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   17499篇
  免费   407篇
  国内免费   99篇
化学   11299篇
晶体学   206篇
力学   533篇
综合类   1篇
数学   2337篇
物理学   3629篇
  2022年   102篇
  2021年   131篇
  2020年   231篇
  2019年   194篇
  2018年   129篇
  2017年   144篇
  2016年   283篇
  2015年   248篇
  2014年   322篇
  2013年   798篇
  2012年   775篇
  2011年   939篇
  2010年   481篇
  2009年   445篇
  2008年   868篇
  2007年   847篇
  2006年   840篇
  2005年   805篇
  2004年   746篇
  2003年   570篇
  2002年   589篇
  2001年   281篇
  2000年   292篇
  1999年   170篇
  1998年   176篇
  1997年   198篇
  1996年   277篇
  1995年   200篇
  1994年   232篇
  1993年   274篇
  1992年   233篇
  1991年   200篇
  1990年   194篇
  1989年   187篇
  1988年   169篇
  1987年   182篇
  1986年   165篇
  1985年   302篇
  1984年   286篇
  1983年   191篇
  1982年   238篇
  1981年   229篇
  1980年   227篇
  1979年   215篇
  1978年   239篇
  1977年   208篇
  1976年   208篇
  1975年   182篇
  1974年   198篇
  1973年   186篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
When depicted on maps as homogenous territorial wholes, ancient states are visually summarized as static entities in a way that conceals the highly fluid dynamics of polity formation, maintenance, and growth. Models derived from studies of animal behavior show that “territory” does not consist of an undifferentiated use of the landscape. Instead, the concept of territory can be parsed into a series of resource‐rich nodes linked by corridors of access, surrounded by unutilized regions and boundaries marked at points of competition. Ancient human groups also can be analyzed as having perceived and occupied landscapes through strategies of flexible networks in which nodes and corridors were surrounded by unutilized spaces around which boundaries were selectively identified and defended. This strategy is identifiable in human social groups at different levels of complexity ranging from hunter‐gatherers through ancient chiefdoms and states. © 2007 Wiley Periodicals, Inc. Complexity 12: 28–35, 2007  相似文献   
53.
A method, combining micro-contact printing (μCP), wet chemical etching and reactive ion etching (RIE), is reported to fabricate microstructures on Si and SiOx. Positive and negative structures were generated based on different stamps used for μCP. The reproducibility of the obtained microstructures shows the methodology reported herein could be useful in Micro-Electro-Mechanical Systems (MEMS), optical and biological sensing applications.  相似文献   
54.
The anti-Parkinson’s agent SIB-1508Y was prepared in six steps from (S)-nicotine in 20% overall yield. The strategy involves a regioselective formylation at C-5 of a 1,4-dihydronicotine intermediate.  相似文献   
55.
Pure adaptive search constructs a sequence of points uniformly distributed within a corresponding sequence of nested regions of the feasible space. At any stage, the next point in the sequence is chosen uniformly distributed over the region of feasible space containing all points that are equal or superior in value to the previous points in the sequence. We show that for convex programs the number of iterations required to achieve a given accuracy of solution increases at most linearly in the dimension of the problem. This compares to exponential growth in iterations required for pure random search.  相似文献   
56.
The synthesis and characterization of a collagen mimetic dendrimer composed of the Gly-Pro-Nleu sequence is described. The dendrimer is built on a ‘first generation’ poly(amidoamine) core and is synthesized in 38% yield. This dendrimer exhibits a melting temperature of 25 °C, which is in between previously studied analogous molecules of identical sequence and length.  相似文献   
57.
The incidence of the cutaneous malignant melanoma is increasing rapidly in the world [Ferlay J, Bray F, Pisani P, et al. GLOBOCAN 2000: Cancer incidence, mortality and prevalence worldwide, Version 1.0 IARC Cancer Base no. 5. Lyon: IARC Press, 2001]. The therapeutic address requires a method having high sensitivity and capability to diagnose such disease at an early stage. We introduce a new diagnostic method based on non-linear methodologies. In detail we suggest that fractal as well as noise and chaos dynamics are the most important components responsible for genetic instability of melanocytes. As consequence we introduce the new technique of the variogram and of fractal analysis extended to the whole regions of interest of skin in order to obtain parameters able to identify the malignant lesion. In a preliminary analysis, satisfactory results are reached.  相似文献   
58.
59.
60.
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