全文获取类型
收费全文 | 20740篇 |
免费 | 229篇 |
国内免费 | 448篇 |
专业分类
化学 | 3134篇 |
晶体学 | 253篇 |
力学 | 308篇 |
综合类 | 62篇 |
数学 | 14465篇 |
物理学 | 3195篇 |
出版年
2024年 | 41篇 |
2023年 | 73篇 |
2022年 | 159篇 |
2021年 | 147篇 |
2020年 | 164篇 |
2019年 | 427篇 |
2018年 | 425篇 |
2017年 | 276篇 |
2016年 | 255篇 |
2015年 | 245篇 |
2014年 | 445篇 |
2013年 | 1146篇 |
2012年 | 582篇 |
2011年 | 1181篇 |
2010年 | 1006篇 |
2009年 | 1207篇 |
2008年 | 1348篇 |
2007年 | 1365篇 |
2006年 | 976篇 |
2005年 | 745篇 |
2004年 | 643篇 |
2003年 | 519篇 |
2002年 | 1169篇 |
2001年 | 1378篇 |
2000年 | 347篇 |
1999年 | 447篇 |
1998年 | 392篇 |
1997年 | 310篇 |
1996年 | 386篇 |
1995年 | 366篇 |
1994年 | 351篇 |
1993年 | 287篇 |
1992年 | 275篇 |
1991年 | 195篇 |
1990年 | 162篇 |
1989年 | 171篇 |
1988年 | 115篇 |
1987年 | 122篇 |
1986年 | 108篇 |
1985年 | 199篇 |
1984年 | 176篇 |
1983年 | 109篇 |
1982年 | 168篇 |
1981年 | 182篇 |
1980年 | 115篇 |
1979年 | 74篇 |
1978年 | 114篇 |
1977年 | 97篇 |
1976年 | 76篇 |
1974年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 37 毫秒
91.
We show that every collection ofw sets such that none contains any other generates at least 3w-2 sets under the operations of taking intersections and unions. In particular, we prove that if the finite distributive lattice ? contains an antichain of sizew, then |?| ≧3w, forw≠1, 2, 3, 6, where the minimal exceptional cases arise from the Boolean algebras ?n withn=0, 1, 2, 3, 4 atoms. 相似文献
92.
We exhibit linear problems for which every linear algorithm has infinite error, and show a (mildly) nonlinear algorithm with finite error. The error of this nonlinear algorithm can be arbitrarily small if appropriate information is used. We illustrate these examples by the inversion of a finite Laplace transform, a problem arising in remote sensing. 相似文献
93.
Françoise Brossier 《Acta Appl Math》1986,5(1):37-85
Our purpose is to calculate waves propagating along the equator in an oceanic domain and the influence of a characteristic mean equatorial circulation on the nature of these waves. Equations satisfied by perturbations of currents and temperature are of the Navier-Stokes type and have been linearized around a stationary solution. Existence and uniqueness of the solution have been proved. Numerical experiments have been carried out and provided us with time-dependent values. The excited waves are exhibited by Fourier analysis of these time series. 相似文献
94.
Peter Smith 《Acta Appl Math》1986,6(3):293-308
The usual notion of a saddle functional in the calculus of variations assumes a vex/concave structure over the product space
of two inner product spaces. Here the ideas extended to include some convexity in both spaces whilst still retaining an overall
saddle property. Dual extremum principles are established for these functionals. Examples include periodic solutions of Duffing's
equation, an iterative scheme and a pair of simultaneous partial differential equations which arise in magnetohydrodynamics. 相似文献
95.
Summary
B-convergence properties of defect correction methods based on the implicit Euler and midpoint schemes are discussed. The property ofB-convergence means that there exist global error bounds for nonlinear stiff problems independent of their stiffness. It turns out that the orders ofB-convergence of these methods coincide with the conventional orders of small (whereL is a Lipschitz constant of the right-hand side). In Part I these assertions are reduced to the validity of the so-called HypothesisA which is discussed in greater detail in Part II. Numerical experiments confirming the theoretical analysis are also given in Part II. 相似文献
96.
