全文获取类型
收费全文 | 63849篇 |
免费 | 2263篇 |
国内免费 | 149篇 |
专业分类
化学 | 39965篇 |
晶体学 | 388篇 |
力学 | 1322篇 |
数学 | 9629篇 |
物理学 | 14957篇 |
出版年
2022年 | 393篇 |
2021年 | 639篇 |
2020年 | 943篇 |
2019年 | 783篇 |
2018年 | 774篇 |
2017年 | 684篇 |
2016年 | 1670篇 |
2015年 | 1446篇 |
2014年 | 1657篇 |
2013年 | 3283篇 |
2012年 | 3231篇 |
2011年 | 3715篇 |
2010年 | 2010篇 |
2009年 | 1668篇 |
2008年 | 3304篇 |
2007年 | 3234篇 |
2006年 | 3012篇 |
2005年 | 2724篇 |
2004年 | 2283篇 |
2003年 | 1833篇 |
2002年 | 1825篇 |
2001年 | 1201篇 |
2000年 | 1040篇 |
1999年 | 823篇 |
1998年 | 766篇 |
1997年 | 739篇 |
1996年 | 859篇 |
1995年 | 745篇 |
1994年 | 783篇 |
1993年 | 853篇 |
1992年 | 711篇 |
1991年 | 532篇 |
1990年 | 601篇 |
1989年 | 488篇 |
1988年 | 516篇 |
1987年 | 494篇 |
1986年 | 451篇 |
1985年 | 740篇 |
1984年 | 707篇 |
1983年 | 603篇 |
1982年 | 632篇 |
1981年 | 623篇 |
1980年 | 584篇 |
1979年 | 527篇 |
1978年 | 599篇 |
1977年 | 562篇 |
1976年 | 473篇 |
1975年 | 452篇 |
1974年 | 459篇 |
1973年 | 441篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
32.
A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions. 相似文献
33.
Demixing during film casting of blends of polystyrene, polymethylmethacrylate, and a symmetric diblock copolymer of styrene and methylmethacrylate is discussed. The concentration fluctuations in the homogeneous solutions were calculated in mean field approximation. The structures in the homogeneous and demixed solutions and in the dry films were measured by small-angle x-ray scattering, and the morphologies of the dry films were characterized by transmission electron microscopy. The structure of the dry blends is evidently already pre-formed in solution. 相似文献
34.
Summary. We generalise and apply a refinement indicator of the type originally designed by Mackenzie, Süli and Warnecke in [15] and
[16] for linear Friedrichs systems to the Euler equations of inviscid, compressible fluid flow. The Euler equations are symmetrized
by means of entropy variables and locally linearized about a constant state to obtain a symmetric hyperbolic system to which
an a posteriori error analysis of the type introduced in [15] can be applied. We discuss the details of the implementation of the refinement
indicator into the DLR--Code which is based on a finite volume method of box type on an unstructured grid and present numerical results.
Received May 15, 1995 / Revised version received April 17, 1996 相似文献
35.
Helmut Schmidhammer Eva Scherb-Bukowiecki Thomas A. Mayer Peter Schnholzer 《Helvetica chimica acta》1994,77(6):1590-1594
The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 . 相似文献
36.
37.
We examine two criteria for balance of a gain graph, one based on binary cycles and one on circles. The graphs for which each criterion is valid depend on the set of allowed gain groups. The binary cycle test is invalid, except for forests, if any possible gain group has an element of odd order. Assuming all groups are allowed, or all abelian groups, or merely the cyclic group of order 3, we characterize, both constructively and by forbidden minors, the graphs for which the circle test is valid. It turns out that these three classes of groups have the same set of forbidden minors. The exact reason for the importance of the ternary cyclic group is not clear. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
38.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
39.
Hugh Thomas 《Order》2006,23(2-3):249-269
In this paper, we study lattices that posess both the properties of being extremal (in the sense of Markowsky) and of being left modular (in the sense of Blass and Sagan). We call such lattices trim and show that they posess some additional appealing properties, analogous to those of a distributive lattice. For example, trimness is preserved under taking intervals and suitable sublattices. Trim lattices satisfy a weakened form of modularity. The order complex of a trim lattice is contractible or homotopic to a sphere; the latter holds exactly if the maximum element of the lattice is a join of atoms. Any distributive lattice is trim, but trim lattices need not be graded. The main example of ungraded trim lattices are the Tamari lattices and generalizations of them. We show that the Cambrian lattices in types A and B defined by Reading are trim; we conjecture that all Cambrian lattices are trim. 相似文献