全文获取类型
收费全文 | 12904篇 |
免费 | 787篇 |
国内免费 | 780篇 |
专业分类
化学 | 6399篇 |
晶体学 | 78篇 |
力学 | 681篇 |
综合类 | 141篇 |
数学 | 2962篇 |
物理学 | 4210篇 |
出版年
2023年 | 116篇 |
2022年 | 344篇 |
2021年 | 320篇 |
2020年 | 280篇 |
2019年 | 286篇 |
2018年 | 261篇 |
2017年 | 287篇 |
2016年 | 316篇 |
2015年 | 288篇 |
2014年 | 421篇 |
2013年 | 793篇 |
2012年 | 474篇 |
2011年 | 485篇 |
2010年 | 436篇 |
2009年 | 700篇 |
2008年 | 774篇 |
2007年 | 810篇 |
2006年 | 709篇 |
2005年 | 502篇 |
2004年 | 461篇 |
2003年 | 463篇 |
2002年 | 486篇 |
2001年 | 418篇 |
2000年 | 388篇 |
1999年 | 339篇 |
1998年 | 326篇 |
1997年 | 207篇 |
1996年 | 155篇 |
1995年 | 155篇 |
1994年 | 145篇 |
1993年 | 155篇 |
1992年 | 236篇 |
1991年 | 125篇 |
1990年 | 98篇 |
1989年 | 79篇 |
1988年 | 88篇 |
1987年 | 91篇 |
1986年 | 72篇 |
1985年 | 71篇 |
1984年 | 75篇 |
1983年 | 44篇 |
1982年 | 92篇 |
1981年 | 168篇 |
1980年 | 180篇 |
1979年 | 177篇 |
1978年 | 164篇 |
1977年 | 101篇 |
1976年 | 108篇 |
1973年 | 77篇 |
1972年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
G. Z. Chelidze 《Mathematical Notes》2000,68(2):263-269
To study intersections of embedded bounded closed sets in Banach space, a numerical parameter was introduced earlier; in a
certain sense, this parameter describes the deviation of the shape of a set from that of a sphere. Critical values of this
parameter for some classes of Banach spaces are determined, a new numerical parameter serving the same purpose is introduced,
and the relation between the two parameters is examined.
Translated fromMatematicheskie Zametki, Vol. 68, No. 2, pp. 303–310, August, 2000. 相似文献
992.
回顾性分析了46例临床被证实为宫内胎物组织残留的病例。结果表明,流产后较长时间有不规则阴道流血,而作B超检查能发现特征性改变。声像图显示,子宫增大,宫内有异常光团和不规则液性暗区或宫腔局部膨隆,周边见很亮光条。认为诊断宫内残留组织,可以结合病只与声像技术较易诊断出来。本组超声诊断符合率达98%。对减少因宫内残留造成的子宫收缩不良、不规则阴道流血等现象,避免并发感染及导致绒癌发生等不良后果,有重要的 相似文献
993.
We have solved a self-consistent problem on interaction of two dipole atoms located at an arbitrary distance from each other
with the field of a quasiresonance light wave, whose intensity is sufficient for the system to manifest nonlinear properties.
The atoms are considered as two-level systems described by means of Bloch optical equations, while the field inside of the
system includes both Coulomb and retarded parts. We consider a situation where atoms are identical and the distance between
them is much smaller than the length of an outer light wave. The distribution of an electric field both inside of a small
object and outside of it is found numerically. It is shown that the amplitude of the electric field in a wave zone depends
substantially on the frequency of the external field and interatomic distance, while the field distribution differs from the
field pattern of an electric dipole. At definite values of the external field intensity an optical multistability is a feature
of the system under investigation. We have elucidated the conditions under which the multistability is manifested in the present
system. The results obtained are considered as the near-field effect in the optics of small objects, which makes it possible
to investigate the structure of small objects by means of optical radiation.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 375–378, May–June, 2000.
The present work was supported by the Russian Foundation for Fundamental Research (grant 98-02-16035) and by a grant from
the Federal Purpose-Oriented Program “Integration.” 相似文献
994.
