全文获取类型
收费全文 | 89980篇 |
免费 | 2365篇 |
国内免费 | 2182篇 |
专业分类
化学 | 33183篇 |
晶体学 | 954篇 |
力学 | 7415篇 |
综合类 | 139篇 |
数学 | 33425篇 |
物理学 | 19411篇 |
出版年
2023年 | 180篇 |
2022年 | 349篇 |
2021年 | 410篇 |
2020年 | 437篇 |
2019年 | 463篇 |
2018年 | 10746篇 |
2017年 | 10548篇 |
2016年 | 6563篇 |
2015年 | 1399篇 |
2014年 | 1014篇 |
2013年 | 1203篇 |
2012年 | 4824篇 |
2011年 | 11636篇 |
2010年 | 6475篇 |
2009年 | 6882篇 |
2008年 | 7576篇 |
2007年 | 9578篇 |
2006年 | 1017篇 |
2005年 | 1908篇 |
2004年 | 1976篇 |
2003年 | 2329篇 |
2002年 | 1412篇 |
2001年 | 595篇 |
2000年 | 607篇 |
1999年 | 425篇 |
1998年 | 390篇 |
1997年 | 318篇 |
1996年 | 402篇 |
1995年 | 291篇 |
1994年 | 182篇 |
1993年 | 197篇 |
1992年 | 147篇 |
1991年 | 147篇 |
1990年 | 119篇 |
1989年 | 126篇 |
1988年 | 98篇 |
1987年 | 97篇 |
1986年 | 94篇 |
1985年 | 71篇 |
1984年 | 61篇 |
1983年 | 58篇 |
1982年 | 56篇 |
1981年 | 48篇 |
1980年 | 51篇 |
1979年 | 48篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
22.
23.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献
24.
Ji-Dong Lou Chun-Ling Gao Li Li Zhi-Gang Fang 《Monatshefte für Chemie / Chemical Monthly》2006,41(10):1071-1074
A new procedure for the selective oxidation of alcohols to the corresponding aldehydes and ketones with potassium permanganate
supported on aluminum silicate at room temperature under solvent-free conditions and shaking is reported. 相似文献
25.
双掺(Tm3+,Tb3+)LiYF4激光器1.5 μm波长激光阈值分析 总被引:1,自引:0,他引:1
由速率方程推出了双掺(Tm^3 ,Tb^3 )离子准四能级系统的激光阈值解析式,讨论了Tm^3 和Tb^3 离子之间的相互作用。分析了1.5μm波长附近的激光阈值和Tm^3 、Tb^3 离子的掺杂原子数分数及晶体长度的关系。结果表明,对于对应Tm^3 离子^3H4→^3F4跃迁的约1.5μm波长的激光,激活离子Tm^3 的掺杂原子数分数过大时,交叉弛豫作用将使系统阈值迅速增加。Tb^3 离子的加入,一方面能抽空激光下能级,起到降低阈值的作用;另一方面亦减少了激光上能级的寿命,使阈值升高。故Tb^3 离子有最佳掺杂原子数分数。对于Tm原子数分数为y=0.01的Tm:LiYF4晶体,Tb^3 离子的最佳掺杂原子数分数为0.002左右,同时表明,激光阈值与晶体长度有关。最佳晶体长度与Tm^3 、Tb^3 离子的掺杂原子数分数以及晶体的衍射损耗和吸收损耗有关。 相似文献
26.
27.
28.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective. 相似文献
29.
Chee Sing Yap 《The Journal of the Operational Research Society》1989,40(7):649-658
This paper describes three case studies which investigated issues relating to the implementation and management of advanced information technology. The benefits derived from information technology were found to vary from one organization to another. These studies provide further evidence to support earlier research findings that senior management has an important role to play in the effective exploitation of information technology, and that the investment approach taken by an organization has a significant effect on the development of computer-based information systems. The effectiveness of a system depends not only on applying the appropriate technology, but also on how successfully technical and behavioural issues are resolved. 相似文献
30.
Stability of chirped bright and dark soliton-like solutions of the cubic complex Ginzburg-Landau equation with variable coefficients 总被引:1,自引:0,他引:1
Fang Fang 《Optics Communications》2006,268(2):305-310
We consider an inhomogeneous optical fiber system described by the generalized cubic complex Ginzburg-Landau (CGL) equation with varying dispersion, nonlinearity, gain (loss), nonlinear gain (absorption) and the effect of spectral limitation. Exact chirped bright and dark soliton-like solutions of the CGL equation were found by using a suitable ansatz. Furthermore, we analyze the features of the solitons and consider the problem of stability of these soliton-like solutions under finite initial perturbations. It is shown by extensive numerical simulations that both bright and dark soliton-like solutions are stable in an inhomogeneous fiber system. Finally, the interaction between two chirped bright and dark soliton-like pulses is investigated numerically. 相似文献