全文获取类型
收费全文 | 3475篇 |
免费 | 559篇 |
国内免费 | 363篇 |
专业分类
化学 | 574篇 |
晶体学 | 36篇 |
力学 | 359篇 |
综合类 | 22篇 |
数学 | 44篇 |
物理学 | 2245篇 |
综合类 | 1117篇 |
出版年
2024年 | 14篇 |
2023年 | 28篇 |
2022年 | 47篇 |
2021年 | 80篇 |
2020年 | 73篇 |
2019年 | 60篇 |
2018年 | 68篇 |
2017年 | 92篇 |
2016年 | 100篇 |
2015年 | 132篇 |
2014年 | 131篇 |
2013年 | 198篇 |
2012年 | 163篇 |
2011年 | 224篇 |
2010年 | 151篇 |
2009年 | 230篇 |
2008年 | 239篇 |
2007年 | 245篇 |
2006年 | 257篇 |
2005年 | 233篇 |
2004年 | 212篇 |
2003年 | 170篇 |
2002年 | 181篇 |
2001年 | 153篇 |
2000年 | 145篇 |
1999年 | 113篇 |
1998年 | 101篇 |
1997年 | 81篇 |
1996年 | 80篇 |
1995年 | 75篇 |
1994年 | 56篇 |
1993年 | 57篇 |
1992年 | 36篇 |
1991年 | 34篇 |
1990年 | 31篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有4397条查询结果,搜索用时 0 毫秒
101.
D. Husain J. Lei F. Castao M. N. Snchez Rayo 《Journal of photochemistry and photobiology. A, Chemistry》1999,120(3):151-159
The collisional behaviour of Ba[6s5d(3DJ)], 1.151 eV above the 6s2(1S0) electronic ground state, in the presence of atomic strontium, has been investigated in the ‘long-time domain' (ca. 100 μs–1 ms) following the pulsed dye-laser excitation of barium vapour at elevated temperature at λ = 553.5 nm (Ba[6s6p(1P1)] ← Ba[6s2(1S0)]. Ba(3DJ) is subsequently produced from the short-lived 1P1 state (τe = 8.37 ± 0.38 ns) by a number of radiative and collisional processes. It may then be monitored in the ‘long-time domain' by atomic spectroscopic marker methods involving either collisional activation of Ba(3DJ) by Ba(1S0) and He buffer gas to yield Ba[6s6p(3PJ)] with subsequent emission from the 3P1 state (τe = 1.2 ± 0.1 μs): Ba[6s6p(3P1)] → Ba[6s2(1S0)] + hv (λ = 791.1 nm). Alternatively, emission from Ba(1P1) may be monitored at long times following the generation of this short-lived state by energy pooling following self-annihilation of Ba(3DJ) + Ba(3DJ) from Ba[6s6p(1P1)] → Ba[6s2(1S0)] + hv (λ = 553.5 nm). The generation of Ba(3DJ) in the presence of atomic strontium yields emission in the long-time domain from Sr[5s5p(3P1)] (τe = 19.6 μs): Sr[5s5p(3P1)] → Sr[5s2(1S0)] + hv (λ = 689.3 nm). Whilst the decay profiles at short times are complex in form, at long times all these atomic profiles show first-order kinetic removal with the decay coefficients for λ = 791.1 nm, 689.3 nm and 553.5 nm emissions in the ratio 1 : 2 : 2, consistent with overall third-order activation of the form: Ba(3DJ) + Ba(3DJ) + Sr(1S0) → Sr(3PJ) + 2Ba(1S0). The mechanism is modelled in detail, including measurement of integrated emission intensities, yielding kinetic data for fundamental collisional processes. The overall rate constant for the third-order collisional activation of Sr[5s5p(3PJ])from 2Ba[6s5d(3DJ)] + Sr[5s2(1S0)] takes the upper limit of 5.8 × 10−27 cm6 atom−2 s−1 (T = 900 K). The rate constant for the two body collisional quenching of Ba[6s5d(3DJ)] by ground state atomic strontium, Sr[5s2(1S0)], is found to be (2.0 ± 0.1) × 10−12 cm3 atom−1 s−1 (T = 900 K). 相似文献
102.
A stretch vibration Hamiltonian of H_2O has been derived by using the second quantization, unitary transformations and the optimization of coefficients. The energy spectrum obtained from this Hamiltonian is in good agreement with that of experiments. The multiphoton excitation and the energy absorption of H_2O in intense laser fields have been calculated. 相似文献
103.
