全文获取类型
收费全文 | 1000篇 |
免费 | 23篇 |
国内免费 | 6篇 |
专业分类
化学 | 551篇 |
晶体学 | 12篇 |
力学 | 70篇 |
数学 | 108篇 |
物理学 | 288篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 15篇 |
2017年 | 22篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 32篇 |
2013年 | 61篇 |
2012年 | 66篇 |
2011年 | 56篇 |
2010年 | 37篇 |
2009年 | 42篇 |
2008年 | 53篇 |
2007年 | 41篇 |
2006年 | 35篇 |
2005年 | 34篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1936年 | 13篇 |
排序方式: 共有1029条查询结果,搜索用时 31 毫秒
991.
Mala Mitra N.H. Molla Pratibha Pal D.P. Bhattacharyya 《Czechoslovak Journal of Physics》2001,51(1):75-88
The moderate energy primary cosmic ray nucleon spectrum has been calculated from the direct measurements of Webber et al., Seo et al., and Menn et al. along with the other results surveyed by Swordy. Using these directly measured primary mass composition results all particle primary nucleon energy spectrum has been constructed using superposition model to estimate the energy spectra of muons from the decay of the cosmic ray non-prompt and prompt mesons in the atmosphere. The Z-factors have been estimated from the CERN LEBC-EHS on the Lorentz invariant cross section results on pp ±X and pp K±X inclusive reactions and FNAL data on ±p ±X reactions, and duly corrected for A--A collisions. Using these Z-factors the meson energy spectra in the atmosphere have been calculated. The sea level muon energy spectra at zenith angles 0°, 45°, 72°, and 75° have been derived from the decay of non-prompt mesons by adopting standard diffusion equation of hadronic cascades. The contribution of charmed mesons to muon spectrum has also been accounted by adapting the conventional procedure. The derived differential sea level muon energy spectra for energies 10 TeV have been found to follow the power law fits of the form N
(E) const. E
-. Our estimated muon energy spectra at zenith angles 75° have been found comparable with the global spectrograph muon flux results of MARS, DEIS, and MSU groups. 相似文献
992.
A. Viswanathan D. Sastikumar P. Rajarajan Harish Kumar A.K. Nath 《Optics & Laser Technology》2007,39(8):1504-1513
AISI 316L stainless steel was laser surface treated with different compositions of Si3N4 and Ti under various laser-processing parameters to improve its surface hardness through reinforcement of Ti-based silicides. The laser-treated regions exhibited improved surface hardness (250–1000 HV), variations in the surface morphology (smooth and bowl like) and presence of cracks and pores depending upon the Si3N4–Ti composition and laser-processing parameters. The study shows that when the Si3N4–Ti composition is 75–25 wt% and laser parameters are 1.5 kW laser power and 1.0 m min−1 scan speed, a laser-treated region with high hardness of about 800 HV and smooth surface morphology as well as free from pores and cracks is observed. The X-ray diffractometer (XRD) and Energy-Dispersive Spectroscopy (EDS) analyses show that the laser surface-treated region has reinforced phase of Ti5Si3 and retained austenitic structure. The reinforced phase gives rise to very high hardness (or wear resistance) and also a corrosion resistance. 相似文献
993.
994.
Keshri Nath Tiwari S.M. Prabhakaran Vaneet Kumar Thakar Snehal Rajendra Shintu Mathew 《Tetrahedron》2018,74(27):3596-3601
We have demonstrated three component reaction of isatin, enaminone and ethyl cyanoacetate leading to sprirooxindole scaffold without catalyst in water. The synthetic protocol has several advantages like wide substrate scope, atom-economy and operationally simple experimental procedures which provides rapid access to library of compounds. The mechanistic details of the reaction has been investigated during the course of study. 相似文献
995.
Eric M. Kercher Shubhankar Nath Imran Rizvi Bryan Q. Spring 《Photochemistry and photobiology》2020,96(2):295-300
Photodynamic therapy (PDT) is an established therapeutic modality that uses nonionizing near-infrared light to activate photocytotoxicity of endogenous or exogenous photosensitizers (PSs). An ongoing avenue of cancer research involves leveraging PDT to stimulate antitumor immune responses; however, these effects appear to be best elicited in low-dose regimens that do not provide significant tumor reduction using conventional, nonspecific PSs. The loss of immune enhancement at higher PDT doses may arise in part from indiscriminate damage to local immune cell populations, including tumor-infiltrating T cells. We previously introduced “tumor-targeted, activatable photoimmunotherapy” (taPIT) using molecular-targeted and cell-activatable antibody–PS conjugates to realize precision tumor photodamage with microscale fidelity. Here, we investigate the immune cell sparing effect provided by taPIT in a 3D model of the tumor immune microenvironment. We report that high-dose taPIT spares 25% of the local immune cell population, five times more than the conventional PDT regimen, in a 3D coculture model incorporating epithelial ovarian cancer cells and T cells. These findings suggest that the enhanced selectivity of taPIT may be utilized to achieve local tumor reduction with sparing of intratumor effector immune cells that would otherwise be lost if treated with conventional PDT. 相似文献
996.
