全文获取类型
收费全文 | 33963篇 |
免费 | 1812篇 |
国内免费 | 1802篇 |
专业分类
化学 | 21774篇 |
晶体学 | 139篇 |
力学 | 473篇 |
综合类 | 613篇 |
数学 | 6556篇 |
物理学 | 8022篇 |
出版年
2023年 | 635篇 |
2022年 | 366篇 |
2021年 | 1386篇 |
2020年 | 648篇 |
2019年 | 779篇 |
2018年 | 532篇 |
2017年 | 552篇 |
2016年 | 710篇 |
2015年 | 793篇 |
2014年 | 1054篇 |
2013年 | 1913篇 |
2012年 | 1225篇 |
2011年 | 1441篇 |
2010年 | 1368篇 |
2009年 | 1788篇 |
2008年 | 1892篇 |
2007年 | 2051篇 |
2006年 | 1551篇 |
2005年 | 957篇 |
2004年 | 942篇 |
2003年 | 931篇 |
2002年 | 3425篇 |
2001年 | 1154篇 |
2000年 | 719篇 |
1999年 | 575篇 |
1998年 | 590篇 |
1997年 | 409篇 |
1996年 | 506篇 |
1995年 | 429篇 |
1994年 | 388篇 |
1993年 | 433篇 |
1992年 | 425篇 |
1991年 | 285篇 |
1990年 | 240篇 |
1989年 | 199篇 |
1988年 | 231篇 |
1987年 | 188篇 |
1986年 | 204篇 |
1985年 | 313篇 |
1984年 | 230篇 |
1983年 | 140篇 |
1982年 | 286篇 |
1981年 | 463篇 |
1980年 | 427篇 |
1979年 | 465篇 |
1978年 | 373篇 |
1977年 | 283篇 |
1976年 | 240篇 |
1974年 | 75篇 |
1973年 | 151篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
当s∈ R,0,〈q, p〈∈∞,0,〈β≤∞且 max{-n/q,-nδ2/qδ1}〈a时,定义了加权Herz—type Triebel-Lizorkin空间kq^q,pF^s β(R^n,ω1,ω2)和Kq^a,pF^sβ(R^n,ω1,ω2),并给出这些空间的一些特征及在这些空间上的Hard—Littlewood极大算子不等式. 相似文献
92.
Roberto E. Madariaga-Garcia 《Topology and its Applications》2007,154(7):1470-1480
Tkachenko showed in 1990 the existence of a countably compact group topology on the free Abelian group of size c using CH. Koszmider, Tomita and Watson showed in 2000 the existence of a countably compact group topology on the free Abelian group of size c2 using a forcing model in which CH holds.Wallace's question from 1955, asks whether every both-sided cancellative countably compact semigroup is a topological group. A counterexample to Wallace's question has been called a Wallace semigroup. In 1996, Robbie and Svetlichny constructed a Wallace semigroup under CH. In the same year, Tomita constructed a Wallace semigroup from MAcountable.In this note, we show that the examples of Tkachenko, Robbie and Svetlichny, and Koszmider, Tomita and Watson can be obtained using a family of selective ultrafilters. As a corollary, the constructions presented here are compatible with the total failure of Martin's Axiom. 相似文献
93.
We construct cellular homotopy theories for categories of simplicial presheaves on small Grothendieck sites and discuss applications to the motivic homotopy category of Morel and Voevodsky. 相似文献
94.
The main results of the paper are as follows: covering characterizations of wQN-spaces, covering characterizations of QN-spaces and a theorem saying that Cp(X) has the Arkhangel'ski?ˇ property (α1) provided that X is a QN-space. The latter statement solves a problem posed by M. Scheepers [M. Scheepers, Cp(X) and Arhangel'ski?ˇ's αi-spaces, Topology Appl. 89 (1998) 265-275] and for Tychonoff spaces was independently proved by M. Sakai [M. Sakai, The sequence selection properties of Cp(X), Preprint, April 25, 2006]. As the most interesting result we consider the equivalence that a normal topological space X is a wQN-space if and only if X has the property S1(Γshr,Γ). Moreover we show that X is a QN-space if and only if Cp(X) has the property (α0), and for perfectly normal spaces, if and only if X has the covering property (β3). 相似文献
95.
The knowledge of hydrocarbon/water phase equilibria is important in the design and operation of equipment for petroleum transport and refining and petrochemical plants. The presence of water in a hydrocarbon mixture can affect the product quality and damage the operation equipment due to corrosion and formation of gas hydrates. Tracing the concentration of hydrocarbons in aqueous media is also important for technical purposes like preventing oil spills and for ecological concerns such as predicting the fate of these organic pollutants in the environment. 相似文献
96.
This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel.
From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission
electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the
block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant
in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different
values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly
oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical
particle model with a locked aspect ratio. 相似文献
97.
通过光谱响应特性实验和记录/读出图像实验,研究了基因变异型细菌视紫红质(BRD96N)分子膜对单色光的光调制特性.发现BRD96N分子膜在550nm—600nm范围内对调制光有吸收增强的现象,且对此范围内不同波长的单色光其调制程度有差异.利用曲线拟和方法发现550nm—600nm吸收增强的变化过程分为快过程和慢过程,其对应的时间常数分别为30s和5min.利用强度调制器的吸收强度与图像灰度之间的关系,分析了560nm—600nm范围内出现图像反转的实验现象.
关键词:
细菌视紫红质D96N分子膜
光谱响应
吸收增强现象
图像反转现象 相似文献
98.
Bahattin Gümgüm Nermin Biricik Feyyaz Durap Ismail Özdemir Nevin Gürbüz Wee Han Ang Paul J. Dyson 《应用有机金属化学》2007,21(8):711-715
Palladium(II) complexes with N,N‐bis(diphenylphosphino)aniline ligands catalyse the Heck reaction between styrene and aryl bromides, affording stilbenes in good yield. The structures of two of the complexes used as pre‐catalysts have been determined by single‐crystal X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
99.
100.
E. V. Ermanyuk 《Experiments in fluids》2002,32(2):242-251
This paper presents a study on affine similitude for the force coefficients of an arbitrary body oscillating in a uniformly
stratified fluid. A simple formula is derived that gives a relation between the force coefficients for a body oscillating
in homogeneous and uniformly stratified ideal fluids. In particular, it implies the existence of a universal nondimensional
similitude criterion for a family of affinely similar bodies, namely, the bodies that can be transformed into each other by
vertical dilation of the initial coordinate system. Theoretical results are verified by experiments with a set of spheroids
having different length-to-diameter ratios. The experimental technique for evaluation of the frequency-dependent force coefficients
is based on Fourier analysis of the time-history of damped oscillation tests.
Received: 25 September 2000 / Accepted: 6 July 2001 Published online: 29 November 2001 相似文献