全文获取类型
收费全文 | 1025篇 |
免费 | 35篇 |
国内免费 | 7篇 |
专业分类
化学 | 613篇 |
晶体学 | 28篇 |
力学 | 22篇 |
数学 | 165篇 |
物理学 | 239篇 |
出版年
2023年 | 6篇 |
2021年 | 14篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 18篇 |
2015年 | 24篇 |
2014年 | 23篇 |
2013年 | 44篇 |
2012年 | 59篇 |
2011年 | 60篇 |
2010年 | 40篇 |
2009年 | 28篇 |
2008年 | 52篇 |
2007年 | 54篇 |
2006年 | 47篇 |
2005年 | 53篇 |
2004年 | 47篇 |
2003年 | 26篇 |
2002年 | 30篇 |
2001年 | 29篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1970年 | 8篇 |
1968年 | 6篇 |
排序方式: 共有1067条查询结果,搜索用时 553 毫秒
1.
Thomas Wittmann Dr. Renée Siegel Nele Reimer Dr. Wolfgang Milius Prof. Dr. Norbert Stock Prof. Dr. Jürgen Senker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):314-323
The resistance of metal–organic frameworks towards water is a very critical issue concerning their practical use. Recently, it was shown for microporous MOFs that the water stability could be increased by introducing hydrophobic pendant groups. Here, we demonstrate a remarkable stabilisation of the mesoporous MOF Al‐MIL‐101‐NH2 by postsynthetic modification with phenyl isocyanate. In this process 86 % of the amino groups were converted into phenylurea units. As a consequence, the long‐term stability of Al‐MIL‐101‐URPh in liquid water could be extended beyond a week. In water saturated atmospheres Al‐MIL‐101‐URPh decomposed at least 12‐times slower than the unfunctionalised analogue. To study the underlying processes both materials were characterised by Ar, N2 and H2O sorption measurements, powder X‐ray diffraction, thermogravimetric and chemical analysis as well as solid‐state NMR and IR spectroscopy. Postsynthetic modification decreased the BET equivalent surface area from 3363 to 1555 m2 g?1 for Al‐MIL‐101‐URPh and reduced the mean diameters of the mesopores by 0.6 nm without degrading the structure significantly and reducing thermal stability. In spite of similar water uptake capacities, the relative humidity‐dependent uptake of Al‐MIL‐101‐URPh is slowed and occurs at higher relative humidity values. In combination with 1H‐27Al D ‐HMQC NMR spectroscopy experiments this favours a shielding mechanism of the Al clusters by the pendant phenyl groups and rules out pore blocking. 相似文献
2.
3.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields. 相似文献
4.
5.
LauraN. Gregerson TrevorC. McMorris JayS. Siegel KimK. Baldridge 《Helvetica chimica acta》2003,86(12):4133-4151
(Hydroxymethyl)acylfulvene (HMAF, irofulven; 4 ), a third‐generation derivative of a natural product extracted from the mushroom Omphalotus illudens, is selectively toxic towards certain forms of malignant tumors. Conversion of HMAF and cognates to stable aromatic derivatives is triggered by thiol attack in vitro and in vivo. Quantum‐chemical methods predict well the structure for several functionalized derivatives of irofulven as compared to known X‐ray crystallographic structures. Computational reaction profiles for thiol attack and aromatic rearrangement of irofulven and illudin S, a toxin from which irofulven is derived, provide insight into HMAF's selectivity and toxicity. Methods used include hybrid density‐functional theory (HDFT), Hartree? Fock (HF), and Møller? Plesset second‐order perturbation theory (MP2). Solvent effects have been explored by means of the new continuum‐solvation method, COSab, presented in an accompanying paper. 相似文献
6.
7.
Zusammenfassung Bei der katalytischen Hydrierung von freien Chinolen werden unter Wasserstoffaufnahme hydroaromatische Verbindungen gebildet, während bei den Chinolen andere Reduktionsmethoden, sowie bei den Chinolacetaten auch die katalytische Hydrierung zur Ausbildung von aromatischen Körpern führen.Unserem verehrten Lehrer, Herrn Prof. Dr.F. Wessely, in Dankbarkeit zum 60. Geburtstag gewidmet. 相似文献
8.
