全文获取类型
收费全文 | 147309篇 |
免费 | 1466篇 |
国内免费 | 394篇 |
专业分类
化学 | 80554篇 |
晶体学 | 2394篇 |
力学 | 6073篇 |
综合类 | 3篇 |
数学 | 13588篇 |
物理学 | 46557篇 |
出版年
2021年 | 1029篇 |
2020年 | 1186篇 |
2019年 | 1256篇 |
2018年 | 1639篇 |
2017年 | 1693篇 |
2016年 | 2543篇 |
2015年 | 1566篇 |
2014年 | 2356篇 |
2013年 | 6059篇 |
2012年 | 4862篇 |
2011年 | 5959篇 |
2010年 | 4202篇 |
2009年 | 4228篇 |
2008年 | 5762篇 |
2007年 | 5541篇 |
2006年 | 5424篇 |
2005年 | 4965篇 |
2004年 | 4460篇 |
2003年 | 4130篇 |
2002年 | 4015篇 |
2001年 | 5553篇 |
2000年 | 3996篇 |
1999年 | 3078篇 |
1998年 | 2116篇 |
1997年 | 2216篇 |
1996年 | 2079篇 |
1995年 | 1925篇 |
1994年 | 1920篇 |
1993年 | 1734篇 |
1992年 | 2226篇 |
1991年 | 2304篇 |
1990年 | 2139篇 |
1989年 | 2110篇 |
1988年 | 2082篇 |
1987年 | 2095篇 |
1986年 | 1912篇 |
1985年 | 2384篇 |
1984年 | 2398篇 |
1983年 | 1915篇 |
1982年 | 1915篇 |
1981年 | 1761篇 |
1980年 | 1748篇 |
1979年 | 2033篇 |
1978年 | 2105篇 |
1977年 | 2053篇 |
1976年 | 1980篇 |
1975年 | 1864篇 |
1974年 | 1851篇 |
1973年 | 1885篇 |
1972年 | 1238篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
901.
902.
Under suitable assumptions, a functional central limit theorem is obtained for a three-dimensional model of Maxwellian molecules. This model is related to a nonlinear Boltzmann-type equation. It will be proved that the family of the distributions induced by fluctuation processes converges weakly. 相似文献
903.
We show how the Landau–Pomeranchuk–Migdal effect on photon production rates in a quark–gluon plasma can be derived via the usual Boltzmann equation. To do this, we first derive the electromagnetic polarization tensor using linear response theory, and then formulate the Boltzmann equation including the collisions mediated by soft gluon exchanges. We then identify the resulting expression for the production rate with that obtained by the field-theoretic formalism recently proposed by Arnold, Moore and Yaffe. To illustrate the LPM effect we solve the Boltzmann equation in the diffusion approximation. 相似文献
904.
Injection laryngoplasty is one of the most frequently performed procedures in patients with voice complaints. Various biomaterials have been used to medialize vocal folds or to treat symptoms of vocal fold scar. The ideal biomaterial would be easily injected through a fine-gauge needle, well tolerated, and long lasting. Injectable collagen preparations fulfill at least two of these criteria, and collagen has been used widely for vocal fold injections. MATERIALS AND METHODS: We present a retrospective review of two unusual complications of collagen injection and a review of the relevant literature on the complications of medical use of collagen compounds. RESULTS: Two patients in whom collagen was injected formed firm submucosal deposits that interrupted the normal mucosal wave and produced significant dysphonia. Surgical removal of these deposits restored the mucosal wave and improved voice quality. Management of this unusual complication of human collagen injection in the vocal fold has not been reported previously. Other complications of collagen injection include hypersensitivity reactions to bovine collagen, local abscess formation at injection sites, and possibly induction of collagen vascular disease in some patients. CONCLUSIONS: Although collagen injections of the vocal fold rarely result in complications, physicians using collagen must be familiar with the types of complications that can occur. Proper diagnosis and prompt management of complications can result in good outcomes. 相似文献
905.
906.
C.M.Lin C.T. Chia Y.J. Shu Y.K. Tseng 《光散射学报》2005,17(3):216-218
Weperformedthehigh-pressureRaman measurementofthethreenanosizedZnOcrystals. Wefoundthesmallerthesize,thehigherthe pressuretoinducethephasetransitionfrom w櫣rzitetorock-saltstructure. High-pressureRamanmeasurementsof nona-shapedZnOcrystalswerepreformed.The… 相似文献
907.
Yoshitomo Ono Naoyuki Kawashima Hiroto Kudo Tadatomi Nishikubo Takabumi Nagai 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2978-2988
The ring‐opening copolymerization of a glycidyl ester derivative having a benzophenone group and the donor–acceptor norbornadiene (D‐A NBD) dicarboxylic acid, 5‐(4‐methoxyphenyl)‐1,4,6,7,7‐pentamethyl‐2,5‐norbornadiene‐2,3‐dicarboxylic acid, monoglycidyl ester derivatives with D‐A NBD dicarboxylic anhydride using tetraphenylphosphonium bromide as a catalyst proceeded smoothly to give novel self‐photosensitizing NBD polymers in good yields. The molecular weight of these polyesters was about 4,000, and lower than that of analogous NBD polymers having no benzophenone group. All the synthesized NBD polymers isomerized smoothly to the corresponding quadricyclane (QC) polymers upon UV irradiation in tetrahydrofuran (THF) solution and in the film state. The rate of the photoisomerization of the D‐A NBD moieties in these polymers was higher than that of the D‐A NBD moieties in the polymer having no photosensitizing group. Furthermore, the rate of the photoisomerization of the D‐A NBD moieties in these polymers was also higher than that of the NBD polymer with low molecular weight photosensitizer in dilute solution. The photo‐irradiated polymers having QC moieties released thermal energies of 146–180 J/g. The D‐A NBD moieties contained in these NBD polymers possessed fair to good fatigue resistance. The degradation of the NBD moieties in these polymers was 15–30% after 50 repeated cycles of interconversion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2978–2988, 2007 相似文献
908.
Ya. I. Korenman N. N. Popova T. A. Kuchmenko 《Russian Journal of Applied Chemistry》2007,80(6):955-959
The quantitative and kinetic parameters of sorption of formic and acetic acids on thin films of various modifiers of piezoelectric quartz resonator electrodes are determined. Parameters of film formation on the electrodes (application procedure and thickness) are optimized. Methods for joint and separate determination of formic and acetic acids in air by piezoelectric microweighing with single- and double-sensor devices are developed. 相似文献
909.
T. Martinez M. Navarrete L. Cabrera F. Juárez A. Ramos K. Vazquez 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(3):569-572
Nine brands of tobacco cigarettes manufactured and distributed in the Mexican market were analyzed by γ-spectrometry to certify
their non-artificial radioactive contamination. Since natural occurring radioactive materials (NORM) 40K, 232Th, 235U, and 239U (and decay products from the latter three nuclides) are the main sources for human radiation exposure, the aim of this work
was to determine the activity of 40K and potassium concentration. Averages of 40K and potassium concentration were of 1.29±0.18 Bq·g−1, and 4.0±0.57%. The annual dose equivalents to the whole body from ingestion and inhalation of 26 Bq 40K were 0.23 μSv and 15.8 μSv, respectively. The corresponding 50 years committed dose equivalents was 0.23 μSv. The total
committed dose to the lungs due to inhalation of 40K in tobacco was 16 μSv. Potassium concentrations obtained in this work were in the same range of those obtained by INAA,
so showing that the used technique is acute, reproducible, and accessible to laboratories equipped with low background scintillation
detectors. 相似文献
910.