全文获取类型
收费全文 | 5650篇 |
免费 | 1040篇 |
国内免费 | 432篇 |
专业分类
化学 | 553篇 |
晶体学 | 14篇 |
力学 | 584篇 |
综合类 | 155篇 |
数学 | 4250篇 |
物理学 | 1566篇 |
出版年
2024年 | 11篇 |
2023年 | 54篇 |
2022年 | 106篇 |
2021年 | 131篇 |
2020年 | 172篇 |
2019年 | 158篇 |
2018年 | 148篇 |
2017年 | 239篇 |
2016年 | 246篇 |
2015年 | 165篇 |
2014年 | 335篇 |
2013年 | 509篇 |
2012年 | 297篇 |
2011年 | 351篇 |
2010年 | 340篇 |
2009年 | 392篇 |
2008年 | 390篇 |
2007年 | 367篇 |
2006年 | 327篇 |
2005年 | 308篇 |
2004年 | 234篇 |
2003年 | 266篇 |
2002年 | 207篇 |
2001年 | 202篇 |
2000年 | 178篇 |
1999年 | 178篇 |
1998年 | 140篇 |
1997年 | 110篇 |
1996年 | 78篇 |
1995年 | 86篇 |
1994年 | 65篇 |
1993年 | 30篇 |
1992年 | 27篇 |
1991年 | 25篇 |
1990年 | 14篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 28篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 12篇 |
1976年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有7122条查询结果,搜索用时 796 毫秒
91.
A. A. Tolstonogov 《Set-Valued Analysis》1998,6(2):129-147
Existence theorems of continuous selectors whose values are fixed points of multivalued contractions are proved. As an application, the existence of continuous selectors to generalized solution sets of partial differential inclusions, depending on a parameter, is obtained. 相似文献
92.
Hans van den Berg Michel Mandjes Rudesindo Núñez-Queija 《Operations Research Letters》2007,35(3):297-307
We study a processor-sharing model in which users choose between a high- and a low-priority service, based on their utility functions and prices charged by the service provider. The latter aims at revenue maximization. The model is motivated by file transmissions in data networks with distributed congestion control. 相似文献
93.
Positive periodic solution for a two-species ratio-dependent predator-prey system with time delay and impulse 总被引:1,自引:0,他引:1
A two-species ratio-dependent predator-prey model with time delay and impulse is investigated. By using the continuation theorem of coincidence degree theory, the existence of a positive periodic solution for this system is established. 相似文献
94.
Consider a queueing system where customers arrive at a circle according to a homogeneous Poisson process. After choosing their positions on the circle, according to a uniform distribution, they wait for a single server who travels on the circle. The server's movement is modelled by a Brownian motion with drift. Whenever the server encounters a customer, he stops and serves this customer. The service times are independent, but arbitrarily distributed. The model generalizes the continuous cyclic polling system (the diffusion coefficient of the Brownian motion is zero in this case) and can be interpreted as a continuous version of a Markov polling system. Using Tweedie's lemma for positive recurrence of Markov chains with general state space, we show that the system is stable if and only if the traffic intensity is less than one. Moreover, we derive a stochastic decomposition result which leads to equilibrium equations for the stationary configuration of customers on the circle. Steady-state performance characteristics are determined, in particular the expected number of customers in the system as seen by a travelling server and at an arbitrary point in time. 相似文献
95.
A. Saxena D. Fabris G. Prete D. V. Shetty G. Viesti B. K. Nayak D. C. Biswas R. K. Choudhury S. S. Kapoor M. Lunardon S. Moretto G. Nebbia S. Pesente V. Rizzi A. M. Samant M. Barbui E. Fioretto M. Cinausero A. Brondi G. La Rana R. Moro E. Vardaci N. Gelli F. Lucarelli 《Nuclear Physics A》2004,730(3-4):299-315
Pre-scission and post-scission multiplicities of neutrons and alpha particles have been simultaneously measured for the fission-like reactions of 340 MeV 28Si on 232Th. Dynamical model calculations using HICOL code predict that about 90% of the observed events are of quasi-fission type while the remaining 10% are from compound nucleus fission decay. Moving source fits were carried out to the observed neutron and alpha particle spectra, measured at different angles with respect to the fragment directions. The pre-scission and post-scission neutron multiplicities are deduced to be 8.7±2.0 and 9.4±2.0, respectively. The corresponding multiplicity values for alpha particles are found to be 0.22±0.08 and 0.1±0.03. From the measured post-scission neutron multiplicity, it is inferred that about 65±20 MeV of the initial excitation energy remains at scission. This may be compared to the value of 85±30 MeV estimated from PACE2 statistical model calculations, adjusted to reproduce the measured pre-scission neutron multiplicity. From a comparison of the Statistical Model predictions with the measured pre-scission neutron multiplicity, the fission delay is estimated to be of 5+7−3×10−20 s which overlaps with the average duration of fission-like process from the contact to the scission point (2×10−20 s) as determined from HICOL-based dynamical calculations. For the delay time deduced as above, the pre-scission alpha particle multiplicity calculated by the PACE2 code is about a factor two larger than the experimental one, demonstrating the difficulties in modelling the alpha particle emission from highly elongated shapes that characterize the fissioning system from the contact point to scission. 相似文献
96.
对一类遗传程序设计问题,提出了简单等长的分布式染色体,取代复杂变长的树结构染色体,使演化算子操作更方便,个体复杂度得到有效控制.用该染色体形式解决割草问题,分析了分布式染色体带来的一些性质,并给出了很好的计算结果. 相似文献
97.
讨论具有无穷时滞中立型泛函微分方程$ \frac{\rm d}{{\rm d}t}\left(x(t)-\int_{-\infty}^{0}g(s,x(t+s)){\rm d}s\right) =A(t,x(t))x(t)+f(t,x_t)$的周期解问题,利用重合度理论中的延拓定理得到了周期解的存在性和唯一性条件;特别地,当$g(s,x)\equiv 0, A(t,x)=A(t)$时, 给出了存在唯一稳定周期解的条件. 相似文献
98.
P. Kh. Atanasova T. L. Bojadjiev S. N. Dimova 《Computational Mathematics and Mathematical Physics》2006,46(4):666-679
Partial critical dependences of the form current-magnetic field in a two-layered symmetric Josephson junction are modeled. A numerical experiment shows that, for the zero interaction coefficient between the layers of the junction, jumps of the critical currents corresponding to different distributions of the magnetic fluxes in the layers may appear on the critical curves. This fact allows a mathematical interpretation of the results of some recent experimental results for two-layered junctions as a consequence of discontinuities of partial critical curves. 相似文献
99.
100.