全文获取类型
收费全文 | 433706篇 |
免费 | 6816篇 |
国内免费 | 2944篇 |
专业分类
化学 | 208338篇 |
晶体学 | 5917篇 |
力学 | 17032篇 |
综合类 | 101篇 |
数学 | 42206篇 |
物理学 | 117246篇 |
无线电 | 52626篇 |
出版年
2020年 | 3484篇 |
2019年 | 3637篇 |
2018年 | 4503篇 |
2017年 | 4358篇 |
2016年 | 6675篇 |
2015年 | 4505篇 |
2014年 | 6801篇 |
2013年 | 16796篇 |
2012年 | 12862篇 |
2011年 | 15489篇 |
2010年 | 11088篇 |
2009年 | 11219篇 |
2008年 | 15177篇 |
2007年 | 15834篇 |
2006年 | 15071篇 |
2005年 | 13969篇 |
2004年 | 12698篇 |
2003年 | 11487篇 |
2002年 | 11366篇 |
2001年 | 12221篇 |
2000年 | 9908篇 |
1999年 | 8102篇 |
1998年 | 7382篇 |
1997年 | 7255篇 |
1996年 | 6817篇 |
1995年 | 6449篇 |
1994年 | 6354篇 |
1993年 | 6027篇 |
1992年 | 6578篇 |
1991年 | 6625篇 |
1990年 | 6354篇 |
1989年 | 6081篇 |
1988年 | 6036篇 |
1987年 | 5479篇 |
1986年 | 5156篇 |
1985年 | 6708篇 |
1984年 | 7058篇 |
1983年 | 5938篇 |
1982年 | 6245篇 |
1981年 | 5987篇 |
1980年 | 5977篇 |
1979年 | 5926篇 |
1978年 | 6310篇 |
1977年 | 6160篇 |
1976年 | 6276篇 |
1975年 | 5834篇 |
1974年 | 5770篇 |
1973年 | 6179篇 |
1972年 | 4238篇 |
1971年 | 3453篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
G. J. Groenewald M. A. Petersen Y. Zucker 《Integral Equations and Operator Theory》1997,28(4):466-491
For an arbitrary rational matrix function, not necessarily analytic at infinity, the existence of a right canonical Wiener-Hopf factorization is characterized in terms of a left canonical Wiener-Hopf factorization. Formulas for the factors in a right factorization are given in terms of the formulas for the factors in a given left factorization. All formulas are based on a special representation of a rational matrix function involving a quintet of matrices. 相似文献
992.
N. Srinivasan R.C. Johnson N. Kasthurikrishnan P. Wong R.G. Cooks 《Analytica chimica acta》1997,350(3):128-271
An overview of membrane introduction mass spectrometry (MIMS) is presented and comparisons are made with other direct sample introduction techniques. Special attention is given to the unique advantages and the limitations of newer variants on the MIMS technique, including affinity MIMS, reverse-phase and trap MIMS. The salient features of the interfaces used in MIMS are summarized and the various membrane materials commonly used are delineated. The applicability of MIMS is illustrated via discussion of
- 1. (i) bioreactor monitoring (represented by yeast fermentation),
- 2. (ii) environmental monitoring (illustrated by analysis of contaminated ground water samples) and
- 3. (iii) on-line chemical reaction monitoring (exemplified by the photolysis of aryl esters).
993.
The specific heat C
total of crystalline and amorphous Eu2(MoO4)3 is measured in the temperature interval 4.5–30 K. The amorphous state is obtained by applying pressure ∼7 GPa at room temperature.
It is found that the specific heat of the crystal at T⩽7.5 K is described by a cubic function of temperature, while the specific
heat of the amorphous sample has a strongly non-Debye character in the entire experimental temperature interval. The curve
of C
total for amorphous europium molybdate is analyzed in a model of soft atomic potentials, and it is shown that it agrees well with
universal low-temperature anomalies of the specific heat of classical glasses obtained by quenching from the liquid.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 623–627 (25 October 1998) 相似文献
994.
