全文获取类型
收费全文 | 399810篇 |
免费 | 5018篇 |
国内免费 | 1277篇 |
专业分类
化学 | 213655篇 |
晶体学 | 6275篇 |
力学 | 16931篇 |
综合类 | 14篇 |
数学 | 45140篇 |
物理学 | 124090篇 |
出版年
2020年 | 3118篇 |
2019年 | 3307篇 |
2018年 | 4224篇 |
2017年 | 4080篇 |
2016年 | 6636篇 |
2015年 | 4422篇 |
2014年 | 6436篇 |
2013年 | 17412篇 |
2012年 | 13110篇 |
2011年 | 15834篇 |
2010年 | 10749篇 |
2009年 | 10477篇 |
2008年 | 14372篇 |
2007年 | 14472篇 |
2006年 | 13824篇 |
2005年 | 12382篇 |
2004年 | 11414篇 |
2003年 | 10055篇 |
2002年 | 9751篇 |
2001年 | 11566篇 |
2000年 | 9000篇 |
1999年 | 7027篇 |
1998年 | 5572篇 |
1997年 | 5656篇 |
1996年 | 5447篇 |
1995年 | 5045篇 |
1994年 | 4854篇 |
1993年 | 4683篇 |
1992年 | 5449篇 |
1991年 | 5177篇 |
1990年 | 5071篇 |
1989年 | 4939篇 |
1988年 | 4903篇 |
1987年 | 4953篇 |
1986年 | 4570篇 |
1985年 | 6156篇 |
1984年 | 6335篇 |
1983年 | 5233篇 |
1982年 | 5549篇 |
1981年 | 5448篇 |
1980年 | 5284篇 |
1979年 | 5470篇 |
1978年 | 5755篇 |
1977年 | 5623篇 |
1976年 | 5576篇 |
1975年 | 5227篇 |
1974年 | 5122篇 |
1973年 | 5252篇 |
1972年 | 3458篇 |
1967年 | 3366篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
241.
In this paper, we consider linear combinations of modified Baskakov operators. By use of several lemmas, we obtain the inverse
theorem (Theorem 1.1) and the saturation (Theorem 1.2) for those linear combinations. 相似文献
242.
243.
J Szeman H Ueda J Szejtli E Fenyvesi Y Machida T Nagai 《Chemical & pharmaceutical bulletin》1987,35(1):282-288
244.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
245.
A new geometrical method to determine the surface damage threshold for ultrashort pulses is presented. It consists in the formation of a surface damage profile by a movement of the sample across the laser beam focus. A single measurement of the maximum transversal dimension of this damage profile, which depends solely on the laser beam power, is used to calculate the local damage threshold intensity. It is also theoretically shown that the damage in the transverse dimension can be controlled under the diffraction-limited spot. 相似文献
246.
M. Brokate D. Rachinskii 《NoDEA : Nonlinear Differential Equations and Applications》2006,13(4):385-411
The paper is concerned with the study of plasticity models described by differential equations with stop and play operators.
We suggest sufficient conditions for the global stability of a unique periodic solution for the scalar models and for the
vector models with biaxial inputs of a particular form, namely the sum of a uniaxial function and a constant term. For another
class of simple biaxial inputs, we present an example of the existence of unstable periodic solutions.
The paper was written during the research stay of D. Rachinskii at the Technical University Munich supported by the research
fellowship from the Alexander von Humboldt Foundation. His work was partially supported by the Russian Science Support Foundation, Russian Foundation for Basic Research (Grant No. 01-01-00146, 03-01-00258), and the Grants of the President of Russia (Grant No. MD-87.2003.01, NS-1532.2003.1). The support is gratefully acknowledged. 相似文献
247.
This paper attempts to develop a theory of sufficiency in the setting of non-commutative algebras parallel to the ideas in
classical mathematical statistics. Sufficiency of a coarse-graining means that all information is extracted about the mutual
relation of a given family of states. In the paper sufficient coarse-grainings are characterized in several equivalent ways
and the non-commutative analogue of the factorization theorem is obtained. As an application we discuss exponential families.
Our factorization theorem also implies two further important results, previously known only in finite Hilbert space dimension,
but proved here in generality: the Koashi-Imoto theorem on maps leaving a family of states invariant, and the characterization
of the general form of states in the equality case of strong subadditivity.
Supported by the EU Research Training Network Quantum Probability with Applications to Physics, Information Theory and Biology
and Center of Excellence SAS Physics of Information I/2/2005.
Supported by the Hungarian grant OTKA T032662 相似文献
248.
The consequences of Ge deposition on Br-terminated Si(1 0 0) were studied with scanning tunneling microscopy at ambient temperature after annealing at 650 K. One monolayer of Br was sufficient to prevent the formation of Ge huts beyond the critical thickness of 3 ML. This is possible because Br acts as a surfactant whose presence lowered the diffusivity of Ge adatoms. Hindered mobility was manifest at low coverage through the formation of short Ge chains. Further deposition resulted in the extension and connection of the Ge chains and gave rise to the buildup of incomplete layers. The deposition of 7 ML of Ge resulted in a rough surface characterized by irregularly shaped clusters. A short 800 K anneal desorbed the Br and allowed Ge atoms to reorganize into the more energetically favorable “hut” structures produced by conventional Ge overlayer growth on Si(1 0 0). 相似文献
249.
M. A. H. Dempster 《Journal of Mathematical Sciences》2006,133(4):1422-1444
This paper gives a comprehensive treatment of EVPI-based sequential importance sampling algorithms for dynamic (multistage)
stochastic programming problems. Both theory and computational algorithms are discussed. Under general assumptions it is shown
that both an expected value of perfect information (EVPI) process and the corresponding marginal EVPI process (the supremum
norm of the conditional expectation of its generalized derivative) are nonanticipative nonnegative supermartingales. These
processes are used as importance criteria in the class of sampling algorithms treated in the paper. When their values are
negligible at a node of the current sample problem scenario tree, scenarios descending from the node are replaced by a single
scenario at the next iteration. On the other hand, high values lead to increasing the number of scenarios descending from
the node. Both the small sample and asymptotic properties of the sample problem estimates arising from the algorithms are
established, and the former are evaluated numerically in the context of a financial planning problem. Finally, current and
future research is described. Bibliography: 49 titles.
__________
Published in Zapiski Nauchnykh Seminarov POMI, Vol. 312, 2004, pp. 94–129. 相似文献
250.
The problem of the stability of a heavy rigid body, bounded by the surface of an ellipsoid and with a cavity in the form of a coaxial ellipsoid, rolling along a straight line on a horizontal rough plane is investigated. It is shown that in the case of a body that is close to being dynamically symmetrical, parametric resonance always occurs leading to instability of the rolling. Each ellipsoid has its own “individual” resonance angular velocity. In the general case, regions in which the necessary stability conditions are satisfied can be distinguished in parameter space. The problem of calculating the resonance coefficient corresponding to instability for parametric resonance in a reversible third-order system is solved. 相似文献