全文获取类型
收费全文 | 4997篇 |
免费 | 484篇 |
国内免费 | 740篇 |
专业分类
化学 | 4666篇 |
晶体学 | 74篇 |
力学 | 11篇 |
综合类 | 20篇 |
数学 | 8篇 |
物理学 | 1442篇 |
出版年
2024年 | 7篇 |
2023年 | 35篇 |
2022年 | 146篇 |
2021年 | 94篇 |
2020年 | 162篇 |
2019年 | 152篇 |
2018年 | 116篇 |
2017年 | 146篇 |
2016年 | 175篇 |
2015年 | 179篇 |
2014年 | 220篇 |
2013年 | 477篇 |
2012年 | 284篇 |
2011年 | 266篇 |
2010年 | 226篇 |
2009年 | 269篇 |
2008年 | 317篇 |
2007年 | 333篇 |
2006年 | 295篇 |
2005年 | 270篇 |
2004年 | 248篇 |
2003年 | 233篇 |
2002年 | 171篇 |
2001年 | 202篇 |
2000年 | 146篇 |
1999年 | 172篇 |
1998年 | 133篇 |
1997年 | 94篇 |
1996年 | 98篇 |
1995年 | 94篇 |
1994年 | 71篇 |
1993年 | 67篇 |
1992年 | 63篇 |
1991年 | 41篇 |
1990年 | 26篇 |
1989年 | 33篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有6221条查询结果,搜索用时 15 毫秒
91.
本文用多组态HXR自洽场方法和优化以Slater径向积分法相结计算了类锂离子(Z=13~17,19)1s~2nl~2LJ(2≤n≤5,0≤l≤4)能级之间的跃迁波长和振子强度,并和实验进行了比较。就软X射线激光跃迁4f—3d而言,本文计算的波长值比其它文献的计算值更接近于观测值。 相似文献
92.
利用离子注入机所产生的低能N+模仿宇宙中低能离子作用于人宫颈癌细胞(HeLa cell),探索其对人类细胞的影响及作用机制。因实验中的低能离子产生和加速要在真空中进行,细胞在离子注入同时将受到真空的影响,为此研究人员利用石蜡油保护细胞以防止注入时的水份蒸发。注入处理完毕后收集细胞,采用傅里叶变换红外光谱法(FTIR)分析真空和低能N+束注入后细胞中大分子的相对含量、构型及其构象变化等方面的信息。结果表明:(1)不同处理后的样品在3 300 cm-1附近吸收谱带存在明显差异。对照样品的特征峰位为3 300 cm-1,而其他样品中除了注入5×1014 N+·cm-2外,红外吸收峰均向长波数方向移动,真空2×1015 N+·cm-2样品的频移尤为明显至3 420 cm-1处。(2)与对照样品相比较,各处理样品的1 378 cm-1处吸收峰峰位均向长波数方向频移。(3)处理样品相对于对照样品而言,2 360 cm-1处吸收峰均向长波数方向移动。该结果说明低能离子注入处理可以引起细胞中核酸、蛋白的含量和构象变化。 相似文献
93.
In the system with two two-level ions confined in a linear trap,
this paper presents a simple scheme to realize the quantum phase
gate (QPG) and the swap gate beyond the Lamb--Dicke (LD) limit.
These two-qubit quantum logic gates only involve the internal states
of two trapped ions. The scheme does not use the vibrational mode as
the data bus and only requires a single resonant interaction of the
ions with the lasers. Neither the LD approximation nor the auxiliary
atomic level is needed in the proposed scheme. Thus the scheme is
simple and the interaction time is very short, which is important in
view of decoherence. The experimental feasibility for achieving this
scheme is also discussed. 相似文献
94.
Enhanced field ionization of water adsorbed on a carbon monoxide-covered, platinum field emitter tip
R. Manghani 《Surface science》2009,603(1):165-172
The influence of carbon monoxide, adsorbed on a platinum field emitter tip, on field ionization of adsorbed water was examined. Ramped field desorption (RFD) measurements of water ionization were performed at 108 K for water layer thicknesses up to 80 ML on a clean or CO-saturated tip surface. In RFD the applied field is ramped linearly in time until water ionization is detected, giving the onset field of ionization. Water ionization yields hydrated hydroxide ions and protons; the hydroxide ions remain within the water layer on the tip, while the hydrated protons are emitted into vacuum. At a low water coverage of 1.5 ML, the CO adlayer substantially reduced the onset field of ionization (that is, facilitated ionization) of water by 40%, from a value of 0.43 V/Å for water on clean Pt to 0.26 V/Å for water on CO-covered Pt. The extent of the reduction gradually diminished with thicker coverages of water and was absent at coverages of 20 ML or greater. The characteristic decay length of the field enhancement was 4.7 ± 1 ML. The results were analyzed with the charge exchange model of ionization kinetics and changes in dipole moments of water adsorbed without and with CO. The analysis reveals that a change in water structure (dipole moment) caused by CO is an important contributor in field enhancement and that the dipole moment for hydrated hydroxide ion in an ice-like layer must be greater than that for bulk ice-like water. The significance of these results with respect to electrochemical oxidation of CO is discussed. 相似文献
95.
