全文获取类型
收费全文 | 843篇 |
免费 | 70篇 |
国内免费 | 1篇 |
专业分类
化学 | 573篇 |
晶体学 | 4篇 |
力学 | 21篇 |
数学 | 79篇 |
物理学 | 169篇 |
无线电 | 68篇 |
出版年
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 24篇 |
2020年 | 30篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 13篇 |
2016年 | 45篇 |
2015年 | 26篇 |
2014年 | 25篇 |
2013年 | 40篇 |
2012年 | 55篇 |
2011年 | 74篇 |
2010年 | 33篇 |
2009年 | 28篇 |
2008年 | 46篇 |
2007年 | 46篇 |
2006年 | 36篇 |
2005年 | 37篇 |
2004年 | 34篇 |
2003年 | 28篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 17篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1966年 | 3篇 |
1960年 | 4篇 |
1958年 | 4篇 |
排序方式: 共有914条查询结果,搜索用时 344 毫秒
761.
Zhen Jiang Ming Li Tan Mahdiar Taheri Qiao Yan Takuya Tsuzuki Michael G. Gardiner Broden Diggle Luke A. Connal 《Angewandte Chemie (International ed. in English)》2020,59(18):7049-7056
The most pressing challenges for light‐driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design strategy is used to address these issues. Key is the use of a benzylimine‐functionalized anthracene group, which red‐shifts the absorption into the visible region and also stabilizes the supramolecular network through π–π interactions. Acid–ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double‐crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self‐healing, and fast visible‐light‐driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects. 相似文献
762.
Pepstatin A and grassystatin A are natural, statine-containing peptides that act as inhibitors of aspartic protease enzymes. In this work, stereoselective fluorination is investigated as a strategy for enhancing the pharmacodynamic and pharmacokinetic properties of these lead compounds. Fluorination is found to modestly affect the protease inhibitory potency, leading to the identification of two highly active new inhibitors of the cancer-associated protease, cathepsin D. However, no dramatic changes are observed in terms of target selectivity, lipophilicity, membrane permeability or metabolic stability. 相似文献
763.
764.
765.
Song Zhang Amirhadi Alesadi Mariia Selivanova Zhiqiang Cao Zhiyuan Qian Shaochuan Luo Luke Galuska Catherine Teh Michael U. Ocheje Gage T. Mason P. Blake J. St. Onge Dongshan Zhou Simon Rondeau‐Gagn Wenjie Xia Xiaodan Gu 《Advanced functional materials》2020,30(27)
Semiconducting donor–acceptor (D–A) polymers have attracted considerable attention toward the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications. Here, polydiketopyrrolopyrrole (PDPP)‐based D–A polymers with varied alkyl side‐chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (Tg) with increasing side‐chain length, which is further verified through coarse‐grained molecular dynamics simulations. Informed from experimental results, a mass‐per‐flexible bond model is developed to capture such observation through a linear correlation between Tg and polymer chain flexibility. Using this model, a wide range of backbone Tg over 80 °C and elastic modulus over 400 MPa can be predicted for PDPP‐based polymers. This study highlights the important role of side‐chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict Tg and elastic modulus of future new D–A polymers. 相似文献
766.
Luke H.D. Schotten H.D. Hadinejad-Mahram H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(12):3271-3282
Time-discrete signals with good autocorrelation properties are used in various applications in communications engineering. From an implementation point of view, usually sequences with a small phase alphabet and a maximal energy efficiency, i.e., a uniform envelope, are most favorable. For this reason, known methods as well as several new construction techniques of binary and quadriphase sequences with optimal or best known autocorrelation properties are discussed in this correspondence. In many cases, the achievable correlation properties can be improved significantly if a single zero element per sequence is accepted. These "almost" binary and "almost" quadriphase sequences are considered as well. The optimality criteria used include the maximum absolute sidelobe and the merit factor of the periodic and the odd-periodic autocorrelation function, respectively. For sequence lengths of up to 44 in the binary case and up to 32 in the quadriphase case, the best known parameters obtained by computer search are compared with the constructed results. 相似文献
767.
A simple, high-yielding synthesis of acetals from the platinum(II)-catalyzed addition of alcohols to alkynes is described. The regioselectivity of the method and its mechanism are also discussed. 相似文献
768.
Luke B.L. Pace P.E. 《IEEE transactions on circuits and systems. I, Regular papers》2007,54(9):2030-2043
The robust symmetrical number system (RSNS) is a symmetrical number system formed such that only one element in each RSNS vector changes between code transitions. This integer Gray-code property makes the RSNS useful in analog-to-digital converters (ADC), direction finding antenna architectures and electro-optical ADCs since it eliminates any encoding errors that can occur when the input signal lies about any code transition point. One of the fundamental difficulties in a hardware application of the RSNS, such as an ADC, is the conversion of the RSNS residue vectors into a more convenient representation such as a binary number. By exploiting the one-to-one correspondence between the RSNS and the residue number system, an efficient process for conversion of the symmetrical residues is formed. The conversion process presented in this paper produces a hardware implementation that is at least an order of magnitude smaller in terms of transistor count than read-only-memory conversion methods, and is easily pipelined to achieve fast conversion speeds. 相似文献
769.
Heinz H. Bauschke Patrick L. Combettes D.R.D. Russell Luke 《Journal of Approximation Theory》2004,127(2):178-192
We consider the problem of finding a best approximation pair, i.e., two points which achieve the minimum distance between two closed convex sets in a Hilbert space. When the sets intersect, the method under consideration, termed AAR for averaged alternating reflections, is a special instance of an algorithm due to Lions and Mercier for finding a zero of the sum of two maximal monotone operators. We investigate systematically the asymptotic behavior of AAR in the general case when the sets do not necessarily intersect and show that the method produces best approximation pairs provided they exist. Finitely many sets are handled in a product space, in which case the AAR method is shown to coincide with a special case of Spingarn's method of partial inverses. 相似文献
770.
Laurel M. Heckman Jonathan B. Grimm Dr. Eric R. Schreiter Dr. Charles Kim Dr. Mark A. Verdecia Brenda C. Shields Dr. Luke D. Lavis 《Angewandte Chemie (International ed. in English)》2016,55(29):8363-8366
Photolabile protecting groups (or “photocages”) enable precise spatiotemporal control of chemical functionality and facilitate advanced biological experiments. Extant photocages exhibit a simple input–output relationship, however, where application of light elicits a photochemical reaction irrespective of the environment. Herein, we refine and extend the concept of photolabile groups, synthesizing the first Ca2+‐sensitive photocage. This system functions as a chemical coincidence detector, releasing small molecules only in the presence of both light and elevated [Ca2+]. Caging a fluorophore with this ion‐sensitive moiety yields an “ion integrator” that permanently marks cells undergoing high Ca2+ flux during an illumination‐defined time period. Our general design concept demonstrates a new class of light‐sensitive material for cellular imaging, sensing, and targeted molecular delivery. 相似文献