997.
The preceding paper showed that, in principle, a high-resolution coherent Raman spectrum can be recovered using femtosecond probe pulses by combined detection in both time and frequency. This measurement is possible even when the pulses are too broad in frequency for conventional frequency-domain spectroscopy and too broad in time for conventional time-domain spectroscopy. In this paper, the method is tested on experimental coherent anti-stokes Raman spectroscopy data from acetonitrile. Compared to theoretical models, experimental data are complicated by noise and incomplete knowledge of the pulse structure. Despite these complications, most of the information in the Raman spectrum is recovered from the data: weak transitions are detected and natural-linewidth resolution is achieved across an 800 cm(-1) spectral range. However, circumstances in which experimental limitations result in missed features or ambiguities in the recovered spectrum are also identified. These results suggest where improvements in measurement and data analysis can be made. 相似文献
998.
Solvatoemissive dual fluorescence emission observed in the three positional isomers of N-(n-pyridylmethyl)-3-nitro-1,8-naphthalimide [n?=?2 (1), 3 (2), 4 (3)] are described. Dual fluorescence emission in this class of compounds occurs from the excited states with extended conjugation via π-stacking interactions. The crystal structure of the compound 1 and the chloride salt of 2 were determined. The compound 1 forms dimeric assemblies through π-stacking interactions. Whereas the structure of the chloride salt of 2 is composed of dimeric assemblies of the cationic part which hold cyclic hydrated anionic assemblies through weak C-H…Cl interactions. Anionic hydrated assemblies between water and chloride ions have cyclic tetrameric structure through O-H…Cl interactions. 相似文献
999.
S. K. Deb Nath 《Applied Physics A: Materials Science & Processing》2014,117(2):857-870
Diffusion of perfluoropolyethers (PFPEs) lubricants on a hard disk surface is an important self healing characteristic to replenish PFPEs lubricants on their uncovered surface. In the present paper, we study the diffusion coefficients of non-functional PFPE Z and PFPE Zdol with functional end groups as a function of lubricant film thickness on a thin DLC (diamond-like) film. Diffusion coefficients of PFPE Z and PFPE Zdol molecules on a DLC film are calculated using the equation of Einstein’s law of diffusion (Guo et al. J. Appl. Phys 93:8707, 2003; Guo Ph.D. thesis, 2006; Chung et al. IEEE Trans. Magn. 45:3644, 2009) considering the movement of their center of mass to reach their equilibrium positions from their original configurations. And it is averaged with the film thickness to show the thickness dependence on the diffusion of PFPEs lubricants on a DLC substrate. Firstly diffusion coefficients of sub-monolayer of partially coverage PFPE Z and PFPE Zdol on a DLC substrate are studied briefly and secondly the diffusion coefficient of monolayer PFPE Zdol on a DLC substrate is also studied elaborately. To support our results, we compare our thickness-dependent diffusion coefficients of PFPE Z and PFPE Zdol with those of published theoretical (Guo Ph.D. thesis, 2006; Chung et al. IEEE Trans. Magn. 45:3644, 2009) and experimental results (Chung et al. Tribol. Lett. 32:35, 2008; Ma et al. Tribol. Lett. 10:203, 2001). Here we study how lubricant film thickness plays an important role on its diffusion. Effects of polar end bead functionality, lubricant film thickness enhance the anisotropic behavior of diffusion coefficients of PFPE Zdol on the DLC substrate. But in the present analysis we consider hard disk carbon overcoat as a thin DLC film and we include all of their atoms within the force cut-off distance with PFPEs lubricant molecules for the interactions to study the thickness dependence on their diffusion coefficients. 相似文献
1000.
The integration of microfluidic devices with micro X‐ray fluorescence (micro‐XRF) spectrometry offers a new approach for the direct characterization of liquid materials. A sample presentation method based on use of small volumes (<5 µl) of liquid contained in an XRF‐compatible device has been developed. In this feasibility study, a prototype chip was constructed, and its suitability for XRF analysis of liquids was evaluated, along with that of a commercially produced microfluidic device. Each of the chips had an analytical chamber which contained approximately 1 µl of sample when the device was filled using a pipette. The performance of the chips was assessed using micro‐XRF and high resolution monochromatic wavelength dispersive X‐ray fluorescence, a method that provides highly selective and sensitive detection of actinides. The intended application of the device developed in this study is for measurement of Pu in spent nuclear fuel. Aqueous solutions and a synthetic spent fuel matrix were used to evaluate the devices. Sr, which has its Kα line energy close to the Pu Lα line at 14.2 keV, was utilized as a surrogate for Pu because of reduced handling risks. Between and within chip repeatability were studied, along with linearity of response and accuracy. The limit of detection for Sr determination in the chip is estimated at 5 ng/µl (ppm). This work demonstrates the applicability of microfluidic sample preparation to liquid characterization by XRF, and provides a basis for further development of this approach for elemental analysis within a range of sample types. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献