全文获取类型
收费全文 | 15093篇 |
免费 | 2741篇 |
国内免费 | 2671篇 |
专业分类
化学 | 10533篇 |
晶体学 | 339篇 |
力学 | 1057篇 |
综合类 | 321篇 |
数学 | 1706篇 |
物理学 | 6549篇 |
出版年
2024年 | 46篇 |
2023年 | 308篇 |
2022年 | 574篇 |
2021年 | 627篇 |
2020年 | 597篇 |
2019年 | 595篇 |
2018年 | 512篇 |
2017年 | 558篇 |
2016年 | 741篇 |
2015年 | 753篇 |
2014年 | 897篇 |
2013年 | 1129篇 |
2012年 | 1311篇 |
2011年 | 1262篇 |
2010年 | 1065篇 |
2009年 | 1023篇 |
2008年 | 1071篇 |
2007年 | 955篇 |
2006年 | 975篇 |
2005年 | 829篇 |
2004年 | 583篇 |
2003年 | 446篇 |
2002年 | 531篇 |
2001年 | 397篇 |
2000年 | 401篇 |
1999年 | 314篇 |
1998年 | 220篇 |
1997年 | 255篇 |
1996年 | 218篇 |
1995年 | 213篇 |
1994年 | 181篇 |
1993年 | 143篇 |
1992年 | 137篇 |
1991年 | 94篇 |
1990年 | 91篇 |
1989年 | 87篇 |
1988年 | 69篇 |
1987年 | 39篇 |
1986年 | 49篇 |
1985年 | 39篇 |
1984年 | 24篇 |
1983年 | 29篇 |
1982年 | 21篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1975年 | 7篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
131.
基于长周期光纤光栅的模式耦合机理,提出一种快速模拟长周期光纤光栅折射率特性的方法。该方法在计算包层模式的有效折射率时分开计算,在环境折射率小于包层折射率时采用二分法和分步搜索法结合计算包层模式的有效折射率,在环境折射率大于包层折射率时采用Nelder-Mead加分步搜索法求解包层模式的有效折射率。在应用谐振波长的决定式求解与环境折射率的匹配的谐振波长时,采用变区间应用二分法求解而不是传统的逐步搜索法求解谐振波长。数值结果与实验结果做了对比,两者基本一致。实践证明,该方法方便快捷,比一般的方法速度提高7倍以上。 相似文献
132.
We report the application of customer-built scanning thermal microscopy (SThM) based on a commercial atomic force microscope to investigate local thermal inhomogeneity of ZnO varistors. The so-called 3ω method, generally used for measuring macroscale thermal conductivity, is set up and integrated with an atomic force microscope to probe the nanoseale thermal property. Remarkably, thermal contrasts of ZnO varistors are firstly imaged by the SThM, indicating the uniform distribution of spinel phases at triple points. The frequency-dependent thermal signal of ZnO varistors is also studied to present quantitative evaluation of local thermal conductivity of the sample. 相似文献
133.
ICP-AES法检测云南稻精米和糙米与土壤矿质元素间的关联性 总被引:4,自引:1,他引:4
采用电感耦合等离子体原子发射光谱法(ICP-AES)对55个云南省水稻改良品种精米、糙米及其相应的土壤18种矿质元素进行测定与分析, 加标回收率在93.1%~110.2%之间, RSD为0.8%~5.1%。18种矿质元素(S, Mo, Ba, Ni, Fe, Cr, Na, Al, Cu, P, Sn, Zn, B, Mn, Mg, Ca, Sr和K)是功能稻米活性成分的重要部分,精米的平均含量依次为P>K>S>Mg>Ca>Zn>Na>Al>Mn>Fe>Cu>B>Mo>Ni>Sn>Cr>Ba>Sr, 糙米P>K>Mg>S>Ca>Zn>Mn>Al>Na>Fe>Cu>B>Mo>Sn>Ni>Cr>Ba>Sr, 而土壤则为Fe>Al> Ca>K>Mg>P>S>Mn>B>Na>Ba>Zn>Cr>Cu>Ni>Sn>Mo>Sr;精米和糙米除S和P外, 16种矿质元素含量均明显低于土壤;精米和糙米间八种微量元素(Mo, Ni, Cr, Sr, Mn, Zn, Cu, Na)间相关性明显比六种宏量元素(P, K, Mg, Ca, S和Al)间关系密切。云南土壤以富铁铝高钙为主而精米和糙米则以磷钾镁硫为主;以精米为主食比糙米更易诱发慢性病。文章结果可能为功能稻米遗传育种、生产以及人类慢性病和矿质营养不良(Fe, Zn和Ca)问题研究的参考。 相似文献
134.
