全文获取类型
收费全文 | 204842篇 |
免费 | 2122篇 |
国内免费 | 701篇 |
专业分类
化学 | 114539篇 |
晶体学 | 3429篇 |
力学 | 8048篇 |
综合类 | 5篇 |
数学 | 20194篇 |
物理学 | 61450篇 |
出版年
2016年 | 2471篇 |
2015年 | 1845篇 |
2014年 | 2571篇 |
2013年 | 8330篇 |
2012年 | 5700篇 |
2011年 | 7132篇 |
2010年 | 4691篇 |
2009年 | 4598篇 |
2008年 | 6477篇 |
2007年 | 6662篇 |
2006年 | 6397篇 |
2005年 | 5873篇 |
2004年 | 5357篇 |
2003年 | 4750篇 |
2002年 | 4690篇 |
2001年 | 5873篇 |
2000年 | 4500篇 |
1999年 | 3620篇 |
1998年 | 2849篇 |
1997年 | 2913篇 |
1996年 | 2881篇 |
1995年 | 2617篇 |
1994年 | 2492篇 |
1993年 | 2401篇 |
1992年 | 2889篇 |
1991年 | 2754篇 |
1990年 | 2723篇 |
1989年 | 2739篇 |
1988年 | 2672篇 |
1987年 | 2663篇 |
1986年 | 2486篇 |
1985年 | 3428篇 |
1984年 | 3440篇 |
1983年 | 2837篇 |
1982年 | 3104篇 |
1981年 | 3013篇 |
1980年 | 2903篇 |
1979年 | 3019篇 |
1978年 | 3265篇 |
1977年 | 3075篇 |
1976年 | 3018篇 |
1975年 | 2866篇 |
1974年 | 2830篇 |
1973年 | 2828篇 |
1972年 | 1825篇 |
1971年 | 1524篇 |
1968年 | 1983篇 |
1967年 | 2157篇 |
1966年 | 1949篇 |
1965年 | 1514篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
43.
In this paper we introduce symplectic invariants for convex Hamiltonian energy surfaces and their periodic trajectories and show that these quentities satisfy several nontrivial relations. In particular we show that they can be used to prove multiplicity results for the number of periodic trajectories.This paper represents results obtained while holding a visiting position at the Courant Institute for Mathematical Sciences, New YorkResearch partially supported by NSF Grant No. DMS-8603149 and a Rutgers University Research Council Grant 相似文献
44.
H. Moers H. Klewe-Nebenius G. Pfennig und H. J. Ache 《Fresenius' Journal of Analytical Chemistry》1987,329(2-3):361-366
Summary The adsorption of gaseous molecular iodine on clean silver surfaces proceeds in the first stage by dissociative chemisorption. After the formation of half a monolayer of chemisorbed iodine atoms the formation of silver iodide begins, which forms a very regular overlayer on top of the substrate. Both iodine species can be distinguished due to a difference in chemical shift of the M4N4, 5N4, 5-Auger transitions. After completion of this overlayer further iodine uptake is slowed down significantly. Above an overlayer thickness of about 10 nm a further progress of the reaction cannot be followed anymore due to the limited information depth of XPS. 相似文献
45.
Mo2Ni3Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo2Ni3Si primary dendrites and the interdendritic Mo2Ni3Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo2Ni3Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance. 相似文献
46.
47.
F. Prez-Willard C. Sürgers H. Von Lhneysen P. Pfundstein 《Physica E: Low-dimensional Systems and Nanostructures》2004,22(4):872-880
The electronic transport through nanostructured bismuth nanobridges has been investigated at low temperatures (T<2 K) and in magnetic fields B up to 8.5 T. The samples show reproducible resistance fluctuations as a function of B, superimposed on a large magnetoresistance of up to 50%. In addition, time-dependent resistance fluctuations in zero magnetic field demonstrate the presence of bistable scatterers in the constriction region of our samples, which are described by two-level systems. Their dynamics are shown to be sensitive to subtle modifications of the static scatterer configuration in their vicinity, which cannot be detected in the sample magnetofingerprint. 相似文献
48.
Yu. A. Kumzerov L. S. Parfen’eva I. A. Smirnov H. Misiorek J. Mucha A. Jezowski 《Physics of the Solid State》2003,45(1):57-60
The thermal conductivity of crystalline chrysotile asbestos made up of hollow tubular Mg3Si2O5(OH)4 filaments is measured in the range 5–300 K. The paper discusses the possibility of using this material in studies of the thermal conductivity of thin filaments of metals and semiconductors incorporated into the channels of crystalline chrysotile asbestos tubes. 相似文献
49.
We provide a rigorous derivation of an asymptotic formula for perturbations in the eigenvalues caused by the presence of a finite number of inhomogeneities of small diameter with conductivity different from the background conductivity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
50.
Dominique Fourdrinier William E. Strawderman 《Annals of the Institute of Statistical Mathematics》2003,55(4):803-816
We consider estimation of loss for generalized Bayes or pseudo-Bayes estimators of a multivariate normal mean vector, θ. In
3 and higher dimensions, the MLEX is UMVUE and minimax but is inadmissible. It is dominated by the James-Stein estimator and by many others. Johnstone (1988,
On inadmissibility of some unbiased estimates of loss,Statistical Decision Theory and Related Topics, IV (eds. S. S. Gupta and J. O. Berger), Vol. 1, 361–379, Springer, New York) considered the estimation of loss for the usual
estimatorX and the James-Stein estimator. He found improvements over the Stein unbiased estimator of risk. In this paper, for a generalized
Bayes point estimator of θ, we compare generalized Bayes estimators to unbiased estimators of loss. We find, somewhat surprisingly,
that the unbiased estimator often dominates the corresponding generalized Bayes estimator of loss for priors which give minimax
estimators in the original point estimation problem. In particular, we give a class of priors for which the generalized Bayes
estimator of θ is admissible and minimax but for which the unbiased estimator of loss dominates the generalized Bayes estimator
of loss. We also give a general inadmissibility result for a generalized Bayes estimator of loss.
Research supported by NSF Grant DMS-97-04524. 相似文献