全文获取类型
收费全文 | 275829篇 |
免费 | 2482篇 |
国内免费 | 1141篇 |
专业分类
化学 | 140865篇 |
晶体学 | 3959篇 |
力学 | 11786篇 |
综合类 | 14篇 |
数学 | 37175篇 |
物理学 | 85653篇 |
出版年
2020年 | 1778篇 |
2019年 | 2044篇 |
2018年 | 4313篇 |
2017年 | 4505篇 |
2016年 | 4712篇 |
2015年 | 3237篇 |
2014年 | 4388篇 |
2013年 | 11837篇 |
2012年 | 11312篇 |
2011年 | 12317篇 |
2010年 | 8177篇 |
2009年 | 7919篇 |
2008年 | 9504篇 |
2007年 | 9680篇 |
2006年 | 8914篇 |
2005年 | 13527篇 |
2004年 | 12307篇 |
2003年 | 9273篇 |
2002年 | 6592篇 |
2001年 | 7406篇 |
2000年 | 5436篇 |
1999年 | 4358篇 |
1998年 | 3634篇 |
1997年 | 3627篇 |
1996年 | 3320篇 |
1995年 | 3159篇 |
1994年 | 2975篇 |
1993年 | 3013篇 |
1992年 | 3420篇 |
1991年 | 3461篇 |
1990年 | 3244篇 |
1989年 | 3178篇 |
1988年 | 3230篇 |
1987年 | 3075篇 |
1986年 | 2954篇 |
1985年 | 4017篇 |
1984年 | 4170篇 |
1983年 | 3419篇 |
1982年 | 3765篇 |
1981年 | 3655篇 |
1980年 | 3528篇 |
1979年 | 3573篇 |
1978年 | 3794篇 |
1977年 | 3621篇 |
1976年 | 3884篇 |
1975年 | 3419篇 |
1974年 | 3552篇 |
1973年 | 3855篇 |
1972年 | 2360篇 |
1971年 | 1810篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Triorganotin(IV) and triorganolead(IV) derivatives of the types Me3Sn(SCZ) and Ph3Pb(SCZ) (where SCZ? is the anion of a semicarbanzone ligand) have been synthesized by substitution reactions of trimethyltin chloride and triphenyl-lead chloride with semicarbazones derived from heterocyclic ketones. The resulting complexes have been characterized by elemental analyses, molecualr weight determinations and conductivity measurements. The mode of bonding has been established on the basis of infrared and 1H, 13C and 119Sn NMR spectroscopic studies. Some respresentative complexes have also been evaluated for their antimicrobial effects on different species of pathogenic fungi and bacteria; the results of these investigations have been reported in the present paper. 相似文献
982.
M. A. Morón C. Romero F. R. Ruiz del Portal 《Journal of Optimization Theory and Applications》1996,91(3):643-649
The purpose of this paper is to seek utility functions satisfying a weak condition which guarantees that the utility optimum always belongs to the compromise set. This set is a special subset of the attainable or feasible set, which is generated through the application of the well-known operational research approach called compromise programming. It is shown that there are large families of utility functions satisfying this condition, thus reinforcing the value of compromise programming as a good surrogate of the traditional utility optimum.Thanks are due to the reviewers for their helpful suggestions. The English editing by Ms. Christine Méndez is appreciated. The authors have been supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT), Madrid, Spain. 相似文献
983.
The temperature disorder of copper ions in the CuCrS2 superionic conductor was studied by X-ray analysis. It is shown that the average square deviations of atoms sharply increase
and become comparable with the distance between neighbouring tetrahedral sites when CuCrS2 transforms into the superionic phase. It is also established that the direction of maximum deviation of atoms is close to
the direction connecting the tetrahedral positions. 相似文献
984.
985.
I. S. Dubenko I. V. Golosovsky E. Gratz R. Z. Levitin A. S. Markosyan I. Mirebeau S. V. Sharygin 《Journal of magnetism and magnetic materials》1995,150(3):304-310
The present neutron diffraction studies have confirmed that TmCo2 represents an exception within the RCo2 series. It was found that, in contrast with other heavy RCo2 compounds, the Co sublattice in TmCo2 does not order magnetically below the Curie temperature (Tc = 3.9 K). This is assumed to be due the fact that in TmCo2 the intersublattice (f-d) molecular field is smaller than the critical field necessary to induce magnetic order within the Co sublattice, as is the case in other RCo2 compounds. Furthermore, we show that the magnetic structure and the onset of long-range order in TmCo2 depend sensitively on the sample preparation, which partly explains the differing results published earlier. 相似文献
986.
