全文获取类型
收费全文 | 8916篇 |
免费 | 1375篇 |
国内免费 | 966篇 |
专业分类
化学 | 5906篇 |
晶体学 | 101篇 |
力学 | 533篇 |
综合类 | 52篇 |
数学 | 805篇 |
物理学 | 3860篇 |
出版年
2024年 | 32篇 |
2023年 | 194篇 |
2022年 | 272篇 |
2021年 | 283篇 |
2020年 | 335篇 |
2019年 | 318篇 |
2018年 | 278篇 |
2017年 | 265篇 |
2016年 | 433篇 |
2015年 | 386篇 |
2014年 | 477篇 |
2013年 | 647篇 |
2012年 | 713篇 |
2011年 | 733篇 |
2010年 | 494篇 |
2009年 | 515篇 |
2008年 | 539篇 |
2007年 | 465篇 |
2006年 | 439篇 |
2005年 | 420篇 |
2004年 | 333篇 |
2003年 | 251篇 |
2002年 | 268篇 |
2001年 | 197篇 |
2000年 | 209篇 |
1999年 | 219篇 |
1998年 | 172篇 |
1997年 | 155篇 |
1996年 | 178篇 |
1995年 | 126篇 |
1994年 | 139篇 |
1993年 | 126篇 |
1992年 | 121篇 |
1991年 | 90篇 |
1990年 | 67篇 |
1989年 | 75篇 |
1988年 | 56篇 |
1987年 | 50篇 |
1986年 | 42篇 |
1985年 | 35篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
1.
Identification of metabolites of rupestonic acid in rat urine by liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry 下载免费PDF全文
Dongyu Gu Yi Yang Qibin Chen Madina Habasi Jiangyu Zhao Haji Akber Aisa 《Biomedical chromatography : BMC》2015,29(4):595-603
Rupestonic acid, a potential anti‐influenza agent, is an important and characteristic compound in Artemisia rupestris L., a well‐known traditional Uighur medicine for the treatment of colds. In the present study, high‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry was used to detect and identify the metabolites in rat urine after oral administration of rupestonic acid. A total of 10 metabolites were identified or partially characterized. The structure elucidations of the metabolites were performed by comparing the changes in accurate molecular masses and fragment ions with those of the parent compound. The results showed that the main metabolites of rupestonic acid in rat urine were formed by oxidation, hydrogenation and glucuronidation. A metabolism pathway was proposed for the first time based on the characterized structures. This metabolism study can provide essential information for drug discovery, design and clinical application of rupestonic acid. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
This study is concerned with a new,explicit approach by means of which forms of the large strain elastic potential for multiaxial rubberlike elasticity may be obtained based on data for a single deformation mode.As a departure from usual studies,here for the first time errors may be estimated and rendered minimal for all possible deformation modes and,furthermore,failure behavior may be incorporated.Numerical examples presented are in accurate agreement with Treloar's well-known data. 相似文献
3.
4.
提出用溶胶粒子表面修饰方法,结合溶胶凝胶技术制备无机催化膜.该方法的基本原理是利用合适的金属配合物在胶粒表面的吸附作用,经溶胶凝胶过程,将活性组分结合到无机膜中.实验测定结果表明:(NiEDTA)2-,VO-3,MoO2-4,(Pd(NH3)4)2+,PdCl2-4,PtCl2-6和RhCl3-6可用来修饰AlOOH溶胶.以Pd/γAl2O3催化膜的制备为例,经三次溶胶凝胶过程,可制得无裂缺的厚度为9μm的Pd/γAl2O3催化膜,膜材料的平均孔直径为6nm,Pd被均匀地分布在膜的顶层,其平均粒径为23nm. 相似文献
5.
6.
Inspired by the recent work [HHM03], we prove two stability results for compact Riemannian manifolds with nonzero parallel spinors. Our first result says that Ricci flat metrics which also admit nonzero parallel spinors are stable (in the direction of changes in conformal structures) as the critical points of the total scalar curvature functional. Our second result, which is a local version of the first one, shows that any metric of positive scalar curvature cannot lie too close to a metric with nonzero parallel spinor. We also prove a rigidity result for special holonomy metrics. In the case of SU(m) holonomy, the rigidity result implies that scalar flat deformations of Calabi-Yau metric must be Calabi-Yau. Finally we explore the connection with a positive mass theorem of [D03], which presents another approach to proving these stability and rigidity results. Dedicated to Jeff Cheeger for his sixtieth birthday 相似文献
7.
C Guéret N Jussien O Lhomme C Pavageau C Prins 《The Journal of the Operational Research Society》2003,54(5):458-465
In this paper, we describe an aircraft loading problem submitted by the French military agency (DGA) as part of a more general military airlift planning problem. It can be viewed as a kind of bi-dimensional bin-packing problem, with heterogeneous bins and several additional constraints. We introduce two-phase methods for solving this NP-hard problem. The first phase consists in building good initial solutions, thanks to two fast algorithms: a list-based heuristic and a loading pattern generation method. Both algorithms call a constraint-based subroutine, able to determine quickly if the items already loaded can be reshuffled to accommodate a new object. The second phase improves these preliminary solutions using local search techniques. Results obtained on real data sets are presented. 相似文献
8.
A reliable method is presented for the chiral separation of three basic drugs (mexiletine, chlorpheniramine and propranolol) with serum albumins (human and porcine, HSA and PSA) as chiral selectors by capillary electrophoresis in combination with the partial filling technique. Based on the systematic optimization of operation variables, the chiral separation of mexiletine, chlorpheniramine and propranolol was achieved in the pH 7.4 phosphate buffer by using HSA, PSA and PSA as selectors, respectively. The chiral recognition ability of HSA and PSA was compared. HSA and PSA show a different chiral recognition ability for each of the three drugs. In addition, the association constants between enantiomeric drugs and proteins were determined to be 2.00 and 3.80 x 10(2) M(-1) for mexiletine and HSA, 0.59 and 1.12 x 10(3) M(-1) for chlorpheniramine and PSA, and 0.87 and 1.42 x 10(3) M(-1) for propranolol and PSA. The method for the chiral separation and determination of association constants possesses the advantages of simple performance, effective avoiding of the interference of the UV detection from protein, and lowering of the reagent consumption. 相似文献
9.
随机化交通灯的二维元胞自动机交通模型 总被引:8,自引:0,他引:8
元胞自动机交通模型以简单的规则反映交通系统中的多种因素,可以分析各种交通现象,且可在计算机上方便、高效地运作·Biham-Middleton-Levine模型(BML模型)实现了二维交通问题的元胞自动机模型的模拟研究·本文对BML模型作了改进,解除了该模型中关于交通灯同步变化的限制·在新模型中,每个路口的交通灯可以自由选定起始工作时间和变化节奏,于是可以更全面、准确地反映交通灯对交通系统性能的影响·本文还对新模型中出现的若干新效应作了解释· 相似文献
10.
Xiaodong Hu 《应用数学学报(英文版)》1993,9(2):97-103
Since the point-to-set maps were introduced by Zangwill[1] in the study of conceptual algorithms, various sufficient conditions for the algorithms to be of global convergence have been established. In this paper, the relations among all these conditions are illustrated by a unified approach; still more, unlike the sufficient conditions previously given in the literature, a new necessary condition is put forward at the end of the paper, so that it implies more applications. 相似文献