全文获取类型
收费全文 | 17687篇 |
免费 | 3128篇 |
国内免费 | 1491篇 |
专业分类
化学 | 10008篇 |
晶体学 | 132篇 |
力学 | 414篇 |
综合类 | 184篇 |
数学 | 6358篇 |
物理学 | 5210篇 |
出版年
2024年 | 29篇 |
2023年 | 327篇 |
2022年 | 275篇 |
2021年 | 378篇 |
2020年 | 608篇 |
2019年 | 580篇 |
2018年 | 573篇 |
2017年 | 492篇 |
2016年 | 695篇 |
2015年 | 772篇 |
2014年 | 1152篇 |
2013年 | 1610篇 |
2012年 | 1084篇 |
2011年 | 1281篇 |
2010年 | 1087篇 |
2009年 | 1112篇 |
2008年 | 1230篇 |
2007年 | 1256篇 |
2006年 | 1022篇 |
2005年 | 781篇 |
2004年 | 724篇 |
2003年 | 722篇 |
2002年 | 626篇 |
2001年 | 471篇 |
2000年 | 436篇 |
1999年 | 392篇 |
1998年 | 335篇 |
1997年 | 255篇 |
1996年 | 244篇 |
1995年 | 277篇 |
1994年 | 220篇 |
1993年 | 166篇 |
1992年 | 170篇 |
1991年 | 94篇 |
1990年 | 89篇 |
1989年 | 78篇 |
1988年 | 82篇 |
1987年 | 41篇 |
1986年 | 45篇 |
1985年 | 77篇 |
1984年 | 54篇 |
1983年 | 17篇 |
1982年 | 64篇 |
1981年 | 51篇 |
1980年 | 38篇 |
1979年 | 39篇 |
1978年 | 39篇 |
1977年 | 27篇 |
1976年 | 30篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
利用普通幂级数发生函数方法,通过对发生函数进行xD算子,得到和式∑k=0^nμ^kf(k)的计算公式,并计算该类和式+ 相似文献
102.
S.A. Grigorian 《Topology and its Applications》2006,153(18):3598-3614
Finite-sheeted covering mappings onto compact connected groups are studied. We show that for a covering mapping from a connected Hausdorff topological space onto a compact (in general, non-abelian) group there exists a topological group structure on the covering space such that the mapping becomes a homomorphism of groups. To prove this fact we construct an inverse system of covering mappings onto Lie groups which approximates the given covering mapping. As an application, it is shown that a covering mapping onto a compact connected abelian group G must be a homeomorphism provided that the character group of G admits division by degree of the mapping. We also get a criterion for triviality of coverings in terms of means and prove that each finite covering of G is equivalent to a polynomial covering. 相似文献
103.
本文用COSY,CHCOR等二维核磁共振技术对TRANILAST,2[]3-(3.4-二甲基苯基)1-氧代-2-丙烯基]氨基]苯甲到进行了~1H、~(13)C NMR谱数据分析及归属,并结合~(13)C弛豫时间T_1 及变温实验对合成产品进行了结构鉴定. 相似文献
104.
从D触发器激励表入手,分别给出了采用单边沿D触发器和双边沿D触发器的2^n进制异步加法计数器、减法计数器的设计方法.在此基础上,采用逻辑函数修改技术,通过实例讨论了基于单边沿D触发器和双边沿D触发器的异步任意进制计数器的设计.该设计方法方便,快速,具有一定的实用意义. 相似文献
105.
We prove a conjecture by F. Ferrari. Let X be the total space of a nonlinear deformation of a rank two holomorphic vector bundle on a smooth rational curve, such that X has trivial canonical bundle and has sections. Then the normal bundle to such sections is computed in terms of the rank of the Hessian of a suitably defined superpotential at its critical points. 相似文献
106.
Jan P. Boroński 《Topology and its Applications》2007,154(18):3156-3166
A set (or a collection of sets) contained in the Euclidean space Rm is symmetric if it is invariant under the antipodal map. Given a symmetric unicoherent polyhedron X (like an n-dimensional cube or a sphere) and an odd real function f defined on vertices of a certain symmetric triangulation of X, we algorithmically construct a connected symmetric separator of X by choosing a subcollection of the triangulation. Each element of the subcollection contains the vertices v and u such that f(v)f(u)?0. 相似文献
107.
构造了第孙中禹种强度不等的非对称三态叠加多模叠加态光场|ψ1(ABC)〉q.利用多模压缩态理论研究了态|ψ1(ABC)〉q第一正交分量高次和压缩.结果发现:①当构成态|ψ1(ABC)〉q的三个多模相干态光场的强度不相等时,在一定条件下,态|ψ1(ABC)〉q的第一正交分量可出现任意幂次的高次和压缩.②当上述的三个多模相干态光场强度相等时,态|ψ1(ABC)〉q的第一正交分量的高次和压缩现象消失.在这种情况下,态|ψ1(ABC)〉q的第一正交分量恒处于NH最小测不准态. 相似文献
108.
Lin and Zhang (J. Roy. Statist. Soc. Ser. B 61 (1999) 381) proposed the generalized additive mixed model (GAMM) as a framework for analysis of correlated data, where normally distributed random effects are used to account for correlation in the data, and proposed to use double penalized quasi-likelihood (DPQL) to estimate the nonparametric functions in the model and marginal likelihood to estimate the smoothing parameters and variance components simultaneously. However, the normal distributional assumption for the random effects may not be realistic in many applications, and it is unclear how violation of this assumption affects ensuing inferences for GAMMs. For a particular class of GAMMs, we propose a conditional estimation procedure built on a conditional likelihood for the response given a sufficient statistic for the random effect, treating the random effect as a nuisance parameter, which thus should be robust to its distribution. In extensive simulation studies, we assess performance of this estimator under a range of conditions and use it as a basis for comparison to DPQL to evaluate the impact of violation of the normality assumption. The procedure is illustrated with application to data from the Multicenter AIDS Cohort Study (MACS). 相似文献
109.
KANG Zihua WANG Mingwei QIAN Jiamei RAO Jun LI Xiujuan ZHENG Tieliu WANG Xuehua 《核工业西南物理研究院年报(英文版)》2004,(1):73-76
Lower hybrid wave (LHW), electro cyclotron (EC) and neutral beam injection (NBI) etc. are the important methods of auxiliary heating. They would be devoted to the HL-2A tokamak step by step. In order to satisfy the debug of each system and the need of the experiment, the system should be equipped with high voltage pulse power (HVPP) according to the requirement. 相似文献
110.
In this paper, an interior point cutting plane method (IPCPM)is applied to solve optimal power flow (OPF) problems. Comparedwith the simplex cutting plane method (SCPM), the IPCPM is simpler,and efficient because of its polynomial-time characteristic.Issues in implementing IPCPM for OPF problems are addressed,including (1) how to generate cutting planes without using thesimplex tableau, (2) how to identify the basis variables inIPCPM, and (3) how to generate mixed integer cutting planes.The calculation speed of the proposed algorithm is further enhancedby utilizing the sparsity features of the OPF formulation. Numericalsimulations on IEEE 14-300-bus test systems have shown thatthe proposed method is effective. 相似文献