全文获取类型
收费全文 | 26952篇 |
免费 | 4771篇 |
国内免费 | 4148篇 |
专业分类
化学 | 20884篇 |
晶体学 | 425篇 |
力学 | 1395篇 |
综合类 | 300篇 |
数学 | 2683篇 |
物理学 | 10184篇 |
出版年
2024年 | 58篇 |
2023年 | 491篇 |
2022年 | 973篇 |
2021年 | 1025篇 |
2020年 | 1158篇 |
2019年 | 1170篇 |
2018年 | 992篇 |
2017年 | 971篇 |
2016年 | 1370篇 |
2015年 | 1350篇 |
2014年 | 1652篇 |
2013年 | 2187篇 |
2012年 | 2486篇 |
2011年 | 2483篇 |
2010年 | 1840篇 |
2009年 | 1814篇 |
2008年 | 2001篇 |
2007年 | 1770篇 |
2006年 | 1625篇 |
2005年 | 1371篇 |
2004年 | 1080篇 |
2003年 | 886篇 |
2002年 | 905篇 |
2001年 | 688篇 |
2000年 | 511篇 |
1999年 | 487篇 |
1998年 | 419篇 |
1997年 | 342篇 |
1996年 | 298篇 |
1995年 | 251篇 |
1994年 | 209篇 |
1993年 | 166篇 |
1992年 | 155篇 |
1991年 | 146篇 |
1990年 | 111篇 |
1989年 | 90篇 |
1988年 | 57篇 |
1987年 | 41篇 |
1986年 | 51篇 |
1985年 | 46篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
931.
Metallic antimony catalyzes the reduction of aromatic nitro compounds to the corresponding N-arylhydroxylamines in good yields with NaBH4 under mild conditions. The azoxybenzenes from autoxidation of N-arylhydroxylamines were also obtained in basic conditions. 相似文献
932.
Under the influence of thiocyanate anions (SCN?) and cetyltrimethyl ammonium bromide (CTAB), NiS flower-like architectures were successfully synthesized by a one-step hydrothermal method. The synthesized flower-like architectures, with a multilayered and highly ordered texture, have diameters of several micrometers. X-ray powder diffraction (XRD) shows that the NiS flower-like architectures are rhombohedral crystalline. On the basis of condition-dependent experiments, the diffusion-limited aggregation (DLA) model and cage effect were used to explain the growth process of rhombohedral crystalline NiS flower-like architectures. Magnetic measurements showed that the coercivity (Hc) of the as-obtained NiS flower-like architectures was 102.14 Oe. 相似文献
933.
934.
A novel temperature-dependent ionic liquid based on 2,2,6,6-tetramethylpiperidine-1-oxyl and polyethylene glycol 600 was developed and used in oxidation of alcohols. Various alcohols were oxidized into their corresponding aldehydes or ketones with good yield and selectivity. Owing to the temperature-dependent property of the catalyst, easy recovery was achieved by simple decantation. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
935.
936.
Yu Dong Tariq Mosaval Hazim J. Haroosh Rehan Umer Hitoshi Takagi Kin‐Tak Lau 《Journal of Polymer Science.Polymer Physics》2014,52(9):618-623
This pilot study elaborates the development of novel epoxy/electrospun polylactic acid (PLA) nanofiber composites at the fiber contents of 3, 5, and 10 wt % to evaluate their mechanical and thermal properties using flexural tests and differential scanning calorimetry (DSC). The flexural moduli of composites increase remarkably by 50.8 and 24.0% for 5 and 10 wt % fiber contents, respectively, relative to that of neat epoxy. Furthermore, a similar trend is also shown for corresponding flexural strengths being enhanced by 31.6 and 4.8%. Fractured surface morphology with scanning electron microscopy (SEM) confirms a full permeation of cured epoxy matrix into nanofiber structures and existence of nondestructive fibrous networks inside large void cavities. The glass transition temperature (Tg) of composites increases up to 54–60 °C due to embedded electrospun nanofibers compared to 50 °C for that of epoxy, indicating that fibrous networks may further restrict the intermolecular mobility of matrix in thermal effects. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 618–623 相似文献
937.
938.
Tao Xu Nikolas A. Savage Guangbin Dong 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(7):1922-1926
The rhodium‐catalyzed formation of all‐carbon spirocenters involves a decarbonylative coupling of trisubstituted cyclic olefins and benzocyclobutenones through C C activation. The metal–ligand combination [{Rh(CO)2Cl}2]/P(C6F5)3 catalyzed this transformation most efficiently. A range of diverse spirocycles were synthesized in good to excellent yields and many sensitive functional groups were tolerated. A mechanistic study supports a hydrogen‐transfer process that occurs through a β‐H elimination/decarbonylation pathway. 相似文献
939.
This paper considers the problem of change point in single index models. In order to obtain asymptotically valid confidence intervals for the estimation of the change point, the convergence rate and asymptotic distribution of the change point estimate is studied. Some simulation results are presented which show that the numerical performance of our estimator is satisfactory. 相似文献
940.