全文获取类型
收费全文 | 16880篇 |
免费 | 419篇 |
国内免费 | 117篇 |
专业分类
化学 | 11984篇 |
晶体学 | 98篇 |
力学 | 330篇 |
数学 | 2921篇 |
物理学 | 2083篇 |
出版年
2021年 | 140篇 |
2020年 | 167篇 |
2019年 | 169篇 |
2018年 | 136篇 |
2017年 | 130篇 |
2016年 | 278篇 |
2015年 | 303篇 |
2014年 | 309篇 |
2013年 | 716篇 |
2012年 | 726篇 |
2011年 | 947篇 |
2010年 | 473篇 |
2009年 | 419篇 |
2008年 | 867篇 |
2007年 | 887篇 |
2006年 | 910篇 |
2005年 | 974篇 |
2004年 | 866篇 |
2003年 | 720篇 |
2002年 | 631篇 |
2001年 | 208篇 |
2000年 | 203篇 |
1999年 | 173篇 |
1998年 | 168篇 |
1997年 | 216篇 |
1996年 | 271篇 |
1995年 | 180篇 |
1994年 | 176篇 |
1993年 | 165篇 |
1992年 | 166篇 |
1991年 | 154篇 |
1990年 | 150篇 |
1989年 | 134篇 |
1988年 | 145篇 |
1987年 | 155篇 |
1986年 | 121篇 |
1985年 | 268篇 |
1984年 | 239篇 |
1983年 | 184篇 |
1982年 | 254篇 |
1981年 | 208篇 |
1980年 | 264篇 |
1979年 | 231篇 |
1978年 | 234篇 |
1977年 | 244篇 |
1976年 | 206篇 |
1975年 | 167篇 |
1974年 | 160篇 |
1973年 | 154篇 |
1971年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
981.
We report the electrochemistry of amino-functionalized multiwalled carbon nanotubes (MWCNTs-NH2) in the pH range from 0.3 to 6.4 using quantitative cyclic voltammetry (CV) and single entity electrochemistry measurements, making comparison with non-functionalized MWCNTs. CV showed the latter to both catalyze the solvent (water) decomposition and to undergo irreversible electro-oxidation forming oxygen containing surface functionality. The MWCNTs-NH2 additionally undergo an irreversible oxidation to an extent which is dependent on the pH of the solution, reflecting the variable amount of deprotonated amino groups present as a function of pH. Nano-impact experiments conducted at the single particle level confirmed the oxidation of both types of MWCNTs, showing agreement with the CV. The pKa of the amino groups in MWCNTs was determined via both electrochemical methods giving consistent values of ca. 2.5.A new and generic approach to the study of the oxidation of different forms of CNTs is found by using quantitative single entity and ensemble electrochemistry measurements. 相似文献
982.
983.
Richard T. Taylor Steven Allison Thanaporn Kamolratanayothin 《Heteroatom Chemistry》1995,6(6):585-587
Treatment of poly(chlorotrifluoroethylene) with allyltin reagents results in the clean replacement of chlorine by the allyl group under free-radical–chain conditions (AIBN, allyltributyltin), affording about a 10% degree of functionalization. An improved method using one-electron reduction of the polymer with cobalt(II) (generated by reduction of chloro(pyridine)bis(dimethylglyoximato)cobalt(III) with Mg) and allyltributyltin gives 50% functionalization. Further modification of the allyl group is realized through hydroboration-oxidation to the alcohol and subsequent Cr(VI) oxidation to the acid. A mechanistic discussion is provided. © John Wiley & Sons, Inc. 相似文献
984.
Cationic group 4 metal alkyl complexes containing tetradentate Schiff base ligands, (acen) Zr(R)+ and (F6-acen) Zr(R)+, are prepared by protonolysis of suitable neutral dialkyl precursors. These complexes display electrophilic behavior and are moderately active ethylene polymerization catalysts in the presence of 1 molar equivalent of AlR3. 相似文献
985.
Three carrageenans derived from red algae and three partially modified carrageenans were tested for their ability to inhibit the formation of new blood capillaries on the chorionallantois membrane of the hen egg. It could be clearly demonstrated that they were better angiogenesis inhibitors than the standard compound suramin. 相似文献
986.
