全文获取类型
收费全文 | 25833篇 |
免费 | 2051篇 |
国内免费 | 1077篇 |
专业分类
化学 | 3507篇 |
晶体学 | 82篇 |
力学 | 6710篇 |
综合类 | 95篇 |
数学 | 2515篇 |
物理学 | 5183篇 |
综合类 | 10869篇 |
出版年
2024年 | 51篇 |
2023年 | 254篇 |
2022年 | 418篇 |
2021年 | 498篇 |
2020年 | 580篇 |
2019年 | 491篇 |
2018年 | 528篇 |
2017年 | 619篇 |
2016年 | 620篇 |
2015年 | 814篇 |
2014年 | 1052篇 |
2013年 | 1455篇 |
2012年 | 1307篇 |
2011年 | 1505篇 |
2010年 | 1067篇 |
2009年 | 1356篇 |
2008年 | 1304篇 |
2007年 | 1610篇 |
2006年 | 1380篇 |
2005年 | 1256篇 |
2004年 | 1164篇 |
2003年 | 1097篇 |
2002年 | 914篇 |
2001年 | 794篇 |
2000年 | 811篇 |
1999年 | 675篇 |
1998年 | 642篇 |
1997年 | 636篇 |
1996年 | 561篇 |
1995年 | 498篇 |
1994年 | 450篇 |
1993年 | 386篇 |
1992年 | 382篇 |
1991年 | 337篇 |
1990年 | 305篇 |
1989年 | 261篇 |
1988年 | 211篇 |
1987年 | 161篇 |
1986年 | 124篇 |
1985年 | 103篇 |
1984年 | 74篇 |
1983年 | 38篇 |
1982年 | 79篇 |
1981年 | 25篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 8篇 |
1971年 | 6篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
71.
72.
The Rio de la Plata is a large and shallow water body that discharges onto the Atlantic Ocean. The main driving forces for the river flow are the bathymetry, tides, the outflow from the Paraná and Uruguay rivers and the winds. A numerical model covering the entire river was set up with the objective of increasing our understanding of the hydrographical features and morphological dynamics in the Estuary. The simulations revealed a counter-clockwise residual circulation in the Samborombón Bay and an eastward net flow near the Uruguayan coast. The residual flow is forced by both the tides and the bathymetry. The residence time for the entire river ranges from 40 to 80 days. However, residence times above 120 days was found in the Samborombón Bay. Three corridors of flow have been identified. 相似文献
73.
本文针对一类非饱和土壤水流问题,提出了基于二次插值的特征差分格式,得到了严谨的L2模误差估计.并作了数值试验,指明方法的有效性. 相似文献
74.
This paper presents results of studies on dc electrical conductivity and transference number measurements on potassium bromate
(KBrO3) complexed polyvinyl chloride (PVC) films prepared by solution cast technique. Temperature dependence of dc electrical conductivity
and transference number data indicated the dominance of ion type charge transport in these specimens. The magnitude of conductivity
increased with increase in concentration of the salt and temperature. Using this (PVC + KBrO3) electrolyte, solid-state electrochemical cells were fabricated, and their discharge profiles were studied under a constant
load of 100 kΩ. Several cell profiles such as open circuit voltage, short circuit current, power density, and energy density
associated with these cells were evaluated and were reported. The features of complexation of the electrolytes were studied
by X-ray diffraction and Fourier transform infrared spectroscopy.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006 相似文献
75.
Transition from chaotic to ordered state has been observed during the initial stage of a discharge in a cylindrical DC glow
discharge plasma. Initially it shows a chaotic behavior but increasing the discharge voltage changes the characteristics of
the discharge glow and shows a period subtraction of order 7 period → 5 period → 3 period → 1 period, i.e. the system goes
to single mode through odd cycle subtraction. On further increasing the discharge voltage, the system goes through period
doubling, like 1 period → 2 period → 4 period. On further increasing the voltage, the system goes to stable state through
two period subtraction, like 4 period → 2 period → stable. 相似文献
76.
We consider a multipath maximum flow problem introduced by Kishimoto (Networks 27(4)(1996)279-291). The focus is on efficient transformation from arc flows into multipath flows, where a multipath flow is a nonnegative combination of multipaths. A new algorithm that is more efficient than existing ones is proposed for the transformation. 相似文献
77.
DING Mingtao WEI Fangqiang ZHANG Jinghong WANG Hongjuan 《武汉大学学报:自然科学英文版》2007,12(4):599-604
By analyzing the observation data from Dongchuan Debris Flow Observation and Research Station and historical data from year 1965 to 1990 gotten from National Astronomical Ob-servatories/Yunnan Observatory,the responding of debris flow in Jiangjia Ravine to Solar Proton Flare is studied. The following conclusion can be drawn. Solar Proton Flare,as one of most im-portant astronomical factors,affects the activity of debris flow in Yunnan. Generally,from 1965 to1990,the more active Solar Pro-ton Flare is,the greater the probability of high frequency and large runoff of debris flow is. On the contrary,the less active Solar Pro-ton Flare is,the greater the probability of low frequency,small runoff,and low sediment transport of debris flow is. 相似文献
78.
79.
80.
In this paper, an interior point cutting plane method (IPCPM)is applied to solve optimal power flow (OPF) problems. Comparedwith the simplex cutting plane method (SCPM), the IPCPM is simpler,and efficient because of its polynomial-time characteristic.Issues in implementing IPCPM for OPF problems are addressed,including (1) how to generate cutting planes without using thesimplex tableau, (2) how to identify the basis variables inIPCPM, and (3) how to generate mixed integer cutting planes.The calculation speed of the proposed algorithm is further enhancedby utilizing the sparsity features of the OPF formulation. Numericalsimulations on IEEE 14-300-bus test systems have shown thatthe proposed method is effective. 相似文献