全文获取类型
收费全文 | 1396篇 |
免费 | 27篇 |
国内免费 | 10篇 |
专业分类
化学 | 797篇 |
晶体学 | 11篇 |
力学 | 42篇 |
数学 | 229篇 |
物理学 | 354篇 |
出版年
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 19篇 |
2013年 | 71篇 |
2012年 | 54篇 |
2011年 | 50篇 |
2010年 | 27篇 |
2009年 | 31篇 |
2008年 | 53篇 |
2007年 | 63篇 |
2006年 | 62篇 |
2005年 | 40篇 |
2004年 | 36篇 |
2003年 | 33篇 |
2002年 | 45篇 |
2001年 | 35篇 |
2000年 | 24篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 23篇 |
1996年 | 22篇 |
1995年 | 20篇 |
1994年 | 21篇 |
1993年 | 27篇 |
1992年 | 20篇 |
1991年 | 16篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 20篇 |
1987年 | 29篇 |
1986年 | 30篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 16篇 |
1982年 | 32篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 23篇 |
1975年 | 21篇 |
1974年 | 27篇 |
1973年 | 19篇 |
1972年 | 12篇 |
1969年 | 8篇 |
排序方式: 共有1433条查询结果,搜索用时 250 毫秒
1.
2.
Guest‐Induced Transformation of a Porphyrin‐Edged FeII4L6 Capsule into a CuIFeII2L4 Fullerene Receptor 下载免费PDF全文
Daniel M. Wood Dr. Wenjing Meng Dr. Tanya K. Ronson Dr. Artur R. Stefankiewicz Prof. Jeremy K. M. Sanders Prof. Jonathan R. Nitschke 《Angewandte Chemie (International ed. in English)》2015,54(13):3988-3992
The combination of a bent diamino(nickel(II) porphyrin) with 2‐formylpyridine and FeII yielded an FeII4L6 cage. Upon treatment with the fullerenes C60 or C70, this cage was found to transform into a new host–guest complex incorporating three FeII centers and four porphyrin ligands, in an arrangement that is hypothesized to maximize π interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity. The new complex shows coordinative unsaturation at one of the FeII centers as the result of the incommensurate metal‐to‐ligand ratio, which enabled the preparation of a heterometallic cone‐shaped CuIFeII2L4 adduct of C60 or C70. 相似文献
3.
M. K. Khosa P. T. Wood S. M. Humphrey W. T. A. Harrison 《Journal of Structural Chemistry》2015,56(6):1130-1135
The syntheses and crystal structures of the layered coordination polymers M(C8H8NO2)2 [M = Mn (1), Co (2), Ni (3) and Zn (4)] are described. These isostructural compounds contain centrosymmetric trans-MN2O4 octahedra as parts of infinite sheets; the ligand bonds to three adjacent metal ions in μ3-N,O,O′ mode from both its carboxylate O atoms and its amine N atom. In each case, weak intra-sheet N–H?O and C–H?O hydrogen bonds may help to consolidate the structure. Crystal data: 1, C16H16MnN2O4, M r = 355.25, monoclinic, P21/c (No. 14), a = 10.6534(2) Å, b = 4.3990(1) Å, c = 15.5733(5) Å, β = 95.1827(10)°, V = 726.85(3) Å3, Z = 2, R(F) = 0.026, wR(F 2) = 0.067. 2, C16H16CoN2O4, M r = 359.24, monoclinic, P21/c (No. 14), a = 10.6131(10) Å, b = 4.3374(4) Å, c = 15.3556(17) Å, β = 95.473(4)°, V = 703.65(12) Å3, Z = 2, R(F) = 0.041, wR(F 2) = 0.091. 3, C16H16N2NiO4, M r = 359.02, monoclinic, P21/c (No. 14), a = 10.6374(4) Å, b = 4.2964(2) Å, c = 15.2827(8) Å, β = 95.9744(14)°, V = 694.66(6) Å3, Z = 2, R(F) = 0.028, wR(F 2) = 0.070. 4, C16H16N2O4Zn, M r = 365.68, monoclinic, P21/c (No. 14), a = 10.6385(5) Å, b = 4.2967(3) Å, c = 15.2844(8) Å, β = 95.941(3)°, V = 694.89(7) Å3, Z = 2, R(F) = 0.038, wR(F 2) = 0.107. 相似文献
4.