This paper studies a particular single-stage power-factor-correction (PFC) switching regulator employing a discontinuous-conduction-mode (DCM) boost-input cell and a continuous-current-mode (CCM) forward output cell. Although this single-stage PFC regulator can provide a reasonably high power factor when its PFC stage is operating in discontinuous mode, substantial reduction in line-current harmonics is possible by applying a suitable frequency-modulation scheme. This paper derives a frequency-modulation scheme and proposes a practical implementation using a simple translinear analog circuit. A quantitative analysis on the total harmonic distortion (THD) of the line current when the circuit is subject to a limited range of frequency variations is presented along with some considerations for practical design. Experimental data obtained from a prototype confirms the effectiveness of the proposed frequency-modulation scheme. The proposed analog translinear circuit allows custom integrated circuit implementation, making it a viable low-cost solution to the elimination of line-current harmonics in switching regulators 相似文献
995.
996.
We present an update of Garland's work on the cohomology of certain groups, construct a class of groups many of which satisfy
Kazhdan's Property (T) and show that properly discontinuous and cocompact groups of automorphisms of (4,4) or (6,3)-complexes
do not satisfy Property (T).
Submitted: September 1996, final version: March 1997 相似文献
997.
Candelier P. Mondon F. Guillaumot B. Reimbold G. Martin F. 《Electron Device Letters, IEEE》1997,18(7):306-308
A simplified flash EEPROM process was developed using high-temperature LPCVD oxide both as flash cells interpoly dielectrics and as peripheral transistors gate oxide (decoding logic). An O2 anneal at 850°C lowers charge trapping and interface trap density induced by Fowler-Nordheim injection. However, electron trapping remains slightly higher than with dry thermal oxide. Similar memory charge loss and write-erase endurance are obtained as for ONO-insulated cells. HTO thus proves to have the required quality and reliability to be used in flash EEPROMs 相似文献
998.
E. M. Telles J. C. S. Moraes A. Scalabrin D. Pereira G. Carelli C. A. Massa A. Moretti F. Strumia 《Journal of Infrared, Millimeter and Terahertz Waves》1995,16(12):2233-2248
We used a Stark-Optoacoustic cell and hybrid waveguide resonators to perform an Infrared and Far Infrared Stark Spectroscopy study on some transitions of13CD3OH. Different behaviours of the transitions in the presence of a d.c. electric field were observed. The Stark splittings of six FIR laser lines ranging from 34 to 136 MHz/kVcm?1 were determined. The analysis of the behaviour of the IR and FIR transitions in the presence of the external electric fields gives important and exclusive information on the levels involved in the transitions. 相似文献
999.
Magnetic Properties of the Cobaltates Na6CoS4, Na6CoSe4, and K6CoS4 The alkali metal cobalt chalcogenides Na6CoS4, Na6CoSe4, and K6CoS4 crystallize in the space group P63mc with Z = 4. The structure is characterized by isolated [CoX4]-tetrahedra. The magnetic susceptibilities show Curie-Weiss behaviour. The deviations at low temperatures are caused by antiferromagnetic interactions. The magnetic moments are discussed with regard to ligand-field parameters. 相似文献
1000.
Modified Stern-Volmer equation is obeyed by bovine serum albumin (BSA)-iodide system showing selective quenching of tryptophanyl
fluorescence of BSA. The fraction of accessible protein fluorescence is 0.56 and the effective Stern-Volmer constant is 290
M-1 at pH 7.4 in 0.005 M phosphate buffer at 25°C. Collisional quenching is operative both in the BSA -I−1 system and the model system, tryptophan-I−1. It is supported by the observed relationship between the ratio of quenching rate constants (k
q
) and diffusion coefficients and alsok
q
with bulk viscosity. 相似文献