全文获取类型
收费全文 | 7357篇 |
免费 | 310篇 |
国内免费 | 52篇 |
专业分类
化学 | 5068篇 |
晶体学 | 40篇 |
力学 | 187篇 |
数学 | 1351篇 |
物理学 | 1073篇 |
出版年
2024年 | 12篇 |
2023年 | 67篇 |
2022年 | 194篇 |
2021年 | 232篇 |
2020年 | 167篇 |
2019年 | 186篇 |
2018年 | 149篇 |
2017年 | 122篇 |
2016年 | 281篇 |
2015年 | 248篇 |
2014年 | 278篇 |
2013年 | 445篇 |
2012年 | 511篇 |
2011年 | 563篇 |
2010年 | 328篇 |
2009年 | 364篇 |
2008年 | 435篇 |
2007年 | 477篇 |
2006年 | 412篇 |
2005年 | 384篇 |
2004年 | 296篇 |
2003年 | 206篇 |
2002年 | 212篇 |
2001年 | 107篇 |
2000年 | 87篇 |
1999年 | 78篇 |
1998年 | 60篇 |
1997年 | 60篇 |
1996年 | 86篇 |
1995年 | 53篇 |
1994年 | 53篇 |
1993年 | 50篇 |
1992年 | 52篇 |
1991年 | 38篇 |
1990年 | 25篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 40篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 34篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 18篇 |
1978年 | 21篇 |
1977年 | 9篇 |
1975年 | 13篇 |
1974年 | 10篇 |
排序方式: 共有7719条查询结果,搜索用时 0 毫秒
111.
112.
113.
Luis Paris 《Geometriae Dedicata》1993,45(2):171-176
We denote by the complement of the complexification of a real arrangement of hyperplanes. It is known that there is a certain technical property, called property D, on real arrangements of hyperplanes such that: if a real arrangement of hyperplanes is simplicial then has property D, and if has property D then is aK(, 1) space. Our main goal is to prove that: if has property D then is simplicial. We also prove that a quasi-simplicial arrangement is always simplicial. 相似文献
114.
Luis P. Chimento 《General Relativity and Gravitation》1993,25(10):979-989
The general solution to the semiclassical backreaction equation is found for conformally invariant free quantum fields in spatially flat homogeneous and isotropic spacetime with Cosmological constant and with no classical source when the ratio of the renormalisation parameters/=9/4. It contains a two-parameter family of bouncing solutions that avoid the singularity. There are several one-parameter families which do not have particle horizons. The stability of these solutions is investigated and it is found that they are stable when and have different signs. However, when both parameters have the same sign the set of stable solutions is restricted by the condition 0 < < 1/9. In both cases these solutions have a final de Sitter stage. 相似文献
115.
Luis O. Pimentel 《International Journal of Theoretical Physics》1993,32(6):979-984
The Weyl equation (massless Dirac equation) is studied in a family of exact solutions of the Einstein equations whose material content is a perfect fluid with stiff equation of state (p=) and which are of Bianchi type I. The field equation is solved exactly for some members of the family. 相似文献
116.
Ingo Althöfer Gautam Das David Dobkin Deborah Joseph José Soares 《Discrete and Computational Geometry》1993,9(1):81-100
Given a graphG, a subgraphG' is at-spanner ofG if, for everyu,v V, the distance fromu tov inG' is at mostt times longer than the distance inG. In this paper we give a simple algorithm for constructing sparse spanners for arbitrary weighted graphs. We then apply this algorithm to obtain specific results for planar graphs and Euclidean graphs. We discuss the optimality of our results and present several nearly matching lower bounds.The work of G. Das and D. Joseph was supported by NSF PYI Grant DCR-8402375. The work of D. Dobkin was supported by NSF Grant CCR-8700917. The work of J. Soares was supported by CNPq proc 203039/87.4 (Brazil) and NSF Grant CCR-9014562. This research was accomplished while G. Das was a student at the University of Wisconsin-Madison. A preliminary version was presented at the Second Scandinavian Workshop on Algorithm Theory, Bergen, Norway, 1990, under the title Generating Sparse Spanners for Weighted Graphs, and proceedings appear in the series Lecture Notes in Computer Science, Springer-Verlag. The preliminary version also appears as Princeton University Technical Report CS-TR-261-90, and as University of Wisconsin-Madison Computer Sciences Technical Report 882. 相似文献
117.
118.
Medrano F Calderón A Yatsimirsky AK 《Chemical communications (Cambridge, England)》2003,(15):1968-1970
Glycine and N,N-dimethylglycine stabilize La(III) hydroxide complexes of the type La2L2(OH)4 which possess phosphodiesterolytic activity close to that observed with most active tetravalent cations like Ce(IV). 相似文献
119.
Using a version of density-functional theory which combines Onsager approximation and fundamental-measure theory for spatially nonuniform phases, we have studied the phase diagram of freely rotating hard rectangles and hard discorectangles. We find profound differences in the phase behavior of these models, which can be attributed to their different packing properties. Interestingly, bimodal orientational distribution functions are found in the nematic phase of hard rectangles, which cause a certain degree of biaxial order, albeit metastable with respect to spatially ordered phases. This feature is absent in discorectangles, which always show unimodal behavior. This result may be relevant in the light of recent experimental results which have confirmed the existence of biaxial phases. We expect that some perturbation of the particle shapes (either a certain degree of polydispersity or even bimodal dispersity in the aspect ratios) may actually destabilize spatially ordered phases thereby stabilizing the biaxial phase. 相似文献
120.
[reaction: see text] A new nonchain 5-endo radical cyclization starting with xanthates was exploited in a short synthesis of (+/-)-alpha-lycorane and the erythrina ring system. 相似文献