全文获取类型
收费全文 | 4757篇 |
免费 | 236篇 |
国内免费 | 1806篇 |
专业分类
化学 | 4384篇 |
晶体学 | 109篇 |
力学 | 54篇 |
综合类 | 41篇 |
数学 | 1549篇 |
物理学 | 662篇 |
出版年
2023年 | 58篇 |
2022年 | 83篇 |
2021年 | 70篇 |
2020年 | 102篇 |
2019年 | 116篇 |
2018年 | 91篇 |
2017年 | 105篇 |
2016年 | 116篇 |
2015年 | 113篇 |
2014年 | 194篇 |
2013年 | 333篇 |
2012年 | 186篇 |
2011年 | 231篇 |
2010年 | 197篇 |
2009年 | 246篇 |
2008年 | 292篇 |
2007年 | 337篇 |
2006年 | 243篇 |
2005年 | 238篇 |
2004年 | 237篇 |
2003年 | 244篇 |
2002年 | 274篇 |
2001年 | 263篇 |
2000年 | 167篇 |
1999年 | 155篇 |
1998年 | 162篇 |
1997年 | 128篇 |
1996年 | 126篇 |
1995年 | 90篇 |
1994年 | 109篇 |
1993年 | 116篇 |
1992年 | 131篇 |
1991年 | 98篇 |
1990年 | 109篇 |
1989年 | 137篇 |
1988年 | 122篇 |
1987年 | 146篇 |
1986年 | 135篇 |
1985年 | 126篇 |
1984年 | 122篇 |
1983年 | 84篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1975年 | 12篇 |
1974年 | 17篇 |
1973年 | 11篇 |
排序方式: 共有6799条查询结果,搜索用时 0 毫秒
31.
The modified wave and scattering operators are shown to be bounded between weighted L
2-spaces for two-body Schrödinger operators with long range potentials. 相似文献
32.
锰结核中硅,铝,铁,镁,磷,钾,锰,钛的XRFA 总被引:1,自引:0,他引:1
本文叙述了用XRF分析锰结核中Si、Al、Fe、Mg、P、K、Mn和Ti的方法。按照通常锰结核的主次成分制备6个人工合成标准,根据Sherman方程计算了已知成分(二元系统)的相对强度。用L-T方求得了互致元素校正的理论α系数(基本的、混合的、修正的),用DATAFLEX151B计算机以BASIC语言汇了“PRA,APU”计算机程序。然后进行非线性回归分析了锰结核样品得到了满意的结果。 相似文献
33.
34.
Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni–P based composition coatings. In this paper, the electroless Ni–P, Ni–P-surfactant, Ni–Cu–P, Ni–P–PTFE and Ni–Cu–P–PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni–P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni–P matrixes has no significant influence on the surface free energy of the coatings. 相似文献
35.
Relativistic treatment of the spin-zero particles subject to the second Poschl-Teller-like potential 下载免费PDF全文
The three-dimensional Klein-Gordon equation is solved for the case of equal vector and scalar second Poschl-Teller potential by proper approximation of the centrifugal term within the framework of the asymptotic iteration method. Energy eigenvalues and the corresponding wave function are obtained analytically. Eigenvalues are computed numerically for some values of n and It is found that the results are in good agreement with the findings of other methods for short-range potential. 相似文献
36.
ICP-AES测定铜合金中的铜及10种杂质元素 总被引:1,自引:0,他引:1
建立了ICP-AES同时测定铜合金中铜及杂质元素磷、硅、锰、铁、镍、钴、锌、铅、铝、锡11种元素的分析方法,通过对样品溶解方法、元素分析谱线的选择和仪器分析参数进行试验比较,确定了实验条件,并对铜合金标准样品进行了精密度和回收率实验.结果表明,相对标准偏差小于3.0%,回收率在90%-110%之间.该方法快速简便,准确度高,可以满足日常检验的分析要求. 相似文献
37.
38.
赵志伟 《光谱学与光谱分析》2002,22(6):895-897
在化学发光分析中,常常要用到碱性条件下鲁米诺与过氧化氢的反应系统,通过催化剂辣根过氧化物酶使反应顺利进行。如果再加入适当的增强剂,则灵敏度提高且发光时间延长,可改善测定的重现性。实验证明,对位酚类衍生物,如:对叔丁基苯酚,对甲苯酚的发光增强作用明显,其发光效率可上升几十倍,发光时间也获得有效延长。 相似文献
39.
The phase behavior of four homologous compounds of 4-n-nonyl-, 4-n-decyl-, 4-n-undecyl-, and 4-n-dodecyl-4′-isothiocyanatobiphenyl (9BT, 10BT, 11BT, and 12BT) was re-investigated to characterize their high-pressure mesophases under pressures up to 150 MPa using a polarizing optical microscope equipped with a high-pressure optical cell and a wide-angle X-ray diffractometer equipped with a high-pressure sample vessel. The pressure-induced mesophases of 9BT and 10BT appearing under pressures above about 60 and 100 MPa, respectively, were identified as nematic (N) and SmA phases, which indicate the reversible Cr–CrE–N–I and Cr–CrE–SmA–I phase transitions under elevated pressure. 11BT and 12BT exhibited the reversible transition of Cr–CrE–SmA–I in the low-pressure regions below about 5 and 23 MPa, respectively. Both the stable CrE phases changed into the monotropic (and metastable) one under higher pressures, in which the Cr–SmA–I and I–SmA–CrE–Cr phase transitions on heating and cooling processes, respectively, were recognized. 相似文献
40.
Gravimetric measurements of thermodesorption of n-hexane and n-heptane were performed under quasi-equilibrium conditions. Differential thermodesorption profiles for ZSM-5 and ZSM-11 showed two peaks, but for Y zeolites, only one thermodesorption peak was observed. A model function, derived from the Langmiur adsorption model, was fitted to the experimental data, and the model parameters (the adsorption entropy and enthalpy) were estimated. The two-step desorption profiles observed for ZSM-5 and ZSM-11 were attributed to the commensurate freezing effect, i.e. a transition in the adsorbed phase resulting in ordering of the adsorbed molecules in the zeolite channels. The results observed for ZSM-11 indicate that the zigzag channels typical for ZSM-5 micropore system are not necessary for this transition to occur. 相似文献