全文获取类型
收费全文 | 10145篇 |
免费 | 1888篇 |
国内免费 | 2752篇 |
专业分类
化学 | 7703篇 |
晶体学 | 283篇 |
力学 | 615篇 |
综合类 | 238篇 |
数学 | 1461篇 |
物理学 | 4485篇 |
出版年
2024年 | 15篇 |
2023年 | 123篇 |
2022年 | 324篇 |
2021年 | 295篇 |
2020年 | 355篇 |
2019年 | 344篇 |
2018年 | 300篇 |
2017年 | 407篇 |
2016年 | 396篇 |
2015年 | 489篇 |
2014年 | 591篇 |
2013年 | 831篇 |
2012年 | 846篇 |
2011年 | 843篇 |
2010年 | 830篇 |
2009年 | 841篇 |
2008年 | 916篇 |
2007年 | 820篇 |
2006年 | 786篇 |
2005年 | 686篇 |
2004年 | 578篇 |
2003年 | 511篇 |
2002年 | 473篇 |
2001年 | 397篇 |
2000年 | 364篇 |
1999年 | 218篇 |
1998年 | 128篇 |
1997年 | 115篇 |
1996年 | 123篇 |
1995年 | 82篇 |
1994年 | 97篇 |
1993年 | 89篇 |
1992年 | 103篇 |
1991年 | 85篇 |
1990年 | 66篇 |
1989年 | 60篇 |
1988年 | 42篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1965年 | 6篇 |
1963年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
利用飞秒光学外差光学克尔效应技术获得了咪唑类离子液体1-丁基-3-甲基咪唑六氟磷酸盐([bmim][PF6])体系中反映分子间相互作用的低频光谱. 结果分析中, 利用Brownian振子时间相关函数的精确表达式对光学克尔效应动力学数据中的核振动部分进行模拟, 在时域上获得各个振动组分的时间演化行为, 并进而通过快速Fourier变换获得各个振动组分的频域光谱和总加和光谱. 此外还利用低频拉曼光谱技术测量了离子液体[bmim][PF6]的低频光谱, 并和飞秒光学外差光学克尔效应实验的结果进行对比, 发现两种方法获得的低频光谱相近. 实验结果表明Brownian振子时间相关函数的精确表达式可用来解析离子液体体系中低频振动的时间演化行为. 相似文献
962.
963.
Tailoring 3,3′‐Dihydroxyisorenieratene to Hydroxystilbene: Finding a Resveratrol Analogue with Increased Antiproliferation Activity and Cell Selectivity 下载免费PDF全文
Yan‐Fei Kang Wen‐Jing Yan Ting‐Wen Zhou Dr. Fang Dai Dr. Xiu‐Zhuang Li Xia‐Zhen Bao Yu‐Ting Du Cui‐Hong Yuan Hai‐Bo Wang Xiao‐Rong Ren Dr. Qiang Liu Dr. Xiao‐Ling Jin Prof. Dr. Bo Zhou Prof. Dr. Jie Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(29):8904-8908
Four novel compounds were designed by “tailoring” 3,3′‐dihydroxyisorenieratene (a natural carotenoid) based on an isoprene unit retention truncation strategy. Among them, the smallest molecule 1 (2,3,6,2′,3′,6′‐hexamethyl‐4,4′‐dihydroxy‐trans‐stilbene) was concisely synthesized in a one‐pot Stille–Heck tandem sequence, and surfaced as a promising lead molecule in terms of its selective antiproliferative activity mediated by blocking the NCI‐H460 cell cycle in G1 phase. Additionally, theoretical calculations and cell uptake experiments indicate that the unique polymethylation pattern of compound 1 significantly induces a conformational change shift out of planarity and increases its cell uptake and metabolic stability. The observation should be helpful to rationally design resveratrol‐inspired antiproliferative agents. 相似文献
964.
965.
966.
用双还原法制备三角形银纳米片及其光学性能 总被引:6,自引:0,他引:6
在硼氢化钠和柠檬酸三钠共存的体系中还原硝酸银, 以聚乙烯吡咯烷酮(PVP)为表面活性剂和保护剂, 水浴加热制备得到三角形银纳米片, 用X射线衍射(XRD)、透射电子显微镜(TEM)、紫外-可见(UV-Vis)吸收光谱、表面增强拉曼散射(SERS)光谱对其进行了表征. 结果表明: 三角形银纳米片产物为立方相金属银, 边长为(100±40) nm, 厚度为(10±5) nm; 产物表现出与球形银纳米粒子完全不同的吸收光谱; 柠檬酸根在银晶核不同晶面的选择吸附、PVP的包覆作用及Ag(111)晶面的层错对产物的形成起决定作用; 与球形纳米颗粒相比, 三角形银纳米片膜对吡啶(Py)分子有显著的SERS活性. 相似文献
967.
Resonance response of a single-degree-of-freedom nonlinear vibro-impact system to a narrow-band random parametric excitation 下载免费PDF全文
The resonant response of a single-degree-of-freedom nonlinear vibro-impact oscillator with a one-sided barrier to a narrow-band random parametric excitation is investigated. The narrow-band random excitation used here is a bounded random noise. The analysis is based on a special Zhuravlev transformation, which reduces the system to one without impacts, thereby permitting the applications of random averaging over "fast" variables. The averaged equations are solved exactly and an algebraic equation of the amplitude of the response is obtained for the case without random disorder. The methods of linearization and moment are used to obtain the formula of the mean-square amplitude approximately for the case with random disorder. The effects of damping, detuning, restitution factor, nonlinear intensity, frequency and magnitude of random excitations are analysed. The theoretical analyses are verified by numerical results. Theoretical analyses and numerical simulations show that the peak response amplitudes will reduce at large damping or large nonlinear intensity and will increase with large amplitude or frequency of the random excitations. The phenomenon of stochastic jump is observed, that is, the steady-state response of the system will jump from a trivial solution to a large non-trivial one when the amplitude of the random excitation exceeds some threshold value, or will jump from a large non-trivial solution to a trivial one when the intensity of the random disorder of the random excitation exceeds some threshold value. 相似文献
968.
We experimentally study the generation and storage of double slow light pulses in a Pr3+:Y2SiO5 crystal. Under electromagnetically induced transparency, a single signal pulse is stored in the spin coherence of the crystal. By simultaneously switching on two control fields to recall the stored information, the spin coherence is converted into two slow light pulses with distinct frequencies. Furthermore, the storage and controlled retrieval of double slow light pulses are obtained by manipulating the control fields. This study of double slow light pulses may have practical applications in information processing and all-optical networks. vspace2mm 相似文献
969.
970.
In situ energy dispersive x-ray diffraction for natural marmatite (Zn0.76Fe0.23S) is performed up to 17. 7 GPa and 623 K. It is fit, ted by the Birch-Murnaghan equation of state (EOS) that Ko and α0 for marmatite are 85(3)GPa and 0.79(16)*10^-4 K^-1, respectively. Fe^2+ isomorphic replacing to Zn^2+ in natural crystal is responsible for high bulk modulus and thermal expansivity of marmatite. Temperature derivative of bulk modulus (OK/OT)p for marmatite is fitted to be -0.044(23) GPaK^-1. The unambiguous B3-B1 phase boundaries for marmatite are determined to be Pupper(GPa)= 15.50 - 0.016T(℃) and Plower (GPa)=9.94-0.012T(℃) at 300-623K. 相似文献