全文获取类型
收费全文 | 103285篇 |
免费 | 4680篇 |
国内免费 | 3274篇 |
专业分类
化学 | 42564篇 |
晶体学 | 1085篇 |
力学 | 8137篇 |
综合类 | 201篇 |
数学 | 34417篇 |
物理学 | 24835篇 |
出版年
2024年 | 96篇 |
2023年 | 625篇 |
2022年 | 922篇 |
2021年 | 1033篇 |
2020年 | 1100篇 |
2019年 | 1056篇 |
2018年 | 11082篇 |
2017年 | 10885篇 |
2016年 | 7233篇 |
2015年 | 2116篇 |
2014年 | 1749篇 |
2013年 | 2184篇 |
2012年 | 6129篇 |
2011年 | 12806篇 |
2010年 | 7160篇 |
2009年 | 7429篇 |
2008年 | 8151篇 |
2007年 | 10253篇 |
2006年 | 1609篇 |
2005年 | 2536篇 |
2004年 | 2390篇 |
2003年 | 2729篇 |
2002年 | 1691篇 |
2001年 | 773篇 |
2000年 | 783篇 |
1999年 | 715篇 |
1998年 | 635篇 |
1997年 | 595篇 |
1996年 | 579篇 |
1995年 | 475篇 |
1994年 | 431篇 |
1993年 | 384篇 |
1992年 | 304篇 |
1991年 | 296篇 |
1990年 | 253篇 |
1989年 | 198篇 |
1988年 | 162篇 |
1987年 | 156篇 |
1986年 | 125篇 |
1985年 | 101篇 |
1984年 | 90篇 |
1983年 | 63篇 |
1982年 | 71篇 |
1981年 | 58篇 |
1980年 | 61篇 |
1979年 | 44篇 |
1914年 | 45篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
周富军 《高校应用数学学报(英文版)》2006,21(2):143-151
§1Introduction Avarietyofpartialdifferentialequationmodelsfortumorgrowthortherapyhave beendevelopedinthelastthreedecades[see2,3,16-18,21-26].Mostofthosemodelsare informoffreeboundaryproblems,andareverydiversified.Rigorousmathematical analysisofsuchfreeboundaryproblemshasdrawngreatinterest,andmanyinteresting resultshavebeenestablished[4-15].Inthispaperwedealwithamathematicalmodeldescribingtumorchemotherapy.In thismodelthetumorisviewedasdenselypacked,radially-symmetricsphereofradiusR(t)contain… 相似文献
942.
This paper derives a theorem of generalized singular value decomposition of quaternion matrices(QGSVD),studies the solution of general quaternion matrix equation AXB-CYD=E,and obtains quaternionic Roth's theorem.This paper also suggestssufficient and necessary conditions for the existence and uniqueness of solutions and explicit forms of the solutions of the equation. 相似文献
943.
Fei Zhao Xiaosong Zhai Xuemei Liu Meng Lian Guoting Liang Jingxiang Cui Haizhou Dong Wentao Wang 《Molecules (Basel, Switzerland)》2022,27(1)
The purpose of this paper was to investigate the effect of high-intensity ultrasonication (HIU) pretreatment before enzymolysis on structural conformations of walnut protein isolate (WPI) and antioxidant activity of its hydrolysates. Aqueous WPI suspensions were subjected to ultrasonic processing at different power levels (600–2000 W) and times (5–30 min), and then changes in the particle size, zeta (ζ) potential, and structure of WPI were investigated, and antioxidant activity of its hydrolysates was determined. The particle size of the particles of aqueous WPI suspensions was decreased after ultrasound, indicating that sonication destroyed protein aggregates. The ζ-potential values of a protein solution significantly changed after sonication, demonstrating that the original dense structure of the protein was destroyed. Fourier transform infrared spectroscopy indicated a change in the secondary structure of WPI after sonication, with a decrease in β-turn and an increase in α-helix, β-sheet, and random coil content. Two absorption peaks of WPI were generated, and the fluorescence emission intensity of the proteins decreased after ultrasonic treatment, indicating that the changes in protein tertiary structure occurred. Moreover, the degree of hydrolysis and the antioxidant activity of the WPI hydrolysates increased after sonication. These results suggest that HIU pretreatment is a potential tool for improving the functional properties of walnut proteins. 相似文献
944.
