全文获取类型
收费全文 | 85212篇 |
免费 | 622篇 |
国内免费 | 418篇 |
专业分类
化学 | 28951篇 |
晶体学 | 828篇 |
力学 | 6944篇 |
数学 | 33218篇 |
物理学 | 16311篇 |
出版年
2022年 | 59篇 |
2021年 | 133篇 |
2020年 | 136篇 |
2019年 | 155篇 |
2018年 | 10545篇 |
2017年 | 10349篇 |
2016年 | 6264篇 |
2015年 | 1074篇 |
2014年 | 526篇 |
2013年 | 798篇 |
2012年 | 4287篇 |
2011年 | 10997篇 |
2010年 | 5942篇 |
2009年 | 6306篇 |
2008年 | 6986篇 |
2007年 | 9130篇 |
2006年 | 614篇 |
2005年 | 1660篇 |
2004年 | 1839篇 |
2003年 | 2238篇 |
2002年 | 1226篇 |
2001年 | 371篇 |
2000年 | 404篇 |
1999年 | 244篇 |
1998年 | 259篇 |
1997年 | 207篇 |
1996年 | 254篇 |
1995年 | 165篇 |
1994年 | 139篇 |
1993年 | 140篇 |
1992年 | 97篇 |
1991年 | 125篇 |
1990年 | 113篇 |
1989年 | 112篇 |
1988年 | 106篇 |
1987年 | 93篇 |
1986年 | 87篇 |
1985年 | 99篇 |
1984年 | 114篇 |
1983年 | 76篇 |
1982年 | 95篇 |
1981年 | 80篇 |
1980年 | 94篇 |
1979年 | 81篇 |
1978年 | 71篇 |
1977年 | 70篇 |
1976年 | 53篇 |
1975年 | 54篇 |
1973年 | 55篇 |
1914年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Katsunori Wakabayashi Mitsutaka Fujita Koichi Kusakabe Kyoka Nakada 《Czechoslovak Journal of Physics》1996,46(4):1865-1866
Anoble mechanism of spin polarization is proposed for finite graphite sheet with edge. For graphite ribbon with zigzag edge, there appear peculiar ‘edge states’. These localized states comprise nearly flat band at the Fermi level, which easily causes magnetic instability. Magnetic structure is suggested from Hartree-Fock analysis of the Hubbard model, where huge magnetic moments are induced at around both of edges by weak HubbardU and are coupled antiferromagnetically with each other. 相似文献
992.
993.
LetK be an algebraically closed field withp:=char (K)>0 andX a bielliptic curve over Spec(K) with genus≥6 and such that the canonical model ofX is ordinary. In this paper we determine all the possible gap sequences of Weierstrass points on such curves. 相似文献
994.
Gur Mosheiov 《The Journal of the Operational Research Society》1996,47(9):1184-1191
We study a problem of scheduling deteriorating jobs, i.e. jobs whose processing times are an increasing function of their starting times. We consider the case of a single machine and linear job-independent deterioration. The objective is to minimize the sum of weighted completion times, with weights proportional to the basic processing times. The optimal schedule is shown to be Λ-shaped, i.e. the sequence of the basic processing times has a single local maximum. Moreover, we show that the problem is solved in O(N log N) time. In the last section we test heuristics for the case of general weights. 相似文献
995.
Gerhard Hasslinger Erik S. Rieger 《The Journal of the Operational Research Society》1996,47(5):640-653
This paper deals with approximate analysis methods for open queueing networks. External and internal flows from and to the nodes are characterized by renewal processes with discrete time distributions of their interarrival times. Stationary distributions of the waiting time, the queue size and the interdeparture times are obtained using efficient discrete time algorithms for single server (GI/G/1) and multi-server (GI/D/c) nodes with deterministic service. The network analysis is extended to semi-Markovian representations of each flow among the nodes, which include parameters of the autocorrelation function. 相似文献
996.
Steve PhillipsJr. 《The Journal of the Operational Research Society》1996,47(5):697-701
The paper presents an application oriented procedure for solving the project management duration/resource tradeoff problem. A procedure is presented for reducing a project from a normal to a crash duration state at a minimum amount of additional resource expenditure assuming a linear utilization functions. The procedure is network based using a graphical Cut Search Approach to locate the minimal resource level at each reduction in total project duration. Activity-on-arc networks and flow networks are utilized. The paper is presented for practical application and for conceptual development as compared to a theoretical treatment. 相似文献
997.
Krishna S Kumar 《Pramana》1993,41(1):45-53
We report on two sensitive tests of lepton universality carried out by the 4 LEP experiments at the Z0 pole. From measurements of the τ polarization in e+ e?→τ + τ ?, the ratios of the vector and axial vector coupling constants of the electron and the tau lepton to the weak neutral current are obtained to beg v e /g a e =0.066±0.015 andg V τ /g A τ =0.070±0.009 respectively. From measurement of the τ lifetime and the τ leptonic branching ratios, the ratio of the coupling constants describing weak leptonic decays of the τ and the μ is measured to beG τ /G μ =0.996±0.008. 相似文献
998.
A review is given of the StandardSU(5) supergravity model. This model has passed an important check regarding unification of the electro-weak and the strong couplings using high precision LEP data. It is shown that for a significant domain of the parameter space the model also satisfies constraints on the SUSY spectrum from CDF and LEP, as well as proton stability and cosmological relic density constraints. 相似文献
999.
A derivatographic method has been developed for the identification and determination of the pyrites content of bauxites and clay minerals. If the sample contains at least 0.2% of pyrite, then at 400–450° a weight increase is indicated on the DTG curve, while a heat liberation is shown on the DTA curve. The amplitude of or the area under, these maxima is proportional to the pyrites content of the sample, although the correlation is not linear. In addition, the effect of experimental conditions on the thermal decomposition of pyrites has been studied. 相似文献
1000.
Hanjiang Dong Zhengping Zhang Man-Ho Lee D. W. Mueller Richard F. Reidy 《Journal of Sol-Gel Science and Technology》2007,41(1):11-17
Sol-gel polymerization of methyltrimethoxysilane (MTMS) in ethanol using a two-step acid/base catalyzed procedure (B2) is
followed by 29Si NMR spectroscopy. Analysis of the structural evolution of the B2 system shows that esterification of monomeric and end
silicon species is rate-limited while that of linear and cyclic species is able to reach pseudoequilibrium in the second basic
step. Condensation reactivity is reduced with increasing network connectivity, however, to a much less degree under B2 conditions
than MTMS polymerization under acidic conditions. Steric effects as well as many other factors are attributed to this trend.
The concentration of cyclic and polycyclic species of the B2 system is nearly 3 times lower compared to the acid-catalyzed
system. The empirical degree of condensation at the gel point is determined to be 0.88. The effects of cyclization and phase
separation on MTMS gelation are discussed for both B2 and acid-catalyzed systems. Based on these results it is believed that
MTMS-based gels form for B2 and not acid-catalyzed conditions due to reduced cyclization, rapid hydrolysis and condensation,
effective use of functional groups, and effective contribution of branched and polycyclic species as crosslinking points to
connect polymeric chains in the B2 system. 相似文献