全文获取类型
收费全文 | 222篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
化学 | 152篇 |
力学 | 10篇 |
数学 | 22篇 |
物理学 | 53篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 16篇 |
2013年 | 15篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有237条查询结果,搜索用时 46 毫秒
211.
Tumor growth and metastasis are ultimately mechanical processes involving cell migration and uncontrolled division. Using a 3D discrete model of cells, we show that increased compliance as observed for cancer cells causes them to grow at a much faster rate compared to surrounding healthy cells. We also show how changes in intercellular binding influence tumor malignancy and metastatic potential. These findings suggest that changes in the mechanical properties of cancer cells is the proximate cause of uncontrolled division and migration and various biochemical factors drive cancer progression via this mechanism. 相似文献
212.
The scaling of the power scaling density (PSD) of the far field noise for subsonic, unheated, axisymmetric jets has been examined based on data obtained from the literature as well as from new experiments. It has been demonstrated that the PSD scales as the Strouhal number (StD) alone for most locations, except at shalloow angles (θ<30°) where the best scaling results with the Helmholtz number times the Doppler factor, HD(1?Mc cos θ). In contrast to the common assumption, scaling with StD times the Doppler factor only degraded the collapse of the data. Also, a “source convection Mach number”, Mc = 0·5 M, rather than the commonly used value of 0·67 M, yielded the best collapse, Mc = 0·5 M agreeing with the recent measurement of jet large-scale structure convection velocity. At θ = 90°, the amplitude of the PSD varies as U6·5, which agrees with the observed U7·5 variation of the overall intensity; a similar power law assumed at θ ~- 30° yields an exponent 8·5 for the PSD. Contrary to claims in the literature, the PSD amplitude was not observed to vary sharply about any critical Reynolds number. For shallow angles, the scaling on HD (1 ? Mc cos θ) also contrasts simple HD scaling previously observed on the basis of one-third octave spectra. 相似文献
213.
Musharraf Zaman Michael R. Taheri Anuradha Khanna 《Applied Mathematical Modelling》1996,20(12):877-889
The importance of dynamic interactions between cable-stayed bridges and heavy moving vehicles, such as trucks and locomotives, has been recognised by bridge engineers for a long time. A structural impedance algorithm is developed for analysing the dynamic response of cable-stayed bridges subjected to traversing vehicles. The bridge deck is modelled as an elastic plate, and the cables are idealised as springs for simplicity. The vehicles are modelled as a series of masses with suspension systems moving with different speeds and accelerations. A comprehensive computer program, CABLESIM, is developed for the static and dynamic analyses of a cable-stayed bridge. The accuracy of the numerical procedure and its computer implementation is verified with the available analytical and experimental results. A parametric study is conducted to investigate the effects of vehicle velocity, girder depth, different types of cable arrangements, and traffic load on the dynamic response of the deck. The numerical results are expected to be important in assessing the dynamics of cable-stayed bridge components and in determining the safety and allowable traffic conditions. 相似文献
214.
Laser-induced thermal stresses on steel surface 总被引:1,自引:0,他引:1
Bekir Sami Yilbas Muhammad Sami Shahzada Zaman Shuja 《Optics and Lasers in Engineering》1998,30(1):25-37
In laser heat treatment of steels, a thin surface layer of austenite forms during heating and subsequent phase change process in the cooling period. However, thermal stress develops due to high-temperature gradient attainment in the surface vicinity which in turn results in microcrack development at the surface. The present study is carried out to compute the temperature profiles due to step input pulse laser radiation and determine the resulting thermal stresses. The study is extended to include three-step input pulses having the same energy content. This provides the comparison for the influence of the pulse length on the resulting thermal stresses. To validate the theoretical predictions, an experiment is conducted to irradiate the AISI 4142 steel surface by an Nd–YAG laser. Microphotography and EDS analysis of the heated regions are carried out. It is found that considerable thermal stress is eveloped at the workpiece surface due to attainment of high-temperature gradient in this region. In addition, microcracks are observed at the surface of the irradiated spot. 相似文献
215.
216.
P. Hayumbu M. B. Zaman N. C. H. Lubaba S. S. Munsanje D. Muleya 《Journal of Radioanalytical and Nuclear Chemistry》1995,199(3):229-238
Samples of natural and manufactures building materials collected around Lusaka have been analyzed for natural radionuclides using -spectrometry. A simple comparison of the specific radioactivities of primordial radionuclides in these materials to the world averages for soil (25 Bq kg–1
238U, 25 Bg kg–1
232Th, 370 Bq kg–1
40K and 89 Bq kg–1 Raeq) shows that, of the nine types of samples analyzed, only burnt clay bricks (for238U,232Th and40K), cement roofing tiles (for238U), building and river sands (for232Th and40K) have greater activities than does soil. Radiological evaluation of specific radioactivities in these materials indicates that all materials meet the external -ray dose limitation of 1.5 mSv y–1, that is, all samples have a radium equivalent activity of less than 370 Bq kg–1. 相似文献
217.
M. A. Kalam A. Hussam M. Khaliquzzaman A. H. Khan M. M. Islam M. B. Zaman M. Husain 《Journal of Radioanalytical and Nuclear Chemistry》1978,46(2):285-297
The problem of spectrochemical analysis of elements in solutions has been investigated for a number of elements across the
periodic table using radioisotope-induced energy dispersive X-ray fluorescence method. In this study a low intensity109Cd X-ray source was used for characteristic X-ray excitation. Experimental parameters such as saturation thickness and critical
thickness have been studied to evaluate their role in this method. Minimum detection limits, sensitivities and the nature
of concentration calibration at critical thickness have been obtained as a function of Z to find the limits of the method.
Results obtained have been discussed in the light of theories and potential areas of applicability of the method have been
indicated. 相似文献
218.
Ashfaque H. Bokhari Munawar Karim Dina N. Al-Sheikh F. D. Zaman 《International Journal of Theoretical Physics》2008,47(10):2672-2678
In this note we consider a general three-dimensional circularly symmetric static metric and investigate possible Killing symmetries it possesses.We then summarize
the work by addressing Einstein equations and briefly discuss their implications on the energy momentum content of some of
the metrics that arise in the process. 相似文献
219.
F. D. Zaman 《Mechanics Research Communications》2001,28(2):171
The diffraction of SH-waves in an infinite elastic plate is studied under general boundary conditions using the Wiener-Hopf technique. A mixed interface boundary value problem is solved as an illustration. 相似文献
220.
Minna H. Chen Jennifer J. Chung Joshua E. Mealy Samir Zaman Elizabeth C. Li Maria F. Arisi Pavan Atluri Jason A. Burdick 《Macromolecular bioscience》2019,19(1)
Shear‐thinning hydrogels are useful for biomedical applications, from 3D bioprinting to injectable biomaterials. Although they have the appropriate properties for injection, it may be advantageous to decouple injectability from the controlled release of encapsulated therapeutics. Toward this, composites of hydrogels and encapsulated microgels are introduced with microgels that are fabricated via microfluidics. The microgel cross‐linker controls degradation and entrapped molecule release, and the concentration of microgels alters composite hydrogel rheological properties. For the treatment of myocardial infarction (MI), interleukin‐10 (IL‐10) is encapsulated in microgels and released from composites. In a rat model of MI, composites with IL‐10 reduce macrophage density after 1 week and improve scar thickness, ejection fraction, cardiac output, and the size of vascular structures after 4 weeks when compared to saline injection. Improvements are also observed with the composite without IL‐10 over saline, emphasizing the role of injectable hydrogels alone on tissue repair. 相似文献