全文获取类型
收费全文 | 11020篇 |
免费 | 1606篇 |
国内免费 | 2107篇 |
专业分类
化学 | 9808篇 |
晶体学 | 115篇 |
力学 | 272篇 |
综合类 | 132篇 |
数学 | 112篇 |
物理学 | 4294篇 |
出版年
2024年 | 22篇 |
2023年 | 126篇 |
2022年 | 280篇 |
2021年 | 346篇 |
2020年 | 417篇 |
2019年 | 371篇 |
2018年 | 354篇 |
2017年 | 488篇 |
2016年 | 590篇 |
2015年 | 555篇 |
2014年 | 637篇 |
2013年 | 1083篇 |
2012年 | 806篇 |
2011年 | 683篇 |
2010年 | 556篇 |
2009年 | 675篇 |
2008年 | 647篇 |
2007年 | 685篇 |
2006年 | 690篇 |
2005年 | 585篇 |
2004年 | 584篇 |
2003年 | 492篇 |
2002年 | 472篇 |
2001年 | 324篇 |
2000年 | 320篇 |
1999年 | 284篇 |
1998年 | 212篇 |
1997年 | 208篇 |
1996年 | 171篇 |
1995年 | 166篇 |
1994年 | 130篇 |
1993年 | 125篇 |
1992年 | 118篇 |
1991年 | 79篇 |
1990年 | 62篇 |
1989年 | 58篇 |
1988年 | 68篇 |
1987年 | 38篇 |
1986年 | 32篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 24篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 18篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information. 相似文献
2.
Mariusz Marć Marek Tobiszewski Bożena Zabiegała Miguel de la Guardia Jacek Namieśnik 《Analytica chimica acta》2015
This review summarizes the different tools and concepts that are commonly applied in air quality monitoring. The monitoring of atmosphere is extremely important as the air quality is an important problem for large communities. Main requirements for analytical devices used for monitoring include a long period of autonomic operation and portability. These instruments, however, are often characterized by poor analytical performance. Monitoring networks are the most common tools used for monitoring, so large-scale monitoring programmes are summarized here. Biomonitoring, as a cheap and convenient alternative to traditional sample collection, is becoming more and more popular, although its main drawback is the lack of standard procedures. Telemonitoring is another approach to air monitoring, which offers some interesting opportunities, such as ease of coverage of large or remote areas, constituting a complementary approach to traditional strategies; however, it requires huge costs. 相似文献
3.
Technical advances in the development of field-deployable capillary and microchip electrophoretic instruments and reports of their deployment between 2013 and 2017 were reviewed. Strategies and considerations in the design of the injection, separation and detection hardware, chemistry and associated infrastructure were discussed from an in-field perspective, with portability, robustness and automation/“ease of use” featuring as key requirements. Integration of functionality is important for adequate in-field performance. Progress was made towards the use of multiple channel devices for increased throughput and/or resolving power, mixing devices for on-line/in-line sample derivatization, battery operation and temperature control. The strengths and weaknesses of the various approaches described in the literature are discussed from the perspective of in-field operation. An overview of the applications of the field electrophoretic instruments is provided, including environmental science and planetary investigation. 相似文献
4.
本文研究了胆绿素的表面增强拉曼光谱。结果表明,在溶液酸度不同时,拉曼光谱特征频率的变化表现出胆绿素的质子化。铜离子与胆绿素的相互作用实验结果说明金属铜离子可与胆绿素生成金属配合物。 相似文献
5.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6. 相似文献
6.
设计合成了用以检测过渡金属离子的荧光化学敏感器体系,它们是由1,8-萘二酰亚胺为荧光团,多胺衍生物为金属离子受体组成.在室温下对其光物理性质的研究中发现,在没有加入过渡金属离子时,由于体系内存在有效的光诱导电子转移过程使得荧光团的荧光被淬灭.加入过渡金属离子后,金属离子受体中的氮原子和过渡金属离子之间的配位作用阻断了光诱导电子转移过程,体系的荧光增强.不同的金属离子受体表现出了和过渡金属离子不同的配位识别能力,并且通过荧光的变化传递出受体-金属离子作用的信息. 相似文献
7.
J Ashenfelter 《Pramana》2002,59(5):713-717
The ESTU began operation in 1988 and achieved the design voltage of 20 MV in 1990. Since that time, improvements to the gas
handling system, negative ion injector, accelerator terminal and control system have greatly increased its capability and
reliability. Today, the ESTU can efficiently produce an extensive assortment of stable ions at wide-ranging energies in support
of low-energy nuclear physics. 相似文献
8.
9.
A novel technique to overcome the long-term drift and hysteresis of a scanning Fabry–Perot filter was developed and applied to wavelength and power monitoring of DWDM system. By using the comb peaks generated by a temperature-stabilized, near threshold-biased Fabry–Perot diode laser as wavelength reference for the scanning Fabry–Perot filter, wavelength and power measurement accuracy of better than ±10 pm and 0.2 dB, respectively, were achieved. 相似文献
10.
用全实加关联方法计算了类锂V20+离子1s23d-1s2nf的跃迁能和偶极振子强度.依据量子亏损理论, 确定了1s2nf系列的量子数亏损,用这些作为能量的缓变函数的量子亏损,实现对该Rydberg系列任意高激发态(n≥10)的能量的可靠预言.将这些分立态振子强度与量子亏损理论相结合,得到在电离域附近束缚态间的偶极跃迁振子强度以及束缚态-连续态跃迁的振子强度密度,从而将V20+离子的这一重要光谱特性的理论预言外推到整个能域. 相似文献