An Assembled Nanocomplex for Improving both Therapeutic Efficiency and Treatment Depth in Photodynamic Therapy 下载免费PDF全文
Hongqian Cao Dr. Lei Wang Dr. Yang Yang Dr. Juan Li Dr. Yanfei Qi Yue Li Ying Li Dr. Hao Wang Prof. Dr. Junbai Li 《Angewandte Chemie (International ed. in English)》2018,57(26):7759-7763
Photodynamic therapy (PDT) shows unique selectivity and irreversible destruction toward treated tissues or cells, but still has several problems in clinical practice. One is limited therapeutic efficiency, which is attributed to hypoxia in tumor sites. Another is the limited treatment depth because traditional photosensitizes are excited by short wavelength light (<700 nm). An assembled nano‐complex system composed of oxygen donor, two‐photon absorption (TPA) species, and photosensitizer (PS) was synthesized to address both problems. The photosensitizer is excited indirectly by two‐photon laser through intraparticle FRET mechanism for improving treatment depth. The oxygen donor, hemoglobin, can supply extra oxygen into tumor location through targeting effect for enhanced PDT efficiency. The mechanism and PDT effect were verified through both in vitro and in vivo experiments. The simple system is promising to promote two‐photon PDT for clinical applications. 相似文献
104.
Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of
riboflavin (RF, vitamin B2) were studied in detail in aqueous solution. The excited triplet state of riboflavin (3RF*) was produced with 337 nm laser, while under 248 nm irradiation, both3RF* and hydrated electron (eaq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity
of3RF* including energy transfer, electron transfer and hydrogen abstraction. The RF·+ was generated by oxidation of SO4
·-radical with the aim of confirming the results of photolysis. 相似文献
105.
柱前衍生—反相高效液相色谱法测定钢铁及合金中铌 总被引:1,自引:0,他引:1
建立了反相液相色谱法测定钢铁及合金中铌的分析方法。采用HNO3 HF H2 SO4 溶解样品 ,用酒石酸络合铌 ,以 2 (5 溴 2 吡啶偶氮 ) 5 二乙基氨基酚为柱前衍生试剂 ,在C18柱上用甲醇 水 (体积比为 5 6∶4 4 )为流动相 ,其中含 0 .0 1mol·L- 1pH为 3.5的HOAc NaOAc缓冲液。在60 0nm处测定了铌的配合物 ,方法检出限为 1.5 μg·g- 1。应用此法直接测定了合金铸铁和中低合金钢样品中铌 ,其加标回收率为 96.8%~ 10 3.2 % 相似文献
106.
Quantum equations of motion describing the energy transfer dynamics via intramolecular anharmonic coupling are presented and solved numerically. Dynamical features of the average excitations of a homogeneous system (SF6) and a heterogeneous system (H/W) are quantitatively discussed in terms of the intramolecular vibrational relaxation (IVR) rates. Possible mechanisms of surface-enhanced desorption via low-power laser radiation are proposed.This work was supported in part by the Office of Naval Research, the Air Force Office of Scientific Research (AFSC), United States Air Force, under Grant AFOSR-82-0046 and the National Science Foundation under Grant No. CHE-8022874Camille and Henry Dreyfus Teacher-Scholar (1975–82) 相似文献
107.
Applied Biochemistry and Biotechnology - 相似文献
108.
用磁控溅射法在Si(111)基片上以不同溅射功率沉积LaNiO3(LNO)薄膜,基片温度370℃,对沉积的薄膜样品进行快速热退火处理(500℃,10min)。使用电感耦合等离子体原子发射光谱(ICP-AES)精确测量不同溅射功率沉积的LNO薄膜退火前后的组分情况。分析发现:LNO薄膜经退火处理后,其中的Ni/La的比值随着溅射功率增大而越接近理想比1:1,其导电性能也越好。另外,我们以相同工艺制备了不同厚度的LNO薄膜顶电极,四探针电阻测试仪和红外椭圆偏振光谱仪测试其电学与红外吸收性能,实验发现:(1)LNO薄膜的电阻率随膜厚的增加而降低,在大约300nm厚时略又有增加趋势;(2)LNO薄膜的红外吸收系数随其厚度的增加而增加,且随红外波长的增大而减小。 相似文献
109.
4G手机无线接入系统设计及实现 总被引:1,自引:0,他引:1
用射频微波电路集成技术设计第4代(4G)手机无线接入系统.从分布参数概念出发,主要在smith圆图上进行电路设计.由微带线进行电路的实现,电路将各功能单元集成在微带基板上,具有体积小、重量轻、可靠性高、与手机其他电路易于共形等特点.运用网络转移参量矩阵理论进行了系统响应预估,结果表明所设计的无线接入系统满足4G移动终端的性能要求. 相似文献
110.
阿肯江·托呼提 《新疆大学学报(理工版)》2005,22(2):237-242
应用弹塑性时程分析方法研究了组合墙结构在竖向和水平地震共同作用下的抗震性能.研究结果表明结构的最大层间位移由于受到竖向地震的影响有向结构中部转移的趋势.而且,层间位移增大. 相似文献