全文获取类型
收费全文 | 26745篇 |
免费 | 5865篇 |
国内免费 | 3345篇 |
专业分类
化学 | 8818篇 |
晶体学 | 326篇 |
力学 | 2224篇 |
综合类 | 296篇 |
数学 | 3497篇 |
物理学 | 20794篇 |
出版年
2024年 | 48篇 |
2023年 | 275篇 |
2022年 | 574篇 |
2021年 | 697篇 |
2020年 | 825篇 |
2019年 | 616篇 |
2018年 | 662篇 |
2017年 | 828篇 |
2016年 | 1008篇 |
2015年 | 993篇 |
2014年 | 1449篇 |
2013年 | 2450篇 |
2012年 | 1633篇 |
2011年 | 1961篇 |
2010年 | 1721篇 |
2009年 | 1893篇 |
2008年 | 1931篇 |
2007年 | 1882篇 |
2006年 | 1785篇 |
2005年 | 1631篇 |
2004年 | 1412篇 |
2003年 | 1325篇 |
2002年 | 1233篇 |
2001年 | 959篇 |
2000年 | 937篇 |
1999年 | 811篇 |
1998年 | 720篇 |
1997年 | 572篇 |
1996年 | 500篇 |
1995年 | 365篇 |
1994年 | 355篇 |
1993年 | 295篇 |
1992年 | 264篇 |
1991年 | 213篇 |
1990年 | 158篇 |
1989年 | 184篇 |
1988年 | 113篇 |
1987年 | 105篇 |
1986年 | 90篇 |
1985年 | 101篇 |
1984年 | 63篇 |
1983年 | 37篇 |
1982年 | 69篇 |
1981年 | 41篇 |
1980年 | 31篇 |
1979年 | 30篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
Bruno Lengeler 《Mikrochimica acta》1987,91(1-6):455-475
The synchrotron radiation (SR) emitted by circulating high-energy electrons has extraordinary properties: The light is intensive and bright, it is tunable and highly collimated, and finally, it is linearly polarized. These exceptional properties have initiated a unique revival of many spectroscopies using electromagnetic radiation. The techniques of special concern for materials analysis which are treated in this article are: X-ray absorption, reflection, fluorescence, diffraction and topography. A number of examples will be given in order to illustrate the possibilities of these techniques when SR is used.On leave of absence from Institut für Festkörperforschung, KFA Jülich, D-5170 Jülich, Federal Republic of Germany 相似文献
22.
普遍认为分布函数f在容器壁上的取值为零,如果情况确实如此,则平衡分布函数在容器壁上将不连续,从而会产生不合理的结果.分析指出了在证明H定理时不应假定f在容器壁上为零. 相似文献
23.
使用SAC/SAC-CI方法,利用D95(d),6-311g**以及cc-PVTZ等基组,对B2分子的基态(X3Σg-)和第一激发态(A3Σu-)的平衡结构和谐振频率进行了优化计算.通过对3个基组的计算结果的比较,得出了D95(d)基组为3个基组中的最优基组的结论;使用D95(d)基组,利用SAC的GSUM(Group Sum of Operators)方法对基态(X3Σg-),SAC-CI的GSUM方法对激发态(A3Σu-)进行单点能扫描计算,用正规方程组拟合Murrell-Sorbie函数,得到了相应电子态的完整势能函数;从得到的势能函数计算了与基态(X3Σg-)和第一激发态(A3Σu-)相对应的光谱常数(Be,αe,ωe和ωeχe),结果与实验数据吻合. 相似文献
24.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
25.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献
26.
Michael R. Caputo 《Natural Resource Modeling》1989,3(2):241-259
This paper analyzes the extent to which standard dynamic renewable resource models possess refutable implications. Both the steady state comparative static and local comparative dynamic properties of the standard model are studied. A unified framework is developed which enables one to analyze the qualitative properties of any standard renewable resource model. This is achieved by explicitly linking the local stability, steady state comparative static, and local comparative dynamic properties of the model. 相似文献
27.
研究了V型三能级原子BEC与双模压缩光场相互作用系统中,忽略原子间相互作用和考虑原子间相互作用时光场的正交压缩和光子数压缩。结果表明,光场的正交压缩依赖于压缩参数,而光子数压缩与压缩参数、光场信号强度有关,在一定条件下,两种压缩可同时存在。原子间相互作用影响两种压缩的涨落随时间变化的周期,以及正交分量涨落随时间变化的幅度,而对光子数压缩涨落随时间变化的幅度几乎无影响。 相似文献
28.
Structural surface velocity distribution is often used to predict structural borne sound radiation. However the sampling interval of velocity should be chosen carefully to increase the prediction accuracy and to reduce the system cost. In this paper, several factors affecting the sampling interval are theoretically analyzed and discussed for a vibrating baffled rectangular plate. A new rule for the determination of the sampling interval is formulated. Using this rule, the results from both numerical simulations and experiments may be explained well. 相似文献
29.
30.
We have obtained expressions of the accelerating effect in Kerr-Newman Kasuya field. These expressionsinclude four parameters: mass m, angular momentum a, electric charge q, and magnetic charge φ. Furthermore we studyits special case (vi = 0). We get the following conclusion. In the gravitation field of souse mass with electric charge qand magnetic charge b, the acceleration of test particle has not only radial component but also transverse component.When θ = 0, the acceleration is minimum, and when θ = π/2, the acceleration is maximum. Furthermore, we discussthe effects of electric charge q and magnetic charge φ respectively. 相似文献