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   479篇
  免费   29篇
  国内免费   2篇
化学   365篇
晶体学   4篇
力学   21篇
数学   43篇
物理学   77篇
  2024年   5篇
  2023年   8篇
  2022年   47篇
  2021年   44篇
  2020年   29篇
  2019年   23篇
  2018年   25篇
  2017年   16篇
  2016年   30篇
  2015年   14篇
  2014年   18篇
  2013年   41篇
  2012年   39篇
  2011年   41篇
  2010年   31篇
  2009年   18篇
  2008年   15篇
  2007年   20篇
  2006年   14篇
  2005年   9篇
  2004年   5篇
  2003年   8篇
  2002年   1篇
  2001年   2篇
  1999年   1篇
  1996年   2篇
  1995年   1篇
  1993年   1篇
  1988年   1篇
  1987年   1篇
排序方式: 共有510条查询结果,搜索用时 15 毫秒
151.
Acta Mathematicae Applicatae Sinica, English Series - In a connected graph G, the distance d(u, v) denotes the distance between two vertices u and v of G. Let W = {w 1, w 2, ···, w...  相似文献   
152.
A simple, rapid and sensitive LC-MS/MS bioanalytical method has been developed to simultaneously quantify Camptosar (CPT-11) and its active metabolite, SN-38, in mouse plasma and tissues. A single step protein precipitation with acetonitrile in 96-well plates was used for sample preparation. Camptothecin (CPT) was used as the internal standard. Fast separation of SN-38, CPT-11 and CPT was carried out isocratically on a C18, 2 mm x 50 mm, 5 microm HPLC column with a mobile phase containing acetonitrile and 20 mM ammonium acetate (pH 3.5) and a 2.5 min chromatographic run time. The API 4000 MS/MS system was operated in positive ionization multiple reaction monitoring mode, and the transitions for SN-38, CPT-11 and CPT were 393.4 --> 349.3, 587.6 --> 167.2 and 349.3 --> 305.3, respectively. The SN-38 and CPT-11 concentrations in samples were calculated from a standard curve of peak area ratios of the analyte to that of the internal standard using a 1/chi2 weighted linear regression. The quantitation limit of 0.5 ng/mL was achieved by using a low sample volume (100 microL) of plasma or tissue homogenates. The assay was linear over the concentration range of 0.5-500 ng/mL with acceptable precision and accuracy. The method was used for the quantification of CPT-11 and SN-38 in plasma and tissues to support a preclinical pharmacokinetics and tissue distribution study of CPT-11 in mice.  相似文献   
153.

The 2:1 molar reaction of [Fe2(CO)6{(µ-SCH2)2CH2}] (1) and a bidentate diphosphine ligand, 1,6-bis(diphenylphosphino)hexane (dpph), in the presence of Me3NO resulted in the isolation of [Fe2(CO)5{Ph2P(CH2)3}{(µ-SCH2)2CH2}]2 (2) as red crystals in 71?% yield. The dpph ligand in compound 2, coordinates two Fe2S2 subunits as bridging mode and hence makes a linkage between two [Fe2(CO)5{(µ-SCH2)2CH2}] fragments. Each Fe2S2 butterfly of the complex consists of two fused Fe(S-C-C-C-S) six-membered rings, one of which attains a chair conformation, and the other is necessarily in a boat conformation. Compound 2 has unequivocally been characterized by elemental analysis, IR, 1H NMR and 31P NMR spectroscopy together with single crystal X-ray diffraction studies. Crystals of 2 are triclinic, space group P-1, a = 9.918(4) Å, b = 10.347(3) Å, c = 14.581(5) Å, α?=?72.239(12)º, β?=?80.342(12)º, γ?=?68.550(14)º and Z = 1.

Graphic Abstract

A novel tetranuclear propane-1,3-dithiolate complex, [Fe2(CO)5{Ph2P(CH2)3}{(μ-SCH2)2CH2}]2 (2), bearing a bridging bis(diphenylphosphino)hexane (dpph) ligand, was synthesized from the Me3NO aided room temperature displacement of carbonyls from [Fe2(CO)6{(μ-SCH2)2CH2}] (1), and structurally characterized.

