全文获取类型
收费全文 | 40985篇 |
免费 | 5268篇 |
国内免费 | 3467篇 |
专业分类
化学 | 18707篇 |
晶体学 | 275篇 |
力学 | 1979篇 |
综合类 | 223篇 |
数学 | 3465篇 |
物理学 | 11192篇 |
综合类 | 13879篇 |
出版年
2024年 | 182篇 |
2023年 | 777篇 |
2022年 | 1319篇 |
2021年 | 1349篇 |
2020年 | 1303篇 |
2019年 | 1149篇 |
2018年 | 1108篇 |
2017年 | 1061篇 |
2016年 | 1513篇 |
2015年 | 1597篇 |
2014年 | 1949篇 |
2013年 | 2467篇 |
2012年 | 2845篇 |
2011年 | 2894篇 |
2010年 | 2022篇 |
2009年 | 2081篇 |
2008年 | 2308篇 |
2007年 | 2106篇 |
2006年 | 1856篇 |
2005年 | 1628篇 |
2004年 | 1235篇 |
2003年 | 1042篇 |
2002年 | 960篇 |
2001年 | 890篇 |
2000年 | 873篇 |
1999年 | 1388篇 |
1998年 | 1161篇 |
1997年 | 1255篇 |
1996年 | 1128篇 |
1995年 | 1062篇 |
1994年 | 883篇 |
1993年 | 778篇 |
1992年 | 676篇 |
1991年 | 596篇 |
1990年 | 573篇 |
1989年 | 475篇 |
1988年 | 393篇 |
1987年 | 308篇 |
1986年 | 184篇 |
1985年 | 125篇 |
1984年 | 66篇 |
1983年 | 52篇 |
1982年 | 53篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1959年 | 1篇 |
1957年 | 7篇 |
1955年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
Zhou Cun-sheng 《科技信息》2008,(23)
本文介绍了一种解非线性代数方程组的数学方法——牛顿-拉夫逊法,并将其应用于电力系统潮流计算中。采用本文方法的计算结果表明该教学方法在电力系统潮流问题中是收敛的;同时计算结果与电力专业软件的计算结果保持了一致,从而验证了结果的正确性。 相似文献
74.
WANG Xibo ZHOU Benhai YU Gei LI Qian 《武汉大学学报:自然科学英文版》2007,12(5):946-950
μC/OS-Ⅱ is an open source real-time kernel adopting priority preemptive schedule strategy. Aiming at the problem of μC/OS-Ⅱ failing to support homology priority tasks scheduling, an approach for solution is proposed. The basic idea is adding round-robin scheduling strategy in its original scheduler in order to schedule homology priority tasks through time slice roundrobin. Implementation approach is given in detail. Firstly, the Task Control Block (TCB) is extended. And then, a new priority index table is created, in which each index pointer points to a set of homology priority tasks. Eventually, on the basis of reconstructing μC/OS-Ⅱ real-time kernel, task scheduling module is rewritten. Otherwise, schedulability of homology task supported by modified kernel had been analyzed, and deadline formula of created homology tasks is given. By theoretical analysis and experiment verification, the modified kernel can support homology priority tasks scheduling, meanwhile, it also remains preemptive property of original μC/OS-Ⅱ. 相似文献
75.
Stabilized hybrid finite element methods based on the combination of saddle point principles of elasticity problems 总被引:2,自引:0,他引:2
Tianxiao Zhou. 《Mathematics of Computation》2003,72(244):1655-1673
How, in a discretized model, to utilize the duality and complementarity of two saddle point variational principles is considered in the paper. A homology family of optimality conditions, different from the conventional saddle point conditions of the domain-decomposed Hellinger-Reissner principle, is derived to enhance stability of hybrid finite element schemes. Based on this, a stabilized hybrid method is presented by associating element-interior displacement with an element-boundary one in a nonconforming manner. In addition, energy compatibility of strain-enriched displacements with respect to stress terms is introduced to circumvent Poisson-locking.
76.
Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm 下载免费PDF全文
A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles. 相似文献
77.
Resistivity-temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere 下载免费PDF全文
The relationship of resistivity versus synthesizing temperature of sol gel YBa_2Cu_3O_y samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ-T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ_{300}=9.83×10^{-3 }Ω·cm at room temperature. The ρ-T curve also showed that the orthorhombic-tetragonal phase transformation of sol-gel YBa_2Cu_3O_y sample occurred at 581℃ for the sample in the rising temperature process, but at 613℃ in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods. 相似文献
78.
Guangchang Zhou Jibao He Issifu I. Harruna 《Journal of polymer science. Part A, Polymer chemistry》2007,45(18):4204-4210
Amphiphilic tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers consisting of one polystyrene block and two poly(N‐isopropylacrylamide) blocks were prepared by the “arm‐first” method in which RAFT polymerization and nonconvalent ligand–metal complexation were employed. The prepared amphiphilic star‐shaped metallopolymers are able to form micelles in water. The size and distribution of the micelles were studied by dynamic light scattering and transmission electron microscopy techniques. Preliminary studies indicate that the polymer concentration and the hydrophilic poly(N‐isopropylacrylamide) block length can affect the morphologies of the formed metal‐interfaced core–shell micelles in water. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4204–4210, 2007 相似文献
79.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
80.
研究了m-维离散Lotka-Volterra竞争系统,并获得了该系统周期解的存在性及其全局吸引性. 相似文献