全文获取类型
收费全文 | 5385篇 |
免费 | 77篇 |
国内免费 | 16篇 |
专业分类
化学 | 3145篇 |
晶体学 | 24篇 |
力学 | 60篇 |
综合类 | 1篇 |
数学 | 594篇 |
物理学 | 1654篇 |
出版年
2020年 | 58篇 |
2019年 | 39篇 |
2018年 | 43篇 |
2016年 | 60篇 |
2015年 | 57篇 |
2014年 | 72篇 |
2013年 | 115篇 |
2012年 | 152篇 |
2011年 | 189篇 |
2010年 | 125篇 |
2009年 | 93篇 |
2008年 | 160篇 |
2007年 | 191篇 |
2006年 | 183篇 |
2005年 | 166篇 |
2004年 | 170篇 |
2003年 | 150篇 |
2002年 | 124篇 |
2001年 | 118篇 |
2000年 | 96篇 |
1999年 | 91篇 |
1998年 | 80篇 |
1997年 | 76篇 |
1996年 | 95篇 |
1995年 | 95篇 |
1994年 | 107篇 |
1993年 | 97篇 |
1992年 | 118篇 |
1991年 | 82篇 |
1990年 | 65篇 |
1989年 | 62篇 |
1988年 | 73篇 |
1987年 | 71篇 |
1986年 | 71篇 |
1985年 | 74篇 |
1984年 | 66篇 |
1983年 | 61篇 |
1982年 | 78篇 |
1981年 | 64篇 |
1980年 | 56篇 |
1979年 | 63篇 |
1978年 | 67篇 |
1977年 | 55篇 |
1976年 | 51篇 |
1975年 | 51篇 |
1974年 | 51篇 |
1973年 | 71篇 |
1972年 | 38篇 |
1971年 | 41篇 |
1956年 | 31篇 |
排序方式: 共有5478条查询结果,搜索用时 0 毫秒
41.
A reactive ionized cluster beam technique (RICB) which was composed of a conventional ICB source and a radical beam source has been used to deposit stable and metastable polycrystalline AlNx (0≤x≤1) films. Using in-situ high energy electron diffraction (HEED) at grazing incidence geometry, crystallographic properties such as structure, preferred orientation and interplanar dspacing values were determined and the relation to deposition parameters investigated. It could be shown that the simultaneous use of the ICB technique and a radical beam source to separately control the kinetic energy of the Al ions and the dissociation rate of molecular nitrogen, allows AlN films to be deposited with variable composition and crystal structures. In-situ HEED used in the transmission mode is an effective tool to investigate the crystallography of growing compound films such as AlNx. 相似文献
42.
Balawant S. Joshi Narayanan Viswanathan Dilip H. Gawad Venkatachalam Balakrishnan Wolfgang von Philipsborn 《Helvetica chimica acta》1975,58(8):2295-2305
Three new alkaloids designated as cyclostachine A (2), cyclostachine B (7) and cyclopiperstachine (10) have been isolated from Piper trichostachyon C. DC. Their structures have been derived on the basis of spectral and degradative studies and confirmed by synthesis. The 1H- and 13C-NMR. spectra of these compounds are discussed. 相似文献
43.
D. Müller J. Gassen F. Scheuer H. D. Sträter P. von Brentano 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,18(3):249-255
We propose a new experimental method (Autocollimation Spectroscopy), which provides a strong suppression of systematic error contributions in the laser resonance spectroscopy of broad resonances. Using a bidirectional laser beam with a fixed wavelength in connection with high current pulsed ion beams an accuracy ofΔE Exp/Γ≈5·10?5 (Γ: resonance width) for the resonance energy seems to be achievable. Applying this technique to 2S-Lamb shift (LS) measurements on medium heavy ions would yield a precision ofΔE Exp/E LS≈1·10?5, i.e. an improvement by a factor up to 100 as compared to present experiments. 相似文献
44.
László von Szentpály Patricio Fuentealba Heinzwerner Preuss Hermann Stoll 《Chemical physics letters》1982,93(6):555-559
Semi-empirical pseudopotentials are used in calculating the ground-state potentials curves for single valence-electron molecular ions. Very accurate results are obtained and a number of predictions given. The ionization energies of the neutral dimers are evaluated. A spectroscopic rule enables us to estimate the A 1Σ+ state of KRb and RbCs. 相似文献
45.
van Heijnsbergen D von Helden G Meijer G Maitre P Duncan MA 《Journal of the American Chemical Society》2002,124(8):1562-1563
The organometallic ions V+-(benzene) and V+-(benzene)2 are produced by laser vaporization in a pulsed nozzle source. They are trapped and mass selected in an ion-trap/time-of-flight mass spectrometer, and their infrared spectra are measured with resonance-enhanced multiphoton photodissociation (IR-REMPD) spectroscopy with a tunable free-electron laser. Vibrational bands in the 600-1800 cm-1 region are characteristic of the benzene molecular moiety perturbed by the metal cation bonding. Experimental data are compared to the IR spectra derived from density functional calculations. Vibrational patterns in V+-(C6H6) indicate that the metal is bound in an eta6 pi-bonding configuration, while V+-(C6H6)2 is a sandwich. Trapped-ion IR-REMPD is a general method to access the vibrational spectroscopy of organometallic ions and their clusters. 相似文献
46.
von Bohlen und Halbach O 《Current protein & peptide science》2005,6(4):355-371
The brain renin-angiotensin system enables the formation of different biological active forms of angiotensins within the brain. All enzymes and peptides necessary for the biosynthesis of these angiotensins have been recognized within the central nervous system. Since there are considerable mismatches concerning the localization of the different enzymes, this system is not fully understood. Moreover, since alternative pathways of the angiotensin biosynthesis exists, localization and generation, especially of the short forms of biologically active angiotensins, are largely enigmatic. The brain renin-angiotensin system mediates several classic physiological effects including body water balance, maintenance of blood pressure, sexual behaviors, and regulation of pituitary gland hormones. Beside these classic functions, the brain renin-angiotensin system has more subtle functions involving complex mechanisms such as learning and memory. The mechanisms of action seem to differ depending on the utilized different bioactive angiotensin fragments, which are formed by the action of a variety of enzymes. This phenomenon appears to represent an important mechanism for neuromodulation. Moreover, there is evidence to suggest that the renin-angiotensin system is involved in neurological disorders, as e.g. Alzheimer's or Parkinson's disease. 相似文献
47.
Quadratically constrained least squares and quadratic problems 总被引:9,自引:0,他引:9
Summary We consider the following problem: Compute a vectorx such that Ax–b2=min, subject to the constraint x2=. A new approach to this problem based on Gauss quadrature is given. The method is especially well suited when the dimensions ofA are large and the matrix is sparse.It is also possible to extend this technique to a constrained quadratic form: For a symmetric matrixA we consider the minimization ofx
T
A
x–2b
T
x subject to the constraint x2=.Some numerical examples are given.This work was in part supported by the National Science Foundation under Grant DCR-8412314 and by the National Institute of Standards and Technology under Grant 60NANB9D0908. 相似文献
48.
49.
50.