We introduce a new class of experiments which provide graphic insights into the propagation of acoustic waves in anisotropic media. Simply stated, we have devised a means of observing the expanding acoustic wavefront from a point disturbance in a solid. The data may be viewed as a movie or a series of snapshots. The observed wavefronts represent the group-velocity surfaces of acoustic waves, which reflect the basic elastic anisotropy of the solid. The technique has been applied to coherent acoustic waves with frequencies in the megahertz range (at ambient temperatures) and to incoherent heat pulses in the hundred-gigahertz range (at liquid-helium temperatures). In this article, we first provide a pedagogical introduction to wave propagation in elastically anisotropic media, reviewing some early methods for visualizing acoustic waves. Next, we describe the “acoustic wavefront imaging” method and give representative results in crystals and composite materials. Finally, we show how this method relates to recent advances in phonon imaging and internal diffraction of ultrasound. 相似文献
987.
Zusammenfassung An feinpolierten, ölbeschichteten V2A-Oberflächen mit jeweils einer gebohrten (d=140 µm) und einer geätzten (d=47 µm) Vertiefung als Keimstelle wurde für Wasserblasen das Wachstum, der Abreißdurchmesser und die Abreißfrequenz gemessen. Für die wärmetransportgesteuerte Blasenbildung liefert der Vergleich mit Beziehungen, die für reine Metallflächen gewonnen wurden, gute Übereinstimmung, so daß keine Einfluß der Ölschicht erkennbar wurde.
Formelzeichen a Temperaturleitfähigkeit - D a Blasenabreißdurchmesser - f Blasenfrequenz - Ja Jakob-Zahl - Pr Prandtl-Zahl /a - q Wärmestromdichte - R Blasenradius - T Temperatur - dynamische Zähigkeit - Wärmeleitfähigkeit - Dichte - Oberflächenspannung - Zeit Indizes g Gas, Dampf - l flüssig - s Sättigung - w Wand Herrn Prof. Dr.-Ing. Karl Stephan zum 60. Geburtstag gewidmet 相似文献
Investigation of single vapor bubbles on surfaces covered with a thin oil film with artificial nuclei
For single vapor bubbles, the growth rates, the detachment diameter, and the frequency were measured on single artificial nuclei, either drilled (d=140 µm) or etched (d=47 µm) into a highly polished stainless steel plate which was covered with a thin oil film. For evaporation controlled by heat transport, good agreement was observed with relations from literature which were obtained for clean surfaces; thus, an effect of the oil film could not be discovered.
Formelzeichen a Temperaturleitfähigkeit - D a Blasenabreißdurchmesser - f Blasenfrequenz - Ja Jakob-Zahl - Pr Prandtl-Zahl /a - q Wärmestromdichte - R Blasenradius - T Temperatur - dynamische Zähigkeit - Wärmeleitfähigkeit - Dichte - Oberflächenspannung - Zeit Indizes g Gas, Dampf - l flüssig - s Sättigung - w Wand Herrn Prof. Dr.-Ing. Karl Stephan zum 60. Geburtstag gewidmet 相似文献
988.
I. R. Gulamov A. A. Karakhodzhaev A. M. Mukhamedzhanov G. K. Nie E. A. Pak R. Yarmukhamedov V. Burjan J. Cejpek V. Kroha J. Křemének M. Kurka 《Czechoslovak Journal of Physics》1990,40(8):875-894
The angular distributions of the (p, d), (d, t) and(3He, ) reactions on13C have been analysed within the framework of DWBA in which additional information on nuclear vertex constants was introduced. Although all these reactions seem to be similar single nucleon transfer, their mechanism is shown to be quite different and so is the information extracted thereof. While from the (p, d) reactions spectroscopic factors may be extracted unambiguously, from the (d, t) reactions it is possible to obtain directly the values of vertex constants only, which in turn are consistent with those determined by extrapolation of the experimental cross sections of the (p, d) reactions to the pole.In the case of (3He, ) reactions, however, the analysis indicates inadequacy of the DWBA concerning the calculations of central partial amplitudes. For a more reliable extraction of structural information, besides the correct normalization of peripheral amplitudes, a contribution of more complex mechanisms must be taken into account. 相似文献
989.
J. S. Bell's classic 1966 review paper on the foundations of quantum mechanics led directly to the Bell nonlocality theorem. It is not widely appreciated that the review paper contained the basic ingredients needed for a nonlocality result which holds in certain situations where the Bell inequality is not violated. We present in this paper a systematic formulation and evaluation of an argument due to Stairs in 1983, which establishes a nonlocality result based on the Bell-Kochen-Specker paradox in quantum mechanics. 相似文献
990.
The sensitivity of neutron-proton scattering observables to the recently reported charge-independence breaking of the isospinT=13
P nucleon-nucleon interaction has been calculated. It is shown that only the analyzing powerA
y
() at extreme forward angles and at =90° c.m. and the spin-correlation coefficientA
zx
() at 90° c.m. exhibit a measurable sensitivity. It is concluded that the determination ofA
y
at 90° c.m. is currently the most accurate approach to verify independently charge-independence breaking in the3
P nucleon-nucleon phase shifts, considering the status of present experimental techniques. 相似文献