The stereochemistry of the hydrogenation of 4-tert-butylmethylenecyclohexane (1) and the use of D2 or D2/H2 mixtures in place of H2 furnishes evidence that hydrogenations using the catalyst precursor [Rh(DIPHOS)(COD)]+BF
4
−
proceed via more than one mechanism. This evidence includes the effect of changes in pressure and added triethylamine upon
the kinetics and isomerization of 1, as well as the distribution of the added deuterium in the products of the reaction of 1 or norbornene with either D2 or H2/D2 mixtures. That an alkene necessarily causes the equilibration of H2/D2 mixtures, although it need not involve any of the alkenes’s hydrogen atoms (e.g., norbornene), provides a clue to the process
by which the mononuclear mechanism proposed by Halpern, which is dominant near one atmosphere of H2, merges into another with increasing pressure. It has been proposed that the cationic complex [Rh(DIPHOS)S2]+ is transformed in the presence of an alkene and hydrogen into a binuclear hydrido complex, such as those described by Sivak
and Muetterties (1979) and Fryzuk (1982), which represent a far more active catalyst than its mononuclear precursor. Such
an intermediate should readily catalyze the H2-D2 equilibration and the isomerization of an alkene in the presence of D2 without necessarily introducing deuterium into the product.
Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 88–97.
Deceased.
The text was submitted by the authors in English.
This work was conducted at the University of Arkansas. 相似文献
9.
Artem Malakho Marc Dussauze Bogdan Lazoryak Frederic Adamietz 《Journal of solid state chemistry》2005,178(6):1888-1897
Crystallization of glasses with compositions (1−x)(0.95 NaPO3+0.05 Na2B4O7)+xNb2O5, x=0.4, 0.43, 0.45, 0.48 was investigated by differential scanning calorimetry and X-ray powder diffraction. Crystallization of two phases was observed in the glasses with x=0.43-0.48. First phase is a sodium niobate with the structure of tetragonal tungsten bronze () and second phase is Na4Nb8P4O32 (). The crystallization of sodium niobate is correlated with increasing of nonlinear optical efficiency reported for thermally poled glasses with x>0.4. The results of Raman spectroscopy show the formation of three-dimensional (3D) niobium oxide framework in the glasses with increase of niobium concentration. This framework is supposed to have tetragonal tungsten bronze structure and to be responsible for nonlinear optical properties of the glass. Second harmonic generation signals of as prepared and crystallized glass after thermal poling are compared. The nucleation and crystallization do not improve the NLO properties of the glasses under study. 相似文献
10.
THE EFFECTS OF THROMBOXANE INHIBITORS ON THE MICROVASCULAR AND TUMOR RESPONSE TO PHOTODYNAMIC THERAPY 总被引:9,自引:0,他引:9
Victor H. Fingar Kimberly A. Siegel T. Jeffery Wieman Karola Weber Doak 《Photochemistry and photobiology》1993,58(3):393-399
Abstract— Vascular stasis and tissue ischemia are known to cause tumor cell death in several experimental models after photodynamic therapy (PDT); however, the mechanisms leading to this damage remain unclear. Because previous studies indicated that thromboxane release is implicated in vessel damage, we further examined the role of throm-boxane in PDT. Rats bearing chondrosarcoma were injected with 25 mg/kg Photofrin® (intravenously) 24 h before treatment. Light (135 J/cm 2 , 630 nm) was delivered to thc tumor area after injection of one of the following inhibitors: (1) R68070: a thromboxane synthetase inhibitor; (2) SQ-29548: a thromboxane receptor antagonist; and (3) Flunarizine: an inhibitor of platelet shape change. Systemic thromboxane levels were determined. Vessel constriction and leakage were evaluated by intravital microscopy. Tumor response was assessed after treatment. Thromboxane levels were decreased more than 50% with SQ-29548 as compared to controls. Thromboxane levels in animals given R68070 and Flunarizine remained at baseline levels. SQ-29548 and R68070 reduced vessel constriction compared to controls, while Flunarizine totally prevented vessel constriction. R68070 and SQ-29548 inhibited vessel permeability compared to PDT controls; Flunarizine did not. Animals given these inhibitors showed markedly reduced tumor cure. These results indicate that the release of thromboxane is linked to the vascular response in PDT. 相似文献