全文获取类型
收费全文 | 63430篇 |
免费 | 18633篇 |
国内免费 | 3131篇 |
专业分类
化学 | 68311篇 |
晶体学 | 361篇 |
力学 | 3094篇 |
综合类 | 242篇 |
数学 | 4711篇 |
物理学 | 8475篇 |
出版年
2024年 | 421篇 |
2023年 | 4308篇 |
2022年 | 2132篇 |
2021年 | 3232篇 |
2020年 | 5301篇 |
2019年 | 3128篇 |
2018年 | 2887篇 |
2017年 | 1318篇 |
2016年 | 6397篇 |
2015年 | 6434篇 |
2014年 | 6032篇 |
2013年 | 6480篇 |
2012年 | 4847篇 |
2011年 | 2764篇 |
2010年 | 4641篇 |
2009年 | 4523篇 |
2008年 | 2372篇 |
2007年 | 1931篇 |
2006年 | 1249篇 |
2005年 | 983篇 |
2004年 | 748篇 |
2003年 | 620篇 |
2002年 | 532篇 |
2001年 | 494篇 |
2000年 | 398篇 |
1999年 | 389篇 |
1998年 | 338篇 |
1997年 | 332篇 |
1996年 | 299篇 |
1995年 | 342篇 |
1994年 | 265篇 |
1993年 | 343篇 |
1992年 | 220篇 |
1991年 | 195篇 |
1990年 | 152篇 |
1988年 | 166篇 |
1981年 | 158篇 |
1980年 | 197篇 |
1979年 | 188篇 |
1978年 | 189篇 |
1977年 | 311篇 |
1976年 | 362篇 |
1975年 | 458篇 |
1974年 | 472篇 |
1973年 | 284篇 |
1972年 | 369篇 |
1971年 | 356篇 |
1970年 | 541篇 |
1969年 | 413篇 |
1968年 | 456篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
关于可达矩阵的求法探讨 总被引:6,自引:0,他引:6
在《离散数学》、《图论》课程中 ,用矩阵表示图时 ,涉及到一类重要的矩阵——可达矩阵 ,它是判别图中任意两点是否有通路的重要手段 ,也是求强分图的重要方法 ,但是可达矩阵的求法比较复杂 .本文针对这一问题 ,对可达矩阵的求法进行了改进 ,提出了一种简单可行的算法 . 相似文献
52.
Prof. Dr. Leszek Stoch 《Journal of Thermal Analysis and Calorimetry》1992,38(9):1947-1948
53.
54.
55.
56.
Guosong Wu Xiaoqin Zeng Wenbin Ding Xingwu Guo Shoushan Yao 《Applied Surface Science》2006,252(20):7422-7429
Ceramic thin films have been widely used to protect the metal substrate as coatings in the past years. In order to improve the poor corrosion resistance of AZ31 magnesium alloy, the study in this paper used the electron beam evaporation method to prepare ceramic PVD films on its surface with TiO2 and Al2O3 as donors, respectively. Atomic force microscopy (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the surface morphology, composition and microstructure of the thin films. Both films deposited on AZ31 took on compact top surface morphologies and grew as amorphous structures on substrate. AES test not only showed that films compositions deviated the standard stoichiometric ratios, but also found that element Mg diffused into films and existed as magnesium oxide in the TiOx film as well as the AlOx film. In the electrochemical corrosion test, the AlOx coating on AZ31 exhibited the largest electrochemical impedance in a 3.5% NaCl solution. But it did not show better corrosion resistance than others for the poorer adhesion. Even if its thickness was small, the TiOx coating on AZ31 exhibited the best corrosion resistance in this study. According to the observation and analysis, the damage of these films on AZ31 in aggressive solutions was mainly due to the existence of pores, microcracks, vacancies and poor adhesion between coating and substrate. 相似文献
57.
Suchada Suntornchashwej Dr. Khanit Suwanborirux Dr. Kazushi Koga Minoru Isobe Prof. Dr. 《化学:亚洲杂志》2007,2(1):114-122
Malyngamide X ( 1 ), the first (7R)‐lyngbic acid connected to a new tripeptide backbone, was isolated from the Thai sea hare Bursatella leachii. The gross structure of 1 was established on the basis of 1D and 2D NMR and mass spectroscopic data. Combination of the NMR spectroscopic experiments with α‐methoxy‐α‐(trifluoromethyl)phenylacetic acid esters, 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol chiral solvating agent, and molecular mechanics of 1 and the synthetic molecular fragments allowed us to determine the absolute stereochemistry of all six stereogenic centers without hydrolytic degradation of the compound. Compound 1 displayed moderate cytotoxic, antitubercular, and antimalarial properties. 相似文献
58.
Chen-liang Li Jin-ping Zeng 《应用数学学报(英文版)》2007,23(1):79-90
We consider several synchronous and asynchronous multisplitting iteration schemes for solving aclass of nonlinear complementarity problems with the system matrix being an H-matrix.We establish theconvergence theorems for the schemes.The numerical experiments show that the schemes are efficient forsolving the class of nonlinear complementarity problems. 相似文献
59.
The fission barrier for ^240pu is investigated beyond the second saddle point in the potentiM energy surface by the constrained relativistic mean field method with the newly proposed parameter set PK1. The microscopic correction for the centre-of-mass motion is essentiM to provide the correct potential energy surface. The shell effects that stabilize the nuclei against the fission is also investigated by the Strutinsky method. The shapes for the ground state, fission isomer and saddle-points, etc, are studied in detail. 相似文献
60.
In this note we study constant mean curvature surfaces in asymptotically flat 3-manifolds. We prove that, outside a given compact subset in an asymptotically flat 3-manifold with positive mass, stable spheres of given constant mean curvature are unique. Therefore we are able to conclude that the foliation of stable spheres of constant mean curvature in an asymptotically flat 3-manifold with positive mass outside a given compact subset is unique.