全文获取类型
收费全文 | 30272篇 |
免费 | 1193篇 |
国内免费 | 1337篇 |
专业分类
化学 | 9812篇 |
晶体学 | 211篇 |
力学 | 449篇 |
综合类 | 69篇 |
数学 | 18135篇 |
物理学 | 4126篇 |
出版年
2024年 | 23篇 |
2023年 | 373篇 |
2022年 | 284篇 |
2021年 | 308篇 |
2020年 | 490篇 |
2019年 | 771篇 |
2018年 | 710篇 |
2017年 | 524篇 |
2016年 | 575篇 |
2015年 | 638篇 |
2014年 | 956篇 |
2013年 | 1827篇 |
2012年 | 1111篇 |
2011年 | 2062篇 |
2010年 | 1623篇 |
2009年 | 2105篇 |
2008年 | 2338篇 |
2007年 | 2172篇 |
2006年 | 1659篇 |
2005年 | 1206篇 |
2004年 | 1117篇 |
2003年 | 1023篇 |
2002年 | 1242篇 |
2001年 | 672篇 |
2000年 | 644篇 |
1999年 | 712篇 |
1998年 | 581篇 |
1997年 | 459篇 |
1996年 | 568篇 |
1995年 | 523篇 |
1994年 | 476篇 |
1993年 | 380篇 |
1992年 | 315篇 |
1991年 | 240篇 |
1990年 | 214篇 |
1989年 | 230篇 |
1988年 | 155篇 |
1987年 | 161篇 |
1986年 | 149篇 |
1985年 | 195篇 |
1984年 | 145篇 |
1983年 | 103篇 |
1982年 | 144篇 |
1981年 | 137篇 |
1980年 | 91篇 |
1979年 | 69篇 |
1978年 | 71篇 |
1977年 | 70篇 |
1976年 | 62篇 |
1971年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Wei Wang Li-Ping Pang Zun-Quan Xia 《应用数学学报(英文版)》2007,23(1):29-38
In this paper,the UV-theory and P-differential calculus are employed to study second-order ex-pansion of a class of D.C.functions and minimization problems.Under certain conditions,some properties ofthe U-Lagrangian,the second-order expansion of this class of functions along some trajectories are formulated.Some first and second order optimality conditions for the class of D.C.optimization problems are given. 相似文献
112.
We propose a new scheme for the long time approximation of a diffusion when the drift vector field is not globally Lipschitz. Under this assumption, a regular explicit Euler scheme–with constant or decreasing step–may explode and implicit Euler schemes are CPU-time expensive. The algorithm we introduce is explicit and we prove that any weak limit of the weighted empirical measures of this scheme is a stationary distribution of the stochastic differential equation. Several examples are presented including gradient dissipative systems and Hamiltonian dissipative systems. 相似文献
113.
We classify all the global phase portraits of the quadratic polynomial vector fields having a rational first integral of degree 2. In other words we characterize all the global phase portraits of the quadratic polynomial vector fields having all their orbits contained in conics. For such a vector field there are exactly 25 different global phase portraits in the Poincaré disc, up to a reversal of sense. 相似文献
114.
The new phenylpropanoid diglycoside ligusinenoside A ( 1 ), and the two new 8,4′‐oxyneolignan(‘8‐O‐4′‐neolignan’) diglycosides ligusinenosides B ( 2 ) and C ( 3 ), together with nine known compounds, were isolated from the rhizomes of Ligusticum sinensis Oliv. The structures of 1 – 3 were elucidated on the basis of spectroscopic analyses. 相似文献
115.
116.
Pál Sohár Gábor Bernáth Géza Stájer Angela E. Szabo 《Magnetic resonance in chemistry : MRC》1989,27(9):872-876
Pentacyclic isoxazolines were obtained by the cycloaddition of benzonitrile oxide to norbornene-azetidinone-fused 3,1-oxazines. The constitutions of two of the isomers obtained, and the configurations and conformations of all products, were determined by means of 1H and 13C NMR spectroscopy and DNOE experiments. 相似文献
117.
Summary We consider a class of infinite delay equations of neutral type which includes Volterrra type integral und integrodifferential equations. Using abstract approximation results (cf. Trotter-Kato-type) for strongly continuous semigroups we develop an approximation scheme which is based on approximation of the system state by Laguerre (and Legendre) polynomials. Numerical examples demonstrate the feasibility of the scheme and show infinite order convergence for smooth data.Supported in part by the Air Force Office of Scientific Research under Contracts AFORS-84-0398 and AFORS-85-0303 and the National Aeronautics and Space Administration under NASA Grant NAG-1-517 and by NSF under Grant UINT-8521208Supported in part by the Air Force Office of Scientific Research under Contract AFORS-84-0398 and in part by the Fonds zur Förderung der wissenschaftlichen Forschung, Austria, under project No. S3206 相似文献
118.
牛顿弦截法预估校正迭代格式的收敛阶 总被引:2,自引:0,他引:2
研究如下形式的牛顿弦截法的预估校正(P.C.)格式:P(预估):~xk+1=xk-(xk-xk-1)f(xk)f(xk)-f(xk-1)C(校正):xk+1=xk-(~xk+1-xk)f(xk)f~(xk+1)-f(xk)证明了它的收敛阶为2.618. 相似文献
119.
Risk related to long-term care (LTC) is high for the elderly. Planning for LTC is now regarded as the ‘third leg’ of retirement planning. In this paper, planning for LTC is integrated with saving and investment decisions for an integrated approach to retirement planning. Optimal LTC insurance purchase decisions are obtained by developing a trade-off between post-retirement LTC costs and LTC insurance premiums paid and coverage received. Integrating insurance purchase with wealth evolution, consisting of saving and investment decisions, allows addressing affordability issues.Two-way branching models are used for the stochastic health events and asset returns. The problem, formulated as a nonlinearly constrained mixed-integer optimization problem, is solved using a heuristic. Sensitivity analyses are performed for initial health and wealth status. Some important aspects of an individual’s behavioral preferences are also addressed in this framework to provide more robust decision support. 相似文献
120.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献