全文获取类型
收费全文 | 26503篇 |
免费 | 1604篇 |
国内免费 | 4383篇 |
专业分类
化学 | 23037篇 |
晶体学 | 1083篇 |
力学 | 225篇 |
综合类 | 219篇 |
数学 | 3689篇 |
物理学 | 4237篇 |
出版年
2024年 | 14篇 |
2023年 | 181篇 |
2022年 | 629篇 |
2021年 | 792篇 |
2020年 | 587篇 |
2019年 | 616篇 |
2018年 | 468篇 |
2017年 | 626篇 |
2016年 | 680篇 |
2015年 | 621篇 |
2014年 | 916篇 |
2013年 | 2026篇 |
2012年 | 1427篇 |
2011年 | 1656篇 |
2010年 | 1627篇 |
2009年 | 1836篇 |
2008年 | 1821篇 |
2007年 | 1823篇 |
2006年 | 1737篇 |
2005年 | 1528篇 |
2004年 | 1500篇 |
2003年 | 1257篇 |
2002年 | 1107篇 |
2001年 | 837篇 |
2000年 | 800篇 |
1999年 | 632篇 |
1998年 | 658篇 |
1997年 | 523篇 |
1996年 | 453篇 |
1995年 | 478篇 |
1994年 | 428篇 |
1993年 | 381篇 |
1992年 | 347篇 |
1991年 | 278篇 |
1990年 | 156篇 |
1989年 | 196篇 |
1988年 | 150篇 |
1987年 | 108篇 |
1986年 | 78篇 |
1985年 | 78篇 |
1984年 | 103篇 |
1983年 | 27篇 |
1982年 | 46篇 |
1981年 | 60篇 |
1980年 | 51篇 |
1979年 | 40篇 |
1978年 | 29篇 |
1977年 | 22篇 |
1976年 | 11篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 224 毫秒
61.
The First Intramolecular Charge Transfer Transition Based on 2-Ureido-4[1H]-pyrimidinone Binding Module 总被引:1,自引:0,他引:1
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported. 相似文献
62.
Solid Phase Synthesis of 2-Substituted 1,3-Oxazin-6-ones Using Resin-bound Cyclic Malonic Acid Ester
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity. 相似文献
63.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
64.
65.
Philip Sinclair 《Discrete Mathematics》2004,286(3):171-175
Let G be a 2-connected graph with minimum degree at least 3. We prove that there exists an even circuit C in G with factorization F={F1,F2} such that G−E(F1) is 2-connected. 相似文献
66.
The authors study the bifurcation problems of rough heteroclinic loop connecting three saddle points for the case β1 > 1, β2 > 1, β3 < 1 and β1β2β3 < 1. The existence, number, coexistence and incoexistence of 2-point-loop, 1-homoclinic orbit and 1-periodic orbit are studied. Meanwhile, the bifurcation surfaces and existence regions are given. 相似文献
67.
Peter Naur 《BIT Numerical Mathematics》1986,26(2):175-187
The questions raised by A. M. Turing in his paper on thought and machines are discussed. Human thought is considered in turn as a concept of normal language usage, as a basic concept of psychology, and as the basis of intellectual activity. It is concluded that neither of these notions of thought identifies something specific that a human being can or cannot do. The imitation game proposed by Turing for deciding whether a machine can think is found to result from an arbitrary empoverishment of the channel of communication between the interrogator and the item under investigation. Turing's notions of thinking are shown to lead to logical difficulties. An alternative view of consciousness, that would place it beyond the reach of any finite test, is finally discussed. 相似文献
68.
69.
In [5] Phillips proved that one can obtain the additive group of any nonstandard model *? of the ring ? of integers by using a linear mod 1 function h : F ?, where F is the α-dimensional vector space over ? when α is the cardinality of *?. In this connection it arises the question whether there are linear mod 1 functions which are neither addition nor quasi-linear. We prove that this is the case. 相似文献
70.
同步荧光法测定食品中维生素B1 总被引:7,自引:0,他引:7
本文研究了食品中维生素B1的同步荧光法测定条件,采用氯化钾-乙醇作柱层析洗脱液,碱性介质中氧化后立即调为中性,并加入表面活性剂OP对体系增稳增敏,取代丁醇萃取,经济方便,用于几种粮食样品的测定,结果满意。 相似文献