全文获取类型
收费全文 | 603755篇 |
免费 | 5095篇 |
国内免费 | 1861篇 |
专业分类
化学 | 294980篇 |
晶体学 | 9052篇 |
力学 | 31532篇 |
综合类 | 16篇 |
数学 | 94259篇 |
物理学 | 180872篇 |
出版年
2021年 | 4286篇 |
2020年 | 4724篇 |
2019年 | 5312篇 |
2018年 | 16934篇 |
2017年 | 16892篇 |
2016年 | 16061篇 |
2015年 | 6836篇 |
2014年 | 10255篇 |
2013年 | 24084篇 |
2012年 | 21503篇 |
2011年 | 31423篇 |
2010年 | 21128篇 |
2009年 | 21419篇 |
2008年 | 26014篇 |
2007年 | 27971篇 |
2006年 | 18763篇 |
2005年 | 17541篇 |
2004年 | 16545篇 |
2003年 | 15379篇 |
2002年 | 14410篇 |
2001年 | 15679篇 |
2000年 | 12002篇 |
1999年 | 9290篇 |
1998年 | 7974篇 |
1997年 | 7834篇 |
1996年 | 7412篇 |
1995年 | 6589篇 |
1994年 | 6642篇 |
1993年 | 6307篇 |
1992年 | 6985篇 |
1991年 | 7168篇 |
1990年 | 6927篇 |
1989年 | 6723篇 |
1988年 | 6598篇 |
1987年 | 6667篇 |
1986年 | 6329篇 |
1985年 | 8123篇 |
1984年 | 8411篇 |
1983年 | 7027篇 |
1982年 | 7201篇 |
1981年 | 6885篇 |
1980年 | 6844篇 |
1979年 | 7063篇 |
1978年 | 7390篇 |
1977年 | 7250篇 |
1976年 | 7280篇 |
1975年 | 6739篇 |
1974年 | 6798篇 |
1973年 | 7007篇 |
1972年 | 4973篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
72.
Using Wagner's polarization technique and EMF method the joinic and silver ionic transport number measurements of various
compositions of the mixed system CdI2-Ag2O-CrO3 have been made. The presence of AgI in these materials has been inferred from the typical β → α phase transition of AgI,
which is characterized by an endothermic peak at around 420 K in the DSC traces of these specimens. While the structural analysis
performed by means of powder X-ray diffraction has revealed the formation of ionic phases involving polycrystalline compounds,
the Fourier transform infrared (FTIR) spectroscopic results have indicated the presence of ionic species thus confirming the
ionic nature of the products. The complex impedance studies carried out in the frequency range 20 Hz - 1 MHz and over the
temperature range 294 – 442 K have revealed that the best conducting composition, namely 55%(CdI2) – 45%(Ag2O·CrO3), would exhibit a silver ionic conductivity of 1.3×10−5Scm−1 at 294 K. 相似文献
73.
de Souza P. A. Garg V. K. Klingelhöfer G. Gellert R. Gütlich P. 《Hyperfine Interactions》2002,139(1-4):705-714
A portable Mössbauer spectrometer, developed for extraterrestrial applications, opens up new industrial applications of MBS. But for industrial applications, an available tool for fast data analysis is also required, and it should be easy to handle. The analysis of Mössbauer spectra and their parameters is a barrier for the popularity of this wide-applicable spectroscopic technique in industry. Based on experience, the analysis of a Mössbauer spectrum is time-consuming and requires the dedication of a specialist. However, the analysis of Mössbauer spectra, from the fitting to the identification of the sample phases, can be faster using by genetic algorithms, fuzzy logic and artificial neural networks. Industrial applications are very specific ones and the data analysis can be performed using these algorithms. In combination with an automatic analysis, the Mössbauer spectrometer can be used as a probe instrument which covers the main industrial needs for an on-line monitoring of its products, processes and case studies. Some of these real industrial applications will be discussed. 相似文献
74.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
75.
Discharges with liquid nonmetallic electrodes of much interest for applications are investigated. It is found that a dc discharge between two streams of tap water in air at atmospheric pressure is stable at a currentof 40≤I≤100 mA. The discharge exists in the diffuse (volume) form with a relatively low current density (∼0.2 A/cm2) and a high (above one kilovolt) voltage drop across the air gap (∼1 cm) between the water electrodes. The current density and voltage depend only slightly on the discharge current. Probe measurements show that three regions can be distinguished in the discharge: two electrode regions (1–2 mm in length) and a discharge column with a constant electric field of ≈0.8 kV/cm (i.e., E/N≈20 Td, because the gas in the discharge is heated up to 1500–2000 K). The average electric field strength near the electrodes is E≈2–3×103 V/cm (E/N≈60–80 Td). The charged particle density in the column is n ∼ 1012 cm−3. The probe measurements of n agree with the previous microwave absorption measurements. The water vapor concentration in the column is also estimated from probe measurements. 相似文献
76.
The present paper analyzes the properties of structural phase transitions under the extremal conditions of high pressures. In the context of the theory of density functional (TDF), the pressures of the B1–B2 transitions are calculated for small alkali-halide crystals as functions of the crystal size. The size effect of the B1–B2 transition – an increase in the transition pressure with the decreasing crystal grain radius – has been established for all investigated halides except lithium fluoride for which the dependence is reverse. 相似文献
77.
We calculate the leading and next-to-leading logarithmic resummed distribution for the jet broadening in deep inelastic scattering,
as well as the power correction for both the distribution and mean value. A truncation of the answer at NLL accuracy, as is
standard, leads to unphysical divergences. We discuss their origin and show how the problem can be resolved. We then examine
DIS specific procedures for matching to fixed order calculations and compare our results to the data. One of the tools developed
for the comparison is an NLO parton distribution evolution code. When compared to PDF sets from MRST and CTEQ it reveals limited
discrepancies in both.
Received: 16 October 2001 / Published online: 12 April 2002 相似文献
78.
Sanzharov N. A. Yarovoi A. T. Bekhtereva E. S. Ulenikov O. N. 《Russian Physics Journal》2002,45(10):1024-1031
Analytical formulas are derived that describe the dependences of the transition probabilities in vibrational-rotational spectra of XY3-type molecules with C
3v
symmetry on the rotational quantum numbers. 相似文献
79.
S. A. Vakulenko 《Journal of Mathematical Sciences》1991,57(3):3093-3096
A generalization of Whitham's asymptotic principle for parabolic equations is stated. An application of this principle to Fisher's one-dimensional nonlinear equation is considered.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Vol. 179, pp. 46–51, 1989. 相似文献
80.