全文获取类型
收费全文 | 45760篇 |
免费 | 3911篇 |
国内免费 | 6397篇 |
专业分类
化学 | 31521篇 |
晶体学 | 1406篇 |
力学 | 1055篇 |
综合类 | 273篇 |
数学 | 8682篇 |
物理学 | 13131篇 |
出版年
2024年 | 86篇 |
2023年 | 474篇 |
2022年 | 1091篇 |
2021年 | 1040篇 |
2020年 | 1355篇 |
2019年 | 1407篇 |
2018年 | 1190篇 |
2017年 | 1443篇 |
2016年 | 1486篇 |
2015年 | 1410篇 |
2014年 | 2042篇 |
2013年 | 3448篇 |
2012年 | 2274篇 |
2011年 | 3508篇 |
2010年 | 2741篇 |
2009年 | 3142篇 |
2008年 | 3318篇 |
2007年 | 3167篇 |
2006年 | 2817篇 |
2005年 | 2622篇 |
2004年 | 2276篇 |
2003年 | 1853篇 |
2002年 | 1685篇 |
2001年 | 1271篇 |
2000年 | 1225篇 |
1999年 | 1046篇 |
1998年 | 855篇 |
1997年 | 769篇 |
1996年 | 686篇 |
1995年 | 681篇 |
1994年 | 633篇 |
1993年 | 553篇 |
1992年 | 446篇 |
1991年 | 323篇 |
1990年 | 224篇 |
1989年 | 216篇 |
1988年 | 172篇 |
1987年 | 128篇 |
1986年 | 127篇 |
1985年 | 134篇 |
1984年 | 109篇 |
1983年 | 71篇 |
1982年 | 95篇 |
1981年 | 83篇 |
1980年 | 89篇 |
1979年 | 63篇 |
1978年 | 62篇 |
1977年 | 45篇 |
1976年 | 31篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Martin A. Bos Bertus Dunnewind Ton van Vliet 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):95-105
Interfacial rheological properties and their suitability for foam production and stability of two vegetable proteins were studied and compared to β-casein. Proteins used ranged from flexible to rigid/globular in the order of β-casein, gliadin and soy glycinin. Experiments were performed at pH 6.7. Network forming properties were characterised by the surface dilational modulus (determined with the ring trough) and the critical falling film length (Lstill) at which a stagnant protein film will break. Gliadin had the highest dilational modulus, followed by glycinin and β-casein, whereas glycinin formed the strongest film against fracture in the overflowing cylinder. The rate of decrease in the surface tension was studied at the air–water (Wilhelmy plate method) and the oil–water interface (bursting membrane) and the dynamic surface tension during compression and expansion in the caterpillar. Gliadin had the lowest equilibrium interfacial tensions and β-casein the lowest dynamic surface tension during expansion. Hardly any foam could be formed at a concentration of 0.1 g/l by shaking. At a concentration of 1.4 g/l most foam was formed by β-casein, followed by gliadin and glycinin. It seems that in the first place the rate of adsorption is important for foam formation. For the vegetable proteins, adsorption was slow. This resulted in lower foamability, especially for glycinin. 相似文献
82.
A subgroup H of a finite group G is said to have the semi cover-avoiding property in G if there is a normal series of G such that H covers or avoids every normal factor of the series. In this paper, some new results are obtained based on the assumption that some subgroups have the semi cover-avoiding property in the group. 相似文献
83.
84.
Michèle Audin 《manuscripta mathematica》2007,124(4):533-550
In this paper, we investigate symplectic manifolds endowed with a Morse–Bott function with only two critical submanifolds,
one of which is Lagrangian while the other one is symplectic. 相似文献
85.
86.
By exploiting the construction of charged field algebras as canonical extensions of CCR current algebras in 1+1 dimensions and nonregular representations of extended algebras, we provide an algebraic construction of local Fermi fields as ultrastrong limits of bosonic variables in all representations which are locally Fock with respect to the ground-state representation of the massless scalar field. 相似文献
87.
Traveling wave Ti:LiNbO3 Mach-Zehnder optical modulators with buried electrodes and etched grooves in the SiO2 buffer layer are analyzed by the finite element method. The tradeoff between the bandwidth BW and the half-wave voltage Vπ is discussed. The value of BW/Vπ is used to weight the total performance of the modulator. Taking a thick buffer layer and etching deep grooves in the buffer layer are demonstrated as two effective methods to improve the performance of the modulator. A 3-dB optical bandwidth of 18 GHz with half-wave voltage 5V at a wavelength of 1.55 pm could be obtained even though the electrode is not very thick. When the requirement of half-wave voltage is not very critical, a bandwidth of more than 100 GHz can be obtained. 相似文献
88.
This Review discusses the synthesis and characterization by our Group of new antibiotics belonging to the class of penicillins, cephalosporins and rifamycins with ferrocenyl and 1, 1′-ferrocenilene residues in the molecule. As reactants for 6-aminopenicillanic acid (6-APA) and 7-aminocephalosporanic acid (7-ACA) the following were used: 1, 1-bis(chlorocarbonyl)ferrocene, ferrocenyl sulfochloride, 1, 1′-ferrocenylenedisulfochloride and thioglycolic acids S-modified with ferrocene. In the synthesis of rifamycins, the hydrazides of the thioglycolic acids, S-modified with ferrocene, were employed as nucleophilic agents. The synthesized intermediates were characterized by elemental analysis, TLC, IR, UV and 1H NMR spectra. The characterization of new antibiotics was made by TLC, IR and UV spectral analysis. Biological activity was tested on Gram-negative and Gram-positive bacteria. Good activity is reported towards Gram-positive bacteria in the case of derivatives containing residues of thioglycolic acid S-modified with ferrocene, the antibacterial activity being similar to that of amoxicillin, carbenicillin and cephalothin. All compounds are inactive towards Gram-negative bacteria. 相似文献
89.
以Nd:MgO:LiNbO_3同时兼作激活介质和非线性光学材料,研究自倍频激光器。用小型氙灯泵浦,在室温下获得二次谐波激光(0.547μm) 阈值小于4.8'J,最大输出400μJ/shot,工作温度范围大于20℃~45℃,无光损伤。 相似文献
90.
微微秒自动调谐参量激光的研究 总被引:3,自引:3,他引:0
采用一对MgO:LiNbO_3角度调谐覆盖了红近外波段0.7~2.2μm,并配以自动波长扫描。文中分析了影响脉冲宽度与线宽的因素,与实验结果相吻合。脉宽<30ps,线宽~1nm(简并波长附近~10nm),单脉冲峰功率达MW级,参量光总能量转换效率达5.4%。 相似文献