Natalie Hell Peter Beiersdorfer Gregory V. Brown Megan E. Eckart Richard L. Kelley Caroline A. Kilbourne Maurice A. Leutenegger Thomas E. Lockard F. Scott Porter Jörn Wilms 《X射线光谱测定》2020,49(1):218-233
X-ray astronomy and ground-based atomic physics have a long history of fruitful collaboration: Sound understanding of the underlying atomic physics is the key to reliable interpretation of the spectra from celestial sources; conversely, astronomical spectra have been used to benchmark and advance atomic physics. This interplay is about to become even more important as we enter a new era of high-resolution X-ray astrophysics with large effective collection area. Although high-resolution observations with the gratings on the Chandra and XMM-Newton observatories continue to drive new science, upcoming planned and proposed missions will open up new discovery space in the near future that is currently challenging to access: high-resolution spectroscopy on extended sources, in the Fe K band, and on short time scales. This review summarizes open questions in these areas and the design parameters for the Hitomi, XRISM, Athena, and Arcus observatories. The expected high quality of spectra taken with these observatories puts new constraints on the accuracy of atomic reference data required to take full advantage of the diagnostic potential of these spectra. 相似文献
987.
Juan M. Muñoz-Ocaña Ainouna Bouziane Farzeen Sakina Richard T. Baker Ana B. Hungría Jose J. Calvino Antonio M. Rodríguez-Chía Miguel López-Haro 《Particle & Particle Systems Characterization》2020,37(6):2000070
A novel procedure to optimize the 3D morphological characterization of nanomaterials by means of high angle annular dark field scanning-transmission electron tomography is reported and is successfully applied to the analysis of a metal- and halogen-free ordered mesoporous carbon material. The new method is based on a selection of the two parameters (μ and β) which are key in the reconstruction of tomographic series by means of total variation minimization (TVM). The parameter-selected TVM reconstructions obtained using this approach clearly reveal the porous structure of the carbon-based material as consisting of a network of parallel, straight channels of ≈6 nm diameter ordered in a honeycomb-type arrangement. Such an unusual structure cannot be retrieved from a TVM 3D reconstruction using default reconstruction values. Moreover, segmentation and further quantification of the optimized 3D tomographic reconstruction provide values for different textural parameters, such as pore size distribution and specific pore volume that match very closely with those determined by macroscopic physisorption techniques. The approach developed can be extended to other reconstruction models in which the final result is influenced by parameter choice. 相似文献
988.
Mario Wolf Alexey Rybakov Richard Hinterding Armin Feldhoff 《Entropy (Basel, Switzerland)》2020,22(11)
Besides the material research in the field of thermoelectrics, the way from a material to a functional thermoelectric (TE) module comes alongside additional challenges. Thus, comprehension and optimization of the properties and the design of a TE module are important tasks. In this work, different geometry optimization strategies to reach maximum power output or maximum conversion efficiency are applied and the resulting performances of various modules and respective materials are analyzed. A Bi2Te3-based module, a half-Heusler-based module, and an oxide-based module are characterized via FEM simulations. By this, a deviation of optimum power output and optimum conversion efficiency in dependence of the diversity of thermoelectric materials is found. Additionally, for all modules, the respective fluxes of entropy and charge as well as the corresponding fluxes of thermal and electrical energy within the thermolegs are shown. The full understanding and enhancement of the performance of a TE module may be further improved. 相似文献
989.
Interactive music uses wearable sensors (i.e., gestural interfaces—GIs) and biometric datasets to reinvent traditional human–computer interaction and enhance music composition. In recent years, machine learning (ML) has been important for the artform. This is because ML helps process complex biometric datasets from GIs when predicting musical actions (termed performance gestures). ML allows musicians to create novel interactions with digital media. Wekinator is a popular ML software amongst artists, allowing users to train models through demonstration. It is built on the Waikato Environment for Knowledge Analysis (WEKA) framework, which is used to build supervised predictive models. Previous research has used biometric data from GIs to train specific ML models. However, previous research does not inform optimum ML model choice, within music, or compare model performance. Wekinator offers several ML models. Thus, we used Wekinator and the Myo armband GI and study three performance gestures for piano practice to solve this problem. Using these, we trained all models in Wekinator and investigated their accuracy, how gesture representation affects model accuracy and if optimisation can arise. Results show that neural networks are the strongest continuous classifiers, mapping behaviour differs amongst continuous models, optimisation can occur and gesture representation disparately affects model mapping behaviour; impacting music practice. 相似文献
990.