全文获取类型
收费全文 | 70450篇 |
免费 | 6651篇 |
国内免费 | 4635篇 |
专业分类
化学 | 21950篇 |
晶体学 | 365篇 |
力学 | 5965篇 |
综合类 | 1217篇 |
数学 | 31173篇 |
物理学 | 21066篇 |
出版年
2023年 | 645篇 |
2022年 | 1015篇 |
2021年 | 2046篇 |
2020年 | 1838篇 |
2019年 | 1910篇 |
2018年 | 1649篇 |
2017年 | 1914篇 |
2016年 | 2251篇 |
2015年 | 1971篇 |
2014年 | 3125篇 |
2013年 | 5362篇 |
2012年 | 3303篇 |
2011年 | 4007篇 |
2010年 | 3700篇 |
2009年 | 4610篇 |
2008年 | 4624篇 |
2007年 | 4702篇 |
2006年 | 3722篇 |
2005年 | 2915篇 |
2004年 | 2666篇 |
2003年 | 2490篇 |
2002年 | 2387篇 |
2001年 | 1973篇 |
2000年 | 1590篇 |
1999年 | 1405篇 |
1998年 | 1307篇 |
1997年 | 1014篇 |
1996年 | 990篇 |
1995年 | 877篇 |
1994年 | 870篇 |
1993年 | 793篇 |
1992年 | 744篇 |
1991年 | 537篇 |
1990年 | 461篇 |
1989年 | 351篇 |
1988年 | 392篇 |
1987年 | 348篇 |
1986年 | 356篇 |
1985年 | 497篇 |
1984年 | 421篇 |
1983年 | 257篇 |
1982年 | 443篇 |
1981年 | 571篇 |
1980年 | 507篇 |
1979年 | 555篇 |
1978年 | 436篇 |
1977年 | 332篇 |
1976年 | 278篇 |
1974年 | 89篇 |
1973年 | 183篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
81.
ABSTRACT Multicolour emissive carbon dots (CDs) are widely investigated by virtue of their merits on fluorescent properties. Method on heteroatom doping assisted with various solvents has been proved efficient in achieving multiple-colour-emissive CDs, especially long-wavelength emission. Herein, a synthesis of multicolour-emissive CDs by controlled surface function is reported. By tuning the thermal-pyrolysis temperature and molar ratio of reactants, optimal emission of the resulted CDs gradually shifts from blue to yellow light with the assistance of different solvents. According to the emissive relationship dependent on excitation, fluorescence lifetimes, and FT-IR of these CDs, the different surface states participated with S and N elements on the surface of carbogenic core govern fluorescent colours of the CDs. In terms of the applications, blue CDs (B-CDs) exhibits high sensitivity for ion detections of Ag+ and Fe3+, which is further illustrated to have different quenching mechanisms each other because that these ions have the affinity interaction with different surface groups of the CDs. Moreover, blue and yellow CDs solutions are mixed with PVP water solution to fabricate white-light CDs/PVP film, which exhibits stable fluorescence with a CIE coordinate of (0.32, 0.33) and endows these CDs as potentially fluorescent nanomaterial in the solid state lighting field. 相似文献
82.
83.
84.
The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr2·6H2O formed. In addition to this double salt, the three single salts LiBr·2H2O, KBr and MgBr2·6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer's electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones. 相似文献
85.
86.
87.
In this paper, we study a host-parasitoid model with Holling II Functional response, where we focus on a special case: the carrying capacity K2 for parasitoids is equal to a critical value
r 1η. It is shown that the model can undergo Bogdanov-Takens bifurcation. The approximate expressions for
saddle-node, Homoclinic and Hopf bifurcation curves are calculated. Numerical simulations, including bifurcation diagrams and corresponding phase portraits, are also given to illustrate the theoretical results. 相似文献
88.
89.
In this paper, a periodic stochastic human immunodeficiency virus (HIV) model with distributed delay and cytotoxic T lymphocytes (CTL) immune response is investigated. First, by It 's formula, we show that the solution with any positive initial value is global and positive. Then, by the stochastic comparison theorem, we obtain the sufficient conditions guaranteeing the existence and global attractivity of infection-free periodic solution. Furthermore, we discuss the existence of the infective periodic solution by Has'minskii theory. Finally, numerical examples are given to illustrate the results. 相似文献
90.