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   270439篇
  免费   11394篇
  国内免费   6885篇
化学   158588篇
晶体学   3829篇
力学   11805篇
综合类   384篇
数学   30208篇
物理学   83904篇
  2022年   2697篇
  2021年   3444篇
  2020年   3949篇
  2019年   3962篇
  2018年   4199篇
  2017年   4216篇
  2016年   6114篇
  2015年   4887篇
  2014年   6471篇
  2013年   12601篇
  2012年   12279篇
  2011年   14019篇
  2010年   9845篇
  2009年   9461篇
  2008年   11999篇
  2007年   11753篇
  2006年   10935篇
  2005年   9886篇
  2004年   8527篇
  2003年   7385篇
  2002年   7200篇
  2001年   7631篇
  2000年   5916篇
  1999年   4664篇
  1998年   3865篇
  1997年   3785篇
  1996年   3783篇
  1995年   3332篇
  1994年   3326篇
  1993年   3093篇
  1992年   3246篇
  1991年   3273篇
  1990年   3029篇
  1989年   2844篇
  1988年   2730篇
  1987年   2656篇
  1986年   2677篇
  1985年   3431篇
  1984年   3442篇
  1983年   2895篇
  1982年   3101篇
  1981年   2849篇
  1980年   2633篇
  1979年   2805篇
  1978年   3004篇
  1977年   3047篇
  1976年   3078篇
  1975年   2811篇
  1974年   2913篇
  1973年   2972篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
A green and sustainable strategy synthesizes clinical medicine warfarin anticoagulant by using lipase‐supported metal–organic framework (MOF) bioreactors (see scheme). These findings may be beneficial for future studies in the industrial production of chemical, pharmaceutical, and agrochemical precursors.  相似文献   
103.
Galkina  E. G.  Zaspel  C. E.  Ivanov  B. A.  Kulagin  N. E.  Lerman  L. M. 《JETP Letters》2019,110(7):481-486
JETP Letters - The motion of domain walls in GdFeCo-type ferrimagnets near the point of compensation of sublattice spins s1 and s2, when the effects of the exchange increase in the limiting wall...  相似文献   
104.
A single-polarization filter comprising a gold-coated photonic crystal fiber based on surface plasmon resonance is designed and investigated. The pattern matching and coupled polarization characteristics analyzed by the full-vector finite element method (FEM) and losses at 1,540 nm are achieved to 1,016.01739 dB/cm (x-pol core mode) and 33.81917 dB/cm (y-pol core mode). The crosstalk (CT) value of the 1,540 nm band is ?853.12653 dB for fiber length L=1,000μm and the bandwidth is 850 nm. The working wavelength of the filter ranges from 1,280 nm to 1,540 nm by varying the diameter of outer air holes (d1), the diameter of inner air holes (d4), the metal film thickness (t), as well as the liquid refractive index (n).  相似文献   
105.
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease.  相似文献   
106.
Cyclohexane and cyclotri-β-alanyl have been used as scaffolds for the design of new C3-symmetric rings incorporating conjugated alkenes and dienes. All three C3-symmetric lactams share the same triangular shape and their crystal system is trigonal. They all belong to the R3 space group, R3m, R3 and R3c, for the increasingly large 12-, 18- and 24-membered rigid rings, respectively. All lactams stack on top of each other, through H-bonds and van der Waals noncovalent interactions, leading to endless supramolecular cylinders and tubes. The largest member of the family leads to tubes, the central pores of which is wide enough to let water in. A common feature of all the lactams is their very large dipole, of around 9 D, according to DFT calculations. Surprisingly, all the resulting cylinders and tubes pack side by side in the crystals, with all the dipoles pointing to the same direction. As a result, all three crystals are anisotropic and appear to be the first members of a new kind of highly polar crystals.  相似文献   
107.
108.
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments.  相似文献   
109.
110.
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained...  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