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   192234篇
  免费   24985篇
  国内免费   16507篇
化学   90129篇
晶体学   1428篇
力学   8388篇
综合类   824篇
数学   15625篇
物理学   52643篇
综合类   64689篇
  2024年   839篇
  2023年   3574篇
  2022年   5882篇
  2021年   6380篇
  2020年   6286篇
  2019年   5430篇
  2018年   5088篇
  2017年   4915篇
  2016年   7223篇
  2015年   7744篇
  2014年   9868篇
  2013年   11906篇
  2012年   14024篇
  2011年   14251篇
  2010年   10288篇
  2009年   10294篇
  2008年   11106篇
  2007年   10157篇
  2006年   9037篇
  2005年   7916篇
  2004年   6099篇
  2003年   4840篇
  2002年   4644篇
  2001年   4221篇
  2000年   4052篇
  1999年   5869篇
  1998年   5350篇
  1997年   5268篇
  1996年   5045篇
  1995年   4396篇
  1994年   3851篇
  1993年   3331篇
  1992年   2882篇
  1991年   2657篇
  1990年   2216篇
  1989年   1890篇
  1988年   1530篇
  1987年   1058篇
  1986年   782篇
  1985年   490篇
  1984年   251篇
  1983年   216篇
  1982年   153篇
  1981年   95篇
  1980年   74篇
  1979年   34篇
  1976年   21篇
  1975年   21篇
  1972年   19篇
  1957年   41篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Let p ∈ [1, ∞), q ∈ [1, ∞), α∈ R, and s be a non-negative integer. Inspired by the space JNp introduced by John and Nirenberg(1961) and the space B introduced by Bourgain et al.(2015), we introduce a special John-Nirenberg-Campanato space JNcon(p,q,s) over Rn or a given cube of R;with finite side length via congruent subcubes, which are of some amalgam features. The limit space of such spaces as p →∞ is just the Campanato space which coincides with the space BMO(the space of functions with bounded mean oscillations)when α = 0. Moreover, a vanishing subspace of this new space is introduced, and its equivalent characterization is established as well, which is a counterpart of the known characterization for the classical space VMO(the space of functions with vanishing mean oscillations) over Rn or a given cube of Rn with finite side length.Furthermore, some VMO-H1-BMO-type results for this new space are also obtained, which are based on the aforementioned vanishing subspaces and the Hardy-type space defined via congruent cubes in this article. The geometrical properties of both the Euclidean space via its dyadic system and congruent cubes play a key role in the proofs of all these results.  相似文献   
2.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results.  相似文献   
3.
4.
5.
6.
Cinnamaldehyde (CA), an active ingredient isolated from the traditional Chinese medicine Cortex Cinnamomi, has a wide range of bioactivities. To clarify the distribution characteristics of CA, a selective and sensitive method utilizing gas chromatography–mass spetrometry was initially developed for simultaneously determining the concentration of CA and its metabolite cinnamyl alcohol in rat tissues. Selected ion masses of m/z 131, 105 and 92 were chosen, and separation of the analytes was performed on a DB‐5 ms (30 m × 0.25 mm, 0.25 µm, thickness) capillary column by gas chromatography–mass spectrometry. The calibration curves demonstrated good linearity and reproducibility over the range of 20–2000 and 20–4000 ng/mL for various tissue samples. Recoveries ranged from 86.8 to 107.5%, while intra‐ and interday relative standard deviations were all <11.3%. The analysis method was successfully applied in tissue distribution studies for CA and cinnamyl alcohol. As CA and cinnamyl alcohol may inter‐convert to one another, simultaneous determination of both analytes provides a comparative and accurate data for tissue study. The concentrations of CA and cinnamyl alcohol remaining in spleen were the highest among the main organs, including heart, liver, spleen, lung, kidney and brain. In addition, there was no long‐term accumulation of CA in rat tissues. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
7.
8.
Journal of Sol-Gel Science and Technology - A novel gas sensing material, La–Y co-doped TiO2 nanoparticles, was synthesized by sol–gel method and applied to detect organic pollutants...  相似文献   
9.
为全面培育卓越农林人才,提高教学培养质量,本研究结合土壤肥料学的课程内容、教学特点及实验方法,对存在的问题进行了剖析,并结合实际针对存在问题做出了相应改革,适时调整《土壤肥料学》实验课程内容和形式。通过删减验证性实验内容,增设综合性实验,传统部分教学内容实现网络化等三方面对该课程的实验课部分进行了改革与实践,以期提高学生综合运用所学《土壤肥料学》的相关知识来解决生产实际问题的能力。  相似文献   
10.
我国初步建立了财政性科技经费监管体系,但是在监督主体、监督制度等方面还存在缺陷,科技经费监督出现诸多问题。建立要加强宏观层面的统筹规划,建立由政府、承担单位和外部主体上下联动、横向联合的立体监督体系。  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