全文获取类型
收费全文 | 16622篇 |
免费 | 2127篇 |
国内免费 | 1970篇 |
专业分类
化学 | 13197篇 |
晶体学 | 248篇 |
力学 | 715篇 |
综合类 | 125篇 |
数学 | 1956篇 |
物理学 | 4478篇 |
出版年
2024年 | 45篇 |
2023年 | 236篇 |
2022年 | 414篇 |
2021年 | 505篇 |
2020年 | 602篇 |
2019年 | 597篇 |
2018年 | 484篇 |
2017年 | 488篇 |
2016年 | 808篇 |
2015年 | 829篇 |
2014年 | 934篇 |
2013年 | 1167篇 |
2012年 | 1362篇 |
2011年 | 1501篇 |
2010年 | 1044篇 |
2009年 | 931篇 |
2008年 | 1121篇 |
2007年 | 979篇 |
2006年 | 947篇 |
2005年 | 808篇 |
2004年 | 706篇 |
2003年 | 578篇 |
2002年 | 670篇 |
2001年 | 477篇 |
2000年 | 364篇 |
1999年 | 333篇 |
1998年 | 218篇 |
1997年 | 180篇 |
1996年 | 132篇 |
1995年 | 129篇 |
1994年 | 121篇 |
1993年 | 93篇 |
1992年 | 86篇 |
1991年 | 115篇 |
1990年 | 89篇 |
1989年 | 68篇 |
1988年 | 64篇 |
1987年 | 47篇 |
1986年 | 40篇 |
1985年 | 49篇 |
1984年 | 28篇 |
1983年 | 32篇 |
1982年 | 27篇 |
1980年 | 27篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 30篇 |
1976年 | 16篇 |
1975年 | 22篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
为了提高强流ECR 离子源的引出束流品质,分别设计了1# 和2# 引出系统,利用束流引出模拟软件PBGUNS 对1# 和2# 引出系统进行了质子束流引出与传输的模拟计算,结合实际测得的发射度数据分析引出系统,发现2# 引出系统比1# 引出系统引出束流品质高。对ECR 离子源引出系统的电势等位线分布等参数引起的球差进行了简单数学推导及MATLAB 绘图,并结合1# 和2# 引出系统束流相图模拟结果证明了球差会使引出束流品质有效发射度增长,通过适当加大电极孔径可改善束流聚焦情况,得到了束流光学聚焦较好的束流引出系统设计。To improve the quality of extracted ion beam from a high current ECR ion source, 1# and 2# extraction systems were designed and tested. The PBGUNS code was used to simulate the 1# and 2# extraction systems of proton ion beam. The emittance measurement results with the two different extraction systems were compared and analyzed with the simulation, the conclusion that more high quality beam extracted from 2# system than 1# system was got. The formula derivation of ECR ion source extraction system spherical aberration and MATLAB drawing was done by the analyzing on the distribution of extraction field equipotentials, effective emittance increasing caused by spherical berration was proved by 1# and 2# extraction systems beam phase space simulation result, beam focusing would be improved if electrode hole size increasing appropriately and a general concept on good optics focusing of ion beam extraction system was proposed finally. 相似文献
113.
Wen‐xiong Shi Yun‐yan Li Jun Xu Gui‐qiu Ma 《Journal of Macromolecular Science: Physics》2013,52(6):1115-1126
The relationship of the phase morphology of polypropylene/polyethylene‐terephthalate (PP/PET) blends and their corresponding compatibilized blends with composition was investigated using digital image analysis. A diameter, d g , was defined and calculated to discuss the phase morphology of this polymer blend system. A figure‐estimation method was introduced to determine the width of the distribution of d g . Based on the method, it is proven that the distribution of d g obeys a log‐normal distribution and consequently, the distribution width, σ was calculated. Further, a fractal dimension, D f , was introduced to describe the distribution of main sizes of the particles of the dispersed phase. The results showed that, while d g increased with the concentration of the dispersed phase, σ and D f show different dependence relations on composition;σ increases monotonously but D f shows a maximum at a PET content of 30%, indicating that, even though the whole size distribution is much broader, the distribution of the main body of size becomes more uniform when the content of PET is less than 30%. 相似文献
114.
The concentrations of 14 elements in Lycium barbarum L. leaves collected from the Qaidam basin (China) were determined by inductively coupled plasma mass spectrometry after microwave assisted digestion. This work presents two goals: (1) to determine 14 elements in L. barbarum leaves; (2) to examine the relationship between elements using correlation analysis, principal component analysis, and cluster analysis. The accuracy and precision were verified against a GBW07605 Tea Leaves certified reference material. The results demonstrated that the method was reliable, reproducible, and suitable for determination of the concentrations of trace elements in L. barbarum leaves. Correlation analysis showed that aluminum–copper, arsenic–zinc, manganese–selenium, and chromium–iron have medium correlation coefficients. Principal component loading for L. barbarum leaves extracted seven components explained about 85% of the total variance. Cluster analysis depicts four clusters: (1) arsenic and titanium; (2) calcium, magnesium, manganese, selenium, and zinc; (3) cobalt, iron, and molybdenum; (4) aluminum, copper, and chromium. 相似文献
115.
