全文获取类型
收费全文 | 37983篇 |
免费 | 1443篇 |
国内免费 | 1303篇 |
专业分类
化学 | 17365篇 |
晶体学 | 363篇 |
力学 | 1839篇 |
综合类 | 122篇 |
数学 | 10080篇 |
物理学 | 10960篇 |
出版年
2023年 | 172篇 |
2022年 | 224篇 |
2021年 | 300篇 |
2020年 | 364篇 |
2019年 | 349篇 |
2018年 | 1446篇 |
2017年 | 1713篇 |
2016年 | 1151篇 |
2015年 | 948篇 |
2014年 | 1013篇 |
2013年 | 1341篇 |
2012年 | 3938篇 |
2011年 | 3160篇 |
2010年 | 2373篇 |
2009年 | 2039篇 |
2008年 | 1180篇 |
2007年 | 1139篇 |
2006年 | 1049篇 |
2005年 | 4809篇 |
2004年 | 4258篇 |
2003年 | 2614篇 |
2002年 | 831篇 |
2001年 | 569篇 |
2000年 | 267篇 |
1999年 | 388篇 |
1998年 | 246篇 |
1997年 | 177篇 |
1996年 | 176篇 |
1995年 | 142篇 |
1994年 | 140篇 |
1993年 | 117篇 |
1992年 | 250篇 |
1991年 | 231篇 |
1990年 | 181篇 |
1989年 | 158篇 |
1988年 | 133篇 |
1987年 | 88篇 |
1986年 | 76篇 |
1985年 | 67篇 |
1984年 | 40篇 |
1979年 | 34篇 |
1976年 | 82篇 |
1975年 | 41篇 |
1974年 | 42篇 |
1973年 | 48篇 |
1972年 | 40篇 |
1970年 | 36篇 |
1969年 | 41篇 |
1968年 | 38篇 |
1966年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
111.
An economical magnetocardiogram (MCG) system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device (SQUID) magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements. 相似文献
112.
Shuguan Ji Zhenxin Liu Shaoyun Shi 《Journal of Mathematical Analysis and Applications》2007,325(2):1306-1313
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate boundary value problems for a class of second order differential equations on the half-line. Some applications are presented to illustrate the potential of this method. 相似文献
113.
Andrzej Wi?nicki 《Journal of Mathematical Analysis and Applications》2002,267(1):158-172
We use a newly introduced concept of neocompactness to study problems from metric fixed point theory. In particular, we give a sufficient condition for a superreflexive Banach space X to have the fixed point property and obtain shorter proofs of some well-known results in that theory. 相似文献
114.
115.
The validity of local parton-hadron duality within the framework of HERWIG and JETSET event generators is investigated. We concentrate one
+
e
– annihilations in LEP 2 energy range as these interactions provide theoretically the cleanest condition for the discussion of this concept. We conclude that the concept of local parton-hadron duality is not valid in either of the two generators considered. 相似文献
116.
通过对气吹式精密播种机田间试验资料的相关分析,发现合格指数A与|D-M|(重播指数与漏播指数之差的绝对值)之间里极显著负相关(r=-0.9312)。在对数据作进一步回归分析的基础上,本文建立了一套“由排种粒数预测排种质量”的方法。 相似文献
117.
In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging. 相似文献
118.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
119.
The laser cladding of Fe-based alloys on a medium carbon steel substrate was performed using a CO2 laser and Ar shielding gas that was blown into a molten pool. The microstructure and cracking susceptibility of the laser-clad layers were studied in terms of carbon additions. Results show that the small change of the carbon content in the alloy powders can obviously change the microstructure and properties of the layers. When the carbon content is in the range of 0.3–0.4 wt.%, the decrease of the carbon content in alloy powders will increase the hardness and toughness of the layers simultaneously under the same process parameters. As a result, crack-free coatings with high hardness can be obtained. As the carbon content increases from 0.2 wt.% to 0.4 wt.%, the segregation ratio of chromium increases, while the segregation ratios of nickel, manganese, and silicon first decrease and then increase. At the same time, a new designing principle concerning the composition and microstructure has been put forward, and the principal mechanisms of strengthening and toughening of the layers are fine-grain strengthening and low carbon martensitic phase transformation strengthening. 相似文献
120.