全文获取类型
收费全文 | 12841篇 |
免费 | 1256篇 |
国内免费 | 1625篇 |
专业分类
化学 | 3642篇 |
晶体学 | 104篇 |
力学 | 221篇 |
综合类 | 59篇 |
数学 | 100篇 |
物理学 | 3861篇 |
无线电 | 7735篇 |
出版年
2024年 | 65篇 |
2023年 | 190篇 |
2022年 | 326篇 |
2021年 | 437篇 |
2020年 | 503篇 |
2019年 | 410篇 |
2018年 | 356篇 |
2017年 | 542篇 |
2016年 | 650篇 |
2015年 | 756篇 |
2014年 | 1062篇 |
2013年 | 1161篇 |
2012年 | 1085篇 |
2011年 | 1010篇 |
2010年 | 659篇 |
2009年 | 730篇 |
2008年 | 774篇 |
2007年 | 820篇 |
2006年 | 726篇 |
2005年 | 473篇 |
2004年 | 471篇 |
2003年 | 399篇 |
2002年 | 310篇 |
2001年 | 282篇 |
2000年 | 231篇 |
1999年 | 183篇 |
1998年 | 154篇 |
1997年 | 142篇 |
1996年 | 110篇 |
1995年 | 109篇 |
1994年 | 93篇 |
1993年 | 86篇 |
1992年 | 69篇 |
1991年 | 68篇 |
1990年 | 29篇 |
1989年 | 33篇 |
1988年 | 74篇 |
1987年 | 26篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
31.
32.
本文讨论的10.6μm线性声光调制器,采用Ge单晶作为声光介质,工作中心频率为80MHz,3db带宽为7MHz。在驱动射频源输出功率8W的条件下,得到器件衍射效率峰值达36%,该器件已作为激光束强度调制器件应用于视频/红外动态图象转换装置中。 相似文献
33.
Hui Ma Lulu Xiao Dongchen Xu Yingrui Geng Xuesong Liu Yong Chen Yongjiang Wu 《Molecules (Basel, Switzerland)》2022,27(9)
Quality control methods of current traditional Chinese medicine (TCM) preparation is time-consuming and difficult to assess in terms of overall efficiency of the drug. A non-destructive rapid near-infrared spectroscopy detection system for key chemical components and biological activity of Lanqin oral solution (LOS), one of the best-selling TCM formulations, was established for comprehensive quality evaluation. Near infrared spectral scanning was carried out on 101 batches of commercial LOS under the penetrated vial state and traditional state. RAW 264.7 cells were cultured to detect the anti-inflammatory ability of LOS, and the reference concentrations of epigoitrin, geniposide, and baicalin were obtained by HPLC. The quantitative models were optimized by three kinds of variable selection methods. The correlation coefficients of prediction value of the models were greater than 0.94. The system also passed the external validation. The performance of the non-invasive models was similar to the traditional models. The established non-destructive system can be applied to the rapid quality inspection of LOS to avoid unqualified drugs from entering the market and ensure drug effectiveness. The biological activity index of LOS was introduced and predicted by NIRs for the first time, which provides a new idea about the quality control of TCM formulations. 相似文献
34.
Abstract The various methods for determining the mode of occurrence of trace metals in sediments and soils have a long history which dates back to the determinations of the availability of metals for plant nutrition performed earlier. Various methods have been developed in the 70′s and 80′s dealing with both single and sequential extraction schemes. Although some schemes received wide acceptance, none of them developed into a commonly accepted procedure. As a result, the information obtained was site-specific and the interpretation of the results scientist-specific. The workshop on single and sequential extraction in sediments and soils held at Sitges 相似文献
35.
36.
37.
针对传统水产养殖存在的弊端,文章设计了一款基于无线传感网、移动互联及云计算等技术的养殖水体环境因子智能化监控系统,可以实现对水体关键环境因子的快速检测、及时反馈和自动调节,对于发展高效、生态、安全的现代水产养殖业具有重要的推动作用。 相似文献
38.
Jeffrey J. Sweterlitsch Perminus Mungara Roger W. Jones Jay-lin Jane 《International Journal of Polymer Analysis and Characterization》2013,18(6):464-468
Soy protein–based polymers offer promising performance properties, but their characteristics are sensitively dependent on production conditions, so on-line monitoring could help provide the needed control during production. Mid-infrared spectroscopy combined with partial least squares offer the needed analysis, but the opacity of many materials in the mid-infrared range limits its conventional application. Transient infrared spectroscopy is a method of acquiring mid-infrared spectra from moving streams in real time that avoids the opacity problem. We apply transient infrared spectroscopy to a polymer of soy protein and polyisoprene-graft-maleic anhydride–modified natural rubber during its compounding extrusion to measure tensile strength and Young's modulus. 相似文献
39.
Formation of “Quasi” Contact or Solvent‐separated Ion Pairs in the Local Environment of Probe Molecules Dissolved in Ionic Liquids 下载免费PDF全文
Matthias Strauch Dr. Christian Roth Falk Kubatzki Prof. Dr. Ralf Ludwig 《Chemphyschem》2014,15(2):265-270
The change from “quasi” contact to “quasi” solvent‐separated ion‐pair configuration in the local environment of a probe molecule in ionic liquids depends on the varying interaction strength of the chosen anions. The ion speciation in these Coulomb fluids could be shown by combining infrared spectroscopy, density functional theory calculations, and natural bond orbital analysis using a low‐self‐clustering probe molecule. 相似文献
40.
On‐Line Monitoring of Chemical Reactions by using Bench‐Top Nuclear Magnetic Resonance Spectroscopy 下载免费PDF全文
Dr. E. Danieli Dr. J. Perlo Dr. A. L. L. Duchateau G. K. M. Verzijl Dr. V. M. Litvinov Prof. Dr. B. Blümich Dr. F. Casanova 《Chemphyschem》2014,15(14):3060-3066
Real‐time nuclear magnetic resonance (NMR) spectroscopy measurements carried out with a bench‐top system installed next to the reactor inside the fume hood of the chemistry laboratory are presented. To test the system for on‐line monitoring, a transfer hydrogenation reaction was studied by continuously pumping the reaction mixture from the reactor to the magnet and back in a closed loop. In addition to improving the time resolution provided by standard sampling methods, the use of such a flow setup eliminates the need for sample preparation. Owing to the progress in terms of field homogeneity and sensitivity now available with compact NMR spectrometers, small molecules dissolved at concentrations on the order of 1 mmol L?1 can be characterized in single‐scan measurements with 1 Hz resolution. Owing to the reduced field strength of compact low‐field systems compared to that of conventional high‐field magnets, the overlap in the spectrum of different NMR signals is a typical situation. The data processing required to obtain concentrations in the presence of signal overlap are discussed in detail, methods such as plain integration and line‐fitting approaches are compared, and the accuracy of each method is determined. The kinetic rates measured for different catalytic concentrations show good agreement with those obtained with gas chromatography as a reference analytical method. Finally, as the measurements are performed under continuous flow conditions, the experimental setup and the flow parameters are optimized to maximize time resolution and signal‐to‐noise ratio. 相似文献