Jesús A. De Loera Raymond Hemmecke Matthias Köppe Robert Weismantel 《Mathematical Programming》2008,115(2):273-290
We show the existence of a fully polynomial-time approximation scheme (FPTAS) for the problem of maximizing a non-negative
polynomial over mixed-integer sets in convex polytopes, when the number of variables is fixed. Moreover, using a weaker notion
of approximation, we show the existence of a fully polynomial-time approximation scheme for the problem of maximizing or minimizing
an arbitrary polynomial over mixed-integer sets in convex polytopes, when the number of variables is fixed.
A conference version of this article, containing a part of the results presented here, appeared in Proceedings of the 17th Annual ACM-SIAM Symposium on Discrete Algorithms, Miami, FL, January 22–24, 2006, pp. 743–748. The first author gratefully acknowledges support from NSF grant DMS-0608785, a 2003 UC-Davis Chancellor’s fellow award,
the Alexander von Humboldt foundation, and IMO Magdeburg. The remaining authors were supported by the European TMR network
ADONET 504438. 相似文献
995.
Classical and modified Lagrangian bounds for the optimal value of optimization problems with a double decomposable structure are examined. For the class of generalized assignment problems, this property of constraints is used to design a Benders algorithm for solving the modified dual problem. Numerical results are presented that compare the quality of classical and modified bounds. 相似文献
996.
Hermite四点插指公式 总被引:2,自引:0,他引:2
颜宇生 《应用数学与计算数学学报》2008,22(1)
文章利用Hermite插值基函数,将求解Hermite四点插指问题转换为求解8个派生出来的多项式插值问题,证明了Hermite四点插指公式的存在唯一性,并用两种方法构造出Hermite四点插指公式,最后给出了一个算例. 相似文献
997.
P. Sigmund 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):111-116
Second-harmonic cross-correlation operates a selection in time-phase among the randomly de-phased contributions to an optical
field that propagated through a scattering medium. It can thus be used to selectively detect the weak contribution remaining
coherent with the incident field.
Received 7 May 1999 相似文献
998.
This paper presents techniques for solving the problem of minimizing investment costs on an existing gas transportation network. The goal of this program is to find, first, the optimal location of pipeline segments to be reinforced and, second, the optimal sizes (among a discrete commercial list of diameters) under the constraint of satisfaction of demands with high enough pressure for all users. 相似文献
999.
Summary A detailed experimental analysis of the inelastic crosssection along the [111]-direction in Co−Ni alloys is presented. Using
a simple model and studying the cross-section as a function of both composition and temperature, it is shown that interesting
information about the h.c.p.-f.c.c. transition can be gained in these alloys.
Riassunto Nel presente lavoro si describe un’analisi sperimentale dettagliata della sezione d’urto anelastica dei neutroni lungo la direzione [111] in leghe Co−Ni. Impiegando un modello relativamente semplice e studiando la sezione d’urto in funzione di temperatura e concentrazione, si mostra che si possono ottenere utili informazioni riguardanti la transizione h.c.p.-f.c.c.相似文献
1000.
R. Giovanelli 《Il Nuovo Cimento D》1987,9(11):1443-1460
Summary Using the Boris mover, or other standard methods, the error pile-up in the computation of the relativistic orbit of charged
particles in electric and magnetic fields becomes quickly excessive, if one wants to keep reasonably limited the number of
points employed to build the particle orbit. An analytical solution becomes, therefore, desirable and its construction is
the subject of the present work.
Riassunto Unsando il metodo di Boris, oppure altri metodi standard, l'accumulazione degli errori nella determinazione numerica delle orbite relativistiche di particelle cariche in campi elettrici e magnetici diventa intollerabile, se il numero dei punti impiegati per costruire le orbite stesse è mantenuto basso. Una soluzione analitica diviene quindi utile, e questa costituisce l'argomento del presente lavoro.
Резюме В рамках стндартных методов погрешность при вычислении релятивистской орбиты заряженных частиц в электронном и магнитном полях становится чрезмерно большой, если для построения орбиты часицы используется ограниченное число точек. В связи с этим конструируется аналитическое решение.相似文献