全文获取类型
收费全文 | 3308篇 |
免费 | 74篇 |
国内免费 | 19篇 |
专业分类
化学 | 1832篇 |
晶体学 | 8篇 |
力学 | 102篇 |
数学 | 550篇 |
物理学 | 650篇 |
无线电 | 259篇 |
出版年
2023年 | 18篇 |
2022年 | 45篇 |
2021年 | 65篇 |
2020年 | 53篇 |
2019年 | 35篇 |
2018年 | 44篇 |
2017年 | 34篇 |
2016年 | 98篇 |
2015年 | 52篇 |
2014年 | 71篇 |
2013年 | 179篇 |
2012年 | 150篇 |
2011年 | 228篇 |
2010年 | 122篇 |
2009年 | 100篇 |
2008年 | 209篇 |
2007年 | 199篇 |
2006年 | 166篇 |
2005年 | 142篇 |
2004年 | 107篇 |
2003年 | 90篇 |
2002年 | 85篇 |
2001年 | 55篇 |
2000年 | 51篇 |
1999年 | 48篇 |
1998年 | 48篇 |
1997年 | 57篇 |
1996年 | 50篇 |
1995年 | 46篇 |
1994年 | 61篇 |
1993年 | 55篇 |
1992年 | 48篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 42篇 |
1984年 | 28篇 |
1983年 | 29篇 |
1982年 | 36篇 |
1981年 | 40篇 |
1980年 | 26篇 |
1979年 | 28篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 20篇 |
1975年 | 20篇 |
1974年 | 17篇 |
1973年 | 20篇 |
排序方式: 共有3401条查询结果,搜索用时 15 毫秒
151.
152.
Enrico Luchinat Letizia Barbieri Matteo Cremonini Alessio Nocentini Claudiu T. Supuran Lucia Banci 《Angewandte Chemie (International ed. in English)》2020,59(16):6535-6539
Structure‐based drug development is often hampered by the lack of in vivo activity of promising compounds screened in vitro, due to low membrane permeability or poor intracellular binding selectivity. Herein, we show that ligand screening can be performed in living human cells by “intracellular protein‐observed” NMR spectroscopy, without requiring enzymatic activity measurements or other cellular assays. Quantitative binding information is obtained by fast, inexpensive 1H NMR experiments, providing intracellular dose‐ and time‐dependent ligand binding curves, from which kinetic and thermodynamic parameters linked to cell permeability and binding affinity and selectivity are obtained. The approach was applied to carbonic anhydrase and, in principle, can be extended to any NMR‐observable intracellular target. The results obtained are directly related to the potency of candidate drugs, that is, the required dose. The application of this approach at an early stage of the drug design pipeline could greatly increase the low success rate of modern drug development. 相似文献
153.
154.
Nativitat Valls Josep Bonjoch Carlos Del Alamo Joan Bosch 《Helvetica chimica acta》1992,75(1):137-144
A stereodivergent synthesis of enantiomerically pure E-nor-15-azayohimbines via condensation of tryptamine with derivatives of pyroglutamate 4 is reported. When the Pictet-Spengler reaction was induced in refluxing aqueous AcOH a nearly equimolar ratio of lactams 7 and 8 was obtained, whereas under kinetic control (TFA, room temperature) the trans-derivative 8 was the major product. In contrast, cyclization of amido acetal 12 with TsOH gave the cis-derivative 7 as preponderant component. 相似文献
155.
Enrico Albizzati Umberto Giannini Gianpiero Morini Maurizio Galimberti Luisa Barino Raimondo Scordamaglia 《Macromolecular Symposia》1995,89(1):73-89
The role of Lewis bases in MgCl2 supported catalysts for olefin polymerization is a subject of continuous interest and discussion in order to obtain more and more active and stereospecific catalysts and to explain their stereoregulating mechanism. Through molecular calculation and conformational analysis it was possible to identify chelating diethers that have the correct oxygen-oxygen distance necessary to tightly coordinate with the Mg ions of the support, even in the presence of other strong Lewis acids, and unable to give secondary reactions with TiCl4, AlR3, Ti-C and Ti-H bonds. The use of these donors has allowed the synthesis of catalytic systems that are both highly active and stereospecific even in the absence of external donors. Kinetic data of propylene polymerization with these catalyst systems are reported. The importance of the distance between the donor atoms in bifunctional Lewis bases has been proved also in the case of new classes of internal donors. Molecular modelling studies have enabled us to formulate models of active sites, located on some corners of MgCl2 crystallites, whose chirality is induced by the presence of a donor molecule in their environment. These models could explain, at least in part, the exceptional increase of isotactic polymer productivity observed for stereospecific catalyst systems, containing only the internal donor, with respect to catalysts lacking the Lewis base and could account for the influence of the donor on the molecular properties of the obtained polymers. 相似文献
156.
Aurelio Liguori Enrico Armentani Alcide Bertocco Andrea Formato Arcangelo Pellegrino Francesco Villecco 《Entropy (Basel, Switzerland)》2020,22(11)
This article lists some tips for reducing gear case noise. With this aim, a static analysis was carried out in order to describe how stresses resulting from meshing gears affect the acoustic emissions. Different parameters were taken into account, such as the friction, material, and lubrication, in order to validate ideas from the literature and to make several comparisons. Furthermore, a coupled Eulerian–Lagrangian (CEL) analysis was performed, which was an innovative way of evaluating the sound pressure level of the aforementioned gears. Different parameters were considered again, such as the friction, lubrication, material, and rotational speed, in order to make different research comparisons. The analytical results agreed with those in the literature, both for the static analysis and CEL analysis—for example, it was shown that changing the material from steel to ductile iron improved the gear noise, while increasing the rotational speed or the friction increased the acoustic emissions. Regarding the CEL analysis, air was considered a perfect gas, but its viscosity or another state equation could have also been taken into account. Therefore, the above allowed us to state that research into these scientific fields will bring about reliable results. 相似文献
157.
158.
159.
160.