全文获取类型
收费全文 | 278633篇 |
免费 | 4982篇 |
国内免费 | 1347篇 |
专业分类
化学 | 158503篇 |
晶体学 | 3546篇 |
力学 | 9945篇 |
综合类 | 62篇 |
数学 | 35748篇 |
物理学 | 77158篇 |
出版年
2021年 | 2080篇 |
2020年 | 2620篇 |
2019年 | 2727篇 |
2018年 | 3652篇 |
2017年 | 3606篇 |
2016年 | 5822篇 |
2015年 | 4139篇 |
2014年 | 5283篇 |
2013年 | 12691篇 |
2012年 | 11359篇 |
2011年 | 12947篇 |
2010年 | 8907篇 |
2009年 | 8360篇 |
2008年 | 11992篇 |
2007年 | 11904篇 |
2006年 | 11156篇 |
2005年 | 10311篇 |
2004年 | 9096篇 |
2003年 | 7905篇 |
2002年 | 7645篇 |
2001年 | 7737篇 |
2000年 | 6082篇 |
1999年 | 4417篇 |
1998年 | 3637篇 |
1997年 | 3532篇 |
1996年 | 3689篇 |
1995年 | 3131篇 |
1994年 | 3282篇 |
1993年 | 3120篇 |
1992年 | 3409篇 |
1991年 | 3366篇 |
1990年 | 3195篇 |
1989年 | 3015篇 |
1988年 | 2956篇 |
1987年 | 2874篇 |
1986年 | 2890篇 |
1985年 | 3817篇 |
1984年 | 3842篇 |
1983年 | 3165篇 |
1982年 | 3416篇 |
1981年 | 3224篇 |
1980年 | 2970篇 |
1979年 | 3121篇 |
1978年 | 3313篇 |
1977年 | 3346篇 |
1976年 | 3396篇 |
1975年 | 3063篇 |
1974年 | 3182篇 |
1973年 | 3243篇 |
1972年 | 2461篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The purpose of the present study was to describe the effects ofacute laryngitis on some aerodynamic, acoustic, and perceptual measures. Eleven subjects with diagnosed acute laryngitis due to upper respiratory infection were recorded during a laryngitic episode and 1 week to 10 days after amelioration of the laryngitic condition. Fundamental frequency values, collapsed across the five vowels, were significantly reduced in the laryngitic compared with the normal speaking condition. The decrease in fundamental frequency associated with acute laryngitis suggests an increase in the mass of the vocal folds. In addition, aerodynamic values differed significantly for the laryngitic condition compared with the normal speaking condition, suggesting the presence of laryngeal hypofunction. Perceptual data indicated that speakers in the laryngitic condition were judged to have a hoarse voice when compared with the normal speaking condition. 相似文献
992.
Parkansky N. Boxman R.L. Goldsmith S. Rosenberg Yu. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(4):543-547
Electrical contact lifetime is often directly determined by arc erosion. A method for reducing are erosion was developed consisting of injecting from an external current source an additional electrical current flowing parallel to the contact surface. This method was examined in three are environments using the additional transverse electrical current with a density less than 1 A/mm2: 1) automobile ignition contacts; 2) pulsed air arc; and 3) low pressure (P=100 mTorr) arc in nitrogen, SEM and X-ray examination showed that application of a transverse current in a contact during arcing changed the phase composition and microstructure of the contact surface. Under optimal conditions, the microstructure which is formed is significantly more erosion resistant than without the transverse current injection 相似文献
993.
We describe high order numerical algorithms for the solution of second order elliptic equations in rectangular domains. These
algorithms are based on the Fourier method in combination with a subtraction procedure. The singularities at the corner points,
arising due to non-smoothness of the boundaries, are treated explicitly using properly constructed singular corner functions.
The present algorithm is a generalization of the Fast Poisson Solver developed in our previous paper.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
994.
995.
