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   789篇
  免费   19篇
  国内免费   5篇
化学   483篇
晶体学   23篇
力学   10篇
数学   148篇
物理学   149篇
  2023年   8篇
  2022年   16篇
  2021年   9篇
  2020年   14篇
  2019年   7篇
  2016年   12篇
  2015年   15篇
  2014年   19篇
  2013年   46篇
  2012年   34篇
  2011年   56篇
  2010年   19篇
  2009年   18篇
  2008年   45篇
  2007年   44篇
  2006年   38篇
  2005年   41篇
  2004年   37篇
  2003年   23篇
  2002年   47篇
  2001年   9篇
  2000年   7篇
  1999年   8篇
  1998年   9篇
  1997年   5篇
  1996年   8篇
  1995年   5篇
  1993年   7篇
  1992年   5篇
  1991年   4篇
  1990年   6篇
  1989年   4篇
  1988年   9篇
  1987年   7篇
  1986年   8篇
  1985年   12篇
  1984年   10篇
  1983年   4篇
  1982年   14篇
  1981年   13篇
  1980年   9篇
  1979年   9篇
  1978年   12篇
  1977年   11篇
  1976年   9篇
  1975年   11篇
  1974年   10篇
  1973年   5篇
  1969年   4篇
  1967年   6篇
排序方式: 共有813条查询结果,搜索用时 1 毫秒
11.
Soft tissue sarcomas (STS) are a rare and highly heterogeneous group of solid tumors, originating from various types of connective tissue. Complete removal of STS by surgery is challenging due to the anatomical location of the tumor, which results in tumor recurrence. Additionally, current polychemotherapeutic regimens are highly toxic with no rational survival benefit. Cold atmospheric plasma (CAP) is a novel technology that has demonstrated immense cancer therapeutic potential. Canady Cold Helios Plasma (CHCP) is a device that sprays CAP along the surgical margins to eradicate residual cancer cells after tumor resection. This preliminary study was conducted in vitro prior to in vivo testing in a humanitarian compassionate use case study and an FDA-approved phase 1 clinical trial (IDE G190165). In this study, the authors evaluate the efficacy of CHCP across multiple STS cell lines. CHCP treatment reduced the viability of four different STS cell lines (i.e., fibrosarcoma, synovial sarcoma, rhabdomyosarcoma, and liposarcoma) in a dose-dependent manner by inhibiting proliferation, disrupting cell cycle, and inducing apoptosis-like cell death.  相似文献   
12.
13.
Cellulose - In this study, three different pulp and paper mill sludge (PPMS) samples collected from different South African mills were chemically and physically characterised to investigate their...  相似文献   
14.
Chu KK  Lim D  Mertz J 《Optics letters》2007,32(19):2846-2848
We describe a technique to enhance both the weak-signal relative sensitivity and the dynamic range of a laser scanning optical microscope. The technique is based on maintaining a fixed detection power by fast feedback control of the illumination power, thereby transferring high measurement resolution to weak signals while virtually eliminating the possibility of image saturation. We analyze and demonstrate the benefits of adaptive illumination in two-photon fluorescence microscopy.  相似文献   
15.
We report an Umpolung strategy of enol ethers to generate oxy‐allyl cation equivalents based on the use of hypervalent iodine reagents. Under mild basic conditions, the addition of nucleophiles to aryloxy‐substituted vinylbenziodoxolone (VBX) reagents, easily available in two steps from silyl alkynes, resulted in the stereoselective formation of substituted aryl enol ethers. The reaction was most efficient with phenols as nucleophiles, but preliminary results were also achieved for C‐ and N‐ nucleophiles. In absence of external nucleophiles, the 2‐iodobenzoate group of the reagent was transferred. The obtained aryl enol ethers could then be transformed into α‐difunctionalized ketones by oxidation. The described “allyl cation”‐like reactivity contrast with the well‐established “vinyl‐cation” behavior of alkenyl iodonium salts.  相似文献   
16.
Using molecular simulations, we study the processes of capillary condensation and capillary evaporation in model mesopores. To determine the phase transition pathway, as well as the corresponding free energy profile, we carry out enhanced sampling molecular simulations using entropy as a reaction coordinate to map the onset of order during the condensation process and of disorder during the evaporation process. The structural analysis shows the role played by intermediate states, characterized by the onset of capillary liquid bridges and bubbles. We also analyze the dependence of the free energy barrier on the pore width. Furthermore, we propose a method to build a machine learning model for the prediction of the free energy surfaces underlying capillary phase transition processes in mesopores.  相似文献   
17.
18.
Good quality single crystals of pure and metal ion (Ni2+) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni2+doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni2+doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.  相似文献   
19.
The possibility of the nitrogen molecule forming a stable dimer is investigated. Through ab initio calculations in an extended contracted-gaussian basis, it is demonstrated that N4 in tetrahedral geometry and N3 + in D 3h geometry are local minimum points on their respective internuclear potential energy surfaces. The N4 molecule is considerably higher in energy than two ground-state N2 molecules and some study of the barrier for N4 decomposition has been made. The bond lengths and force constants for the two systems are shown to be similar to their hydrocarbon counterparts, C4H4 and C3H3 +, tetrahedrane and cyclopropenyl cation. Other related systems are discussed as well.  相似文献   
20.
String theory is an attempt to combine all of the known physical forces into a single unified framework. A powerful new type of duality symmetry has recently been discovered in string theory which has led to important breakthroughs. What were previously considered to be five distinct string theories are now known to be different aspects of an underlying structure called M-theory. In addition to strings, extended objects of higher dimension or 'branes', play a key role. We review these developments and discuss the impact that they are having on quantum field theory and the quantum properties of black holes.  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