首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   174483篇
  免费   1647篇
  国内免费   515篇
化学   90810篇
晶体学   3121篇
力学   7299篇
综合类   3篇
数学   19618篇
物理学   55794篇
  2020年   1473篇
  2019年   1630篇
  2018年   2062篇
  2017年   2133篇
  2016年   3299篇
  2015年   1975篇
  2014年   3242篇
  2013年   8004篇
  2012年   5954篇
  2011年   7067篇
  2010年   5128篇
  2009年   5111篇
  2008年   6706篇
  2007年   6599篇
  2006年   6208篇
  2005年   5623篇
  2004年   5193篇
  2003年   4698篇
  2002年   4538篇
  2001年   5245篇
  2000年   3900篇
  1999年   2996篇
  1998年   2502篇
  1997年   2406篇
  1996年   2271篇
  1995年   2133篇
  1994年   2114篇
  1993年   2019篇
  1992年   2323篇
  1991年   2261篇
  1990年   2224篇
  1989年   2145篇
  1988年   2142篇
  1987年   2144篇
  1986年   2044篇
  1985年   2665篇
  1984年   2723篇
  1983年   2408篇
  1982年   2512篇
  1981年   2327篇
  1980年   2299篇
  1979年   2437篇
  1978年   2472篇
  1977年   2405篇
  1976年   2451篇
  1975年   2376篇
  1974年   2333篇
  1973年   2509篇
  1972年   1627篇
  1971年   1339篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
It is proved in this paper that the characteristic function of the half-space is not a multiplier for the pair (B pq 1/p , B p 1/p ), 1<p<, 1<q . In addition, necessary and sufficient conditions are found for the validity of the inclusion.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 135, pp. 36–50, 1984.  相似文献   
992.
It is generally believed that the uncertainty relation q p1/2, where q and p are standard deviations, is the precise mathematical expression of the uncertainty principle for position and momentum in quantum mechanics. We show that actually it is not possible to derive from this relation two central claims of the uncertainty principle, namely, the impossibility of an arbitrarily sharp specification of both position and momentum (as in the single-slit diffraction experiment), and the impossibility of the determination of the path of a particle in an interference experiment (such as the double-slit experiment).The failure of the uncertainty relation to produce these results is not a question of the interpretation of the formalism; it is a mathematical fact which follows from general considerations about the widths of wave functions.To express the uncertainty principle, one must distinguish two aspects of the spread of a wave function: its extent and its fine structure. We define the overall widthW and the mean peak width w of a general wave function and show that the productW w is bounded from below if is the Fourier transform of . It is shown that this relation expresses the uncertainty principle as it is used in the single- and double-slit experiments.  相似文献   
993.
Static softening of AISI 321 steel after cold and hot deformation characterizing the industrial thermomechanical treatment was studied by means of tensile tests and TEM. The deformation temperature, the strain and the grain size were the main parameters determining the final softening. The results can be applied for optimization of the solution annealing.  相似文献   
994.
995.
The production of two quark/gluon jets in \(p\bar p\) collisions is analyzed. We determine the cross section dependence on the transverse momentum, the rapidities, and on the two-jet invariant mass, and we evaluate the sensitivity of the results on the theoretical input assumptions and the experimental cuts. We extrapolate these results into the TeV energy region.  相似文献   
996.
An extensive investigation is made of electron correlations in the ground state of hydrocarbon molecules. This is done by starting from a semiempirical self-consistent field (SCF) calculation. The interatomic correlations are studied by means of a previously developed local approach to the correlation problem. It is demonstrated that the various contributions to the interatomic correlation energy can be described by simple analytical expressions which depend on the type of bond as well as on the bond lengths and angles. The results are easily understood in physical terms. The intraatomic correlations are obtained from an atoms in molecules type of approach as elaborated by Lievin et al. It makes use of a population analysis of the ground-state wave function as well as of calculations for the C and H atoms. We have then a very simple, and as it turns out rather accurate calculational scheme at hand. The computational times involved are of the same order as those for the fast SCF programs. As an application of the theory we have calculated the correlation energy difference between naphthalene and azulene.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday  相似文献   
997.
The physical principles of atomic and nuclear polarization by the tilted-foil interaction as applied to the production of polarized emitters for NMR probes are discussed.  相似文献   
998.
The thermal hysteresis of Joule's absorption of infrared radiation in then-type semiconductor magnetoplasma is analysed. Such bistability is connected with the temperature dependence of the relaxation time of free electrons, their density being constant. The resonant Joule's absorption bistability of the pumping infrared wave near a Langmuir resonance of free electrons is discussed as well as the hysteresis cross-modulation of an infrared probing wave by means of a pumping microwave. The possibilities of smooth detuning of the hysteresis regime due to a magnetic-field control and low energy thresholds of these regimes are illustrated for InSb thin films in relatively weak magnetic fieldsH1–2 kG.  相似文献   
999.
1000.
Zusammenfassung Es wird über die Synthese von verschiedenen methylsubstituiertens-Triazolo[4,3—b]pyridazinen berichtet. Außerdem wurdens-Triazolo[4,3—b]pyridazin und seine 7-Methyl- und 6-Chlor-Derivate der homolytischen Methylierung unterworfen, die Reaktionsgemische gaschromatographisch auf einzelne Methyl-s-triazolo[4,3—b]pyridazine aufgetrennt und die Verbindungen identifiziert.
Syntheses of pyridazines, XXVI: Synthesis and homolytic methylation of s-triazolo[4.3—b]pyridazines
The syntheses of some methyl substituteds-triazolo[4,3—b]-pyridazines are reported.s-Triazolo[4.3—b]pyridazine and its 7-methyl and 6-chloro analogs were submitted to homolytic methylations and the obtained reaction mixtures were separated by gas chromatography into particular components which were then identified.
  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号