An investigation of the electrical properties of reduced ceria, CeO2?x, carried out on single crystals, shows that CeO2?x provides one of the clearest examples of hopping conduction and the small polaron mechanism. Included are conductivity and Seebeck coefficient measurements at constant x, obtained by sealing off the specimen chamber after reduction. The Seebeck coefficient is independent of temperature, suggesting that the number of carriers is constant. On the other hand, the mobility is activated, with activation energy Eh = 0.40 eV at small x and increasing to 0.52 eV at x = 0.25. The results for the mobility preexponential are consistent with the adiabatic theory of small polaron behavior. A puzzling feature of the Seebeck data as a function of x is that, for low x, the data fit the well-known Heikes formula, without a degeneracy factor of 2 for spin. Nevertheless, these data are interpreted to show that the proportion of mobile carriers decreases as x increases, presumably because of the presence of short-range ordered configurations which immobilize some carriers. 相似文献
97.
研制纳米级厚度的Ru薄膜电极,并运用电化学原位FTIR反射光谱研究碱性介质中CO的吸附。检测到CO以线型吸附态为主,但也存在少量桥式吸附态,分别在1960和1780cm^-1附近红出红外吸收谱峰。发现纳米Ru膜电极具有异常红外效应,即CO谱峰方向倒反,强度增强和半峰宽增加,测得在碱性溶液中吸附态CO的红外吸收被增强了33倍,其增强因子是酸性溶液中的两倍左右。 相似文献
98.
1 INTRODUCTIONIron- sulfurproteins are found in mostofthe life forms,yetitisnotuntilaround1 96 0 that there are iron- sulfur proteins in photosynthetic organism〔1〕,nitrogen- fix-ing bacteria〔2〕,and submitochondrial fractions of mammalian origin〔3〕,etc〔4 ,5〕,it isoxidoreductive systems.There are various kinds of iron- sulfur clusters active posi-tions in these proteins,they play an important role in transmitting electrons.Bymany kinds and complex properties of biology,different iro… 相似文献
99.
污染物甲胺为电子给体可见光下Pt/ZnIn2S4光催化制氢 总被引:1,自引:1,他引:0
用水热法制备了ZnIn2S4固溶体,并通过XRD和UV-vis漫反射光谱进行了表征.研究了一甲胺、二甲胺和三甲胺为给电子体,在Pt/ZnIn2S4上的可见光光催化制氢及自身的降解反应.3种甲胺都能显著提高光催化分解水制氢活性,同时自身得到很好的降解.电子给体的放氢活性顺序为:TMADMAMMA.通过红外衰减全反射(ATR-IR)法检测电子给体在ZnIn2S4表面的吸附行为,吸附强度大小依次为MMADMATMA.光催化活性与分子结构和在催化剂表面的吸附行为有关.3种污染物浓度对放氢活性的影响都符合Langmuir-Hinshelwood动力学模型.讨论了可能的化学反应机理. 相似文献
100.
May Lee Low Cheang Wei Chan Pei Ying Ng Ing Hong Ooi Mohd Jamil Maah Soi Moi Chye 《Journal of Coordination Chemistry》2017,70(2):223-241
Three ternary copper(II) complexes, [Cu(phen)(L-phe)Cl]·2H2O, [Cu(phen)(L-leu)Cl]·4½H2O, and [Cu(phen)(L-tyr)Cl]·3H2O, and four binary copper(II) complexes, [Cu(phen)Cl2], Cu(L-phe)2·½H2O, Cu(L-leu)2·½H2O, and Cu(L-tyr)2·H2O (where phen = 110-phenanthroline, L-phe = L-phenylalanine, L-tyr = L-tyrosine, L-leu = L-leucine and Cl- = chloride), were synthesized and characterized by elemental analysis, spectroscopic techniques (FTIR, UV–visible, fluorescence spectroscopy), magnetic susceptibility, molar conductivity, and lipophilicity measurement. X-ray diffraction determination of a single crystal of [Cu(phen)(L-tyr)Cl] showed two independent molecules in the asymmetric unit, each with the same distorted square pyramidal geometry about copper(II). p-Nitrosodimethylaniline assay revealed that the three ternary complexes were better inducers of reactive oxygen species over time than binary complexes, CuCl2, and free ligands. All the copper(II) complexes in this series inhibited the three proteolytic activities in the order Trypsin-like > Caspase-like > Chymotrypsin-like. In terms of anticancer properties, the copper(II)-phen complexes had GI50 values of less than 4 μM against MCF-7, HepG2, CNE1 and A549 cancer cell lines, more potent than cisplatin. 相似文献