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   2835篇
  免费   111篇
  国内免费   41篇
化学   1745篇
晶体学   21篇
力学   105篇
数学   570篇
物理学   546篇
  2023年   31篇
  2022年   85篇
  2021年   99篇
  2020年   115篇
  2019年   121篇
  2018年   84篇
  2017年   72篇
  2016年   157篇
  2015年   97篇
  2014年   123篇
  2013年   177篇
  2012年   202篇
  2011年   198篇
  2010年   111篇
  2009年   99篇
  2008年   124篇
  2007年   125篇
  2006年   109篇
  2005年   97篇
  2004年   83篇
  2003年   42篇
  2002年   67篇
  2001年   32篇
  2000年   43篇
  1999年   24篇
  1998年   32篇
  1997年   20篇
  1996年   22篇
  1995年   16篇
  1994年   24篇
  1993年   21篇
  1992年   18篇
  1991年   20篇
  1990年   16篇
  1989年   15篇
  1988年   22篇
  1987年   19篇
  1986年   12篇
  1985年   20篇
  1984年   19篇
  1983年   5篇
  1982年   32篇
  1981年   25篇
  1980年   22篇
  1979年   28篇
  1978年   7篇
  1977年   11篇
  1976年   10篇
  1975年   6篇
  1974年   6篇
排序方式: 共有2987条查询结果,搜索用时 9 毫秒
51.
A novel method combining the experimental data at only two different mixed mode fractures and an empirical interface toughness function has been proposed to establish the interfacial toughness function of a bimaterial in submicron scale. The modified four-point bend specimen was used in experiment to evaluate the first type of mixed mode fracture, while the sandwiched cantilever specimen was employed to get the second one. An empirical interface toughness function reflecting quite accurately the delamination behavior was adopted as a typical one. The obtained results investigated that the proposed method could be used to calibrate not only the interfacial fracture criteria at pure modes but also at any mixed mode fracture of bimaterials in submicron scale.  相似文献   
52.
53.
54.
55.
Let Z denote a Hermite process of order q1 and self-similarity parameter H(12,1). This process is H-self-similar, has stationary increments and exhibits long-range dependence. When q=1, it corresponds to the fractional Brownian motion, whereas it is not Gaussian as soon as q?2. In this paper, we deal with a Vasicek-type model driven by Z, of the form dXt=a(b?Xt)dt+dZt. Here, a>0 and bR are considered as unknown drift parameters. We provide estimators for a and b based on continuous-time observations. For all possible values of H and q, we prove strong consistency and we analyze the asymptotic fluctuations.  相似文献   
56.
An extension of a capillary electrophoresis instrument coupled to a sequential injection analysis manifold was developed for automated measurements with on-line solid-phase extraction preconcentration. An in-house built capacitively coupled contactless conductivity detector was employed for sensitive detection with narrow capillaries of 25 μm internal diameter. The system was assembled into standardized 19 in. frames and racks for easy transport and mobile deployment. The system can be left running unattendedly without manual intervention with good operation stability. To demonstrate the application of the system, a method for the determination of four drugs, namely ibuprofen, diclofenac, naproxen and bezafibrate, was developed with enrichment factors of up to several hundreds. Detection of the drug residues down to the nM-scale was found possible and the method was found suitable for the detection of ibuprofen in the waste water of a hospital in Hanoi.  相似文献   
57.
Abstract

The reaction of potassium isopropyl dithiocarbonate with 4-chloro-3,5-dinitrobenzotrifluoride in dimethylformamide at 25–30°C afforded the titled phenothiazine (1) and sulfide (2). The reaction of bis(2,6-dinitro-4-trifluoromethylphenyl)-sulfide or the above halogen compound with sodium hydrosulfide in the same solvent at 80–90°C furnished 1. At 25–30°C the latter reaction afforded the titled disulfide (3). Possible mechanisms and supporting nmr, ir and mass spectral data are discussed.  相似文献   
58.
Thermoluminescence response at different irradiation temperatures and photon energies has been studied. Analyses of the glow curve and the peak height of TLD 200, 600, 700 and CaSO4:Dy for irradiations using 60Co, 137Cs and 226Ra were made.  相似文献   
59.
Using the Fourier transform spectra of the acetylene molecule recorded near 1.5-μm, the intensities of 111 lines belonging to seven hot bands of the main isotopologue 12C2H2 have been retrieved by means of a multispectrum fitting procedure. Considering the density of lines in the spectra, and the fact that the measured bands are the weakest observed, the accuracy of the measurements is around 10%. At first stage, an empirical treatment of these data has been performed, leading to the vibrational transition dipole moment squared and some Herman–Wallis coefficients. Then the measured line intensities of this work and collected ones from the literature have been treated simultaneously within the framework of the effective operator approach.  相似文献   
60.
Abstract

The reaction of electron-rich alkynes such as ethoxyacetylene or propynyldiethylamine with a transient terminal phosphinidene complex such as [PhP?W(CO)5] directly yields the corresponding phosphole complexes via a formal [2 + 2 + I] cycloaddition involving two molecules of alkyne and one phosphorus center.  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