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   8037篇
  免费   1245篇
  国内免费   1218篇
化学   6080篇
晶体学   94篇
力学   509篇
综合类   104篇
数学   1029篇
物理学   2684篇
  2024年   21篇
  2023年   156篇
  2022年   324篇
  2021年   296篇
  2020年   347篇
  2019年   331篇
  2018年   288篇
  2017年   266篇
  2016年   382篇
  2015年   354篇
  2014年   441篇
  2013年   589篇
  2012年   693篇
  2011年   756篇
  2010年   499篇
  2009年   497篇
  2008年   596篇
  2007年   490篇
  2006年   414篇
  2005年   378篇
  2004年   287篇
  2003年   245篇
  2002年   232篇
  2001年   204篇
  2000年   166篇
  1999年   161篇
  1998年   141篇
  1997年   132篇
  1996年   134篇
  1995年   125篇
  1994年   106篇
  1993年   82篇
  1992年   79篇
  1991年   65篇
  1990年   50篇
  1989年   41篇
  1988年   29篇
  1987年   33篇
  1986年   16篇
  1985年   22篇
  1984年   9篇
  1983年   7篇
  1982年   3篇
  1981年   5篇
  1980年   1篇
  1975年   1篇
  1974年   1篇
  1959年   1篇
  1957年   3篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
981.
In this study we have used two fluorescent probes, tetrakis(diisopropylguanidino)-zinc-phthalocyanine (Zn-DIGP) and N-methylmesoporphyrin IX (NMM), to monitor the reassembly of “split” G-quadruplex probes on hybridization with an arbitrary “target” DNA. According to this approach, each split probe is designed to contain half of a G-quadruplex-forming sequence fused to a variable sequence that is complementary to the target DNA. Upon mixing the individual components, both base-pairing interactions and G-quadruplex fragment reassembly result in a duplex–quadruplex three-way junction that can bind to fluorescent dyes in a G-quadruplex-specific way. The overall fluorescence intensities of the resulting complexes were dependent on the formation of proper base-pairing interactions in the duplex regions, and on the exact identity of the fluorescent probe. Compared with samples lacking any “target” DNA, the fluorescence intensities of Zn-DIGP-containing samples were lower, and the fluorescence intensities of NMM-containing samples were higher on addition of the target DNA. The resulting biosensors based on Zn-DIGP are therefore termed “turn-off” whereas the biosensors containing NMM are defined as “turn-on”. Both of these biosensors can detect target DNAs with a limit of detection in the nanomolar range, and can discriminate mismatched from perfectly matched target DNAs. In contrast with previous biosensors based on the peroxidase activity of heme-bound split G-quadruplex probes, the use of fluorescent dyes eliminates the need for unstable sensing components (H2O2, hemin, and ABTS). Our approach is direct, easy to conduct, and fully compatible with the detection of specific DNA sequences in biological fluids. Having two different types of probe was highly valuable in the context of applied studies, because Zn-DIGP was found to be compatible with samples containing both serum and urine whereas NMM was compatible with urine, but not with serum-containing samples.  相似文献   
982.
In this paper, we will establish the existence and nonexistence of traveling waves for nonlinear cellular neural networks with finite or infinite distributed delays. The dynamics of each given cell depends on itself and its nearest m left or l right neighborhood cells where delays exist in self-feedback and left or right neighborhood interactions. Our approach is to use Schauder?s fixed point theorem coupled with upper and lower solutions of the integral equation in a suitable Banach space. Further, we obtain the exponential asymptotic behavior in the negative infinity and the existence of traveling waves for the minimal wave speed by the limiting argument. Our results improve and cover some previous works.  相似文献   
983.
We prove a uniqueness theorem in terms of value distribution for meromorphic solutions of a class of nonlinear partial differential equations of first order, which shows that such solutions f are uniquely determined by the zeros and poles of fcj (counting multiplicities) for two distinct complex numbers c1 and c2.  相似文献   
984.
A new method of moving asymptotes for large-scale minimization subject to linear equality constraints is discussed.In this method,linear equality constraints are deleted with null space technique and the descending direction is obtained by solving a convex separable subproblem of moving asymptotes in each iteration. New rules for controlling the asymptotes parameters are designed and the global convergence of the method under some reasonable conditions is established and proved.The numerical results show that the new method may be capable of processing some large scale problems.  相似文献   
985.
Empirical likelihood(EL) ratio statistic on θ = g(x) is constructed based on the inverse probability weighted imputation approach in a nonparametric regression model Y = g(x) + ε(x ∈ [0,1]p) with fixed designs and missing responses,which asymptotically has χ12 distribution.This result is used to obtain a EL based confidence interval on θ.  相似文献   
986.
In this work, strongly continuous semigroups of pseudocontractions are studied based on an implicit iterative algorithm. Strong convergence theorems of fixed points are obtained in an arbitrary Banach space.  相似文献   
987.
将动态递归的可计算一般均衡方法应用于碳关税征收影响的研究,建立了测算美国征收碳关税对中国经济与环境影响的动态递归可计算一般均衡模型,并在模型中引入技术进步参数以刻画能源节约型技术进步.模型以2007年作为基年,包含37个生产部门和7个国内国外账户.应用该模型模拟了2020年起美国征收碳关税,在税率从20美元每吨碳排放到80美元每吨碳排放的13种情景下,到2030年期间对我国碳排放和经济发展的不同影响,进而测算在不同的能源节约型技术进步条件下,碳关税对我国经济与环境影响的变动.  相似文献   
988.
989.
In this paper,we determine the estimates exact in order for the trigonometric widths and the best n-term trigonometric approximations of the generalized classes of periodic functions BΩp,θ in the space Lq for some values of parameters p,q.  相似文献   
990.
A concise approach to the tetrahydroxanthone natural products employing vinylogous addition of siloxyfurans to benzopyryliums and a late-stage Dieckmann cyclization has been developed. With this methodology, chiral, racemic forms of the natural products blennolides B and blennolide C have been synthesized in a maximum of four steps from a 5-hydroxychromone substrate. The regio- and diastereoselectivity of the vinylogous additions was probed using computational studies, which suggested the involvement of Diels-Alder-like transition states.  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