  相似文献   
154.
Plumeria rubra (L.) is a traditional folkloric medicinal herb used to treat cardiovascular disorders. The present investigation was methodically planned to investigate the pharmacological foundations for the therapeutic effectiveness of P. rubra in cardiovascular illnesses and its underlying mechanisms. Ex vivo vaso-relaxant effects of crude leaf extract of P. rubra were observed in rabbit aorta ring preparations. Hypotensive effects were measured using pressure and force transducers connected to the Power Lab data acquisition system. Furthermore, P. rubra displayed cardioprotective properties in rabbits when they were exposed to adrenaline-induced myocardial infarction. In comparison to the intoxicated group, the myocardial infarction model showed decreased troponin levels, CK-MB, LDH, ALT, ALP, AST, and CRP, as well as necrosis, apoptosis, oedema, and inflammatory cell enrollment. P. rubra has revealed good antioxidant properties and prolonged the noradrenaline intoxicated platelet adhesion. Its anticoagulant, vasorelaxant, and cardioprotective effects in both in vivo and ex vivo investigations are enabled by blocking L-type calcium channels, lowering adrenaline, induced oxidative stress, and tissue tear, justifying its therapeutic utility in cardiovascular disorders.  相似文献   
155.
The current article investigates the impact of the bioconvection in an unsteady flow of magnetized Cross nanofluid with gyrotactic microorganisms and activation energy over a linearly stretched configuration. The analysis has been performed by utilizing the realistic Wu's slip boundary and zero mass flux conditions. The effects of nonlinear thermal radiation and the activation energy are also addressed. The governing flow equations are deduced to a dimensionless form by considering suitable transformations which are numerically targeted via a shooting algorithm. The physical visualization of each physical parameter governing the flow problem has been displayed graphically for distribution of velocity, temperature, concentration and motile microorganisms. The numerical treatment for the variation of skin friction coefficient, local Nusselt number, local Sherwood number and motile density number is performed in tabular forms.  相似文献   
156.
James SW  Ishaq I  Ashwell GJ  Tatam RP 《Optics letters》2005,30(17):2197-2199
The response of the transmission spectrum of cascaded long period gratings (LPGs) to the deposition of nanostructured coatings by use of the Langmuir-Blodgett technique is investigated. The phase of the interference fringes within the LPGs' attenuation bands is shown to be highly sensitive to the optical thickness of the coating, for thicknesses of the order of 100 nm.  相似文献   
157.
Targeting the tumor microenvironment (TME) provides opportunities to modulate tumor physiology, enhance the delivery of therapeutic agents, impact immune response and overcome resistance. Photodynamic therapy (PDT) is a photochemistry-based, nonthermal modality that produces reactive molecular species at the site of light activation and is in the clinic for nononcologic and oncologic applications. The unique mechanisms and exquisite spatiotemporal control inherent to PDT enable selective modulation or destruction of the TME and cancer cells. Mechanical stress plays an important role in tumor growth and survival, with increasing implications for therapy design and drug delivery, but remains understudied in the context of PDT and PDT-based combinations. This review describes pharmacoengineering and bioengineering approaches in PDT to target cellular and noncellular components of the TME, as well as molecular targets on tumor and tumor-associated cells. Particular emphasis is placed on the role of mechanical stress in the context of targeted PDT regimens, and combinations, for primary and metastatic tumors.  相似文献   
158.
Journal of Thermal Analysis and Calorimetry - The use of Li-ion battery in electric vehicles is becoming extensive in the modern-day world owing to their high energy density and longer life. But...  相似文献   
159.
对HL-2A 偏滤器靶板和固定孔栏位置的石墨瓦进行了离线激光诱导击穿光谱(LIBS)测量,比较分析了沉积行为,初步得到了不同位置沉积层粒子种类(Fe、Si、H、D 等元素)及其深度的变化。与飞行时间二次离子质谱仪(TOF-SIMS)所得结果进行了对比,发现离子深度变化形貌趋同。根据沉积层有效信号激光数,得到激光烧蚀速率约为270nm/脉冲。  相似文献   
160.
A fast, selective and reproducible solid‐phase membrane microtip extraction (SPMMTE) HPLC method has been developed and validated for the analyses of ibuprofen, ketoprofen, and flurbiprofen from human plasma. The analysis was carried out on a C18 (150 × 4.6 mm; 5 μm) column. The mobile phase used was water–acetonitrile (55:45, v/v) adjusted to pH 3.0 using trifluoroacetic acid, at a flow rate 0.5 mL/min with a detection wavelength of 225 nm. The values for the capacity factors for the profen samples ranged from 0.47 to 1.50. The values for the selectivity factor (α) for ketoprofen–flurbiprofen, flurbiprofen–ibuprofen and ibuprofen–ketoprofen combinations from human plasma samples were 1.99, 1.00 and 2.10, respectively. The resolution factors (Rs) for ketoprofen–flurbiprofen, flurbiprofen–ibuprofen and ibuprofen–ketoprofen from plasma samples were 3.00, 1.50 and 4.10, respectively. The percentage recoveries of ibuprofen, ketoprofen, and flurbiprofen from human plasma were 75–85%. All of the profens were separated within 7.0 min, indicating a relatively fast method. During the development of the SPMMTE procedure the parameters of pH, contact time, desorption and types of solvents were optimized. The final method was also found to be efficient, effective and inexpensive. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
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