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991.
采用密度泛函理论的COSMO模型模拟了在DMF溶剂中三种不同体积的钯配体Pd(PR3)n (n=1,2) (PR3=PH3, PMe3, PtBu3)与溴苯氧化加成的反应过程. 对比双配体Pd(PR3)2的裂解能以及双配体钯Pd(PR3)2和单配体钯Pd(PR3)氧化加成过程的能垒;结果表明,小体积的配体PH3和PMe3是以双配位的形式参加氧化加成过程的,而较大体积的配体PtBu3是以单配位钯的形式参加氧化加成过程的. 相似文献
992.
Shear Thickening Fluids Based on Additives with Different Concentrations and Molecular Chain Lengths 总被引:1,自引:0,他引:1
将二氧化硅颗粒和不同分子链长添加剂颗粒分散到聚乙二醇分散介质中制得剪切增稠液样品,研究了添加剂的不同含量和不同分子链长对剪切增稠液流变性能的影响. 对其流变特性的研究表明,随着添加剂含量的增加和分子链长的增长,样品的剪切增稠效应增强明显,并用大粒子簇的形成对增强机理给出了合理的解释. 相似文献
993.
This paper investigates the two species totally asymmetric simple exclusion process (TASEP) with constrained boundaries and site sharing in a one-lane system. The model is reminiscent of pedestrian traffic crossing a narrow pathway in both directions. In boundaries, particles can enter the system only if the corresponding sites are empty. The new aspect of this study compared to previous two species TASEP models is that the oppositely moving particles do not exchange their positions each other but by sharing the same site. Monte Carlo simulations have shown that the spontaneous symmetry breaking is observed in high-low-density phase and asymmetric low-low-density phase. The flipping processes are also observed in both phases. The maximal current phase appears for sufficiently large sharing probability. Histograms of two species of particles and average currents are computed. The results are also compared with the Bridge model [Evans et al., Phys. Rev. Lett. 74 (1995) 208] which means that two species of particles can exchange their positions with a certain probability when they meet together. It is shown that our model exhibits higher current than that in the Bridge model. 相似文献
994.
The object of this paper is to reveal the relation between dynamics of the fractional system and its dimension defined as a sum of the orders of all involved derivatives. We take the fractional Lorenz system as example and regard one or three of its orders as bifurcation parameters. In this framework, we compute the corresponding bifurcation diagrams via an optimal Poincaré section technique developed by us and find there exist two routes to chaos when its dimension increases from some values to 3. One is the process of cascaded period-doubling bifurcations and the other is a crisis (boundary crisis) which occurs in the evolution of chaotic transient behavior. We would like to point out that our investigation is the first to find out that a fractional differential equations (FDEs) system can evolve into chaos by the crisis. Furthermore, we observe rich dynamical phenomena in these processes, such as two-stage cascaded period-doubling bifurcations, chaotic transients, and the transition from coexistence of three attractors to mono-existence of a chaotic attractor. These are new and interesting findings for FDEs systems which, to our knowledge, have not been described before. 相似文献
995.
As huge complex systems consisting of geographic regions, natural resources, people and economic entities, countries follow the allometric scaling law which is ubiquitous in ecological, and urban systems. We systematically investigated the allometric scaling relationships between a large number of macroscopic properties and geographic (area), demographic (population) and economic (GDP, gross domestic production) sizes of countries respectively. We found that most of the economic, trade, energy consumption, communication related properties have significant super-linear (the exponent is larger than 1) or nearly linear allometric scaling relations with the GDP. Meanwhile, the geographic (arable area, natural resources, etc.), demographic (labor force, military age population, etc.) and transportation-related properties (road length, airports) have significant and sub-linear (the exponent is smaller than 1) allometric scaling relations with area. Several differences of power law relations with respect to the population between countries and cities were pointed out. First, population increases sub-linearly with area in countries. Second, the GDP increases linearly in countries but not super-linearly as in cities. Finally, electricity or oil consumption per capita increases with population faster than cities. 相似文献
996.
光纤加速度传感器研究进展 总被引:5,自引:0,他引:5
光纤加速度传感器与传统加速度传感器相比,不但能抗电磁干扰,而且体小、质轻、动态范围宽、精度高、能在恶劣环境下工作,因此受到各先进国家军事与商业领域的极大重视,各种实用的光纤加速度传感器不断涌现。主要有光强调制型和相位调制型两大类。光强调制式有反射式、透射式和偏振式等等。相位调制式有Mach-Zender干涉仪、Michelson干涉仪和Fabry-Perot干涉仪。有一维的,也有二维的;有与水听器组合在一起的,也有与光纤陀螺仪组合的光纤加速度传感器。最小的已经做到2.5cm长,直径仅0.25mm;测量精度已能达到1μg;共振频率可达到10kHz。为了克服温度不稳定性对测量精度的影响,人们采用了3×3耦合器解调法,双光路法,由单臂式改成推挽式等。一旦关键技术得以克服,光纤加速度传感器将会在惯性导航和其它领域发挥更重要的作用。本文将分别介绍目前各种类型光纤加速度传感器的结构、特点、走向实用化存在的问题。 相似文献
997.
本文采用了一种简单的功率监测法,观察了KrF准分子激光对掺锗光纤折射率影响的非线性过程。观察到子纤芯折射率扰动过程中非稳定现象、饱和现象和折射率扰动的非线性。 相似文献
999.
应用微扰展开法了“跳跃模型”给出了空间电荷场前三阶分量随时间,外加电场等变化的解析表达式,同时讨论了外加电场对各阶空间电荷场建立的影响,当扩散与外加电场可比拟时,外加电场对空间电荷场的影响不大,随着空间电荷场阶数的提高,其达到最大饱和值所需的外加电磁越小,在外加电场作用下,空间电荷场各阶分量随时间呈振荡衰减,直到达到饱和,外加是场越大,振荡越强烈,周期越短,在考虑高阶分量的贡献后,空间电荷场的振荡 相似文献
1000.