全文获取类型
收费全文 | 5019篇 |
免费 | 209篇 |
国内免费 | 31篇 |
专业分类
化学 | 3782篇 |
晶体学 | 24篇 |
力学 | 66篇 |
数学 | 657篇 |
物理学 | 730篇 |
出版年
2024年 | 8篇 |
2023年 | 31篇 |
2022年 | 150篇 |
2021年 | 193篇 |
2020年 | 123篇 |
2019年 | 144篇 |
2018年 | 151篇 |
2017年 | 115篇 |
2016年 | 201篇 |
2015年 | 177篇 |
2014年 | 202篇 |
2013年 | 305篇 |
2012年 | 359篇 |
2011年 | 389篇 |
2010年 | 239篇 |
2009年 | 180篇 |
2008年 | 337篇 |
2007年 | 339篇 |
2006年 | 278篇 |
2005年 | 274篇 |
2004年 | 209篇 |
2003年 | 156篇 |
2002年 | 141篇 |
2001年 | 50篇 |
2000年 | 41篇 |
1999年 | 45篇 |
1998年 | 39篇 |
1997年 | 29篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 33篇 |
1993年 | 21篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1973年 | 8篇 |
1954年 | 5篇 |
排序方式: 共有5259条查询结果,搜索用时 234 毫秒
951.
Classic demonstrations of the phonemic restoration effect show increased intelligibility of interrupted speech when the interruptions are caused by a plausible masking sound rather than by silent periods. Previous studies of this effect have been conducted exclusively under anechoic or nearly anechoic listening conditions. This study demonstrates that the effect is reversed when sounds are presented in a realistically simulated reverberant room (broadband T(60) = 1.1 s): intelligibility is greater for silent interruptions than for interruptions by unmodulated noise. Additional results suggest that the reversal is primarily due to filling silent intervals with reverberant energy from the speech signal. 相似文献
952.
Yulin Ren Sijin Wu Sijie Chen Joanna E. Burdette Xiaolin Cheng A. Douglas Kinghorn 《Molecules (Basel, Switzerland)》2021,26(18)
Docking profiles for (+)-strebloside, a cytotoxic cardiac glycoside identified from Streblus asper, and some of its derivatives and Na+/K+-ATPase have been investigated. In addition, binding between (+)-strebloside and its aglycone, strophanthidin, and several of their other molecular targets, including FIH-1, HDAC, KEAP1 and MDM2 (negative regulators of Nrf2 and p53, respectively), NF-κB, and PI3K and Akt1, have been inspected and compared with those for digoxin and its aglycone, digoxigenin. The results showed that (+)-strebloside, digoxin, and their aglycones bind to KEAP1 and MDM2, while (+)-strebloside, strophanthidin, and digoxigenin dock to the active pocket of PI3K, and (+)-strebloside and digoxin interact with FIH-1. Thus, these cardiac glycosides could directly target HIF-1, Nrf2, and p53 protein–protein interactions, Na+/K+-ATPase, and PI3K to mediate their antitumor activity. Overall, (+)-strebloside seems more promising than digoxin for the development of potential anticancer agents. 相似文献
953.
Modesto T. López-López Pavel Kuzhir Georges Bossis Pavel Mingalyov 《Rheologica Acta》2008,47(7):787-796
In this work, we describe methods for the preparation of suspensions of micron-sized iron particles grafted with different
surfactants. The aim is to obtain well-dispersed magnetorheological (MR) fluids. The effectiveness of the surfactants as dispersants
was analyzed quantitatively by means of rheological measurements. With this objective, the viscosity of the suspensions was
measured, and the results were compared with the prediction of the Batchelor’s formula (Batchelor, J Fluid Mech 83:97–117, 1977). The effect of dispersion on the MR properties of the suspensions was also studied. It was found that the
quality of the dispersion of a suspension does not have an important effect on the magnitude of the field-induced yield stress
but does on the change of viscosity induced by the field. It was also found that the transition from the solid-like state
to the liquid-like one happens very smoothly for well-dispersed suspensions, contrarily to the abrupt transition for poorly
dispersed suspensions. 相似文献
954.
LetA be an elementary abelianq-group acting on a finiteq′-groupG. We show that ifA has rank at least 3, then properties ofC
G(a)′, 1 ≠a ∈A restrict the structure ofG′. In particular, we consider exponent, order, rank and number of generators.
This author was supported by the NSF.
This author was supported by CNPq-Brazil. 相似文献
955.
Plasma Chemistry and Plasma Processing - 相似文献
956.
Ellen Matthaei-Schulz Tony Flaherty Colm Flannery Tony Randles Odile Lefeuvre Pavel Zinin Laurent Robert 《Mikrochimica acta》2000,133(1-4):11-15
For quantitative assessment of the properties of hard coatings there is an increasing demand for testing methods with high
reliability of the test results, especially concerning the independence of the method and the comparability between different
laboratories. This includes the knowledge about all the factors which influence the test procedure itself, determination of
best testing conditions, testing of these conditions in round-robins to get a view of the comparability of results, and formulation
of guidelines for standardization. In a European project several test methods for hard coatings on steel were investigated
for this purpose and the elastic moduli of the coating and coating thickness were determined non-destructively by means of
quantitative acoustic microscopy. This method and the instruments available had not yet been certified in the fields of coatings
simply owing to the absence of standardised signal processing, followed by the determination of sound velocities and materials
parameter extraction. For this purpose four laboratories carried out investigations and measurements on reference samples
and on two types of hard coatings (titanium nitride and C-doped chromium) on M2 tool steel. 相似文献
957.
