全文获取类型
收费全文 | 95291篇 |
免费 | 3636篇 |
国内免费 | 2077篇 |
专业分类
化学 | 36393篇 |
晶体学 | 962篇 |
力学 | 7671篇 |
综合类 | 73篇 |
数学 | 33828篇 |
物理学 | 22077篇 |
出版年
2023年 | 393篇 |
2022年 | 422篇 |
2021年 | 652篇 |
2020年 | 737篇 |
2019年 | 739篇 |
2018年 | 10962篇 |
2017年 | 10677篇 |
2016年 | 6907篇 |
2015年 | 1646篇 |
2014年 | 1341篇 |
2013年 | 1699篇 |
2012年 | 5447篇 |
2011年 | 12130篇 |
2010年 | 6727篇 |
2009年 | 7058篇 |
2008年 | 7714篇 |
2007年 | 9729篇 |
2006年 | 1216篇 |
2005年 | 2082篇 |
2004年 | 2113篇 |
2003年 | 2378篇 |
2002年 | 1442篇 |
2001年 | 579篇 |
2000年 | 567篇 |
1999年 | 542篇 |
1998年 | 464篇 |
1997年 | 434篇 |
1996年 | 470篇 |
1995年 | 357篇 |
1994年 | 282篇 |
1993年 | 305篇 |
1992年 | 196篇 |
1991年 | 221篇 |
1990年 | 178篇 |
1989年 | 159篇 |
1988年 | 147篇 |
1987年 | 127篇 |
1986年 | 125篇 |
1985年 | 100篇 |
1984年 | 99篇 |
1983年 | 66篇 |
1982年 | 73篇 |
1981年 | 61篇 |
1980年 | 72篇 |
1979年 | 54篇 |
1978年 | 47篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
61.
62.
给出了线和n-2的n阶(0,1)-矩阵的最大积和式的积分表达式,并证明了该积分表达式与[1]得到的组合表达式等价。 相似文献
63.
Alexander Krasnosel'skii Dmitrii Rachinskii 《NoDEA : Nonlinear Differential Equations and Applications》2002,9(1):93-115
We consider autonomous systems with a nonlinear part depending on a parameter and study Hopf bifurcations at infinity. The
nonlinear part consists of the nonlinear functional term and the Prandtl--Ishlinskii hysteresis term. The linear part of the
system has a special form such that the close-loop system can be considered as a hysteresis perturbation of a quasilinear
Hamiltonian system. The Hamiltonian system has a continuum of arbitrarily large cycles for each value of the parameter. We
present sufficient conditions for the existence of bifurcation points for the non-Hamiltonian system with hysteresis. These
bifurcation points are determined by simple characteristics of the hysteresis nonlinearity. 相似文献
64.
According to an induced-matter approach, Liu and Wesson obtained the rest mass of a typical particle from the reduction of a 5D Klein–Gordon equation to a 4D one. Introducing an extra-dimension momentum operator identified with the rest mass eigenvalue operator, we consider a way to generalize the 4D Dirac equation to 5D. An analogous normal Dirac equation is gained when the generalization reduces to 4D. We find the rest mass of a particle in curved space varies with spacetime coordinates and check this for the case of exact solitonic and cosmological solution of the 5D vacuum gravitational field equations. 相似文献
65.
Claudia-Elisabeth Wulz 《Czechoslovak Journal of Physics》2002,52(3):C155-C170
The principal physics goals of the Compact Muon Solenoid experiment under construction at the Large Hadron Collider at CERN in Geneva are reviewed. Procedures to search for the Standard Model Higgs boson, supersymmetric Higgses and other supersymmetric particles are described. 相似文献
66.
67.
利用拟合实测的TEMP Ⅱ型加速器磁绝缘二极管(MID)电压波形及其焦点附近束流密度曲线,建立了Gaussian分布模型,据此计算了与靶作用的离子的能量及数量,采用Monte Carlo(MC)方法计算了沉积在靶内的能量.并以此作为热源,与流体动力学(HD)模型相结合,对不同的靶状态采用相应的状态方程,模拟计算了靶内压力演化情况; 同时对烧蚀产生的等离子体采用理想气体状态方程, 结合HD方程组, 模拟计算了喷发过程中压力的空间演化过程.
关键词:
强流脉冲离子束
Gaussian模型
HD方程
数值研究 相似文献
68.
This paper proposes two constructive heuristics for the well-known single-level uncapacitated dynamic lot-sizing problem. The proposed heuristics, called net least period cost (nLPC) and nLPC(i), are developed by modifying the average period cost concept from Silver and Meal's heuristic, commonly known as least period cost (LPC). An improved tie-breaking stopping rule and a locally optimal decision rule are proposed in the second heuristic to enhance performance. We test the effectiveness of the proposed heuristics by using 20 benchmarking test problems frequently used in the literature. Furthermore, we perform a large-scale simulation study involving three factors, 50 experimental conditions, and 100?000 randomly generated problems to evaluate the proposed heuristics against LPC and six other well-known constructive heuristics in the literature. The simulation results show that both nLPC and nLPC(i) produce average holding and setup costs lower than or equal to those of LPC in every one of the 50 experimental conditions. The proposed heuristics also outperform each of the six other heuristics evaluated in all experimental conditions, without an increase in computational requirements. Lastly, considering that both nLPC and nLPC(i) are fairly simple for practitioners to understand and that lot-sizing heuristics have been commonly used in practice, there should be a very good chance for practical applications of the proposed heuristics. 相似文献
69.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection. 相似文献
70.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献