全文获取类型
收费全文 | 20132篇 |
免费 | 3413篇 |
国内免费 | 1826篇 |
专业分类
化学 | 13906篇 |
晶体学 | 188篇 |
力学 | 1105篇 |
综合类 | 77篇 |
数学 | 2117篇 |
物理学 | 7978篇 |
出版年
2024年 | 68篇 |
2023年 | 424篇 |
2022年 | 760篇 |
2021年 | 798篇 |
2020年 | 794篇 |
2019年 | 800篇 |
2018年 | 778篇 |
2017年 | 618篇 |
2016年 | 1025篇 |
2015年 | 934篇 |
2014年 | 1160篇 |
2013年 | 1499篇 |
2012年 | 1837篇 |
2011年 | 1857篇 |
2010年 | 1215篇 |
2009年 | 1138篇 |
2008年 | 1256篇 |
2007年 | 1097篇 |
2006年 | 1039篇 |
2005年 | 827篇 |
2004年 | 638篇 |
2003年 | 451篇 |
2002年 | 476篇 |
2001年 | 354篇 |
2000年 | 291篇 |
1999年 | 424篇 |
1998年 | 304篇 |
1997年 | 316篇 |
1996年 | 301篇 |
1995年 | 257篇 |
1994年 | 222篇 |
1993年 | 218篇 |
1992年 | 152篇 |
1991年 | 163篇 |
1990年 | 132篇 |
1989年 | 101篇 |
1988年 | 88篇 |
1987年 | 71篇 |
1986年 | 70篇 |
1985年 | 55篇 |
1984年 | 58篇 |
1983年 | 32篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1978年 | 13篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The crystallization behavior of miscible syndiotactic polystyrene (sPS) and atactic polystyrene (aPS) blends with different sPS/aPS weight ratios was investigated in supercritical CO2 by using Fourier‐transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. Supercritical CO2 and aPS exhibited different effects on the conformational change of sPS and competed with each other. Increasing the content of amorphous aPS in the blends made its effect on the conformational change of sPS gradually surpass that of supercritical CO2. Supercritical CO2 favored the formation of the helical conformation of sPS in lower temperature range and the all trans planar conformation in higher temperature range, instead of forming the latter one only in higher temperature range in ambient atmosphere. However, increasing aPS content in the blends pushed the range for forming the helical conformation to lower temperature and made the all trans planar conformation dominant in aPS/sPS 25/75 blend after treating in supercritical CO2 above 60 °C. The all trans planar zigzag conformation was more favorable than the helical conformation after mixing aPS in sPS in supercritical CO2. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1755–1764, 2007 相似文献
32.
对西安地区150例0~3岁儿童进行了六种微量元素:钙、锌、铜、铁、镁、硒的检测,发现微量元素缺乏可导致急慢性感染、免疫力低下、小儿营养不良、贫血、发育迟缓等症状。并对小儿营养不良、喂养不当进行矫正。其中铁、钙、锌同时缺乏占50%。 相似文献
33.
34.
ChujiangCai ZhigangShen MingzhuWang ShulinMa YushanXing 《中国颗粒学报》2003,1(4):156-161
This paper reports the use of a colloidal Pd^0 catalysis system to metallize the surface of precipitators separated from coal fly-ash, and metals such as Cu, Ni etc. are deposited on the precipitators surface. Alternatively, according to the characteristic surface of cenospheres, an Ag coating catalysis system is adopted to first deposit Ag on the cenospheres surface, followed, if necessary, by the deposition of other metals such as Cu, Ni, etc. on the Ag coating to produce monolayer and multilayer metal-coated cenospheres. The surface characteristics and the morphologies of the metal coatings are examined in detail with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) techniques. It can be shown that the quality of metal coatings derived from the Aa coatina catalysis system, is better than that of the colloidal Pd^0 catalysis system. 相似文献
35.
Summary The potential of liquid chromatography-mass spectrometry (LC-MS) has been studied for the simultaneous determination of sixteen carbamate and organophosphorus pesticides in honeybees using a traditional sample preparation protocol based on acetone extraction and dichloromethane partitioning. The performances of both atmospheric pressure chemical ionization (APCI) and electrospray (ES) interfaces were compared. APCI offered better sensitivity and specificity for a higher range of pesticides. Limits of quantification were from 0.01 to 0.17 mg kg–1, at which recoveries obtained were between 64 and 93%, except for pirimicarb that was at 13%, with relative standard deviations ranging from 7 to 20%. Fenitrothion, fenoxycarb, methiocarb and phoxim were found in bees from Valencian Community beehives at concentrations between 0.03 and 3.75 mg kg–1. 相似文献
36.
37.
本文研究由双障碍问题导出的一类B可微函数的性质,并在一定条件下证明了求解相应的B可微方程阻尼牛顿法的全局收效性和二阶收效性.数值例子表明这一算法是有效的. 相似文献
38.
The goal of this paper is to compute the shape Hessian for a generalized Oseen problem with nonhomogeneous Dirichlet boundary
condition by the velocity method. The incompressibility will be treated by penalty approach. The structure of the shape gradient
and shape Hessian with respect to the shape of the variable domain for a given cost functional are established by an application
of the Lagrangian method with function space embedding technique.
This work was supported by the National Natural Science Fund of China (No. 10371096) for ZM Gao and YC Ma. 相似文献
39.
第Ⅰ种强度不对称三态叠加多模叠加态光场N次方Y压缩—第一正交相位分量的压缩情况 总被引:2,自引:0,他引:2
根据量子力学中的线性叠加原理,构造了由三个强度不等的多模相干态光场|{Zj(A)}>q、|{Zj(B)}>q和|{Zj(C)}>q的线性叠加所组成的第Ⅰ种强度不对称三态叠加多模叠加态光场|ψl(ABC)>q.利用多模压缩态理论,研究了态|ψl(ABC)>q的第一正交方分量(即磁场分量)的广义非线性等幂次N次方Y压缩特性.结果发现:①在上述各多模相干态光场中各模的强度和各模的初始相位各不相等的情况下,态|ψl(ABC)>q的第一正交分量-磁场分量在一定的条件下,总可呈现出周期性变化的、任意等幂次的N次方Y压缩效应;②当上述各多模相干态光场的强度和各模的初始相位相等时,态|ψl(ABC)>q的磁场分量的N次方Y压缩现象消失,态|ψl(ABC)>q可恒处于等幂次N-Y最小测不准态. 相似文献
40.
Angular momentum effect in prescission particle multiplicities for a light system by diffusion model
W. Ye W. Q. Shen Z. D. Lu J. Feng Y. G. Ma J. S. Wang K. Yuasa-Nakagawa T. Nakagawa 《Zeitschrift für Physik A Hadrons and Nuclei》1997,359(4):385-389
The effect of angular momentum on the competition between fission and particle emission during light system fission process was studied via fission diffusion model. The prescission particle multiplicities were found to increase with decreasing angular momentum. The experimental prescission proton and α particle multiplicities can be fitted for 10.6 MeV/nucleon 84Kr(27Al,binary fission) reaction with this model. Entrance channel effect found in [1] is proved to be angular momentum effect. 相似文献