ABSTRACT A new catalytic kinetic fluorescent quenching method for the determination of trace gold(III) was investigated. The method was based on the catalytic effect of gold on oxidation of 3-(3′-methylphenyl)-5- (2′-arsenoxylphenylazo) rhodanine by hydrogen peroxide in potassium hydrogen phthalate–hydrochloric acid (pH = 3.4). Under the optimum conditions, the great decrease of fluorescence intensity has a linear relationship against the concentration of gold in the range of 0 to 12.0 µg·L?1 with a detection limit of 6.0 × 10?10g·L?1. The coexistent metal ions can be separated, and gold can be enriched by TBP resin of solid-phase extraction, which greatly improves the selectivity and sensitivity of the system. The method can be used to determine trace amounts of gold in ore samples successfully with satisfactory results. 相似文献
116.
Abstract The response of suspensions of spices and spice mixtures in water to high pressure treatment was investigated. Inactivation of the microbial load–mainly aerobic and unaerobic spore formers–was strongly dependent on water activity and temperature. Samples were completely decontaminated after three pressure cycles (30 min at 80 MPa followed by 30 min at 350 MPa) at 70 °C at a minimum water activity of 0.91. Pressure treated samples were examined for sensory and chemical changes. No significant changes in odour and appearance were recognized by a trained sensory panel, nor were changes in the volatile compounds of the samples detected by static headspace gaschromatography. 相似文献
117.
E. Alp M. Borland S. Davey K. Harkay Gabrielle Long Jorg Maser 《Synchrotron Radiation News》2013,26(1):31-34
Twenty years is a long time, but it seems to me as if it were yesterday when the three of us—Michel Belakhovsky, Christian Riekel and I—first scientists of the Experiments Division (except the directors) at the not yet created European Synchrotron Radiation Facility, living in a temporary and not very solid building, made the last corrections to the text of the famous “Red Book,” the ESRF Foundation Phase Report published in February 1987. The floor was shaking in our office when Ruprecht Haensel, the first Director General, walked along the corridor…. We had convened workshops of experts in the various fields to define the first set of beamlines to be built at the ESRF. The program was quite complete, comprising inelastic scattering, imaging (topography), microfocusing, small angle scattering, nuclear resonance, high energy, etc. Costs were particularly difficult to estimate, but finally we were not so far from the real figures. 相似文献
118.
Gabrielle Long 《Synchrotron Radiation News》2013,26(1):46-47
More than 250 scientists from 22 countries gathered in Chicago, Illinois, from July 30 to August 2, 2006, to participate in the Fifth International Conference on Synchrotron Radiation in Materials Science (SRMS-5). The SRMS conference is held every two years, bringing together leading-edge researchers in the materials sciences making use of synchrotron radiation. The conference, which was organized and hosted this year by Argonne National Laboratory and the Advanced Photon Source, provided an overview of the latest research developments in a broad range of areas, such as polymers and biomaterials, magnetic and superconducting materials, glasses and ceramics, engineering materials, materials under extreme conditions, complex oxides, innovative instrumentation, membranes, and thin films. The aim of SRMS-5 was to highlight recent breakthroughs in materials science using synchrotron radiation and to open doors to future innovation and discovery. 相似文献
119.
CLIFFORDMARTINGALESΦ-EQUIVALENCEBETWEENS(f)ANDf¥LONGRULIN;QIANTAO(InstituteofMathematics,AcademiaSinica,Beijing100080,China.)... 相似文献
120.
海藻酸钠/大豆蛋白共混凝胶微球的结构 总被引:3,自引:1,他引:3
利用钙离子交联海藻酸钠/大豆分离蛋白共混溶液,制得海藻酸钠/大豆分离蛋共混凝胶微球.结果表明,海藻酸钠和大豆分离蛋白质量配比的不同以及各组分间相互作用的变化,微球呈现不同的微观结构.将微球干燥后置于水中溶胀,微球的尺寸无法回复到干燥前的尺寸,这是由于真空干燥处理使水分子挥发,促进微球内组分间形成了强的氢键作用所致.此外,用碱处理该共混微球,发现由于大豆分离蛋白溶解以及部分钙离子被置换析出,微球塌陷且内部形成了大孔. 相似文献