全文获取类型
收费全文 | 42571篇 |
免费 | 2493篇 |
国内免费 | 2225篇 |
专业分类
化学 | 20803篇 |
晶体学 | 432篇 |
力学 | 2161篇 |
综合类 | 150篇 |
数学 | 10718篇 |
物理学 | 13025篇 |
出版年
2023年 | 314篇 |
2022年 | 344篇 |
2021年 | 461篇 |
2020年 | 606篇 |
2019年 | 585篇 |
2018年 | 1639篇 |
2017年 | 1792篇 |
2016年 | 1343篇 |
2015年 | 1184篇 |
2014年 | 1268篇 |
2013年 | 1682篇 |
2012年 | 4350篇 |
2011年 | 3555篇 |
2010年 | 2720篇 |
2009年 | 2313篇 |
2008年 | 1454篇 |
2007年 | 1465篇 |
2006年 | 1389篇 |
2005年 | 5136篇 |
2004年 | 4420篇 |
2003年 | 2757篇 |
2002年 | 960篇 |
2001年 | 714篇 |
2000年 | 392篇 |
1999年 | 465篇 |
1998年 | 376篇 |
1997年 | 304篇 |
1996年 | 295篇 |
1995年 | 249篇 |
1994年 | 238篇 |
1993年 | 189篇 |
1992年 | 306篇 |
1991年 | 279篇 |
1990年 | 223篇 |
1989年 | 201篇 |
1988年 | 164篇 |
1987年 | 98篇 |
1986年 | 73篇 |
1985年 | 80篇 |
1984年 | 71篇 |
1983年 | 48篇 |
1982年 | 38篇 |
1976年 | 81篇 |
1975年 | 37篇 |
1974年 | 41篇 |
1973年 | 49篇 |
1972年 | 39篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
91.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
92.
The Kα to Lα and Kβ to Lβ intensity ratios of seven elements have been measured following photoionization at 59.5 keV by using a Si (Li) detector
(FWHM=155 eV at 5.96 keV). The intensity ratios were determined by measuring K and L x-rays emitted from a standard target of a given element. The theoretical values of the Kα to Lα and Kβ to Lβ intensity ratios were calculated using theoretically tabulated values of shell/subshell photoionization cross sections,
fluorescence yields, Coster-Kronig transition probabilities, and radiative decay rates for ηKLi≠ and ηKLi=0. The measured values are in good agreement with theoretical results.
From Optika i Spektroskopiya, Vol. 97, No. 2, 2004, pp. 186–189.
Original English Text Copyright ? 2004 by A. Kü?ük?nder, S?ğüt, E. Kü?ük?nder, Büyükkasap.
This article was submitted by the authors in English. 相似文献
93.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
94.
95.
The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.04,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis. 相似文献
96.
Ewa Stró?yna 《Journal of Differential Equations》2003,193(1):239-259
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence. 相似文献
97.
YunFei Liu ShengCai Shi ShengLin Yu 《International Journal of Infrared and Millimeter Waves》2003,24(12):2069-2077
When electromagnetic waves propagate through a wire grid, there will be some evanescent space harmonics generated around the wire grid. In this paper, we mainly investigate their effects on the transmission characteristics of a Gaussian beam by cylindrical wire grids. The results are compared with those without taking account of evanescent space-harmonics. 相似文献
98.
99.
The properties of pulsed laser vapor doping on p-Si(1 0 0) with a KrF (248 nm) excimer pulsed laser (248 nm) and BCl3 gas are reported in this paper. The doped samples are characterized by the resistance measured using a four-probe method, since the sheet resistance changes with the carrier concentration of the sample. The doping effects with the variation of laser energy density, pulse number, and the pressure of BCl3 were investigated in terms of the sheet resistance. In this way, the optimized parameters were obtained and used for the positive heavy doping on p-Si(1 0 0) and p-Si(1 1 1). Then, using a square mesh under the above conditions, an image doping was completed. Finally, the metal–semiconductor Ohmic contacts were realized by plating Ag and Cu films on the doped surface. 相似文献
100.
Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations. 相似文献