The sulphur K-edge x-ray absorption spectra of SO2 multilayer and of SO2 submonolayer adsorbed on Cu(100) are analysed. It is found that the dominant spectral features are of a molecular origin. The results support earlier findings that the SO2 molecule stands perpendicular to the surface. Use of non-selfconsistent potentials does not lead to a good quantitative agreement between theory and experiment. 相似文献
996.
C Z Shi Z Y Zhang L Z Zhuang 《Science in China. Series B, Chemistry, life sciences & earth sciences》1991,34(9):1098-1104
The effect of hormones on progesterone secretion by 6-8 week human trophoblast tissue cultured in serum-free medium has been investigated. GnRH at low concentration (10(-10)-10(-8) mol/L) stimulated progesterone secretion, while high dose (10(-6)-10(-5) mol/L) produced inhibitory effect. The progesterone secretion could be significantly decreased by addition of anti-hCG antiserum or monoclonal anti-hCG IgG in a dose- and time-dependent manner. Various concentrations of TRH, PGE2, PGF2 alpha, testosterone and estradiol were found to be ineffective. These data indicate clearly that progesterone production by human trophoblast tissue at early gestation stage is under the modulation of GnRH and hCG. 相似文献
997.
S. G. Barsov A. L. Getalov S. L. Ginsburg V. P. Koptev S. P. Kruglov L. A. Kuzmin S. V. Maleyev E. I. Maltsev S. M. Mikirtychyants N. A. Tarasov G. V. Shcherbakov V. G. Grebinnik V. N. Duginov A. B. Lazarev V. G. Olshevski S. N. Shilov V. A. Zhukov I. I. Gurevich B. F. Kirillov A. I. Klimov B. A. Nikolski A. V. Pirogov A. N. Ponomarev V. A. Suetin 《Hyperfine Interactions》1991,64(1-4):415-419
The zero field μSR-method has been used to study the magnetism in the disordered magnetic alloy Fe82−xNixCr18 near the three-critical, pointx=25. The dynamic and static local field distributions are analyzed. The difference between spin-glass states obtained either
from the paramagnetic or after the double transition is discussed. 相似文献
998.
999.
The radiative capture of ultracold neutrons traversing thin and thick homogeneous layers of matter is analyzed. The applicability range of the formulas for the probabilities of reflection, transmission, and capture in thick layers (under certain conditions, they admit a simple interpretation—it is often quoted in the literature—that is based on the effective capture cross section, which is in inverse proportion to the velocity of a neutron in matter) is investigated, along with the conditions under which there arises the effective capture cross section. 相似文献
1000.
V. P. Koshelets S. V. Shitov L. V. Filippenko P. N. Dmitriev A. N. Ermakov A. S. Sobolev M. Yu. Torgashin 《Radiophysics and Quantum Electronics》2003,46(8-9):618-630
We overview recent achievements in the field of cryogenic submillimeter-wave receivers based on superconductor–insulator–superconductor (SIS) tunnel junctions. The main attention is paid to the novel superconducting integrated receivers (SIRs) with an on-chip superconducting local oscillator. The single-chip microcircuit of the receiver, which integrates a quantum mixer based on the nonlinearity of a quasi-particle current in the SIS junction, a planar superconducting receiving antenna, and a cryogenic local oscillator, is described. Being dc-powered only by batteries, such a microcircuit operates as a submillimeter-wave superheterodyne receiver without any additional microwave equipment. Such receivers are very attractive for radioastronomical research, space communication systems, and monitoring of the environment from satellites, balloons, and special aircraft. A breadboard of a superconducting spectrometer with a phase-locked flux-flow oscillator (FFO) has been developed and tested. A frequency resolution better than 10 kHz was reached at a frequency of 365 GHz. We describe a balloon-borne 500-650 GHz integrated spectrometer for oblique atmospheric sounding, developed for the international Terahertz Limb Sounder (TELIS) project. The first flight is scheduled for 2005. 相似文献