S.P. Feofilov A.A. Kaplyanskii A.B. Kulinkin R.I. Zakharchenya 《Journal of luminescence》2009,129(12):1689-1691
The results of optical studies of Cr3+ and Eu3+ ions doped nanocrystalline ferroelectric BaTiO3 produced by the sol-gel process (particle size 20-40 nm) are reported. The Cr3+ impurity ions 2E-4A2 (R-lines) fluorescence spectra in BaTiO3 revealed significant differences from that reported in literature for the bulk material. At least three types of Cr3+ centers were found in the spectra. The temperature dependence of optical second harmonic generation in nanocrystalline BaTiO3: Eu3+ shows a strong hysteresis in C4v-Oh ferroelectric phase transition region, which was explained by the ordering effects in the system of electric dipole moments of dipole nanocrystals. The temperature dependencies of radiative lifetime of Eu3+5D0 excited level reveal some hysteresis too. The possibility of influence of the ordering in the system of BaTiO3:Eu3+ nanocrystals on the effective index of refraction of the medium and thus on the Eu3+5D0 radiative lifetime, due to the local field effects is discussed. 相似文献
96.
Roberto M. Serikawa Masahiro Isaka Qinqquan Su Takashi Usui Tatsuya Nishimura Hirokazu Sato 《高压研究》2013,33(1-6):477-489
Abstract Electrochemical evolution of hydrogen gas, oxygen gas and chlorine at the electrodes is the usual reaction in conventional electrolysis of aqueous salt solution. However, here we demonstrate that the electrolysis governing reaction in hydrothermal solutions is different from the electrolysis performed at atmospheric pressure and temperatures up to 100°C. Experimental electrolytic reaction of aqueous salt solution carried out inside a sealed 300-mL batch autoclave showed that; accumulation of hydrogen gas, oxygen gas and chlorine is highly suppressed under hydrothermal (250°C and 7 MPa) conditions. We have also observed that, when organics are present in the aqueous salt solution being hydrothermally electrolyzed, an effective oxidation of organics is accomplished. Furthermore, for hydrothermal electrolytic oxidation (HEO) with oxygen gas added, experimentally observed TOC removal profile demonstrates apparent anodic oxidation electrical current efficiency of almost 200% for highconcentrated acetic acid solutions. 相似文献
97.
The 6.4 GHz ECR ion source that was indigenously developed a few years ago has been operating continuously for injecting oxygen
and neon beams to the cyclotron since 1997. VEC-ECR is a single stage high magnetic field ion source provided with a negatively
biased electron repeller placed on the axis, near the injection mirror point. The supply of cold electrons and use of low
mass mixing gas improve the stability of ECR plasma. Very recently, the effect of aluminum oxide coating on the copper plasma
chamber wall has been studied. The plasma chamber wall was coated with aluminum by vacuum evaporation method and then exposed
to oxygen gas to form aluminum oxide. It was noticed that the process substantially shifts the charge state distribution to
the higher charge state with an enhancement of ion current by an order of magnitude. With the aluminized plasma chamber, the
VEC-ECR can now produce 12 μA of O7+, 6.5 μA of Ar12+, 1.5 μA of Kr20+ and 1.0 μA of Xe31+. 相似文献
98.
99.
勾秉聪 《原子与分子物理学报》1997,14(4):505-510
采用马鞍点变分方法和复数转动技术,计算了类锂离子2s2p2p2S三激发共振态的能量,并运用截断变分方法得到能量改进量,以及计算了相对论效应、质量极化效应,从而获得了高精度的能量计算值。还计算了该系统的Auger宽度,位移和辐射跃迁率。 相似文献
100.
Jian-Ping Li Lian-Zhong Deng Ye Zheng Peng-Peng Ding Tian-Qing Jia Zhen-Rong Sun Jian-Rong Qiu Shi-An Zhang 《Frontiers of Physics》2020,15(2):22603-68
The spectral phase of the femtosecond laser field is an important parameter that affects the up-conversion(UC)luminescence efficiency of dopant lanthanide ions.In this work,we report an experi-mental study on controlling the UC lmiiinescence efficiency in Sm^3+:NaYF4 glass by 800-nm femtosec-ond laser pulse shaping using spectral phase modulation.The optimal phase control strategy efficiently enhances or suppresses the UC luminescence intensity.Based on the laser-power dependence of the UC luminescence intensity and its comparison with the luminescence spectrum under direct 266-nm fem-tosecond lciser irradiation,we propose herein an excitation model combining non-resonant two-photon absorption with resonance-media ted three-photon absorption to explain the experimental observations. 相似文献