测量光纤外腔Fabry-Perot干涉仪的白光干涉术 总被引:5,自引:4,他引:1
提出了一种基于白光干涉术测量低锐度光纤外腔Fabry Perot干涉仪(EFPI)的方法用宽带光源注入F P腔,在接收端用一高锐度的可调谐光纤F P滤波器对EFPI的反射光谱进行扫描,获得了周期性变化的光谱输出为了测量出EFPI的腔长,对光谱信号进行傅里叶变换,得到光谱的周期,由此求出EFPI的绝对腔长证明了用低锐度EFPI的测量准确度由腔长决定F P腔越长,测量准确度越高在腔长分别是200 μm,400 μm和600 μm时,测量的腔长与实际腔长相同. 相似文献
945.
具有高机械强度的掺Er3+∶TeO2-Nb2O5玻璃的光谱性质研究 总被引:1,自引:1,他引:0
熔制了掺铒碲铌玻璃样品(100-XTeO2-XNb2O5(X=5,10,15,20 mol%),测试了其密度、折射率、转变温度、析晶温度、维氏机械强度、吸收光谱、荧光光谱、荧光寿命等参量。利用Judd-Ofelt和McCumber理论分别计算了铒离子强度参量Ωt (t=2, 4, 6)和受激发射截面σemi的大小,研究了掺铒碲铌玻璃样品光谱参量对Nb2O5成分的依赖性,并与典型的碲锌钠玻璃(75TeO2-20ZnO-5Na2O)在热学、机械强度、光谱性质和放大品行四个方面进行了比较. 相似文献
946.
Shaofei Song Jingjie Jiang Ehsan Nikbin Jane Y. Howe Ian Manners Mitchell A. Winnik 《Chemical science》2022,13(2):396
Self-assembly of crystalline-coil block copolymers (BCPs) in selective solvents is often carried out by heating the mixture until the sample appears to dissolve and then allowing the solution to cool back to room temperature. In self-seeding experiments, some crystallites persist during sample annealing and nucleate the growth of core-crystalline micelles upon cooling. There is evidence in the literature that the nature of the self-assembled structures formed is independent of the annealing time at a particular temperature. There are, however, no systematic studies of how the rate of cooling affects self-assembly. We examine three systems based upon poly(ferrocenyldimethylsilane) BCPs that generated uniform micelles under typical conditions where cooling took pace on the 1–2 h time scale. For example, several of the systems generated elongated 1D micelles of uniform length under these slow cooling conditions. When subjected to rapid cooling (on the time scale of a few minutes or faster), branched structures were obtained. Variation of the cooling rate led to a variation in the size and degree of branching of some of the structures examined. These changes can be explained in terms of the high degree of supersaturation that occurs when unimer solutions at high temperature are suddenly cooled. Enhanced nucleation, seed aggregation, and selective growth of the species of lowest solubility contribute to branching. Cooling rate becomes another tool for manipulating crystallization-driven self-assembly and controlling micelle morphologies.In the self-assembly of crystalline-coil block copolymers in solution, heating followed by different cooling rates can lead to different structures. 相似文献
947.
The growth rates of crystal interfaces have been measured by using a new technique — the laser diffraction metering technique. It is simple, visualized, fast and has high precision. This paper describes the basic principle, operation method and the precision of the technique. 相似文献
948.
Tianning Cui Qinghua Qin Wenmin Yan Tao Wang Jianxun Zhang 《Acta Mechanica Solida Sinica》2021,34(1):12-26
A new concept of lightweight structure,namely amorphous-alloy-reinforced perforated armor(ARPA)consisting of the amorphous alloy coating and perforated metal substrate plate,is proposed.The ballistic performance of the ARPA is investigated numerically.The failure modes of ARPA and projectiles are identified,and the defeating mechanism of the ARPA is explored.It is shown that the amorphous alloy coating is helpful for enhancing the target’s ballistic performance by seriously eroding and fracturing the penetrators.The effects of coating thickness,initial impact velocity and impact angle are also discussed for the target’s ballistic performance.The optimal design of coating thickness may be necessary for enhancing the ballistic resistance of ARPAs. 相似文献
949.
New ANCF solid-beam element: relationship with Bézier volume and application on leaf spring modeling
Acta Mechanica Sinica - An eight-node solid-beam element based on absolute nodal coordinate formulation (ANCF) which uses cubic interpolation at the longitudinal direction and linear at the... 相似文献
950.