全文获取类型
收费全文 | 39536篇 |
免费 | 1397篇 |
国内免费 | 151篇 |
专业分类
化学 | 20761篇 |
晶体学 | 205篇 |
力学 | 1082篇 |
综合类 | 7篇 |
数学 | 6661篇 |
物理学 | 12368篇 |
出版年
2023年 | 254篇 |
2021年 | 340篇 |
2020年 | 495篇 |
2019年 | 383篇 |
2018年 | 525篇 |
2017年 | 515篇 |
2016年 | 1069篇 |
2015年 | 811篇 |
2014年 | 926篇 |
2013年 | 1989篇 |
2012年 | 1782篇 |
2011年 | 1923篇 |
2010年 | 1290篇 |
2009年 | 1074篇 |
2008年 | 1800篇 |
2007年 | 1681篇 |
2006年 | 1614篇 |
2005年 | 1444篇 |
2004年 | 1253篇 |
2003年 | 1031篇 |
2002年 | 914篇 |
2001年 | 869篇 |
2000年 | 702篇 |
1999年 | 490篇 |
1998年 | 427篇 |
1997年 | 424篇 |
1996年 | 522篇 |
1995年 | 461篇 |
1994年 | 498篇 |
1993年 | 505篇 |
1992年 | 553篇 |
1991年 | 382篇 |
1990年 | 390篇 |
1989年 | 350篇 |
1988年 | 329篇 |
1987年 | 342篇 |
1986年 | 313篇 |
1985年 | 500篇 |
1984年 | 482篇 |
1983年 | 403篇 |
1982年 | 427篇 |
1981年 | 422篇 |
1980年 | 421篇 |
1979年 | 406篇 |
1978年 | 394篇 |
1977年 | 394篇 |
1976年 | 364篇 |
1975年 | 357篇 |
1974年 | 346篇 |
1973年 | 294篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
211.
G. Dlubek R. Krause O. Brümmer J. Tittes 《Applied Physics A: Materials Science & Processing》1987,42(2):125-127
Positron-lifetime measurements have been used to study the annealing of vacancies in neutron-irradiated GaAs. The vacancies which are interpreted as defects in the Ga sublattice disappear in a single annealing stage (at 500°C in GaAs doped with Si or Zn, and at 600°C in Cr-doped GaAs). 相似文献
212.
213.
C. Scheidenberger K. Beckert P. Beller F. Bosch C. Brandau D. Boutin L. Chen B. Franzke H. Geissel R. Knöbel C. Kozhuharov J. Kurcewicz S. A. Litvinov Yu. A. Litvinov M. Mazzocco G. Münzenberg F. Nolden W. R. Plaß M. Steck B. Sun H. Weick M. Winkler 《Hyperfine Interactions》2006,173(1-3):61-66
One important goal of the ILIMA project at FAIR is the study of masses and decay properties of relativistic isomeric beams
stored and cooled in the planned storage-ring complex. A new scheme is described, where a storage-cooler ring is used for
high-resolution mass separation. Experimental results on the separation of the isobaric pair 140Pr-140Ce are presented.
P. Beller, deceased. 相似文献
214.
Let R be a local ring and let (x
1, …, x
r) be part of a system of parameters of a finitely generated R-module M, where r < dimR
M. We will show that if (y
1, …, y
r) is part of a reducing system of parameters of M with (y
1, …, y
r) M = (x
1, …, x
r) M then (x
1, …, x
r) is already reducing. Moreover, there is such a part of a reducing system of parameters of M iff for all primes P ε Supp M ∩ V
R(x
1, …, x
r) with dimR
R/P = dimR
M − r the localization M
P of M at P is an r-dimensional Cohen-Macaulay module over R
P.
Furthermore, we will show that M is a Cohen-Macaulay module iff y
d is a non zero divisor on M/(y
1, …, y
d−1) M, where (y
1, …, y
d) is a reducing system of parameters of M (d:= dimR
M). 相似文献
215.
216.
In this paper we address the problem of scheduling unit time jobs in a flowshop to minimize makespan under a discrete renewable resource constraint. We propose algorithms having complexityO(n) for special cases of two machine and three machine problems. For the three machineN P-hard problem we develop a branch and bound procedure and several upper and lower bounds. We test the efficiency of the procedure and report our computational experience.Suna Kondakci was a visiting assistant professor at the Industrial Engineering Department, Purdue University, when the paper was revised. 相似文献
217.
218.
A quick sample preparation method was used for the determination of sulphur and trace metals in oil and oily products by the ICP with a minitorch. Stable aqueous emulsions of oils and oil products were made by using two kinds of emulsifiers (one with low sulphur content, the other sulfonated). Aqueous standard solutions can be used for the preparation of calibration solutions. The contents of S, Al, Cr, Cu, Fe, Mg, Ni and Pb in aqueous emulsions were determined and the results were in good agreement with the composition of oil standard solutions used for control analysis procedure. 相似文献
219.
Modelling financial and insurance time series with Lévy processes or with exponential Lévy processes is a relevant actual practice and an active area of research. It allows qualitatively and quantitatively good adaptation to the empirical statistical properties of asset returns. Due to model incompleteness it is a problem of considerable interest to determine the dependence of option prices in these models on the choice of pricing measures and to establish nontrivial price bounds. In this paper we review and extend ordering results of stochastic and convex type for this class of models. We also extend the ordering results to processes with independent increments (PII) and present several examples and applications as to α-stable processes, NIG-processes, GH-distributions, and others. Criteria are given for the Lévy measures which imply corresponding comparison results for European type options in (exponential) Lévy models. 相似文献
220.
Susanne K. Wiedmer Toni Andersson Marika Sündermann Marja‐Liisa Riekkola Heikki Tenhu 《Journal of Polymer Science.Polymer Physics》2007,45(19):2655-2663
Cationic polyelectrolytes were synthesized and used as semipermanent coating materials for capillaries in electrophoresis. The polyelectrolytes used were a homopolymer of poly(methacryl oxyethyl trimethylammonium chloride) (PMOTAC) and its poly(ethylene glycol) (PEG)‐grafted analogue. Two PMOTAC polyelectrolytes, with molar masses of 85,000 and 300,000 g/mol, and PEG‐grafted PMOTAC with a molar mass of 280,000 g/mol were synthesized and then characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. Attachment of the polyelectrolytes to the wall of the fused silica capillary for electrophoresis caused the electroosmotic flow (EOF) to reverse. The polyelectrolyte coatings were tested over the pH range 2–11 at different buffer ionic strengths, and the most stable and strongest anodic EOFs were obtained at acidic pH values with low ionic strength buffers. Between runs the capillary is merely rinsed for 2 or 3 min with the background electrolyte solution. With the PMOTAC coatings at pH values ≤5, the RSDs of the EOFs were less than 2.9% after 60 injections. The effects of the molar mass of the polycation and of PEGylation of PMOTAC on the interactions between the polycations and basic proteins were studied at acidic pH values. The differences in the effective electrophoretic mobilities, resolution values, and plate numbers of the proteins with the different coatings were due to the EOF, as demonstrated through calculations of reduced mobilities, relative resolution values, and relative plate numbers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2655–2663, 2007 相似文献