全文获取类型
收费全文 | 480128篇 |
免费 | 5704篇 |
国内免费 | 1818篇 |
专业分类
化学 | 264885篇 |
晶体学 | 7706篇 |
力学 | 20010篇 |
综合类 | 11篇 |
数学 | 53103篇 |
物理学 | 141935篇 |
出版年
2018年 | 3970篇 |
2017年 | 3807篇 |
2016年 | 6594篇 |
2015年 | 4716篇 |
2014年 | 6828篇 |
2013年 | 20909篇 |
2012年 | 14535篇 |
2011年 | 18176篇 |
2010年 | 11927篇 |
2009年 | 11742篇 |
2008年 | 16416篇 |
2007年 | 16535篇 |
2006年 | 15660篇 |
2005年 | 14667篇 |
2004年 | 13166篇 |
2003年 | 11807篇 |
2002年 | 11588篇 |
2001年 | 13642篇 |
2000年 | 10397篇 |
1999年 | 8336篇 |
1998年 | 6835篇 |
1997年 | 6904篇 |
1996年 | 6614篇 |
1995年 | 6269篇 |
1994年 | 5925篇 |
1993年 | 5812篇 |
1992年 | 6678篇 |
1991年 | 6487篇 |
1990年 | 6167篇 |
1989年 | 6191篇 |
1988年 | 6198篇 |
1987年 | 6180篇 |
1986年 | 5783篇 |
1985年 | 7914篇 |
1984年 | 8158篇 |
1983年 | 6769篇 |
1982年 | 7391篇 |
1981年 | 7134篇 |
1980年 | 6970篇 |
1979年 | 7129篇 |
1978年 | 7624篇 |
1977年 | 7304篇 |
1976年 | 7383篇 |
1975年 | 6863篇 |
1974年 | 6803篇 |
1973年 | 7256篇 |
1972年 | 4594篇 |
1971年 | 3659篇 |
1968年 | 3966篇 |
1967年 | 3996篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
75.
A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions. 相似文献
76.
R. Notoya 《Russian Journal of Electrochemistry》2002,38(3):255-260
It is found that the density (number of the component ion or molecule in 1 cm3) of a molten salt could be expressed as a function of the product of the electron donating and accepting properties of the component anion and cation. This equation is very useful for estimating the density of any molten salt at high temperature with the standard deviation accurately. 相似文献
77.
78.
Investigated is the dependency of the crack tip opening displacement (CTOD) on the local microstructure of the heat affected zone in high-strength low-alloy (HSLA) microalloyed steel. Since the initiation of the crack tip location could not be controlled in fatigue, any possible correlation between heat iput in welding and fracture toughness could be smeared. Modified CTOD data are defined; they show that the fracture resistance of the weld joint decreased as the heat input increased. 相似文献
79.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献
80.
The barotropic compressible Navier–Stokes equations in an unbounded domain are studied. We prove the unique existence of the solution (u, p) of the system (1.1) in the Sobolev spaceHk + 3 × Hk + 2provided that the derivatives of the data of the problem are sufficiently small, wherek ≥ 0 is any integer. The proof follows from an analysis of the linearized problem, the solvability of the continuity equation, and the Schauder fixed point theory. Similar smoothness results are obtained for a linearized form of (1.1). 相似文献