全文获取类型
收费全文 | 2848篇 |
免费 | 481篇 |
国内免费 | 469篇 |
专业分类
化学 | 2091篇 |
晶体学 | 53篇 |
力学 | 161篇 |
综合类 | 38篇 |
数学 | 520篇 |
物理学 | 935篇 |
出版年
2024年 | 8篇 |
2023年 | 79篇 |
2022年 | 120篇 |
2021年 | 122篇 |
2020年 | 144篇 |
2019年 | 181篇 |
2018年 | 151篇 |
2017年 | 111篇 |
2016年 | 153篇 |
2015年 | 157篇 |
2014年 | 173篇 |
2013年 | 236篇 |
2012年 | 265篇 |
2011年 | 208篇 |
2010年 | 174篇 |
2009年 | 178篇 |
2008年 | 186篇 |
2007年 | 157篇 |
2006年 | 125篇 |
2005年 | 101篇 |
2004年 | 83篇 |
2003年 | 93篇 |
2002年 | 84篇 |
2001年 | 58篇 |
2000年 | 62篇 |
1999年 | 41篇 |
1998年 | 33篇 |
1997年 | 33篇 |
1996年 | 44篇 |
1995年 | 36篇 |
1994年 | 20篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 17篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有3798条查询结果,搜索用时 328 毫秒
941.
The optogalvanic effect (OGE) may be used to detect specific species in a plasma (ions, atoms, radicals, or molecules) by selective laser excitation of the plasma. The plasma itself is merely the reservoir of electronically excited, ionized, and atomized species. Compared with conventional ICP-AES, OGE has many advantages: no external detector, zero background, no interferences, and greater versatility. Since the photoacoustic (PA) and ionization rate change (IRC) components of the OGE signal can be separated, optogalvanic spectroscopy can exhibit a further selectivity based on this discriminatory ability. The OGE method has been applied to iodine analysis. By careful selection of the operating conditions, pure atomic and pure molecular iodine signals constitute the PA and IRC profiles, respectively. The best detection limit, in a somewhat primitive experiment, is 10−7μg/ml of I2, which is comparable to laser-induced fluorescence. This detection limit can be improved by at least three orders of magnitude by optimizing the experimental conditions. 相似文献
942.
Weiwei Cao Hongde Gai Bo Zhu Yimin Wu Chunlei Zhang 《Applied Physics A: Materials Science & Processing》2012,108(2):451-456
Novel urchin-like CdS was synthesized via a facile solvothermal route without any assistant agent. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, high-resolution transmission electron, and photoluminescence spectrophotometer. Based on time-resolved experiments, a possible growth mechanism of 3D urchin-like CdS microspheres was initially proposed. Furthermore, morphology control of CdS was achieved by adjusting the quantity addition of TGA to obtain the 1D CdS nanowires. 相似文献
943.
944.
Wei Hong SONG Xuan Zhen JIANG* Department of Chemistry Zhejiang University Hangzhou 《中国化学快报》2001,(3)
Dimethyl malonate (DMM) is an important organic synthesis intermediate. Traditional synthetic method by reaction of mono-chloroacetic acid with sodium cyanide1 is poisonous and complicated. Therefore, an interest in green synthesis routes of DMM has risen greatly. The several processes for preparing DMM by carbonylation of methyl chloroacetate catalyzed by Co2(CO)8 have been reported2~5. However, Co2(CO)8 is unstable and must be prepared under high pressure (12 Mpa). Moreover, the yield… 相似文献
945.
