全文获取类型
收费全文 | 1632篇 |
免费 | 122篇 |
国内免费 | 92篇 |
专业分类
化学 | 1360篇 |
力学 | 28篇 |
综合类 | 39篇 |
数学 | 99篇 |
物理学 | 320篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 83篇 |
2021年 | 48篇 |
2020年 | 82篇 |
2019年 | 110篇 |
2018年 | 72篇 |
2017年 | 108篇 |
2016年 | 91篇 |
2015年 | 42篇 |
2014年 | 66篇 |
2013年 | 70篇 |
2012年 | 69篇 |
2011年 | 69篇 |
2010年 | 80篇 |
2009年 | 94篇 |
2008年 | 63篇 |
2007年 | 87篇 |
2006年 | 73篇 |
2005年 | 67篇 |
2004年 | 65篇 |
2003年 | 66篇 |
2002年 | 60篇 |
2001年 | 44篇 |
2000年 | 33篇 |
1999年 | 34篇 |
1998年 | 26篇 |
1997年 | 24篇 |
1996年 | 17篇 |
1995年 | 29篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1846条查询结果,搜索用时 671 毫秒
201.
稀土元素在中草药中的应用及其前景 总被引:7,自引:0,他引:7
本文介绍了稀土元素在中草药中的应用及其前景,探讨了稀土元素对中草药药效的影响,引用文献39篇。 相似文献
202.
浙江分布的中国种子植物特有属研究 总被引:5,自引:1,他引:4
郑朝宗 《浙江大学学报(理学版)》1998,25(2):75-80
浙江分布的中国种子植物特有属有49 属, 含63 种, 隶属于30 科, 其中有3 属为浙江特有属;在49 属
中, 单种属29 个, 少种属10 个, 多种属10 个;特有属的特征概括为:单种特有属的比例大, 木本属占优势、
具有相对的原始或古老性和珍稀濒危性以及具有明显的温带性质;浙西北山区, 特别是西天目山是中国
特有属在浙江的分布中心;浙江与全国各省区的共有属的关系为华东(46 属)>华中(36 属)>华南(32)
>西北(16 属), 而与东北和华北两地的关系很少有联系;浙江与毗邻省份的特有属相似性分析, 其与江西
和安徽的关系比与福建和江苏更为密切. 相似文献
203.
Chinese Spring Tal kr phlb plants were developed by hybridizing Tal common wheat and Chinese Spring phlb mutant and backcrosses. When Chinese Spring Tal kr phlb plants were crossed with some wild species of Triticeae, much more seeds of wide hybridization can be obtained without artificial emasculation and pollination because of the existence of Tat and kr genes. The homoeologous chromosomes between common wheat and the wild species of Triticeae can also pair and exhibit cross-over in the hybrid F1 plants because of the existence of the phlb gene. So that more alien desirable genes can be transferred to common wheat rapidly. Therefore, Chinese Spring Tal kr phlb plants become a powerful tool for wide hybridization and transferring alien desirable genes to common wheat. 相似文献
204.
56种中药内微量铝的含量测定 总被引:2,自引:1,他引:1
分别采用等离子体发射光谱法和4,5-二溴苯基荧光酮-二溴化十六烷基三甲铵荧光法测定了56种中药内微量铝的含量. 相似文献
205.
椰胡是具有地方特色的拉弦乐器之一,多用于演奏广东音乐和广东戏曲、曲艺的伴奏。但对其发声强度一直未进行过科学的测试。本文介绍在华南理工大学半消声室内参照ISO(GB)标准对椰胡声功率级的测量工作。由两位资深乐师分别用两把椰胡在pp,mp,f和ff力度下演奏单音、音阶和乐曲,对每一把椰胡的每一测试内容,由十通道测试设备同步测试中心频率为100~10000 Hz的1/3倍频带声压级谱,通过计算获得每把椰胡在演奏每项内容时的声功率级和动态范围。通过对两把椰胡的测试结果进行平均,获得该乐器在演奏上述内容时的典型声功率级数值及频谱。文中并将半消声室内的测试结果与混响室内的测试结果相对比,探讨测试环境对测试结果的影响。民族乐器发声强度及其频谱特性的获得是开展民族音乐厅堂音质研究的基础。 相似文献
206.
