全文获取类型
收费全文 | 75715篇 |
免费 | 8253篇 |
国内免费 | 8754篇 |
专业分类
化学 | 37460篇 |
晶体学 | 2048篇 |
力学 | 10130篇 |
综合类 | 848篇 |
数学 | 24109篇 |
物理学 | 18127篇 |
出版年
2024年 | 112篇 |
2023年 | 876篇 |
2022年 | 1135篇 |
2021年 | 1887篇 |
2020年 | 2147篇 |
2019年 | 1968篇 |
2018年 | 1900篇 |
2017年 | 2297篇 |
2016年 | 2691篇 |
2015年 | 2393篇 |
2014年 | 3719篇 |
2013年 | 5694篇 |
2012年 | 4500篇 |
2011年 | 5173篇 |
2010年 | 4581篇 |
2009年 | 5088篇 |
2008年 | 5009篇 |
2007年 | 4976篇 |
2006年 | 4518篇 |
2005年 | 3994篇 |
2004年 | 3595篇 |
2003年 | 3212篇 |
2002年 | 2773篇 |
2001年 | 2252篇 |
2000年 | 2135篇 |
1999年 | 1883篇 |
1998年 | 1756篇 |
1997年 | 1444篇 |
1996年 | 1230篇 |
1995年 | 1153篇 |
1994年 | 1038篇 |
1993年 | 864篇 |
1992年 | 855篇 |
1991年 | 627篇 |
1990年 | 472篇 |
1989年 | 417篇 |
1988年 | 370篇 |
1987年 | 257篇 |
1986年 | 198篇 |
1985年 | 247篇 |
1984年 | 247篇 |
1983年 | 90篇 |
1982年 | 168篇 |
1981年 | 152篇 |
1980年 | 114篇 |
1979年 | 124篇 |
1978年 | 99篇 |
1977年 | 90篇 |
1976年 | 56篇 |
1975年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
图G称为K1,n-free图,如果它不含K1,n作为其导出子图.对K1,n-free图具有给定性质的[a,b]-因子涉及到最小度条件进行了研究,得到一个充分条件. 相似文献
122.
F. Balibrea 《Topology and its Applications》2006,153(12):2092-2095
Recently, Forti, Paganoni and Smítal constructed an example of a triangular map of the unite square, F(x,y)=(f(x),g(x,y)), possessing periodic orbits of all periods and such that no infinite ω-limit set of F contains a periodic point. In this note we show that the above quoted map F has a homoclinic orbit. As a consequence, we answer in the negative the problem presented by A.N. Sharkovsky in the eighties whether, for a triangular map of the square, existence of a homoclinic orbit implies the existence of an infinite ω-limit set containing a periodic point. It is well known that, for a continuous map of the interval, the answer is positive. 相似文献
123.
烷基硫酸盐表面张力的量子化学研究 总被引:1,自引:0,他引:1
用AMl量子化学计算法优化了十三烷基硫酸根阴离子和——CH3在不同取代位的十二烷基硫酸根阴离子的几何构型,得到最优构型时最高占据分子轨道能级EHOMO、最低空轨道能级ELUMO、电子能量Eele和偶极矩μ等数据.将这些电子结构数据分别与表面张力相拟合,得到很好的相关性。文中讨论了——CH3在不同位置取代对表面张力的影响。 相似文献
124.
本文首先将文[1]中的BLD映射推广为弱(L1,L2)-BLD映射,并证明了如下正则性结果:存在两个可积指数 P1=P1(n,L1,L2)<n<q1=q1(n,L1,L2),使得对任意弱(L1,L2)-BLD映射f∈(Ω,Rn),都有f∈(Ω,Rn),即f为(L1,L2)-BLD映射. 相似文献
125.
本文主要解决奇异非光滑方程组的解法。应用一种新的次微分的外逆,我们提出了牛顿法和不精确牛顿法,它们的收敛性同时也得到了证明。这种方法能更容易在一引起实际应用中实现。这种方法可以看作是已存在的解非光滑方程组的方法的延伸。 相似文献
126.
Chemical bonding in isolated molecules and crystals of zwitterionic pentacoordinate silicon chelates
The electronic structures of a number of zwitterionic pentacoordinate silicon chelates were investigated using the results of X-ray diffraction studies and quantum-chemical calculatoins by the MPW1PW91/6-311G(d) method. The topological analysis of the electron density distribution function and the study in the framework of the natural bond orbital partitioning scheme showed that the character of chemical bonding in the axial fragments of the molecules under consideration changes from dative to three-center, four-electron as the silicon atom assumes a trigonal-bipyramidal coordination. 相似文献
127.
Chuanming Zong 《Monatshefte für Mathematik》2002,134(3):247-255
In this article we study the simultaneous packing and covering constants of two-dimensional centrally symmetric convex domains.
Besides an identity result between translative case and lattice case and a general upper bound, exact values for some special
domains are determined. Similar to Mahler and Reinhardt’s result about packing densities, we show that the simultaneous packing
and covering constant of an octagon is larger than that of a circle.
(Received 17 January 2001; in revised form 13 July 2001) 相似文献
128.
A. D. Matveev 《Journal of Applied Mechanics and Technical Physics》2003,44(5):721-726
Modified three-dimensional formulations of bending problems of homogeneous elastic plates and beams are considered. Modification of the known three-dimensional formulations reduces to using additional constraints imposed on displacement functions. An advantage of the formulations proposed is that complex fixing conditions of plates and beams can be taken into account. 相似文献
129.
Various techniques for building relaxations and generating valid inequalities for pure or mixed integer programming problems without special structure are reviewed and compared computationally. Besides classical techniques such as Gomory cuts, Mixed Integer Rounding cuts, lift-and-project and reformulation–linearization techniques, a new variant is also investigated: the use of the relaxation corresponding to the intersection of simple disjunction polyhedra (i.e. the so-called elementary closure of lift-and-project cuts). Systematic comparative computational results are reported on series of test problems including multidimensional knapsack problems (MKP) and MIPLIB test problems. From the results obtained, the relaxation based on the elementary closure of lift-and-project cuts appears to be one of the most promising. 相似文献
130.
We establish the existence and stability of multidimensional transonic shocks for the Euler equations for steady potential compressible fluids. The Euler equations, consisting of the conservation law of mass and the Bernoulli law for the velocity, can be written as a second-order, nonlinear equation of mixed elliptic-hyperbolic type for the velocity potential. The transonic shock problem can be formulated into the following free boundary problem: The free boundary is the location of the transonic shock which divides the two regions of smooth flow, and the equation is hyperbolic in the upstream region where the smooth perturbed flow is supersonic. We develop a nonlinear approach to deal with such a free boundary problem in order to solve the transonic shock problem. Our results indicate that there exists a unique solution of the free boundary problem such that the equation is always elliptic in the downstream region and the free boundary is smooth, provided that the hyperbolic phase is close to a uniform flow. We prove that the free boundary is stable under the steady perturbation of the hyperbolic phase. We also establish the existence and stability of multidimensional transonic shocks near spherical or circular transonic shocks.