Xiao‐Xuan Zou Wei Yang Guo‐Qiang Zheng Bang‐Hu Xie Ming‐Bo Yang 《Journal of Polymer Science.Polymer Physics》2007,45(21):2948-2955
The crystallization and phase morphology of the injection‐molded isotactic polypropylene (iPP)/syndiotactic polypylenen (sPP) blends were studied, focusing on the difference between the skin layer and core layer. The distribution of crystallinity of PPs in the blends calculated based upon the DSC results shows an adverse situation when compared with that in the neat polymer samples. For 50/50 wt % iPP/sPP blend, the SEM results indicated that a dispersed structure in the skin layer and a cocontinuous structure in the core layer were observed. A migration phenomenon that the sPP component with lower crystallization temperature and viscosity move to the core layer, whereas the iPP component with higher crystallization temperature and viscosity move to the skin layer, occurred in the iPP/sPP blend during injection molding process. The phenomenon of low viscosity content migrate to the low shear zone may be due to the crystallization‐induced demixing based upon the significant difference of crystallization temperature in the sPP and iPP. This migration caused the composition inhomogeneity in the blend and influenced the accuracy of crystallinity calculated based upon the initial composition. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2948–2955, 2007 相似文献
946.
Xuan Ding Ye Chen Shenghui Chen Jun Li Xiaofeng Wang Huaping Wang 《Journal of Macromolecular Science: Physics》2013,52(6):1199-1207
A series of aromatic polysulfonamides with various monomer ratios of 4,4′-diaminodiphenylsulfone (p-DDS) and 3,3′-diaminodiphenylsulfone (m-DDS) were synthesized to investigate the relationship between copolymer composition and their properties. The copolymer composition was determined from nuclear magnetic resonance (NMR). It was found that the copolymer composition of the polysulfonamides varied little from the monomer ratio; thus, similar reactivity of the two diaminodiphenylsulfones was shown by the results. From the analysis of the thermal properties of the polysulfonamides, high thermal stability of the copolymers was shown both in N2 and air and the decomposition temperature exhibited little dependence on the copolymer composition. However, the glass transition temperatures (Tg ) decreased obviously with increasing m-DDS segments, which is helpful to improve the solubility and spinnability of these polysulfonamides. 相似文献
947.
A fast and reliable method to calibrate LiNbO3-based polarization controllers (PCs) presented theoretically and experimentally. Particle swarm optimization (PSO) algorithm is used as an adaptive searching algorithm. Experimental results show that PSO algorithm is powerful in calibrating LiNbO3-based multistage PCs. Only less than one minute is spent for all stages of the PC to be calibrated thoroughly. 相似文献
948.
Thierry Coulhon Xuan Thinh Duong 《Transactions of the American Mathematical Society》1999,351(3):1151-1169
It has been asked (see R. Strichartz, Analysis of the Laplacian, J. Funct. Anal. 52 (1983), 48-79) whether one could extend to a reasonable class of non-compact Riemannian manifolds the boundedness of the Riesz transforms that holds in . Several partial answers have been given since. In the present paper, we give positive results for under very weak assumptions, namely the doubling volume property and an optimal on-diagonal heat kernel estimate. In particular, we do not make any hypothesis on the space derivatives of the heat kernel. We also prove that the result cannot hold for under the same assumptions. Finally, we prove a similar result for the Riesz transforms on arbitrary domains of .
949.
Davar Khoshnevisan Yimin Xiao 《Proceedings of the American Mathematical Society》2003,131(8):2611-2616
A probability measure on is called weakly unimodal if there exists a constant such that for all 0$">,
Here, denotes the -ball centered at with radius 0$">.
(0.1) |
Here, denotes the -ball centered at with radius 0$">.
In this note, we derive a sufficient condition for weak unimodality of a measure on the Borel subsets of . In particular, we use this to prove that every symmetric infinitely divisible distribution is weakly unimodal. This result is then applied to improve some recent results of the authors on capacities and level sets of additive Lévy processes.
950.
Cheng Lu ZHANG Ping Yan BIE Xuan Jia PENG Xin Fu PAN* Department of Chemistry National Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2002,13(10)
Most diterpenoids exhibit significant bioactivities, such as antidermatophytic, antibact- erial, and antioxidant. Although a large number of aromatic tricyclic diterpenoids have been isolated, there are a few of them having ethyl substituent. The synthesis of this type diterpenoids has been seldom reported. In order to further study the relationship between the structure and bioactivities of the diterpenoid, we extended the diterpene synthesis1,2,3. It is desirable to report herein the syn… 相似文献