全文获取类型
收费全文 | 91457篇 |
免费 | 3202篇 |
国内免费 | 4173篇 |
专业分类
系统科学 | 3366篇 |
丛书文集 | 3036篇 |
教育与普及 | 2698篇 |
理论与方法论 | 365篇 |
现状及发展 | 547篇 |
研究方法 | 283篇 |
综合类 | 88524篇 |
自然研究 | 13篇 |
出版年
2024年 | 427篇 |
2023年 | 913篇 |
2022年 | 1493篇 |
2021年 | 1716篇 |
2020年 | 1172篇 |
2019年 | 519篇 |
2018年 | 850篇 |
2017年 | 1040篇 |
2016年 | 1133篇 |
2015年 | 2192篇 |
2014年 | 3108篇 |
2013年 | 3083篇 |
2012年 | 3442篇 |
2011年 | 4005篇 |
2010年 | 4012篇 |
2009年 | 4278篇 |
2008年 | 4863篇 |
2007年 | 4663篇 |
2006年 | 3837篇 |
2005年 | 3871篇 |
2004年 | 2812篇 |
2003年 | 2643篇 |
2002年 | 2767篇 |
2001年 | 2881篇 |
2000年 | 2739篇 |
1999年 | 4418篇 |
1998年 | 3736篇 |
1997年 | 3838篇 |
1996年 | 3700篇 |
1995年 | 3037篇 |
1994年 | 2885篇 |
1993年 | 2427篇 |
1992年 | 2107篇 |
1991年 | 1958篇 |
1990年 | 1688篇 |
1989年 | 1586篇 |
1988年 | 1286篇 |
1987年 | 832篇 |
1986年 | 480篇 |
1985年 | 181篇 |
1984年 | 36篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1973年 | 9篇 |
1972年 | 11篇 |
1968年 | 12篇 |
1967年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
对几种新生入馆教育方式的优缺点进行了比较分析,以山东商务职业学院图书馆为例,详细介绍了宣传片拍摄要领及技巧,提出了一种综合性的新生入馆教育新模式. 相似文献
12.
13.
随着智能手机的迅猛发展,Wi Fi的全民时代到来,手机网络游戏越来越得到人们的青睐.首先设计了基于Android系统的斗地主纸牌游戏的功能模块、类以及数据库,实现了客户端注册、登录、游戏房间选择、多人斗地主以及服务器端接收多个用户连接请求且管理用户信息功能,然后对该游戏中的关键技术进行了详细描述,最后展示了游戏的运行界面.测试效果表明,软件界面友好、操作便捷,能够满足手机用户对斗地主游戏的基本需求. 相似文献
14.
驱动桥壳轻量化设计对于提高承载能力、降低生产成本具有重要的意义.本文在驱动桥壳有限元分析和疲劳分析计算的基础上建立驱动桥壳多目标优化模型,对重型卡车驱动桥壳进行参数化设计,建立正交试验表,利用田口方法和综合评价方法对驱动桥壳的疲劳性能稳健性和质量进行优化设计.优化结果表明,此方法可以应用于驱动桥壳的多目标优化,优化后驱动桥壳的疲劳稳健性能得到提高,减轻了质量,因此节约了桥壳材料,降低了生产和运营成本,提高了设计水平. 相似文献
15.
Geochemistry of Clayey Aquitard Pore Water as Archive of Paleo-Environment,Western Bohai Bay 总被引:1,自引:0,他引:1
The record of paleo-environment in clayey aquitard pore water is much more effective relative to aquifer groundwater owing to the low permeability of clayey aquitard. Oxygen-18 (18O), deuterium (D), an... 相似文献
16.
17.
This paper studies the optimal investment problem for an insurer and a reinsurer. The basic claim process is assumed to follow a Brownian motion with drift and the insurer can purchase proportional reinsurance from the reinsurer. The insurer and the reinsurer are allowed to invest in a risk-free asset and a risky asset. Moreover, the authors consider the correlation between the claim process and the price process of the risky asset. The authors ?rst study the optimization problem of maximizing the expected exponential utility of terminal wealth for the insurer. Then with the optimal reinsurance strategy chosen by the insurer, the authors consider two optimization problems for the reinsurer: The problem of maximizing the expected exponential utility of terminal wealth and the problem of minimizing the ruin probability. By solving the corresponding Hamilton-Jacobi-Bellman equations, the authors derive the optimal reinsurance and investment strategies, explicitly. Finally, the authors illustrate the equality of the reinsurer's optimal investment strategies under the two cases. 相似文献
18.
讨论了3×3阶正交矩阵的特征值和迹的关系,证明了迹为整数的3×3阶正交矩阵的谱可由迹确定,为应用广泛的3×3阶正交矩阵的谱的计算提供了简单实用的方法. 相似文献
19.
Au@Cu_2O core-shell nanorods with tunable thickness of Cu_2O shell were synthesized and their linear and nonlinear optical responses were investigated. Two transverse plasmon resonance peaks were observed when the Au nanorods were coated with Cu_2O shells, which were adjusted by the Cu_2O shell thickness. The nonlinear absorption of the Au@Cu_2O nanorods is enhanced by 5 times at the longitudinal plasmon resonance wavelength compared with that of bare Au nanorods. More intriguingly, largely enhanced nonlinear refraction and suppressed nonlinear absorption at the transverse plasmon resonance wavelength were observed in the Au@Cu_2O nanorods. Our findings indicate the existence of strong local field enhancement at the interface between the Au core and the Cu_2O shell, which would provide a promising strategy in designing plasmonic nonlinear nanodevices with good nonlinear figures of merit. 相似文献
20.
Through molecular dynamics(MD)simulation,the dependencies of temperature,grain size and strain rate on the mechanical properties were studied.The simulation results demonstrated that the strain rate from 0.05 to 2 ns~(–1 )affected the Young’s modulus of nickel nanowires slightly,whereas the yield stress increased.The Young’s modulus decreased approximately linearly;however,the yield stress firstly increased and subsequently dropped as the temperature increased.The Young’s modulus and yield stress increased as the mean grain size increased from 2.66 to6.72 nm.Moreover,certain efforts have been made in the microstructure evolution with mechanical properties association under uniaxial tension.Certain phenomena such as the formation of twin structures,which were found in nanowires with larger grain size at higher strain rate and lower temperature,as well as the movement of grain boundaries and dislocation,were detected and discussed in detail.The results demonstrated that the plastic deformation was mainly accommodated by the motion of grain boundaries for smaller grain size.However,for larger grain size,the formations of stacking faults and twins were the main mechanisms of plastic deformation in the polycrystalline nickel nanowire. 相似文献