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   532720篇
  免费   4754篇
  国内免费   1287篇
化学   268498篇
晶体学   6420篇
力学   26735篇
综合类   17篇
数学   69932篇
物理学   167159篇
  2021年   4996篇
  2020年   5481篇
  2019年   6222篇
  2018年   8893篇
  2017年   9119篇
  2016年   11897篇
  2015年   6346篇
  2014年   10583篇
  2013年   23672篇
  2012年   18922篇
  2011年   22133篇
  2010年   16588篇
  2009年   16493篇
  2008年   20710篇
  2007年   20565篇
  2006年   18665篇
  2005年   18769篇
  2004年   17711篇
  2003年   15160篇
  2002年   13913篇
  2001年   14742篇
  2000年   11364篇
  1999年   8768篇
  1998年   7613篇
  1997年   7363篇
  1996年   6427篇
  1995年   6111篇
  1994年   6140篇
  1993年   5871篇
  1992年   6231篇
  1991年   6750篇
  1990年   6454篇
  1989年   6338篇
  1988年   6187篇
  1987年   6025篇
  1986年   5752篇
  1985年   7309篇
  1984年   7682篇
  1983年   6455篇
  1982年   6728篇
  1981年   6234篇
  1980年   5901篇
  1979年   6429篇
  1978年   6668篇
  1977年   6594篇
  1976年   6540篇
  1975年   6251篇
  1974年   6071篇
  1973年   6389篇
  1972年   4673篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
The effect of bacterial and fungal activities on organic matter degradation in Brazilian soils was studied by a microcalorimetric method. Bacteria and fungi isolated from tropical soils and added to: Rhodic eutrudox (R), Typic eutrudox (V) and Quartzipsamment (Q) soils amended separately with moisture (control) (A) and 25% of cattle manure (E), municipal refuse compost (L), earthworm casts (H) or 23 μg of trifluralin (T) were investigated. The number of colony forming units in soil suspension was quantified by microscopy and inoculated in respective soil. All processes were measured at intervals of 7 days over a period of 35 days. The exothermic thermal effect (μJ) per cm3 of bacteria or fungi per gram of dry soil, respectively, for each substrate was: [(9±1), (4±1)] RA; [(478±24), (105±5)] RE; [(121±6), (71±4)] RL; [(121±6), (71±4)] RH; [(8±1); (3±1)] RT; [(10±1), (9±1] VA; [(347±17), (261±13)] VE; [(71±4), (28±1)] VL; [(22±1), (33±2)] VH; [(7±1), (10±1)] VT; [(19±1), (12±1)] QA; [(1301±65), (46±2)] QE; [(89±4), (9±1)] QL; [(130±7), (11±1)] QH; [(32±2), (8±1)] QT. The calorimetric values are higher for bacteria than for fungi. In general, the results showed higher activities in the soil amended with cattle manure than with other additives.  相似文献   
992.
The odd excited negative binomial states are introduced using the photon creation operator by repeated application on negative binomialstates. These states interpolate between the odd displaced Fock states and the odd excited pure thermal states. In this paper both squeezing phenomena (normal squeezing and amplitude squared squeezing) are discussed. Besides discussion of the Glauber second-order correlation function, investigations are carried out for the quasi-probability distribution functions (Wigner function and Q-function). Finally the Pegg-Barnett phase probability distribution is computed for these states.  相似文献   
993.
Relationships between the electrodynamic (wave propagation constants) and quantum-mechanical parameters (probability of induced transitions) of interaction between energy quanta and particles of the medium are derived for dipole and paramagnetic interaction types. It is demonstrated that quantum-mechanical parameters are generally complex.  相似文献   
994.
We prove that any irreducible faithful representation of an almost torsion-free Abelian group G of finite rank over a finitely generated field of characteristic zero is induced from an irreducible representation of a finitely generated subgroup of the group G.  相似文献   
995.
Kovalevskii  A. A. 《Mathematical Notes》2003,74(5-6):637-646
We establish the existence of a weak solution to the Dirichlet problem belonging to a Sobolev space for nonlinear elliptic equations of second order with right-hand sides from a wide class of functions defined in terms of the logarithmic function.  相似文献   
996.
The fine-structure parameters of a series of configurations of the first ion of indium and the gyromagnetic ratios in intermediate coupling are calculated by a semiempirical method in the single-configuration approximation.  相似文献   
997.
998.
999.
In the paper we describe automorphisms and derivations of simple Lie algebras of family R. The Lie algebra of the automorphism group is found. Bibliography: 11 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 305, 2003, pp. 165–186.  相似文献   
1000.
We study initial boundary value problems for linear scalar evolutionpartial differential equations, with spatial derivatives ofarbitrary order, posed on the domain {t > 0, 0 < x <L}. We show that the solution can be expressed as an integralin the complex k-plane. This integral is defined in terms ofan x-transform of the initial condition and a t-transform ofthe boundary conditions. The derivation of this integral representationrelies on the analysis of the global relation, which is an algebraicrelation defined in the complex k-plane coupling all boundaryvalues of the solution. For particular cases, such as the case of periodic boundaryconditions, or the case of boundary value problems for even-orderPDEs, it is possible to obtain directly from the global relationan alternative representation for the solution, in the formof an infinite series. We stress, however, that there existinitial boundary value problems for which the only representationis an integral which cannot be written as an infinite series.An example of such a problem is provided by the linearized versionof the KdV equation. Similarly, in general the solution of odd-orderlinear initial boundary value problems on a finite intervalcannot be expressed in terms of an infinite series.  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