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   401033篇
  免费   3735篇
  国内免费   1250篇
化学   211316篇
晶体学   6896篇
力学   17688篇
综合类   12篇
数学   42889篇
物理学   127217篇
  2020年   3251篇
  2019年   3681篇
  2018年   4571篇
  2017年   4565篇
  2016年   6825篇
  2015年   4245篇
  2014年   6915篇
  2013年   17707篇
  2012年   12936篇
  2011年   15928篇
  2010年   11309篇
  2009年   11269篇
  2008年   14552篇
  2007年   14433篇
  2006年   13610篇
  2005年   12333篇
  2004年   11315篇
  2003年   10223篇
  2002年   9994篇
  2001年   12013篇
  2000年   9166篇
  1999年   7131篇
  1998年   5817篇
  1997年   5718篇
  1996年   5471篇
  1995年   5035篇
  1994年   4895篇
  1993年   4815篇
  1992年   5532篇
  1991年   5561篇
  1990年   5312篇
  1989年   5264篇
  1988年   5326篇
  1987年   5228篇
  1986年   4946篇
  1985年   6577篇
  1984年   6782篇
  1983年   5368篇
  1982年   5636篇
  1981年   5605篇
  1980年   5310篇
  1979年   5745篇
  1978年   5820篇
  1977年   5877篇
  1976年   5765篇
  1975年   5263篇
  1974年   5286篇
  1973年   5257篇
  1972年   3679篇
  1968年   3114篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Role of readily hydrolyzable polysaccharides of larch wood in production of board materials is studied.  相似文献   
992.
X-ray reflectivity (XRR), X-ray fluorescence (XRF) and small angle X-ray scattering (SAXS) techniques are used to the monitoring of Cu/porous low κ processes, which are developed for the next generation (≤65 nm) integrated circuits. Sensitivity of XRR and XRF is sufficient to detect drifts of the copper barrier layer, copper seed layer and Cu CMP (chemical-mechanical polishing) processes. Their metrology key parameters comply with production requirements. SAXS allows determining the pore structure of low κ films: average pore size and pore size distribution.  相似文献   
993.
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated.  相似文献   
994.
995.
An energy-dependent partitioning scheme is explored for extracting a small number of eigenvalues of a real symmetric matrix with the help of genetic algorithm. The proposed method is tested with matrices of different sizes (30 × 30 to 1000 × 1000). Comparison is made with Löwdin’s strategy for solving the problem. The relative advantages and disadvantages of the GA-based method are analyzed  相似文献   
996.
This paper presents our recent simulation results and novel designs of single mode large cross-section glass-based waveguides for photonic integrated circuits (PICs). Simulations were performed using an in-house Finite Difference (FD) based mode solver and the FD Beam propagation Method (FD-BPM). Our simulation results show that this innovative technology could provide a simplified means to couple optical energy efficiently between optical components in a single chip. This would provide the base for the future large-scale integration of optical components in PICs. The novel idea of using single mode large cross-section glass-based waveguides as an optical integration platform is an evolutionary innovative solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. This allows easy and efficient optical coupling between optical components and optical fibres, removing costly and tedious alignment problems and considerably reducing optical coupling losses in PICs. We expect that the glass-based waveguide PICs technology will enable the emergence of a new generation of compact, reliable, high speed, and multifunctional devices.  相似文献   
997.
It is shown that the presence of mixed-culture growth in batch fermentation processes can be very accurately inferred from total biomass data by means of the wavelet analysis for singularity detection. This is accomplished by considering simple phenomenological models for the mixed growth and the more complicated case of mixed growth on a mixture of substrates. The main quantity provided by the wavelet analysis is the Hölder exponent of the singularity that we determine for our illustrative examples. The numerical results point to the possibility that Hölder exponents can be used to characterize the nature of the mixed-culture growth in batch fermentation processes with potential industrial applications. Moreover, the analysis of the same data affected by the common additive Gaussian noise still lead to the wavelet detection of the singularities although the Hölder exponent is no longer a useful parameter.  相似文献   
998.
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   
999.
1000.
In the present paper, we study the rate of convergence in simultaneous approximation for the Bézier variant of the Baskakov-Beta operators by using the decomposition technique of functions of bounded variation.  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