全文获取类型
收费全文 | 114494篇 |
免费 | 18881篇 |
国内免费 | 12230篇 |
专业分类
化学 | 61137篇 |
晶体学 | 920篇 |
力学 | 5685篇 |
综合类 | 523篇 |
数学 | 10111篇 |
物理学 | 35860篇 |
无线电 | 31369篇 |
出版年
2024年 | 296篇 |
2023年 | 3011篇 |
2022年 | 3104篇 |
2021年 | 4406篇 |
2020年 | 4715篇 |
2019年 | 4131篇 |
2018年 | 3648篇 |
2017年 | 3497篇 |
2016年 | 5098篇 |
2015年 | 5278篇 |
2014年 | 6339篇 |
2013年 | 8081篇 |
2012年 | 9813篇 |
2011年 | 10084篇 |
2010年 | 7040篇 |
2009年 | 7071篇 |
2008年 | 7581篇 |
2007年 | 6707篇 |
2006年 | 6443篇 |
2005年 | 5364篇 |
2004年 | 3771篇 |
2003年 | 3140篇 |
2002年 | 2883篇 |
2001年 | 2470篇 |
2000年 | 2318篇 |
1999年 | 2661篇 |
1998年 | 2313篇 |
1997年 | 2130篇 |
1996年 | 2077篇 |
1995年 | 1765篇 |
1994年 | 1565篇 |
1993年 | 1296篇 |
1992年 | 1168篇 |
1991年 | 977篇 |
1990年 | 759篇 |
1989年 | 572篇 |
1988年 | 446篇 |
1987年 | 352篇 |
1986年 | 355篇 |
1985年 | 290篇 |
1984年 | 181篇 |
1983年 | 130篇 |
1982年 | 112篇 |
1981年 | 66篇 |
1980年 | 49篇 |
1979年 | 16篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
971.
J2EE(Java 2平台企业版)是当前建立和开发各种Web应用的主流平台,MVC(模型-视图-控制)体系结构是当今设计交互式应用的事实标准.文中结合MVC在J2EE Web中的应用,通过电子政务系统开发实践,提出了一个具体的实现方案,描述了应用系统设计,给出了表示层、控制层、代理层、业务逻辑层、数据访问层和数据存储层等层次的明确划分,阐述了各层的功能作用以及层与层之间的关系,并针对具体业务给出了实现的部分具体内容,为在J2EE环境下开发结构良好、易于维护、易于扩展的Web应用提供了可行方案. 相似文献
972.
We demonstrate a 511 W laser diode pumped composite Nd:YAG ceramic laser. The optical pumping system is consisted of five laser diode stacked arrays arranged in a pentagonal shape around the ceramic rod whose size is φ6.35×144mm. When the pumping power is 1600 W, the cw laser output up to 511 W at 1064nm can be obtained with a linear piano-piano cavity, and the optical-to-optical efficiency is 31.9%. To our knowledge, this is the highest value of laser output by using a newly invented composite Nd:YAG ceramic rod as the gain medium. 相似文献
973.
Condition monitoring and life prediction of the vehicle engine is an important and urgent problem during the vehicle development process. The vibration signals that are closely associated with the engine running condition and its development trend are complex and nonlinear. The chaos theory is used to treat the nonlinear dynamical system recently. A novel chaos method in conjunction with SVD (singular value decomposition)denoising skill are used to predict the vibration time series. Two types of time series and their prediction errors are provided to illustrate the practical utility of the method. 相似文献
974.
Lanthanide Complexes for Oligomerization of Phenyl Isocyanate 总被引:1,自引:0,他引:1
IntroductionThestudyonthereactivitiesoflanthanidecomplexesto wardisocyanateshasattractedmuchattention .Ithasbeenre portedthatlanthanidealkoxides,1anddivalentdiaza pentadi enyllanthanidecomplexes2 canbeusedasthesinglecompo nentinitiatorsforisocyanatespolymerization .Recentlyourre searchgrouphasalsofoundthatlanthanoceneamide ,3diva lentaryloxideofsamarium4 ,5anddivalentsamarocene6 areallactivefortheoligomerizationofphenylisocyanate,andtheactivespeciesforthesethreesystemswereallsuccessfullyisolat… 相似文献
975.
The optical-limiting property of an optically active phthalocyanine derivative with different configuration in chloroform solution was measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σex of the derivative was determined with the Z-scan technique. The results showed that the phthalocyanine derivative possesses larger σex than the ground state absorption cross-section σ0, indicating that it is a material for reverse saturable absorption. And it is specially noticed that the change in the optically active configuration affects its optical-limiting property significantly. 相似文献
976.
977.
978.
简要介绍了全板电镀镍金加工过程中镀金面发白现象及改善措施。特别是针对高位发白(或粗糙)的产生原因和处理过程进行较为详细的描述,并对工艺在此处理过程中存在问题进行了简要剖析。 相似文献
979.
980.
Tie-Jun Liu Yue-Sheng Wang Chuanzeng Zhang 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(4):267-282
The main interest of this study is a new method to solve the axisymmetric frictionless contact problem of functionally graded
materials (FGMs). Based on the fact that an arbitrary curve can be approached by a series of continuous but piecewise linear
curves, the FGM is divided into a series of sub-layers with shear modulus varying linearly in each sub-layer and continuous
at the sub-interfaces. With this model, the axisymmetric frictionless contact problem of a functionally graded coated half-space
is investigated. By using the transfer matrix method and Hankel integral transform technique, the problem is reduced to a
Cauchy singular integral equation. The contact pressure, contact region and indentation are calculated for various indenters
by solving the equations numerically.
An erratum to this article can be found at 相似文献