全文获取类型
收费全文 | 7958篇 |
免费 | 616篇 |
国内免费 | 573篇 |
专业分类
化学 | 4870篇 |
晶体学 | 90篇 |
力学 | 425篇 |
综合类 | 55篇 |
数学 | 774篇 |
物理学 | 2933篇 |
出版年
2025年 | 13篇 |
2024年 | 104篇 |
2023年 | 183篇 |
2022年 | 282篇 |
2021年 | 306篇 |
2020年 | 332篇 |
2019年 | 331篇 |
2018年 | 222篇 |
2017年 | 213篇 |
2016年 | 324篇 |
2015年 | 343篇 |
2014年 | 381篇 |
2013年 | 447篇 |
2012年 | 598篇 |
2011年 | 639篇 |
2010年 | 395篇 |
2009年 | 342篇 |
2008年 | 403篇 |
2007年 | 376篇 |
2006年 | 376篇 |
2005年 | 303篇 |
2004年 | 244篇 |
2003年 | 211篇 |
2002年 | 157篇 |
2001年 | 158篇 |
2000年 | 158篇 |
1999年 | 183篇 |
1998年 | 145篇 |
1997年 | 135篇 |
1996年 | 125篇 |
1995年 | 119篇 |
1994年 | 114篇 |
1993年 | 79篇 |
1992年 | 78篇 |
1991年 | 86篇 |
1990年 | 59篇 |
1989年 | 37篇 |
1988年 | 36篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 19篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有9147条查询结果,搜索用时 0 毫秒
1.
2.
本文主要论证了在不完全市场条件下带风险指数的金融均衡的存在性,并揭示其均衡结构的特征.本文中建立的模型是一、二期货币投入产出金融经济且具有可微的资产结构,这一模型包括了许多具有特殊资产结构的均衡模型,如实资产结构、虚资产结构、恒秩资产结构的均衡模型.因此本文的这一模型具有广泛的应用前景和实用价值.接着给出了本文的金融均衡的存在性定理,再借助微分拓扑给出它的证明过程,这一证明过程较之以前证明均衡存在性的经典方法(如Duffie,D&W.Shfer(1985)的方法)要简便得多.同时也应注意到本文的这一结论既适用于资产市场下会随机风险因素的情形,也适用于商品空间为无限维的情形,除此之外,还给出了怎样判别资产结构是否属于T类的判别法,为检验均衡存在性提供了更为便利的途径.最后,本文论证了在金融市场里,尽管由于稀缺性的存在,从而导致均衡分配的多样化,然而均衡分配集却形成了一光滑子流,但该流形的维数与稀缺性有关.换句话说,尽管市场是不完全的,但均市分配不确定性的反却是可比的.如此使得人们对均衡资产结构的认识更进一步. 相似文献
3.
Long-Mei Zeng Xiong Fu Jing-Yu Su Florecita De Guzman J. Francis Schmitz M. Bilayet Hossain Dick van Der Helm 《中国化学》1991,9(2):136-143
Three pyrrololactam alkaloids have been isolated from the marine sponge Phacellia fusca Schmidt collected from the South China Sea, and their structures were determined as 1–3 , on the grounds of spectral data. This is the first report of these compounds from this sponge. The structure of 1 was confirmed by X-ray analysis. 相似文献
4.
A cobalt(II) tetrakisphenylporphyrin (Co(II)TPP) film modified glassy carbon electrode (Co(II)TPP-GCE) was prepared by just coating Co(II)TPP solution on the surface of the electrode. It can be used for the simultaneous determination of ascorbic acid and uric acid. The anodic peaks of AA and UA can be separated well. Owing to the strongly hydrophobic property of porphyrin, the modified electrode has good stability and long life. The linear range for UA and AA were 2.0 x 10(-6)-1.0 x 10(-4) M and 9.0 x 10(-6)-2.0 x 10(-3) M with detection limits of 5.0 x 10(-7) and 5.0 x 10(-6) M, respectively. Furthermore, metalloporphyrins of other kinds were also used to construct modified electrodes. Their performances were inferior compared with that of the Co(II)TPP modified electrode. 相似文献
5.
6.
7.
South MS Case BL Dice TA Franklin GW Hayes MJ Jones DE Lindmark RJ Zeng Q Parlow JJ 《Combinatorial chemistry & high throughput screening》2000,3(2):139-151
A parallel solution-phase library synthesis of functionalized diaminobenzamides is described. The four-step library synthesis is accomplished using polymer-assisted solution-phase (PASP) synthesis techniques. This high-yielding, multi-step sequence utilizes sequestering resins for the removal of reactants, reactant by-products, and employs a resin capture/release strategy as a key library synthesis step. Step one of the sequence relies on the displacement of an activated fluoro-group from the aromatic ring of 1a, b with a variety of primary amines to introduce the first diversity position. Step two is hydrolysis of the benzoate ester to a benzoic acid which is subsequently captured on a polyamine resin, washed, and released to give 4a, b in pure form. Step three utilizes PASP resins to mediate the amide coupling of a benzoic acid with a variety of primary amines to give the aminonitrobenzamides 5a, b and introduces the second diversity position. Step four is the parallel reduction of the aminonitrobenzamides 5a, b to the functionalized diaminobenzamides 6a, b. This library synthesis proceeds with high overall purities which average 80 % over the 4-step sequence. 相似文献
8.
Xiu-Lin Zeng Wang-Hua Chen Jia-Cong Liu Jin-Lin Kan 《Journal of Molecular Structure》2007,810(1-3):47-51
Three density-functional methods (B3P86, B3PW91, and B3LYP) are employed to investigate the O–NO2 bond lengths, frontier orbital energies, and O–NO2 bond dissociation energies (BDEs) of n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN), triethylene glycol dinitrate (Tri-EGDN), and tetraethylene glycol dinitrate (Tetra-EGDN). It is found that the O–NO2 bond lengthens (destabilizes) in the order of IPN, NPN, EHN, Tetra-EGDN, and Tri-EGDN. From the data of frontier orbital energies (EHOMO, ELUMO), and energy gaps (ΔE), we estimate the relative thermal stability ordering of five nitrates and their corresponding radicals. The predicted BDEs of O–NO2 bond in NPN, IPN, EHN, Tri-EGDN, and Tetra-EGDN, are 176.6, 174.5, 168.1, 156.1, and 159.3 kJ mol−1, respectively. Based on the finding that the present results of BDEs are well coincident with the experimental results of apparent activation energies from the literature, we can draw a conclusion that the experimental thermolysis of five nitrates is only unimolecular homolytical cleavage of the O–NO2 bonds. 相似文献
9.
A simple method was used to prepare a "switchable" electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solutions of 1,10-phenanthroline or 2,2'-bipyridine. The electroactive form of the electrode could be reverted back to the nonelectroactive form by rinsing the electrode. Surface IR results showed that both dodecanethiol and 1,10-phenanthroline exist in the mixed monolayer. 相似文献
10.
A two-tiered organizing scheme with multiple-length scales for construction of dandelion-like hollow CuO microspheres has been elucidated: (1) mesoscale formation of rhombic building units from smaller nanoribbons via oriented aggregation and (2) macroscopic organization of these units into the CuO microspheres. This self-assembly concept may also be applicable to other metal oxides by creating geometric constraints for constructional units. 相似文献