Joanna Kobyłecka Bogdan Ptaszyński Anna Zwolinńska 《Monatshefte für Chemie / Chemical Monthly》2000,131(1):1-11
Summary. Sparingly water soluble complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine (glyphosate, NPMG) of the general formulae C3H6O5NPPb, C3H6O5NPCdċ2H2O, and C3H6O5NPZn were synthesized. The complexes were also precipited from a dilute Roundup solution, and their solubility in water was
determined. Thermal, diffractometric, and IR spectrophotometric analyses were carried out. It was found that the metal is
bonded to glyphosate through the oxygen atoms of the carboxylic and phosphonate groups; metal-nitrogen binding is absent in
the above compounds. Studying the complexing behaviour in solution by UV spectrophotometry pointed out that a complex of the
composition Pb(II) : NPMG=1:1 with an absorption band at 232 nm is formed. Its stability constant as determined by Job’s method is logK=5.9±0.1. Using potentiometric techniques, the dissociation constant of N-phosphonomethylglycine and the stability constants
of its complexes with cadmium (II) and zinc (II) were determined.
Received June 30, 1999/Accepted July 21, 1999. 相似文献
958.
Pavel Hradil Lubomír Kvapil Jan Hlav
Tom Weidlich Antonín Ly
ka Karel Lemr 《Journal of heterocyclic chemistry》2000,37(4):831-837
The cyclization of phenacyl anthranilate has been studied with the aim to develop the synthesis of 2‐(2′‐aminophenyl)‐4‐phenyloxazole. However, a different course of the reaction than expected was observed. 2‐Phenyl‐2‐hydroxymethyl‐4‐oxo‐1,2,3,4‐tetrahydroquinazoline ( 3a ) was formed by the reaction of phenacyl anthranilate ( 2 ) with ammonium acetate under various conditions. 3‐Hydroxy‐2‐phenyl‐4(1H)‐quinolinone ( 4 ) arose by heating compound 3a in acetic acid. The same compound was obtained by melting compound 3a , but the yield was lower. Different types of products resulted in the reaction of compound 3a with acetic anhydride. Under mild conditions acetylated products 2‐acetoxymethyl‐2‐phenyl‐4‐oxo‐1,2,3,4‐tetrahydroquinazoline ( 7a ) and 2‐acetoxymethyl‐3‐acetyl‐2‐phenyl‐4‐oxo‐1,2,3,4‐tetrahydroquinazoline ( 8 ) were prepared. If the reaction was carried out under reflux of the reaction mixture, molecular rearrangement took place to give cis and trans 2‐methyl‐4‐oxo‐3‐(1‐phenyl‐2‐acetoxy)vinyl‐3,4‐dihydroquinazolines ( 9a and 9b ). All prepared compounds have been characterised by their 1H, 13C and 15N NMR spectra, IR spectra and MS. 相似文献
959.
Joanna Józefowska Marek Mika Rafał Różycki Grzegorz Waligóra Jan Weglarz 《Mathematical Methods of Operations Research》2000,52(3):489-499
In this paper a discrete-continuous project scheduling problem is considered. In this problem activities simultaneously require
discrete and continuous resources. The processing rate of each activity depends on the amount of the continuous resource allotted
to this activity at a time. All the resources are renewable ones. The activities are nonpreemtable and the objective is to
minimize the makespan. Discretization of this problem leading to a classical (i.e. discrete) project scheduling problem in
the multi-mode version is presented. A simulated annealing (SA) approach to solving this problem is described and tested computationally
in two versions: with and without finding an optimal continuous resource allocation for the final schedule. In the former
case a nonlinear solver is used for solving a corresponding convex programming problem. The results are compared with the
results obtained using SA for the discrete-continuous project scheduling problem where the nonlinear solver is used for exact
solving the continuous part in each iteration. The results of a computational experiment are analyzed and some conclusions
are included. 相似文献
960.
Pavel Bleher Bernard Shiffman Steve Zelditch 《Communications in Mathematical Physics》2000,208(3):771-785
This note is concerned with the scaling limit as N→∞ of n-point correlations between zeros of random holomorphic polynomials of degree N in m variables. More generally we study correlations between zeros of holomorphic sections of powers L
N
of any positive holomorphic line bundle L over a compact K?hler manifold. Distances are rescaled so that the average density of zeros is independent of N. Our main result is that the scaling limits of the correlation functions and, more generally, of the “correlation forms”
are universal, i.e. independent of the bundle L, manifold M or point on M.
Received: 17 March 1999 / Accepted: 5 August 1999 相似文献