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   204185篇
  免费   1716篇
  国内免费   592篇
化学   102363篇
晶体学   3340篇
力学   9290篇
综合类   5篇
数学   22473篇
物理学   69022篇
  2021年   1658篇
  2020年   1798篇
  2019年   1999篇
  2018年   2699篇
  2017年   2601篇
  2016年   3770篇
  2015年   2306篇
  2014年   3614篇
  2013年   9088篇
  2012年   7242篇
  2011年   8736篇
  2010年   6047篇
  2009年   5913篇
  2008年   7912篇
  2007年   8081篇
  2006年   7729篇
  2005年   6893篇
  2004年   6428篇
  2003年   5650篇
  2002年   5491篇
  2001年   6426篇
  2000年   4933篇
  1999年   3798篇
  1998年   3040篇
  1997年   3046篇
  1996年   2795篇
  1995年   2615篇
  1994年   2464篇
  1993年   2340篇
  1992年   2693篇
  1991年   2672篇
  1990年   2600篇
  1989年   2396篇
  1988年   2449篇
  1987年   2448篇
  1986年   2279篇
  1985年   2960篇
  1984年   3217篇
  1983年   2631篇
  1982年   2801篇
  1981年   2771篇
  1980年   2637篇
  1979年   2727篇
  1978年   2821篇
  1977年   2820篇
  1976年   2886篇
  1975年   2671篇
  1974年   2646篇
  1973年   2777篇
  1972年   1763篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method.  相似文献   
152.
The polarization structure of nonparaxial spatial solitons in a transparent medium with the electronic mechanism of Kerr nonlinearity is studied theoretically. It is demonstrated analytically in the weak nonparaxiality approximation that the regime of polarization locking, in which all the field components have the same propagation constant, is the only stable regime. Estimates of the rate of transition of the initial metastable regime of rotation of the polarization ellipse to the regime of polarization locking are presented. Based on a numerical solution of the nonlinear Maxwell equations, the presence of the nonparaxial regime of polarization locking is confirmed and the main characteristics of the corresponding spatial solitons are obtained.  相似文献   
153.
A recently demonstrated [1] in-vacuo template-stripping process is applied to the study of platinum films stripped from ultra-flat silicon-oxide surfaces. Template-stripped (TS) Pt surfaces, prepared with a range of post-deposition annealing times prior to being stripped from the templating surface in an ultra-high vacuum (UHV) environment, are examined by UHV scanning tunneling microscopy (STM). These studies reveal that without post-deposition annealing, TS Pt surfaces are largely made up of poorly-ordered, granular nanostructures undesirable for many applications. The post-deposition annealing treatments explored in the study result in the emergence and continuous growth of large smooth crystallites. Issues with crystallite orientation relative to the TS surface and artefacts arising as a result of the epoxy used in the template-stripping process are presented and discussed in relation to optimizing the template-stripping procedure for specific applications such as self-assembled monolayer (SAM) formation for molecular electronics. PACS 68.37.Ef; 68.47.De; 68.55.Jk; 81.05.Bx; 81.15.Ef  相似文献   
154.
155.
A modernized conception of hierarchical structure of reality is proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–6, December, 1980.  相似文献   
156.
The classical (first integral) methods of studying restrictions on the possible motion of gravitationally interacting bodies are reviewed. The simple and flexible inequality method is extended to a similar approach to the relationship between possible forbidden motion and (asymptotic) symmetries in the relativistic few-body problem. This extended method is used to reproduce the standard results of bounded motion for a test particle in a Schwarzschild geometry. The existence of bounded motion is shown for the general relativistic few-body problem and the difficulties in determining such bounded motion is analysed. The use of this approach to obtaining a relativistic alternative to the classical Roche lobe analysis in contact binaries is discussed.  相似文献   
157.
The concept of strong interactions need not be limited to the sector of physics taken by QCD. While this domain is investigated by RHIC, LHC will be able to probe potential new strong interactions simultaneously: Finding the precise mechanism for electroweak symmetry breaking is one of the prime problems of physics. Intricately linked to this point is the question after the true nature or even the existence of the Higgs boson. Here, we present stronly interacting theories providing an explanation for the hierarchy problem and leading to a light composite Higgs boson, favoured by experimental data. Our variation of the standard model is consistent with precision data. We achieve this accordance by using technifermions in a higher representation of their gauge group. Anomaly conditions require at least one extra lepton family for some of the theories whereby they contain a natural dark matter candidate. We can accurately determine the masses of said leptons from experimental data.  相似文献   
158.
We consider three one-dimensional quantum, charged and spinless particles interacting through delta potentials. We derive sufficient conditions which guarantee the existence of at least one bound state.  相似文献   
159.
Butyltins were analyzed in waters from California river and lake marinas and were detected at the part per trillion (ppt) level in most locations. The tributyltin:dibutyltin (TBT/DBT) ratios in the fresh waters were similar to those in their saline counterparts indicating like rates of degradation in the two salinity regimes.  相似文献   
160.
A natural criterion for dimensional full-valuedness of locally compact spaces with finitely generated local homology is given.  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