全文获取类型
收费全文 | 16629篇 |
免费 | 1670篇 |
国内免费 | 705篇 |
专业分类
化学 | 9977篇 |
晶体学 | 137篇 |
力学 | 724篇 |
综合类 | 52篇 |
数学 | 2829篇 |
物理学 | 5285篇 |
出版年
2023年 | 219篇 |
2022年 | 310篇 |
2021年 | 376篇 |
2020年 | 498篇 |
2019年 | 424篇 |
2018年 | 446篇 |
2017年 | 437篇 |
2016年 | 836篇 |
2015年 | 685篇 |
2014年 | 788篇 |
2013年 | 1319篇 |
2012年 | 1181篇 |
2011年 | 1251篇 |
2010年 | 855篇 |
2009年 | 768篇 |
2008年 | 834篇 |
2007年 | 648篇 |
2006年 | 635篇 |
2005年 | 452篇 |
2004年 | 385篇 |
2003年 | 339篇 |
2002年 | 342篇 |
2001年 | 288篇 |
2000年 | 257篇 |
1999年 | 279篇 |
1998年 | 265篇 |
1997年 | 233篇 |
1996年 | 233篇 |
1995年 | 198篇 |
1994年 | 175篇 |
1993年 | 154篇 |
1992年 | 153篇 |
1991年 | 144篇 |
1990年 | 105篇 |
1989年 | 104篇 |
1988年 | 107篇 |
1987年 | 106篇 |
1986年 | 98篇 |
1985年 | 113篇 |
1984年 | 101篇 |
1983年 | 97篇 |
1982年 | 80篇 |
1981年 | 91篇 |
1980年 | 93篇 |
1979年 | 83篇 |
1978年 | 86篇 |
1977年 | 96篇 |
1976年 | 77篇 |
1974年 | 77篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
甲基红染料掺杂的聚乙烯醇薄膜光存储特性的实验研究 总被引:1,自引:0,他引:1
用2倍频小型YAG激光(532nm)作为写入光和擦除光,用He-Ne激光器623.8nm线作为读出光,用CCD作为探测器,研究了不同写入光功率下,甲基红/聚乙烯醇(MR/PVA)薄膜光栅生长的动力学过程和不同擦除光功率下,光栅擦除的动力学过程.结合光栅生长曲线的波动现象,对光存储机制进行了新的探讨.实验发现,两写入光和读出光的功率配比为1:1:1时,可获得最大衍射效率,提出读出光对写入过程具有双重作用的物理模型,对此实验结果给出了合理的解释. 相似文献
82.
The validity of local parton-hadron duality within the framework of HERWIG and JETSET event generators is investigated. We concentrate one
+
e
– annihilations in LEP 2 energy range as these interactions provide theoretically the cleanest condition for the discussion of this concept. We conclude that the concept of local parton-hadron duality is not valid in either of the two generators considered. 相似文献
83.
84.
Operator Matrix Forms of Positive Operators 总被引:2,自引:0,他引:2
If a 3-tuple (A:H1→H1,B:H2→H1,C:H2→H2)of operators on Hibert spaces is given,we proved that the operator ~↑A:=(↑A ↓B^*↑B ↓C) on H=H1 H2 is ≥0 is and only if A≥0,R(B)∪→R(A^1/2) and C≥B^* A^ b,where A^ is the generalized inverse of A.In general,A^ is a closed operator,but since R(B)∪→R(A^1/2,B^* A^ B is bounded yet. 相似文献
85.
86.
Š. Jakševičius 《Lithuanian Mathematical Journal》1992,32(2):174-180
Kaunas Academy of Agriculture, 4324 Noreikiškés, Lithuania. Translated from Lietuvos Matematikos Rinkinys, Vol. 32, No. 2,
pp. 221–228, April–June, 1992. 相似文献
87.
For improved mechanical and water‐swelling properties of chitosan films, a series of transparent films were prepared with dialdehyde starch as a crosslinking agent. Fourier transform infrared and X‐ray analysis results demonstrated that the formation of Schiff's base disturbed the crystallization of chitosan. The mechanical properties and water‐swelling properties of the films were significantly improved. The best values of the tensile strength and breaking elongation were 113.1 MPa and 27.0%, respectively, when the dialdehyde starch content was 5%. All the crosslinked films still retained obvious antimicrobial effects toward S. aureus and E. coli, and they showed potential for biomedical applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 993–997, 2003 相似文献
88.
X. Y. Yang H. C. Gao X. L. Tan H. Z. Yuan G. Z. Cheng S. Z. Mao S. Zhao L. Zhang J. Y. An J. Y. Yu Y. R. Du 《Colloid and polymer science》2004,282(3):280-286
1H chemical shift changes of sodium 4-decyl naphthalene sulfonate (SDNS) at 313 K show that its critical micellar concentration lies between 0.82 and 0.92 mmol/dm3, which is in the same range as that of the previous study at 298 K. The spin–lattice relaxation time, spin–spin relaxation time and two-dimensional nuclear Overhauser enhancement spectroscopy experiments give information about the structure of the SDNS micelle and the dynamics of the molecules in the micelle. The size of the SDNS micelle remains almost unchanged in the temperature range from 298 to 313 K as deduced by analyzing the self-diffusion coefficient. Special arrangement of the naphthyl rings of SDNS in the micelles affects the packing of these hydrophobic chains. The methylene groups of the alkyl chain nearest the naphthalene groups penetrate into the aromatic region, which results in a more tightly packed hydrophobic micellar core than that of sodium dodecyl sulfonate. 相似文献
89.
In this paper we develop a numerical method for computing higher order local approximations of center manifolds near steady states in Hamiltonian systems. The underlying system is assumed to be large in the sense that a large sparse Jacobian at the equilibrium occurs, for which only a linear solver and a low-dimensional invariant subspace is available. Our method combines this restriction from linear algebra with the requirement that the center manifold is parametrized by a symplectic mapping and that the reduced equation preserves the Hamiltonian form. Our approach can be considered as a special adaptation of a general method from Numer. Math. 80 (1998) 1-38 to the Hamiltonian case such that approximations of the reduced Hamiltonian are obtained simultaneously. As an application we treat a finite difference system for an elliptic problem on an infinite strip. 相似文献
90.
František Toman Ludvík Beneš 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):231-236
Differential molar adsorption enthalpies (DMAE) were determined by gas chromatographic measurements of specific retention
volume of vapors on the surface of two forms of Mg–Al hydrotalcite. A linear dependence of the DMAE on the number of the carbon
atoms in hydrocarbons was observed for both form of hydrotalcite. The dependence of the differential molar adsorption enthalpies
on the number of chlorine atoms in organic molecules is discussed. A linear dependence of DMAE on the molecular weight of
chloroderivatives of methane and ethylene on the basic form in an order monochloromethane < dichloromethane < trichloromethane
or vinylidene chloride < 1,1-dichloroethylene < trichloroethylene was found. 相似文献