Screening and analysis of an antineoplastic compound in Rhizoma Chuanxiong by means of in vitro metabolism and HPLC-MS 总被引:1,自引:0,他引:1
A new screening and analysis method that combines in vitro metabolism with high-performance liquid chromatography-mass spectrometry
(HPLC-MS) was developed for the screening and analysis of an antineoplastic compound, coniferyl ferulate, which is present
in the rhizome of Rhizoma Chuanxiong. Infrared (IR), ultraviolet visible spectroscopy (UV-Vis), nuclear magnetic resonance (NMR) and element analysis were used
to identify the molecular structure of coniferyl ferulate. The quantitative analysis of coniferyl ferulate in different extracts
of Rhizoma Chuanxiong was carried out, and the metabolism of coniferyl ferulate was investigated by in vitro incubation with rat liver homogenate.
The metabolite of coniferyl ferulate, ferulic acid ethyl ester, was identified by HPLC-MS, UV-Vis and IR. In addition, antineoplastic
activities of coniferyl ferulate and ferulic acid ethyl ester were detected by the MTT assay. The observed inhibition rate
of coniferyl ferulate on the activity of HeLa cells was over 80% at 5.4 ng μl−1. However, its metabolite, ferulic acid ethyl ester, showed no antineoplastic activity in vitro.
相似文献
207.
Zhang J Tao D Duan J Liang Z Zhang W Zhang L Huo Y Zhang Y 《Analytical and bioanalytical chemistry》2006,386(3):586-593
A comprehensive two-dimensional liquid chromatographic (2D-LC) separation system based on the combination of a CN column and
a Merck Chromolith Flash reversed-phase column was developed for the separation of components in Adinandra nitida, one type of traditional Chinese medicine (TCM). The two dimensions were connected by a ten-port, dual-position valve controlled
automatically by software written in-house. The effluents were detected by both ultraviolet and atmospheric pressure chemical
ionization source ion trap tandem mass spectrometry (MS). The calculated peak capacity of the 2D-LC–MS/MS system was above
1240. More than 57 components were resolved in the methanol extract from Adinandra nitida leaves, and five of these were identified based on their relative retention times, molecular weights and MS/MS spectra. 相似文献
208.
Pu‐Jun Jin Zheng‐Quan Yao Mao‐Lin Zhang Yu‐Hu Li Hui‐Ping Xing 《Journal of Raman spectroscopy : JRS》2010,41(2):222-225
A blue pigment was identified by micro‐Raman spectroscopy, X‐ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX) and X‐ray diffraction (XRD). The test sample, a funerary lacquer tray, belongs to West Han Dynasty (206 BC–AD 8) of China and was decorated with faint blue patterns. The result from Raman spectroscopy showed that the faint blue is covellite (CuS) due to the presence of a characteristic peak at 474.5 cm−1, which further was confirmed by XRF, SEM–EDX and XRD. This research indicated that CuS had been used as a blue pigment to decorate lacquer wares from the West Han Dynasty in China. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
209.
Evolution of Chinese airport network 总被引:2,自引:0,他引:2
With the rapid development of the economy and the accelerated globalization process, the aviation industry plays a more and more critical role in today’s world, in both developed and developing countries. As the infrastructure of aviation industry, the airport network is one of the most important indicators of economic growth. In this paper, we investigate the evolution of the Chinese airport network (CAN) via complex network theory. It is found that although the topology of CAN has remained steady during the past few years, there are many dynamic switchings inside the network, which have changed the relative importance of airports and airlines. Moreover, we investigate the evolution of traffic flow (passengers and cargoes) on CAN. It is found that the traffic continues to grow in an exponential form and has evident seasonal fluctuations. We also found that cargo traffic and passenger traffic are positively related but the correlations are quite different for different kinds of cities. 相似文献
210.
建立灵敏、可靠的中药材中农药多残留的检测方法对保证中药材的质量和安全十分重要.制备了磁性亲水亲脂平衡萃取材料Fe3 O4@PLS,将其应用于农药多残留的磁性基质固相分散萃取中,并结合高效液相色谱-串联质谱法(HPLC-MS/MS)检测了金银花、菊花和三七块根(干)3种中药材中76种农药残留量.研究通过扫描电子显微镜(S... 相似文献