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   32312篇
  免费   4781篇
  国内免费   5884篇
化学   23740篇
晶体学   332篇
力学   1952篇
综合类   350篇
数学   4301篇
物理学   12302篇
  2024年   36篇
  2023年   419篇
  2022年   606篇
  2021年   784篇
  2020年   969篇
  2019年   1074篇
  2018年   840篇
  2017年   764篇
  2016年   1251篇
  2015年   1313篇
  2014年   1561篇
  2013年   1970篇
  2012年   2293篇
  2011年   3567篇
  2010年   2341篇
  2009年   2343篇
  2008年   2010篇
  2007年   1735篇
  2006年   1660篇
  2005年   1580篇
  2004年   2235篇
  2003年   1544篇
  2002年   1656篇
  2001年   1287篇
  2000年   883篇
  1999年   760篇
  1998年   660篇
  1997年   517篇
  1996年   439篇
  1995年   394篇
  1994年   323篇
  1993年   644篇
  1992年   623篇
  1991年   435篇
  1990年   412篇
  1989年   402篇
  1988年   159篇
  1987年   69篇
  1986年   77篇
  1985年   83篇
  1984年   54篇
  1983年   41篇
  1982年   37篇
  1981年   20篇
  1980年   7篇
  1979年   18篇
  1978年   13篇
  1977年   10篇
  1976年   7篇
  1974年   6篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
991.
黑腔靶X光转换,输运的定量测量   总被引:1,自引:1,他引:0  
为了测量黑腔靶X光引光效率、转换效率,我们设计了相应的分解靶(泄漏靶)实验,1989~1992年在″神光″装置上共进行了四次漏靶分解实验,利用灵敏度作了绝对标定的平响应X光二极管对漏靶注入孔、引光孔流出的X光角分布进行了测量,测出了x光角分布,得到了黑腔靶X光转换效率为50%~60%,引光效率约6%,为以后辐射驱动内爆研究的理论计算和靶的优化设计提供了重要的数据。  相似文献   
992.
We investigate classical electronic collisions with a He(+) ion. Scattering functions, such as the scattering angle, collisional time, or energy of the outgoing electron, all exhibit an interesting hierarchial self-similar structure, which can be interpreted in terms of the indefinite number of electronic returns to the vicinity of the nucleus, encounters between electrons, and Keplerian excursions of electrons during the collisional processes. Based on this mechanism a binary coding is introduced to organize the dynamics of this three-body system and to provide an understanding of the self-similarity among generations of scale magnification, which yields escape rates that vary with the sectional cut into the parameter space. The self-similarity displayed within a single generation, on the other hand, can be simply tied to the periods of the two independent electronic excursions. The physical interpretation and the symbolic dynamics introduced here are generally useful for three-body collisional systems, including atomic, molecular, or stellar collisions.  相似文献   
993.
Let be a univariant function, and letg(x) be the average of (x,u) asu runs over the unit sphere in n . We give a necessary and sufficient condition forg to be a kernel function, i.e., thatg be inL 1 ( n ) and have integral 1. The result is used to give a constructive proof of the density of the ridge functions based upon the function .  相似文献   
994.
Some of the blending interpolation methods (which) stated by a convex combination technique are presented. This includes C1 ,C2 blending triangular interpolanls and C1 -blending quadrilateral inter polanls for surfaces. The mentioned methods can be generalized to the construction of C" blending interpolants.  相似文献   
995.
Let be a quadratic form with integer coefficients and letp denote a prime. Cochrane[1] proved that ifn≥4 then has a solution satisfying , where . The aim of the present paper is to generalize the above result to finite fields.  相似文献   
996.
Summary We study the asymptotic stability of the stochastic flows on a class of compact spaces induced by a diffusion process in SL(n, R) or GL(n, R). These compact spaces are called boundaries of SL(n, R), which include SO(n), the flag manifold, the sphereS n–1 and the Grassmannians. The one point motions of these flows are Brownian motions. For almost every, , we determine the set of stable points. This is a random open set whose complement has zero Lebesgue measure. The distance between any two points in the same component of this set tends to zero exponentially fast under the flow. The Lyapunov exponents at stable points are computed explicitly. We apply our results to a stochastic flow onS n–2 generated by a stochastic differential equation which exhibits some nice symmetry.Research supported in part by Hou Yin Dong Education Foundation of China On leave from Nankai University, Tianjin, China  相似文献   
997.
998.
近年来,随着LB膜研究的进展,成膜材料的种类逐渐增多、其中有关酞菁衍生物LB膜材料的报道较多。本文合成了下述新型结构的化合物:  相似文献   
999.
钼钨铌磷杂多化合物的研究(Ⅰ):杂多酸的合成和表征   总被引:4,自引:0,他引:4  
提出了分步酸化一分步加料合成[PNb_2Mo_xW_(10-x)O_(40)]~(5-)(x=0,2,4,6)系列杂多酸的方法,给出了最佳配料比和生成反应的pH值,并进行了红外、紫外、极谱、电位滴定及热稳定性研究。  相似文献   
1000.
The primary reaction of photosensitization of Hypocrellin A (HA) has been studied byusing techniques of ESR, spin-trapping and spin-counteraction. The experiments show thatHA is able to generate not only ~1O_2,but also O_2~-·OH and HA~- which are observed for thefirst time. The conversion of generating active oxygen into generating nonoxygen free rad-ical is confirmed as well. Based on the characteristics of the primary reaction which gene-rates these active substances (transient products), it is proposed that the photosensitized dam-age for the biological system by HA is probably related to not only ~1O_2 itself, but also amultiple effect from ~1O_2 as well as O_2~-,·OH and HA~+ free radical.  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