全文获取类型
收费全文 | 8648篇 |
免费 | 246篇 |
国内免费 | 230篇 |
专业分类
化学 | 1263篇 |
晶体学 | 108篇 |
力学 | 57篇 |
综合类 | 23篇 |
数学 | 6172篇 |
物理学 | 1501篇 |
出版年
2023年 | 34篇 |
2022年 | 87篇 |
2021年 | 110篇 |
2020年 | 77篇 |
2019年 | 207篇 |
2018年 | 184篇 |
2017年 | 126篇 |
2016年 | 75篇 |
2015年 | 86篇 |
2014年 | 231篇 |
2013年 | 467篇 |
2012年 | 251篇 |
2011年 | 469篇 |
2010年 | 402篇 |
2009年 | 558篇 |
2008年 | 660篇 |
2007年 | 643篇 |
2006年 | 555篇 |
2005年 | 445篇 |
2004年 | 359篇 |
2003年 | 274篇 |
2002年 | 284篇 |
2001年 | 226篇 |
2000年 | 244篇 |
1999年 | 257篇 |
1998年 | 203篇 |
1997年 | 166篇 |
1996年 | 197篇 |
1995年 | 158篇 |
1994年 | 162篇 |
1993年 | 126篇 |
1992年 | 99篇 |
1991年 | 78篇 |
1990年 | 55篇 |
1989年 | 68篇 |
1988年 | 48篇 |
1987年 | 58篇 |
1986年 | 42篇 |
1985年 | 52篇 |
1984年 | 41篇 |
1983年 | 36篇 |
1982年 | 43篇 |
1981年 | 28篇 |
1980年 | 41篇 |
1979年 | 21篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有9124条查询结果,搜索用时 15 毫秒
171.
In this paper we prove the semialgebraic version of Palais' covering homotopy theorem, and use this to prove Bredon's covering mapping cylinder conjecture positively in the semialgebraic category. Bredon's conjecture was originally stated in the topological category, and a topological version of our semialgebraic proof of the conjecture answers the original topological conjecture for topological G-spaces over “simplicial” mapping cylinders. 相似文献
172.
Ligia E. Zamora G. A. Perez Alcazar J. M. Greneche S. Suriñach 《Hyperfine Interactions》2006,168(1-3):1057-1063
Fe60Mn10Al20Nb10, (Fe60Mn10Al30)95Nb5 and (Fe60Mn10Al30)90Nb10 ball milled powdered alloys were investigated using X-ray diffraction, Mössbauer spectrometry, thermomagnetic (TGM) and magnetization measurements. We studied the influence of Nb content and of different milling times on the structural and magnetic properties. Two main features can be concluded: (1) the FeAlMn induces a BCC phase whatever the Nb content is, and (2) as both increasing Nb content and milling time give rise to an highly disordered state in conjunction with a decrease of the ferromagnetic behavior. 相似文献
173.
Chi-So Lee 《中国化学会会志》1987,34(3):207-210
A differential pulse polarographic method for the determination of nitrate ion has been developed. With 0.5 M CaCl2 as supporting electrolyte, NO?3 is reduced to give a peak with E1/2=–1.836 Volt vs. the Ag/AgCl electrode. The differential pulse polarographic peak height is proportional to the nitrate concentration from 20 to 60 ppm. The detection limit for nitrate is 2 ppm in pure aqueous solution. In the determination of 40 ppm nitrate a relative precision (relative standard deviation) of less than 2% was achieved. Nitrite interferes seriously and should be absent if accurate results are required. The method has been applied to the determination of nitrate in Ammonium Uranyl Tricarbonate (AUT) Solution, results obtained by this method are compared to those obtained by ion chromatography. The agreement between the two sets of results suggests that the DPP method can be used with a fair degree of confidence. 相似文献
174.
Yevhen Zelenyuk 《Topology and its Applications》2007,154(2):339-357
A topological space X is called almost maximal if it is without isolated points and for every x∈X, there are only finitely many ultrafilters on X converging to x. We associate with every countable regular homogeneous almost maximal space X a finite semigroup Ult(X) so that if X and Y are homeomorphic, Ult(X) and Ult(Y) are isomorphic. Semigroups Ult(X) are projectives in the category F of finite semigroups. These are bands decomposing into a certain chain of rectangular components. Under MA, for each projective S in F, there is a countable almost maximal topological group G with Ult(G) isomorphic to S. The existence of a countable almost maximal topological group cannot be established in ZFC. However, there are in ZFC countable regular homogeneous almost maximal spaces X with Ult(X) being a chain of idempotents. 相似文献
175.
176.
Martin Schlichenmaier 《Letters in Mathematical Physics》1990,19(2):151-165
Krichever-Novikov algebras of meromorphic vector fields with more than two poles on higher genus Riemann surfaces are introduced. The structure of these algebras and their induced modules of forms of weight is studied. 相似文献
177.
Summary The good Boussinesq equationu
tt
=–u
xxxx
+u
xx
+(u
2)
xx
has recently been found to possess an interesting soliton-interaction mechanism. In this paper we study the nonlinear stability and the convergence of some simple finite-difference schemes for the numerical solution of problems involving the good Boussinesq equation. Numerical experimentas are also reported. 相似文献
178.
Summary The problem of the construction of an equilibrium surface taking the surface tension into account leads to Laplace-Young equation which is a nonlinear elliptic free-boundary problem. In contrast to Orr et al. where an iterative technique is used for direct solution of the equation for problems with simple geometry, we propose here an alternative approach based on shape optimization techniques. The shape of the domain of the liquid is varied to attain the optimality condition. Using optimal control theory to derive expressions for the gradient, a numerical scheme is proposed and simple model problems are solved to validate the scheme. 相似文献
179.
E. Mieloszyk 《Periodica Mathematica Hungarica》1990,21(1):43-53
Applying Bittner's operational calculus we present a method to give approximate solutions of linear partial differential equations of first order
相似文献
180.
G. Tardos 《Combinatorica》1989,9(4):385-392
By thequery-time complexity of a relativized algorithm we mean the total length of oracle queries made; thequery-space complexity is the maximum length of the queries made. With respect to these cost measures one can define polynomially time- or space-bounded deterministic, nondeterministic, alternating, etc. Turing machines and the corresponding complexity classes. It turns out that all known relativized separation results operate essentially with this cost measure. Therefore, if certain classes do not separate in the query complexity model, this can be taken as an indication that their relativized separation in the classical cost model will require entirely new principles.A notable unresolved question in relativized complexity theory is the separation of NPA co NPA fromP
A under random oraclesA. We conjecture that the analogues of these classes actually coincide in the query complexity model, thus indicating an answer to the question in the title. As a first step in the direction of establishing the conjecture, we prove the following result, where polynomial bounds refer to query complexity.If two polynomially query-time-bounded nondeterministic oracle Turing machines accept precisely complementary (oracle dependent) languages LA and {0, 1}*LA under every oracle A then there exists a deterministic polynomially query-time-bounded oracle Turing machine that accept LA. The proof involves a sort of greedy strategy to selecting deterministically, from the large set of prospective queries of the two nondeterministic machines, a small subset that suffices to perform an accepting computation in one of the nondeterministic machines. We describe additional algorithmic strategies that may resolve the same problem when the condition holds for a (1–) fraction of the oracles A, a step that would bring us to a non-uniform version of the conjecture. Thereby we reduce the question to a combinatorial problem on certain pairs of sets of partial functions on finite sets. 相似文献
|