全文获取类型
收费全文 | 1195篇 |
免费 | 33篇 |
专业分类
化学 | 658篇 |
晶体学 | 10篇 |
力学 | 41篇 |
数学 | 86篇 |
物理学 | 433篇 |
出版年
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2016年 | 16篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 54篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 38篇 |
2009年 | 28篇 |
2008年 | 55篇 |
2007年 | 61篇 |
2006年 | 64篇 |
2005年 | 45篇 |
2004年 | 46篇 |
2003年 | 34篇 |
2002年 | 28篇 |
2001年 | 29篇 |
2000年 | 25篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 22篇 |
1994年 | 29篇 |
1993年 | 34篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 22篇 |
1977年 | 14篇 |
1976年 | 25篇 |
1975年 | 14篇 |
1974年 | 19篇 |
1973年 | 11篇 |
1972年 | 10篇 |
排序方式: 共有1228条查询结果,搜索用时 15 毫秒
141.
The attenuation of thermal radiation within a dilute cloud of pulverised coal and ash is investigated experimentally and theoretically, for different ranges of particle size. An empirical expression is developed for obtaining the absorptivity and emissivity of a coal/ash cloud. A new nomogram is also presented on the basis of this expression. 相似文献
142.
The large values of integrated cross sections for the excitation and de-excitation of nuclear isomers in (γ, γ′) reactions
provide strong encouragement for the feasibility of an optically pumped gamma-ray laser. For this reason, sources of possible
spurious contamination of the measurements were carefully considered. This paper reviews an analysis of possible sources as
well as experimental limits on contamination of the isomeric yields. The question of spurious contributions from (n, γ) or
(n, n′) reactions was examined by estimating the level of thermal, epithermal and fast neutron fluxes based on possible source
material in the accelerator environments. Such possibilities were severely reduced by the range of photon energies employed
in the studies of 1.5-6 MeV. The expected fluxes were below levels necessary to produce significant isomeric yields in this
energy range. Next, experiments were conducted in accordance with standard neutron activation-foil techniques to directly
measure any fluxes of neutrons in the accelerator environments. Measurements for fast neutron fluxes were completely negative
under even the most likely conditions with a 6 MeV medical linac. Measurable fluxes of thermal and epithermal neutrons were
obtained. However, in typical cases the amount of isomeric activation due to “slow” neutrons was 1% of the total activation
and 6% in the worst case based on measured fluxes and known values of cross sections.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
143.
Tetyana A Mykhaylyk Stephen Collins Chintan Jani Ian W Hamley 《European Polymer Journal》2004,40(8):1715-1721
The ozone etching of thin films of a commercial polystyrene-polyisoprene-polystyrene (PS-PI-PS) triblock copolymer (Vector 4111) was studied using atomic force microscopy (AFM) and ellipsometry. The major phase of the copolymer consists of PI (82 wt.%) and the copolymer forms a cylindrical structure upon annealing. Moderate ozone doses (1.4% wt/wt) were used to etch the copolymer. This revealed two stages of the ozonation: rapid etching of the PI fragments followed by slow compacting of the remaining PS cylinders. Under certain conditions ozone treatment results in the formation of nanosized grooves in a PS matrix which is suitable for lithographic processes. 相似文献
144.
The Relationship Between VHI Scores and Specific Acoustic Measures of Mildly Disordered Voice Production 总被引:1,自引:0,他引:1
This study was designed to examine the relationship between the Voice Handicap Index (VHI) and acoustic measures of voice samples common in clinical practice. Fifty participants, 38 women and 12 men, ranging in age from 19 to 80 years, with a mean age of 49 years, served as participants. Of these 50 participants, 17 participants could be included in the acoustic analysis of voice based on measures of error calculated with the TF32 software. All participants completed the VHI and provided voice samples including three trials of the sustained vowel /A/ at a comfortable loudness level as well as a connected speech sample consisting of the Zoo Passage. Acoustic measures were made with TF32 and Cool Edit software and included fundamental frequency, jitter %, shimmer %, signal-to-noise ratio, mean root-mean-square intensity, fundamental frequency standard deviation, aphonic periods, and breath groups. Results indicate that these measures were not predictive of overall VHI score, and no cohesive or predictable pattern was identified when comparing individual measures with overall VHI or with each subscale item. Likely contributions to this lack of correlation and subsequent clinical implications are discussed, as well as the direction for further research. 相似文献
145.
I. C. S. F. Jardim J. C. de Andrade C. H. Collins E. Collins 《Journal of Radioanalytical and Nuclear Chemistry》1985,96(6):621-627
Modifications of the conventional precipitation method for purifying -metallophthalocyanines give a product essentially free of the usual occluded impurities, significantly decreasing the total metallic content of extracted radionuclides. Application of the improved method to the preparation of an -CoPc target is described. 相似文献
146.
James C. Collins 《Experimental Mechanics》1970,10(2):19N-23N
Small computers are being considered for data acquisitiion and control functions in physical-testing laboratories. As with any new device, the potential user does not have an appreciation of the peripheral problems which will accompany the computer. This paper lists some of the advantages of computer ownership and describes some of the unexpected problems which the innocent user may encounter. 相似文献
147.
148.
149.
C. B. Collins 《General Relativity and Gravitation》1977,8(9):717-721
Certain gravitational systems are described for which particular equations of state are singled out by means of purely mathematical considerations. The fact that these equations of state are realistic, and indeed the most relevant to the physical systems under study, suggests that locked into Einstein's field equations lies some information about local physical conditions, and that in order to describe gravitating systems, it is not always necessary to draw on extraneous branches of physics.This essay received an honorable mention (1976) from the Gravity Research Foundation-Ed. 相似文献
150.
Mossbauer spectroscopy and X-ray diffraction techniques were used to investigate the iron oxides and other mineral phase developments
in calcareous and noncalcareous soil samples after firing at ≈ 1000°C. Well crystalline haematite with larger particle size
was produced in the fired non-calcareous soil. On the other hand, while goethite in the strongly calcareous natural material
was transformed into haematite at the oven drying temperature, non of the latter was detected after firing at 1050°C. This
could be related to the reaction between CaO, quartz and aluminosilicates at 800°C to produce calcium aluminosilicates which
may have hindered the growth of haematite above this temperature. 相似文献