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   5067篇
  免费   112篇
  国内免费   21篇
化学   3436篇
晶体学   23篇
力学   104篇
数学   771篇
物理学   866篇
  2023年   20篇
  2022年   54篇
  2021年   77篇
  2020年   65篇
  2019年   66篇
  2018年   58篇
  2017年   57篇
  2016年   134篇
  2015年   129篇
  2014年   115篇
  2013年   264篇
  2012年   247篇
  2011年   279篇
  2010年   171篇
  2009年   189篇
  2008年   257篇
  2007年   271篇
  2006年   240篇
  2005年   243篇
  2004年   233篇
  2003年   169篇
  2002年   174篇
  2001年   68篇
  2000年   82篇
  1999年   92篇
  1998年   74篇
  1997年   70篇
  1996年   76篇
  1995年   41篇
  1994年   61篇
  1993年   65篇
  1992年   59篇
  1991年   46篇
  1990年   42篇
  1989年   41篇
  1988年   42篇
  1987年   48篇
  1986年   56篇
  1985年   72篇
  1984年   60篇
  1983年   51篇
  1982年   73篇
  1981年   49篇
  1980年   73篇
  1979年   56篇
  1978年   38篇
  1977年   30篇
  1976年   39篇
  1975年   33篇
  1974年   25篇
排序方式: 共有5200条查询结果,搜索用时 0 毫秒
1.
A consistent quantization with a clear notion of time and evolution is given for the anisotropic Kantowski–Sachs cosmological model. It is shown that a suitable coordinate choice allows to obtain a solution of the Wheeler–DeWitt equation in the form of definite energy states, and that the results can be associated to two disjoint equivalent theories, one for each sheet of the constraint surface.  相似文献   
2.
A time discrete scheme is used to approximate the solution toa phase field system of Penrose–Fife type with a non-conservedorder parameter. An a posteriori error estimate is presentedthat allows the estimation of the difference between continuousand semidiscrete solutions by quantities that can be calculatedfrom the approximation and given data.  相似文献   
3.
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   
4.
5.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions.  相似文献   
6.
A new access to 5‐phenyl‐5,6,7,8‐tetrahydro‐1,6‐naphthyridines 25a‐28a (n=1) and 5‐phenyl‐6,7,8,9‐tetrahydro‐5H‐pyrido[3,2‐c]azepines 25b‐28b (n=2) has been developed by first preparing the functional pyridine moiety followed by intramolecular cyclization forming the partially reduced ring.  相似文献   
7.
8.
9.
We prove a large deviation theorem from the hydrodynamical limit for the empirical measure of Ginzburg-Landau and zero range processes in infinite volume starting from deterministic initial configurations. In the Ginzburg-Landau case the main tool is the study of the evolution of the H?1 norm and in the zero range case the attractiveness which allows couplings.  相似文献   
10.
Summary. Free radical couplings from furan, as cheap starting material, were studied in view of developing a rapid strategy en route to the synthesis of derivatives of nonactin. The chain containing the alcohol function was introduced in one or two steps in 86% yield. For the introduction of the second chain with the ester function two different coupling methods were tested. Starting from the advanced intermediates obtained nonactin derivatives can be prepared by catalytic hydrogenation of the furan ring.  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