首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   509篇
  免费   32篇
  国内免费   6篇
化学   409篇
力学   5篇
数学   61篇
物理学   72篇
  2023年   1篇
  2022年   4篇
  2021年   6篇
  2020年   7篇
  2019年   12篇
  2018年   7篇
  2017年   8篇
  2016年   17篇
  2015年   12篇
  2014年   15篇
  2013年   27篇
  2012年   42篇
  2011年   64篇
  2010年   31篇
  2009年   25篇
  2008年   49篇
  2007年   26篇
  2006年   29篇
  2005年   35篇
  2004年   25篇
  2003年   27篇
  2002年   22篇
  2001年   10篇
  2000年   8篇
  1999年   2篇
  1998年   3篇
  1997年   2篇
  1996年   3篇
  1995年   4篇
  1994年   1篇
  1993年   2篇
  1992年   2篇
  1991年   2篇
  1990年   2篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1985年   3篇
  1984年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1975年   1篇
  1967年   1篇
  1879年   1篇
排序方式: 共有547条查询结果,搜索用时 359 毫秒
61.
Qualitative and quantitative profiling of six different categories of urinary phospholipids (PLs) from patients with prostate cancer was performed to develop an analytical method for the discovery of candidate biomarkers by shotgun lipidomics method. Using nanoflow liquid chromatography–electrospray ionization–tandem mass spectrometry, we identified the molecular structures of a total of 70 PL molecules (21 phosphatidylcholines (PCs), 11 phosphatidylethanolamines (PEs), 17 phosphatidylserines (PSs), 11 phosphatidylinositols (PIs), seven phosphatidic acids, and three phosphatidylglycerols) from urine samples of healthy controls and prostate cancer patients by data-dependent collision-induced dissociation. Identified molecules were quantitatively examined by comparing the MS peak areas. From statistical analyses, one PC, one PE, six PSs, and two PIs among the PL species showed significant differences between controls and cancer patients (p < 0.05, Student’s t test), with concentration changes of more than threefold. Cluster analysis of both control and patient groups showed that 18:0/18:1-PS and 16:0/22:6-PS were 99% similar in upregulation and that the two PSs (18:1/18:0, 18:0/20:5) with two PIs (18:0/18:1 and 16:1/20:2) showed similar (>95%) downregulation. The total amount of each PL group was compared among prostate cancer patients according to the Gleason scale as larger or smaller than 6. It proposes that the current study can be utilized to sort out possible diagnostic biomarkers of prostate cancer.  相似文献   
62.
Three gallosilicate natrolites with closely similar chemical composition but differing in the distribution of Si and Ga over crystallographically different tetrahedral sites (T-sites) show striking differences in their cation exchange performance. The ability to exchange Na(+) by the larger alkali metal cations decreases upon increasing the size of the cation, as expected, but also with the degree of T-atom ordering. To seek an insight into this phenomenon, the crystal structures of 11 different zeolites, which show variations in degree of T-atom ordering, nature of countercation, and hydration state, have been refined using synchrotron diffraction data. While the three as-made sodium materials were characterized to have a low, medium, and high degree of ordering, respectively, their pore sizes are close to the size of the bare Na(+) cation and much smaller than that of the larger alkali cations, which are nonetheless exchanged into the materials, each one at a different level. Interestingly, large differences are also manifested when the Na(+) back-exchange is performed on the dehydrated K(+) forms, with crystallographic pore sizes too small even to allow the passage of Na(+). Although the thermodynamic data point to small differences in the enthalpy of the Na(+)/K(+) exchange in the three materials, comparison of the "static" crystallographic pore sizes and the diameter of the exchanged cations lead us to conclude that during the exchange process these zeolites undergo significant deformations that dynamically open the pores, allowing cation traffic even for Cs(+) in the case of the most disordered material. In addition to the very large topological flexibility typical of the natrolite framework, we propose as a hypothesis that there is an additional flexibility mechanism that decreases the rigidity of the natrolite chain itself and is dependent on preferential siting of Si or Ga on crystallographically different T-sites.  相似文献   
63.
Photochromic compound-conjugated fluorescent fullerene-silica nanoparticles prepared by the reverse-microemulsion method was utilized for photoswitchable cellular imaging by repeatable irradiation of ultraviolet and visible light.  相似文献   
64.
Endosome-escapable poly(amino acid) nanoparticles composed of iron oxide nanocrystals and anticancer drugs were prepared and demonstrated high T(2) relaxivity coefficients and higher efficacy attributed to the endosomolytic ability of the conjugated histidine moiety.  相似文献   
65.
A series of Zn2+‐selective two‐photon fluorescent probes (AZnM1−AZnN) that had a wide range of dissociation constants (KdTP=8 nm‐ 12 μM ) were synthesized. These probes showed appreciable water solubility (>3 μM ), cell permeability, high photostability, pH insensitivity at pH>7, significant two‐photon action cross‐sections (86–110 GM) upon complexation with Zn2+, and can detect the Zn2+ ions in HeLa cells and in living tissue slices of rat hippocampal at a depth of >80 μm without mistargeting and photobleaching problems. These probes can potentially find application in the detection of various amounts of Zn2+ ions in live cells and intact tissues.  相似文献   
66.
Two‐photon microscopy (TPM) has become an indispensible tool in biology and medicine owing to the capability of imaging the intact tissue for a long period of time. To make it a versatile tool in biology, a variety of two‐photon probes for specific applications are needed. In this context, many research groups are developing two‐photon probes for various applications. In this Focus Review, we summarize recent results on model studies and selected examples of two‐photon probes that can detect intracellular free metal ions in live cells and tissues to provide a guideline for the design of useful two‐photon probes for various in vivo imaging applications.  相似文献   
67.
A fast automatic calibration system for a sound level meter in an anechoic environment has been developed. The precise and fast generation of the constant frequency-independent acoustic pressure field and reduction of digital voltmeter readout to sound pressure level were achieved by a newly designed software algorithm, assuming the system linearity. The performance test justified the assumed linearity, and showed that the searching speed was sufficiently fast within the small error limit.  相似文献   
68.
We construct examples which distinguish clearly the classes of p-hyponormal operators for 0<p?∞. In addition, we show that those examples classify the classes of w-hyponormal, absolute-p-paranormal, and normaloid operators on the complex Hilbert space. Only a few examples of p-hyponormal operators have been examined. Our technique can provide many examples related to the above operators.  相似文献   
69.
Two transient absorptions have been detected in the 266 nm laser photolysis of 2-phenylheptamethyltrisilane in cyclohexane solution at room temperature, and their time evolution was recorded in the presence and absence of air and added trapping agents. The shorter-lived 440 nm transient (t1/2 < 20μs) is tentatively assigned to the silylene :SiMePh and the more persistent 380 nm transient to the disilene MePhSiSiMePh. The reactivity of this silylene is much lower than had been expected.  相似文献   
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号