L-Histidine benzyl ester di-p-toluenesulphonate is, contrary to a previous report, easily prepared by a very simple direct esterification procedure. 相似文献
5.
A. Dominic Fortes Ian G. Wood Matthias J. Gutmann 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(4):324-329
Hexaaquamagnesium(II) sulfate pentahydrate, [Mg(H2O)6]SO4·5H2O, and hexaaquamagnesium(II) chromate(II) pentahydrate, [Mg(H2O)6][CrO4]·5H2O, are isomorphous, being composed of hexaaquamagnesium(II) octahedra, [Mg(H2O)6]2+, and sulfate (chromate) tetrahedral oxyanions, SO42− (CrO42−), linked by hydrogen bonds. There are two symmetry‐inequivalent centrosymmetric octahedra: M1 at (0, 0, 0) donates hydrogen bonds directly to the tetrahedral oxyanion, T1, at (0.405, 0.320, 0.201), whereas the M2 octahedron at (0, 0, ) is linked to the oxyanion via five interstitial water molecules. Substitution of CrVI for SVI leads to a substantial expansion of T1, since the Cr—O bond is approximately 12% longer than the S—O bond. This expansion is propagated through the hydrogen‐bonded framework to produce a 3.3% increase in unit‐cell volume; the greatest part of this chemically induced strain is manifested along the b* direction. The hydrogen bonds in the chromate compound mitigate ∼20% of the expected strain due to the larger oxyanion, becoming shorter (i.e. stronger) and more linear than in the sulfate analogue. The bifurcated hydrogen bond donated by one of the interstitial water molecules is significantly more symmetrical in the chromate analogue. 相似文献
6.
The 2,5-diketopiperazine (DKP) moiety is a core feature of many natural products and medicinally relevant scaffolds. As part of our efforts directed towards a total synthesis of penicisulfuranol B, we have developed and report herein: (1) the preparation of an N-hydroxy diketopiperazine intermediate accessible via a molybdenum-mediated oxidation of a parent diketopiperazine, and (2) further synthetic studies leading to a novel spirocyclic dihydrobenzofuran-containing diketopiperazine. 相似文献
7.
8.
Stephen K. Taylor Dawn DeYoung Lloyd J. Simons James R. Vyvyan ‡ Mary A. Wemple Noelle K. Wood 《合成通讯》2013,43(9):1691-1701
The nucleophilic opening of epoxides by nitrile enolates using an efficient, convenient protocol is described. The diastereoselectivity of this reaction was explored and found to give syn:anti ratios ranging from 1.1:1.0 to 4.8:1.0. 相似文献
9.
David J. Wood Lars Carlsson Martin Eklund Ulf Norinder Jonna Stålring 《Journal of computer-aided molecular design》2013,27(3):203-219
We propose that quantitative structure–activity relationship (QSAR) predictions should be explicitly represented as predictive (probability) distributions. If both predictions and experimental measurements are treated as probability distributions, the quality of a set of predictive distributions output by a model can be assessed with Kullback–Leibler (KL) divergence: a widely used information theoretic measure of the distance between two probability distributions. We have assessed a range of different machine learning algorithms and error estimation methods for producing predictive distributions with an analysis against three of AstraZeneca’s global DMPK datasets. Using the KL-divergence framework, we have identified a few combinations of algorithms that produce accurate and valid compound-specific predictive distributions. These methods use reliability indices to assign predictive distributions to the predictions output by QSAR models so that reliable predictions have tight distributions and vice versa. Finally we show how valid predictive distributions can be used to estimate the probability that a test compound has properties that hit single- or multi- objective target profiles. 相似文献
10.
J. L. Pore D. S. Cross C. Andreoiu R. Ashley G. C. Ball P. C. Bender A. S. Chester A. Diaz Varela G. A. Demand R. Dunlop A. B. Garnsworthy P. E. Garrett G. Hackman B. Hadinia B. Jigmeddorj A. T. Laffoley A. Liblong R. Kanungo B. Noakes C. M. Petrache M. M. Rajabali K. Starosta C. E. Svensson P. J. Voss Z. M. Wang J. L. Wood S. W. Yates 《The European Physical Journal A - Hadrons and Nuclei》2017,53(2):27