全文获取类型
收费全文 | 27388篇 |
免费 | 1181篇 |
国内免费 | 147篇 |
专业分类
化学 | 18603篇 |
晶体学 | 215篇 |
力学 | 491篇 |
数学 | 3277篇 |
物理学 | 4308篇 |
无线电 | 1822篇 |
出版年
2023年 | 200篇 |
2022年 | 231篇 |
2021年 | 412篇 |
2020年 | 521篇 |
2019年 | 504篇 |
2018年 | 363篇 |
2017年 | 310篇 |
2016年 | 809篇 |
2015年 | 677篇 |
2014年 | 831篇 |
2013年 | 1307篇 |
2012年 | 1695篇 |
2011年 | 1884篇 |
2010年 | 1098篇 |
2009年 | 935篇 |
2008年 | 1564篇 |
2007年 | 1481篇 |
2006年 | 1445篇 |
2005年 | 1343篇 |
2004年 | 1187篇 |
2003年 | 906篇 |
2002年 | 939篇 |
2001年 | 479篇 |
2000年 | 395篇 |
1999年 | 384篇 |
1998年 | 387篇 |
1997年 | 363篇 |
1996年 | 367篇 |
1995年 | 314篇 |
1994年 | 338篇 |
1993年 | 318篇 |
1992年 | 271篇 |
1991年 | 205篇 |
1990年 | 242篇 |
1989年 | 203篇 |
1988年 | 201篇 |
1987年 | 185篇 |
1986年 | 176篇 |
1985年 | 284篇 |
1984年 | 273篇 |
1983年 | 200篇 |
1982年 | 214篇 |
1981年 | 194篇 |
1980年 | 200篇 |
1979年 | 173篇 |
1978年 | 206篇 |
1977年 | 208篇 |
1976年 | 151篇 |
1975年 | 155篇 |
1974年 | 172篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
This paper presents the problems in the implementation of multipoint connections at switching level using the example of an ATM switching network. By choosing the proper routeing mechanism and the appropriate architecture of the switching element, a switching network can gradually be adapted to an increasing share of multipoint traffic. The first section describes the problems with the handling of multipoint connections within a multiple stage connection oriented switching network. In particular this refers to the routeing of the cells through the switching network. Several alternatives on this issue are discussed. Both, the selected approach based on a differentiated self-routeing mechanism and the corresponding cell format are introduced. In the second part of this article several switch architectures are compared in respect of their multipoint capability. It is demonstrated that at present the most promising solution are switching elements based on the principle of central buffering. A single chip solution using this concept is employed in the presented switching network. 相似文献
82.
83.
A combined-modality treatment program consisting of botulinum toxin injection (Botox) and voice therapy was used to treat 17 subjects diagnosed with adductor spasmodic dysphonia (ADD SD). Ten subjects with ADD SD served as the control and were given Botox only. Voice therapy after Botox injection was directed toward reducing the hyperfunctional vocal behaviors, primarily glottal overpressure at voice onset and anterior-posterior squeezing. The results indicated that subjects who underwent combined-modality treatment maintained significantly higher mean airflow rates for significantly longer periods. Moreover, there was a carryover effect in these patients when they received Botox only. Adductor spasmodic dysphonia is treated most effectively when intrinsic laryngeal muscle spasms are reduced or eliminated by Botox injection and extrinsic hyperfunctional vocal behaviors are treated with voice therapy 相似文献
84.
As pan of a biomimetic approach towards me marine triterpene teurilene (2), the synthesis of the chiral diepoxide 3 is described. Aiming at the synthesis of the squalene tetraepoxide 1, double Sharpless epoxidation led to the intermediate bisglycidic alcohol 7 being subject to a stereochemical analysis. 相似文献
85.
86.
87.
Simon Thomas 《Archive for Mathematical Logic》1998,37(7):483-493
We study the relationship between the cofinality of the infinite symmetric group and the cardinal invariants and . In particular, we prove the following two results.
Theorem 0.1
It is consistent with
ZFC
that there exists a simple
$P_{\omega_{1}}$
-point and that
$c(Sym(\omega)) = \omega_{2} = 2^{\omega}$
.
Theorem 0.2
If there exist both a simple
$P_{\omega_{1}}$
-point and a
$P_{\omega_{2}}$
-point, then
$c(Sym(\omega)) = \omega_{1}$
.
Received: 7 March 1996 相似文献
88.
We consider a spatially distributed hybrid system consisting of a convection/reaction system in which the reaction switches discontinuously in time between modes, independently at each spatial point on reaching “switching thresholds”. The model involves a novel formulation for evolution of the free boundary between the modal regions. 相似文献
89.
90.
We give combinatorial proofs that certain families of differences of products of Schur functions are monomial-positive. We
show in addition that such monomial-positivity is to be expected of a large class of generating functions with combinatorial
definitions similar to Schur functions. These generating functions are defined on posets with labelled Hasse diagrams and
include for example generating functions of Stanley's (P,ω)-partitions.
T.L. was supported in part by NSF DMS-0600677. 相似文献