全文获取类型
收费全文 | 1356篇 |
免费 | 51篇 |
国内免费 | 4篇 |
专业分类
化学 | 947篇 |
晶体学 | 7篇 |
力学 | 14篇 |
数学 | 173篇 |
物理学 | 185篇 |
无线电 | 85篇 |
出版年
2023年 | 16篇 |
2022年 | 27篇 |
2021年 | 20篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 31篇 |
2015年 | 32篇 |
2014年 | 37篇 |
2013年 | 72篇 |
2012年 | 65篇 |
2011年 | 91篇 |
2010年 | 52篇 |
2009年 | 50篇 |
2008年 | 77篇 |
2007年 | 84篇 |
2006年 | 85篇 |
2005年 | 77篇 |
2004年 | 59篇 |
2003年 | 68篇 |
2002年 | 47篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 22篇 |
1998年 | 14篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 22篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1974年 | 7篇 |
排序方式: 共有1411条查询结果,搜索用时 515 毫秒
151.
Ole J. Nielsen Howard W. Sidebottom Linda Nelson Jack J. Treacy Denis J. O'farrell 《国际化学动力学杂志》1989,21(12):1101-1112
The gas phase reaction of OH radicals with dimethyl sulfide (CH3SCH3, DMS) has been studied using both an absolute and a relative technique at 295 ± 2 K and a total pressure of 1 atm. The absolute rate technique of pulse radiolysis combined with kinetic spectroscopy was applied. Using this technique a rate constant of (3.5 ± 0.2) × 10?12 cm3 molecule?1 s?1 was obtained. For the relative rate method, rate constants for the reaction of OH with DMS were found to increase with increasing concentrations of added NO. These results are compared with the large body of kinetic and mechanistic data previously reported in the literature. 相似文献
152.
Electroless copper grains were deposited on a Pd seed layer under varying bath conditions. The seed layer was determined to
have a (111) texture using grazing incident x-ray (GIX) diffraction. Multiple nucleation sites in the grain boundaries were
imaged using a scanning tunneling microscope. Continual copper growth produced row-like structures. The texture of the electrolessly
deposited copper (ED-Cu) grains were determined to be (111). No radial grain orientation for the Pd seed layer or the ED-Cu
thin film was detected using GIX diffraction. Atomic force microscope images indicated continual Cu nucleation throughout
the deposition process. PdH was formed as a by-product of the electroless deposition process, and detected by x-ray diffraction. 相似文献
153.
George Vahala Pavol Pavlo Linda Vahala Min Soe 《Czechoslovak Journal of Physics》1996,46(11):1063-1083
Thermal Lattice Boltzmann (TLBE) techniques are used to consider the time evolution of free-decaying two dimensional (2D) turbulence induced by a double velocity shear layer. In particular, we consider the effect of this turbulence at a Reynolds number of 2555 on a strong temperature gradient. Since all structures are resolved on the 1024×1024 grid, the Smagorinsky model is employed to compute directly the eddy viscosity and eddy diffusivity. These transport coefficients play an integral part in large eddy simulations at very high Reynolds numbers where a direct simulation cannot resolve all excited scales. TLBE codes have the virtue of being readily extended to 3D, can readily handle nonperiodic geometries, and are ideally suited for multi-parallel computer architectures.This work was supported by a joint US-Czech DoE Grant #93066. Computations were performed under the auspices of the SPP (Special Parallel Processing) on the C90 at NERSC. 相似文献
154.
155.
We examine the different ways a set ofn points in the plane can be connected to form a simple polygon. Such a connection is called apolygonization of the points. For some point sets the number of polygonizations is exponential in the number of points. For this reason we restrict our attention to star-shaped polygons whose kernels have nonempty interiors; these are callednondegenerate star-shaped polygons.We develop an algorithm and data structure for determining the nondegenerate star-shaped polygonizations of a set ofn points in the plane. We do this by first constructing an arrangement of line segments from the point set. The regions in the arrangement correspond to the kernels of the nondegenerate star-shaped polygons whose vertices are the originaln points. To obtain the data structure representing this arrangement, we show how to modify data structures for arrangements of lines in the plane. This data structure can be computed inO(n
4) time and space. By visiting the regions in this data structure in a carefully chosen order, we can compute the polygon associated with each region inO(n) time, yielding a total computation time ofO(n
5) to compute a complete list ofO(n
4) nondegenerate star-shaped polygonizations of the set ofn points. 相似文献
156.
Linda Lesmak 《Discrete Mathematics》1976,14(2):165-169
A graph G of order p ? 3 is called n-hamiltonian, 0 ? n ? p ? 3, if the removal of any m vertices, 0 ? m ? n, results in a hamiltonian graph. A graph G of order p ? 3 is defined to be n-hamiltonian, ?p ? n ? 1, if there exists ?n or fewer pairwise disjoint paths in G which collectively span G. Various conditions in terms of n and the degrees of the vertices of a graph are shown to be sufficient for the graph to be n-hamiltonian for all possible values of n. It is also shown that if G is a graph of order p ? 3 and , then G is n-hamiltonian. 相似文献
157.
Decomposition of a symmetric matrix 总被引:5,自引:0,他引:5
Summary An algorithm is presented to compute a triangular factorization and the inertia of a symmetric matrix. The algorithm is stable even when the matrix is not positive definite and is as fast as Cholesky. Programs for solving associated systems of linear equations are included.The authors gratefully acknowledge research support from NSF grant MCS75-06510, NSF grant MCS75-23333, and ONR contract N00014-69-A-0200-1017, respectively 相似文献
158.
159.
160.
Linda Lesniak-Foster 《Journal of Combinatorial Theory, Series B》1977,22(3):263-273
With each nonempty graph G one can associate a graph L(G), called the line graph of G, with the property that there exists a one-to-one correspondence between E(G) and V(L(G)) such that two vertices of L(G) are adjacent if and only if the corresponding edges of G are adjacent. For integers m ≥ 2, the mth iterated line graph Lm(G) of G is defined to be L(Lm-1(G)). A graph G of order p ≥ 3 is n-Hamiltonian, 0 ≤ n ≤ p ? 3, if the removal of any k vertices, 0 ≤ k ≤ n, results in a Hamiltonian graph. It is shown that if G is a connected graph with δ(G) ≥ 3, where δ(G) denotes the minimum degree of G, then L2(G) is (δ(G) ? 3)-Hamiltonian. Furthermore, if G is 2-connected and δ(G) ≥ 4, then L2(G) is (2δ(G) ? 4)-Hamiltonian. For a connected graph G which is neither a path, a cycle, nor the graph K(1, 3) and for any positive integer n, the existence of an integer k such that Lm(G) is n-Hamiltonian for every m ≥ k is exhibited. Then, for the special case n = 1, bounds on (and, in some cases, the exact value of) the smallest such integer k are determined for various classes of graphs. 相似文献