全文获取类型
收费全文 | 44355篇 |
免费 | 8161篇 |
国内免费 | 8953篇 |
专业分类
化学 | 32863篇 |
晶体学 | 953篇 |
力学 | 2976篇 |
综合类 | 672篇 |
数学 | 5325篇 |
物理学 | 18680篇 |
出版年
2024年 | 129篇 |
2023年 | 737篇 |
2022年 | 1618篇 |
2021年 | 1676篇 |
2020年 | 1723篇 |
2019年 | 1805篇 |
2018年 | 1550篇 |
2017年 | 1735篇 |
2016年 | 2046篇 |
2015年 | 2388篇 |
2014年 | 2937篇 |
2013年 | 3647篇 |
2012年 | 4168篇 |
2011年 | 4201篇 |
2010年 | 3330篇 |
2009年 | 3444篇 |
2008年 | 3769篇 |
2007年 | 3103篇 |
2006年 | 2947篇 |
2005年 | 2414篇 |
2004年 | 1854篇 |
2003年 | 1479篇 |
2002年 | 1485篇 |
2001年 | 1291篇 |
2000年 | 1154篇 |
1999年 | 859篇 |
1998年 | 538篇 |
1997年 | 493篇 |
1996年 | 436篇 |
1995年 | 358篇 |
1994年 | 366篇 |
1993年 | 298篇 |
1992年 | 256篇 |
1991年 | 181篇 |
1990年 | 184篇 |
1989年 | 131篇 |
1988年 | 125篇 |
1987年 | 89篇 |
1986年 | 92篇 |
1985年 | 62篇 |
1984年 | 44篇 |
1983年 | 46篇 |
1982年 | 35篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 29篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1957年 | 8篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
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
2.
从点电荷的电势计算公式出发推导出了瓣形均匀带电面在其直径处的电势分布.进一步讨论了均匀带电半球面在其底面以及均匀带电球面内部和外部的电势分布. 相似文献
3.
GAO Jing ZHOU Xiaohua CHEN Xun Chongqing University Chemical Engineering Department Chongqing China 《Chinese Journal of Reactive Polymers》2006,(2)
1. INTRODUCTION In the process of coking plant, about 30%~35% sulfur is transformed to H2S and some other sulfide, which form impurity in coal gas together with NH3 and HCN. Only 0.1% H2S containing in air can lead to die, so it is very important to carry on desulphurization and decyanation with coal gas [1~3]. Currently desulphurization and decyanation craft technique have Dry Oxidation Technology, Wet Oxidation Technology and Liquid Absorption Technology [2] three main kinds. The… 相似文献
4.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
5.
WU Jian-Jun GAO Zi-You SUN Hui-Jun 《理论物理通讯》2006,46(7)
In this paper, based on the utility preferential attachment, we propose a new unified model to generate different network topologies such as scale-free, small-world and random networks. Moreover, a new network structure named super scale network is found, which has monopoly characteristic in our simulation experiments. Finally, the characteristics ofthis new network are given. 相似文献
6.
本文首先将文[1]中的BLD映射推广为弱(L1,L2)-BLD映射,并证明了如下正则性结果:存在两个可积指数 P1=P1(n,L1,L2)<n<q1=q1(n,L1,L2),使得对任意弱(L1,L2)-BLD映射f∈(Ω,Rn),都有f∈(Ω,Rn),即f为(L1,L2)-BLD映射. 相似文献
7.
本文主要解决奇异非光滑方程组的解法。应用一种新的次微分的外逆,我们提出了牛顿法和不精确牛顿法,它们的收敛性同时也得到了证明。这种方法能更容易在一引起实际应用中实现。这种方法可以看作是已存在的解非光滑方程组的方法的延伸。 相似文献
8.
Inspired by the recent work [HHM03], we prove two stability results for compact Riemannian manifolds with nonzero parallel spinors. Our first result says that Ricci flat metrics which also admit nonzero parallel spinors are stable (in the direction of changes in conformal structures) as the critical points of the total scalar curvature functional. Our second result, which is a local version of the first one, shows that any metric of positive scalar curvature cannot lie too close to a metric with nonzero parallel spinor. We also prove a rigidity result for special holonomy metrics. In the case of SU(m) holonomy, the rigidity result implies that scalar flat deformations of Calabi-Yau metric must be Calabi-Yau. Finally we explore the connection with a positive mass theorem of [D03], which presents another approach to proving these stability and rigidity results. Dedicated to Jeff Cheeger for his sixtieth birthday 相似文献
9.
10.