全文获取类型
收费全文 | 58447篇 |
免费 | 6278篇 |
国内免费 | 3855篇 |
专业分类
化学 | 27579篇 |
晶体学 | 256篇 |
力学 | 3875篇 |
综合类 | 910篇 |
数学 | 17416篇 |
物理学 | 18544篇 |
出版年
2023年 | 429篇 |
2022年 | 792篇 |
2021年 | 1810篇 |
2020年 | 1354篇 |
2019年 | 1438篇 |
2018年 | 1148篇 |
2017年 | 1289篇 |
2016年 | 1576篇 |
2015年 | 1663篇 |
2014年 | 2352篇 |
2013年 | 4039篇 |
2012年 | 2690篇 |
2011年 | 3120篇 |
2010年 | 2750篇 |
2009年 | 3364篇 |
2008年 | 3548篇 |
2007年 | 3673篇 |
2006年 | 3040篇 |
2005年 | 2296篇 |
2004年 | 2152篇 |
2003年 | 2164篇 |
2002年 | 4451篇 |
2001年 | 2075篇 |
2000年 | 1543篇 |
1999年 | 1320篇 |
1998年 | 1261篇 |
1997年 | 994篇 |
1996年 | 936篇 |
1995年 | 804篇 |
1994年 | 744篇 |
1993年 | 734篇 |
1992年 | 721篇 |
1991年 | 469篇 |
1990年 | 384篇 |
1989年 | 337篇 |
1988年 | 324篇 |
1987年 | 277篇 |
1986年 | 271篇 |
1985年 | 392篇 |
1984年 | 315篇 |
1983年 | 183篇 |
1982年 | 356篇 |
1981年 | 523篇 |
1980年 | 479篇 |
1979年 | 518篇 |
1978年 | 395篇 |
1977年 | 309篇 |
1976年 | 267篇 |
1974年 | 85篇 |
1973年 | 162篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
151.
In this paper, we prove convergence rates for spherical spline Hermite interpolation on the sphere Sd−1 via an error estimate given in a technical report by Luo and Levesley. The functionals in the Hermite interpolation are either point evaluations of pseudodifferential operators or rotational differential operators, the desirable feature of these operators being that they map polynomials to polynomials. Convergence rates for certain derivatives are given in terms of maximum point separation. 相似文献
152.
Sufficient conditions are established for the asymptotic behavior of solutionsof nonlinear delay differential equations x′(t)+sum from i=1 to m(pi(t)x(t-т_i))=F(t,x_t),t≥0where 0<т_1<т_2<…<т_m≤r,pi∈C([0,∞)),i=1,2,…,m,F∈C([0,∞)×C_0,R).C_0=C([-r,0],R)equipped with the sup norm ||·|| forsome r>0. A new result is established, some known results are improved. 相似文献
153.
154.
两相同部件温贮备可修的人机系统解的性质分析 总被引:5,自引:1,他引:4
郭卫华 《数学的实践与认识》2003,33(7):88-95
本文首先用强连续算子半群理论证明了两相同部件温贮备可修的人机系统动态非负解的存在唯一性 ,然后证明了 0是系统主算子的本征值 ,并得到 0本征值对应的本征向量是正的 ,从而系统存在稳态正解 . 相似文献
155.
工程施工中运输网络优化方案 总被引:5,自引:0,他引:5
施工工地运输方案的优化设计可以归结为 :按施工期要求设计运输线路或验证已有线路通行能力 ,计算总线路中影响提高流量的关键路段 ,取得最小费用最大流 .本文运用图论理论这一数学工具把实际问题抽象为有向网络 ,进而建立数学模型 .此方法理论上严密 ,解题步聚直观清晰 ,对水利、公路、水路、铁路等其它运输系统有普遍意义 . 相似文献
156.
Modular and quasimodular solutions of a specific second order differential equation in the upper-half plane, which originates from a study of supersingular j-invariants in the first author's work with Don Zagier, are given explicitly. Positivity of Fourier coefficients of some of the solutions as well as a characterization of the differential equation are also discussed. 相似文献
157.
研究了Birkhoff系统的Hojman定理的几何基础.建立了系统的运动微分方程和Hojman守恒 定理,利用现代微分几何给出了Birkhoff系统的Hojman定理的一个证明.
关键词:
Birkhoff系统
Hojman定理
对称性
微分几何 相似文献
158.
J. T. Hoeft M. Polcik D. I. Sayago M. Kittel R. Terborg R. L. Toomes J. Robinson D. P. Woodruff M. Pascal G. Nisbet C. L. A. Lamont 《Surface science》2003,540(2-3):441-456
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding. 相似文献
159.
François Ledrappier Mark Pollicott 《Bulletin of the Brazilian Mathematical Society》2005,36(2):143-176
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually
associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension
of the geodesic flow. 相似文献
160.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions. 相似文献