135.
136.
Characteristics of xenon-lamp pumped pyrromethene 567-doped dye laser based on polymethylmethacrylater 下载免费PDF全文
The solid-state medium containing pyrromethene 567 (PM567) in a polymethylmethacrylate polymer host is shown to lase under the flash lamp excitation. The experimental setup is an ordinary industrial product without special design. The bulk transmission losses, the output energy, and the other lasing properties are compared. The medium with the lowest transmission loss, measured to be 0.392 %/cm at 633 nm, gives a laser output of 130 mJ with a slope efficiency of 0.082%. 相似文献
137.
The effect of the relative phase (?) between the probe and driving fields on the gain without inversion (GWI) in a Doppler broadened open quasi Λ-type four level atomic system with vacuum induced coherence (VIC) for both co- and counter-propagating probe and driving fields cases is studied. It is shown that: (1) GWI and the probe detuning region in which GWI exists are very sensitive to variation of the relative phase; when values of the other parameters keep unvarying, by adjusting value of ?, the largest GWI can be obtained. (2) The Doppler width (D) also has dramatically modulation role on the phase-dependent GWI. When value of D is smaller, the value of ? which corresponds to the largest value of GWI is about π, when value of D is large enough, it is about π/2. (3) GWI varies periodically with ? varying, the period is 2π, but the concrete variation rule is closely related to value of D. (4) In the co-propagating case we can obtain much larger GWI than that in the counter-propagating case. 相似文献
138.
139.
本文描述了在通常的夸克势模型中的夸克蜕定域、色屏蔽及核力特性,对所得核子—核子绝热近似势和散射相移进行了定性描述:既有排斥心,又有中程吸引,但没有Van der Waals力问题,变分给出蜕定域的数值也是合理的,对质心运动效应、色屏蔽形式的影响以及各种单夸克基矢的关系和选择问题进行了专门的研究。 We introduce the quark delocalization and color screening into the usual quark modeland the property of nuclear force. The resulting N-N phase shifts and the adiabatic potential aredescribed qualitatively well: there are exclusion core and also intermediate range attraction, but thereis no Van der Waals force. The delocalization parameter obtained from variational method is alsoreasonable. we consider especially the effect of mass center motion, the effect of forms of colorscreening... 相似文献
140.
A new type of bismuth silicate glass (Bi2O3-SiO2-ZnO-Al2O3-La2O3) doped with Tm2O3 is prepared by melt-quenching method. The thermal stability of the glass is examined by differential scanning calorimetry. No crystallization peak is found. Using the absorption and emission spectra, the absorption and emission cross-sections are calculated. Their maximum data are 2.9×10-21cm2 at 1663 nm and 4.7×10-21cm2 at 1826 nm, respectively. Using the Judd-Ofelt theory, the radiation transition probabilities and radiative lifetimes are obtained. The extended overlap integral method is applied to analyze energy transfer process among the Tm3+ ions. The transfer constants of cross-relaxation and energy migration among the Tm3+ ions at the 3H4 level are 7.60×10-40 and 14.98×10-40 cm6 /s, respectively. The critical transfer radius for cross-relaxation is 0.99 nm. The cross relaxation process is easy to realize and is favorable for obtaining ~2-μm laser. 相似文献