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   270668篇
  免费   4657篇
  国内免费   2092篇
化学   128423篇
晶体学   3637篇
力学   14576篇
综合类   74篇
数学   41708篇
物理学   88999篇
  2022年   1478篇
  2021年   1728篇
  2020年   1843篇
  2019年   1923篇
  2018年   11142篇
  2017年   11850篇
  2016年   7558篇
  2015年   3288篇
  2014年   3619篇
  2013年   7842篇
  2012年   10991篇
  2011年   20471篇
  2010年   12622篇
  2009年   12683篇
  2008年   17588篇
  2007年   21082篇
  2006年   6561篇
  2005年   12740篇
  2004年   8491篇
  2003年   7723篇
  2002年   5732篇
  2001年   4802篇
  2000年   3892篇
  1999年   2987篇
  1998年   2560篇
  1997年   2489篇
  1996年   2436篇
  1995年   2239篇
  1994年   2178篇
  1993年   2017篇
  1992年   2204篇
  1991年   2352篇
  1990年   2118篇
  1989年   2100篇
  1988年   2035篇
  1987年   1915篇
  1986年   1841篇
  1985年   2336篇
  1984年   2486篇
  1983年   2021篇
  1982年   2195篇
  1981年   2079篇
  1980年   2002篇
  1979年   2146篇
  1978年   2325篇
  1977年   2109篇
  1976年   2198篇
  1975年   2087篇
  1974年   2131篇
  1973年   2169篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
891.
We prove estimates in weighted Hölder norms for a solution to the model linear problem related with the one-phase Stefan problem with a small multiplier ε at time derivative in the heat equation. These estimates are uniform with respect to parameter ε and are significant in justification of passage to the limit in the one-phase Stefan problem as the specific heat tends to zero. Bibliography: 8 titles.  相似文献   
892.
We describe W-geometry of two-dimensional Toda systems associated with the Lie algebra C n . __________ Translated from Fundamental’naya i Prikladnaya Matematika (Fundamental and Applied Mathematics), Vol. 11, No. 1, Geometry, 2005.  相似文献   
893.
The details of the mechanical effects (twinning and microcracking) are clarified at various stages of dynamic fatigue of PbTiO3 crystals using a polarization microscope and selective etching.  相似文献   
894.
Layers of recombinant spider silks and native silks from silk worms were prepared by spin-coating and casting of various solutions. FT-IR spectra were recorded to investigate the influence of the different mechanical stress occurring during the preparation of the silk layers. The solubility of the recombinant spider silk proteins SO1-ELP, C16, AQ24NR3, and of the silk fibroin from Bombyx mori were investigated in hexafluorisopropanol, ionic liquids and concentrated salt solutions. The morphology and thickness of the layers were determined by Atomic Force Microscopy (AFM) or with a profilometer. The mechanical behaviour was investigated by acoustic impedance analysis by using a quartz crystal microbalance (QCMB) as well as by microindentation. The density of silk layers (d<300 nm) was determined based on AFM and QCMB measurements. At silk layers thicker than 300 nm significant changes of the half-band-half width can be correlated with increasing energy dissipation. Microhardness measurements demonstrate that recombinant spider silk and sericine-free Bombyx mori silk layers achieve higher elastic penetration modules EEP and Martens hardness values HM than those of polyethylenterephthalate (PET) and polyetherimide (PEI) foils.  相似文献   
895.
896.
Normal human, hemoglobin free erythrocyte ghosts were labelled with14C–N-Ethylmaleimide and incubated at two different temperatures 4°C and 37°C. Gel electrophoresis, autoradiography and nuclear scintillation counting techniques were used in analysing which proteins were labelled. The results of the experiments with incubation at 4°C and 37°C indicated that 35% of the NEM was associated with spectrin and 50% was bound to spectrin- actin complex.  相似文献   
897.
Iron alloys and aluminum were nitrogen implanted in a controlled oxygen atmosphere and the role of hydrogen on the surface etching mechanisms studied. The surface composition was analyzed by in situ photoemission electron spectroscopy (XPS). In iron alloys, hydrogen strongly etches oxygen, improving nitrogen retention on the surface. On the other hand, hydrogen removes nitrogen from aluminum surfaces, with a deleterious effect on the nitriding effectiveness. The oxygen removal in iron alloys is associated with the catalytic effect of electrons in d-orbitals and the nitrogen removal in aluminum is associated with a steric effect.  相似文献   
898.
Labour scheduling plays an important and critical role in Sainsburys day to day operations and profitability. The integrated workforce management solution for Sainsburys is an intelligent solution for the operational deployment of human resources, integrated business forecasting, generation and calculation of workload and staff scheduling. The workforce management technology has provided Sainsburys with a fully web-based and centralised system that produces optimised schedules for all employees satisfying the forecasted demand of work with granularity of fifteen minutes. The system is configured to respect all operational and business requirements as well as employee contractual constraints. This paper introduces the workforce management solution system designed, developed and implemented for Sainsburys. We concentrate on two modelling structures, namely the work pattern model and optimisation model, and briefly discuss the optimisation process.  相似文献   
899.
In this work, the high-spin ferric form of the E7Q mutant of human neuroglobin (E7Q-NGB) is studied by X-band continuous-wave electron paramagnetic resonance (CW EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy. It is shown that the use of matched pulses in the HYSCORE experiment is essential to observe the nitrogen spectral contributions. The validity of approximating the high-spin Fe(III) system (S=5/2) as an effectiveS=1/2 system is tested and the consequences for the HYSCORE simulations are highlighted. Comparative HYSCORE experiments combined with deuterium exchange experiments for aquometmyoglobin and ferric E7Q-NGB clearly show that the heme iron of the latter protein is pentacoordinated, lacking the distal water. Furthermore, CW EPR experiments show that, at high pH, the E10K residue is coordinating to the heme iron in this globin. These observations are corroborated by resonance Raman experiments and could also be reproduced for other E7 mutants of human and mouse neuroglobin. Finally, the proton and nitrogen hyperfine and nuclear quadrupole parameters obtained for ferric E7Q-NGB are discussed in detail.  相似文献   
900.
In this paper we describe the cold atom clock PHARAO, designed for microgravity operation. All elements of the PHARAO engineering model have been manufactured and delivered to CNES, the French space agency. We present the clock design, its main characteristics, and initial science operation. PHARAO is one of the main components of the Atomic Clock Ensemble in Space payload that is scheduled to fly on board the International Space Station in 2010. PACS 07.87.+v; 06.30.Ft; 95.55.Sh; 32.80.Pj  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