全文获取类型
收费全文 | 222749篇 |
免费 | 1209篇 |
国内免费 | 677篇 |
专业分类
化学 | 80343篇 |
晶体学 | 3027篇 |
力学 | 15356篇 |
综合类 | 8篇 |
数学 | 56215篇 |
物理学 | 69686篇 |
出版年
2022年 | 538篇 |
2021年 | 488篇 |
2020年 | 449篇 |
2019年 | 434篇 |
2018年 | 18001篇 |
2017年 | 18606篇 |
2016年 | 9842篇 |
2015年 | 2255篇 |
2014年 | 1401篇 |
2013年 | 2951篇 |
2012年 | 9542篇 |
2011年 | 23723篇 |
2010年 | 13947篇 |
2009年 | 14469篇 |
2008年 | 18780篇 |
2007年 | 23892篇 |
2006年 | 2903篇 |
2005年 | 10631篇 |
2004年 | 6956篇 |
2003年 | 7005篇 |
2002年 | 4020篇 |
2001年 | 3410篇 |
2000年 | 2755篇 |
1999年 | 1751篇 |
1998年 | 1329篇 |
1997年 | 1227篇 |
1996年 | 1218篇 |
1995年 | 995篇 |
1994年 | 871篇 |
1993年 | 789篇 |
1992年 | 1073篇 |
1991年 | 1081篇 |
1990年 | 967篇 |
1989年 | 894篇 |
1988年 | 880篇 |
1987年 | 938篇 |
1986年 | 790篇 |
1985年 | 1036篇 |
1984年 | 985篇 |
1983年 | 715篇 |
1982年 | 717篇 |
1981年 | 681篇 |
1980年 | 651篇 |
1979年 | 785篇 |
1978年 | 820篇 |
1977年 | 734篇 |
1976年 | 669篇 |
1975年 | 560篇 |
1974年 | 591篇 |
1973年 | 576篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A novel technique to overcome the long-term drift and hysteresis of a scanning Fabry–Perot filter was developed and applied to wavelength and power monitoring of DWDM system. By using the comb peaks generated by a temperature-stabilized, near threshold-biased Fabry–Perot diode laser as wavelength reference for the scanning Fabry–Perot filter, wavelength and power measurement accuracy of better than ±10 pm and 0.2 dB, respectively, were achieved. 相似文献
102.
103.
Dual fractional cutting plane algorithms, in which cutting planes are used to iteratively tighten a linear relaxation of an integer program,
are well-known and form the basis of the highly successful branch-and-cut method. It is rather less well-known that various primal cutting plane algorithms were developed in the 1960s, for example by Young. In a primal algorithm, the main role of the cutting
planes is to enable a feasible solution to the original problem to be improved. Research on these algorithms has been almost
non-existent.
In this paper we argue for a re-examination of these primal methods. We describe a new primal algorithm for pure 0-1 problems based on strong valid inequalities and give some encouraging computational results. Possible extensions to the case of general
mixed-integer programs are also discussed. 相似文献
104.
Yasuyuki Kawahigashi 《Communications in Mathematical Physics》2002,226(2):269-287
We study the recent construction of subfactors by Rehren which generalizes the Longo–Rehren subfactors. We prove that if
we apply this construction to a non-degenerately braided subfactor N⊂M and α±-induction, then the resulting subfactor is dual to the Longo–Rehren subfactor M⊗M
opp⊂R arising from the entire system of irreducible endomorphisms of M resulting from αplusmn;-induction. As a corollary, we solve a problem on existence of braiding raised by Rehren negatively. Furthermore, we generalize
our previous study with Longo and Müger on multi-interval subfactors arising from a completely rational conformal net of factors
on S
1 to a net of subfactors and show that the (generalized) Longo–Rehren subfactors and α-induction naturally appear in this context.
Received: 11 September 2001 / Accepted: 7 October 2001 相似文献
105.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献
106.
Julio Castellanos 《Mathematische Zeitschrift》2002,239(4):777-802
We consider complete ideals supported on finite sequences of infinitely near points, in regular local rings with dimensions
greater than two. We study properties of factorizations in Lipman special *-simple complete ideals. We relate it to a type
of proximity, linear proximity, of the points, and give conditions in order to have unique factorization. Several examples
are presented.
Received: 2 February 2000 / in final form: 14 March 2001 / Published online: 18 January 2002 相似文献
107.
108.
109.
Y.Y. Lee 《Applied Acoustics》2002,63(11):1157-1175
The nonlinear natural frequency of a rectangular box, which consists of one flexible plate and five rigid plates, is studied in this paper. The flexible plate is assumed to vibrate like a simple piston. The behavior of the structural-acoustic coupling between the flexible plate and the air cavity is analyzed by using the proposed finite element modal method. The system finite element equation is reduced and expressed in terms of the modal coordinates with small degrees of freedom by using the proposed reduction method. The system nonlinear stiffness matrix representing the large amplitude vibration can be transformed to be a constant modal matrix. The natural frequencies are determined by using the harmonic balance method to solve the eigenvalue equations of the structural-acoustic system. The effect of the cavity depth on the natural frequencies and convergence studies are discussed in detail. 相似文献
110.
Annegret K. Wagler 《Mathematical Methods of Operations Research》2002,56(1):127-149
An edge e of a perfect graph G is critical if G−e is imperfect. We would like to decide whether G−e is still “almost perfect” or already “very imperfect”. Via relaxations of the stable set polytope of a graph, we define two
superclasses of perfect graphs: rank-perfect and weakly rank-perfect graphs. Membership in those two classes indicates how
far an imperfect graph is away from being perfect. We study the cases, when a critical edge is removed from the line graph
of a bipartite graph or from the complement of such a graph. 相似文献