全文获取类型
收费全文 | 38633篇 |
免费 | 1855篇 |
国内免费 | 4523篇 |
专业分类
化学 | 28284篇 |
晶体学 | 567篇 |
力学 | 228篇 |
综合类 | 160篇 |
数学 | 10669篇 |
物理学 | 5103篇 |
出版年
2024年 | 30篇 |
2023年 | 253篇 |
2022年 | 534篇 |
2021年 | 655篇 |
2020年 | 674篇 |
2019年 | 1761篇 |
2018年 | 940篇 |
2017年 | 1642篇 |
2016年 | 1017篇 |
2015年 | 962篇 |
2014年 | 1336篇 |
2013年 | 3303篇 |
2012年 | 2003篇 |
2011年 | 2610篇 |
2010年 | 1937篇 |
2009年 | 2205篇 |
2008年 | 2592篇 |
2007年 | 2711篇 |
2006年 | 2322篇 |
2005年 | 1888篇 |
2004年 | 1822篇 |
2003年 | 1499篇 |
2002年 | 1253篇 |
2001年 | 1084篇 |
2000年 | 1048篇 |
1999年 | 891篇 |
1998年 | 760篇 |
1997年 | 677篇 |
1996年 | 576篇 |
1995年 | 654篇 |
1994年 | 508篇 |
1993年 | 431篇 |
1992年 | 407篇 |
1991年 | 282篇 |
1990年 | 204篇 |
1989年 | 176篇 |
1988年 | 133篇 |
1987年 | 103篇 |
1986年 | 118篇 |
1985年 | 144篇 |
1984年 | 118篇 |
1983年 | 63篇 |
1982年 | 107篇 |
1981年 | 109篇 |
1980年 | 90篇 |
1979年 | 96篇 |
1978年 | 87篇 |
1977年 | 58篇 |
1976年 | 55篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Magnetic Properties of the Cobaltates Na6CoS4, Na6CoSe4, and K6CoS4 The alkali metal cobalt chalcogenides Na6CoS4, Na6CoSe4, and K6CoS4 crystallize in the space group P63mc with Z = 4. The structure is characterized by isolated [CoX4]-tetrahedra. The magnetic susceptibilities show Curie-Weiss behaviour. The deviations at low temperatures are caused by antiferromagnetic interactions. The magnetic moments are discussed with regard to ligand-field parameters. 相似文献
92.
Hiromichi Kurosu Mizuyo Kikuchi Isao Ando 《Journal of Polymer Science.Polymer Physics》1995,33(5):769-775
The solid-state 15N CP/MAS NMR spectra and 15N spin-lattice relaxation times (T1) of doped and dedoped 15N-labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high-resolution solid-state 15N NMR. The 15N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half-width of the 15N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wiley & Sons, Inc. 相似文献
93.
94.
许多乙酰芳胺类化合物具有优异的生物活性,例如除草剂苯噻草胺,可抑制细胞生长和分裂,防除稻田中禾本科杂草[1];杀菌剂甲霜灵可防治作物霜霉病[2]。本文将具有多种生物活性的嘧啶基团引入到乙酰芳胺结构中[3],合成下列10个未见文献报道的标题化合物Ⅰ,通... 相似文献
95.
Oleg Borodin 《Combinatorica》1993,13(1):121-125
The weight of an edge in a graph is the sum of the degrees of its end-vertices. It is proved that in each 3-polytope there exists either an edge of weight at most 13 for which both incident faces are triangles, or an edge of weight at most 10 which is incident with a triangle, or else an edge of weight at most 8. All the bounds 13, 10, and 8 are sharp and attained independently of each other. 相似文献
96.
97.
A self-avoiding polygon (SAP) on a graph is an elementary cycle. Counting SAPs on the hypercubic lattice ℤ
d
withd≥2, is a well-known unsolved problem, which is studied both for its combinatorial and probabilistic interest and its connections
with statistical mechanics. Of course, polygons on ℤ
d
are defined up to a translation, and the relevant statistic is their perimeter.
A SAP on ℤ
d
is said to beconvex if its perimeter is “minimal”, that is, is exactly twice the sum of the side lengths of the smallest hyper-rectangle containing
it. In 1984, Delest and Viennot enumerated convex SAPs on the square lattice [6], but no result was available in a higher
dimension.
We present an elementar approach to enumerate convex SAPs in any dimension. We first obtain a new proof of Delest and Viennot's
result, which explains combinatorially the form of the generating function. We then compute the generating function for convex
SAPs on the cubic lattice. In a dimension larger than 3, the details of the calculations become very cumbersome. However,
our method suggests that the generating function for convex SAPs on ℤ
d
is always a quotient ofdifferentiably finite power series. 相似文献
98.
Summary We prove convergence and error estimates in Sobolev spaces for the collocation method with tensor product splines for strongly elliptic pseudodifferential equations on the torus. Examples of applications include elliptic partial differential equations with periodic boundary conditions but also the classical boundary integral operators of potential theory on torus-shaped domains in three or more dimensions. For odd-degree splines, we prove convergence of nodal collocation for any strongly elliptic operator. For even-degree splines and midpoint collocation, we find an additional condition for the convergence which is satisfied for the classical boundary integral operators. Our analysis is a generalization to higher dimensions of the corresponding analysis of Arnold and Wendland [4]. 相似文献
99.
The response to Hg(II) of a thin all-solid-state Te-doped silver chalcogenide membrane, described by the general formula Ag2 + δSe1 − xTex, which has been electrochemically prepared following a previously proposed approach, has been investigated. The kinetics of formation of the membrane's secondary dynamic response to Hg(II) has been successfully combined with the precise timing and transient signal, typical for flow-injection (FI) measurements, in developing a sensitive and reliable mercury FI detector. Under optimized stream conditions it exhibits a linear Nernstian response, with a double slope of the calibration graph of 59 mV dec−1, over the mercury(II) concentration range 10−6 − 10−3 M, the typical sample throughput amounting to about 70 samples per hour. The observed chemical amplification of the signal is due to the specificity of the processes dominating the initial step in formation of the steady-state signal of the membrane to mercury. The analytical performance of the Hg(II) FI detector, as regards sensitivity, reproducibility, selectivity and long-term stability has been thoroughly investigated. The exact procedure for membrane electrodeposition is given and the potential of the proposed approach as a cost-effective way for preparing chalcogenides of unique structure and properties has been outlined in the above context. 相似文献