全文获取类型
收费全文 | 158679篇 |
免费 | 1053篇 |
国内免费 | 1238篇 |
专业分类
化学 | 104949篇 |
晶体学 | 31篇 |
力学 | 803篇 |
综合类 | 46篇 |
数学 | 1011篇 |
物理学 | 43430篇 |
综合类 | 10700篇 |
出版年
2022年 | 99篇 |
2020年 | 89篇 |
2018年 | 130篇 |
2017年 | 93篇 |
2016年 | 172篇 |
2015年 | 139篇 |
2014年 | 273篇 |
2013年 | 234篇 |
2012年 | 14185篇 |
2011年 | 19766篇 |
2010年 | 3369篇 |
2009年 | 759篇 |
2008年 | 14826篇 |
2007年 | 15166篇 |
2006年 | 15609篇 |
2005年 | 14827篇 |
2004年 | 11622篇 |
2003年 | 8596篇 |
2002年 | 7573篇 |
2001年 | 4850篇 |
2000年 | 6201篇 |
1999年 | 1503篇 |
1998年 | 555篇 |
1997年 | 466篇 |
1996年 | 2308篇 |
1995年 | 1542篇 |
1994年 | 2037篇 |
1993年 | 2815篇 |
1992年 | 2415篇 |
1991年 | 1058篇 |
1990年 | 1009篇 |
1989年 | 895篇 |
1988年 | 680篇 |
1987年 | 658篇 |
1986年 | 779篇 |
1985年 | 705篇 |
1984年 | 173篇 |
1983年 | 114篇 |
1982年 | 132篇 |
1981年 | 97篇 |
1979年 | 96篇 |
1971年 | 95篇 |
1970年 | 133篇 |
1959年 | 142篇 |
1958年 | 229篇 |
1957年 | 161篇 |
1956年 | 114篇 |
1955年 | 113篇 |
1954年 | 95篇 |
1948年 | 178篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We report the properties of a compact diode-pumped continuous-wave Nd:GdV04 laser with a linear cavity and different Nd-doped laser crystals. In a 0.2at.% Nd-doped Nd:GdVO4 laser, 1.54 W output laser power is achieved at 912nm wavelength with a slope efficiency of 24.8% at an absorbed pump power of 9.4W. With 0.3at.% Nd-doping concentration, we can obtain the either single-wavelength emission at 1064nm or 912nm or the dual-wavelength emission at 1064nm and 912nm by controlling the incident pump power. From an incident pump power of 11.6 W, the 1064nm emission between ^4Fa/2 and ^4I11/2 is suppressed completely by the 912nm emission between ^4Fa/2 and ^4I9/2. We obtain 670 mW output of the 912nm single-wavelength laser emission with a slope efficiency of 5.5% by taking an incident pump power of 18.4 W. Using a Nd:GdV04 laser with 0.4at.% Nd-doping concentration, we obtain either the single-wavelength emission at 1064nm or the dual-wavelength emission at both 1064nm and 912nm by increasing the incident pump power. We observe a strong competition process in the dualavelength laser. 相似文献
42.
本书为施普林格出版社出版的《物理学先进教材丛书》中的一卷。这套丛书包含物理学流行和广泛关注的多种专题,也包含对现代物理学研究前沿的介绍。本书介绍光电子学器件及其在集成光学和纤维光学系统中的应用,特别强调这些应用中的物理学及相关的数学等。本书初版于1982年,分别在1984年、1991年和1995年出版第2、3、4版。本书为2002年出版的第5版。 相似文献
43.
G.J. Zalmai Qing-hong Zhang 《应用数学学报(英文版)》2007,23(2):217-234
In this paper,we discuss a large number of sets of global parametric sufficient optimality condi-tions under various gcneralized (η,ρ)-invexity assumptions for a semi-infinite minmax fractional programmingproblem. 相似文献
44.
J. J. EGOZCUE J. L. DIAZ-BARRERO V. PAWLOWSKY-GLAHN 《数学学报(英文版)》2006,22(4):1175-1182
The set of probability functions is a convex subset of L1 and it does not have a linear space structure when using ordinary sum and multiplication by real constants. Moreover, difficulties arise when dealing with distances between densities. The crucial point is that usual distances are not invariant under relevant transformations of densities. To overcome these limitations, Aitchison's ideas on compositional data analysis are used, generalizing perturbation and power transformation, as well as the Aitchison inner product, to operations on probability density functions with support on a finite interval. With these operations at hand, it is shown that the set of bounded probability density functions on finite intervals is a pre-Hilbert space. A Hilbert space of densities, whose logarithm is square-integrable, is obtained as the natural completion of the pre-Hilbert space. 相似文献
45.
G.A.Gamal M.AbouZied A.A.Ebnalwaled 《中国物理快报》2005,22(6):1530-1532
Single crystals of red Tl2S5 were prepared by a special modified vertical Bridgman and Stockbarger technique.This growth was performed in our laboratory. The influences of temperature on the electrical conductivity, Hall mobility, carrier concentration, and thermoelectric power (TEP) were carried out in the temperature range 277-413K. Throughout these measurements, various physical parameters such as effective mass of charge carriers,carrier mobility, diffusion coefficient, and the relaxation time for both majority and minority carriers were found. 相似文献
46.
活动标形法的论述首推苏步青译,佐佐木重夫著《微分几何学》,还有的著作从外微分形式引入活动标形,本文论证取曲面的正交曲率网为参数网时,曲面论的基本公式就是活动标形的微分形式,并用其分析了点啮合齿轮传动误差. 相似文献
47.
The authors give the necessary and sufficient conditions for a generalized circle in a Weyl hypersurface to be generalized circle in the enveloping Weyl space. They then obtain the neccessary and sufficient conditions under which a generalized concircular transformation of one Weyl space onto another induces a generalized transformation oil its subspaces. Finally, it is shown that any totally geodesic or totally umbilical hypersurface of a generalized concircularly flat Weyl space is also generalized concircularly flat. 相似文献
48.
用原位IR研究了CO在Co/SiO_2催化剂上的吸附,并考察了吸附的CO与H_2、H_2O的相互作用。CO在Co/SiO_2上的吸附显示出四种不同的吸收峰。2002、2027cm~(-1)归属于端基CO吸附;2120cm~(-1)归属于CO在钴离于上的吸附;1870cm~(-1)为CO的桥式吸附;1720cm~(-1)则为多中心吸附。当温度高于370K时,吸附的CO会完全脱附。H_2与吸附的CO相互作用可削弱CO吸收峰的强度,并逐步在低波数(1980cm~(-1))处产生一个小肩。水与吸附的CO相互作用产生一种甲酸基物种(1585、1390cm~(-1))。该物种被认为是Kòlbel-Engelhardt反应的中间体。 相似文献
49.
A. BOURHIM 《数学年刊B辑(英文版)》2004,25(3):369-382
In this note, the local spectral properties of unilateral operator weighted shifts arestudied. 相似文献
50.
The notion of a fuzzy retract was introduced by Rodabaugh (1981). The notion of a fuzzy pairwise retract was introduced in 2001. Some weak forms and some strong forms of α-continuous mappings were introduced in 1988 and 1997. The authors extend some of these forms to the L-fuzzy bitopological setting and construct various α-fuzzy pairwise retracts. The concept of weakly induced spaces in the case L = [0,1] was introduced by Martin (1980). Liu and Luo (1987) generalized this notion to the case that L is an arbitrary F-lattice and introduced the notion of induced L-fts. Several results are obtained, especially, for L-valued pairwise stratification spaces. 相似文献