全文获取类型
收费全文 | 573141篇 |
免费 | 5766篇 |
国内免费 | 1597篇 |
专业分类
化学 | 302491篇 |
晶体学 | 8654篇 |
力学 | 26799篇 |
综合类 | 22篇 |
数学 | 68066篇 |
物理学 | 174472篇 |
出版年
2021年 | 5030篇 |
2020年 | 5412篇 |
2019年 | 6132篇 |
2018年 | 8179篇 |
2017年 | 8071篇 |
2016年 | 11876篇 |
2015年 | 7125篇 |
2014年 | 11359篇 |
2013年 | 26065篇 |
2012年 | 20159篇 |
2011年 | 24459篇 |
2010年 | 17850篇 |
2009年 | 17832篇 |
2008年 | 22738篇 |
2007年 | 22568篇 |
2006年 | 20666篇 |
2005年 | 18497篇 |
2004年 | 17200篇 |
2003年 | 15252篇 |
2002年 | 15207篇 |
2001年 | 16928篇 |
2000年 | 12816篇 |
1999年 | 10019篇 |
1998年 | 8299篇 |
1997年 | 8149篇 |
1996年 | 7809篇 |
1995年 | 7028篇 |
1994年 | 7002篇 |
1993年 | 6747篇 |
1992年 | 7564篇 |
1991年 | 7730篇 |
1990年 | 7372篇 |
1989年 | 7249篇 |
1988年 | 7211篇 |
1987年 | 7076篇 |
1986年 | 6694篇 |
1985年 | 8661篇 |
1984年 | 8867篇 |
1983年 | 7132篇 |
1982年 | 7223篇 |
1981年 | 7147篇 |
1980年 | 6624篇 |
1979年 | 7271篇 |
1978年 | 7403篇 |
1977年 | 7446篇 |
1976年 | 7391篇 |
1975年 | 6820篇 |
1974年 | 6725篇 |
1973年 | 6869篇 |
1972年 | 4972篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A. Ya. Samuilov L. A. Zenitova I. N. Bakirova Ya. D. Samuilov 《Russian Journal of Applied Chemistry》2008,81(8):1419-1422
Thermodynamic parameters of reactions of methyl and phenyl isocyanates with a series of compounds were determined by quantum-chemical calculations. The products of these reactions model for various functional groups present in commercial polyurethanes. The thermodynamic stability series for compounds formed from aliphatic and aromatic isocyanates were constructed. 相似文献
52.
M. K. Bratenko Yu. V. Kadel’nik V. A. Chornous M. V. Vovk 《Russian Journal of Organic Chemistry》2008,44(2):247-250
Oximes of 4-(4-pyrazolyl)-3-buten-2-onees obtained by successive reaction of 3-aryl-4-formylpyrazoles with acetone and hydroxylamine at the treatment with iodine suffered an oxidative cyclization yielding 3-aryl-4-(5-isoxazolyl)pyrazoles. 相似文献
53.
K. S. Trofimova V. G. Dronov N. S. Shaglaeva R. G. Sultangareev 《Russian Journal of Applied Chemistry》2008,81(4):730-731
Possibilities of utilization of by-products formed in manufacture of epichlorohydrin are considered. A promising way to utilize wastes from production of epichlorohydrin by synthesis of 2,3-dichloropropene from 1,2,3-trichloropropane is suggested. 相似文献
54.
S. A. Bulgakova A. I. Mashin I. A. Kazantseva D. E. Kashtanov M. M. Jones G. S. Tsepkov A. V. Korobkov A. V. Nezhdanov 《Russian Journal of Applied Chemistry》2008,81(8):1446-1451
Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined. 相似文献
55.
The dynamic structure factors (DSFs) of several strong glasses (SF6, SF10, BK7, SUPRASIL) measured by Brillouin light scattering spectroscopy are reported. Spectra have been collected, at and above room temperature, at two scattering angles, θ=90° and θ=180° corresponding to exchanged wavevector q values ranging from 0.0256 to 0.0448 nm−1. In particular we find that the isotropic spectral lineshapes are in all cases well described by the simple hydrodynamic theory of an amorphous solid. The width of the Brillouin peaks are found to be consistent with the predicted q2 dependence at both investigated temperatures. This damping is however found to account only partially for the strong asymmetry of the Brillouin line clearly visible on a logarithmic intensity scale. As a matter of fact there is an excess intensity in the very low frequency plateau underlying the central component. The height of this plateau and hence the entire lineshape is well reproduced if a relaxation process is taken into account in the hydrodynamic equations. Owing to the intense elastic scattering we are able to determine unambiguously only the ratio between amplitude and characteristic time of this process which quantifies the sound dispersion to be of the order of a few percent in all samples. The temperature dependence of the parameters indicates that this relaxation cannot be attributed to thermally activated relaxation phenomena. These general findings favorably compare with molecular dynamics simulation results on similar systems. 相似文献
56.
We consider the problem of determining the stress distributionin a finite rectangular elastic layer containing a Griffithcrack which is opened by internal shear stress acting alongthe length of the crack. The mode III crack is assumed to belocated in the middle plane of the rectangular layer. The followingtwo problems are considered: (A) the central crack is perpendicularto the two fixed lateral surfaces and parallel to the othertwo stress-free surfaces; (B) all the lateral surfaces of therectangular layer are clamped and the central crack is parallelto the two lateral surfaces. By using Fourier transformations,we reduce the solution of each problem to the solution of dualintegral equations with sine kernels and a weight function whichare solved exactly. Finally, we derive closed-form expressionsfor the stress intensity factor at the tip of the crack andthe numerical values for the stress intensity factor at theedges of the cracks are presented in the form of tables. 相似文献
57.
Electrohydrodynamic instability in homeotropically oriented nematic samples of 4'-n-octyl-4-cyano-biphenyl and 4'n-alkyloxy-4-cyanobiphenyl, (n = 8.9) have been studied in an a.c. electric field. The domain patterns during the instability in these compounds in a very low frequency a.c. field are very similar to those in a d.c. field. The domain patterns observed at higher frequencies have been identified as 'maltese crosses' or 'crossed isogyres'. The electro-convective 'isotropic' flows near the electrode play an important role in the observed instability. 相似文献
58.
W M Niessen M A de Kraa E R Verheij P J Bergers G F La Vos U R Tjaden J van der Greef 《Rapid communications in mass spectrometry : RCM》1989,3(1):1-4
On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL. 相似文献
59.
N. Vogel 《等离子体物理论文集》1989,29(1):11-24
The stepwise increase of the burning voltage of short break arcs has been found not only in a gas but also in vacuum. It is suggested that the effect is associated with the occurrence of a positive anode fall which enhances ionisation phenomena near the anode. This view is supported by the simultaneous registration of arc current, burning voltage, light emission from the anode region, of spectral lines of ions, atoms and continuum from the near anode plasma. The phenomena occur beyond a critical gap distance which can be related to the characteristic geometry of the discharge. 相似文献
60.
The synthesis and characterization of a new homologous series of compounds, the 2-cyano-1,3-phenylene bis[4-(4-n-alkoxyphenyliminomethyl)benzoates] derived from 2-cyanoresorcinol is reported. All the compounds are enantiotropic mesogens and exhibit the fascinating B7 mesophase. The characterization of the mesophase was performed using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies. 相似文献