全文获取类型
收费全文 | 16675篇 |
免费 | 2570篇 |
国内免费 | 1498篇 |
专业分类
化学 | 5071篇 |
晶体学 | 150篇 |
力学 | 2901篇 |
综合类 | 277篇 |
数学 | 5574篇 |
物理学 | 6770篇 |
出版年
2024年 | 24篇 |
2023年 | 204篇 |
2022年 | 398篇 |
2021年 | 465篇 |
2020年 | 414篇 |
2019年 | 400篇 |
2018年 | 420篇 |
2017年 | 672篇 |
2016年 | 809篇 |
2015年 | 693篇 |
2014年 | 874篇 |
2013年 | 1383篇 |
2012年 | 933篇 |
2011年 | 983篇 |
2010年 | 858篇 |
2009年 | 1032篇 |
2008年 | 1065篇 |
2007年 | 1074篇 |
2006年 | 911篇 |
2005年 | 755篇 |
2004年 | 728篇 |
2003年 | 698篇 |
2002年 | 628篇 |
2001年 | 481篇 |
2000年 | 503篇 |
1999年 | 461篇 |
1998年 | 421篇 |
1997年 | 322篇 |
1996年 | 291篇 |
1995年 | 279篇 |
1994年 | 232篇 |
1993年 | 158篇 |
1992年 | 122篇 |
1991年 | 128篇 |
1990年 | 95篇 |
1989年 | 85篇 |
1988年 | 89篇 |
1987年 | 70篇 |
1986年 | 53篇 |
1985年 | 85篇 |
1984年 | 51篇 |
1983年 | 31篇 |
1982年 | 56篇 |
1981年 | 38篇 |
1980年 | 50篇 |
1979年 | 56篇 |
1978年 | 39篇 |
1977年 | 38篇 |
1976年 | 40篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 552 毫秒
71.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
72.
Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase. 相似文献
73.
74.
75.
Y. Yavin 《Journal of Optimization Theory and Applications》1993,78(1):77-91
Stochastic optimal control techniques are applied to compare the performance of identical medium-range air-to-air missiles which have different thrust-mass profiles. The measure of the performance is the probability of reaching a lock-on-point with a favorable range of guidance and flight parameters, during a fixed time interval [0,t
f
], given that, during the flight, the trajectories of the missile are subjected to a variety of constraints including dynamic pressure constraints. 相似文献
76.
一种改进的计算探测器校正因子的相关抽样方法 总被引:1,自引:0,他引:1
对于小尺寸探测器处于大块介质的情形, 在探测器的校正因子的Monte Carlo模拟中, 存在两个难题: 一是由于探测器尺寸很小粒子难以到达探测器并发生碰撞; 二是两个随机变量比值难以达到要求精度. 本文使用经过改进的粒子碰撞自动重要抽样方法, 再结合相关抽样方法, 解决了这两个难题, 并在MCNP-4C程序平台上加以实现. 除了粒子碰撞自动重要抽样以外, 还选用了其他3种方法: 直接模拟、区域分裂、强迫碰撞+Dxtran球分别与相关抽样方法结合, 对一个简化的探测器校正因子计算模型进行了计算. 实际计算结果表明, 相关抽样方法无论与哪种方法结合, 都起到了提高相关量计算效率的作用; 而它与粒子碰撞自动重要抽样结合, 比其他方法具有明显的优越性. 相似文献
77.
Longlan Cui Hong Xu Ping He Keiko Sumitomo Yoshinori Yamaguchi Hongchen Gu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5285-5295
A hybrid emulsion polymerization was formulated for synthesizing Fe3O4/polystyrene composite latex. This system, containing binary droplets that are magnetic (Mag)‐droplets with a diameter of 100–200 nm and styrene (St)‐droplets with a diameter of 3–4 μm, was obtained by mixing Mag‐miniemulsion and St‐macroemulsion. With extremely low surfactants concentration (?critical micelle concentration, CMC), the nucleated loci are selectively controlled in the Mag‐droplets, as the result of smaller droplet size and larger surface ratio. Both water‐soluble potassium persulfate (KPS) and oil‐soluble 2,2′‐azobis(2‐isobutyronitrile) was adopted to initiate the polymerization. In the presence of KPS, magnetic polystyrene latices with particles size of 60–200 nm, narrow size distribution, and high magnetite content (86 wt % measured by TGA) were attained successfully. The synthesized magnetic Fe3O4/polystyrene latices assembled into well‐ordered hexagonal structure in the surface of a carbon supported copper grid. The influence of various parameters on various aspects of the as‐synthesized Fe3O4/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag‐miniemulsion and St‐macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5285–5295, 2007 相似文献
78.
Jae-Yeon Lee Eugene Lubarsky Ben T. Zinn 《Proceedings of the Combustion Institute》2005,30(2):1757-1764
This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which “instantaneously” change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach was to break up the feedback between the combustion process heat release and combustor pressure oscillations that drive the instability by changing the characteristics of the combustion process (e.g., the characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (NanomiserTM), which can vary its fuel spray properties, to investigate the dependence of acoustics–combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. This study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using combustion zone chemiluminescence distributions, which were obtained by Abel’s deconvolution synchronized with measured acoustic data, it has been shown that the instabilities were mostly driven midway between the combustor centerline and wall, a short distance downstream from the flame holder, where the mean axial flow velocity is approximately zero in the vortex near the flame holder. The results of this study strongly suggest that a “slow” active control system that employs controllable fuel injectors could be effectively used to prevent the onset of detrimental combustion instabilities. 相似文献
79.
对拟线性椭圆变分不等式的障碍最优控制问题(即以障碍为控制变量)进行了研究.指标泛函为Lagrange型,其中含有控制变量二阶导数的p次幂,这使得最优性条件的推导颇为不易.对所考虑的问题给出了最优控制的存在性定理以及必要条件. 相似文献
80.
在非线性项满足全局Lipschitz条件下,本文研究了一类It型非线性时滞关联随机大系统的分散鲁棒控制问题.系统的时滞是关于状态和控制输入的.基于Lyapunov泛函及线性矩阵不等式(LMI)的分析方法,得到了无记忆状态反馈控制器使整个时滞关联随机大系统可镇定的充分条件. 相似文献