全文获取类型
收费全文 | 4516篇 |
免费 | 144篇 |
国内免费 | 41篇 |
专业分类
化学 | 2892篇 |
晶体学 | 28篇 |
力学 | 108篇 |
数学 | 967篇 |
物理学 | 706篇 |
出版年
2023年 | 32篇 |
2022年 | 98篇 |
2021年 | 114篇 |
2020年 | 99篇 |
2019年 | 112篇 |
2018年 | 96篇 |
2017年 | 70篇 |
2016年 | 150篇 |
2015年 | 115篇 |
2014年 | 136篇 |
2013年 | 248篇 |
2012年 | 264篇 |
2011年 | 303篇 |
2010年 | 196篇 |
2009年 | 170篇 |
2008年 | 285篇 |
2007年 | 216篇 |
2006年 | 227篇 |
2005年 | 232篇 |
2004年 | 214篇 |
2003年 | 145篇 |
2002年 | 150篇 |
2001年 | 49篇 |
2000年 | 48篇 |
1999年 | 63篇 |
1998年 | 50篇 |
1997年 | 35篇 |
1996年 | 72篇 |
1995年 | 38篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 31篇 |
1991年 | 32篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 28篇 |
1982年 | 34篇 |
1981年 | 29篇 |
1980年 | 12篇 |
1979年 | 21篇 |
1978年 | 34篇 |
1977年 | 18篇 |
1976年 | 24篇 |
1975年 | 11篇 |
1974年 | 16篇 |
1973年 | 14篇 |
排序方式: 共有4701条查询结果,搜索用时 0 毫秒
951.
952.
Frederico Furtado Victor Ginting Felipe Pereira Michael Presho 《Transport in Porous Media》2011,90(3):927-947
A numerical method used for solving a two-phase flow problem as found in typical oil recovery is investigated in the setting of physics-based two-level operator splitting. The governing equations involve an elliptic differential equation coupled with a parabolic convection-dominated equation which poses a severe restriction for obtaining fully implicit numerical solutions. Furthermore, strong heterogeneity of the porous medium over many length scales adds to the complications for effectively solving the system. One viable approach is to split the system into three sub-systems: the elliptic, the hyperbolic, and the parabolic equation, respectively. In doing so, we allow for the use of appropriate numerical discretization for each type of equation and the careful exchange of information between them. We propose to use the multiscale finite volume element method (MsFVEM) for the elliptic and parabolic equations, and a nonoscillatory difference scheme for the hyperbolic equation. Performance of this procedure is confirmed through several numerical experiments. 相似文献
953.
954.
955.
Victor V. Dotsenko Sergey G. Krivokolysko Victor P. Litvinov 《Journal of heterocyclic chemistry》2011,48(1):162-167
Upon treatment with H2O2/KOH in EtOH or with Na2CO3/H2O2 in acetone, cycloalkylidene‐α‐(4‐arylthiazol‐2‐yl)acetonitriles afforded 2‐(4‐arylthiazol‐2‐yl)‐1‐oxaspiro[2.5]octane‐2‐carboxamides and 2‐(4‐arylthiazol‐2‐yl)‐1‐oxaspiro[2.4]heptane‐2‐carboxamides in excellent yields (76–100%). J. Heterocyclic Chem., 2011. 相似文献
956.
Leonid G. Voskressensky Larisa N. KulikovaSergey V. Gozun Victor N. KhrustalevTatiana N. Borisova Anna V. ListratovaMaxim V. Ovcharov Alexey V. Varlamov 《Tetrahedron letters》2011,52(32):4189-4191
The first synthesis of tetrahydrochromeno[4,3-d]azocines via an alkyne-induced expansion reaction is described. 相似文献
957.
Stanislav Naryzhny Nikolay Klopov Natalia Ronzhina Elena Zorina Victor Zgoda Olga Kleyst Natalia Belyakova Olga Legina 《Electrophoresis》2020,41(12):1118-1124
The human proteome is composed of a diverse and heterogeneous range of gene products/proteoforms/protein species. Because of the growing amount of information about proteoforms generated by different methods, we need a convenient approach to make an inventory of the data. Here, we present a database of proteoforms that is based on information obtained by separation of proteoforms using 2DE followed by shotgun ESI–LC–MS/MS. The database's principles and structure are described. The database is called “2DE-pattern” as it contains multiple isoform-centric patterns of proteoforms separated according to 2DE principles. The database can be freely used at http://2de-pattern.pnpi.nrcki.ru . 相似文献
958.
Dmitry V. MoiseevVera A. Morugova Alexey V. Gushchin Victor A. Dodonov 《Tetrahedron letters》2003,44(15):3155-3157
A new catalytic system based on triarylstibines for C-arylation of unsaturated compounds is proposed. It was found for a model reaction, the C-arylation of methyl acrylate, that in the presence of equimolar amounts of peroxide and catalytic amounts of a palladium compound (4 mol%), triarylstibines can act as mild efficient arylating agents. 相似文献
959.
Hook (Berberidaceae) has yielded the lactams (±)-nuevamine (7) and (±)-lennoxamine (8). Nuevamine is the first known isoindoloisoquinoline alkaloid, while lennoxamine is an isoindolobenzazepine structurally related to (±)-chilenine (3). 相似文献
960.
Motivated by applications in universal data compression algorithms we study the problem of bounds on the sizes of constant weight covering codes. We are concerned with the minimal sizes of codes of lengthn and constant weightu such that every word of lengthn and weightv is within Hamming distanced from a codeword. In addition to a brief summary of part of the relevant literature, we also give new results on upper and lower bounds to these sizes. We pay particular attention to the asymptotic covering density of these codes. We include tables of the bounds on the sizes of these codes both for small values ofn and for the asymptotic behavior. A comparison with techniques for attaining bounds for packing codes is also given. Some new combinatorial questions are also arising from the techniques.Part of this work was done while the first and third authors were visiting Bellcore. The third author was supported in part by National Science Foundation under grant NCR-8905052. Part of this work was presented in the Coding and Quantization Workshop at Rutgers University, NJ, October 1992. 相似文献