全文获取类型
收费全文 | 243239篇 |
免费 | 2428篇 |
国内免费 | 878篇 |
专业分类
化学 | 130482篇 |
晶体学 | 3689篇 |
力学 | 9905篇 |
综合类 | 2篇 |
数学 | 27099篇 |
物理学 | 75368篇 |
出版年
2020年 | 1783篇 |
2019年 | 2046篇 |
2018年 | 2482篇 |
2017年 | 2403篇 |
2016年 | 3827篇 |
2015年 | 2594篇 |
2014年 | 3901篇 |
2013年 | 11182篇 |
2012年 | 8096篇 |
2011年 | 10012篇 |
2010年 | 6574篇 |
2009年 | 6487篇 |
2008年 | 8999篇 |
2007年 | 9154篇 |
2006年 | 8383篇 |
2005年 | 7846篇 |
2004年 | 7002篇 |
2003年 | 6216篇 |
2002年 | 6140篇 |
2001年 | 7206篇 |
2000年 | 5368篇 |
1999年 | 4228篇 |
1998年 | 3553篇 |
1997年 | 3578篇 |
1996年 | 3299篇 |
1995年 | 3138篇 |
1994年 | 2953篇 |
1993年 | 3018篇 |
1992年 | 3307篇 |
1991年 | 3340篇 |
1990年 | 3156篇 |
1989年 | 3108篇 |
1988年 | 3169篇 |
1987年 | 3039篇 |
1986年 | 2934篇 |
1985年 | 3997篇 |
1984年 | 4152篇 |
1983年 | 3400篇 |
1982年 | 3752篇 |
1981年 | 3649篇 |
1980年 | 3525篇 |
1979年 | 3552篇 |
1978年 | 3783篇 |
1977年 | 3610篇 |
1976年 | 3819篇 |
1975年 | 3388篇 |
1974年 | 3519篇 |
1973年 | 3819篇 |
1972年 | 2327篇 |
1971年 | 1789篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
951.
B. F. Matzanke U. Möllmann R. Reissbrodt V. Schünemann A. X. Trautwein 《Hyperfine Interactions》1998,112(1-4):123-128
Iron uptake of the 57Fe-siderophores ferricrocin, rhizoferrin and citrate in M. smegmatis was analyzed by in situ Mössbauer spectroscopy. Siderophore dependent uptake and metabolic utilization patterns of 57Fe were found. Rhizoferrin is accumulated in the organism and, therefore, represents a suitable candidate for the synthesis of novel siderophore-antibiotics conjugates. 相似文献
952.
J. Odeurs R. Coussement C. L'abbé G. Neyens G.R. Hoy E.E. Alp W. Sturhahn T. Toellner C. Johnson 《Hyperfine Interactions》1998,113(1-4):455-463
A new time integrated method for the study of resonant nuclear scattering of synchrotron radiation in the forward direction
or in Bragg directions is introduced. This method gives in principle similar information as the well known time differential
method. A brief comparison of both methods is presented. The idea is to excite coherently the nuclei incorporated in two absorbers,
one moving with respect to the other. The fields radiated by the nuclei from both absorbers interfere and each time the nuclear
energy in one absorber matches, by Doppler modulation, the nuclear energy of the other, an extremum in the time integrated
intensity is observed. The results of the first experiments at the Advanced Photon Source at the Argonne National Laboratory
will be presented.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
953.
954.
SINGLE MACHINE SCHEDULING WITH CONTROLLABLE PROCESSING TIMES AND COMPRESSION COSTS (PART I:EQUAL TIMES AND COSTS) 总被引:1,自引:0,他引:1
Most papers in scheduling research have treated individual job processing times as fixed parameters. However, in many practical situations, a manager may control processing time by realloeating resources. In this paper, authors consider a machine scheduling problemwith controllable processing times. In the first part of this paper, a special case where the pro-cessing times and compression costs are uniform among jobs is discussed. Theoretical results are derived that aid in developing an O(n^2) algorithm to slove the problem optimally. In the second part of this paper, authors generalize the discussion to general case, An effective heuristic to the genera/ problem will be presented. 相似文献
955.
This paper concerns methods by which a trusted authority can distribute keys and/or broadcast a message over a network, so that each member of a privileged subset of users can compute a specified key or decrypt the broadcast message. Moreover, this is done in such a way that no coalition is able to recover any information on a key or broadcast message they are not supposed to know. The problems are studied using the tools of information theory, so the security provided is unconditional (i.e., not based on any computational assumption).In a recent paper st95a, Stinson described a method of constructing key predistribution schemes by combining Mitchell-Piper key distribution patterns with resilient functions; and also presented a construction method for broadcast encryption schemes that combines Fiat-Naor key predistribution schemes with ideal secret sharing schemes. In this paper, we further pursue these two themes, providing several nice applications of these techniques by using combinatorial structures such as orthogonal arrays, perpendicular arrays, Steiner systems and universal hash families. 相似文献
956.
957.
W.-H. Steeb M. A. Van Wyk R. Stoop 《International Journal of Theoretical Physics》1998,37(10):2653-2655
We describe a one-dimensional chaotic map wherethe Liapunov exponent is a smooth function of a controlparameter. 相似文献
958.
We use integrals of Cauchy type and the complex potentials of S. G. Lekhnitskii to solve the problem of the stress-strain
state of a piecewise-homogeneous anisotropic rock during the working of a horizontal seam of mineral. We study the stress
distribution in the deloaded zones. Three figures, 1 table. Bibliography: 4 titles.
Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 27, 1997, pp. 81–86. 相似文献
959.
960.
Induced ferroelectric S*C phases are formed by non-chiral SC host phases doped with chiral dipolar guest molecules. In those mixtures the spontaneous polarization Ps and the tilt angle Θ has been investigated as a function of the mole fraction xG of the chiral dopant. In most cases the reduced polarization P0 = PS/ sin Θ has been found to depend linearly on xG. The polarization power which is defined by δP=(∂P0/∂xG)ΔT is discussed in terms of the molecular structure of the chiral dopants. There are systems in which P0(xG) deviates positively from linearity. This behaviour can be understood by considering a local field correction to P0. By assuming a local field of Lorentz type a theoretical relation for P0(xG) has been derived which explains the experimental results. The effect of a local field is considerable if the transverse dipole moment and the polarizability of the chiral dopant are large. 相似文献