. aeroginosa, B. Subtilus and E. coli and found considerably active against S. aureus, P. aeroginosa and E. coli. 相似文献
993.
994.
995.
996.
Uncertainty Analysis of Radionuclide Transport in a Fractured Coastal Aquifer with Geothermal Effects 总被引:1,自引:0,他引:1
Groundwater flow and radionuclide transport at the Milrow underground nuclear test site on Amchitka Island are modeled using two-dimensional numerical simulations. A multi-parameter uncertainty analysis is adapted and used to address the effects of uncertainties associated with the definition of the modeled processes and the values of the parameters governing these processes. In particular, we focus on the effects on radioactive transport of uncertainties associated with conduction and convection of heat relative to the uncertainties associated with other flow and transport parameters. These include recharge, hydraulic conductivity, fracture porosity, dispersivity and strength of matrix diffusion. The flow model is conceptualized to address the problem of density-driven flow under conditions of variable salinity and geothermal gradient. The conceptual transport model simulates the advection–dispersion process, the diffusion process from the high-velocity fractures into the porous matrix blocks, and radioactive decay.For this case study, the uncertainty of the recharge-conductivity ratio contributes the most to the output uncertainty (standard deviation of mass flux across the seafloor). The location of the freshwater–saltwater transition zone changes dramatically as this ratio changes with the thickness of the freshwater lens and the location of the seepage face changing as well. In the context of radionuclide transport from the nuclear test cavity that is located in the area where the transition zone is uncertain, travel times of radionuclide mass from the cavity to the seepage face along the seafloor are significantly impacted. The variation in transition zone location changes the velocity magnitude at the cavity location by a large factor (probably an order of magnitude). When this effect is combined with porosity and matrix diffusion uncertainty, the uncertainty of transport results becomes large. Although thermal parameters have an effect on the solution of the flow problem and also on travel times of radionuclides, the effect is relatively small compared to other flow and transport parameters. 相似文献
997.
Richard G. Koegel Hassan K. Sreenath Richard J. Straub 《Applied biochemistry and biotechnology》1999,77(1-3):105-115
Valuable co-products derived from fractionation of alfalfa herbage give the resulting fibrous fraction an economic advantage
as a feed stock for ethanol or other organic products. Alfalfa fiber was saccharified and fermented with or without a liquid
hot water (LHW) pretreatment. The LHW pretreatment hydrolyzed approximately 60% of the original fiber, yielding a high cellulose
residue and aliquid extract. These yielded predominantly hexoses and pentoses, respectively, after enzymatic saccharification.
Yields of ethanol and lactic acid resulting from fermentations are given. 相似文献
998.
A novel long lifetime organic membrane-based thin-film Cu(II) microsensor has been elaborated. The advantages of the suggested microsensor include: excellent stability, long lifetime, and reasonable good selectivity. The significant improvements of the lifetime (>4 months) of the organic membrane-based thin-film microsensors have been realized for the first time using new-type electrodeposition treatment of the solid-state substrate surface in combination with a new nebulization method for applying the organic membrane coating mixture on the thin-film gold substrate. The electrochemical behavior of the thin-film microsensor in terms of ionic sensitivity, limit of detection, the effect of the pH, dynamic response time, Nernstian response interval, selectivity coefficients and lifetime has been evaluated. The results are compared to those obtained with the conventional ion-selective and coated graphite rod macroelectrodes prepared with the same ionophore. The reliability of the suggested thin-film microsensor with the low cost of its microfabrication makes it promising for the miniaturized application. 相似文献
999.
Chaos control of a spinning disk model via delayed feedback method is presented. The feedback gain is obtained and adapted according to a minimum entropy (ME) algorithm. In this method, stabilizing an unstable fixed point of the system Poincare map is achieved by minimizing the entropy of point distribution on the Poincare section. Simulation results show the feasibility of the proposed method in applying the delayed feedback technique for chaos control of spinning disks. 相似文献
1000.