全文获取类型
收费全文 | 18710篇 |
免费 | 1636篇 |
国内免费 | 1055篇 |
专业分类
化学 | 5957篇 |
晶体学 | 94篇 |
力学 | 1775篇 |
综合类 | 84篇 |
数学 | 1118篇 |
物理学 | 4429篇 |
综合类 | 7944篇 |
出版年
2024年 | 52篇 |
2023年 | 227篇 |
2022年 | 376篇 |
2021年 | 363篇 |
2020年 | 461篇 |
2019年 | 421篇 |
2018年 | 355篇 |
2017年 | 534篇 |
2016年 | 542篇 |
2015年 | 662篇 |
2014年 | 797篇 |
2013年 | 1504篇 |
2012年 | 997篇 |
2011年 | 1044篇 |
2010年 | 784篇 |
2009年 | 892篇 |
2008年 | 844篇 |
2007年 | 1046篇 |
2006年 | 983篇 |
2005年 | 964篇 |
2004年 | 854篇 |
2003年 | 762篇 |
2002年 | 659篇 |
2001年 | 608篇 |
2000年 | 511篇 |
1999年 | 552篇 |
1998年 | 495篇 |
1997年 | 407篇 |
1996年 | 342篇 |
1995年 | 329篇 |
1994年 | 288篇 |
1993年 | 259篇 |
1992年 | 207篇 |
1991年 | 180篇 |
1990年 | 175篇 |
1989年 | 162篇 |
1988年 | 192篇 |
1987年 | 97篇 |
1986年 | 94篇 |
1985年 | 101篇 |
1984年 | 61篇 |
1983年 | 32篇 |
1982年 | 50篇 |
1981年 | 37篇 |
1980年 | 20篇 |
1979年 | 37篇 |
1978年 | 9篇 |
1976年 | 5篇 |
1973年 | 6篇 |
1972年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
常凯 《淮北煤炭师范学院学报(自然科学版)》1996,(2)
本文采用变分法研究了量子阱中类氢杂质的束缚能的压力效应,尤其在阱较窄的情形下,其压力效应更为显著. 相似文献
32.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献
33.
34.
Y. Yavin 《Journal of Optimization Theory and Applications》1993,78(1):77-91
Stochastic optimal control techniques are applied to compare the performance of identical medium-range air-to-air missiles which have different thrust-mass profiles. The measure of the performance is the probability of reaching a lock-on-point with a favorable range of guidance and flight parameters, during a fixed time interval [0,t
f
], given that, during the flight, the trajectories of the missile are subjected to a variety of constraints including dynamic pressure constraints. 相似文献
35.
简析"静止液体内部压强公式验证"实验的设计策略 总被引:1,自引:1,他引:0
“静止液体内部压强公式验证”在现行教材中有两种实验方法。通过分析实验的设计策略,说明其作用、效果及操作上的困难,指出合理的与不合理诸因素,从而提出改进实验的方法,化难为易,提高实验教学效果。 相似文献
36.
1 Introduction Inrecentyears,boththetheoreticalandexperimentalinvestigationsonlasercoolingandtrappinghavebecomeoneofthemajorfieldsinatomic,molecularandoptical physics[1~ 8] .Thedevelopmentoflasercoolingandtrappingtechnologyisimportantfortheapplicationssu… 相似文献
37.
This paper investigates mutual influence of duct and room acoustics in the whole fan-duct-plenum-room integrations. Applying the parametric design language of finite element software ANSYS (APDL), dimensional and positional influence on system acoustics has been studied. Models with different room dimensions, duct lengths, duct cross-sections, duct locations, duct discharges and duct elbow were constructed, and their characteristics were compared qualitatively. Results show that small rooms, short ducts, large duct cross-sections and bell mouth duct discharges help to increase room sound pressure levels (SPLs); SPLs in ducts and plenums are sensitive to duct dimensions and duct discharge types but insensitive to duct locations and room dimensions; duct elbows have relatively indistinct acoustic influence in each component. Based on the calculation results, a semi-experimental method was proposed for simply and approximately evaluating indoor acoustic spectra of fan-duct-plenum-room integrations, then an example was used to demonstrate the prediction process. Finally, by adopting several ideal models, sound field constitutions, duct and room wall admittances and duct end reflection were explored quantitatively. This study may give a detailed understanding of fan-duct-plenum-room acoustics for researchers, also it might provide a new, simple and approximate prediction method for professionals to evaluate and improve fan-ducted acoustics. 相似文献
38.
Bubble pressure points of ethanol–1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea refrigerant) mixtures from the third Industrial Fluid Properties Simulation Challenge are computed using publicly available molecular simulation software. Several published force fields are compared against the known answers provided in the contest guidelines and the best force fields are used to make predictions for the unknown results. 相似文献
39.
Let E
n:y
2=x
3−n
2
x denote the family of congruent number elliptic curves. Feng and Xiong (2004) equate the nontriviality of the Selmer groups
associated with E
n
to the presence of certain types of partitions of graphs associated with the prime factorization of n. In this paper, we extend the ideas of Feng and Xiong in order to compute the Selmer groups of E
n.
2000 Mathematics Subject Classification Primary—11G05; Secondary—14H52, 14H25, 05C90 相似文献
40.
陈昌华 《重庆工商大学学报(自然科学版)》2007,(9):173-176
就业压力没有很好地转化为学生的学习动力,形成了就业压力大而学习动力以及学习投入不足的矛盾。提出尊重学生的专业选择、加强学生学习兴趣的培养、缓解就业压力、增强学习劲头和增加学习投入等解决办法。 相似文献