全文获取类型
收费全文 | 32648篇 |
免费 | 1862篇 |
国内免费 | 1747篇 |
专业分类
化学 | 19556篇 |
晶体学 | 137篇 |
力学 | 539篇 |
综合类 | 626篇 |
数学 | 7331篇 |
物理学 | 8068篇 |
出版年
2023年 | 226篇 |
2022年 | 341篇 |
2021年 | 1360篇 |
2020年 | 642篇 |
2019年 | 748篇 |
2018年 | 511篇 |
2017年 | 530篇 |
2016年 | 705篇 |
2015年 | 778篇 |
2014年 | 982篇 |
2013年 | 1889篇 |
2012年 | 1188篇 |
2011年 | 1378篇 |
2010年 | 1314篇 |
2009年 | 1735篇 |
2008年 | 1868篇 |
2007年 | 1992篇 |
2006年 | 1484篇 |
2005年 | 909篇 |
2004年 | 835篇 |
2003年 | 946篇 |
2002年 | 3436篇 |
2001年 | 1169篇 |
2000年 | 731篇 |
1999年 | 604篇 |
1998年 | 599篇 |
1997年 | 385篇 |
1996年 | 415篇 |
1995年 | 367篇 |
1994年 | 390篇 |
1993年 | 430篇 |
1992年 | 428篇 |
1991年 | 280篇 |
1990年 | 231篇 |
1989年 | 192篇 |
1988年 | 223篇 |
1987年 | 190篇 |
1986年 | 199篇 |
1985年 | 313篇 |
1984年 | 228篇 |
1983年 | 142篇 |
1982年 | 286篇 |
1981年 | 463篇 |
1980年 | 423篇 |
1979年 | 465篇 |
1978年 | 370篇 |
1977年 | 279篇 |
1976年 | 238篇 |
1974年 | 74篇 |
1973年 | 151篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
151.
In this paper we first give a lower bound on multiplicities for Buchsbaum homogeneous k-algebras A in terms of the dimension d, the codimension c, the initial degree q, and the length of the local cohomology modules of A. Next, we introduce the notion of Buchsbaum k-algebras with minimal multiplicity of degree q, and give several characterizations for those rings. In particular, we will show that those algebras have linear free resolutions. Further, we will give many examples of those algebras. 相似文献
152.
Let E\subset \Bbb R
s
be compact and let d
n
E
denote the dimension of the space of polynomials of degree at most n in s variables restricted to E . We introduce the notion of an asymptotic interpolation measure (AIM). Such a measure, if it exists , describes the asymptotic behavior of any scheme τ
n
={ \bf x
k,n
}
k=1
dnE
, n=1,2,\ldots , of nodes for multivariate polynomial interpolation for which the norms of the corresponding interpolation operators do
not grow geometrically large with n . We demonstrate the existence of AIMs for the finite union of compact subsets of certain algebraic curves in R
2
. It turns out that the theory of logarithmic potentials with external fields plays a useful role in the investigation. Furthermore,
for the sets mentioned above, we give a computationally simple construction for ``good' interpolation schemes.
November 9, 2000. Date revised: August 4, 2001. Date accepted: September 14, 2001. 相似文献
153.
本文针对单件小批量生产系统 ,建立了模糊优化的动态随机投入产出模型 ,同时给出了该模型的递推解法 ,并用此模型对某单件小批企业在生产计划期的商品量进行了规划 相似文献
154.
本文对星载光学系统遮光罩消杂光结构的优化设计做了初步探讨。提出了遮光罩和挡光环消杂光设计的基本原则。给出了一种二级遮光罩结构寸的优化设计方法和一种遮光罩内壁上挡光环位置优化设计方法,并对一级和二级遮光罩进行了初步的分析比较。 相似文献
155.
The current status of the R & D activities is presented on electron beam processing of polymers being carried out at TRCRE. Topics included are sterilization of medical products, graft polymers for selective separation or absorbents and curing of liquid prepolymer-monomer systems. 相似文献
156.
New Spiro Compounds from Cyclophosphazenes and Cyclodi[phosphadiazanes] Chlorocyclophosphazenes (Cl2P = N)3 and (Cl2p = N)4 react with dihydrazidophosphoric acid derivatives in THF in the presence of triethylamine to give the spirocyclic compounds Cl4N3P3(NHN(CH3))2P(S)OC6H5, Cl6N4P4(NHNH)2P(S)OC6H5. Constitutions have been confirmed by MS, NMR, IR and elemental analysis. 相似文献
157.
Solomon Fekade Mulugeta Bekele 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):369-374
We analyze the relaxation behavior of a bistable system when the background temperature profile is inhomogeneous due to the
presence of a localized hot region (blowtorch) on one side of the potential barrier. Since the diffusion equation for inhomogeneous
medium is model-dependent, we consider two physical models to study the kinetics of such system. Using a conventional stochastic
method, we obtain the escape and equilibration rates of the system for the two physical models. For both models, we find that
the hot region enhances the escape rate from the well where it is placed while it retards the escape rate from the other well. However, the value of the escape rate from the well where the hot region is placed differs
for the two models while that of the escape rate from the other well is identical for both. This work, for the first time,
gives a detailed report of the similarities and differences of the escape rates and, hence, exposes the common and distinct
features of the two known physical models in determining the way the bistable system relaxes.
Received 25 September 2001 相似文献
158.
Peptidic aminopeptidase inhibitors, bestatin, phebestin and probestin have been prepared by stereo- and regiocontrolled reactions from a common α,β-epoxy ester precursor. 相似文献
159.
In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl-N-carbazolyl)-6-(N-carbazolyl)-2,4-hexadyine] (polya-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings. 相似文献
160.
Dragos Ghioca 《Journal of Number Theory》2007,125(1):85-94
We study the v-adic distance from the torsion of a Drinfeld module to an affine variety. 相似文献